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  • Chemistry  (233)
  • Life and Medical Sciences  (29)
  • Chemical Engineering  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    Properties of membranes from polyelectrolyte complexes consisting of methyl glycol chitosan, [2-(diethylamino)ethyl]dextran, and poly(potassium vinyl sulfate) (1987)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 2631-2642 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Water-insoluble polyelectrolyte complexes (PEC) were prepared by mixing methyl glycol chitosan (MGC, 1) and [2-(diethylamino)ethyl]dextran (EA, 2) with poly(potassium vinyl sulfate) (PVSK, 3) in aqueous solution at various hydrogen ion concentrations. Elemental analyses, IR spectroscopy, and solubilities of PEC reveal that PEC differ in molecular structure and properties according to pH. It seems that the degree of dissociation and the conformation of MGC, EA, and PVSK change with pH. PEC membranes were made by casting from solutions of all kinds of PEC, and transport phenomena through the membrane of PEC prepared in 4 wt.-% HCl solution were investigated under various conditions. The driving force of the transport depends on the membrance potential, Donnan potential, and diffusion potential, according to measurements of the transport ratio of Na+ and the electric potential difference between the left- and right-hand side of the membrane. Moreover, the permeability of K+ is higher than that of Na+.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1987.021881114
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  • 2
    Electronic Resource
    Electronic Resource
    A two-dimensional NMR study of exchange behavior of amide hydrogens in a lysozyme derivative with an extra cross-link between Glu35 and Trp 108 - quenching of cooperative fluctuations and effects on the protein stability (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 131-143 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two dimensional nmr spectra [correlated spectroscopy (COSY), homonuclear Hartmann-Hahn (HOHAHA), nuclear Overhauser effect spectroscopy (NOESY)] have been observed for cross-linked lysozyme, a chemically modified lysozyme derivative with an extra ester cross-link between residues E35 and W108. Eight shifted cross-peaks were found in the fingerprint region of COSY spectra. By searching COSY, HOHAHA and NOESY spectra, they have been assigned to A32, E35, S36, I58, A107, W108, V109, and A110. The NOE connectivities (dNN and dαN) found for the cross-linked lysozyme are quite similar to those for the intact lysozyme.Exchange behavior of amide hydrogens has been studied for both intact and cross-linked lysozymes by observing the fingerprint region of COSY spectra. Hydrogen exchange reactions were carried out at pH 7.0 and at several temperatures. There exist 41 amide hydrogens whose exchange reactions are detectable under this experimetal conditon. Not only exchange rates but also their activation enthalpies were determined for individual amide hydrogens. They are classified into two groups, which are called categories III and IV. Category III hydrogens are distributed in relatively flexible peripheral parts of protein, and category IV hydrogens are deeply buried in the core region of protein. Category III hydrogens are exchanged through localized unfolding around their sites with a low activation enthalpy ranging from 10 to 25 kcal/mol. The formation of an extra cross-link affects neither the exchange rate nor the activation enthalpy of category III hydrogens. However, amide hydrogens of residues 34-39 in the vicinity of the hinge are exceptions. They are easily exchanged in the intact lysozyme but their exchange rates are drastically retarded by cross-linking. In the intact lysozyme, structural fluctuations mediating the exchange of category IV hydrogens are highly cooperative with a large activation enthalpy. These large-scale structural fluctuations are the global unfolding of the overall structure and also concerted motions within a domain. Especially near 38°C, it was found that the dominant fluctuation occurring in the α-domain is different from that in the β-domain. However, these concerted motions are strongly quenched by the formation of the cross-link because of the cooperativity of such a large-scale fluctuation. The stabilization of a localized area of protein by cross-linking results in the great suppression of large-scale and concerted motions. The exchange rates of category IV hydrogens are extremely retarded in the cross-linked lysozyme, so that they are exchanged through the so-called penetration mechanism characterized by a low activation enthalpy. These expeimental results are discussed with regard to the contribution of cross-linking to the stabilization of the folded structure of protein. © 1997 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Crystal structures of Boc-D- and L-Iva-L-Pro-OBZl: Unturned conformation of Aib-Pro sequence unaffected by replacement of Me with Et in Aib (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 1207-1212 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of the isovaline (Iva) containing dipeptides, Boc-D-Iva-L-Pro-OBzl and Boc-L-Iva-L-Pro-OBzl, were determined by x-ray diffraction. The diastereomeric peptides were shown to adopt unturned conformations closely similar to each other (φIva 52°, ψIva 46°, φPro-65°, and ψPro 143° for D-Iva-L-Pro sequence and φIva 52°, ψIva 44°, φPro -63°, and ψpro 148° for L-Iva-L-Pro sequence). The Pro ring of each peptide was in Cγ-endo conformation. The unusually large ∠CIva-NPro-CδPro values (131° in both peptides) were observed, that was due to steric repulsion between the δ-methylene of Pro and the alkyl side chain of Iva residue. These conformations were essentially the same as that of the corresponding α-aminoisobutyric acid (Aib)-containing peptide Boc-Aib-L-Pro-OBzl. The result has demonstrated that replacement of either one of the two methyl groups of the Aib residue in Boc-Aib-L-Pro-OBzl with an ethyl group does not cause any significant change in the unturned conformation of the dipeptide. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330807
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  • 4
    Electronic Resource
    Electronic Resource
    Specificity of trypsin digestion and conformational flexibility at different sites of unfolded lysozyme (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 217-226 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fourteen tryptic peptides and nine intermediates were identified as products of trypsin digestion of reduced and S-3-(trimethylated amino) propylated lysozyme. Kinetics of the appearance and disappearance of these products were observed by monitoring the peak areas on the chromatogram. In spite of the complicated reaction pathways, kinetics of the digestion of proteins and several intermediate products show simple decay curves with a single rate constant. In this paper, the trypsin susceptibility of the individual cleavage site is defined as a hydrolytic rate constant of the susceptible peptide bond in the presence of 10 nM trypsin. The cleavage sites of unfolded lysozyme are classified into two groups in terms of the trypsin susceptibility: one has a high susceptibility (10-20 h-1) and the other a low susceptibility (1.0-2.0 h-1). In the unfolded state of lysozyme, in conclusion, the region from residues 15 to 61 has a strong resistance to trypsin digestion; on the other hand, the C-terminal half of the polypeptide chain is flexible enough to fit into the active site of trypsin.In addition, six kinds of pentapeptides were synthesized as analogues of lysozyme fragments including Arg 14, Arg 21, Lys 33, Arg 45, Arg 61, and Arg 73. Kinetics of typtic digestion of them were observed. Both kcat and KM were determined for these synthetic pentapeptides. The susceptibility of each cleavage site in pentapeptides is determined and compared with that corresponding in proteins. The susceptibility is usually higher when the susceptible peptide chain is flexible. However, susceptibilities of a few sites in proteins are lower than those in pentapeptides. This means that the peptapeptides, this means that the peptide chains tend to fold locally to prevent trypsin from binding to the sites. It was found that the sites of Arg 21 and Arg 45 are indeed resistant to trypsin, but the site of Lys 33 is not so much, although the hydrolytic rate at Lys 33 itself is extremely slow. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340208
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  • 5
    Electronic Resource
    Electronic Resource
    Assignment of the disulfide bonds in the sweet protein brazzein (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 553-556 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermostable sweet protein brazzein consists of 54 amino acid residues and has four intramolecular disulfide bonds, the location of which is unknown. We found that brazzein resists enzymatic hydrolysis at enzyme/substrate ratios (w/w) of 1:100-1:10 at 35-40°C for 24-48 h. Brazzein was hydrolyzed using thermolysin at an enzyme/substrate ratio of 1:1 (w/w) in water, pH 5.5. for 6 h and at 50°C. The disulfide bonds were determined, by a combination of mass spectrometric analysis and amino acid sequencing of cystine-containing peptides, to be between Cys4-Cys52, Cys16-Cys37, Cys22-Cys47, and Cys26-Cys49. These disulfide bonds contribute to its thermostability. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Mammalian Alkaloids: O-Methylation of (±)-Norcoclaurine-1-carboxylic Acid and Related Isoquinolines Including (S)- and (R)-Norcoclaurine with 14C-Labeled S-Adenosyl-L-Methionine in Presence of Mammalian Catechol O-Methyltransferase (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 426-432 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (±)-Norcoclaurine-1-carboxylic acid (5) and the derived dihydroisoquinolinone 6 (present as quinonemethide 6a at pH 7) afforded, on methylation with 14C-labeled S-adenosyl-L-methionine in the presence of mammalian catechol O-methyltransferase, exclusively the 7-O-methylated congeners 7 and 9, respectively. High stereoselectivity of the O-methylation was observed with (-)-(S)- and (+)-(R)-norcoclaurine (2a and 2b, resp.), affording 80% of 6-O-methylated isoquinoline 12 and 20% of the 7-O-methylated isomer 11 from 2a, and the reversed proportion of 12 and 11 from 2b. Synthesis of the reference amino acid 8 was achieved by Pictet-Spengler condensation of O-benzyl-protected dopamine 17 with benzyl-protected keto acid 20 (→ 21) followed by methylation with diazomethane (→22 + 23) and removal of the protecting groups by acid hydrolysis. It is considered unlikely that amino acids such as 5 constitute important precursors in the biosynthesis of isoquinolines related to reticuline.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730222
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  • 7
    Electronic Resource
    Electronic Resource
    Syntheses and Structures of Transition-Metal Complexes of Mesoionic Olate, Thiolate, Selenolate, and Cyclopentadienide (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1157-1159 
    Details
    ISSN: 0009-2940
    Keywords: Mesoionic compounds ; Transition metal complexes ; Tetrazolium-4-olate,-4-thiolate,-4-selenolate-, 4-cyclo-pentadienide, complexes with molybdenum or chromium carbonyls ; 1,2,4-Triazolium-3-thiolate, complex with pentacarbonylmolybdenum ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dicarbonyl(η1-cyclopentadienyl)iron(II) complex 5 of 1,3-diphenyltetrazolium-5-olate (4) and the pentacarbonylmolybdenum(0) complexes 7, 11, and 9 of 1,3-diphenyltetrazolium-5-thiolate (6), -5-selenolate (10), and 5-methyl-1,4-diphenyl-1,2,4-triazolium-3-thiolate (8) as well as tricarbonylchromium(0) complex 13 and -molybdenum(0) complex 14 of 1,3-diphenyltetrazolium-5-cyclopentadienide (12) have been prepared. Their physicochemical properties are discussed on the basis of spectroscopic properties.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260515
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  • 8
    Electronic Resource
    Electronic Resource
    Charge-Transfer-Komplexe von Metalldithiolenen mit Viologenen (1987)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 120 (1987), S. 1011-1016 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Charge transfer complexes of the type [ML2]2-[RV]2+ are prepared from viologens (RV2+) and dianionic metal dithiolenes ([ML2]2-; M=Zn, Cd, Hg; L=a substituted 1,2-ethenedithiolate). The solid state structure consists of separated pseudocolumns of tetrahedral metal dithiolenes and twisted viologens. While there is no evidence for short contacts within a column, an intercolumnar interaction is indicated by Zn-H and S-H distances of 3.27 and 2.87 Å, respectively. UV-VIS spectra exhibit an ion pair charge transfer band in the range of 460-660 nm (∊=400-1900). Its location is predominatly determined by the nature of the ethenedithiolate ligand inducing shifts of 70-200 nm while the metal has only a weak influence. Formation constants of the 1:1 ion pairs are in the range of 100-600 1 mol-1. Spectrophotometric analysis reveals the presence of further adducts with different composition.
    Notes: Charge-Transfer-Komplexe des Typs [ML2]2-[RV]2+ werden aus Viologenen (RV2+) und dianionischen Metalldithiolenen ([ML2]2-; M=Zn, Cd, Hg; L=ein substituiertes 1,2-Ethendithiolat) synthetisiert. Die Festkörperstruktur besteht aus getrennten Pseudosäulen tetraedrischer Metalldithiolene und verdrillter Viologene. Für intrakolumnare Wechselwirkungen gibt es keine Hinweise, für interkolumnare sprechen dagegen die kurzen Zn-H- und S-H-Abstände von 3.27 und 2.87 Å. UV-VIS-Spektren enthalten eine Ionenpaar-Charge-Transfer-Bande im Bereich von 460-660 nm (∊=400-1900). Deren Lage wird hauptsächlich durch die Natur des Ethendithiolat-Liganden festgelegt, welcher Verschiebungen von 70-200 nm induziert. Das Zentralmetall übt nur einen schwachen Einfluß aus. Die Bildungskonstanten der 1:1-Ionenpaare liegen im Bereich von 100-600 1 mol-1. Spektrophotometrische Analysen deuten auf das Vorliegen weiterer Ionenassoziate unterschiedlicher Zusammensetzung.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19871200621
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and Chemical Transformations of 1,3-Diaryltetrazolium Salts. Preparation of Mercury(II) and Palladium(II) Complexes of 1,3-Diaryltetrazolylene and Reactions of 5-Substituted 1,3-Diphenyltetrazolium Salts with Nucleophiles (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1149-1155 
    Details
    ISSN: 0009-2940
    Keywords: Mesoionic compounds ; Tetrazolium salts, 1,3-diaryl- ; Carbenes, mesoionic ; Carbene-metal complexes ; Nucleophilic substitution ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Diaryltetrazolium salts 5 and 6 have been prepared by nitric acid oxidation of the corresponding 5-thiolates 4. The reaction of 5 with mercury(II) acetate gives (1,3-diaryltetrazolylene)mercury(II) complexes 7, which provide 5-halotetrazolium salts 8 - 10 by treatment with halogen. 1,3-Diphenyltetrazolylene (16), generated in situ by proton abstraction of 1,3-diphenyltetrazolium salts 5a or 6a, has been trapped with p-(dimethylamino)benzenediazonium tetrafluoroborate to form 18/18′. The palladium(II) complex 19 of 1,3-diphenyltetrazolylene has been prepared by oxidative addition of tetrakis(triphenylphosphane)palladium(0) to 5-chlorotetrazolium salt 8. The reactivity of various 5-substituted tetrazolium salts toward carbon nucleophiles depends on the nature of the substituents at C-5. With electronegative substituents, nucleophilic substitution proceeds at C-5, whereas electron-donating substituents direct the nucleophiles towards N-2 yielding ring-cleaved products.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260514
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  • 10
    Electronic Resource
    Electronic Resource
    Functional monomers and polymers, 40Part 39: M. Miyata, K. Takemoto, Polym. J. 9, 111 (1977). A convenient synthesis of N-(2-methacryloyloxy)ethyl derivatives of nucleic acid bases (1977)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 178 (1977), S. 1211-1214 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1977.021780423
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