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  • Wiley-Blackwell  (327)
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  • 1
    Electronic Resource
    Electronic Resource
    Effects of pH and temperature on cardioactive polypeptides from sea anemones: A 1H-nmr study (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1143-1157 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of pH and temperature on the 300-MHz 1H-nmr spectra of three cardioactive polypeptides from sea anemones, anthopleurin-A from Anthopleura xanthogrammica (AP-A) and Anemonia sulcata toxins I and II (ATX I and II), are described. AP-A and ATX II exhibit major spectral heterogeneity. Evidence from the pH and temperature studies and from high performance liquid chromatography indicates that this heterogeneity is conformational rather than chemical in origin. By contrast, purified isotoxins of ATX I show no evidence of conformational heterogeneity. The pKa values of most of the ionizable groups in these polypeptides are not strongly perturbed by interactions in the tertiary structure, with the exception of one of the Asp carboxylates, which has a pKa of ≲ 2 in AP-A and ATX II and 3.0 in ATX I. Protonation of this carboxylate, suggested to be Asp-9, leads to a conformational change in all three molecules. All three polypeptides are thermally stable, showing some conformational changes but not major unfolding at elevated temperatures.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270708
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  • 2
    Electronic Resource
    Electronic Resource
    Specific assignment of resonances in the 1H-nmr spectrum of the polypeptide toxin I from Anemonia sulcata (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 489-506 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The assignment of a large number of resonances in the 300-MHz 1H-nmr spectrum of the polypeptide neurotoxin Anemonia sulcata toxin I is described. The initial identification of spin systems is made using both one- and two-dimensional nmr spectra. The subsequent assignment of these spin systems to specific residues in the molecule is based largely on the observation in two-dimensional spectra of through-space connectivities between Hα and NH resonances from adjacent residues in the amino acid sequence. Using these techniques, the full spin systems of 22 residues are specifically assigned, together with partial assignments for a further 8. Many of the spin systems from the remaining 16 residues have been defined, although not yet specifically assigned. From the pattern of through-space connectivities between protons from adjacent residues in the sequence, some inferences may be drawn concerning the secondary structure of this polypeptide in aqueous solution.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250308
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  • 3
    Electronic Resource
    Electronic Resource
    Peptide mechanics: A force field for peptides and proteins working with entire residues as smallest units (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1003-1017 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The central ingredient of any structure modeling tool is a molecular model or force field that accounts for proper geometry and energy calculation. For protein and peptide modeling based on entire amino acids as building blocks, we describe a peptide force field in which each amino acid is represented by a single point in space, taken at the position of the α-carbon atom. Apart from the positional coordinates, these units carry the two torsional angles ϕ and Ψ as additional degrees of freedom to account for the orientations of the peptide links. While some of the energy terms are analogous to expressions in atomic force fields, the presence of the angular variables leads to fundamental differences with new features and additional terms with no atomic counterparts.The force field reproduces secondary structure elements with very good accuracy. Globular parts of tertiary packing stay near the experimental structures with a rms deviation in C-α positions of 0.1-0.3 nm and about 25° in ϕ and Ψ depending on the size of the structure. A tendency for larger discrepancies is observed in exposed loops or terminal segments the conformations of which may be strongly influenced by neighboring domains.Finally, a scope of possible applications is presented. They range from modeling activities, such as model building by homology, to coarse scanning of conformation space in conformation analysis and structure determination. An extension to a dynamics model would offer the possibility to eliminate the less interesting high-frequency modes that in all-atom force-field dynamics absorb most of the computational effort.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320811
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  • 4
    Electronic Resource
    Electronic Resource
    On the Position of the Intramolecular Equilibrium between Opened and Aromatic-Ring Stacked Forms in Ternary Complexes Composed of Adenosine 5′-triphosphate, Mg2+ or Zn2+, and L-Tryptophanate, and in Related Ternary SystemsPart XXXII of the series ‘Ternary Complexes in Solution’; for part XXXI see [1]. (1979)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 62 (1979), S. 1723-1735 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intramolecular and dimensionless equilibrium constant, K′, for the equilibrium between open and aromatic-ring stacked isomers of ternary complexes formed between adenosine 5′-triphosphate, inosine 5′-triphosphate, or uridine 5′-triphosphate, Mg2+ or Zn2+, and L-tryptophanate, 2,2′-bipyridyl (bipy), or 1,10-phenanthroline (phen) have been estimated by 1H-NMR. shift measurements in D2O (I = 0.1M, NaNO3; 27°). The approximate equilibrium constants K′ are ≥ 20, ≥ 20, 1.2, 0.9, 0.7, 0.5, and 0.3 for the ternary complexes Zn (phen) (ATP)2-, Mg (phen) (ATP)2-, Zn (bipy) (ATP)2-, Zn (bipy) (ITP)2-, Zn (bipy) (UTP)2-, Zn (trp) (ATO) 3-, and Mg (trp) (ATP)3-, respectively. The percentages of the stacked isomers decrease in the order Zn (phen) (ATP)2- (≥ 95%) ≫ Zn (bipy) (ATP)2- (55%) 〉 Zn (bipy) (ITP)2- (48%) 〉 Zn (bipy) (UTP)2- (∼ 40%), which coincides with the order of stability of the binary metal-free adducts (phen) (ATP)4- 〉 (bipy) (ATP)4- ≃ (bipy) (ITP)4- 〉 (bipy) (UTP)4-; the corresponding stability constants are KABA = 28.2 ± 4.7, 8.1 ± 2.6, 8.8 ± 1.8, and ∼ 1 (M-1), respectively (D2O; I = 0.1 M, NaNO3; 27°): these series reflect the decreasing size of the aromatic-ring systems forming the stacks. The indole moiety of tryptophan resembles 2,2′-bipyridyl rather than 1,10-phenanthroline and K(trp)(ATP)(trp) = 6.2 ± 1.8 M-1 for (trp) (ATP)4-. Implications with respect to the stability of ternary complexes, and to biological systems are indicated briefly.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19790620605
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  • 5
    Electronic Resource
    Electronic Resource
    Some symmetry aspects of the local-mode description of vibrational structureAbstracted from an invited talk given by one of us (W.M.G.) at the American Conference on Theoretical Chemistry, Boulder, Colorado, June 1978. (1978)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 14 (1978), S. 703-708 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the local-mode description of vibrational structure, the nuclear coordinates - unlike the usual normal coordinates - do not reflect the molecular symmetry. Accordingly, the local-mode product wave functions must be symmetry adapted. We discuss this simple procedure in light of its implications for the localization of vibrational energy and the dissociation limits of molecular excited states. These properties are in turn related to the separability of the total nuclear Hamiltonian and to the different ways in which the vibrational anharmonicity is “absorbed” by the local and normal coordinates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560140516
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical interpretation of the anomalous behavior of some macromolecules (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 191-199 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently, one of the members of this group (Fritz) has observed some unusual properties of rouleaugenic polymer solutions. It was found that the diffusion coefficient of polystyrene spheres in these solutions displayed an expected fall followed by an unexpected rise in values when the radii of these particles are changed. In this paper we present some of these experiments and provide a thermodynamic interpretation of the rise in the values of the diffusion coefficient.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340717
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  • 7
    Electronic Resource
    Electronic Resource
    Generic shapes for the conformation analysis of macrocyclic structures (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1429-1441 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new algorithm for the systematic generation of conformations of macrocyclic systems is presented. The procedure is based on the concept of generic shapes that are found in such structures. These shapes are characterized by a selection of harmonics which occur in an approximate Fourier representation of the atomic coordinates of the rings. Following a fixed protocol, a limited set of in-plane and out-of-plane circular harmonics is used to define an ensemble of generic ring shapes. These generic shapes are used as start structures for energy minimizations by a given force-field method. To account for the possibility of having several final conformations originating from the same generic shape, the corresponding initial structure is taken several times and subjected to a randomization step before minimization. The resulting conformations that fall within a preset low-energy band are collected and screened for duplicates and enantiomers. The efficiency of this procedure (ratio between the number of accepted conformations and the total number of energy minimizations) depends on the flexibility of the macrocyclic system. The efficiency is generally quite high for very flexible rings. According to the proposed protocol, the number of generic shapes used as start structures grows as the square of N(lnN), where N is the ring size. The algorithm lends itself to conformational analyses of medium-size and large rings as well as of loops spanned between fixed structural units.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710607
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  • 8
    Electronic Resource
    Electronic Resource
    Comments on the Bose condensation of phonons in the biological systems (1983)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 23 (1983), S. 709-712 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Following the conjecture of Fröhlich that the Bose condensation of phonons is the dominant biological effect, Wu and Austin derived from the Fröhlich Hamiltonian an expression for the relaxation time which is inversely proportional to the temperature by using the technique of Green's function. In this paper, we have generalized the Wu and Austin expression by improving their approximations with the superconducting canonical transformation and obtained the relaxation time depending exponentially on the inverse temperature. Moreover, we have checked our expression by using a different method based on the “continued fraction expansion” and also employed this technique to derive the dielectric constant for this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560230239
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  • 9
    Electronic Resource
    Electronic Resource
    The Pagodane Route to Dodecahedranes Directed Conversions - The Pagodane → Bissecododecahedradiene StageDedicated to Prof. Dr. William von E. Doering on the occasion of his 75th birthday. (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 1697-1717 
    Details
    ISSN: 0009-2940
    Keywords: Pagodane → dodecahedrane pathways ; Pagodane opening reactions ; Cage effects ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three conceptual routes (A, B, C) from [1.1.1.1]pagodane (1) to pentagonal dodecahedrane (2) are evaluated by MM2 (MM3) calculations. After limited experimental success with a catalytic one-pot route (A), a more selective transformation along one of two stepwise routes (B/C) is explored. An expeditious entry into route C is achieved by hydrogenolytic cyclobutane opening in 1; secopagodane 7 (100%), however, resists both progression along route C (dehydrogenative C - C bond formation to isododecahedrane 8) and crossover into route B (hydrogenolysis to bissecododecahedrane 5). The first transformation along route B, the 2sigma;→2π-isomerization of the highly strained 1 to bissedodecahedra-1,10(11)-diene 3, is not attainable by metal catalysis and cannot productively be brought about by thermal activation: The necessarily very high reaction temperatures (〉 700°C) enforce instead a mechanistically interesting fragmentation into two C10H10 halves to give ultimately naphthalene. The very rapid pagodane opening occurring after one-electron oxidation, too, is not a preparatively useful alternative. Highly efficient, on the other hand, is a two-step process affording a high yield of the product and consisting of regiospecific, photochemically induced bromine addition to the central four-membered ring (→ dibromosecopagodane 37) followed by reductive bromine elimination (→ diene 3). In spite of the necessarily rather severe reaction conditions in both steps, this procedure is applicable to the preparation of various 3,8-difunctionalized bissecodienes (dienedione 11, diene diesters 43, 50, 52, dichlorodiene 56). Limitations of this procedure are met with the 4,4,9,9-tetrachloropagodane 60 (inert) and the [2.2.1.1]pagodane 80 (bridgehead bromination). The lateral half-cages of the (seco)-pagodane structures are explored for preparatively (dis)advantageous steric effects, that might be later exploited on the way towards functionalized dodecahedrane derivatives.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250727
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  • 10
    Electronic Resource
    Electronic Resource
    The Pagodane Route to Dodecahedranes Unsaturated (Hyperstable) and Saturated BissecododecahedranesDedicated to Prof. Dr. Günther Maier on the occasion of his 60th birthday (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 1719-1739 
    Details
    ISSN: 0009-2940
    Keywords: Bissecododecahedranes, saturated, unsaturated ; Homoconjugation ; Hyperstability ; Addition reactions ; Cage effects ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In bissecododecahedra-1,10(11)-dienes, the syn-periplanar and unusually proximate arrangement of the π bonds is responsible for extraordinary physical properties such as strong throughspace homoconjugation, low oxidation potentials, and a special reactivity pattern. In pursuit of route B to dodecahedranes[1], the hyperstability predicted (MM2) for these bissecodienes and the related monoenes has been experimentally verified only for the latter in their resistance towards catalytic hydrogenation. Non-hydrogenative saturation of (3,8-difunctionalized) bissecodienes (3, 8, 13) and monoenes (4, 9, 14) becomes increasingly hampered due to the increased steric congestion on the more spherical molecular surfaces but can be achieved in „high-driving-force” reactions [cis-hydroxylation (26, 27, 41, 42), epoxidation (38, 54, 57, 58, 60, 63, 80, 83), cyclopropanation (55, 59, 61, 64]. In contrast, cycloadditive four-, five- (73), and six-membered (76) ring annulation again is limited to monoadditions. The half-cages in the bissecododecahedrane structures provide for remarkable steric steering and protection [e.g. anti-selective protonation (alkylation) of carbanions 57a (84a)2-, lack of hydrazone formation from ketones 58, 89, resistance of syn-bis(acid chloride) 86 towards hydrolysis.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250728
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