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  • General Chemistry  (1,786)
  • Cell & Developmental Biology  (458)
  • 1995-1999  (2,244)
  • 1996  (2,244)
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  • 1995-1999  (2,244)
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  • 201
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Stereoselective Reaction of a Chiral Hydroxy-Stabilized Metal-Free Enolate (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 382-384 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric synthesis ; chirality ; enolates ; hydrogen bonds ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of acetophenone with tetrabutylammonium hydroxide affords the tetrabutylammonium enolate of phenyl (2-hydroxy-2-phenyl)propyl ketone. The crystal structure of this chiral enolate shows intramolecular hydrogen bonding between the hydroxyl group and the enolate oxygen atom. Furthermore, the α-methylene units of the ammonium counterion form hydrogen bonds to the basic enolate C and O atoms and to the O atom of the hydroxy group. This three-point bonding occurs selectively on the Re,Re side, a phenomenon which may be responsible for the direction of diastereo-selectivity in the epoxide-forming reaction of the enolate with N-bromosuccinimide.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020405
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  • 202
    Electronic Resource
    Electronic Resource
    A 2,3-Connected Tellurium Net and the Cs3 Te22 Phase (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 390-397 
    Details
    ISSN: 0947-6539
    Keywords: band structures ; hypervalent bonding ; semiempirical calculations ; tellurium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bonding in the recently reported Cs3 Te22 phase, which contains both Te8 rings and remarkable Te6 sheets, is studied by approximate molecular orbital theory. Our focus is on the geometric and electronic features of the unique 2,3-connected Te net found as a substructure in this phase. The calculations show that both the linear and T-shaped Te geometries in the 2,3-connected Te net of Cs3 Te22 are determined by their particular electron count. Both types of tellurium atoms are hypervalent; we make connections to other well known hypervalent molecules, such as XeF2, I3-, and BrF3. Several possible variations and distortions of this net are discussed, all of which are found to be less stable. The discrete crown-shaped Te8 units that appear in the phase show normal covalent bonding and should occur in smaller molecular entities, too. According to our computations, Cs3 Te22 should be metallic. Two structurally related phases, CsTe7 and Cs2 Te15, are suggested.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020407
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  • 203
    Electronic Resource
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    A New Experimental Method to Determine the Mutual Orientation of Helices in Coiled-Coil Proteins: Structural Information about the Dimeric Interface of cJun, cFos, GCN4, and gp41Part of this paper was presented at the 13th American Peptide Symposium, Edmonton, Alberta (Canada), June 20-25, 1993. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 403-411 
    Details
    ISSN: 0947-6539
    Keywords: helices ; proteins ; structure elucidation ; viral proteins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Disruption of protein dimers interacting by a leucine zipper motif represents a new potential pharmaceutical target. However, structural information concerning the exact nature of the interacting helices is usually not available. Towards this end, we have developed a disulfide-trapping approach capable of distinguishing between the ad and gd modes of dimerization (Fig. 1), thus providing information useful in the design of small molecules that interfere with helix-helix interactions. We designed and synthesized nine cysteine-substituted peptide fragments: GCN 4(g), GCN 4(a), GCN 4(d), cFos(g), cFos(a), cFos(d), cJun(g), cJun(a), and cJun(d), and evaluated the covalent crosslinking rates for them and their binary mixtures. Neither homogeneous cJun nor cFos dimerized and crosslinked, but their binary mixtures did with t1/2 of formation a 〉 d 〉 g, indicating to cFos-cJun heterodimerization according to ad mode (Fig. 1 a). Similarly, GCN 4 dimerized and crosslinked in the ad fashion; this result was in excellent agreement with the published X-ray structure. Next, we investigated the mode of gp 41 dimerization, which appears critical for HIV-1 replication The gp41 cysteinesubstituted fragments gp 41(g), gp 41(a), and gp 41(d) also dimerized and crosslinked, but with a different order of t1/2 of formation g 〉 d 〉 a, thus providing evidence that gp41 dimerizes in the gd mode (Fig. 1 b). Thus, the crosslinking experiments allow rapid elucidation of structural details of macromolecular interactions in aqueous media. These findings should prove useful in the design of compounds that inhibit macromolecular association.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020409
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  • 204
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    1,3-Alternate Calix[4]arenecrown-5 Conformers: New Synthetic Ionophores with Better K+/Na+ Selectivity than Valinomycin (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 436-445 
    Details
    ISSN: 0947-6539
    Keywords: binding studies ; calixarenes ; crown ethers ; ionophores ; membranes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New 25,27-dialkoxycalix-[4]arenecrown-5 conformers 8, 10, and 11 have been synthesized and studied. The compounds 8a and 8b, fixed in 1,3-alternate structure, have been obtained in 57 and 40% yield, respectively, by reaction of the corresponding 25,27-dialkoxycalix[4]arenes 7a-b with tetraethylene glycol di-p-toluenesulfonate in the presence of Cs2CO3. The cone 10a and 10b and the partial cone 11 conformers were obtained by selective demethylation of the 25,27-dimethoxycalix[4]arenecrown-5 (6a) and subsequent dialkylation with NaH/DMF and KOtBu/THF, respectively. In the solid state (X-ray), compound 6a adopts a flattened cone conformation, which is also found to be most abundant in CD3CN and CD3OD solution. Upon complexation with potassium picrate compound 6a was converted quantitatively into the 1,3-alternate conformation. All new ligands synthesized were used in the extraction of alkali metal cations from H2O into CHCl3, and as active components in supported liquid membranes and in chemically modified field effect transistors. Results were compared to those obtained with with the natural antibiotic valinomycin 1. All ligands showed high selectivity for potassium. Ligand 8a, fixed in the 1,3-alternate conformation, is more selective than valinomycin and shows the highest K+/Na+ selectivity known so far.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020413
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  • 205
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    9-Borabarbaralanes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 458-461 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; barbaralanes ; borabarbaralanes ; Cope rearrangement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of MgCOT(thf)x with tBuBF2 or PhBCl2 affords the first 9-borabarbaralanes 2 (C8H8BR, a: R = tBu; b: R=Ph). With the aminoboron dihalides BCl2NiPr2 and BCl2N(SiMe3)tBu 9-borabicyclo[4.2.1]-nona-2,4,7-trienes 3 (a: R=NiPr2, b: R=N(SiMe3)tBu) and the trans-9-borabicyclo[4.3.0]nona-2,4,7-triene 4 are obtained. The bicyclic compounds 3a and 3 b are converted into 9-borabarbaralanes 2c and 2 d, respectively, by irradiation in solution as well as by heating. All 9-borabarbaralanes 2 are fluxional in solution. In the crystalline state, the B-phenyl derivative 2b displays a well-ordered van der Waals crystal structure. The theoretical prediction that the degenerate Cope rearrangement in barbaralanes will be retarded by π-acceptor groups in the 9 position has been verified. Quantum chemical calculations employing density functional theory support and help interpret the experimental findings. The isoelectronic 9-barbaralyl cations, in contrast, have such high Cope barriers that other rearrangement pathways are followed instead.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020416
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  • 206
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    A Novel Route to Racemic and Nonracemic Products of the Ugi Reaction: Synthesis of Ugi′s Labile α-Adducts from Iminoaziridines and Carboxylic Acids, and their TransformationsIminoaziridines, Part 7 [1]. Part 6: ref. [37].Dedicated to Professor Ivar Ugi on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 462-469 
    Details
    ISSN: 0947-6539
    Keywords: aziridines ; imides ; isoimides ; rearrangements ; Ugi reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iminoaziridines (11) are highly reactive synthetic equivalents for three of the four components in the Ugi four-component condensation. Thus, iminoaziridines react rapidly with carboxylic acids at temperatures as low as -20°C to afford α-amino isoimides (14), which are identical to the elusive α-adducts of isocyanides in the Ugi reaction. 1,4-Migration of the acyl group (O → α-N) in 14 furnishes the α-acylamino amides 15. Very little, if any, racemisation is observed when carboxylic acids react with nonracemic iminoaziridines [(R)-11 a,c], which are readily available. Mumm rearrangement by O → N-acyl 1,3-migration to afford α-amino imides (16 e, f) competes if the O → α-N 1,4-shift is slowed down by steric hindrance. The latter acyl shift is catalysed by carboxylic acids while the former is not. The iminoaziridines (R)-11 a,c react quantitatively and without racemisation with hydrazoic acid to produce the 5-aminoalkyltetrazoles (R)-21 a,c.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020417
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  • 207
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    Supramolecular Motifs: Concerted Multiple Phenyl Embraces between Ph4P+ Cations Are Attractive and Ubiquitours (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 481-486 
    Details
    ISSN: 0947-6539
    Keywords: cations ; crystal structures ; phenyl rings ; supramolecular chemistry ; tetraphenylphosphonium ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Examination of the Cambridge Structural Database reveals that Ph4P+ cations in crystals associate through phenyl-phenyl nonbonded interactions which are attractive, concerted, and widespread. Intermolecular phenyl-phenyl conformations, which are offset-face-to-face (off), edge-to-face (ef) or vertex-to face (vf), combine in five classes of supramolecular motifs for {Ph4P+}2 pairs, namely the sextuple phenyl embrace (SPE) with (ef)6 and offset sextuple phenyl embrace (OSPE) containing (off)1 (ef)2(ef/vf)2, the translational quadruple phenyl embrace (TQPE) with (ef)4, the parallel quadruple phenyl embrace (PQPE) with (off)1(vf)2, and the double phenyl embrace (DPE) with (off)1. Typical intermolecular attractive energies (kJ per mol of {Ph4P+}2) for these motifs are SPE 85, OSPE 57, TQPE 70, PQPE 41, DPE 34. There is strong interpenetration of the cations in these motifs: 489/770 structures in the CSD have P⃛P≤7 Å (spherical Ph4P+ has a van der Waals diameter of 13.6 Å). Of the 812 instances of P⃛P ≤7 Å, 86% are SPE, 10% are OSPE, 2% are TQPE, and only 2% are unclassified, Average P⃛P separations in the PQPE and DPE are 8.3 Å. Centrosymmetry is prevalent in all except the TQPE, which has implications for the engineering of noncentric crystals.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020505
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  • 208
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    Electron-poor 2,3-Dihydro-1,3-Diborolyl Complexes of Iron and Ruthenium: Synthesis, Reactivity, and Crystal and Electronic Structures of an Iron Sandwich ComplexDedicated to Professor Herbert Schumann on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 487-494 
    Details
    ISSN: 0947-6539
    Keywords: boron compounds ; diboroles ; Group 8 complexes ; sandwich complexes ; semi-empirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition product of sodium hydride and the 2,3-dihydro-1,3-diborole (CiPr)2(BEt)2CHMe (3c) reacted with [{(C5Me5)FeCl}x] to produce the green sandwich complex [(C5Me5)Fe{n5-(CiPr)2(BEt)2CMe}] (2 c), which formally contains 16 valence electrons (VE). Complex 2c has unexpected structural properties in the solid state: the 1,3-diborolyl ring is extremely folded (41°), and the Fe-C2 distance is short (1.90 Å). Analogously, violet Ru complexes 4a,c,d were obtained from 3a,c, NaH or tBuLi, and [{(C5Me5)RuCl}4]. With the less bulky heterocycles 3 b,e the new 30 VE triple-decker complexes [(C5Me5)Ru{μ,n5-(CR1)2(BR2)2CMe}RuH(C5Me5)] (5b,e) were formed, which contain a Ru-H bond. Cyclic voltammetric studies revealed the existence of stable anions 2c- and 4d- formed by reversible one-electron reduction at -1.26 and -1.40 V, respectively (vs. SCE). The red-brown anions were further characterized by ESR spectroscopy following stepwise reduction of the neutral species with potassium in THF. Addition of CO to 4a and 4d led to formation of the monocarbonyl complexes [(C5Me5)Ru(CO){n5-(CR1)2-(BR2)2CMe}] (6a,d), and 6d was characterized by X-ray structure analysis. The heterocycle in 6d is less folded (19°) than in 2 c. Its CO ligand causes a 28.5° tilt of the cyclic ligands. Reaction of CO with 2 c yielded a red product of unknown structure. The electronic structure of 2 was studied by EH-MO theory, which revealed a unique bonding in the sandwich. The s̰ electron density of the B-C bonds participates in the bonding to the iron atom; this demonstrates that the number of bonding electrons is the same as in ferrocene. Thus, the complexes 2 actually have 18 VE.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020506
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    Nucleophilic Addition of Secondary Phosphines to Cationic Dienyl Tricarbonyliron Complexes: A novel Route to Optically Active PhosphinesOptically Active Transition Metal Complexes, Part 6. Part 5: U. Englert, M. Käser, A. Salzer, Inorg. Chem. 1995, 34, 6231-6232. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 523-528 
    Details
    ISSN: 0947-6539
    Keywords: carbonyl complexes ; chiral ligands ; iron complexes ; phosphorus ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Secondary phosphines such as HPPh2 and to the cationic iron dienyl complex [η5-(1R)-ethylnopadienyl)Fe-(CO)3]+ (1) by nucleophilic addition. The phosphonium salt initially formed is readily deprotonated to yield an optically active tertiary phosphine [(n4-(1 R)-ethylnopadienePPh2)Fe(CO)3] (2b). A similar reaction also occurs with [C6H7Fe-(CO)3]+ (3) and [C7H9Fe(CO)3]+ (4) to give [(C6H7PPh2)Fe(CO)3] (5) and [(C7H9PPh2)Fe(CO)3] (6) in good yields. The mechanism of formation of these novel phosphines is discussed. Complex 2 b crystallizes in the space group P212121 (no. 19); 5 crystallizes in the space group P21/c (no. 14). Like other monodentate optically active phosphines, 2 b is capable of coordinating to transition metal complexes. It forms palladium complexes on reaction with [{μ-chloro(allyl)palladium}2] as well as with [{μ-chloro[(N,N-dimethylamino-kN-2-methyl)phenyl-kC]palladium}2] (11). The latter reaction product crystallizes in the space group P31 (no. 144).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020511
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  • 210
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    Synthesis of Methyl 5′-Thio-α-isomaltoside via an Acyclic Monothioacetal and its Behavior toward Glucoamylase (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 556-560 
    Details
    ISSN: 0947-6539
    Keywords: binding studies ; glucoamylase ; isomaltoses ; oligosaccharides ; thiosugars ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl 5′-thio-α-isomaltoside (1), which contains the ring-sulfur analogue of the nonreducing glucoside of isomaltose, was synthesized from gentiobiose through a novel ring opening-recyclization approach. The nonreducing glucoside of per-O-benzylated phenyl 1-thio-β-gentiobioside underwent O-5′-C-1′ bond cleavage with dimethyl-boron bromide and thiolacetic acid to give the acyclic monothioacetal 4 with the 1-thioglucopyranoside at the reducing end intact. The HO-5′ group in 4 was inverted by a standard oxidation-reduction process with good efficiency. Recyclization under Mitsunobu condition allowed C-5′-S-1′ bond formation with inversion of configuration at C-5′, to give 1 after functional group interconversion. TLC analysis showed that 1, unlike isomaltose, was not hydrolyzed by glucoamylase from Rhizopus niveus. A fluorometric assay confirmed that the dissociation constant (Kd) for 1 with the enzyme was 39 mM at 20°C, which is comparable with that for isomaltose. A binding assay involving fluorescence titration of the enzyme-1 complex with gluconolactone indicated that the disaccharide 1 was bound to the catalytic and noncatalytic subsites. Since isomaltose is known to bind only to the noncatalytic subsites, this result indicates a relatively high affinity of the 5-thioglucose moiety for the catalytic subsite.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020515
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  • 211
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    A new nickel(III) oxide family: MSr3NiO6 (M = Sc, In, Tm, Yb and Lu) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 737-741 
    Details
    ISSN: 0947-6539
    Keywords: Jahn-Teller distortions ; magnetic properties ; neutron powder diffraction ; nickel oxides ; X-ray powder diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new phases MIIISr3NiIIIO6 have been prepared for M = Sc, In, Tm, Yb and Lu. Thermogravimetric analysis indicates that these phases are stoichiometric nickel(III) oxides. Rietveld refinement of their crystal structures from powder X-ray diffraction data confirms that they adopt the rhombohedral K4CdCl6- type structure (space group R\documentclass{article}\pagestyle{empty}\begin{document}$ \bar 3 $\end{document}c, a = 9.6595 (2) and c = 10.8546 (3) Å for ScSr3NiO6). The M site is fully occupied for M = Sc and In, but a deficiency of scattering for M = Tm, Yb and Lu is shown to be due to Ni substitution through a simultaneous refinement of the YbSr3NiO6 structure using X-ray and time-of-flight neutron diffraction data. The refined composition is (Yb0.83Ni0.17)-Sr3NiO6. The magnetic suseptibilities of the M = Sc, In and Lu samples show Curie-Weiss behaviour down to 6K; however, ScSr3NiO6 shows a broad transition between 250 and 290 K, with Curie-Weiss behaviour above and below this anomaly. This transition is thought to be between the statically and dynamically Jahn-Teller distorted regimes of octahedrally coordinated, low-spin Ni3+.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chem.1460020616
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  • 212
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    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020620
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  • 213
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    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020701
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  • 214
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    Formation of bridging nitride versus terminal oxovanadium promoted by a vanadium(II) macrocyclic complex (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 767-771 
    Details
    ISSN: 0947-6539
    Keywords: bridging ligands ; dinitrogen reduction ; nitrides ; vanadium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [VCl2(tmeda)2] with the tetralithium salt of octaethylporphyrinogen (oepg)[Li(thf)]4 initially yielded a monomeric VII complex [(oepg)-VLi4Cl2(thf)4] (1). Treatment of this species with tetramethylethylenediamine afforded a mixture from which [(oepg)-V(thf)2][Li(tmeda)2].0.5 toluene (2 a) (or 2 b when ethyl is replaced by nPr) and the unprecedented nitrido-bridged dimeric species [{oepg)V}2(m̈-N)(m̈-Li) 4]-[Li(tmeda)2] (3) were isolated and characterized. The bridging nitrogen atom probably originated from the cleavage of dinitrogen, since the same reaction carried out under exclusion of N2 gave [(oepg)VO]-[Li(tmeda)]2 (4), where the oxo atom probably originated from deoxygenation of THF. The connectivity of 1, 2 b, 3, and 4 was demonstrated by X-ray analysis.
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    URL: http://dx.doi.org/10.1002/chem.1460020705
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    Biomimetic ion-binding monolayers on gold and their characterization by AC-impedance spectroscopy (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 759-766 
    Details
    ISSN: 0947-6539
    Keywords: ionophores ; impedance spectroscopy ; membrane models ; monolayers ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel ion-binding monolayers on gold surfaces are presented where the molecular design is based upon the natural ion binder ferrichrome. The new ion binders possess hydroxamate coordinating groups arranged in C2 symmetry (bishydroxamate binder, BHB) or C3 symmetry (trishydroxamate binder, THB), and a separate dialkyl sulfide moiety, which serves as an anchor to the gold substrate. The separation between the ion-binding cavity and the attachment site to the gold allows each parameter to be controlled separately, namely, cavity size, its symmetry and external envelope, as well as the functional group used for immobilization. The monolayers were characterized with respect to ellipsometric thickness, wettability (advancing and receding contact angles (CAs) for water), and surface coverage; the latter is determined by metal underpotential deposition (UPD). It is shown that the introduction of hydrophobic side chains (i-butyl) improves the CAs, thickness, and surface coverage of the monolayers. A detailed analysis of the alternating-current (AC) impedance spectra is presented for THB monolayers on gold electrodes, where the impedance data are fitted to an equivalent circuit model. It is shown that the AC response in a wide frequency range can be used to probe ion binding and release in monolayer systems on electrodes.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/chem.1460020704
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    Self-assembling tetrathiafulvalene-based rotaxanes and catenanes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 624-633 
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    ISSN: 0947-6539
    Keywords: catenanes ; macrocycles ; rotaxanes ; self-assembly ; tetrathiafulvalenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general stepwise approach is described for the preparation of tetrathiafulvalene (TTF)-based linear and monoand dimacrocyclic compounds incorporating one or two 1,4-dioxyphenylene, 9,10-dioxyanthrylene, or 1,5- or 2,6-dioxynaphthylene units from readily available starting materials. By utilizing the π-π stacking interactions of the TTF unit with the dipyridinium dication of 1,1′-[1,4-phenylenebis (methylene)] bis-4,4′-bipyridinium bis(hexafluorophosphate), a rotaxane and two [2]catenanes were synthesized starting from the linear and monomacrocyclic compounds, respectively. From the dioxyphenylene-based dimacrocycle, three [3]pseudocatenanes (trans, cis, and a mixture of cis/trans isomers) were obtained with the trans compound as the major product. From the dioxyanthrylene dimacrocycle, only the trans-[3]pseudocatenane was obtained. Catenane products were formed quantitatively from the 1,5-dioxynaphthylene dimacrocycle in a template-directed reaction, affording a trans-[3]pseudo-catenane together with a [4]pseudocatenane (mixture of cis/trans isomers). From the 2,6-dioxynaphthylene dimacrocycle, a cis-[3]pseudocatenane was obtained as the major product and a trans-[3]pseudocatenane as the minor one. For the [3]pseudocatenanes (i.e., both the cis and trans catenanes), in which the TTF units were clamped by the tetracationic macrocycle, isomerizations were completely prevented even in the presence of trifluoroacetic acid. All new rotaxanes and catenanes were characterized by electrospray mass spectrometry, and the cis- and trans- [3]pseudocatenanes were additionally investigated by 1H NMR spectroscopy. The electrochemical and spectral properties of the rotaxane and the catenanes are reported. Catenane formation increases the redox potentials of the TTF unit. The results demonstrate the versatility of TTF as a building block in the construction of supramolecular structures.
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    Conformational studies of chiral vinylogous sulfonamidopeptides (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 644-655 
    Details
    ISSN: 0947-6539
    Keywords: conformation ; crystal structure ; molecular modeling ; NMR spectroscopy ; sulfonamido-pseudopeptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational preferences of chiral vinylogous aminosulfonic acids (vs-amino acids) and of the corresponding oligomers (vs-peptides) were investigated by a combination of X-ray crystallography, variable-temperature (VT) 1H NMR spectroscopy, FT-IR spectroscopy, and NOE experiments. The major source of conformational freedom in the monomers is the rotation around the C—C bond connecting the double bond with the allylic stereocenter (N—C*—C=C). The allylic conformational perferences can be altered in the oligomers by the formation of secondary structures enforced by hydrogen bonding. Twelve-membered-ring hydrogen bonding is detected in the crystal structure of vs-dipeptide 9, while fourteen-membered-ring bydrogen bonding is the most common folding pattern for the oligomers in chloroform solution. The experimental results are complemented by computer modeling: suitable force-field (FF) parameters for the unsaturated sulfonamide group nwere develiped from ab initio calculations. A Goodman-Still systematic pseudo-Monte-Carlo search was used for the conformational search. The conformers were minimized in chloroform with the GB/SA model. The calculations correctly predicted both the size of the hydrogen-bonded ring and its relative importance, in agreement with the experimental data in solution.
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    URL: http://dx.doi.org/10.1002/chem.1460020606
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    Dimensional reduction in II-VI materials: A2Cd3Q4 (A = K, Q = S, Se, Te; A = Rb, Q = S, Se), novel ternary low-dimensional cadmium chalcogenides produced by incorporation of A2Q in CdQ (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 656-666 
    Details
    ISSN: 0947-6539
    Keywords: cadmium compounds ; chalcogen compounds ; crystal structure ; dimensionality ; photoluminescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the isomorphous, layered chalcogenides K2Cd3S4 (I), Rb2Cd3S4 (II), K2Cd3Se4 (III), Rb2Cd3Se4 (IV), and K2Cd3Te4 (V) in molten A2Qx fluxes in reported (A = K, Rb; Q = S, Se, Te; x = 2 to 3). The compounds form as (Cd3Q4)n2n- layers interspersed with A + cations; the layers are composed of Cd3Q2-4 units shaped as truncated cubes. The compounds have room-temperature band gaps of 2.75, 2.92, 2.36, 2.37, and 2.26 eV for I, II, III, IV, and V, respectively, and also display strong photoluminescence. The thermal analysis data for all compounds are reported. The properties of these compounds are compared with those of the three-dimensional compounds CdS, CdSe, and CdTe, as well as those of the nanometer-sized CdQ clusters. A conceptual context is presented to connect all these different types of compounds.
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    Cyclobis(paraquat-4,4′-biphenylene)-an organic molecular square(Molecular Meccano), Part 8: for Part 7, see P. R. Ashton, P. T. Glink, J. F. Stoddart, P. A. Tasker, A. J. P. White, D. J. Williams, Chem. Eur. J. 1996, 2, 729-736. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 877-893 
    Details
    ISSN: 0947-6539
    Keywords: catenanes ; second-sphere coordination ; self-assembly ; template syntheses ; topological stereoisomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Template-directed syntheses of cyclobis(paraquat-4,4′-biphenylene) (1)- a Molecular square-have been achieved by use of π-electron-rich macrocyclic hydroquinone-based and acyclic ferrocene-based templates. In particular, the use of a polyether-disubstituted ferrocene derivative as a template permits synthesis of 1 (which is accessible only in very low yields without templates) on a preparative scale. Furthermore, the use of a macrocyclic hydroquinone-based polyether template in corporating an ester function in one polyether chain-an (oriented) macrocycle-affords a 1 : 1 mixture of two topologically stereoisomeric [3]catenanes. Ester hydrolysis of the π-electron-rich macrocyclic components mechanically interlocked with 1 within the catenated structures releases the tetracationic cyclophane in quantitative yield as a result of the degradation of the [3]catenanes. The molecular square has been characterized by X-ray crystallography, FAB mass spectrometry, 1H NMR and 13C NMR spectroscopies, and elemental analysis. The binding properties of 1 and of the smaller cyclophane cyclobis(paraquat-p-phenylene) toward a series of π-electronrich guests have also been investigated with the above techniques and UV/VIS spectroscopy. The self-assembly of the resulting supramolecular complexes in solution and in the solid state is driven mainly by π-π stacking interactions and hydrogen-bonding interactions, as well as by edge-to-face T-type interactions. In particular, the complexation of ferrocene or a ferrocene-based derivative within the cavity of 1 suggests the possibility of constructing functioning ferrocene-based molecular and supramolecular devices that can be controlled electrochemically in the form of catenanes, rotaxanes, and pseudorotaxanes.
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    Resonance-assisted O-H ⃛ O hydrogen bonding: Its role in the crystalline self-recognition of β-diketone enols and its structural and IR characterization (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 925-934 
    Details
    ISSN: 0947-6539
    Keywords: crystal engineering ; diketone enols ; hydrogen bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fact that hydrogen bonding is normally stronger than other nonbonding attractive forces can be exploited for the rational design of molecular crystals with known packing features and specific physical properties (crystal engineering). In the present paper the problem of obtaining homodromous molecular chains controlled by strong O-H ⃛ O interactions is investigated, particular attention being paid to β-chains, that is, infinite hydrogen-bonded chains of β-diketone enol fragments ⃛ O=C—C=C—OH ⃛, which are linked by stronger-than-usual resonance-assisted hydrogen bonds (RAHBs) and are intrinsically interesting as prototypes of a large family of switching proton bistate molecular devices. Accordingly, the crystal and molecular structures of thirteen new compounds containing the 1,3-cyclopentanedione and 1,3-cyclohexanedione fragment (or their heterocyclic analogues) were determined, and most of them were found to give the expected β-chain packing pattern. Comparison with literature data makes it possible to identify seven fundamental β-chain patterns, which can be shown to be selected by reason of the relative encumbrances of the substituents. Furthermore, a general analysis of all functional groups able to form strong O—H ⃛ O bonds reveals a semiquantitative correspondence between the O—H ⃛ O measurable parameters (O ⃛ O, H ⃛ O and O—H distances, and ṽ(O—H) IR stretching frequencies) and the hydrogen bond energy EHB, and a hierarchy of chemical functionalities that are well characterized by limited EHB ranges and that, in decreasing order of energy, can direct the crystal packing process.
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    Oxidative addition of aryl halides to transient anionic à-aryl-palladium(0) intermediates - application to palladium-catalyzed reductive coupling of aryl halides (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 957-966 
    Details
    ISSN: 0947-6539
    Keywords: catalysis ; C-C coupling ; mechanistic studies ; oxidative addition ; palladium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates and mechanism of the reactions of a series of aryl-ligated, anionic palladium(0) complexes Ar-Pd0-(PPh3)-2 with para-substituted iodobenzenes were investigated by means of transient electrochemistry. The reaction was found to be first order in each reactant and to proceed similarly to oxidative addition of aryl halides to the halide-ligated species X-Pd0(PPh3)-2, although much faster and less sensitive to electronic factors. Owing to the short lifetime (t1/2 ≍ 1 - 5 ms) of the product of this reaction, it could not be characterized in detail. However, based on kinetic results, this transient species is thought to be an anionic pentacoordinated bisarylpalladium(II) complex, which undergoes rapid loss of halide ligand to yield, most probably, a bisarylpalladium(II) neutral species. Based on the study of this reaction and on previously reported results, we propose a mechanism for the palladium-catalyzed homocoupling of aryl halides consisting of a catalytic cycle initiated by oxidative addition of an aryl halide to a zerovalent tris-ligated palladium center. Two-electron reduction of the pentacoordinated arylpalladium(II) anionic species thus formed gives a tris-ligated anionic arylpalladium(0) center, which undergoes oxidative addition with a second aryl halide molecule to eventually lead to a bisaryl-palladium(II) neutral species. Reductive elimination of a bisaryl molecule from this center closes the catalytic cycle by regenerating the initial zerovalent palladium complex. The application of this sequence to the catalytic heterocoupling of aryl halides is discussed, and it is concluded, on the basis of Hammett correlations, that statistical yields should be observed, in agreement with the results obtained for preparative reactions in DMF.
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    Photoreactions of phenyl-substituted N-(pent-4-enyl-1-oxy)pyridine-2(1 H)-thiones (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1014-1023 
    Details
    ISSN: 0947-6539
    Keywords: alkoxy radicals ; cyclizations ; pyridinethiones ; radicals ; tetrahydrofurans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of hitherto unknown N-(pent-4-enyl-1-oxy)pyridine-2(1 H)-thiones (6) were prepared from substituted pent-4-enyl tosylates or benzylic chlorides. On irradiation with incandescent light heterocycles 6 liberated alkoxy radicals 2, which were studied for rearrangement reactions. Surprisingly, all transformations involving the 1-phenylpent-4-enyl-1-oxy radical (2a), for example, to give the substituted thioether 8, 2-bro-momethyl-5-phenyltetrahydrofuran (11), or the tetrahydrofuran 14a, were not stereoselective. On the other hand 2-, 3- mono-, and 1,5-disubstituted pent-4-enyl-1-oxy radicals 2d-e and 2g cyclized in good yields and with good to excellent stereoselectivities to give the corresponding 2,4-cis- and 2,3-trans-phenyltetra-hydrofurfuryl radicals 3d-e, and the trans-2-benzyl-5-methyl substituted intermediate 3g. The major reaction mode of the 4-phenylpent-4-enyl-1-oxy radical (2f) was the 6-endo cyclization, which afforded 3-phenyltetrahydropyran (13f) as the major product (endo:exo = 93:7) after trapping with hydrogen donors. According to the experimental data of the present study, the unusual reactivity of the 1-phenylpent-4-enyl-1-oxy radical (2a) in 5-exo-trig ring closures could be caused by a coplanar arrangement of the benzyloxy moiety in the transition state of the cyclization. This interaction would lock the radical center in 2a in a preferred conformation, which would result in similar steric effects for both cis- and trans- cyclizations.
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    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.1460020901
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    Oxidation products of organic trisulfanes: Molecular structures and energies of various isomers of the dimethyltrisulfane oxides Me2S3O and Me2S3O and of 1,3-tBu2S3O2Sulfur Compounds, Part 193; for Part 192 see R. Steudel, Ind. Eng. Chem. Res. 1996, 35, 1417. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1060-1067 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; rotamers ; stereoisomers ; sulfane oxides ; torsional potentials ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio MO calculations (MP 2/6-311 G**//HF/6-311 G**) have been performed for several isomers (including rotamers) of Me2S3O and Me2S3O2. MeS(O)SSMe exists as five rotamers; the most stable form (1a) has a helical backbone CSSSC with S-S bond lengths of 206.0 (SIISII) and 212.4 pm (SIISII). The most stable rotamer of MeS-S(O)SMe (2a), is less stable than 1a by 10.7 kJ mol-1; it is of Cs, symmetry, while a rotamer of Cs symmetry (2b) is less stable than 2a by only 1.4 kJ mol-1. Both 2a and 2b are stabilized by O ⃛ H hydrogen bonds. The S-S bond lengths of 2a are 210.0 and 212.0 pm; the CSSSC chain is not helical (CSSS torsion angles 166.3 and -75.4°). The 1,3-dioxide MeS(O)-SS(O)Me (3) has two equivalent chiral centers and exists as diastereomers. The most stable isomer 3a (RR)/(SS) is of C2 symmetry with methyl groups trans to each other; the SO bonds form an angle of about 90°. The meso form 3b is less stable than 3a by 17.2 kJ mol-1 and the rotamers 3c and 3d are less stable by 25.6 kJ mol-1 and 28.4 kJ mol-1, respectively. The trisulfane-1.2-dioxide MeS(O)-S(O)SMe has two nonequivalent chiral centers and exists as five isomers. The most stable form, the (RS)/(SR) form 4a, is less stable than 3a by 21.4 kJ mol-1 and is characterized by SS bonds of 220.9 (SIIISIII) and 208.3 pm (SIIISII). The rotamer 4b is less stable by 5.9 kJ mol-1. The isomers 4c, 4d, and 4e are all of (SS)/(RR) configuration and are less stable than 4a by 6.3, 12.7, and 12.0 kJ mol-1. For comparison, ab initio MO calculations (HF/6-311 G*) for tBuS(O)SS(O)-tBu yielded two diastereomers of practically identically energy that both contain helical CSSSC backbones. The (RS) form is less stable than the (RR)/(SS) form by 1.8 kJ mol-1.
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    Redox Properties of the Diatomic Bare Iron Chalcogenides FeO and FeS in the Gas PhaseDedicated to Professor Helmut Baumgartel on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1230-1234 
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    ISSN: 0947-6539
    Keywords: ab initio calculations ; iron oxide ; iron sulfide ; mass spectrometry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron-transfer behavior of the binary iron chalcogenides FeO and FeS has been examined by means of mass spectrometry and ab initio calculations using the averaged coupled-pair functional (ACPF) method. The experimental and theoretical results are in good agreement with each other and also with previous studies. The ionization energies (IE) of the diatomic species are found to be IE(FeO) = 8.8±0.2 eV, IE(FeO+) = 17.9±0.4 eV, IE(FeS) = 8.3±0.3 eV, and IE(FeS+) = 16.3±0.5 eV. Two new diatomic dications, FeS2+ and FeO2+, are shown to exist as metastable minima on the corresponding potential-energy surfaces. The data enable an evaluation of the intrinsic gas-phase redox properties of FeS and FeO, and the comparison demonstrates that iron sulfide is more prone to undergo facile reduction and oxidation than iron oxide.
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    Graphical abstract (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1347-1351 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.19960021103
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    Self-Assembly of Heterobimetallic Complexes and Reactive Nucleophiles: A General Strategy for the Activation of Asymmetric Reactions Promoted by Heterobimetallic Catalysts (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1368-1372 
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    ISSN: 0947-6539
    Keywords: heterobimetallic catalysts ; Michael additions ; multifunctional catalysts ; nitroaldol reactions ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heterobimetallic asymmetric catalysts, such as the lanthanum-lithium-binaphthol complex (La Li-BINOL), the aluminum-lithium-binaphthol complex (AlLi-BINOL), and a newly prepared gallium-sodium-binaphthol complex (Ga Na-BINOL), have been self-assembled with reactive nucleophiles, such as lithium nitronates and sodium malonates, to generate more efficient catalysts than the parent heterobimetallic catalysts. For example, by the combined use of La Li-BINOL (1 mol%; contains one H2O molecule) and BuLi (0.9 mol%) as the catalyst system, asymmetric nitroaldol reactions are greatly accelerated in all cases without a decrease in the optical purity of the nitroaldol products. Kinetic analyses have also been carried out on the Ga Na-BINOL-catalyzed Michael reaction of dibenzyl malonate with cyclohexenone, with or without NaOtBu. The calculated rate constants show that the combined use of Ga Na-BINOL and NaOtBu as the catalyst gives reaction rates that are about 50 times faster than with Ga Na-BINOL alone. This activation method should be useful for other asymmetric reactions catalyzed by heterobimetallic complexes.
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    Investigation of the Self-Assembly Pathway of Pentanuclear Helicates by Electrospray Mass Spectrometry (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1395-1398 
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    ISSN: 0947-6539
    Keywords: bipyridine ligands ; helicates ; kinetics ; mass spectrometry ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-assembly of the pentanuclear double helicates Hh, Ha and He from the corresponding oligobipyridine strands Lh, La and Le and Cu1 ions has been investigated by NMR and electrospray mass spectrometry (ESMS). Where as Hh is assembled rapidly (in less than 20 min), He (about 20 h) and especially Ha (about 60 h) form much more slowly. The rate decreases strongly with increasing steric bulk of the substituents in the 4,4′-positions on the bipyridine units; this indicates that the search processes (wrapping, unwrapping) that lead to the final helicate are strongly hindered by the size of the substituents. The ESMS data give information about the species present in solution under different conditions and allow the formulation of possible formation pathways, which may involve, in particular, helicates of hairpin type.
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    A Novel Type of Resonance-Stabilised Dicobalt Complex with a Cyclopentadienylidene Bridge - Synthesis, Structure and Electronic Properties of [(C5R5)Co(μ-C5H4)Co(L)(C5R5)'] (L = C2H4, CO, CNtBu, PR3, P(OMe)3; R = H, Me) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1453-1465 
    Details
    ISSN: 0947-6539
    Keywords: carbenes ; CH activation ; dinuclear complexes ; sandwich complexes ; spin equilibria ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dinuclear μ-cyclopentadienylidene complexes [(C5R5)Co(μ-C5H4)-Co(C2H4)(C5R'5)] (5) [5aa (R = R' = H), 5ab (R = H, R' = Me), 5ac (R = H, R'5 = H4Me), 5ba (R = Me, R' = H), 5bb (R = R' = Me) and 5da (R5 = Me4Et, R' = H)] were synthesised from [(C5R5)Co(η4-C5H6)] (4) [4a (R = H), 4b (R = Me), 4d (R5 = Me4Et)] and [(C5R'5)Co(C2H4)2] (1) [1a (R' = H), 1b (R' = Me) and 1c (R'5 = H4Me)]. In these reactions, both CH bonds of the methylene group of coordinated cyclopentadiene are activated under mild conditions. Substitution of the ethylene ligand in 5 by L leads to the carbonyl, isocyanide, phosphine, and phosphite derivatives [(C5R5)Co(μ-C5H4)Co(L)-(C5R'5)] [6aa, 6ab, 6ba, 6bb (L = CO), 7aa (L = tBuNC), 8aa, 8ab (L = PMe3), 9aa (L = PMe2Ph), 10aa (L = PMePh2) and 11aa (L = P(OMe)3)]. The crystal structures of 5aa, 5ab, 5ba, 6aa and 8aa have been determined. The experimental geometry is rationalised in terms of two limiting structures with μ-η4:η1 and μ-η5:η1 coordination of the bridging cyclopentadienylidene ligand. On the basis of the 18 valence electron rule, zwitterionic character is assigned to latter. This structure is preferred when L is an acceptor ligand, as in 6. In solution, 5-11 are fluxional with rapid rotation about the very short cobalt-carbene C bond. In addition the hindered rotation of the ethylene ligand in 5ab was studied by DNMR spectroscopy. In solution, a singlet-triplet equilibrium was established by variable-temperature NMR spectroscopy for 8aa. The temperature-dependent 1H NMR line shifts were analysed by means of an isotropic shift model to give 24≤ΔH° ≤ 32 kJ mol-1 and 45≤ΔS° ≤74 J mol-1 K-1 with the triplet state being preferred by entropy at higher temperatures.
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    Cesium Fluoride-Bromine Intercalation Compounds (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1303-1307 
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    ISSN: 0947-6539
    Keywords: bromine compounds ; cesium compounds ; crystal structure ; fluorides ; intercalation compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CsF reacts with Br2 to form the two intercalation compounds CsF·Br2 and 2CsF·Br2. The former consists of layers of CsF squares separated by layers of Br2 molecules oriented perpendicular to the CsF layers. 2CsF·Br2 is a second-stage compound, composed of two layers of CsF followed by one layer of bromine molecules. Iodine cannot replace bromine; instead, it reacts with CsF to form Cs2I8, and probably CsIF6 between 0° and 120 °C. Chlorine does not react at all with CsF. Bromine reacts with RbF only superficially, and after a long time some RbBr3 is observed; RbF and I2 give RbI3.
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    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021101
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    The Role of Water Exchange in Attaining Maximum Relaxivities for Dendrimeric MRI Contrast AgentsHigh-Pressure NMR Kinetics, Part 72; part 71, see ref. [1]. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1607-1615 
    Details
    ISSN: 0947-6539
    Keywords: contrast agents ; dendrimers ; gadolinium complexes ; ligand exchange ; magnetic resonance imaging ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Macrocyclic GdIII complexes attached to dendrimers represent a new class of potential MRI contrast agents. They have an extended lifetime in the blood pool, which is indispensable for their application in magnetic resonance angiography, and high relaxivities, which reduce the dose required to produce quality images. We performed a variable-temperature and -pressure 17O NMR study in aqueous solution and at 14.1, 9.4, and 1.4 T on the water exchange and rotational dynamics of three macrocyclic GdIII complexes based on polyamidoamine dendrimers, as well as on the GdIII complex of the monomer unit with the linker group. The water exchange rates k298ex for generation 5 [G5(N{CS}N-bz-Gd-{DO3A}{H2O})52], generation 4 [G4(N-{CS}N-bz-Gd{DO3A}{H2O})30], generation 3 [G3(N{CS}N-bz-Gd{DO3A}-{H2O})23], and the monomer [Gd(DO3A-bz-NO2)(H2O)] complexes are 1.5±0.1, 1.3±0.1, 1.0±0.1, and 1.6±0.1 × 106 s-1, respectively, and the activation volumes ΔV≢ of water exchange on the latter two compounds are + 3.1±0.2 and + 7.7±0.5 cm3 mol-1, indicating dissociatively activated exchange reactions ({CS}N-bz-{DO3A}=1-(4-isothiocyanatobenzyl)amido-4,7,10-tri(acetic acid)tetraazacyclododecane). The rotational correlation times for the dendrimers are 4 to 8 times longer than for monomeric or dimeric GdIII poly(amino carboxylates). As a consequence of the slow rotation, the proton relaxivities of these dendrimer complexes are considerably higher than those of smaller complexes. However, the low water exchange rates prevent the dendrimer proton relaxivities from attaining the values expected from the increase in the rotational correlation times. Modifications of the chelating ligand may result in a faster water exchange and thus allow the full benefit of slow rotation to be achieved.
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    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020101
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    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.19960020102
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    What Do Ab Initio Calculations Predict for the Structure of Lithiated Azaenolates of Peptides? (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 9-18 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; azaenolates ; NMR chemical shifts ; peptides ; Ramachandran maps ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structures and conformations of the azaenolate lithium salts of amides (formamide, acetamide, and N-methylacetamide) and of the dipeptide model N-formylalaninamide were investigated by means of ab initio MO theory. Four possible structures of the lithiated C-enolates of acetamide were also included in the study. All structures were calculated at the HF/6-31+G(d) and MP2(fc)/6-31 + G(d)/HF/6-31 + G(d) levels; the lithiated azaenolates of formamide were also investigated at higher theoretical levels (up to MP4(fc)/6-311 + G(d,p)/MP2(fc)/6-311 + G(d,p)). For the lithiated azaenolates of all amides investigated, the most stable structure contains a four-membered ring in which the lithium ion is complexed by the oxygen and nitrogen atoms; the substituents attached to the carbon and nitrogen atoms of the azaenolate are in a cis arrangement. The lithiated azaenolates of acetamide are predicted to be more stable than the corresponding C-enolates. To simulate solvation, calculations on complexes of the lithiated azaenolates of formamide with up to three molecules dimethyl ether were also performed, and all azaenolates of amides were also reoptimized by ab initio reaction-field calculations. Both solvation models reduce the preference for lithium-chelated cis structures. The Ramachandran maps of the dilithiated bis(azaenolate) of N-formylalaninamide (having cis or trans arrangements of the azaenolate substituents) were scanned by MNDO calculations for conformational accessible regions. Thirteen stable structures were subsequently optimized at the HF/6-31 + G(d) ab initio level. The global minimum resembles a peptide in C7 conformation, but other conformations, not known for peptides, are close in energy. The structures of dimers of the lithiated azaenolates of N-methylacetamide and of glycinaldehyde were also calculated. The NMR chemical shielding of carbon, nitrogen, and oxygen atoms in all structures were predicted ab initio by using the gauge-including atomic orbital (GIAO) method.
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    Ab Initio ECP/DFT Calculation and Interpretation of Carbon and Oxygen NMR Chemical Shift Tensors in Transition-Metal Carbonyl ComplexesDedicated to Professor Paul von Ragué Schleyer on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 24-30 
    Details
    ISSN: 0947-6539
    Keywords: density-functional theory ; NMR chemical shifts ; pseudopotentials ; relativistic effects ; transition-metal complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon and oxygen NMR chemical shift tensors for Group 6 hexacarbonyl complexes M(CO)6 (M = Cr, Mo, W) have been calculated by using a combination of quasirelativistic metal effective-core potentials and density-functional theory. Comparison with high-resolution solid-state shift tensors indicates excellent agreement between theory and experiment. The sensitivity of the shifts to the W-C distance in W(CO)6 is discussed. A breakdown of the shielding tensor components into contributions from localized molecular orbitals allows the detailed interpretation of the trends on going down Group 6, and of differences to free CO. Group trends in the carbon shielding tensors are related largely to contributions from M-C σ-bonding orbitals. The presence of occupied metal (n-1)p and (n-1)d orbitals is partly responsible for the changes on going from free to metalbound CO. The origin of the less pronounced trends in the oxygen shielding tensors is more complicated. The influence of scalar relativistic effects on the shift tensors has been studied for W(CO)6 and is found to be relatively small, in spite of considerable changes in the W-C distance.
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    Permethyltitanocene Derivatives with Naked Chalcogen Ligands: Synthesis of [(Cp*2Ti)2(μ-E)] and [Cp*2Ti(μ2-E2)] and the Role of the Terminal Chalcogenides [Cp*2Ti(E)] in Their Interconversion (E = Se, Te) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1221-1229 
    Details
    ISSN: 0947-6539
    Keywords: chalcogen compounds ; metallocenes ; selenium compounds ; tellurium compounds ; titanium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Permethyltitanocene hydride, [Cp*2TiH], reacts with elemental selenium or tellurium to give the products [(Cp*2Ti)2(μ-E)] (E = Se, 1a Te, 1b), [Cp*2Ti(μ2-E2)] (E = Se, 2a; Te, 2b) and [Cp*2Ti(μ2-Se3)] (3), depending on the equivalency of the chalcogen employed. Dinuclear compounds 1 are paramagnetic and have D2d (idealized) structures, as shown by X-ray structural analysis of μ-telluride 1b; they may be converted to diamagnetic dichalcogenides 2 through further reaction with the appropriate chalcogen. Derivatives 2 are monomeric in the solid state, as shown by X-ray structural analysis of ditelluride 2b, and in solution, as demonstrated by multinuclear NMR spectroscopy. Combination of diselenide 2a and ditelluride 2b results in partial redistribution to the mixed species [Cp*2Ti(μ2-SeTe)], suggesting dimeric structures of formula [Cp*2Ti(μ-E-E)2 TiCp*2] may be accessible in solution. The dichalcogenides and the triselenide may be converted back to complexes 1 by treatment with a chalcogen-abstracting agent. The possible involvement of monomeric terminal chalcogenides [Cp*2Ti(E)] in the interconversion of 1 and 2 was probed experimentally and computationally by means of Density Functional Theory calculations on [Cp2M(E)] (M = Ti, E = O, S, Se, Te; M = Zr, E = O, Te). Several unsuccessful attempts to generate and trap [Cp*2Ti(Te)] are described. The results of these studies suggest that [Cp*2Ti(Te)] has a very weak Ti-Te bond and a readily accessible triplet excited state. These factors, along with the small size of titanium, render this member of the [Cp*2M(E)] family of complexes difficult to trap with Lewis bases, in contrast to many other congeners in the series of Group 4 terminal chalcogenides.
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    A Theoretical Study of the Additivity of Proton Affinities in Aromatics: Polysubstituted Benzenes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1251-1257 
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    ISSN: 0947-6539
    Keywords: ab initio calculations ; benzenes ; electrophilic substitutions ; proton affinities ; QSAR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An additivity rule for proton affinities (PAS) in polysubstituted benzenes is derived from the MP2(fc)/6-31 G**//HF/6-31 G* + ZPE(HF/6-31 G*) theoretical model by use of the concepts of homodesmic reactions and independent substituents. The performance of the additivity rule of thumb is very good; this is evidenced by the excellent agreement of the estimated PAS with the latest experimental data. We believe that the additivity should work for larger aromatic compounds too. The PA increments, which characterize the influence of each substituent on a particular site of the benzene ring undergoing electrophilic substitution, proved useful in discussing various chemical properties of this family of compounds.
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    Me3TTF-PO3H2, a Redox Phosphonic Acid and Its Monoanilinium Salt [PhNH+3][Me3TTF-PO(OH)O-], the Electrocrystallized Neutral (Zwitterionic) π Radical [Me3TTF-PO(OH)O-]·+, and Their Associated Lamellar Constructions in the Solid State (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1275-1282 
    Details
    ISSN: 0947-6539
    Keywords: crystal engineering ; hydrogen bonds ; phosphonates ; radical cations ; tetrathia fulvalenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Me3TTFLi (TTF = tetrathiafulvalene) with ClP(O)-(OEt)2 followed by hydrolysis with Me3SiBr affords the novel π-donor molecule trimethyltetrathiafulvalenylphosphonic acid (Me3TTF-PO3H2) in a partially oxidized form. Subsequent reduction and neutralization with aniline gives the corresponding phosphonate monoanilinium salt. A unique hydrogen-bonded hexagonal net is identified within the lamellar structure of [PhNH+3][Me3TTF-PO(OH)O-], which is described by analogy with the anti-CaSi2 structure type. Electrocrystallization of the former salt yields single crystals of a neutral (zwitterionic) π radical, formulated as [Me3TTF-PO(OH)O-]·+. Their structure reveals the presence of hydrogen-bonded molecular ribbons whose association creates a novel layered architecture similar to that obtained within radical cation salts of π-donor molecules of larger spatial extension. The analysis of the calculated HO-MO-HOMO intermolecular interaction energies demonstrates that these slabs contain strong π-π intermolecular interactions despite the nonexistence of any 2D network of short S ⃛S contacts. The spin susceptibility of [Me3TTF-PO-(OH)O-]·+, determined by single-crystal ESR measurements, is characteristic of triplet excitons, the origin of which may be understood from the electronic structure of the compound.
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    URL: http://dx.doi.org/10.1002/chem.19960021015
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    Kinetic Analysis of the Stepwise Platination of Single- and Double-Stranded GG Oligonucleotides with Cisplatin and cis-[PtCl(H2O)(NH3)2]+ (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1283-1291 
    Details
    ISSN: 0947-6539
    Keywords: antitumour agents ; DNA ; kinetics ; nucleotides ; platinum complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report the first direct comparison of the kinetics of platination of defined single- and double-stranded DNA with the anticancer drug cisplatin. The courses of the reactions of the 14-mer duplex d(A-T-A-C-A-T-G-G-T-A-C-A-T-A)·d(T-A-T-G-T-A-C-C-A-T-G-T-A-T) with [15N]cisplatin and cis-[PtCl(H2O)-(15NH3)2]+ and of each of the single strands with [15N]cisplatin have been studied at 298 K, pH 6, by [1H, 15N] NMR spectroscopy. As expected the reactions of cisplatin proceed via cis-[PtCl(H2O)(NH3)2]+, and lead to two monofunctional adducts on the duplex and two on the GG single strand. In both the GG single strand and the duplex, one of the two G's is platinated faster than the other (by a factor of ca. 4). Remarkably, ring closure on the duplex to form the GG chelate occurs about an order of magnitude faster for one monofunctional adduct than for the other. The latter monofunctional adduct has distinctive 1H and 15N NMR chemical shifts for Pt-NH3, and is very long-lived (persists for 〉5 d). The Pt-Cl bond in this monofunctional adduct is protected from hydrolysis by the duplex. In contrast, the two monofunctional adducts on the GG single strand undergo ring closure at about the same rate. Equilibria between kinked and distorted forms of the GG platinated duplex, the platination of G's on the complementary strand, and the potential biological significance of long-lived monofunctional adducts of platinum drugs with DNA are discussed.
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    URL: http://dx.doi.org/10.1002/chem.19960021016
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    Mitogenic effect of erythropoietin on neonatal rat cardiomyocytes: Signal transduction pathways (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 461-468 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The mitogenic effect of recombinant human erythropoietin (rHuEpo) on primary cultures of neonatal rat cardiac myocytes was observed. rHuEpo triggered a dose-dependent increase in myocyte proliferation. The hormone effect over optimally grown control culture 1 day after addition was maximum with 0.5 U/ml and was inhibited with anti-rHuEpo. Inhibitors of enzymatic pathways known to be involved in the cytokines intracellular mechanism such as genistein (tyrosine kinase inhibitor), 2-nitro-4-carboxiphenyl-N,N-diphenylcarbamate (phospholipase C [PLC] inhibitor), and 1-(5-isoquinolinylsufonyl)-2-methyl-piperazine (protein kinase C [PKC] inhibitor) prevented the mitogenic action of rHuEpo. Also the inhibition of Na+-K+-ATPase activity by ouabain blunted the stimulatory action of rHuEpo on cell proliferation. The mitogenic action of the hormone was correlated with cardiac membrane paranitrophenilphosphatase (pNPPase) and PKC activity, since concentrations of rHuEpo that stimulate DNA synthesis increased pNPPase and PKC activity. Moreover, the enzymatic inhibition of tyrosine kinase, PLC, and PKC attenuated the stimulatory action of rHuEpo upon cardiac pNPPase activity. In this paper we demonstrate a non-hematopoietic action of rHuEpo showing both mitogenic and enzymatic effect upon primary myocyte cell culture and on pNPPase activity of neonatal rat heart. These effects are related to the capacity of rHuEpo to stimulate Na+-K+-ATPase activity and appear to be secondary to the activation of tyrosine kinase and PKC, indicating that in the rHuEpo mediated mitogenic action on cardiomyocytes involves the activation of the same enzymatic pathways that have been described by other cytokines in different tissues. © 1996 Wiley-Liss, Inc.
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    Hypoxia decreases constitutive nitric oxide synthase transcript and protein in cultured endothelial cells (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 469-476 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Endothelial cell-generated nitric oxide (NO) accounts in large part for the labile vasodilator termed endothelium-derived relaxing factor. Two distinct types of NO synthase exist: a “constitutive” type (cNOS), found in endothelial cells, and an “inducible” enzyme. Endothelial cells sense pO2 levels in the range of 70-20 torr and respond to this hypoxia by inducing transcription of genes which encode the vasoactive proteins PDGF-B and endothelin-1. Exposure of human or bovine endothelial cells to low oxygen tensions results in a profound decrease in the transcript for cNOS and a corresponding fall in cNOS protein levels. The ability of endothelial cells exposed to hypoxia to produce NO in response to bradykinin, a stimulator of cNOS activity, was coordinately impaired. Cobalt inhibited the expression of cNOS transcripts, suggesting a mechanism comparable to that by which oxygen tension regulates expression of other vasoregulatory genes. In the presence of actinomycin-D, hypoxia had no effect on cNOS transcripts, suggesting that new gene transcription is required for cNOS suppression. The reducing agents PDTC and N-Ac did not mimic cNOS gene suppression by hypoxia, suggesting that this suppression is not related to the redox state of the intracellular environment. Thus, regulation of cNOS function in response to environmental factors can occur at the level of gene expression as well as at the level of enzyme activation. © 1996 Wiley-Liss, Inc.
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    Lipoxygenase metabolites induced expression of adhesion molecules and transendothelial migration of monocyte-like HL-60 cells is linked to protein kinase C activation (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 477-487 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Studies have shown that, among lipoxygenase metabolites examined, 15(S)-hydroperoxy-5,8,11,13-eicosa-tetraenoic acid (15[S]-HPETE), at micromolar concentrations, selectively causes injury to cultured endothelial cells. We investigated whether physiologically relevant concentrations of lipoxygenase metabolites affected the expression of cell adhesion molecules (CAMs) involved in the adhesion of leukocytes and/or the accumulation of leukocytes in the vascular endothelium, these being the initial events in endothelial cell injury. Among lipoxygenase metabolites, 15(S)-HPETE and 12(S)-HETE, at nanomolar concentrations, induced surface expression of a subset of cell adhesion molecules (CAM), ICAM-1, ELAM-1, and VCAM-1, in human umbilical vein endothelial cells (HUVEC), which is associated with an increased binding activity of the transcription factor, NF-κB, to the consensus motif common to the CAM genes in the HUVEC nuclear extracts. Furthermore, 15(S)-HPETE (1 nM) caused a threefold increase in the rate of transendothelial migration of vitamin D3-differentiated HL-60 monocyte-like cells and showed a thirtyfold increase in the phosphorylation of PECAM-1, an adhesion molecule involved in endothelial cell-cell adhesion. Both an antibody to PECAM-1 and the protein kinase C inhibitor, GF 109203X, reduced 15(S)-HPETE-induced transmigration of monocyte-like HL-60 cells by approximately 75% and 85%, respectively. Treatment of HUVEC with a phosphatase inhibitor, calyculin A, augmented both the phosphorylation of PECAM-1 and transmigration of monocyte-like HL-60 cells induced by 15(S)-HPETE. Our results show that 15(S)-HPETE, at physiological concentrations, induced activation of protein kinase C in HUVEC and leads to the phosphorylation of PECAM-1, thus facilitating the migration of monocyte-like HL-60 cells across the endothelial cell monolayer. It is suggested that phosphorylation/dephosphorylation events in PECAM-1 are important in regulating the trafficking of monocytes across the endothelial cell monolayer. © 1996 Wiley-Liss, Inc.
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    Synergistic stimulation of gamma-glutamyl transpeptidase and alkaline phosphatase activities by retinoic acid and astroglial factors in immortalized rat brain microvessel endothelial cells (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 451-460 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The immortalized rat brain microvessel endothelial cell line RBE4 was used to investigate the in vitro regulation of two blood-brain barrier specific enzymes, gamma-glutamyl transpeptidase (GTP) and alkaline phosphatase (ALP). The effects of bFGF, astroglial factors, and retinoic acid (a cell differentiation agent) on GTP and ALP activities were separately or simultaneously studied in order to define optimal culture conditions for induction of these two specific enzymes of the blood-brain barrier. In the present study, a phenotypically distinct subpopulation of endothelial cells has been shown to develop from confluent cobblestone monolayers of RBE4 immortalized cerebral endothelial cells. These distinct cells were present within multicellular aggregates and specifically exhibited GTP and ALP activities. Addition of bFGF, astroglial factors, or retinoic acid induced the formation of these three-dimensional structures and in consequence an increase in GTP and ALP activities. For retinoic acid and astroglial factors, this increase could also be explained by the stimulation of either GTP or ALP expression in the phenotypically distinct positive cells associated with aggregates. Simultaneous treatment with retinoic acid and astroglial factors had a synergistic effect on GTP and ALP expression and thus may allow these distinct cells to evolve toward a more differentiated state. Since such results were also obtained with physiological concentrations of retinoic acid, we suggest that addition of this agent might contribute to greater differentiation of cells in in vitro blood-brain barrier models where endothelial cells are cocultured with astrocytes. © 1996 Wiley-Liss, Inc.
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    Inhibition of cellular proliferation and modulation of insulin-like growth factor binding proteins by retinoids in a bovine mammary epithelial cell line (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 488-499 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Retinoids are potent inhibitors of growth and tumor progression in many mammary carcinoma cell lines, though regulation of growth in nontumorigenic mammary epithelial cells by retinoids is less clear. Here, we have characterized the inhibition of MAC-T (a nontransformed bovine mammary epithelial cell line) cellular proliferation by retinoids and their role in regulating insulin-like growth factor binding proteins (IGFBPs). Retinoic acid (RA) (100 nM) was a potent inhibitor of MAC-T cell proliferation. Retinol was 10-100 times less effective. Neither retinoid could completely arrest growth at noncytotoxic concentrations. Retinoic acid inhibited cellular proliferation by 1 h (P 〈 .05), but inhibition was fivefold greater by 24 h (P 〈 .01). This second stage of growth inhibition (after 12 h) was dependent upon protein synthesis. However, RA-induced inhibition of cellular proliferation did not persist, with thymidine incorporation increasing toward control levels by 4 days in culture. Retinoic acid was less effective in inhibiting thymidine incorporation when cells were stimulated with insulin, des(1-3) IGF-I, or Long(R3) IGF-I when compared to cells stimulated with native IGF-I or serum. Inhibition of proliferation by RA was associated with increased levels of IGFBP-2 in conditioned media and in plasma membrane preparations. Treatment with insulin or des(1-3) IGF-I resulted in the appearance of IGFBP-3 in conditioned media and on the cell surface. However, RA significantly reduced IGFBP-3 levels in conditioned media and eliminated IGFBP-3 associated with the plasma membrane. Thus, RA is a potent but transient inhibitor of bovine mammary epithelial cell proliferation, and this growth inhibition is correlated with increased IGFBP-2 accumulation and inhibition of IGF-I stimulated IGFBP-3 protein secretion. © 1996 Wiley-Liss, Inc.
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    Protein kinase C mediates up-regulation of urokinase and its receptor in the migrating keratinocytes of wounded cultures, but urokinase is not required for movement across a substratum in vitro (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 500-511 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Both in cell culture and in vivo, keratinocytes that are migrating in response to a wound express enhanced levels of both urokinase-type plasminogen activator (uPA) and the uPA cell surface receptor (uPA-R). To explore the mechanism of this up-regulation, keratinocyte cultures were treated prior to wounding with a variety of metabolic and growth factor inhibitors in order to evaluate their effect on uPA and uPA-R expression. Actinomycin D and cycloheximide inhibited the up-regulation of both uPA and uPA-R, as determined by immunohistochemistry, indicating that RNA and protein syntheses are required for their induction in migrating keratinocytes. Neither removal of protein growth factors from the medium nor addition of inhibitory antibodies to a number of growth factors depressed uPA or uPA-R induction; these findings suggest that a variety of exogenous or endogenous growth factors [i.e., basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), transforming growth factor-α (TGF-α), amphiregulin, and tumor necrosis factor-α (TNF-α)] do not have a critical role in the induction of uPA or uPA-R. In contrast, when protein kinase C (PKC) was either down-regulated with bryostatin 5 or inhibited with Ro31-8220 or staurosporine, the expression of both uPA and uPA-R was greatly decreased in migrating keratinocytes. Furthermore, pharmacologic activation of PKC enhanced uPA levels in non-wounded cultures. These data suggest that the enhanced expression of uPA and uPA-R in migrating keratinocytes is mediated by selective activation of PKC in these cells, perhaps secondary to alterations in the cytoskeleton induced by wounding. To test the requirement for uPA during keratinocyte migration in vitro, the extent of migration was quantified in the presence and absence of a variety of inhibitors in the wounded culture model. Migration was not altered by actinomycin D, cycloheximide, any of the above growth factor inhibitors, anti-uPA antibodies, a variety of inhibitors of uPA or plasmin enzymatic activity, or exogenous uPA. The independence of keratinocyte migration in vitro from uPA was further suggested by experiments which combined the phagokinetic assay of migration and the zymographic assay for pericellular uPA activity; no relationship was observed between pericellular uPA activity and the motility of individual cells. © 1996 Wiley-Liss, Inc.
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    Expression of hydrogen peroxide and glutathione metabolizing enzymes in human skin fibroblasts derived from donors of different ages (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 512-522 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have examined the activities and mRNA abundance of two hydrogen peroxide metabolizing enzymes (glutathione peroxidase and catalase), glutathione concentration, and the activities of several enzymes that influence glutathione concentration, including glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G-6-PD), and γ-glutamylcysteine synthetase (γ-GCS), in 29 skin fibroblast lines derived from donors ranging in age from 14 gestational weeks to 94 years of age. H2O2 metabolizing enzyme activities and mRNA abundances were greater in skin fibroblast cultures established from postnatal donors than in fetally derived cultures. There were no significant differences in either of these parameters in cell lines established from postnatal donors of different ages. Total glutathione concentration decreased with age, but GR activity appeared to be unaffected by age. In order to estimate the ability of the cultures to produce NADPH (an important component of cellular redox status and a cofactor for GR), we determined glucose-6-phosphate dehydrogenase activity and mRNA abundance. We were unable to directly measure γ-GCS activity or mRNA abundance in any of the skin lines or in fetal lung fibroblasts; however, we were able to indirectly demonstrate the presence of this enzyme by stimulating fetal lung fibroblasts with H2O2 following treatment with L-buthionine-S,R-sulfoximine (BSO), an inhibitor of γ-GCS activity. These results show that some, but not all, age-associated differences in antioxidant defense levels are maintained in a culture environment and are consistent with the hypothesis that developmental stages of life are associated with lower antioxidant defense levels than are present in postnatal phases of life. © 1996 Wiley-Liss, Inc.
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    Mechanisms of α-thrombin, histamine, and bradykinin induced endothelial permeability (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 562-569 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: α-Thrombin, bradykinin, and histamine are endogenous mediators that increase endothelial permeability. We examined the mechanism by which these three vasoactive mediators could alter permeability to albumin of human umbilical vein endothelial cells (HUVEC). HUVEC were grown to confluence on Transwell membranes and we monitored the flux of fluorescein isothiocyanate-labeled human serum albumin across the membrane from the upper to lower chamber of the Transwell. Addition of α-thrombin, bradykinin, or histamine increased the permeability coefficient of the HUVEC monolayer. At 30 min the permeability coefficient for α-thrombin was 4.92 × 10-6 cm/sec while histamine was 4.47 × 10-6 cm/sec. Maximum changes in the permeability coefficient were about three-fold control baseline values (1.59 × 10-6 cm/sec). There was also a temporal difference in the magnitude of the permeability coefficient. α-Thrombin and bradykinin induced HUVEC permeability was increased for the first 90 min after which it returned to control levels. In contrast, histamine increased the permeability of the HUVEC monolayer throughout the 2 h experiment. To determine a possible intracellular mechanism of the altered permeability coefficients, HUVEC were labeled with FURA-2 and intracellular calcium was monitored by digital fluorescence ratio imaging. Maximum intracellular calcium in HUVEC was increased by α-thrombin (245 ± 20 nM) and histamine (210 ± 22 nM), but not by bradykinin (70 ± 7 nM) as compared to control (69 ± 10). Fluorescent photomicrographs of HUVEC stimulated with the three agonists indicated that α-thrombin and histamine substantially altered HUVEC f-actin arrangement, while bradykinin had no effect on HUVEC f-actin distribution. These data support previous in vitro and in vivo studies demonstrating increased permeability by all three agonists. These data also show, for the first time, that histamine and α-thrombin increased permeability by calcium-dependent intracellular pathways, but bradykinin operates through a calcium-independent mechanism. © 1996 Wiley-Liss, Inc.
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    Masthead (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996) 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041670301
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    Excess protein in nuclei isolated from heat-shocked cells results from a reduced extractability of nuclear proteins (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 369-379 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: An excellent correlation has been established between the quantity of protein associated with nuclei isolated from heat-shocked cells and the level of hyperthermic cell killing. However, controversy remains about whether increases in nuclear-associated protein result from a heat-induced migration of cytoplasmic proteins into the nucleus or because hyperthermia reduces the solubility of nuclear proteins in the detergent buffers commonly used to isolate nuclei. To address this controversy, the nuclear protein content was measured in whole and detergent-extracted cells before and following hyperthermia. It was found that hyperthermia caused no significant change in the nuclear protein content of whole, unextracted cells, and when fluorescently labeled proteins were microinjected into the cytoplasm no gross change in the selective permeability of the nuclear membrane to soluble proteins was observed during or following hyperthermia. Measurements in extracted cells showed that the detergent buffers removed protein from both the nucleus and cytoplasm of control, nonheated cells and that hyperthermia reduced the extractability of both nuclear and cytoplasmic proteins. The amount of protein found in nuclei isolated from heated cells approached that observed in nuclei within nonheated whole cells as the hyperthermic exposure was increased. Thus, the dose-dependent, two- to threefold increase in the protein content of nuclei isolated from heated cells represents a heat-induced reduction in the extractability of proteins normally present within cell nuclei and does not result from a mass migration of cytoplasmic proteins into the nucleus, although some specific proteins (e.g., the 70 KDa heat shock protein) do migrate to the nucleus following heat shock. Differential scanning calorimetry (DSC) measurements of whole cells, isolated nuclei, cytoplasts, and karyoplasts supported these conclusions and suggested that most of the detergent-insoluble proteins remaining in the nuclei and cytoplasm of heated cells are in their native state. Thus, a relatively small amount of denatured protein may be sufficient to initiate and sustain insoluble protein aggregates comprised of mostly native proteins. Analyses of the DSC data also implied that the previously identified critical target proteins, predicted to have a Tm of 46.0°C, are present in both the nucleus and cytoplasm. © 1996 Wiley-Liss, Inc.
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    Transforming growth factor β (TGF-β) expression in isolated and cultured rat hepatocytes (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 394-405 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: It is still a subject of debate whether hepatocytes have the ability to express TGF-β. Therefore, we investigated in freshly isolated and in monolayer cultures of rat hepatocytes the expression of TGF-β isoforms at the RNA and protein level applying RT-PCR, immunocytochemistry, immunoblotting, and functional assays of TGF-β, TGF-β1, -β2, and -β3 transcripts were detected in cultured cells, and the level of mRNA increased up to 48/72 h, but TGF-β1 transcripts were absent in freshly isolated cells. Using APAAP stainings the proteins of all three TGF-β isoforms were observed in hepatocyte cultures from 5-96 h, but in hepatocytes in the liver in situ and in freshly isolated cell suspensions TGF-β staining was negative. SDS-PAGE under reducing conditions followed by Western blotting detected in cell lysates the subunit of mature TGF-β at about 13 kd. Analysis of TGF-β bioactivity with the mink cell (Mv1Lu) proliferation inhibition assay and competitive radioligand assay confirmed in activated (i.e., acidified and subsequently neutralized) hepatocyte-conditioned media the presence of TGF-β, which, however, is almost entirely in the latent form. It is concluded that TGF-β can be expressed in cultured hepatocytes and that the level of expression is quickly upregulated under abnormal, not yet known, microenvironmental conditions. © 1996 Wiley-Liss, Inc.
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    Nongenomic regulation of protein kinase C isoforms by the vitamin D metabolites 1α,25-(OH)2D3 and 24R,25-(OH)2D3 (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 380-393 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Prior studies have shown that vitamin D regulation of protein kinase C activity (PKC) in the cell layer of chondrocyte cultures is cell maturation-dependent. In the present study, we examined the membrane distribution of PKC and whether 1α,25-(OH)2D3 and 24R,25-(OH)2D3 can directly regulate enzyme activity in isolated plasma membranes and extracellular matrix vesicles. Matrix vesicle PKC was activated by bryostatin-1 and inhibited by a PKC-specific pseudosubstrate inhibitor peptide. Depletion of membrane PKC activity using isoform-specific anti-PKC antibodies suggested that PKCα is the major isoform in cell layer lysates as well as in plasma membranes isolated from both cell types; PKCζ is the predominant form in matrix vesicles. This was confirmed in Western blots of immunoprecipitates as well as in studies using control peptides to block binding of the isoform specific antibody to the enzyme and using a PKCζ-specific pseudosubstrate inhibitor peptide. The presence of PKCζ in matrix vesicles was further verified by immunoelectron microscopy. Enzyme activity in the matrix vesicle was insensitive to exogenous lipid, whereas that in the plasma membrane required lipid for full activity. 1,25-(OH)2D3 and 24,25-(OH)2D3 inhibited matrix vesicle PKC, but stimulated plasma membrane PKC when added directly to the isolated membrane fractions. PKC activity in the matrix vesicle was calcium-independent, whereas that in the plasma membrane required calcium. Moreover, the vitamin D-sensitive PKC in matrix vesicles was not dependent on calcium, whereas the vitamin D-sensitive enzyme in plasma membranes was calcium-dependent. It is concluded that PKC isoforms are differentially distributed between matrix vesicles and plasma membranes and that enzyme activity is regulated in a membrane-specific manner. This suggests the existence of a nongenomic mechanism whereby the effects of 1,25-(OH)2D3 and 24,25-(OH)2D3 may be mediated via PKC. Further, PKCζ may be important in nongenomic, autocrine signal transduction at sites distal from the cell. © 1996 Wiley-Liss, Inc.
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    Deletion of specific protein kinase C subspecies in human melanoma cells (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 406-412 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: It has been shown that tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), stimulates the proliferation of normal human melanocytes, whereas it inhibits the growth of human melanoma cell lines. The expression of protein kinase C (PKC) subspecies, the major intracellular receptors for TPA, was examined in normal melanocytes and the four melanoma cell lines HM3KO, MeWo, HMV-1, and G361. PKC was partially purified and then separated into subspecies by column chromatography on Mono Q and hydroxyapatite successively, and finally subjected to immunoblot analysis using antibodies specific for the PKC subspecies. Of the PKC subspecies examined, δ-, ε-, and ζ-PKC were detected in both normal melanocytes and the four melanoma cell lines. In contrast, both α-PKC and β-PKC were expressed in normal melanocytes, whereas either α-PKC or β-PKC was detected in melanoma cells. Specifically, HM3KO, MeWo, and HMV-1 cells were shown to contain α-PKC but not β-PKC, while G361 cells expressed β-PKC but not α-PKC. The growth of these melanoma cells was suppressed by TPA treatment, and the growth of the G361 cells lacking α-PKC was inhibited more efficiently than the other melanoma cell lines which lacked β-PKC. It was further shown that β-PKC was not detected in freshly isolated human primary or metastatic melanoma tissues. These results suggest that the expression of α-PKC or β-PKC may be altered during the malignant transformation of normal melanocytes and that loss of α-PKC or β-PKC may be related to the inhibitory effect of TPA on the growth of melanoma cells. © 1996 Wiley-Liss, Inc.
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    Control of retinoic acid receptor expression in mouse melanoma cells by cyclic AMP (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 413-421 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Retinoic acid receptor (RAR) α and γ mRNAs were constitutively expressed in B16 melanoma cells with or without retinoic acid (RA) treatment. RARβ mRNA, however, was significantly expressed only after exposure to RA. Induction of RARβ by RA occurred within 1 h and was not inhibited by cycloheximide (i.e., did not require new protein synthesis). All three RAR mRNA levels were dramatically decreased with 8-bromo-cyclic AMP treatment and could not be rescued by addition of RA. Analysis of RARγ revealed that this decrease occurred within 1 h of exposure to 8-bromo-cyclic AMP and was not blocked by simultaneous treatment with cycloheximide. The stability of RARγ mRNA was not altered by cyclic AMP treatment. Nuclear extracts from 8-bromo-cyclic AMP-treated cells showed a large decrease in protein binding to a retinoic acid response element (RARE) oligonucleotide compared to control cells. This correlated with a marked reduction of RA-stimulated RARE-reporter gene activity in transfected cells which were treated with cyclic AMP. Pretreatment of B16 cells with cyclic AMP prior to RA addition dramatically reduced induction of PKCα, an early marker of RA-induced cell differentiation. Thus, cyclic AMP can antagonize the action of RA most likely via its ability to inhibit RAR expression. © 1996 Wiley-Liss, Inc.
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    Upregulation of molecular motor-encoding genes during hepatocyte growth factor-and epidermal growth factor-induced cell motility (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 422-433 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) are known to stimulate the locomotion of epithelial cells in culture. However, the molecular mechanisms which mediate these important changes are poorly understood. Here we have determined the effects of HGF and EGF on hepatocyte morphology, cytoskeletal organization, and the expression of molecular motor-encoding genes. Primary cultures of hepatocytes were treated with 10 ng/ml of HGF or EGF and observed with phase and fluorescence microscopy at 10, 24, and 48 h after treatment. We found that, over time, treated cells spread and became elongated after 24 h of treatment while forming long processes with dramatic alterations in the microtubule and actin cytoskeletons by 48 h. Quantitative Northern blot analysis was performed to measure expression of cytoskeletal-(β-actin, α-tubulin) and molecular motor-(dynein, kinesin, and myosin Iα and II) encoding genes which may contribute to this change in form. We observed the highest increase in levels of expression for myosin II (3.3-fold), kinesin (2.7-fold), myosin Iα (2.2- fold), and α-tubulin (1.9-fold) after only 2 h of treatment with HGF. In contrast, EGF upregulated the expression of myosin Iα (2.4-fold), kinesin (1.5-fold), and dynein (1.5-fold) at 10 h. The expression of the β-actin gene remained constant in HGF-treated cells, while EGF induced a slight upregulation after 10 h of treatment. These results show for the first time that a selective upregulation of molecular motor-encoding genes correlates with alterations in cell shape and motility induced by HGF and EGF. © 1996 Wiley-Liss, Inc.
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    Hepatocellular carcinoma cells resist necrosis during anoxia by preventing phospholipase-mediated calpain activation (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 434-442 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Although hepatocellular carcinoma (HCC) cells are more resistant to anoxic injury than normal hepatocytes, the mechanisms responsible for this differential sensitivity remain obscure. Because enhanced calpain protease activity contributes to hepatocyte necrosis, we tested the hypothesis that HCC cells resist anoxia by preventing calpain activation. Cell viability in two rat HCC cell lines (N1S1 and McA-RH7777 cells) was fourfold greater compared to rat hepatocytes after 4 h of anoxia. Although calpain activity increased twofold in rat hepatocytes during anoxia, no increase in calpain activity occurred in HCC cells. Western and Northern blot analysis revealed greater or equivalent expression of calpains and calpastatin in HCC cells compared to hepatocytes. Because increases in cytosolic free Ca++ (Cai++) and phospholipid degradation products regulate calpains in vitro, we measured Cai++ and phospholipid degradation. Ca++i did not change in any cell types during 60 min of anoxia. In contrast, phospholipid degradation was fourfold greater in hepatocytes compared to HCC cells. Melittin, a phospholipase A2 activator, increased calpain activity and cell necrosis in all cell types; melittin-induced cell necrosis was ameliorated by a calpain protease inhibitor. In summary, these data demonstrate for the first time 1) calpain activation without a measureable increase in Ca++i, 2) phospholipase-mediated calpain activation in hepatocytes and HCC cells, and 3) the adaptive mechanism responsible for the resistance of HCC cells to anoxia - an inhibition of phospholipid-mediated calpain activation. Interruption of phospholipase-mediated calpain activation may be a therapeutic strategy for preventing anoxic cell injury. © 1996 Wiley-Liss, Inc.
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    Basic fibroblast growth factor (FGF-2) protects rat cochlear hair cells in organotypical culture from aminoglycoside injury (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 443-450 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Given the evidence that basic fibroblast growth factor (FGF-2) can protect neural and retinal cells from degeneration, we evaluated the potential of this growth factor to protect sensory cells in the inner ear. When sensory cells of the organ of Corti are exposed to aminoglycoside antibiotics such as neomycin either in vivo or in vitro, significant ototoxicity is observed. The in vitro cytotoxic effects of neomycin are dose and time dependent. In neonatal rat organ of Corti cultures, complete inner and outer hair cell destruction is observed at high (mM) concentrations of neomycin while inner hair cell survival and severely damaged outer hair cells are noted at moderate (μM) concentrations, with a maximal effect observed after 2 days of culture. Approximately 50% of cochlear outer hair cells are lost at a dose of 35 μM neomycin, and most surviving cells show disorganized stereocilia. Inner hair cells show primarily disorganization of their stereocilia. A significant protective effect is observed when the organ of Corti is pre-treated with FGF-2 (500 ng/ml) for 48 hours, and then FGF-2 is included with neomycin in the culture medium. A greater extent of outer hair cell survival and a significant decrease in stereociliary damage are noted with FGF-2. However, disorganization of inner hair cell stereocilia is unaffected by FGF-2. The protective effect of FGF-2 is specific, since interleukin-1B, nerve growth factor, tumor necrosis factor, and epidermal growth factor are ineffective, while retinoic acid and transforming growth factor alpha show only a moderate protective effect. These results confirm the potential of molecules like FGF-2 for preventing cell death due to a variety of causes. © 1996 Wiley-Liss, Inc.
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    Differentiation potential of conditionally immortalized mesenchymal progenitor cells from adult marrow of a H-2Kb-tsA58 transgenic mouse (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 523-538 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Primary cultures were initiated from marrow, spleen, and bone explants of an adult H-2Kb-tsA58 transgenic mouse (immortomouse). All cultures were initiated in immortalizing conditions, and an additional marrow culture was first incubated for 1 week in standard conditions and then switched to immortalizing conditions. Marrow cells immediately immortalized were designated the marrow immediate population (MIP); those immortalized after 1 week were termed the marrow delayed population (MDP). MIP and MDP cells both contained a mixture of fibroblastic or flattened cells, and the MIP cells contained an additional subpopulation of adipocytic (Oil Red-O positive) cells. Alkaline phosphatase expression was induced by dexamethasone (10-7 M) in MDP cells while MIP, spleen, and bone explant cells had only a low level of expression. MDP and MIP cells differentiated into bone when combined with porous calcium phosphate ceramics and implanted subcutaneously into nude mice while bone- and spleen-derived cells did not. Clones were isolated from the MDP and MIP cell populations and tested for differentiated phenotypes. Some MIP-derived clones exhibited adipocytic characteristics while MDP-derived subclones were negative. Histologic examination of porous ceramic implanted clones showed that all of the clones had osteogenic potential. Clones exposed to either dexamethasone, human recombinant bone morphogenetic protein-2, or horse serum plus hydrocortisone showed differences in expression of adipocytic or osteogenic markers. These immortalized cultures have retained both adipocytic and osteogenic potential even after 1 year of continuous culture, and provide a model system for clonal analysis of the developmental potential of marrow-derived mesenchymal precursor cells. © 1996 Wiley-Liss, Inc.
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    Zinc transport across an endothelium includes vesicular cotransport with albumin (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 539-547 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Bovine pulmonary arterial endothelial cells (BPAEC) were grown on permeable polycarbonate membrane filters suspended between two compartments representing the blood vessel lumen and the interstitium. This in vitro model of an endothelium was subjected to a battery of tests to unravel the mechanisms of zinc transport from the blood into peripheral tissues. Transport of 65Zn across BPAEC from media containing zinc concentrations up to 50 μmol/L exhibited both saturable and nonsaturable kinetics. Vmax of the saturable component was 246 ± 43 pmol/(h × cm2) and Km was 2.3 ± 1.3 μmol/L. Transport was pH and temperature sensitive and substantially influenced by albumin and histidine concentrations, but not influenced by analogous minerals or metabolic inhibitors. Inhibition of coated vesicle formation by depletion of intracellular potassium reduced 65Zn transport. Albumin carrying a zinc ion crossed the endothelium more rapidly than zinc-free albumin. When evaluated together, this body of evidence supports the existence of two major pathways of zinc transport across the pulmonary endothelium, but neither involves entry into the endothelial cells. One pathway involves receptor-mediated cotransport with albumin by transcytotic vesicles. The other is nonsaturable and involves cotransport with albumin and low molecular weight ligands, principally histidine, through intercellular junctions and nonselective, bulk-fluid transcytosis. © 1996 Wiley-Liss, Inc.
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    Actin polymerization in human eosinophils, unlike human neutrophils, depends on intracellular calcium mobilization (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 548-555 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Eosinophils represent major effector cells in the allergic inflammation. In contrast to neutrophils, the mechanism of eosinophil activation during the inflammatory response is poorly understood. In this study, the relation between calcium fluxes, chemotaxis, and actin polymerization in eosinophils from healthy non-atopic donors was investigated. Pre-incubation of eosinophils with the intracellular calcium chelator BAPTA dose-dependently prevented an increase in the intracellular calcium concentration ([Ca2+]i), whereas the depletion of extracellular calcium in the test medium had no effect. The chemotactic response of eosinophils, which was measured by the modified boyden chamber technique upon stimulation with RANTES, C5a and PAF, was dose-dependently inhibited by the chelation of intracellular calcium as well as inactivation of the cells in Ca2+-depleted medium. To evaluate whether other cell functions which are involved in the migratory response of eosinophils might be dependent on intracellular and extracellular calcium, actin polymerization was investigated. Flow-cytometric measurement of F-actin with NBD-phallacidin revealed that actin polymerization in human eosinophils in response to RANTES, C5a, and PAF was dose-dependently inhibited by the intracellular calcium chelator BAPTA. Since it is well known that actin polymerization in neutrophils is not affected by chelation of intracellular calcium, actin polymerization in these cells was investigated under the same conditions as for eosinophils. In contrast to eosinophils, BAPTA did not inhibit actin polymerization in neutrophils. In summary, these data demonstrate that intracellular calcium fluxes represent a prerequisite for eosinophil chemotaxis and actin polymerization in human eosinophils. Furthermore, regulation of actin polymerization in eosinophils differed from that of neutrophils on the level of intracellular calcium fluxes. © 1996 Wiley-Liss, Inc.
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    Regulation of human dermal papilla cell production of insulin-like growth factor binding protein-3 by retinoic acid, glucocorticoids, and insulin-like growth factor-1 (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 167 (1996), S. 556-561 
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    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Insulin-like growth factor-1 (IGF1) has been reported to stimulate hair elongation and to facilitate maintenance of the hair follicle in anagen phase. However, little is known about IGF1 signaling in the hair follicle. In this study we investigate the effects of IGF1, glucocorticoids, and retinoids on dermal papilla (DP) cell production of insulin-like growth factor binding proteins (IGFBPs). IGFBPs comprise a family of IGF binding proteins that are produced and released by most cell types. They bind to IGFs to either enhance or inhibit IGF activity. In the present report we identify IGFBP-3 as being produced and released by cultured human dermal papilla (DP) cells. IGFBP-3 levels are increased fivefold by retinoic acid, eightfold by dexamethasone, and tenfold by IGF1. DP cells are known to produce IGF1, and so the observed stimulation of DP cell IGFBP-3 production by IGF1 is consistent with the idea that DP cells possess the IGF transmembrane receptor kinase and are autoregulated by IGFs. The level of another IGFBP, tentatively identified as IGFBP-2, is, in contrast, not regulated by these agents. IGFBP-3 has been shown to inhibit the activity of IGFs in a variety of systems. Our results are consistent with a model in which retinoids and glucocorticoids inhibit IGF action on DP cells and surrounding matrix cells by stimulating increased DP cell production of IGFBP-3. The IGFBP-3, in turn, forms a complex with free IGF1 to reduce the concentration of IGF1 available to stimulate hair elongation and maintenance of anagen phase. © 1996 Wiley-Liss, Inc.
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    BMP-1 and the astacin family of metalloproteinases: A potential link between the extracellular matrix, growth factors and pattern formation (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 439-442 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Members of the astacin family of metalloproteinases such as human bone morphogenetic protein 1 (BMP-1) have previously been linked to cell differentiation and pattern formation during development through a proposed role in the activation of latent growth factors of the TGF-β superfamily. Recent finding(1) indicate that BMP-1 is identical to pro-collagen C-proteinase, which is a metalloproteinase involved in extracellular matrix (ECM) formation. This observation suggests that a functional link may exist between astacin metalloproteinases, growth factors and cell differentiation and pattern formation during development. Taken together, current studies indicate that BMP-1 and possibly other astacin metalloproteinases are multifunctional enzymes that act directly on growth factors and the ECM. In combination, these dual actions would have profound effects on developmental processes.
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    Genes, cellular interactions and cell lineages in the determination of plant trichome spacing (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 443-445 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Conceptual developments have defined concrete questions about the timing and precise location of cellular pattern formation. Plants in general, and the trichomes of Arabidopsis in particular, are remarkably suited for research on these problems. Genetic analysis requires the quantitative characterizations of the developmental processes by which patterning occurs. Larkin et al.(1) have provided measures of the non-random distances between trichomes. They have also obtained evidence about the cell lineages leading to trichome development, and this evidence constrains the possible role of intracellular programs. Continued genetic analysis may call for the identification of mutations that are expressed only during development and whose effects are corrected before the phenotype matures.
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    The role of chromosome ends during meiosis in Caenorhabditis elegans (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 447-452 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Chromosome ends have been implicated in the meiotic processes of the nematode Caenorhabditis elegans. Cytological observations have shown that chromosome ends attach to the nuclear membrane and adopt kinetochore functions. In this organism, centromeric activity is highly regulated, switching from multiple spindle attachments all along the chromosome during mitotic division to a single attachment during meiosis. C. elegans chromosomes are functionally monocentric during meiosis. Earlier genetic studies demonstrated that the terminal regions of the chromosomes are not equivalent in their meiotic potentials. There are asymmetries in the abilities of the ends to recombine when duplicated or deleted. In addition, mutations in single genes have been identified that mimic the meiotic effects of a terminal truncation of the X chromosome. The recent cloning and characterization of the C. elegans telomeres has provided a starting point for the study of chromosomal elements mediating the meiotic process.
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    The structural puzzle of how serpin serine proteinase inhibitors work (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 453-464 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Serine proteinase cleavage of proteins is essential to a wide variety of biological processes and is primarily regulated by protein inhibitors. Many inhibitors are conformationally rigid simulations of optimal serine proteinase substrates, which makes them highly efficient competitive inhibitors of target proteinases. In contrast, members of the serpin family of serine proteinase inhibitors display extensive flexibility and polymorphism, particularly in their reactive site segments and in β-sheet secondary structure, which can take up and expel strands. Reactive site and β-sheet polymorphism appear to be coupled in the serpins and may account for the extreme stability of serpinproteinase complexes through the insertion of the reactive site strand into a β-sheet. These unusual properties may have opened an adaptive pathway of proteinase regulation that was unavailable to the conformationally rigid proteinase inhibitors.
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    Control and integration of cell signaling pathways during C. Elegans vulval development (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 473-480 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Vulval development in the Caenorhabditis elegans hermaphrodite represents a simple, genetically tractable system for studying how cell signaling events control cell fata decisions. Current models suggest that proper specification of vulval cell fates relies on the integration of multiple signaling systems, including one that involves a receptor tyrosine kinase (RTK)→Ras→mitogen activated protein kinase (MAPK) cascade and one that involves a LIN-12/Notch family receptor. In this review, we first discuss how genetic strategies are being used to identify and analyze components that control vulval cell fate decisions. We then describe the different signaling systems that have been elucidated and how they relate to one another. Finally, we highlight several recently characterized genes that encode positive regulators, negative regulators or potential targets of the RTK→Ras→MAPK cascade involved in vulval induction.
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    Green life: Control of chloroplast gene transcription (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 465-471 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Chloroplasts and other plastids are plant cell organelles that account for major biochemical functions. They contain their own gene expression system but are integrated into the signaling network of the entire cell. Both nuclear and plastid genes are involved in chloroplast biogenesis, and the gene expression pathways both inside and outside the organelle are subject to developmental and environmental control. The plastid transcription apparatus reflects this general scheme, with a basic organelle-encoded enzymatic machinery surrounded by factors that may be encoded by nuclear genes. Among the transcription regulatory mechanisms thought to play a role during plastid development are: (1) differential usage of promoter elements; (2) phosphorylation of transcription factors by a protein kinase, which is itself subject to phosphorylation and redox control; (3) dynamic changes in the composition of the transcription apparatus. In etioplasts, the dominating polymerase ‘B’ is a bacterial-type enzyme, whereas the major chloroplast polymerase ‘A’ is a much larger enzyme reminiscent of those in the nucleus. These two enzyme forms may share common components and recruit others during development.
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    Molecular biology is not difficult - if you know how to do it Methods in Plant Molecular Biology. A Laboratory Course Manual (1995). P. Maliga, D. F. Klessig, A. R. Cashmore, W. Gruissem and J. E. Varner (ed.). Cold Spring Harbor Laboratory Press, New York. xiii+446 pp. $110 cloth; ISBN 0 87969-450-5. $75 plastic comb binding; ISBN 0 87969-386-X (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 519-520 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    Is something wrong with the tree of life? (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 523-527 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A recent study(1) of sequence data from many different proteins has suggested that contemporary prokaryotes and eukaryotes may have shared a common ancestor as recently as 2 billion years ago (the molecular clock). Strong evidence from the geological record, however, indicates that oxygen-producing microorganisms, perhaps similar to modern cyanobacteria, existed 3.5 billion years ago. The fossil evidence, therefore, suggests that any common ancestor of prokaryotes and eukaryotes must have existed at least 1.5 billion years earlier than suggested by the molecular clock evidence. The discrepancy between molecular and geological evidence for the age of modern cells is considered here, as are aspects of gene descent in the tree of life that might help to account for it.
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    Adherens junctions in the Drosophila embryo: The role of E-cadherin in their establishment and morphogenetic function (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 609-612 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The integrity of epithelia depends largely on specialised adhesive structures, the adherens junctions. Several of the components required for building these structures are highly conserved between vertebrates and insects (e.g. E-cadherin and α- and β-catenin), while others have so far been found only in invertebrates (e.g. crumbs). Two recent papers(1,2) show that the Drosophila E-cadherin is encoded by the gene shotgun. Phenotypic analyses of shotgun as well as armadillo (β-catenin) and crumbs mutants provide new insights into the mechanisms by which adherens junctions are built and, further, show that the requirement for E-cadherin largely depends on the morphogenetic activity of an epithelium.
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    Retinoic acid, HOX genes and the anterior-posterior axis in chordates (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 613-616 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In vertebrate development, the HOX genes act to specify cell identity along much of the anterior-posterior axis of the embryonic central nervous system. In all vertebrates examined to date, the vitamin A metabolite retinoic acid is implicated in the patterning of the anterior posterior axis and the induction of HOX gene expression. Two recent papers have extended the study of retinoic acid induction of HOX genes to the closest relatives of the vertebrates, amphioxus and tunicates(1,2). In both these species, exogenous retinoic acid is able to induce ectopic expression of HOX 1 genes in the anterior central nervous system. This suggests that retinoic acid control of anterior-posterior axis formation and HOX induction is not specific to vertebrates. However, in the more distantly related echinoderms and arthropods, retinoic acid does not seem to act in the same way. Thus the role of retinoic acid in anterior-posterior axis specification may be a chordate innovation, perhaps linked to the evolution of another chordate character, the dorsal neural tube.
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    Lens development and crystallin gene expression: many roles for Pax-6 (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 621-630 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The vertebrate eye lens has been used extensively as a model for developmental processes such as determination, embryonic induction, cellular differentiation, transdifferentiation and regeneration, with the crystallin genes being a prime example of developmentally controlled, tissue-preferred gene expression. Recent studies have shown that Pax-6, a transcription factor containing both a paired domain and homeodomain, is a key protein regulating lens determination and crystallin gene expression in the lens. The use of Pax-6 for expression of different crystallin genes provides a new link at the developmental and transcriptional level among the diverse crystallins and may lead to new insights into their evolutionary recruitment as refractive proteins.
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    The roles of heterogeneous nuclear ribonucleoproteins (hnRNP) in RNA metabolism (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 747-756 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In eukaryotic cells, messenger RNAs are formed by extensive posttranscriptional processing of primary transcripts, assembled with a large number of proteins and processing factors in ribonucleoprotein complexes. The protein moiety of these complexes mainly constitutes a class of about 20 major polypeptides called heterogeneous nuclear ribonucleoproteins or hnRNPs. The function and the mechanism of action of hnRNPs is still not fully understood, but the identification of RNA binding domains and RNA binding specificities, and the development of new functional assays, has stimulated interest in them. In contrast to previous models that hypothesised a mere structural (histone-like) function, a more diversified and dynamic role for these proteins is now emerging. In fact, they can be viewed as a subset of the trans-acting pre-mRNA maturation factors. They might actively participate in post-transcriptional events such as regulated splicing and mRNA export. Moreover, recent data suggest an involvement of some of these proteins in molecular diseases. Here we present an overview of the most relevant properties of hnRNPs and discuss some emerging ideas on theiir roles.
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    Genomic evolution in mice and men: Imprinted genes have little intronic content (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 773-775 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    Unraveling the late stages of recombinational repair: Metabolism of DNA junctions in Escherichia coli (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 757-765 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: DNA junctions are by-products of recombinational repair, during which a damaged DNA sequence, assisted by RecA filament, invades an intact homologous DNA to form a joint molecule. The junctions are three-strand or four-strand depending on how many single DNA strands participate in joint molecules. In E. coli, at least two independent pathways to remove the junctions are proposed to operate. One is via RuvAB-promoted migration of four-strand junctions with their subsequent resolution by RuvC. In vivo, RuvAB and RuvC enzymes might work in a single complex, a resolvasome, to clean DNA from used RecA filaments and to resolve four-strand junctions. An alternative pathway for junction removal could be via RecG-promoted branch migration of three-strand junctions, provided that an as yet uncharacterized endonuclease activity incises one of the strands in the joint molecules.
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    recA mutants of E. coli K12: A personal turning point (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 767-772 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A first year graduate student, Ann Dee Margulies, changed my research career in 1962 by challenging me to direct her in the isolation of recombination-deficient mutants of Escherichia coli K-12. She succeeded in isolating two mutants, which conjugated with donor strains and received the donor DNA, but could not recombine that DNA with their own chromosomes. Ann Dee showed that both mutants were much more sensitive to UV radiation than was the wild type. Furthermore, she showed that one of these mutants carried a single mutation affecting both recombination and resistance. This work, published in 1965, was the first demonstration of the recA gene of E. coli. Subsequent work led to the discovery of many more recombination genes, the phenomenon of post replication-recombination repair, the invention of the SOS hypothesis and the discovery of genes encoding proteins with similar primary structure and function in all major groups of organisms. This article honors the memory of Ann Dee.
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    Quote/Unquote (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 776-776 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    Masthead (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996) 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    Signaling mechanisms mediating synapse formation (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 777-780 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Recent experiments have begun to decipher the molecular dialog that mediates differentiation at sites of synaptic between neurons and their targets. It had been hypothesized that the protein agrin is released by axon terminals at embryonic neuromuscular junctions and binds to a receptor on the myofiber surface to trigger postsynaptic differentiation. Now a genetic ‘Knockout’ experiment has confirmed the essential role of agrin in signaling between developing nerve and muscle(1). A second ‘knockout’ has shown that the muscle-specific receptor tyrosine kinase MuSK is a critical element in the agrin-induced signaling cascade(2). Additional results suggest that MuSK may comprise a portion of the agrin receptor(3).
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    Epigenetic factors and midbrain dopaminergic neurone development (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 817-824 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In the mammalian brain dopamine systems play a central role in the control of movement, hormone release, emotional balance and reward. Alteration of dopaminergic neurotransmission is involved in Parkinson's disease and other movement disorders, as well as in some psychotic syndromes. This review summarises recent findings, which shed some light on signals and cellular interactions involved in the specification and maturation of the dopaminergic function during neurogenesis. In particular we will focus on three major issues: (1) the differentiation of dopaminergic neurones triggered by direct contact with the midbrain floor plate cells through the action of sonic hedgehog; (2) the neurotrophic factors acting on dopaminergic neurones; and (3) the role of target striatal cells on the survival and the axonal growth of developing or grafted dopaminergic neurones.
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    Electric fields and the nuclear membrane (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 849-850 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    The boundaries of chaos and of order. Biochemical Oscillations and Cellular Rhythms. The molecular basis of periodic and chaotic behavior (1996). By Albert Goldbeter. Cambridge University Press. pp. xvii+605. £65. ISBN 0521 40307 3 (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 851-852 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    Quote/Unquote (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 854-854 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    Untangling the web. Internet for the Molecular Biologist (1996). By S. R. Swindell, R. R. Miller and S. A. Myers. Horizon Scientific. 187pp. £19.95/$32.50 (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 852-852 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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    Obesity genes and the regulation of body fat content (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 867-874 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Physiological investigation has demonstrated that the central nervous system monitors body composition and adjusts energy intake and expenditure to stabilize total adipose tissue mass. Genetic variations in the signalling molecules involved in this regulatory system account for the heritable component of body fat content. The application of molecular techniques to rodent models of Mendelian obesity has resulted in the characterization of five loci at which mutations produce an abnormal accumulation of body fat. The genes at these loci include agouti, which encodes a molecule that antagonizes the binding of alpha melanocyte-stimulating hormone to its receptor; fat, which encodes carboxypeptidase E; tubby, which encodes a putative phosphodiesterase; obese, which encodes a circulating satiety protein; and diabetes, which encodes the receptor for the obese gene product. A more detailed understanding of the functional interrelationships of these genes should lead to important new insights into the causes and potential therapies for human obesity.
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    Striving for atomic resolution in biomolecular topography: The scanning force microscope (SFM) (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 925-935 
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    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The invention in 1986 of scanning force microscopy (SFM) provided a new and powerful tool for the investigation of biological structures. SFM yields a three-dimensional view at nanometer resolution of the surface topography associated with biological objects. The potential for imaging either macromolecules or biomolecules and cells under native (physiological) conditions is currently being exploited to obtain functional information at the molecular level. In addition, the forces involved in individual bimolecular interactions are being assessed under static and dynamic conditions. In this report we focus on the imaging capability of the SFM. The rather broad spectrum of applications represented is intended to orient the prospective user of biological SFM.
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    URL: http://dx.doi.org/10.1002/bies.950181112
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    The vagaries of variegating transgenes (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 919-923 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Expression of transgenes in mice, when examined with assays that can distinguish individual cells, is often found to be heterocellular, or variegated. Line-to-line variations in expression of a transgene may be due largely to differences in the proportion of cells in which it is expressed. Variegated silencing by centromeric heterochromatin is well described, but other factors may also affect transgene silencing in mice. Tandem arrays of transgenes themselves form heterochromatin, and some cell lineages may tend to silence transgenes because of extensive facultative heterochromatin in their nuclei. The cis-acting transcriptional control elements within a transgene inhibit silencing, and strainspecific differences in chromatin proteins may strongly influence the extent of variegation. The accessibility of multiple differentiated cell lineages in mice suggests that they may provide a tool for dissecting the role of chromatin-mediated silencing in cell differentiation and tissue-specific gene expression.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/bies.950181111
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    Quote/Unquote (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 940-940 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950181114
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    Masthead (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996) 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950181201
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    Human biology: A special issue (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 941-942 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950181202
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    Mitochondrial genetics and human disease (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 983-991 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Mitochondria contain a molecular genetic system to express the 13 protein components of the electron transport system encoded in the mitochondrial genome (mtDNA). Defects in the function of this system result in some diaseases, many of which are multisystem disorders, prominently involving highly aerobic, postmitotic tissues. These defects can be caused by large-scale rearrangements of mtDNA, by point mutations, or by nuclear gene mutations resulting in abnormalities in mtDNA. Although any of these mutations would be expected to produce a similar clinical phenotype by compromising oxidative phosphorylation, the surprising and puzzling result is that different clinical phenotypes are generally associated with specific mtDNA mutations. Moreover, the same mutation can produce a distinct clinical phenotype in different individuals or pedigrees. MtDNA rearrangements are also found in aged individuals, but at a subclinical level, suggesting that normal and pathological processes can differ by the effect of genetic or environmental factors on the error rate of mtDNA replication.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bies.950181208
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    Human somatic cell gene therapy (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 999-1007 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The prelude to successful human somatic gene therapy, i.e. the efficient transfer and expression of a variety of human genes into target cells, has already been accomplished in several systems. Safe methods have been devised to do this using non-viral and viral vectors. Potentially therapeutic genes have been transferred into many accessible cell types, including hematopoietic cells, hepatocytes and cancer cells, in several different approaches to ex vivo gene therapy. Successful in vivo gene therapy requires improvements in tissuetargeting and new vector design, which are already being sought. Gene-transfer protocols have been approved for human use in inherited diseases, cancer and acquired disorders. Althouth the results of these trials to date have been somewhat disappointing, human somatic cell gene therapy promises to be an effective addition to the arsenal of approaches to the therapy of many human diseases in the 21st century if not sooner.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bies.950181210
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    Believe it or not. Human sperm competition: Copulation, masturbation and infidelity (1995). R. Robin Baker and Mark A. Bellis. Chapman and Hall. pp. xvi+353. Price £45. ISBN 0-412-36920-6 (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 338-339 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950180414
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    Non-exotic sex determination Sex Determination, Differentiation and Intersexuality in Placental Mammals (1995). By R. H. F. Hunter. Cambridge University Press. xxi+310 pp. £80/$79.95 hardback. ISBN 0 521 46218 5 (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 520-521 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950180617
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    Masthead (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996) 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950180701
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    Quote/Unquote (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 522-522 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950180618
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    The Rho GTPase regulates protein kinase activity (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 529-531 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Rho, a member of the Ras superfamily of small GTPases, has multiple biological roles: it regulates signal trasduction pathways linking extracellular growth factors to the assembly of actin stress fibres and focal adhesion complexes; it is required for G1 progression and activates the SRF transcription factor when quiescent fibroblasts are stimulated to grow; and it plays a role later in the cell cycle during cytokinesis. Two groups have recently succeeded in identifying downstream effectors of Rho that may mediate some of these biological effects. One protein identified by both groups is protein kinase N (PKN), a serine/threonine kinase whose catalytic domain is closely related to that of protein kinase C(1,2).
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/bies.950180703
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    Plant cell enlargement and the action of expansins (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 533-540 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Plant cells are caged within a distended polymeric network (the cell wall), which enlarges by a process of stress relaxation and slippage (creep) of the polysaccharides that make up the load-bearing network of the wall. Protein mediators of wall creep have recently been isolated and characterized. These proteins, called expansins, appear to disrupt the noncovalent adhesion of matrix polysaccharides to cellulose microfibrils, thereby permitting turgor-driven wall enlargement. Expansin activity is specifically expressed in the growing tissues of dicotyledons and monocotyledons. Sequence analysis of cDNAs indicates that expansins are novel proteins, without previously known functional motifs. Comparison of expansin cDNAs from cucumber, pea, Arabidopsis and rice shows that the proteins are highly conserved in size and amino acid sequence. Phylogenetic analysis of expansin sequences suggests that this multigene family diverged before the evolution of angiosperms. Speculation is presented about the role of this gene family in plant development and evolution.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bies.950180704
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    Dosage compensation in Drosophila and the ‘complex’ world of transcriptional regulation (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 541-547 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The purpose of this review is to draw attention to the mechanism of dosage compensation in Drosophila as a model for the study of the regulation of gene activity through the modulation of transcription. Dosage compensation resembles some mechanisms of transcriptional regulation, found in widely divergent organisms, that do not play a role in the activation of silent genes but determine the level of activity of genes that have been induced through the action of specific activators. It differs from other known regulatory mechanisms in that its effect is to achieve, on average, a twofold change in gene activity levels. This review introduces the notion that, in order to yield such a defined level of regulation, the mechanism of dosage compensation in Drosophila, and perhaps in Caenorhabditis as well, incorporates elements that govern both transcriptional enhancement and repression within the same multi-protein regulatory complex.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bies.950180705
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    Cytokinins in plant senescence: From spray and pray to clone and play (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 557-565 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Three approaches have been used to investigate the inhibitory role of the cytokinin class of phytohormones in plant senescence: external application of cytokinins, measurement of endogenous cytokinin levels before and during senescence, and manipulation of endogenous cytokinin production in transgenic plants. In transgenic plant studies, endogenous cytokinin levels are manipulated by expression of IPT, a gene encoding isopentenyl transferase. Transgenic plants expressing IPT from a variety of promoters exhibit developmental and morphological alterations and often display retarded leaf senescence. A recently developed autoregulatory senescence-inhibition system targets cytokinin production quantitatively, spatially and temporally, and results in transgenic plants that exhibit significantly delayed senescence without abnormalities. These transgenic studies not only confirm the regulatory role of cytokinins in plant senescence, but also provide a way to manipulate senescence for potential agricultural applications.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bies.950180707
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