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  • Articles  (129)
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  • Articles  (129)
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  • 1
    Electronic Resource
    Electronic Resource
    A complex between isoprene and copper(I) chloride: synthesis and structural characterization (1991)
    s.l. : American Chemical Society
    Organometallics 10 (1991), S. 1317-1319 
    Details
    ISSN: 1520-6041
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/om00051a021
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  • 2
    Electronic Resource
    Electronic Resource
    Reconstruction of low-resolution three-dimensional density maps from one-dimensional small-angle X-ray solution scattering data for biomolecules (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 350-363 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A Monte Carlo type reconstruction algorithm (Saxs3D) to yield low-resolution three-dimensional structures from one-dimensional small-angle X-ray scattering data (SAXS) is presented. It is demonstrated that Saxs3D reliably reproduces the shape of several test protein structures, with their respective SAXS profiles calculated theoretically from their known high-resolution atomic coordinate sets. A reconstruction for experimentally obtained scattering data for GroEL, a molecular chaperone, correctly reproduced the gross structural features of GroEL. Compared to other reconstruction methods described in the literature, Saxs3D has the advantage of allowing for any topology of the target structure, does not require any prior estimation of its dimensions, is fast and conceptually very simple.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889899015976
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  • 3
    Electronic Resource
    Electronic Resource
    Conformational attractors on the Ramachandran map (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 506-517 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Frequency distributions of protein backbone dihedral angles φ and ψ have been analyzed systematically for their apparent correlation with various crystallographic parameters, including the resolution at which the protein structures had been determined, the R factor and the free R factor, and the results have been displayed in novel differential Ramachandran maps. With improved sensitivity compared with conventionally derived heuristic Ramachandran maps, such differential maps automatically reveal conformational `attractors' to which φ/ψ distributions converge as the crystallographic resolution improves, as well as conformations tied specifically to low-resolution structures. In particular, backbone angular combinations associated with residues in α-helical conformation show a pronounced consolidation with substantially narrowed φ/ψ distributions at higher (better) resolution. Convergence to distinct conformational attractors was also observed for all other secondary-structural types and random-coil conformations. Similar resolution-dependent φ/ψ evolutions were obtained for different crystallographic refinement packages, documenting the absence of any significant artificial biases in the refinement programs investigated here. A comparison of differential Ramachandran maps derived for the R factor and the free R factor as independent parameters proved the better suitability of the free R factor for structure-quality assessment. The resolution-based differential Ramachandran map is available as a reference for comparison with actual protein structural data under WebMol, a Java-based structure viewing and analysis program (http://www.cmpharm.ucsf.edu/cgi-bin/webmol.pl).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444998013353
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  • 4
    Electronic Resource
    Electronic Resource
    Brownian dynamics simulation of the lateral distribution of charged membrane components (1996)
    Springer
    European biophysics journal 24 (1996), S. 125-135 
    Details
    ISSN: 1432-1017
    Keywords: Membrane ; Brownian dynamics simulation ; Electrostatics ; Debye-Hückel theory ; Diffusion ; Lateral distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Brownian dynamics simulations were performed to study the contribution of electric interactions between charged membrane components to their lateral distribution in a two-dimensional viscous liquid (bilayer lipid membrane). The electrostatic interaction potential was derived from an analytical solution of the linearized Poisson-Boltzmann equation for point charges in an electrolyte solution — membrane — electrolyte solution system. Equilibrium as well as dynamic quantities were investigated. The lateral organization of membrane particles, modelled by mobile cylinders in a homogeneous membrane separating two electrolyte solutions was described by spatial distribution functions, diffusion coefficients and cluster statistics. Disorder, local order and crystal-like arrangements were observed as a function of the particle charge, the closest possible distances between the charges and the particle density. The simulations revealed that the system is very sensitive to the position of the charges with respect to the electrolyte solution — membrane interface. Electrostatic interactions of charges placed directly on the membrane surface were almost negligible, whereas deeper charges demonstrated pronounced interaction. Biologically relevant parameters corresponded at most to local and transient ordering. It was found that lateral electric forces can give rise to a preferred formation of clusters with an even number of constituents provided that the closest possible charge-charge distances are small. It is concluded that lateral electrostatic interactions can account for local particle aggregations, but their impact on the global arrangement and movement of membrane components is limited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00180269
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  • 5
    Electronic Resource
    Electronic Resource
    Über die Dilactonbildung aus 2.5-Bis-[bis-(β-hydroxy-äthyl)-amino]-terephthalsäure-dimethylester im alkalischen Medium (1966)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 99 (1966), S. 3910-3913 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2.5-Bis-[bis-(β-hydroxy-äthyl)-amino]-terephthalsäure-dimethylester (1) reagiert in alkalihaltigen wäßrigen Lösungen unter doppeltem Ringschluß zum 5.11.Dioxo-1.7-bis-[β-hydroxyäthyl]-1.2.3.7.8.9-hexahydro-5H.11H-benzo[1.2-e:4.5-e′]bis[1.4]oxazepin (2). Die Reaktion ist erster Ordnung in bezug auf die Esterkonzentration; Hydroxylionen wirken katalytisch. Es wird ein Reaktionsmechanismus vorgeschlagen, der über Anionen von 1 verläuft.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19660991224
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis, Structure and Reactions of the Homoleptic Alkyne Nickel(0) Complex (Alkyne)4Ni3 (Alkyne: 2-methyl-4-trimethylsilyl-3-butyn-2-ol)Dedicated to Professor Walter Siebert on the occasion of his 60th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 1457-1461 
    Details
    ISSN: 0009-2940
    Keywords: Nickel(0) ; Alkyne complexes ; Hydrogen bonds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of (cdt)Ni (cdt: cyclododeca-1,5,9-triene) with 2 equivalents of 2-methyl-4-trimethylsilyl-3-butyn-2-ol leads to the selective formation of the homoleptic complex (alkyne)4Ni3 (compound 3), which can be isolated in excellent yields. The solid-state structure of 3 exhibits three Ni centers, forming a bent Ni3 chain connected by two bridging alkynes. The other two alkynes are terminally coordinated. Additionally, the trimeric units are stabilized by three intramolecular hydrogen bonds. Two intermolecular hydrogen bonds connect the trimeric units to form a polymer rope. According to the 13C- and 1H-NMR spectra in THF the structure of the complex 3 in solution is very similar to that in the solid state. The reaction of 3 with some alkynediols and with 2,5,5-trimethylhex-3-yn-2-ol affords compounds of the type (alkyne)2Ni. Cot (cot: 1,3,5,7-cyclooctatetraene) converts 3 into [(cot)Ni]2, which in turn reacts with 2,5-dimethylhex-3-yne-2,5-diol to form the dimeric complex (alkyne)2Ni2(cot) 6. X-ray analysis of 6 reveals a very symmetrical structure in which cot connects both Ni(0) centers at opposite sides of the ring system.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961291210
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  • 7
    Electronic Resource
    Electronic Resource
    CO2-Aktivierung an Übergangsmetallzentren: Simulation enzymatischer CO2-Fixierungs- und Transferreaktionen durch elektronenreiche (Diazadien)magnesium- und -mangan-Komplexe (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 1529-1536 
    Details
    ISSN: 0009-2940
    Keywords: Carbon dioxide fixation ; Metal complexes ; Diazadiene ligands ; Carboxylation ; Enzyme models ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Activation of CO2 at Transition-Metal Centres: Simulation of Enzymatic CO2 Fixation and Transfer Reactions by Electron-Rich (Diazadiene)magnesium and -manganese ComplexesElectron-rich diazadiene complexes of Mg and Mn can be used as model compounds for enzymatic carboxylation reactions e.g. the „dark reaction“ of the photosynthesis or in biotinedependent CO2 conversion reactions. The activity of the complexes to fix and transfer carbon dioxide strongly depends on the nature of the metal (Mg and Mn are active central atoms, other transition metals are inactive), the π aciditiy of the chelate ligand, and the structure of the complexes. The dimeric manganese complex IIa, the structure of which could be determined by X-ray structure analysis, is one of the most active compounds. NMR studies reveal that the CO2 transfer to substrates with active C - H bonds takes place in the coordination sphere of the metal atom. Carrier of activated CO2 is the N - COO group.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250703
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  • 8
    Electronic Resource
    Electronic Resource
    Metallorganische CO2-Speichersysteme aus Nickel(0)-1-azadieneinheiten und ihre Reaktivität bei der Carboxylierung von Acetophenon (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 281-287 
    Details
    ISSN: 0009-2940
    Keywords: Carbon dioxide fixation ; 1-Azadiene ligands ; Nickel(0) complexes ; Carboxylation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organometallic CO2 Reservoires from Nickel(0)-1-Azadiene-Type Ligands and Their Reactivity in the Carboxylation of Acetophenone1-Azadiene-type ligands yield with nickel(0) binuclear organometallic compounds of the type [Ni(1-azadiene)n,]2 (n = 1, 2). The structures of the complexes 1 (n = 2, ligand A) and 3 (n = 1, ligand C) have been characterized by X-ray crystallography. 1 is unreactive towards CO2, 3 and similar compounds are able to react with CO2 to give metallacyclic carbamato complexes of Ni(II). In these compounds CO2 is activated and can carboxylate acetophenone to yield benzoylic acid upon protolysis. These reactions mimic biologic conversion reactions of CO2 into organic material by organometallics. - The addition of two moles of the (bpy)Ni(0)-fragment [from (bpy)Ni(COD)] to 3 gives the tetranuclear complex 6. The X-ray analysis of the monomeric model compound (bi-py)Ni(A) (11) shows that only the olefin part is coordinated. 6 and 11 can also react with CO2. Cu(I) complexes with 1-azadiene-type ligands are not reactive towards CO2.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19951280312
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  • 9
    Electronic Resource
    Electronic Resource
    (Allyl)zirconium(IV) Complexes with the N,N′ -bis(trimethylsilyl)benzamidinato (“siam”) Ligand  -  Molecular Structures and η1-η3 Interconversions of the Allyl GroupsDedicated to Professor R. Gleiter on the occasion of his 60th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 1389-1393 
    Details
    ISSN: 0009-2940
    Keywords: Benzamidinate ; Zirconium complexes ; Allyl ligands ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexes of the type (siam)2Zr(allyl)2 (1a) and (siam)Zr(allyl)nClm are described (2a: n = 1, m = 2; 2b: n = 2, m = 1; 2c: n = 3, m = 0; siam: N,N′ -bis(trimethylsilyl)benzamidinato group). The molecular structure of 1a shows that both allyl groups are differently bonded. One allyl ligand is η3-, the other η1-coordinated. The X-ray crystal structure of the tris-(allyl) complex 2c shows a chiral molecule with two η3-allyl ligands. The third allyl ligand is coordinated in a mode intermediate between η3 and η1, thus serving as a model for an intermediate in the η3-η1 intramolecular rearrangement of the allyl ligands observed in solution. Temperature-dependent 1H- and 13C-NMR spectra of 1a, 2b and 2c indicate a rapid η1-η3 rearrangement of the allyl groups at 60°C. At -50°C two different coordination modes of the allyl groups can be observed in the case of 2b and 2c.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961291113
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  • 10
    Electronic Resource
    Electronic Resource
    Fixation of Carbon Dioxide by Oxalic Amidinato Magnesium Complexes: Structures and Reactions of Trimetallic Magnesium Carbamato and Related Complexes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1055-1064 
    Details
    ISSN: 1434-1948
    Keywords: Carbon dioxide fixation ; Magnesium ; N ligands ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of oxalic amidines R1-N=C(NHR2)-C(NHR2)=N-R1 with CH3MgX followed by uptake of CO2 results in the formation of the trimeric carbamato complexes [R1-N=C(NR2-COO)-C(NR2COO)=N-R1]3Mg3(THF)6 (2a: R1 = R2 = Ph; 2b: R1 = R2 = p-tolyl) as the thermodynamically stable final products of the reaction. Their X-ray crystal structures show that the three metal centres are in a linear arrangement. The central magnesium ion is octahedrally surrounded by six O-donor atoms of the μ2-carbamato bridges, while both peripheral magnesium ions are facially coordinated by three O-donor atoms of the carbamato groups and three THF molecules. This coordination sphere can be considered as a structural model for the active centre in the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme. Compound 2a reacts with ZnCl2 or CoBr2, with CO2 elimination, to form dimeric complexes of the type [X2M(oxalamidinato)MX2][Mg(DMF)6] (M = Zn, Co; X = Cl, Br). X-ray crystal structure analyses show that the d-metals are tetrahedrally coordinated. The magnesium-bromide-containing intermediates in the formation of 2a and 2b are able to transfer CO2 to acetophenone, thus simulating the CO2 activation step in enzymatic biotin-dependent carboxylation reactions.
    Additional Material: 7 Ill.
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