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  • 1985-1989  (9,542)
  • 1975-1979  (13,827)
  • 1986  (9,542)
  • 1979  (7,433)
  • 1976  (6,394)
  • Chemistry  (20,214)
  • Life and Medical Sciences  (2,885)
  • General Chemistry  (2,659)
  • Electron microscopy  (278)
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  • 1985-1989  (9,542)
  • 1975-1979  (13,827)
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  • 101
    Electronic Resource
    Electronic Resource
    Masthead (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250101
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  • 102
    Electronic Resource
    Electronic Resource
    The relation of ion pairs to protein hydration: An IR spectroscopic and X-ray crystallographic survey (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 317-335 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report here a novel ir technique that we use to determine the apparent van't Hoff's energy for the distillation of water from protein amide and acid groups. The method is used to study the hydration properties of ten different proteins. The results show that water removal from the environment of ion-paired acid groups (those ≤ 4 Å from a basic group on the protein surface) requires less energy than water removal from the environment of nonpaired acid groups. These observations are supported by an analysis of the solvent distributions in protein crystal structures. A model is proposed for the interaction between water and protein acid groups, and this model is used to account for the distributions and properties of certain eye-lens proteins.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250212
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  • 103
    Electronic Resource
    Electronic Resource
    A polynucleotide CD probe: Interactions with oligomers of a polycationic amine that exhibit positive extrinsic bands at 〉 300 nm (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 407-429 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A set of large positive extrinsic CD bands ([θ]333 = 2.6 X 104 deg-cm2/decimole phosphate) in the 〉 300 nm region as well as diminution of the intrinsic signals (θ275) have been observed in the CD spectra of various nucleic acids complexed with the achiral compound, N-poly{α-[N-(4-pyridylethylene-4-pyridyl-N′-)α′-p-xylyl]dibromide}-4-pyridylethylene-4-pyridinium bromide, (polymer X).1,2,5 The signal changes are attributed to the binding of polymer X chromophores isogeometrically to the DNA helix in an ordered chiral arrangement. Fractionation of polymer X gives 10 well-separated oligomers. The oligomers were characterized by nmr. Their interactions with DNA have been investigated with respect to r(r = ratio of equivalents of polymer X charge/g-atoms DNA phosphorus) and n (oligomer chain length). In all cases where n ≥ 1, [θ]333 increases linearly with increasing r between 0 and 0.32, and is accompanied by a corresponding decrease in [θ]275, which becomes negative as r approaches .32. Extrinsic band intensities reveal a dependence on n up to n = 5, above which increases in nonspecific binding result in a reduction in normalized band intensities. Polymer X shows a strong preference for B-form nucleic acids and induces maximum extrinsic CD signal intensities with A-T homopolymers. Alterations in helix hydration are believed to accompany complex formation. Inversions in [θ]275 of the octamer X-poly(dA-dT) complex have been attributed to the “alternating B” conformation of poly(dA-dT).3 Similar inversions are not observed in other nucleic acid-octamer X complexes. Visible and CD spectrometry data from competition studies in the presence of the antibiotics actinomycin D (AMD), daunomycin (DM), and distamycin A (DST) are consistent with “nonclassical” intercalation as the mode of binding, and these data place the potential binding site in or near the hydrophobic region of the minor groove. Reductions in [θ]333 with increasing urea further implicate the involvement of hydrophobic interactions in the formation of an asymmetric complex. Stabilization of the helix results in all cases as evidenced by alterations in Tm; corresponding changes, however, in cooperativity are not clearly discernable. Viscosity and light-scattering data indicate no changes in molecular weight due to aggregation, and as such are not consistent with a transition to the ψ-DNA upon complex formation.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250304
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  • 104
    Electronic Resource
    Electronic Resource
    Vacuum UV CD of the low-salt Z-forms of poly(rG-dC)·poly(rG-dC), and poly(dG-m5dC)·poly(dG-m5dC) (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 519-523 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vacuum CD spectra of poly(rG-dC)·poly(rG-dC) and poly(dG-m5dC)·poly(dG-m5dC) have been obtained for the low-salt Z-conformations of both polymers. The spectra are very similar to those for the high-salt Z-forms. This behavior is consistent with the suggestion that the low- and high-salt Z-forms are comprised of different proportions of ZI- and ZII-conformations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250310
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  • 105
    Electronic Resource
    Electronic Resource
    Chain association of pectic molecules during calcium-induced gelationPart of this work has been presented at the 7th European Polymer Network Group Meeting, September 10-14, 1984, Manchester, England. (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 455-468 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chain association of pectic molecules with different levels and patterns of esterification during calcium-induced gelation was studied by methods such as light scattering, viscometry, and determination of calcium activity coefficient and of calcium transport parameter. A gel point can be determined, assuming a power law including a critical ratio (equivalent concentration of calcium ions/pectin carboxylic groups) and quasi-critical exponents varying in the range 0.50-1.26. The values of these critical parameters were discussed as a function of polymer concentration, of level and pattern of esterification, and of the nature of the divalent counterion. The lower these values are, the better, apparently, the gel-forming ability of the pectins is.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250306
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  • 106
    Electronic Resource
    Electronic Resource
    Models of thioredoxin hairpin structures: Conformational properties of β-turn containing sequences (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 555-570 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sequences 74-91 and 77-91 of E. coli thioredoxin, which according to x-ray structure contain an irregular β-turn, a hairpinlike structural element, have been synthesized and their conformational properties in solution have been investigated by means of CD spectroscopy. In addition, analogs of these sequences, containing the regular β-turn element Gly-Pro-(Gly)2, have also been prepared and investigated. These are BOC-Ile-Gly-Pro-(Gly)2-Val-OMe (III) and BOC-(Ile)3Gly-Pro-(Gly)2-(Val)5-OMe (IV) that on the basis of probability, should form hairpin structures stabilized by intramolecular interactions. While the natural sequences were shown to be unable to adopt structures characterized by an intrinsic conformational stability, the two analogs showed evidence of intramolecular folding in methanol and trifluoroethanol-water solution. In particular, the CD spectra are indicative of β-structure. The most interesting case was observed for compound IV, as the highest degree of conformational order was present in solutions containing a large proportion of water. In addition, the formation of this structure took place in a highly cooperative manner. The results are utilized to discuss whether and to what extent conformationally stable folding peptide units of small size can be formed in aqueous solution.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250404
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  • 107
    Electronic Resource
    Electronic Resource
    Halogenated nucleic acids: Effects of 5-fluorouracil on the conformation and properties of a polyribonucleotide and its constituentsThis investigation was supported by PHS Grant number CA-25438, awarded by the National Cancer Institute, DHHS. (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 571-600 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational properties of 5-fluorouracil derivatives are compared to uracil derivatives. FUrd, 5′-FUMP, and poly(FU) are studied as a function of pH and temperature by 19F- and 1H-nmr spectroscopy, and the corresponding uracil derivatives by 1H-nmr spectroscopy. FUrd exhibits no significant conformational changes with solution pH (5-10). In contrast, at low pH (6-7) 5′-FUMP and 5′-UMP show similar conformational features, while at high pH (9) 5′-FUMP shows significant conformational alterations. Also, poly(U) and poly(FU) are conformationally similar at low pH, but increasing pH induces changes in poly(FU). These changes are observed in the backbone [γ(C4′-C5′)], furanose, and furanose-base conformations. The apparent pKa of N3-H ionization of the FUra base is determined by 1H- and 19F-nmr to range from 7.5 to 8.2 [FUrd 〈 5′-FUMP 〈 5′-FUDP 〈 poly(FU)]. These observations are interpreted as a result of electrostatic interactions generated between the ionized phosphate group and the negatively charged base moiety as the pH is raised. The interaction properties of poly(FU) with ApA are studied by 1H- and 19F-nmr spectroscopy, and these properties compared to those published for poly(U). Poly(FU) forms a complex with ApA inducing upfield 1H-shifts in both components, and downfield 19F- shifts in poly(FU). The base stoichiometry of the complex for poly(U)·ApA is 2U:1A at various U/A ratios. In contrast, the base stoichiometry of the poly(FU)·ApA complex appears to be dependent on the FU/A ratio. At high FU/A ratio, the complex is 2FU:1A, and as the FU/A ratio approaches unity the complex becomes 1FU:1A.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250405
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  • 108
    Electronic Resource
    Electronic Resource
    Sequential polypeptides containing arginine as histone models: Synthesis and conformational studies (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 655-675 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sequential polypeptides (L-Arg-X-Gly)n, where X represents amino acid residues Ala, Val, and Leu, were prepared as models of arginine-rich histones to be used in studying their structure and their interactions with DNA. The polymerization was carried out on the pentachlorophenyl active esters of the appropriate tripeptides, while the toluene-4-sulfonyl group was used for protecting the arginine guanido group. CD was employed to investigate the conformation of (L-Arg-X-Gly)n polymers in aqueous solutions, at different pH, as well as in trifluoroenthanol and hexafluoroisopropyl alcohol solutions. In aqueous solutions (at pH 7 and 12) the prepared sequential polymers behaved as a random coil. The CD spectra in various trifluoroethanol-water or hexafluoroisopropyl alcohol-water mixtures indicated that the degree of helical conformation of the studied polytripeptides increased in the order of Ala → Val → Leu. The opposite was true for the β-structure. Characteristics of β-turn are excluded from the poly(L-Arg-L-Leu-Gly), which assumed the most pronounced helical conformation. The poly(L-Arg-L-Val-Gly) exerts a significant preference to the β-turn structure compared to that of poly(L-Arg-L-Ala-Gly). Thus the probability for helical, β-structure or β-turn conformations of the polymers was analyzed in relation to the bulkiness and length, and to the special features of the X-residue side chain (β-branching). We concluded that the prepared sequential arginine-containing polypeptides are plausible models for histone fractions, f3 and f2α1.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250410
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  • 109
    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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  • 110
    Electronic Resource
    Electronic Resource
    Masthead (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250401
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  • 111
    Electronic Resource
    Electronic Resource
    Macroscopic polarity of connective tissue is due to discrete polar structures (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 601-606 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Applying scanning optical harmonic microscopy to biological tissue for the first time, we have discovered that the macroscopic polarity of rat-tail tendon is due to a coherent network of discrete polar structures. This finding permits isolation of these structures for further detailed analysis, which should lead to their complete characterization and thus to a solution of the twenty-year-old mystery of connective tissue polarity.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250406
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  • 112
    Electronic Resource
    Electronic Resource
    On an exact starting expression for macromolecular hydrodynamic models (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 627-637 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A calculational method developed by G. K. Youngren and A. Acrivos [J. Fluid Mech. 75, 377 (1975)] expresses the fluid forces exerted over the surface of an immersed body in terms of differences between body and fluid motions. As opposed to bead-model approaches, this method starts from an essentially exact hydrodynamic expression, and therefore should be of particular interest to those workers trying to obtain accurate coefficients needed to characterize the diffusive and viscoelastic behavior of macromolecules with complex shapes. However, Youngren and Acrivos's treatment has not been widely adopted nor even used as a proper starting place for higher order bead-model methods. This is probably related to the unfamiliar appearance of their exact expression, which involves two surface integral terms as opposed to the single summation involved in bead models. We show that their expression may be rewritten in the expected analogous form involving one surface integral term whenever stick boundary conditions are applied to a rigid body or a flexible body composed of rigid segments. For spherical segments, we obtain Rotne-Prager-type bead-model results by following typical assumptions. Extensions to deformable particles are considered, in which internal friction can be represented by an arbitrarily viscous internal fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250408
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  • 113
    Electronic Resource
    Electronic Resource
    Sequence-dependent conformations of DNA duplexes: The TATA segment of the d(G-G-T-A-T-A-C-C) duplex in aqueous solution (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 693-706 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The base and sugar protons of the d(G-G-T-A-T-A-C-C) duplex have been assigned from two-dimensional correlated (COSY) and nuclear Overhauser effect (NOESY) measurements in D2O solution at 25°C. The nucleic acid protons have been assigned from NOEs between protons on adjacent bases on the same and partner strands, as well as from NOEs between the base protons and their own and 5′-flanking H1′, H2′, H2″, H3′, and H4′ sugar protons. These assignments are confirmed from coupling constant and NOE connectivities within the sugar protons of a given residue. Several of these NOEs exhibit directionality and demonstrate that the d(G-G-T-A-T-A-C-C) duplex is a right-handed helix. The relative magnitude of the NOEs between the base protons and the sugar H2′ protons of its own and 5′-flanking sugar demonstrate that the TATA segment of the d(G-G-T-A-T-A-C-C) duplex adopts a B-DNA type helix geometry in solution, in contrast to the previous observation of a A-type helix for the same octanucleotide duplex in the crystalline state.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250412
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  • 114
    Electronic Resource
    Electronic Resource
    Masthead (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250501
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  • 115
    Electronic Resource
    Electronic Resource
    A mechanism for the large anisotropic swelling of DNA films (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 765-770 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250502
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  • 116
    Electronic Resource
    Electronic Resource
    Calorimetric studies of the polynucleotide analog poly(-)2-[2-(thymin-1-yl) propanamido]propenoic acid (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 787-794 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermally elicited structural and conformational transitions of the polynucleotide analog, poly(-)-2-[2-(thymin-1-yl)propanamido]propenoic acid, P(-)TDHA, have been studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermogravmetric analysis (TGA). The differential scanning calorimetry curves obtained on solid P(-)TDHA samples exhibited five distinct transitions. The transition occurring at 50°C is attributed to a disruption of interactions involving thymine-thymine stacking. In contrast the transition observed at 83°C is attributed to a hydrogen-bonding interaction involving the thymine residues, whereas the transition occurring at 110°C is assigned to hydrogen bonding of the carboxylic acid side-chain groups. The transitions observed at 50, 83, and 110°C are reversible if the heated and quenched sample is allowed to equilibrate in an atmosphere of high humidity. The transition occurring at 127°C is viewed as a structural rearrangement of the polymer backbone that does not involve the participation of water molecules. The transition observed at a temperature above 197°C is attributed to a structural modification of the polymer resulting from decomposition. Solutions of P(-)TDHA in 0.1M phosphate buffer at pH 7.05 showed only a single transition at 50°C, which is in accord with an observed transition in the solid state assigned to the disruption of base-stacking interactions. The average enthalpy for the transition at 50°C was 0.92 cal/g in the solid state and 1.08 cal/g for the solution, which provides additional support for the assignment.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250504
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  • 117
    Electronic Resource
    Electronic Resource
    Effective diffusion rate through a polymer network: Influence of nonspecific binding and intersegment transfer (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 811-821 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effective diffusion rate of a tracer molecule through a polymer network can be influenced by nonspecific binding. If such binding occurs, the local density fluctuations (segmental diffusion) of the network molecules will contribute to the net displacements of tracer molecules. If the network is strongly interconnected by entanglement or cross-linking, these local motions will only carry the tracer molecules over a small region, and effective transport would require dissociation and reassociation of the tracer molecule to another part of the network. Alternatively, tracer molecules could be transferred directly (intersegment transfer) between different parts of the network whenever they are brought sufficiently close by the density fluctuations. A wormlike-chain model for the segmental diffusion of a polymer is used to describe the network motions and to derive the effective diffusion rate for a tracer molecule as a function of network density and binding constant with or without intersegment transfer contributing. It is found that the density dependence for the effective diffusion of ethidium bromide through dense DNA solutions studied by photobleaching recovery [R. D. Icenogle and E. L. Elson (1983) Biopolymers 22, 1949-1966] agrees with an intersegment-transfer mechanism limited by the segmental DNA motions. The calculations are also applied to a model for the intracellular diffusion of molecules loosely bound to the cytomatrix. If intersegment transfer dominates it can account for the observed size independence for the intracellular diffusion rates of various injected macromolecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250506
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  • 118
    Electronic Resource
    Electronic Resource
    Experimental tests of a geometrical abstraction of fibrin polymerization (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 905-929 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By combining measurements of the enzymatic release of fibrinopeptide A (FPA) with measurements of intensity and linewidth of Rayleigh scattering from fibrin polymer solutions prior to gelation, we have systematically tested a variety of predictions that can be made on the basis of a simple geometrical abstraction of fibrin polymerization. The experimental investigations include FPA content of fibrin polymers, aggregation of fibrin with fibrinogen, enzyme kinetics, shift of the chemical equilibrium by adding Gly-Pro-Arg-Pro or fibrinogen to the polymer solution, evolution of the polymerization, and influence of fibrinopeptide B release. Among the considered geometrical abstractions there is only one that survives the experimental tests and at the same time is compatible with the electron micrographs by other authors. The main conclusions that can be drawn are (1) the location of binding sites A must be taken from the structure of the fibrinogen molecule proposed by Hoeprich and Doolittle [Biochemistry (1983) 22, 2049-2055], (2) The fibrinogen monomer is basically centrosymmetric, (3) the state of polymerization is reversible and corresponds to a chemical equilibrium, and (4) Michaelis-Menten enzyme kinetics can be applied.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250511
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  • 119
    Electronic Resource
    Electronic Resource
    Structure of native proteoglycan aggregates from chick limb-bud chondrocytes (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 931-946 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Laser light-scattering has been used to investigate the size of native proteoglycan aggregates (PGA-aA1) from day-8 chick limb-bud chondrocyte cultures isolated under associative extraction and purification conditions in 0.4M guanidinium chloride (GdnHCl) solution. Dynamic light-scattering measurements yielded a hydrodynamic radius, Rs, of 244 ± 10 nm for PGA-aA1 in 0.4M GdnHCl, and a weight-average molecular weight (Mw) of 150 ± 50 × 106 was obtained from a Zimm plot. Disaggregation in 4.0M GdnHCl aqueous solution yielded proteoglycan subunits (PGS) with Rs = 39 ± 2 nm, Mw = 1.6 ± 0.3 × 106, which reassembled in 0.4M GdnHCl to form “reconstituted native” aggregates (PGA-raA1) with Rs = 121 ± 6 nm, Mw = 17 ± 3 × 106. A second specimen of PGA-aA1 had Rs = 192 ± 10 nm, Mw = 100 ± 10 × 106. The latter value was estimated from an empirical relationship between Mw and Rs. After dissociation, this specimen reassembled to form PGA-raA1 with Rs = 85 ± 5 nm, Mw = 12 ± 1 × 106. These data are compared with those for a specimen of reconstituted aggregate (PGA-A1) that had been extracted under dissociative conditions and then reaggregated by dialysis to 0.4M GdnHCl aqueous solution, for which Rs = 138 ± 9 nm, Mw = 45 ± 8 × 106. From these values, we have calculated the weight-average number of subunits per aggregate Nw: 111 for PGA-aA1 and 12 for raA1 (70 and 7 for the second PGA-aA1 and PGA-raA1 specimen, respectively) as compared to 32 for PGA-A1. The numbers of subunits per aggregate were also determined from electron micrographs of spread specimens. The latter results show the same trends as those obtained by light scattering, but lead in each case to lower numbers of subunits per aggregate. These data demonstrate conclusively that PGA samples exhibit a higher degree of aggregation in solution than visualized in typical electron microscopy (EM) preparations, probably due to disaggregation during EM specimen preparation. Since Nw determined both by light scattering (LS) and by EM are larger for native versus reconstituted aggregate samples, our data point to a more compact aggregation of subunits along the hyaluronic acid (HA) chains in the former.
    Additional Material: 7 Ill.
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    Kinetics of nonspecific binding reactions of proteins with DNA flexible coils: Site-based and molecule-based association reactions (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 985-1008 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Domain effects on the pseudo-first-order kinetics of the reversible and irreversible association of proteins or other ligands with nucleic acids containing multiple binding sites are treated using the classical reaction-diffusion equation applied to a spherical cell model of the nucleic acid solution and a diffuse-sphere model for the nucleic acid chain molecule. Both uniform and Gaussian distributions of chain segments are analyzed. In general, the details of the segment distribution do not have a major effect on the kinetics of association. Domain effects are best examined experimentally by determining the effect of the molecular weight of the nucleic acid on the kinetics of the association reaction. A theoretical framework is presented that permits such data to be analyzed simply. Kinetic studies over a wide range of nucleic acid molecular weights are required in order to separate the contributions of diffusion and reaction to the observed kinetics, and to determine the contributions of site-based and molecule-based elements to the rate constants.
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    URL: http://dx.doi.org/10.1002/bip.360250603
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    2′5′-linked polynucleotides do form a double-stranded helical structure: A result from the energy minimization study of A2′p5′A (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 729-752 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental results on 2′5′-linked subunit systems of nucleic acids are interpreted to substantiate the view that the 2′5′-linked polynucleotides cannot form double-stranded helical structures. In order to look into this aspect of the 2′5′-linked units, as well as to make a detailed comparison between the conformational characteristics of 3′5′- and 2′5′-linked systems, we carried out an exhaustive theoretical study on A2′p5′A. The method was to compute the various terms of energy contributions to a conformational state and then to minimize the total energy, permitting all the relevant dihedral angles to adjust themselves. Four hundred thirty two probable starting conformations were considered for this treatment, but we found only 10 of them to come under low-energy states, i.e., within 5 kcal/mol energy difference with reference to the global minimum energy state. The characteristic properties of these 10 conformations were compared in detail with those previously obtained on the corresponding 3′5′-linked subunit, as well as such units with other base sequences. As a further step, a model-building study was undertaken. Using the backbone-course, base-stacking, and hydrogen-bonding possibilities of the 10 low-energy conformations of the dimer A2′p5′A, double-stranded helical structures were scrutinized for the 2′5′-linked polynucleotide. Of a few reasonable forms, a right-handed duplex structure satisfied our requirements. We describe this new duplex, making comparisons with the standard A- and B-form states of DNA. The available experimental and theoretical results on 2′5′-linked systems are also analyzed.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360250414
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    Conformation of dioxopiperazines. III. Conformational-energy calculations and evaluation of specific forces contributing to the intramolecular dioxopiperazine-phenyl ring-ring folding in cyclo(glycyl-phenylalanyl) (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 771-786 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational energy calculations on cyclo(glycyl-L-phenylalanyl), c(Gly-Phe), were carried out by means of the semiempirical MO CNDO/2 method. They corroborated earlier experimental findings that in c(Gly-Phe) the conformations with an aromatic side-chain ring folded over the dioxopiperazine (DOP) ring contribute significantly to the overall equilibrium, provided that the empirical optimization of the DOP ring geometry, extracted from x-ray data, rather than that of the CNDO/2-derived data is used throughout the computations. Following these studies, more detailed calculations, based partly on CNDO/2-derived data and partly on experimental data, were carried out to clarify the question, which are the forces responsible for this ring-ring stacking? In contrast to early suggestions, it was found that the quadrupole-quadrupole and dispersion interactions mainly contribute to folded conformations of c(Gly-Phe). Some implications of this finding on devising force fields for molecular-mechanics calculations of peptides are briefly outlined.
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    URL: http://dx.doi.org/10.1002/bip.360250503
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    Structural variation of native cellulose related to its source (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 851-861 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: X-ray diffraction diagrams of 80 specimens, mainly from woody plants, were recorded and resolved into characteristic reflections of cellulose I. Significant differences were observed in d-spacings and integrated intensity ratios between softwoods and hardwoods. Of the lattice parameters, the monoclinic angle was found to be correlated with plant taxonomy and tended towards the right angle in the more advanced taxonomic groups. We have therefore demonstrated that the crystal structure of natural cellulose shows some variations related to the source of the cellulose.
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    URL: http://dx.doi.org/10.1002/bip.360250508
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    Molecular cartography of globular proteins with application to antigenic sites (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 863-883 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method, molecular cartography, is introduced as a way to quantitate the topographic structure of a protein surface. The method is applied to the problem of antigenic determinants, and it is used to examine local and global topography of reported antigenic regions on the surface of myoglobin and lysozyme. In nine antigenic sites taken from the literature and studied in detail, no local property was found in sites that was not also found in remaining regions of the surface. However, a strong correlation was found between antigenic sites and regions of the surface that are globally exposed. This finding suggests that global exposure of the protein surface may play a primary role in determining the antigenic structure of the protein. Molecular cartography may be useful in other instances of protein-protein interactions such as those between proteolytic enzymes and their substrates.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360250509
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    Structural information from electric dichroism measurements of DNA and alternating GC nucleic acids in solution: The question of base tilt (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 885-904 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Values of the apparent intrinsic dichroism of the 260-nm transition of duplex poly(dG-dC) and poly(dG-m5dC) in both B- and Z-conformations are determined from electric dichroism (ED) measurements by extrapolation of the data at high field strengths. These values are compared to each other and to values of the intrinsic dichroism calculated for the Z- and B-forms generated respectively from the crystal structure coordinates [(1981) A. H. J. Wang, G. J. Quigley, F. J. Kolpak, G. Van der Marel, T. H. Van Boom & A. Rich, Science 211, 171-176.] of the d(CpGpCpGpCpGp) hexamer and from the coordinates [(1982) A. V. Fratini, M. L. Kopka, H. R. Drew & R. E. Dickerson, J. Biol. Chem. 257, 14686-14707.]. of the terminal CpGpCpGp base pairs of the crystal of straight B-form dodecamer d(CpGpCpGpApApTpTpCpGpCpGp). Direct association of the dichroism with the orientation of the optical transition moments with respect to the helix axis of poly(dG-dC) implies that the average tilt of the bases is much different than the values calculated from the structural coordinates. The experimental values for both the B- and Z-forms are, however, almost identical to those observed with fragments of “random” sequence B-form DNA of the same molecular length. It is argued that this descrepancy and other anomalies reported in the literature are due to the theoretically predicted unusual high field behavior associated with diffuse ion atmosphere polarization. Unlike either permanent dipoles or induced moments based on bond polarizabilities, the orienting dipole energy from the polarization of the counterions surrounding DNA approaches a finite limiting value, dependent on DNA length, at very high field strengths. This can result in extrapolated dichroisms that do not reflect structure at perfect orientation, but rather structure at some limiting orientation. Consequently, we believe, the conclusion drawn from ED measurements on short fragments of DNA that the bases are highly tilted from the perpendicular to the helix axis by propeller twisting or otherwise is suspect.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360250510
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    Masthead (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250601
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    Total optical activity of agarose: Relation to observable transitions in the vacuum ultraviolet (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 959-973 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The changes in optical activity that accompany and characterize the coil-helix and helix-coil transitions of agarose in aqueous solutions and gels have been investigated by combined quantitative analysis of data from vacuum ultraviolet circular dichroism (VUCD) and optical rotary dispersion (ORD). VUCD of agarose in the high-temperature coil state shows a single accessible Gaussian band centered at ∼183 nm. In the helix state this band is blue-shifted by ∼9 nm, and the intensity is increased by a factor of ∼2.6. Spectra at intermediate temperatures can be fitted to within experimental error by linear combination of coil and helix spectra, the relative proportions required providing an index of the extent of conformational ordering. ORD spectra throughout the conformational transition have a common form and differ only in absolute magnitude. The temperature course of conformational ordering derived from ORD intensity is in close agreement with the values obtained from VUCD. In both the coil and helix states the accessible VUCD band is positive, while the overall ORD is negative, indicating strong negative CD activity at lower wavelength. The ORD contribution corresponding to the positive VUCD band was calculated by Kronig-Kramers transform, and it was subtracted from the total ORD to give the residual ORD from all other optically active transitions of the molecule. In both the coil and helix states, this residual ORD could be fitted to within experimental error by a single Gaussian CD band at ∼149 nm. A negative band at this wavelength has been reported previously for agarose films, but the observed intensity, relative to that of the lower energy positive band, is substantially smaller than the fitted value under hydrated conditions. In both the coil and helix states the total optical activity of agarose, characterized by observed ORD spectra, can be matched to within experimental error by Kronig-Kramers transform of the 149-nm negative band and the smaller positive band at higher wavelength, with no necessary involvement of deeper-lying transitions. The significance of this conclusion for fundamental understanding of carbohydrate optical activity is discussed.
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    URL: http://dx.doi.org/10.1002/bip.360250514
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    Thermodynamic parameters for the helix-coil thermal transition of ribonuclease-S-peptide and derivatives from 1H-nmr data (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1031-1053 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Values for the thermodynamic quantities, ΔH° = 11.8 ± 2.0 Kcal/mole and ΔS° = 43.6 ± 6.0 e.u., of the 3-13 helix-coil equilibrium of isolated S-peptide (19 residue N-terminal fragment of ribonuclease A) in aqueous solution (3 m M, 1M NaCl, pD 5.4) have been determined from a joint analysis of the Thr 3γ, Ala 6β, Phe 8meta, and Phe 8para 1H chemical shift vs temperature curves (-7 to 80°C) in several aqueous-trifluorethanol mixtures. Chemical shifts in the coil and in the helix have been determined for up to 16 protons belonging to the 3-13 fragment. Thermodynamic parameters have also been determined for C-peptide (13 residue fragment) and a number of S-peptide derivatives. From the variation of the values of the thermodynamic parameters at pD 2.5, 5.4, and 8.0, a quantitation of the two helix-stabilizing side-chain interactions can be made: (1) Δ(ΔH°) ≃ 5 Kcal/mole and Δ(ΔS°) ≃ 18 e.u. for the salt bridge Glu 2- … Arg 10+ and (2) Δ(ΔH°) ≃ 3 Kcal/mole and Δ(ΔS°) = 9 e.u. for the one in which the His 12+ imidazolium group is involved, presumably a partial stacking with the Phe 8 side chain.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360250605
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    Influence of different tripeptides on the stability of the collagen triple helix. II. An experimental approach with appropriate variations of a trimer model oligotripeptide (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1081-1086 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A collagen model peptide comprising three covalently cross-linked chains (Ala-Gly-Pro)8 with a stable triple-helix conformation was utilized as the constant part of elongated model peptides of different composition. The tripeptides Gly-Pro-Hyp, Gly-Pro-Ala, Gly-Pro-Pro, Gly-Pro-Ser, Gly-Ala-Hyp, Gly-Phe-Hyp, Gly-Glu-Hyp, Gly-Ala-Lys, and Gly-Pro-Phe were coupled at the N-terminal to the cross-linked peptide. The transition temperatures determined by CD measurements are higher for the peptides containing the Gly-X-Hyp sequences followed by those with the Gly-Pro-Y sequences. In experiments with combinations of two different tripeptides coupled to the constant part of the cross-linked model peptides higher transition temperatures were observed if the sequence of helix-promoting tripeptides was not interrupted.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360250608
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    Masthead (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250701
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    Collagen fibrillogenesis in vitro: An investigation of the thermal memory effect and of the early events occurring during fibril assembly using dynamic light scattering (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1185-1207 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dynamic light scattering has been used to characterize a variety of lathyritic rat skin collagen solutions. The technique was used to monitor the onset of fibril assembly in vitro and to investigate the thermal memory effect. Although the incorporation of thermal memory was demonstrated by reheating the sample and subsequently observing a shortened turbidimetric lag phase, no significant differences between naive solutions and ones exhibiting thermal memory could be detected using photon correlation spectroscopy. This suggests that subtle changes in the state of the collagen molecules rather than extensive changes in the degree of aggregation are responsible for the thermal memory effect. During fibrillogenesis, no large-scale changes in the distribution of monomers or aggregates occur until near the end of the lag phase.
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    URL: http://dx.doi.org/10.1002/bip.360250703
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    Chiral discrimination in the energetics of formation of diastereomeric adducts involving polypeptides (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1249-1258 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral discrimination in the energetics of formation of diastereomeric pairs between iron (III)-complex ions bound to poly(L-glutamate) or poly (D-glutamate) and L-catecholamines was measured by differential microcalorimetry at 25°C. When the association of substrates by Fe-polypeptide systems was virtually complete, diastereomeric discrimination energies of a few hundred calories per mol were observed, while diastereomeric discrimination entropies were found to be negligibly small. These results are consistent with the finding that the overall stereoselectivity in the electron transfer reaction between the optically active catecholamines and enantiomeric iron(III) materials - corresponding to Δ(ΔG≠) values around 900 cal/mol - is largely controlled by transition state effects in the kinetics.
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    URL: http://dx.doi.org/10.1002/bip.360250706
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    Gel formation by fibrin oligomers without addition of monomers (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1337-1344 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Soluble fibrin oligomers were formed by reacting fibrinogen with thrombin under fine clotting conditions where the action of thrombin is the rate-determining step for polymerization, and by inhibiting the reaction shortly before gelation. Oligomeric fibrin was separated from unreacted fibrinogen and small oligomers by gel permeation chromatography. Electron microscopy revealed that the largest soluble fibrin oligomers resemble the protofibrils present in fine clots, but are somewhat shorter and entirely lack the twisted, trifunctional junctions that contribute to the elastic properties of fine clots. When thrombin was added to the soluble fibrin oligomers, polymerization resumed and clots were formed at a more rapid rate than from fibrinogen at the same concentration and resulted in a less-opaque clot under coarse clotting conditions. The results confirm a prediction of a theory for the polymerization of fibrin and provide additional evidence that the final state of a coarse fibrin clot depends on the mobility of protofibrils during its formation.
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    URL: http://dx.doi.org/10.1002/bip.360250712
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    Sequence-dependence of the CD of synthetic double-stranded RNAs containing inosinate instead of guanylate subunits (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1735-1750 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The CD spectra and melting profiles have been measured for nine synthetic double-stranded RNAs containing I · C instead of G · C base pairs: poly[r(I) · r(C)], poly[r(I-C) · r(I-C)], poly[r(A-I-C) · r(I-C-U)], poly[r(A-C) · r(I-U)], poly[r(A-I) · r(C-U)], poly[r(A-C-C) · r(I-I-U)], poly[r(A-A-C) · r(I-U-U)], poly[r(A-C-U) · r(A-I-U)], and poly[r(A-U-C) · r(I-A-U)]. CD spectra have not previously been reported for the latter six of these polymers. The substitution of inosinate for guanylate led to recognizable CD differences, with all but two of the polymers having two resolved positive bands above 230 nm. Also, the I-containing RNAs differed from their G-containing counterparts in the almost complete absence of negative CD bands at long wavelengths and in the reduction of negative CD bands near 210 nm. First-neighbor comparisons showed that the CD spectra of the I-containing RNAs were consistent with the nearest-neighbor sequences of the polymers, as previously shown for G-containing RNAs (D. M. Gray, J.-J. Liu, R. L. Ratliff, and F. S. Allen, Biopolymers (1981) 20, 1337-1382). Moreover, two of the first-neighbor comparisons involved spectra of poly[r(A) · r(U)] and poly[r(I) · r(C)], polymers known to be in the A family of conformations in fibers (S. Arnott, D. W. L. Hukins, S. D. Dover, W. Fuller, and A. Hodgson, (1973) J. Mol. Biol. 81, 107-122). Thus, differences in the CD spectra of I- and G-containing RNAs could be simply explained as resulting from differences in the hypoxanthine and guanine chromophores, without invoking differences in conformation. Finally, melting temperatures of the I-containing RNAs were found to vary much less with base composition than do the melting temperatures of G-containing RNAs, since A · U base pairs are closer to I · C than to G · C base pairs in stability.
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    URL: http://dx.doi.org/10.1002/bip.360250914
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    A positron annihilation study of hydrated DNA (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1865-1874 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Positron annihilation measurements are reported for hydrated DNA as a function of water content and as a function of temperature (20 to -180°C) for samples containing 10 and 50% wt of water. The ortho-positronium mean lifetime and its intensity show distinct variations with the degree of hydration and with temperature for the 50% sample. The 10% water sample was relatively insensitive to temperature variation. The results indicate that hydrated DNA containing up to 10% water behaves as a rigid crystalline solid but that the rigidity markedly decreases with a further increase in water content until, for approximately 50% water, its properties resemble more those of a highly viscous fluid.
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    URL: http://dx.doi.org/10.1002/bip.360251005
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    Comparison of the effects of cationic porphyrins on DNA properties: Influence of GC content of native and synthetic polymers (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1837-1858 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Interactions of meso-tetra(4-N-methylpyridyl)porphyrin [TMpyP(4)], meso-tetra(2-N-methylpyridyl)porphyrin [TMpyP(2)], and meso-tetra(para-N-trimethylanilinium)porphyrin (TMAP) with several native and synthetic DNAs were studied by a variety of physical techniques: nmr (31P and 1H), absorption spectroscopy, viscosity, and flow dichroism (FD). Of the three porphyrins studied, only the interaction of TMpyP(4) with poly [d(G-C)2] was fully consistent with intercalation. In particular, a large increase in viscosity, a downfield 31P-nmr signal (ca. -1 ppm), and upfield imino proton signals (11 to 12 ppm range) were observed. Comparison of the effects of TMpyP(4) on DNAs of different GC contents revealed larger changes in solution viscosity with increased GC content. However, the characteristic changes in 31P- and 1H-nmr spectra were not observed. The viscosity increases observed in studies with poly[d(A-C)(G-T)] and C. Perf. DNA were much lower than with poly[d(G-C)2], M. Lys. DNA, and calf thymus DNA. Thus, GC sequence and content are clearly important. The principal change in the 31P-nmr signal of native DNA is the appearance of a very broad shoulder centered at ca. -2.0 ppm, which is larger in M. Lys. DNA than in C. Perf. DNA. FD studies indicate highly ordered TMpyP(4) cations arranged perpendicular to the DNA axis of calf thymus DNA. Together, these results suggest the major effects of TMpyP(4) on DNA properties are due to strong GC-binding interactions that influence DNA structure. The data are consistent with combined intercalative and outside binding interactions of TMpyP(4) with GC regions of DNA. In contrast, similar studies with TMAP suggest that it influences AT regions of DNA by an outside binding mode. On the other hand, TMpyP(2) effects on DNA properties are consistent with nonselective outside binding.
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    URL: http://dx.doi.org/10.1002/bip.360251003
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  • 137
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    Conformational properties of somatostatin. VI. In a methanol solution (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1895-1908 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The peptide hormone, somatostatin, has been studied by nmr at 500 MHz in a methanol solution and at low temperature (263 K) in order to investigate a possible similarity with conformationally restricted biologically active analogs. The more pronounced predominancy of one conformer already present in a water solution is demonstrated. No evidence has been shown for interactions between Phe11 and other Phes in the molecule.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251007
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  • 138
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    Thermodynamics of water-biopolymer interactions: Irreversible sorption by a single, uniform sorbent phase (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1967-1979 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sorption isotherms of water vapor by solid biopolymers are necessary for the determination of thermodynamic quantities for water-biopolymer interactions. Such isotherms are generally irreversible, so equilibrium thermodynamics may not be applicable. General relationships are derived for thermodynamic quantities of sorption when the sorbent is a single uniform phase. In general, use of the Clausius-Clapeyron equation allows correct determination of differential entropies of sorption. However, calorimetric data are also necessary for the correct determination of other thermodynamic quantities. The single uniform phase model appears more useful than a domain model in explaining the hysteresis seen in water-biopolymer sorption isotherms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360251011
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  • 139
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    Specificity in DNA interactions: An nmr investigation of the interaction of propidium with oligodeoxyribonucleotides containing normal and G · T base pairs (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1997-2015 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of propidium with three self-complementary oligodeoxyribonucleotides has been investigated by 1H- (base-pair imino proton assigned by 1D NOE and saturation transfer methods) and 31P-nmr as a function of ratio of propidium to oligomer (from zero to saturation) and temperature. The three oligomers are dTATATGCGCATATA (1), dTATATGTGCATATA (2), which has the same sequence as 1 except for the mismatched base pair at position 7, and dTATGTGCATA (3), which is a shortened version of 2. The imino proton chemical-shift changes of 1 on titration with propidium can be explained by the effects of the ring-current anisotropy of propidium at intercalation (3.4 Å) and next-neighbor sites (6.8 Å). The results indicate that propidium binds with neighbor exclusion but with no significant specificity for any intercalation site in the sequence of 1. The addition of propidium to 1 results in general downfield shifts of all 31P signals, as expected for a nonspecific intercalator. Imino and 31P-nmr spectra for 2 indicate that this oligomer forms a hydrogen-bonded G · T base pair at position 7 with little change in base pairing and stacking of base pairs 1-6 compared to 1. The results for addition of propidium to 2 and 3 are quite different than with 1. At low ratio only secondary shifts (6.8 Å) are seen for the G and T imino protons of base-pair 7 on addition of propidium. At higher ratios of propidium, the signals for these G and T protons are lost in 2 and severely broadened in 3, even at low temperature. The other potential intercalation sites in 2 and 3 appear to bind propidium strongly and without significant specificity as with 1. 31P spectra of 2 in the presence of propidium show the expected downfield shifts and broadening. Thus, the minor differences in local helix geometry in 1, and in 2 and 3, away from the G · T base pair do not significantly affect propidium intercalation specificity. Having one or two G · T base pairs at a site, however, makes intercalation in the standard manner significantly less favorable.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251013
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  • 140
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    An analysis of circular intensity differential scattering measurements: Studies on the sperm cell of eledone cirrhosa (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2043-2064 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This study represents the first systematic attempt to characterize the possible sources of artifacts that can interfere with the measurement of circular intensity differential scattering (CIDS) as a function of the scattering angle. A theoretical analysis of the effect of imperfect incident circular polarizations in the measurement of baselines from nonchiral scatterers and in the signals from chiral samples is derived. From this analysis the requirements of the tolerance on the quality of the incident circular polarizations to unequivocally measure the CIDS effect are established. The protocol for alignment of the CIDS instrument and the characterization of the incident polarizations utilized in these studies are described in detail. CIDS measurements on suspensions of helical sperm cells are presented. The experimental results are modeled computationally with the use of the current CIDS theory. Good agreement between the data and the computations is obtained. The results clearly indicate the ability of CIDS to provide information on the long-range chiral organization of samples in solution.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251103
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  • 141
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    The dielectric constant of a folded protein (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2097-2119 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The goal of this paper is to obtain a theoretical estimate of the dielectric constant of a folded protein. To this end, we develop a form of the Kirkwood-Fröhlich dielectric theory that applies to polar solids and folded proteins. The resulting theory incorporates a factor expressing the degree to which dipolar groups are constrained within the material's structure, as well as a generalized form of Kirkwood's correlation factor. The theory is applied to a hypothetical isotropic protein composed of randomly oriented α-helices and having a number density of dipolar groups equal to that found in actual proteins. The factor of constraint and the generalized dipole correlation factor are calculated using normal mode analysis. Temperature factors are also computed by normal mode analysis and are in reasonable agreement with those found experimentally. The computed dielectric constant is low; the best estimate is that it falls between 2.5 and 4.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251106
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  • 142
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    Molecular orbital calculations on the oligopeptides netropsin, distamycin and related compounds (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2065-2082 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the antibiotics netropsin, distamycin A, and related compounds has been examined by various theoretical models. Calculations of both the Pariser-Parr-Pople (PPP) and the semiempirical CNDO/S types can account for the absorption spectrum of netropsin and distamycin A. The CD spectrum has been calculated for the conformation of netropsin found in the crystal structure of a netropsin/DNA dodecamer. Not all the CD spectral features can be attributed entirely to the chiral conformation of netropsin, indicating that there are significant interactions between netropsin and DNA. A CD calculation was also performed for distamycin A in a similar conformation. An examination of the charge-density maps of the excited states suggests that there is substantial charge transfer from the pyrrole ring to either of the adjacent peptide linkages in these systems. At higher energies, even longer distance charge transfer can be observed. Similar behavior was seen in the monomers pyrrole-2-carboxamide and 3-(formylamino)pyrrole.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360251104
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  • 143
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    Masthead (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360251201
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  • 144
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    A novel peptide conformation: First unequivocal observation of the oxy-analog of a β-bendThis paper is part 157 of the Linear Oligopeptides series; for part 156 see Ref. 1. (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2237-2253 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The x-ray diffraction analysis of the N-benzyloxycarbonyl homo-tripeptide from α-amino-isobutyric acid has shown the occurrence of an incipient 310-helix characterized by one type-III (or type-III′) β-bend followed by one oxy-analog of the same type of β-bend. This represents the first unequivocal observation of the latter conformation, where the O - H group of the COOH moiety present at the C-terminus of the peptide main chain plays the role of the hydrogen-bonding donor. These results have been compared with those of the same peptide in its monohydrate form and of its methyl ester derivative, the x-ray diffraction structures of which are also described here.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251203
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    Synthesis of fragments by classical solution methods for use in cytochrome c semisynthesisThe amino acid residues, except glycine, are of the L-configuration. For a simpler description, the customary L-designation for individual amino acid residues is omitted. Standard abbreviations for amino acid derivatives and peptides are used according to the suggestion of the IUPAC-IUB Commission on Biochemical Nonemclature (1972) Biochemistry 11, 1726-1732. (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2271-2279 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report details of the chemical synthesis of two fragments reproducing the C-terminal sequences 71-108 and 70-108 of Saccharomices cerevisiae cytochrome c. Preparation of the fragments employed classical solution methods and a fragment-condensation strategy; they have been used, together with a third fragment (sequence 67-108) [L. Moroder, B. Filippi, G. Borin & F. Marchiori (1975) Biopolymers 14, 2061-2074], in the semisynthesis of chimeric cytochromes [C. J. A. Wallace, G. Corradin, F. Marchiori & G. Borin (1986) Biopolymers 25, 2121-2132].
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251205
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  • 146
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    Evidence for a folded structure of met-enkephalin in membrane mimetic systems: 1H-nmr studies in sodiumdodecylsulfate, lyso-phosphatidylcholine, and mixed lyso-phosphatidylcholine/sulfatide micelles (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2315-2323 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H-nmr spectra of Met-enkephalin dissolved in aqueous solution of sodiumdodecylsulfate (SDS) micelles are reported as a function of pH and temperature. The temperature behavior of the amide protons is compared with that observed for the same peptide dissolved in aqueous solution of lyso-phosphatidylcholine (LPC) and lyso-phosphatidylcholine-sulfatide (LPC-SH) micelles. The temperature coefficients are affected by the micelle polarity, which suggests that the peptide backbone is not remote from the micelle surface. pH titration performed in the presence of SDS micelles gives a number of intrinsic and extrinsic pKa values, indicative of a folded structure of the opioid molecule. This conformation is characterized by the existence of an intramolecular hydrogen bond involving the Met-5 amide proton and an interaction of the N-terminal residue with the aliphatic side chains of both Phe-4 and Met-5.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251209
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  • 147
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    Helix → β conformational transition of poly(L-lysine) on dye binding (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2349-2358 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of an azo dye, 4′-dimethyl amino azo benzene-4-carboxylic acid (DAAC) to poly(L-lysine) (PLL) in basic aqueous solutions at 20°C has been studied. The azo dye was found to bind to PLL when its side-chain amino groups are in the uncharged state. This was found to be a cooperative phenomenon, and the binding constant and cooperativity factor have been evaluated. The binding of the dye was found to result in a conformational transition of PLL from the α-helix to the β-sheet, which in turn helps in increased dye binding.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251212
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  • 148
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    Concentration of protein in fibrin fibers and fibrinogen polymers determined by refractive index matching (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2375-2384 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have used refractive index matching to determine the concentration of protein in the fibers in fibrin clots and of needlelike crystals of native fibrinogen. Our results are in agreement with those of Carr and Hermans [(1978) Macromolecules 11, 46-50], as determined by light scattering - namely, that protein makes up about 20% of the volume of the fiber. However, we have found that the protein concentration is strongly dependent on ionic strength. An increase in ionic strength caused a substantial drop in the protein concentration. In a buffer containing 100 mM NaCl, the protein concentration was 26.6-29.8 g of protein per 100 cm3 of polymer, and at 200 mM NaCl it was reduced to 22.1-23.1 g/100 cm3.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360251214
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  • 149
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    Chemical synthesis of polysaccharides. 7. Enzymatic hydrolysis of (1 → 6)-α-DL-glucopyranan (DL-dextran) (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1955-1965 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrolysis of (1 → 6)-α-DL-glucopyranan (synthetic DL-dextran) by an endo-dextranase from a Penicillium species was examined in an acetate buffer solution (pH 5.3) at 37°C. Three samples of different tacticities (isotactic dyad content, 55, 63, and 72%) were employed with a clinical dextran for comparison. Colorimetric determination of the reducing end units of the saccharides produced during hydrolysis showed that the maximum degrees of hydrolysis based on the D-glucose units, (D.H.)D, for the DL-dextrans were 21.4, 27.8, and 33.0% in the order of increasing isotacitic dyad content, whereas the (D.H.)D value for the clinical dextran was 51.9%. A statistical treatment of the enzymatic hydrolysis is proposed to interpret the experimental results.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251010
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  • 150
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    D-Isomeric replacements within the 6-9 core sequence of ac-[Nle4]-α-MSH4-11-NH2: A topological model for the solution conformation of α-melanotropin (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2029-2042 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analogs of Ac-[Nle4]-α-MSH4-11-NH2 and Ac-[Nle4, D-Phe7]-α-MSH4-11-NH2 were prepared with D-isomeric replacements at the His6, Arg8, and Trp9 residues. The requirement for an indole moiety at position 9 also was evaluated by replacement with L-leucine in both parent fragment analogs. D-isomeric replacements at positions 6 and 8 in either series were detrimental to biological potency in frog (Rana pipiens) and lizard skin (Anolis carolinensis) in vitro melanotropic assays. However, Ac-[Nle4, D-Trp9]-α-MSH4-11-NH2 and Ac-[Nle4, D-Phe7, D-Trp9]-α-MSH4-11-NH2 were equipotent and 10 × more potent than Ac-[Nle4]-α-MSH4-11-NH2, respectively, in the lizard skin bioassay, and 30 and 1900 times more potent in the frog skin bioassay. Ac-[Nle4, D-Phe7, D-Trp9]-α-MSH4-11-NH2 was 3 × more potent than α-MSH in the frog skin bioassay. Proton nmr studies in aqueous solution revealed a marked preservation of the backbone conformation of these linear analogs. Chemical-shift variations due to the through-space anisotropic influence of the core aromatic amino acid residues permitted evaluation of side-chain topology. The observed topology was consistent with nonhydrogen-bonded β-like structure (φ = -139°, ψ = +135° for L-amino acids; φ = +139°, ψ = -135° for D-amino acids) as the predominant solution conformation. The biological and conformational data suggest that high melanotropic potency requires a close spatial arrangement of the His6, Phe7, and Arg8 side chains.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251102
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  • 151
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    Cytochrome c chimerae from natural and synthetic fragments: Significance of the biological properties (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2121-2132 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analogs of natural proteins have application in basic research, in medicine, and increasingly, in industry. Of the many methods developed for the fabrication of modified proteins, semisynthesis has so far been the most productive [R. E. Offord (1983) Proc. Eur. Peptide Symp., 17 31-42]. The technique of fragment-condensation semisynthesis takes as its basic raw material the native protein; fragments derived from it are manipulated by sequential degradation and resynthesis before recombination. While gene manipulation may overtake protein manipulation in general usefulness, certain types of analogs will remain accessible only by semisynthesis. Fragment condensation semisynthesis, as described above, has been used in preparing cytochrome c analogs [C. J. A. Wallace (1979) Proc. Am. Peptide Symp. 6, 609-612]. To overcome the difficulty of replacing amino acids far from convenient cleavage sites, a number of variants of the method have also been used. These include fragment-specific chemical modification [C. J. A. Wallace & K. Rose (1983) Biochem. J. 215, 651-658] and solid-phase synthesis of small [P. J. Boon, G. I. Tesser, H. H. K. Brinkhof & R. J. F. Nivard (1981) Proc. Eur. Peptide Symp. 16, 127-130] or large fragments [L. E. Barstow, R. S. Young, E. Yakali, J. J. Sharp, J. C. O'Brien, P. W. Berman & H. A. Harbury (1977) Proc. Natl. Acad. Sci. USA 74, 4148-4250]. The latter study gave low final recoveries, so we have prepared large peptides (38-42 residues) by classical solution methods. We have examined both their use in the reformation of the complete protein, and the physical and biochemical properties of the product analogs compared with those of the native proteins.
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    URL: http://dx.doi.org/10.1002/bip.360251107
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  • 152
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    The effect of monovalent cations on the association behavior of guanosine 5′-monophosphate, cytidine 5′-monophosphate, and their equimolar mixture in aqueous solution (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2149-2172 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H- and 31P-nmr spectroscopy have been used to investigate the self-association of M2(5′-CMP) [M = Li+, Na+, K+, Rb+, or (CH3)4 N+; 5′-CMP = cytidine 5′-monophosphate], the self-association of Li2(5′-GMP) (5′-GMP = guanosine 5′-monophosphate), and the heteroassociation of 5′-GMP and 5′-CMP (1 : 1 mole ratio) in aqueous solution as a function of the nature of the monovalent cation. Proton spectral differences for the different 5′-CMP salts exhibit a cation-size dependence and have been ascribed to a change in the stacking geometry. An average stacking association constant of 0.63 ± 0.24M-1 at 1°C, consistent with the weak stacking interactions of the cytosine bases, was determined for the 5′-CMP salts. Heteroassociation of 5′-GMP and 5′-CMP follows the reverse of the cation order for the formation of ordered aggregates of 5′-GMP. Heteroassociation occurs in the presence of Li+, Na+, and Rb+ ions, but only self-association occurs for the K+ nucleotides. Li2(5′-GMP), which does not form ordered species, self-associates to form disordered base stacks with a stacking constant of 1.63 ± 0.11M-1 at 1°C.
    Additional Material: 15 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360251109
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  • 153
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    Structural investigation of poly-L,D-proline, a synthetic ion channel across bilayer membranes: Crystal structure and molecular conformation of two tetra-D,L-proline derivatives (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2227-2236 
    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 and molecular conformations of two tetraproline derivatives with alternating configurations Boc(D-Pro,L-Pro)2OH and Boc(D-Pro,L-Pro)2OCH3 are investigated in connection with the ability of the homologous polymer to selectively increase (as an ion channel) the ion permeability across bilayer membranes. Both tetramers are characterized by the cis-trans alternating conformation of the peptide bonds, which formally transforms in a turn of the poly-D,L-proline channel after a cis-trans change of the central peptide residue.
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    URL: http://dx.doi.org/10.1002/bip.360251202
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  • 154
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    Sol-sol structural transition of aqueous agarose systems (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2255-2269 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A structural transition is reported to occur in aqueous sols of agarose, an electrically uncharged biostructural polysaccharide. The transition has no measurable effect on size dispersity on the shape of the solute polysaccharide as observed by precision photon correlation spectroscopy. It originates a low-angle pattern of scattered light similar to that which monitors phase separations in polymer blends. Thus, it must be due to some extent to spatially modulated polymer clustering, typical of spinodal decomposition. In the interval of temperatures studied, it precedes very distinctly in time the thermoreversible sol-gel transition, which is known to be promoted at higher concentrations. It also anticipates to an appreciable extent the spatial density modulation observed in the gel. Although reported here for the first time, a spinodal decomposition of the sol that precedes and possibly triggers the processes leading to gelation does not come unexpectedly in terms of site-bond correlated-percolation theory. In general, this occurrence raises the question as to whether the spontaneous onset of regions of higher and lower polymer concentration (spinodal separation) may be regarded as a novel path for biomolecular interactions and the self-assembly of order in biomolecular systems.
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    URL: http://dx.doi.org/10.1002/bip.360251204
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  • 155
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    Energy transfer in polynucleotide homopolymers and copolymers (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 2309-2313 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the fluorophore Tb3+ as a reporter, the effect of thallium (Tl+1) on the transfer of energy in polyribonucleotides and polydeoxynucleotides at room temperature has been studied. In p(G), p(G, I), and pd(G)6 thallium greatly increases the transfer of uv energy absorbed by the bases to Tb3+. In DNA, p(G, U), p(G, A), p(A, U), p(X), p(A), p(U), p(I), pd(G, A)6, and pd(G, T)5 thallium has little or no effect. Thallium increases intersystem crossing to the triplet states only in p(G), p(G, I), and pd(G)6, and the triplets overlap the excited singlet state in Tb3+. In those G- and X-containing polymers showing little thallium effect, the evidence suggests that intersystem crossing is comparatively high to begin with. These polymers, including DNA, appear to transfer absorbed energy to triplet states efficiently at room temperature.
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    URL: http://dx.doi.org/10.1002/bip.360251208
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  • 156
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    Chemistry-Experiment and Theory. Von B. G. Segal. John Wiley & Sons, New York - Chichester - Brisbane - Toronto - Singapore 1985. 1000 S., ca. 42.50 $. ISBN 0-471-80811-3 (1986)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 20 (1986), S. 67-67 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19860200207
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  • 157
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    Preparation of Optically Active Secondary Amines by Thermal Decomposition of (Methylbenzyl)urea Analogs: Absolute Configuration of (+)- and (-)-Mecamylamine. Preliminary CommunicationThe full paper will be published elsewhere.Patent application has been filed. (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 283-287 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermolysis of the (α-methylbenzyl)urea diastereoisomers 4 and 5 of (±)-mecamylamine ((±)-1) and 6 and 7 of (±)-1-noreseroline O-methyl ether ((±)-3) in refluxing alcohol afforded optically pure amines in high yield, besides optically pure carbamates of (α-methylbenzyl)amine which can be recycled. The absolute configuration of (-)-mecamylamine hydrochloride ((-)-1 · HCl) was determined by X-ray diffraction analysis.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690205
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  • 158
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    2,5-Chinonmethide des 1,6-Methano[10]annulens mit S,N- und N,N-Acylketenacetal StrukturMeinem hochverehrten Lehrer, Prof. Dr. Siegfried Hünig, Würzburg, zum 65. Geburtstag gewidmet (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 315-328 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,5-Quinonemethides of 1,6-Methano[10]annulene with the Structures of S,N- and N,N-Acylketene AcetalsInvestigation on the chemical reactivities of 2-(tert -butoxy)-1,6-methano[10]annulene and the syntheses of the compounds 2, 4, 6-8, 11, 13-22 are described; the results of 1H- and 13C-NMR-spectroscopic measurements are reported.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690209
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  • 159
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    1,2-Epoxycarotinoide. 6. Mitteilung. Isolierung von 1′,2′-Epoxy-1′,2′-dihydro-ε,ψ-carotin aus der ‘Delta-Mutanten’-Tomate (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 340-344 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Epoxycarotenoids Isolation of 1′,2′-Epoxy-1′,2′-dihydro-ε,ψ-carotene from a ‘Delta Mutant’ TomatoFrom ‘Delta Mutant’ tomatoes, optically active 1′,2′-epoxy-1′,2′-dihydro-ε,ψ-carotene (7) was isolated. According to the CD data, the configuration is 6R and presumably 2′S.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690212
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  • 160
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    (Cholestanyloxycarbonyl)benzyl esters as peptide substituents: Conformational properties of fully protected oligo-L-lysines with C-terminal (cholestanyloxycarbonyl)benzyl and benzyl ester moieties (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 350-358 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This study involves L-lysine oligo peptides, protected at the N-terminus by the Nps and at the ε-amino functions by Boc groups. Two series were prepared from dimer to octamer, one containing the p-[(cholestan-3β-yloxy)carbonyl]benzyl, the other one the benzyl ester group at the C-terminus. Conformational analyses were performed by IR absorption. The occurrence of the intermolecular β-structure in the solid state and in CH2Cl2 solution was demonstrated for the highest oligomers. The relative stabilities of the self-associated species were determined by adding a variety of polar solvents to the CH2Cl2 solutions. The cholestanyl-containing peptides have a lower propensity to self-aggregate than the benzyl-ester analogues. Self-aggregation and decreasing solubility run in parallel. It was also directly shown that soluble urea derivatives may disrupt intermolecular H-bonds in CH2Cl2, a point of practical interest, particularly in solid-phase peptide synthesis.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690214
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  • 161
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    Die toxischen und sedierend wirkenden Bufadienolide von Kalanchoedaigremontiana HAMETet PERR (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 359-367 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Toxic and Sedative Bufadienolides of Kalanchoe daigremontiana HAMET et PERR.From the toxic Crassulacee Kalanchoe daigremontiana five biosynthetically related bufadienolides have been isolated and structurally elucidated by X-ray and 1H- and 13C-NMR spectroscopy. The compounds were identified as bersaldegenin 1,3,5-orthoacetate (2), bersaldegenin 1-acetate (4), bersaldegenin 3-acetate (3), 1β,3β,5,11α,14-pentahydroxy-12,19-dioxo-5β,14β-bufa-20,22-dienolide 1,3,5-orthoacetate ( = daigremontianin; 1), and 3β-acetoxy-1β,5,14-trihydroxy-5β,14β-bufa-20,22-dienolide ( = daigredorigenin-3-acetate, 5). According to the pharmacological investigations, the two orthoacetates 1 and 2 comprise the positive inotropic, sedative, and toxic activity of the plant.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690215
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  • 162
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    Enantioselective Synthesis of D-erythro-Sphingosine and of Ceramide (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 368-373 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enynol 2 was transformed into D-erythro-sphingosine 11 (7 steps, 46%) and into ceramide 1 (8 steps, 41% overall yield). The key steps were the mono-epoxidation of the enynol 5 (Ti(t-BuO)4, (-)-D-diethyl tartrate, t-BuOOH) to 6 (86%, ≥ 98% ee), the regioselective intramolecular opening of the oxirane 6 via the benzylurethane 7, and the reductive tranformation of the acetylene 9 into the oxazolidinone 10 (Li, EtNH2, 88%).
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690216
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  • 163
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    An ESR Study of the Radical Cations of Tetrathiafulvalene (TTF) and Electron Donors Containing the TTF Moiety (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 141-151 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hyperfine data and g factors are reported for the radical cations of tetrathiafulvalene (TTF; 1) and of its derivatives 2-13. From the intense satellite spectra of 1+-13+ not only the coupling constants of the 33S isotopes in the TTF moiety could be determined, but also, in favourable cases, those of the 13C isotopes in the central double bond. The former values range from 0.370 (8+) to 0.470 mT (4+) and the latter from 0.255 (8+) to 0.360 mT (4+) in the radical cations of bis(ethylenedithio)-TTF (8+) and tetracyano-TTF (4+). The radical cation of TTF (1+) exhibits intermediate values, 0.425 for the 33S and 0.285 mT for the 13C isotopes. The spin population in 1+-13+ resides, to a large extent, in the central S2C = CS2 part of the π-system. It tends to increase (decrease) by substitution with electron-accepting (donating) groups in the 2,3,6,7-positions of TTF.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690117
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  • 164
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    Conformation-Odor Relationships in Norlabdane Oxides (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 163-173 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational factors have been found responsible for the dramatic change in odor between (-)-deoxyambreinolide (12) and its (+)-epi derivative 13. The presumably molecular event during the receptor interaction has been simulated by the diastereoisomeric 11-methyl-ambrox derivatives 3 and 5 as model compounds.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690120
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  • 165
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    Crystal Structures of Chiral Ionophores: Bis(9,9′-spirobifluorene)-26-crown-4 and -32-crown-6 (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 626-631 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray crystal structures of bis(9,9′-spirobifluorene)-26-crown-4βbenzene solvate (monoclinic, a = 15.47 Å, b 11.265 Å, c = 15.220 Å, β = 91.54°, space group C2) and bis(9,9′-spirobifluorene)-32-crown-6·dichloromethane solvate (tetragonal, a = 20.958 Å, c = 11.779 Å, space group P41212) are described. Both compounds act as enantioselective ionophores for α-aminoalcohols.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690312
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  • 166
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    Steric Effects on Reaction Rates. Part VIII. The Significance of Front Strain Release in Solvolysis of Bridgehead Derivatives (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 635-645 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The steric requirements of leaving groups for 14 bridgehead derivatives have been examined using MM2 calculations. The strain varies almost monotonously throughout the series upon variation of the leaving group from H to C1, OH, CH3, CH3CH2O, (CH3)3CO, (CH3)3C and no significant trends for differential F-strain effects are detected expect for the perhydrophenalene derivative 13. The experimental rates of solvolysis of bridgehead derivatives correlate well with the calculated steric energy differences between substrate R-X and the corresponding carbenium ion R⊕. However, the strain calculations using the more recent force-fields (MM2) disagree, in part, with those reported in the literature: chloride and p-toluenesulfonate leaving groups correlate with identical slopes, and the perhydrotriquinacene derivative 10 shows no anomalous behavior. The calculations suggest that F-strain and C,C-hyperconjugation should not play any dominant role in bridgehead solvolysis.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690314
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  • 167
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    Die Synthese und der thermische Zerfall des 1,2-Diazabenzo[e]-semibullvalens und dessen Beziehung zur Thermolyse des Benzobenzvalens (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 670-675 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Synthesis and the Thermal Decay of 1,2-Diazabenzo[e]semibullvalene and its Relation to the Thermolysis of BenzobenzvaleneThe [4 + 2]-photoadduct of naphthalene and 4-phenyl-4H-1,2,4-triazol-3,5-dione (PTAD) was subjected to a triplet-sensitized di-π-methane rearrangement. Hydrolysis of the resulting urazol 15 gave a stable semicarbazide 16 which by nickel-peroxide oxidation gave 1,2-diazabenzo[e]semibullvalene (10). At 40 °C, the latter decays in CHCl3 solution to produce benzofulvene (2) as the principal product, accompanied by benzobenzvalene (1) and small amounts of naphthalene. This decay reaction is rationalized in terms of a 1,3-dipolar cycloreversion which is followed by denitrogenation to give indenyl carbene (19). The thermolysis of 1 in solution is believed to proceed via the same carbene. At present, these findings provide only a partial answer to the benzobenzvalene enigma (i.e., in solution at 150°, 1 gives 2, but in the gas-phase at 300°, 1 yields naphthalene). MeOH is shown to add readily to 10 in a homologous Michael addition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690317
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  • 168
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    Formale Totalsynthese von (±)-Isocomen durch Anwendung der α-Alkinon-Cyclisierung (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 659-669 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formal Total Synthesis of (±)-Isocomen by Application of the α-Alkinon CyclizationA total synthesis of the racemic form of the sesquiterpene isocomene (A) was accomplished by application of the cyclopentenone anellation B→D (Scheme 1) which includes the α-alkynone cyclization C→D, a gas-phase flow thermolytic process. Starting with the known product 2 (Scheme 3) of the anellation B→D, the elaboration of ring C of A proceeded in 9 steps to the α-alkynone 16 (Scheme 5) which was cyclized at 540° selectively to give the angularly fused triquinane 4 (77%). A two-step procedure then led to 5 (Scheme 6), a last but one intermediate in a known total synthesis of (±)-A. The conversion of 16 to 4 also demonstrated the compatibility of an acetoxy function with the anellation sequence B→D.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690316
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  • 169
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    Photochemical Rearrangements of 5,6-Epimino-5,6-dihydro-β-ionone and Derivatives (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 692-697 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On irradiation at -20°, 5,6-epimino-5,6-dihydro-β-ionone (E)-3 rearranges to the products 6 and 7. The N-methyl derivative (E)-4 does not lead to any photoproduct upon brief irradiation; on prolonged irradiation, only unspecific photodecomposition is observed. The N-acylated derivative (E)-5 undergoes rapid (E)/(Z)-isomerization and slow rearrangement to 12 and 13.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690320
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  • 170
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    Pteridine. Teil LXXX.Teil LXXIX: [1]. Synthese, Reaktionen und Photochemie von Pteridinthionen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 708-717 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis, Reactions, and Photochemistry of PteridinethionesThe pteridine-6(5H)-thione 1 and various pteridine-7(8H)-thiones (13, 22, 26) have been synthesized, and their photochemical reactivity has been investigated under aerobic conditions. The formation of different photooxidation products is pH-dependent. In acidic to neutral media, disulfides (2, 15, 23, 29) are formed, whereas neutral to alkaline solutions favour the formation of pteridinesulfinic (3, 17) and -sulfonic acids (6, 16, 24, 30). Prolonged irradiation of the disulfides 2 and 15 led to the intensively yellow fluorescing bis(thio)dilumazines 19 and 20, respectively.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690323
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  • 171
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    Cacospongione A, cacospongienone A, and cacospongienone B, new C21 difuran terpenoids from the marine sponge Cacospongiascalaris SCHMIDT of the Côte d' Azur (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 726-733 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sponge Cacospongia scalaris (family Thorectidae), collected at the Cap de Nice (Cǒte d'Azur), is shown to contain a series of truncated, linear C21 difuran terpenoids comprising the known sponge products furospongin-1 ((+)-1), furospongin-2 (2), and dihydrofurospongin-2 ((-)-(E)-3), besides the new products cacospongione A ((-)-4), cacospongienone A ((-)-(Z)-6), and cacospongienone B ((-)-(E)-6), whose absolute configurations have been assigned by chemical correlations with (+)-1. Possibly, one of the two cacospongienones is an artifact, as these two terpenoids interconvert on standing. This is the first finding of linear C21 difuran terpenoids, which are typical of the Spongiidae, in a member of the family Thorectidae.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690325
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  • 172
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    Mitteilungen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 749-750 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690327
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  • 173
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    Deoxy-nitrosugars 12th communication11th Communication: [1]. Synthesis of isosteric mono-phosphonate analogues of β-and α-D-fructose 2,6-bisphosphate (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 751-760 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthesis of the isosteric mono-phosphonate analogues 2a and 19 of the β-and α-D-fructose 2,6-bisphosphate, respectively, is described. Chain elongation of the 1-deoxy-1-nitro-D-arabinose 3 (Scheme 1) by a Henry reaction with paraformaldehyde followed by protection of the resulting alcohol (methoxymethyl ether) and a radical-chain substitution by nitromethane anion gave the key intermediates, the gluco-anhydroalditol 6 and the manno-anhydroalditol 7. These products equilibrated under basic conditions. Conversion of 7 to the aldehyde 9, Abramov reaction of 9 with diphenyl phosphite followed by deoxygenation according to Barton gave the phosphonate 11 (Scheme 2). Selective hydrogenolysis of 11, phosphorylation and deprotection gave 2 which was converted to the tetrasodium salt 2a. Similarly, 6 was transformed into the isosteric phosphonate analogue 19 of the α-D-fructose 2,6-bisphosphate (Scheme 3).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690402
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  • 174
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    Sequence dependence of secondary-structure formation part IVPart III: [1]. Helix-forming potential of amphiphilic oligopeptides containing aib residues (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 786-792 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational properties of Aib-containing oligopeptides having the propensity to adopt amphiphilic helical conformations were investigated by CD spectroscopy in solution. The peptides CF3COOH.H-Pro-Glu-[Ala-Aib-Glu-Aib-]4Gly-OH (I), HCl.H-Pro-Ala-Aib-[Gul-Ala-Ala-Aib-]2Glu-Ala-Aib-Gly-PEGM (II), and CF3COOH.H-Ala-Aib-[Glu-Glu-Ala-Aib-]3PEGM (III) were synthesized according to the general principles of the liquid-phase method for peptide synthesis. Peptides I-III exhibit helical conformations in CF3CH2OH, MeOH, and in H2O at acidic pH; however, at pH 7, only II forms a stable helix, whereas I and III are predominantly in an unordered conformation. Some general features for the construction of amphiphilic helices are discussed in the light of the experimental data.
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    URL: http://dx.doi.org/10.1002/hlca.19860690405
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  • 175
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    Conformational Analysis of Endoperoxides Grafted onto Bicyclo[2.2.n]alkanes as a Test of the Rigidity of the Bicyclic Skeleton. Photo-oxidation of [2.2.2] Hericene and 2,3,5,6-Tetramethylidenebicyclo[2.2.n]alkanesInteraction between non-conjugated chromophores, Part 24. Part 23, see [1a]. For a preliminary report, see communication No. ONII-10, Autumn Meeting of the Swiss Chemical Society, Bern, Oct. 18, 1985. (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 761-772 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photo-oxidation of [2.2.2]hericene (6) gave successively the endoperoxides 11 (9,10,11,12-tetramethylidene-4,5-dioxatricyclo[6.2.2.02,7]dodec-2(7)-ene), the bis-endoperoxide 16 (15,16-dimethylidene-4,5,11,12-tetraoxatetracyclo[6.6.2.02,7.o9,14]hexadeca-2(7),9(14)-diene), and the tris-endoperoxide 19 (4,5,11,12,17,18-hexaoxapentacyclo[6.6.6.02,7.09,14.015,20]icosa-2(7),9(14),15(20)-triene). The endoperoxides 11, 16, and 19 were formed in the presence or in the absence of a dye sensitizer. The sensitized photo-oxidations of 2,3,5,6-tetramethylidenebicyclo[2.2.2]octane (4), 5,6,7,8-tetramethylidenebicyclo[2.2.2]oct-2-ene (5), 2,3,5,6-tetramethylidenebicyclo[2.2.1]-heptane (7), and 2,3,5,6-tetramethylidene-7-oxabicyclo[2.2.1]heptane (8) gave successively the corresponding mono-endoperoxides 9, 10, 12, and 13 and the bis-endoperoxides 14, 15, 17, and 18, respectively. Low-temperature NMR spectra of the bis-endoperoxides 14 and 16 indicated that their C2 and Cs conformers have the same stability. Similarly, there was no difference in the enthalpy of the D3 and C2 conformers of the tris-endoperoxide 19. The following reactivity sequence was observed for the sensitized photo-oxidations of 6-8 and 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene (23): 6 + 1O2→11 〉 7 + 1O2→12〉8 + 1O2→13〉23 + 1O2→24, a trend parallel with that reported for the ethylenetetracarbonitrile (TCNE) cycloadditions to the same polyenes. The rate-constant ratios k1/k2 and k2/k3 for the three successive photo-oxidations of [2.2.2]hericene (6) did not differ significantly from unity, in contrast with the Diels-Alder additions of 6. Similarly, the rate-constant ratios k1/k2 for the two successive photo-oxidations of tetraenes 7 and 8 were significantly smaller than those reported for the successive TCNE cycloadditions to 7 to 8. The endoperoxide formations are not sensitive to the change in the exothermicity of the reactions but they are sensitive to the electronic properties (IP's) of the polyenes.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690403
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    Ion-Molecule reaction in the gas phase part VIFor Part V, see [1]. Regioselective SN2 reaction from terpenoid diastereoisomeric diols using CI/NH4+Dedicated to Prof. Tino Gäumann on the occasion of his 60th birthday (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 806-815 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A stereospecific and regioselective SN2 mechanism (Walden inversion) is observed during studies involving modified terpenoid epimeric diols in a high-pressure ion source using ammonia as a reagent gas.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690408
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  • 177
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    Three Novel Spin-Labeled Substrates for Enzymatic Incorporation into Nucleic Acid Lattices (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 345-349 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of one C(4)-spin-labeled uridine-5′-diphosphate (C(4)-UDP) and two nitroxide-containing 2′-deoxyuridine-5′-triphosphate (dUTP) analogs are reported. The C(4)-UDP derivative was incorporated into copolymers by polynucleotide phosphoxylase (PNPase); one of the two dUTP analogs, substituted at position C(4), was a good substrate for TdT, whereas the other one, substituted at position C(5), served as substrate for E. coli DNA polymerase (Pol I).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690213
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  • 178
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    Reaktionen von 3-substituiertem 5-Trifluormethyl-1,3,4-oxadiazol-2(3H)-on mit NucleophilenIX. Mitt. über Synthese von Heterocyclen. VIII. Mitt. s. [1].Vorgetragen an der Herbstversammlung der Schweizerischen Chemischen Gesellschaft am 18. Oktober 1985 in Bern. (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 333-339 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 3-Substituted 5-Trifluoromethyl-1,3,4-oxadiazol-2(3H)-one with NucleophilesThe 3-substituted 5-trifluoromethyl-1,3,4-oxadiazolones 3, 4, 13, and 15 are attacked by N- and S-nucleophiles either at the ring C-atom C(2) or C(5). Depending on the nature of the substituent and the nucleophile, the ring-opening products 7, 10, 12, and 14 or the ring-enlargement products 16 are formed. The reaction of 4 with thiols is a novel variant of the Grob-type fragmentation. The reactivity of the 1,3,4-oxadiazolones is compared with that of the analogous 1,3,4-thiadiazolones. The structures of the new compounds were elucidated by 1H- and 13C-NMR spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690211
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  • 179
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    Synthese von 4,4-disubstituierten 1,3-Thiazol-5(4H)-thionen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 374-388 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 4,4-Disubstituted 1,3-Thiazol-5(4H)-thionesAn easy synthesis for the 1,3-thiazol-5(4H)-thiones 5, a class of heterocycles which have hitherto only been available with difficulty, is described. Reaction of 3-amino-2H-azirines 25 with thiocarboxylic acids at 0° yields monothiodiamides of type 20 (Scheme 6) which, on treatment with Lawesson reagent at 100°, undergo thiation and cyclization to give 5 in good yield.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690217
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  • 180
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    Herstellung von disubstituierten Maleinsäure-anhydriden mit Hilfe von reaktiven 2-Oxo-3H-imidazo[1,2-a]pyridinium-Verbindungen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 396-403 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of Disubstituted Maleic Anhydrides from Reactive 2-Oxo-3H-imidazo[1,2-a]pyridinium CompoundsA new useful method for the preparation of disubstituted maleic anhydrides, most of them bearing additional functional groups in the side chain, is described. The key step of the synthesis consists of the addition of 2-oxo-3H-imidazo[1,2-a]pyridinium compounds to a variety of different Michael acceptors.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690219
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  • 181
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    Konfigurationsbestimmung von geometrischen Isomeren mittels selektiver 13C{1H}-NOE-Differenzspektroskopie (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 898-904 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Application of Selective 13C{1H}-NOE Difference Spectroscopy in Determination of the Configuration of (Z)/(E)-IsomersHeteronuclear 13C{1H}-NOE studies have been performed to elucidate the configuration at the imino double bond in N,N′-Dicyanoquinonediimines. Selective low-power irradiation of the neighbouring ring protons in compounds 1-5 increases the signal intensities of CN as well as of the imino-C-atoms in the 13C-NMR spectra. The increase of signal intensity can easily be detected by the difference spectroscopy. The results of this investigation are in good agreement with a recently published study on the stereochemistry of N,N′-Dicyanoquinonediimines, based on the interpretation of 13C-chemical shifts.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690417
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  • 182
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    Synthese und Strukturaufklärung von Merucathin und Pseudomerucathin. Zwei Inhaltstoffe von Catha edulis FORSK (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 918-926 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Structure Elucidation of Merucathine and Pseudomerucathine. Two Constituents of Catha edulis FORSK.Starting from L-alanine, two constituents of Catha edulis FORSK. (3R,4S)-4-amino-1-phenyl-1-penten-3-ol ((3R,4S)-4, merucathine) and (3S,4S)-4-amino-1-phenyl-1-penten-3-ol ((3S,4S)-4, pseudomerucathine) were synthesized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690420
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    Mitteilungen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 955-956 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690424
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  • 184
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    1,4-Dithiafulvene aus der Umsetzung von 4,4-disubstituierten 1,3-Thiazol-5(4H)-thionen mit AcetylenderivatenVorläufige Mitteilung s. [1]. (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 419-429 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,4-Dithiafulvenes, Products of the Reaction of 4,4-Disubstituted 1,3-Thiazol-5(4H)-thiones and Acetylenic CompoundsOn heating in toluene, 4,4-disubstituted 1,3-thiazol-5(4H)-thiones 1 and acetylenecarboxylates or acetylenecarbonitriles 2 undergo a cyclosubstitution reaction to yield 2-methylidene-1,3-dithiol derivatives 3 (1,4-dithiafulvenes) and a nitrile. Further heating of 3a and 3b in the presence of excess 2a leads to the isomeric 2,3-dihydrothiophene-2-thiones 4a and 4b, respectively. The benzodithiafulvene 14 has been formed in a similar reaction from 1a and in situ generate benzyne.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690223
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  • 185
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    Perimeter-Type Structures in Charged [4n + 2] Annuleno [4n + 2] annulenes. The Importance of the Frontier-Orbitals (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 949-954 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetra(tert-butyl)[14]annuleno[14]annulene 1 is transformed, via alkali metal reduction, into its radical monoanion, dianion, radical trianion, and tetraanion. The paramagnetic species are characterized by ESR and ENDOR spectroscopy and the diamagnetic species by 1H- and 13C-NMR spectroscopy. Well-resolved ESR and NMR spectra can only be obtained, if the reduction is carefully monitored. For the interpretation of the data, the ions derived from the structurally related [14]- and [22]annulenes 3 and 5 as well from the tetra(tert-butyl)[14]annuleno[18]annulene 2 serve as suitable model compounds. While the behavior of the neutral annulenoannulene 1 is governed by that of the [14]annulene-subunit, the corresponding ionic systems can best be described as macrocyclic perimeters. This outcome can be rationalized by the nodal properties of the frontier MO's.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690423
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  • 186
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    Stereoselective Reduction of δ-Hydroxy-β-ketoesters (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 803-805 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of δ-hydroxy-β-ketoesters 1 was investigated with three different reducing agents. In several instances, high selectivity in favor of syn-1,3-diols was observed.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690407
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  • 187
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    Anion Selectivity of Metalloporphyrins in Membranes (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 849-854 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lipophilic Co(III) and Mn(III) complexes of 5,10,15,20-tetrakis[4-(hexyloxycarbonyl)phenyl]porphyrin act as positively charged carriers for anions and induce anion selectivities in membranes clearly deviating from the sequence of classical anion exchangers. Different anion selectivities are observed for the Co(III) and Mn(III) porphyrins.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690411
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  • 188
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    Approaches to 1H-Cyclopropa[l]phenanthrenes. Eliminations with 1a,9b-Dihydro-1H-cyclopropa[l]phenanthrene Derivatives (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 855-864 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Base-induced elimination of the sulfonium salt 2i in the presence of furan affords the addition products 7 and 8, derived from 1H-cyclopropa[l]phenanthrene (1) and the isomeric cyclopropene 5a (Scheme 3). Upon oxidation, the selenide 2c yields phenanthrene-9-methanol (9), presumably via 1. No evidence for the intermediate 1 is obtained from sulfoxide pyrolysis with 2e, which leads to products formed by radical pathways (Scheme 5). Reductive elimination of the disulfone 3b gives half-reduction to monosulfone 2g and complete reduction to cyclopropane 2 as well as 9-methylphenanthrene (15), but no evidence for the intermediate 1.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690412
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  • 189
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    Fluorine-Containing Organozinc Reagents Part 1 A Simple Synthesis of 2,2-Dichloro-3,3,3-trifluoropropanol (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 881-886 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compound 1, which can be regarded as a synthetic equivalent of substituted 1,1,1-trifluoroacetone 2, is prepared by Zn-induced reductive addition of 1,1,1-trichloro-2,2,2-trifluoroethane (3) to formaldehyde (4). A brief survey of the scope of this C—C-bond formation leading to a variety of new CF3-containing synthetic building blocks is also given.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690415
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  • 190
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    Intramolekulare 1,3-dipolare Cycloadditionen mit alkenyl-substituierten 3,4-DiarylsydnonenTeilweise in vorläufigen Mitteilungen veröffentlicht [1] [2].Als Sydnone werden mesoionische 1,2,3-Oxadiazol-5-one (1,2,3-Oxadiazolium-5-olate, Anhydro-5-hydroxy-1,2,3-oxadiazolium-hydroxide) bezeichnet [3]. (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 927-940 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intramolecular 1,3-Dipolar Cycloaddition Reactions of Alkenyl-substituted 3,4-DiarylsydnonesThe 3,4-diarylsydnones 1 and 12a-e with an allyl or alkenyloxy substituent on the N(3)-phenyl group have been synthesized by classical methods starting from 2-allylaniline and the corresponding alkenyloxyanilines, respectively (Schemes 2 and 3). Whereas the allyl-substituted sydnone 1 undergoes an intramolecular 1,3-dipolar cycloaddition at room temperature in solution to yield 13 (Scheme 4), the alkenyloxy-substituted sydnones 12a-e are thermally stable. On irradiation of 1 and 12a-d, formation of the fused dihydropyrazoles 2 and 14a-d (Schemes 1 and 5) is observed. In the case of 12d, the yield of 14d is very low, and the symmetric 1,2,3-triazole 15a has been isolated as the main product. A very likely reaction mechanism for the formation of the photoproducts involves decarboxylation of the sydnones to give a nitrile-imine which undergoes an intramolecular 1,3-dipolar cycloaddition onto the C=C bond.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690421
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  • 191
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    Intramolecular Oxygen Transfer on the Ozonolysis of a Diphenylcyclopentene Derivative (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 941-948 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ozonolysis of cis-3,4a,7,7a-tetrahydro-3,3-dimethyl-6,7a-diphenylcyclopenta[1,2,4]trioxine (1) in CH2Cl2 at -78° gave the secondary endo ozonide 2 (43% yield) and an acetal 3 (27% yield) derived from O-insertion at the ortho position of the C(7a) phenyl substituent. Both structures were elucidated by X-ray. Repetition of the ozonolysis in MeOH/CH2Cl220:3 at -78° also gave the same two products in 12 and 15% yields, repectively, together with the hemiperacetal 4 (54% yield) formally derived from the secondary ozonide by addition of MeOH.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690422
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  • 192
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    Masthead (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690501
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  • 193
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    Isoswerosid, ein neues Secoiridoidglycosid aus den Wurzeln des Zwergholunders Sambucus ebulus L. (Caprifoliaceae). 2. Mitteilung über die Inhaltsstoffe der Zwergholunderwurzel (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1113-1119 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isosweroside, a New Secoiridoid Glycoside from the Roots of Sambucus ebulus L. (Caprifoliaceae)The paper describes the isolation and structure elucidation of isosweroside (6-(β-D- glucopyranosyloxy)-methyl-9-vinyl-2,8-dioxabicyclo[3.3.1]non-6-en-3-one), the first Valeriana-type secoiridoid glycoside from the roots of Sambucus ebulus L. along with the two known glycosides ebuloside and morroniside.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690519
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  • 194
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    Synthèse d'acétals de désoxy-3-hydroxyamino-3-furannoses. Note de laboratoire (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1132-1136 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 3-Deoxy-3-(hydroxyamino)furanose AcetalsReduction of sugar ketoximes with NaBH3CN under acidic conditions constitutes a good synthetic pathway to deoxy(hydroxyamino)sugar derivatives. These compounds which are useful building blocks for the preparation of analogs of various classes of biologically important carbohydrates are reasonably stable.
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  • 195
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    1,3-Dioxanone Derivatives from β-Hydroxy-carboxylic Acids and Pivalaldehyde. Versatile Building Blocks for Syntheses of Enantiomerically Pure Compounds. A Chiral Acetoacetic Acid Derivative Preliminary Communication (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1147-1152 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (R)-3-Hydroxybutyric acid (from the biopolymer PHB) and pivalaldehyde give the crystalline cis - or (R,R)-2-(tert-butyl)-6-methyl-1,3-dioxan-4-one (1a), the enolate of which is stable at low temperature in THF solution and can be alkylated diastereoselectively (→3, 4, 5, and 7). Phenylselenation and subsequent elimination give an enantiomerically pure enol acetal 10 of aceto-acetic acid. Some reactions of 10 have been carried out, such as Michael addition (→11), alkylation on the CH3 substituent (→13), hydrogenation of the C=C bond (→1a) and photochemical cycloaddition (→16). The overall reactions are substitutions on the one stereogenic center of the starting β-hydroxy acid without racemization and without using a chiral auxiliary.
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    URL: http://dx.doi.org/10.1002/hlca.19860690523
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  • 196
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    Diastereoselectivity and Reactivity in the Diels-Alder Reactions of α-Chloronitroso Ethers (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1137-1146 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the α-chloronitroso ether 1, obtained from the hydroximolactone 2 and tert-butyl hypochlorite (89%), was established by X-ray crystallographic analysis. The [4 + 2] cycloadditions of 1 with the dienes 3 and 8-11 led to the N-unsubstituted 3,6-dihydro-2H-1,2-oxazines 6 and 12-16 in high enantiomeric excess (Table 1). Due to the additional α-alkoxy group, the reactivity of 2 is much superior to the one of known α-chloronitrosoalkanes. The reactive conformation of 1 was deduced from the X-ray analysis as well as the high diastereoselectivity of the cycloadditions. The importance of the α-alkoxy group was evidenced from the similar reactivity of the racemic α-chloronitroso ethers 25-27 which were prepared from the hydroximo ethers 28-30 and tert-butyl hypochlorite.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690522
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    Desoxy-nitrozucker 14. Mitteilung13. Mitteilung: [1]. 1-C-Nitroglycale. Herstellung und Umsetzung mit einigen Stickstoff-Nucleophilen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1191-1204 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1-C-Nitroglycals. Preparation and Reaction with Some Nitrogen NucleophilesAcetylation of the 1-deoxy-1-nitromannopyranoses 2 and 6 was accompagnied by spontanous β-elimination to give the 1-C-nitroglucals 3 and 7, respectively, while acetylation of the gluco- and galacto-configurated 1-deoxy-1-nitropyranoses 8 and 14 gave the acetates 9 and 15, respectively (Scheme 1). The acetylation of the ribo- and arabino-configurated 1-deoxy-1-nitrofuranoses 19 and 21 also occurred without β-elimination to give the acetates 20 and 22, respectively (Scheme 2). Mild base treatment of the previously described O-acetylnitro-β-D-glucose 4, the O-acetylnitro-β-D-pyranoses 9 and 15, and the O-acetylnitro-β-D-furanoses 17, 20, and 22 gave the 1-C-nitroglycals 3, 10, 16, 18 and 23, respectively (Scheme 1 and 2). The previously obtained 1-C-nitroglucal 3 was deacetylated by treatment with MeOH in the presence of KCN or sodium m-nitrophenolate to give the free nitroglucal 5. Deacetylation of the benzylidene protected 1-C-nitroglucal 10 (MeOH, NaOMe) gave the 4,6-O-benzylidene-1-C-nitroglucal 11 and traces of the 2-O-methyl-1-C-nitromannoses 12 and 13. The UV, IR, 1H-NMR and 13C-NMR spectra of the 1-C-nitroglycals are discussed. In solution, the 1-C-nitroglycals 1, 5, 7, 10, 11, and 16 adopt approximately a 4H5- and 3 a flattened 4H5 conformation. The structure of 5 was established by X-ray analysis. In the solid state, 5 adopts a sofa conformation, which is stabilized by an intramolecular H-bond. The β-addition of NH3 to the 1-C-nitroglucals 7 and 10 was followed by an O→ N acetyl migration to give exclusively anomeric pairs of the N-acetyl-1-nitromannosamine derivatives 24/25 and 26/27, respectively (Scheme 3). The β-addition of methylamine, octadecylamine, and tryptamine to the 1-C-nitroglucal 11 also stereoelectronically controlled and gave the crystalline N-alkyl-1-nitromannosamines 28, 29, and 30, respectively. The stereoelectronically controlled β-addition of NH3 to the 1-C-nitrogalactal 16, followed by acetylation, yielded exclusively the talosamine derivative 31, while the reversible β-addition of azide ions to 16 gave the anomeric 2-azido-1-nitrogalactoses 32 and 33. The β-addition of azide ions to the 1-C-nitroglucal 1 led to the 2-azido-1-nitromannose 34. In the presence of excess formaldehyde, this addition was followed by a Henry reaction. Chromatography of the crude product was accompagnied by solvolytic removal of the NO2 group to give the 3-azidomannoheptulose 35 in high yields (Scheme 4).
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19860690527
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    Comparison of the Complexation of Open-Chain and Cyclic N2S2 Ligands with Cu+ and Cu2+ (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1216-1223 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexation properties of the open-chain N2S2 ligands 1-4 are described and compared to those of analogous N2S2 macrocycles 5-7. With Cu2+, the open-chain ligands give complexes with the stoichiometry CuL2+ and CuLOH+, the stabilities and absorption spectra of which have been determined. The ligand field exerted by these ligands is relatively constant and independent of the length of the chain. With Cu+, the species CuLH23+, CuLH2+, and CuL+ were identified and their stabilities measured. The redox potentials calculated from the equilibrium constants and measured by cyclic voltammetry agree and lie between 250 and 280 mV against SHE. The comparison between open-chain and cyclic ligands shows that (1) a macrocyclic effect is found for Cu2+ but not for Cu+, (2) the ligand-field strength is very different for the two types of ligands, and (3) the redox potentials span a larger interval for the macrocyclic than for the open-chain complexes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690529
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  • 199
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    Nucleotides. Part XXVPart XXIV: [1].. Chemical synthesis of the hexaribonucleotide C-A-A-C-C-A (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1768-1777 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical synthesis of the ribo-hexamer C-A-A-C-C-A has been achieved by two different routes applying the phosphotriester approach and using the (p-nitrophenyl)ethyl group for phosphate protection. The 2′-hydroxy groups as well as the terminal 2′,3′-diol function have been blocked by the (tert-butyl) dimethylsilyl group as permanent protection throughout all the synthetic steps with great success. Final deblocking of all protective groups could be performed with 80% yield to give the hexamer 23. The various protected intermediates have been characterized by elemental analysis and UV spectra.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19860690734
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    Errata (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1787-1787 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690736
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