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  • Polymer and Materials Science  (2,161)
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  • 1970-1974  (4,049)
  • 1960-1964
  • 1910-1914
  • 1973  (4,049)
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  • 1970-1974  (4,049)
  • 1960-1964
  • 1910-1914
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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 12 (1973), S. 121-125 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Despite its being weaker base poly(2-vinylpyridine) polymerized DL-β-phenylalanine NCA at a much faster rate than pyridine and α-picoline. Poly(2-vinylpyridine) adsorbs NCA by hydrogen bonding with the cooperation of a few pyridine groups. This results in a high local concentration of NCA. The syndiotactic configuration of pyridine group seemed to be least suitable for the cooperative hydrogen bonding. Adsorbed NCA is activated to form an “activated” NCA which in turn reacts with an NCA adsorbed on the same polymer chain. Since the polymer chain is flexible, this intramolecular reaction takes place frequently, resulting in the acceleration of polymerization. The intramolecular reaction along the polymer chain is dependent on the degree of polymerization of polymer catalyst. A suitable model was proposed for the intramolecular reaction to explain the effect of degree of polymerization.
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  • 3
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Bromouracil-substituted DNA was isolated form B. Subtilis and phage PBSH. The three DNA fractions of Different densities (TT, TB, and BB) were irradiated with u.v. (313nm). The number of single-strand and double-strand breaks was determined. The breakage rates are given. It was found that in hybrid DNA (TB) double-strand breaks occur depending linearly on dose. In BB-DNA the observed double-Strand bresks can be divided into two fractions with a linear and quadratic dose dependence respectively. The results can be explained by assuming intramolecular energy transfer from the BU-containing strand to its complementary strand.
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  • 4
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    New York : Wiley-Blackwell
    Biopolymers 12 (1973), S. 229-235 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Differential enthalpic analysis of a series of 3′,5′-cyclic nucleotides indicates that homolytic cleavage of the six-membered phosphate ring occurs either immediately prior to or concurrent with decomposition of the crystal lattice. Homolysis is followed by a rapid polymerization to yield oligonucleotides. The enthalpies of these reactions have, with the exception of guanosine 3′,5′-cyclic phosphate, almost identical values of 25 kcal/mole. The anomalous case is attributed to a more stabilized phosphate ring as a result of hydrogen bonding through the two position of the purine ring. The pair of overlapping exothermic peaks observed in each of the thermograms for cAMP and cIMP is related to the presence of two conformational arrangements within the unit cell of each compound.
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total energy and the electronic properties of some syn purine nucleosides have been determined as a function of the rotation angle around the C-N glycosidic linkage. Invariably, the crystallographic coordinates provide a state lying at or very near the minimum on the potential energy curve according to the extended Hückel parametrization here employed. The ribose moiety always carries a net positive charge whereas the base is always negatively charged. Changes in dipole moment magnitudes for the overall structure as well as in net atomic charges are noted upon rotation around the glycosidic linkage indicating that potential functions for polynucleotides may be in error if such changes are ignored.
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  • 6
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    Biopolymers 12 (1973), S. 341-352 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measuring the equivalent noise resistance of Na-DNA solutions in NaCl provides in formation about the free ino atmosphere. In an Arrhenius type diagram, the helix → coil transition is clearly brought Out. A Calculation of the number of free ions in the solution as function of temperature, reveals once more the process of ejection of compensating Na+ ions form the macromolecules during the thermal transconformation.
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  • 7
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    Biopolymers 12 (1973), S. 423-433 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical properties in different solvents of gramicidin-bis (salicylaldimine) Cu(II) and (5-I-salicyladimine) Cu(II) chelates are intercepted in terms of their molecular structure. A molecular model for the inversion of Contton effects in two different classes of solvents is proposed. This explanation is supported by the study of optical properties of model compounds.
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  • 8
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    Biopolymers 12 (1973) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses are described for two N-benzyloxycarbonylpeptide tert-butoxycarbonylhydrazides which correspond to positions 24-34 and 35-44, respectively, of the primary structure of baker's yeast iso-1-cytochrome c. The two peptide derivatives were coupled via the azide procedure to form the N-benzyloxycarbonylheneicosapeptide tert-butoxycarbonylhydrazide (sequence 24-44).
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  • 10
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    Biopolymers 12 (1973), S. 647-654 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The primary amine initiated homopolymerization of γ-benzyl-L-glutamate NCA in dioxane at 25°C, 35°C, 50°C, and 65°C has been investigated. The reactions were virtually independent of temperature indicating an activation energy of less than 1 kcal/mole. The entropy of activation was estimated to be -65 entropy units at 300°K. The reaction proceeded in two stages. The first stage was zero-order with respect to monomer, whereas the second was first-order with respect to monomer. Both stages were first-order with respect to initiator. These results were interpreted by assuming that the rate constant for propagation was not independent of the degree of polymerization up to the point where a conformational transition to α-helix occurred.
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  • 11
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis is described of the N-benzyloxycarbonyldecapeptide tert-butoxycarbonylhydrazide, which corresponds to the sequence 57-66 of baker's yeast iso-1-cytochrome c. The peptide derivative was synthesized coupling two smaller subunits via the Rudinger modified azide procedure.
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  • 12
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    Biopolymers 12 (1973), S. 791-798 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of interaction between proflavine and poly I.poly C at 25°C, neutral pH, and moderate ionic strength have been studied by relaxation methods. The qualitative features of this system resemble those previously reported by Crothers and co-workers for proflavine-DNA and proflavine-poly A·poly U interactions-two relaxations are observed coresponding to a fast bimolecular step followed by a slower isomerization. These results can best be accommodated by a two-step mechanism leading from the free dye through an “outside-bound” complex to the intercalated complex. Quantitative comparison of the various rate constants for proflavine binding to different double-helical polynucleotides shows that the rates are slower for both ribohomopolymer pairs than for DNA. The rates for poly I·poly C are approximately three times faster than these for poly A·poly U.
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  • 13
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Infrared and Raman spectra of aqueous poly(rA-rU)·poly(rA-rU), the double-helical complex containing strands of alternating riboadenylate and ribouridylate residues, display significant differences from one another and from corresponding spectra of poly(rA)·poly(rU), the double-helical complex of riboadenylate and ribouridylate homopolymers. Parallel studies on the copolymer and homopolymer complexes by cesium sulfate density gradient centrifugation, ultraviolet absorption spectroscopy, hydrogenion titration, 1-N oxidation of adenine residues by monoperphthalic acid and X-ray diffraction reveal, however, that the geometry of base pairing between adenine and uracil is closely similar in each complex and apparently of the Watson-Crick type. Therefore the differences observed between vibrational spectra of poly (rA-rU)·poly (rA-rU) and poly(rA)·poly(rU) are not due to different base-pairing schemes but may be attributed to differences in vibrational coupling between vertically stacked bases. Vibrational coupling may also account for the differences between infrared and Raman spectra of the same complex. Thus, the present results indicate that infrared and Raman frequencies of RNA in the region 1750-1550 cm-1 should be dependent on the base sequence.
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  • 14
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    Biopolymers 12 (1973), S. 857-867 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple model is introduced to investigate the stability of a sedimenting entanglement. The sedimenting entanglement is represented by a sedimenting sieve. Solvent can pass through it, but single-chain molecules that flow into it become entangled and their flow decreases or, if permanent entanglements form, ceases entirely. With this model we are able to find the conditions under which the mass of a sedimenting entanglement remains constant, grows or decays to a stable value, grows beyond limit, or decays to the mass of a single chain. The theory is applied to the sedimentation of small concentrations of large chain molecules in solutions of small chain molecules in solutions of small chain molecules for the case in which the entanglements are long-lived. Equations are derived which, (1) give the stable entanglement mass as a function of rotor speed and concentration and, (2) for a given concentration predict the rotor speed at which the entanglement mass grows without limit. Numerical results for small concentrations of T2 DNA sedimenting in solutions of T7 DNA are presented.
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  • 15
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    Biopolymers 12 (1973), S. 931-936 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 16
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    Biopolymers 12 (1973) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 17
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    Biopolymers 12 (1973), S. 993-1010 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution bebavior of poly-L-proline Form II has been studied in water and aqueous salt solutions by both elastic and quasi-elastic light -scattering techniques. The results of this study suggest that polyproline Form II can exist in water at 24 °C as an associated polymer complex and that certain salts which do not appear to affect the helix integrity, e.g., guanidinium-HCl, resutl in dissociation of the aggregate. Other neutral salts, of the variety effective in mediating unfolding of the Form II helix (e.g., 4M NaClO4) also induce aggregate dissociation, but 4M CaCl2 results in enhanced aggregation of polyproline. Kinetic experiments indicate that a time of 20 hours is necessary for the completion of the “large” to “small” transformation (at 22°C) which is induced by the addition of 4M NaClO4. Thus it appears that neutral salts additives in aqueous solutions of polyproline influence both the state of aggregation and the conformation of this polymer.
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  • 18
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    Biopolymers 12 (1973), S. 1047-1052 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dielectric relaxation of namtive DNA and DNA-proflavine complexes at different DNA phosphate (P) to dye (D) ratios, were investigated in the frequency range 100 c/sec to 100 Kc/sec. The proflavine molecules were found to have a profound effect on the static dielectric constant and the relaxation time of the polymers. The static dielectric constant was oberserved to decrese with increasing level of added proflavine. At P/D = 1, the variation of dielectric constant with frequency was small. Relaxation time (τ) was greater for the DNA-proflavine complexes compared to that for free DNA, Maximum value of the relaxation time was obtained at P/D = 10. The increase in the relaxation time and decrease in the static dielectric constant were attributed to the increase in length and meutralization of surface charges of the DNA molecules, respectively, as aresult of proflavine binding.
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  • 19
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fluorescence depolarization experiments performed on labaled poly-L-proline Forme II suggest the occurrence of aggrgation in water while 6M guanidinium-HCl induces dissociation. The solvent 4M CaCl2 results in a reduction of polymer structural orgganization. These findings corroborate suggestion of polyproline aggregation and solution behavior in aqueous neutral salt solytion (see preceding article).
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  • 20
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    Biopolymers 12 (1973), S. 1053-1062 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A detailed study on the deuterium NMR of hydrated collagen in the presence of alkali and alkaline earth salt is reported. The effect of different salts in reducing the deuteron quadrupole splitting are similer at low molar content of salt. At higher salt contents, larger ions are more effective. The ressults are explained by the blocking of water binding sites to collagen by hydrated ions. When the temperature is reduced, only part of the adsorbed water iss frozen, and the amount of “unfreezable water” decreases with the increase in ionic sizes(LiCl 〈 MgCl2 〈 KCL 〈 KCNS). The freezing temperature is also lowered in the presence of salts. A description of the structure of hydrated collagen based upon the observed facts is given.
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  • 21
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly-γ-L-glutamic acid has been synthesized by the activated pentachlorophenyl ester polymerization method and the molecule weight of the polymer was found to be 16,000. Comparative conformational studies on the synthetic and on the native polyglutamic acid mbtained from B. anthracis and B. subtilis were carried out using optical rotatory dispersion, circular dichroism, peptide absorption spectrum, and titration data. These results show that poly-γ-glutamic acid does not exhibit any conformational order under the conditions of investigation. At low degrees of ionization, restriction of conformational freedom via random “hypercoiling” of the chain appears likely.
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  • 22
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ultraviolet absorption, fluorescence excitation and emission, and fluorescence anisotropy demonstrate that the polycyclic aromatic hydrocarbone 3,4-benzpyrene, Pyrene, anthracene, and 9-methylanthracene bind to histone IV after the sow conformational change in the presence of divalent phosphate anion. These hydrocarbons do not bind, within our limits of detection, to histone IV in the diosorderde form at low pH or to the form produced by the fast conformational change when the slow change is prevented. High anisotropy values for the bound hydrocarbon indicate a high degree of aggregation for the histone IV.
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  • 23
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aggregation of native acid-soluble collagen (N-ASC) and of pronase-treated acid soluble collagen (P-ASC) was examined in solution under conditions which varied from those of minimum collagen-collagen interaction to those leading to incipient fiber formation. Molecular weights and weight distributions were determined in the analytical ultracentrifuge using the Yphantis high speed sedimentation equilibrium and Aarchiblad approach-to-equilibrim techniques. The aggregation was pH and ionic strength dependent in each case. Under conditions of minimum aggregation (low pH, low ionic strength), N-ASC showed the presence of permant aggregates. At higher pH and ionic strength, a higher fraction of aggregate was formed but these were of the same charcter and molecular weight as the permanent aggregates. The aggregates were of a single molecular size, with a weight of 1.5 × 106 daltons, compared with a monomer collagen weight of 3.1 × 105 daltons. The P-ASC formed aggregates also but to a much lower extent and the maximum aggregate size corresponded to dimers in molecular weight. These data show the major importance of molecular end-regions in collagen aggregation to form native type fibers and, by virtue of the discrete size of the N-ASC aggregates, support the microfibrillar hypothesis for the assembly of collagen fibrills.
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  • 24
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    Biopolymers 12 (1973), S. 1387-1419 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sedimentation coefficient and intrinsic viscosity of nicked and closed circular PM2 bacteriophage DNA have been measured as a function of pH in the alkaline region. A gradual increase in the sidimentation coefficient, and a corresponding decrease in the intrinsic viscosity, are observed for the superhelical (closed) circle in the pH region from 10.5 to about 10.9. This has been tentatively interpreted in terms of the known dependence of sedimentation coefficient upon the number of superhelical turns. At slightly higher pH values, the curve passes through the minimum (sedimentation coefficient) and maximum (intrinsic viscosity) expected when the superhelical turns present at neutral pH are unwound by partial alkaline denaturation. Sedimentation studies of the relaxed (nicked) circular species have revealed the existence of DNA forms in the pH region from 11.27 to 11.37 which sediment considerably faster than the closed circle in the same pH region. These have been identified as partially denatured nicked circles, in which varying fractions of the duplex structure have undergone alkaline denaturation, but strand separation has not yet occurred. Varying fractions of a slower species, either undenatured or completely denatured nicked circles, are also observed in some of these experiments. A corresponding result is observed in the intrinsic viscosity vs. pH curve.When nicked circular PM2 DNA is exposed to various alkaline pH's, rapidly neutralized, and sedimented at neutral pH, the expected sharp transition from native to denatured (strand-separated) molecules is seen. However, a very narrow pH range is noted in which native and denatured forms coexist in a single experiment. The above experiments carried out upon the closed form also reveal a narrow pH range in which the bulk of the transition from native closed circles to the collapsed cyclic coil takes place, in acccord with an earlier study on a different DNA. This transition is shown never to be completely effected, however, as there is a fraction (7-8%)of the closed circles which renature to the native form, regardless of the alkaline pH employed. This same phenomenon was not observed in the case of artificially closed λb2b5c DNA circles. Possible explanations for some of the above results are discussed.
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  • 25
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    Biopolymers 12 (1973), S. 1505-1513 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymerizations of DL-phenylalanine NCA by block copolymers of sarcosine and DL-phenylalanine, designated by (Phe)m(Sar)n and capable of reaction at the phenylalanyl terminal, were investigated in nitrobenzene solution at 25°C. With increasing n for constant m (m = 0, 1, 2, and 5), the polymerization rate greatly increased. Previously the acceleration of the initiation reaction in the polymerization of DL-phenylalanine NCA by polysarcosine (m = 0) was reported. The present results showing the acceleration by the copolymers of sarcosine and DL-phenylalanine indicate the presence of the polymer effect in the propagation reaction as well. However, the polymer effect was most marked with polysarcosine (m = 0), and decreased with increasing m.The same polymerizations by sequential copolymers composed of ten sarcosine units and two DL-phenylalanine units were also investigated. Again with these copolymer catalysts the polymerization rate was larger than that by monomeric amines. But the polymer effect decreased sharply when the phenylalanine units take positions near the terminal amine group of the copolymer catalyst.These two deteriorating effects of the phenylalanine unit have been interpreted in terms of the decrease of the flexibility of polymer chain, caused possibly by an intramolecular hydrogen bond of the phenylalanine unit.
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  • 26
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    Biopolymers 12 (1973), S. 2057-2073 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Accurate equilibrium binding data for the oxygenation of hemoglobin are used (a) to show that various models for cooperativity are inconsistent with the best available experimental data, (b) to determine the equilibrium constants for binding of 2,3-diphosphoglycerate to hemoglobin molecules in intermediate stages of oxygenation, and (c) to deduce a mechanism for allosteric effects in hemoglobin which is consistent with the best available experimental data. The total free energy of cooperativity is defined and discussed.
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  • 27
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    Biopolymers 12 (1973), S. 2151-2159 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A conductivity dispersion has been measured at very low frequencies (VLF) on several concentrated DNA solutions. By measuring simultaneously their electric birefringence decay, it is shown that the dielectric relaxation (which is related to the conductivity dispersion) is due to the molecular orientation. Different polarization mechanisms are discussed. It is concluded that the DNA polarizability measured in the VLF range can only be explained by the orientation of a permanent ionic dipole. It is suggested that such permanent dipoles could be caused by small differences in the ionic composition between the two molecular “ends;” the difference could either be stable (asymmetrical localization of protein impurities for instance) or transient (fluctuating dipoles explained by the Kirkwood-Schumaker theory).
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  • 28
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 29
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    Biopolymers 12 (1973), S. 2199-2209 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present work, the synthesis of the three primary oligomers of α-L-glutamic acid is described; the general formula is the following: [I] The choice of protective groups at the both ends of the chain allows for the good solubility in the water and the liberation of free carboxyl groups on the side chain. Thus, models are obtained for the study of thermodynamic properties of solutions and especially of the interactions between polyanions and cations. The prepared products are characterized by different techniques such as mass spectrometry potentiometry, tonometry, and thin-layer chromatography. The results are in agreement and lead to the conclusions that the molecules have the general formula of [I] and are stereoregular.
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  • 30
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In continuation of our studies on the effect of the base and the phosphate groups on the glycosyl and the sugar-phosphate backbone conformation, we have carried out semi-empirical potential energy calculations on the common 5′- and 3′5′-ribopyrimidine mono- and diphosphates by considering simultaneous rotations about the glycosyl (χ) and the C(4′)-C(5′) (ψ) bonds. This calculation provides an assessment of the nature and orientation of the base on the sugar-phosphate backbone conformation of nucleotides and polynucleotides. It is found that the attractive inetractions between the 5′-phosphate group and the base mutually stabilize the antiand the gauche-gauche (gg) conformations about χ and ψ, respectively, in 5′-ribopyrimidine nucleotides. The introduction of the 3′-phosphate group as in 3′,5′-ribopyrimidine diphosphates, still leaves the anti-gg as the most favored conformation with the important difference that the probability of occurrence of the anti, gauche-trans (gt) is how substantially increased. This is dependent to a large extent on the sugar conformation and to a lesser extent on the base. Uracil and thymine show a greater probability for the anti-gt than cytosine. The syn conformation is considerably less likely and its occurrence is also dependent on the base type, cytosine showing a lesser tendency than uracil and thymine. For the syn base, the most favourec conformation for ψ is gt, since gg is sterically disallowed and tg is destabilized by electrostatic repulsive interactions between the 3′ and 5′-phosphate groups. Thus, there is a striking correlation between the glycoysl and the backbone C(4′)-C(5′) bond conformations. The rest of the bonds of the backbone are considerable less dependent on the glycosyl conformation. These studies reveal that in poly-ribopyrimidine nucletides the majority of the nucleotide residues are expected to occur in the anti-gg conformation.
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    Biopolymers 12 (1973), S. 2335-2349 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of poly dispersity on the nuclear magnetic resonance spectra of samples of poly-γ-benzyl-L-glutamateein the helix-random coil transition is studied. In the transitionregion the α-CH proton resonance shows two peaks whose behavior does not change appreciably upon fractionation by gel permeation chromatography. Theoretical spectra were computed with both a polydispersity model of the transition and a model for slow nucleationof helix from completely random coil molecules. The results suggest that the double peak behavior in the nmr spectra results from a slow rate of helix nucleation rather than polydispersity.
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    Biopolymers 12 (1973), S. 2691-2712 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A conformational analysis has been carried out for the cyclic peptide antibiotic alamethicin. Unlikely structures were first eliminated by constructing van der Waals' energy maps for near-neighbor contacts and using these maps to generate forty complete alamethicin structures free of steric overlaps. The energies of the forty conformations were minimized; optimizing all dihedral angles first in sets and then simultaneously, to give a family of five low-energy structures. In the conformation of lowest energy three of the seven α-amino isobutyric acid residues occur in a six-residue α-helix and three at the two chain reversals. Judged by the change in conformational energy as a function of the change in dihedral angle, the flexibility of the chain is determined by both the type of peptide unit and its position in the molecule.The model has features consistent with reported circular dichorism and surface balance measurements and has two polar centers separated by a lipophilic region. It does not contain the large central pore required by some theories for the action of alamethicin on cell membrances. It therefore probably acts by altering membrance structres rather than by shuttling ions through a pore in the membrance.
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  • 33
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    Topics: Chemistry and Pharmacology
    Notes: The conformation and packing scheme for guanosine-3′, 5′-cytidine monophosphate, GpC, were computed by minimizing the classical potential energy. The lowest energy conformation of the isolated molecule had dihedral angles in the range of helical RNA's and the sugar pucker was C3′ endo. This was used as the starting conformation in a packing search over orientation space, the dihedral angles being flexible in this step also. The packing search was restricted by constraints from our x-ray data, namely, (1) the dimensions of the monoclinic unit cell and its pseudo-C2 symmetry (the real space group is P21), (2) the location of the phosphorous atom, and (3) the orientation of the bases. In addition, a geometric function was devised to impose Watson-Crick base pairing. Thus, a trial structure could be sought without explicit inclusion of intermolecular potentials. An interactive computer graphics system was used for visualizing the calculated structures.The packing searches yielded two lowest energy schemes in which the molecules had the same conformation (similar to double-helical RNA) but different orientations within the unit cell. One of these was refined by standard x-ray methods to a discrepancy index of 14.4% in the C2 pseudocell. This served as the starting structure for the subsequent refinement in the real P21 cell.5
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  • 34
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    Biopolymers 12 (1973), S. 2789-2802 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model for the hydration behavior of human stratum corneum has been developed from measurements on in vitro samples isolated in a manner which minimized tissue treatment and trauma. Water sorption/desorption rate measurements as a function of water activity, temperature, and tissue integrity are reported. These data, together with thermodynamic data (infrared and nmr results reported earlier) are consistent with a model in which rapidly sorbed/desorbed water (ca. 0.5 mg water/mg stratum corneum) is associated with (“bound” by) the tissue, while slowly sorbed/desorbed “free” water (up to 12 mg water/mg stratum corneum) is kinetically restricted and probably intracellular in location. Both equilibrium water binding and desorption kinetic data suggest structural changes of this cellular water barrier upon hydration. Evidence for hysteresis in water sorption isotherms (reported by others) could not be reproduced.
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    Biopolymers 12 (1973), S. 2831-2852 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly(ortho-, meta-, and para-γ-nitrobenzyl-L-glutamates) were studied by circular dichroism (CD) and optical rotatory dispersion (ORD) in two helicogenic solvents, hexafluoroisopropanol (HFIP) and dichloroethane (EDC), and two non-helicogenic solvents, dichloracetic acid (DCA) and trifluoroacetic acid (TFA). The corresponding glutamates were also studied in DCA and TFA. The symmetric nitrobenzylic chromophore is optically active when the polymers are in solution in DCA and TFA. The corresponding glutamates are also optically active under the same conditions. Thus, it was not possible to explain the origin of the optical activity of the side-chain chromophore when the polymer is in solution in a helicogenic solvent. Nevertheless, from a side-chain dichroic band, a helix-coil transition curve was determined and the stability of each poly(γ-nitrobenzyl-L-glutamate) given; this stability depends on the position of the nitro substituent on the aromatic ring.
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    Biopolymers 12 (1973), S. 53-64 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: Sedimentation constant and intrinsic viscosity were measured on purified tropocollagens extracted from earthworm-cuticle and lathyritic ratskin. A cartesian diver viscometer was used to make viscosity measurements at small shear stress and to avoid the effects of surface forces. By comparing the experimental data with the hydrodynamic theories of wormlike-coil of Ullman a value of 1300 Å has been assigned for the persistence length of these tropocollagens. Other factors which may affect the estimate are discussed.
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    Biopolymers 12 (1973), S. 45-51 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The CD spectra of DNA from various sources (T2; T4; Cd; Escherichia coli; calf thymus; Streptomyces chrysomalis) were investigated. A new band Δε210 in the CD spectra of glucosylated DNA of the T even phages was found. The temperature dependence of the CD spectra of DNA was obtained over a wide range of temperatures, including those of the helix-coil transition.The band Δε275 for all DNAs does not appreciably change in the range of the helix-coil transition. The monotonic increase of this band before melting, and its decrease after melting is observed with an increase in temperature.The amplitude of the CD band Δε245 for all the DNAs studied and Δε210 (glucosylated DNA) parallels the change of E260 absorbance.
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    Biopolymers 12 (1973), S. 575-587 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: By analyzing the effect of urea and guanidine hydrochloride on the circular dichroism of many polypeptides and proteins, it is concluded that under conditions of high concentration of the perturbant and at low temperatures the resultant state approached is that of a local extended helix structure instead of a completely random coil. Intensification by urea and guanidine hydrochloride of the circular dichroism bands of poly-L-proline II leads to the proof that the mechanism of interaction of urea and guanidine hydrochloride with proteins is through hydrogen bonding to the backbone carbonyl group.
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    Biopolymers 12 (1973), S. 541-558 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interactions between chondroitin-6-sulfate (chondroitin sulfate C) and poly-L-lysine have been studied as models for investigation of possible complex formation between fibrous proteins and mucopolysaccharides. Results obtained using circular dichroism spectroscopy show that poly-L-lysine adopts the α-helical conformation in dilute aqueous salt solution at pH 7 when mixed with chondroitin-6-sulfate, rather than the “charged-coil” observed in the absence of this mucopolysaccharide. This conformation-directing interaction is at a maximum when the ratio of lysine to disaccharide residues is 1 : 1. Changes in the CD spectrum of a 1 : 1 mixture following increase in the salt concentration, or addition of non-polar solvents, indicate that the interaction is ionic in nature. No such effects are observed for non-sulfated mucopolysaccharides mixed with poly-L-lysine, suggesting that, for chondroitin-6-sulfate, it is the sulfate groups rather than the carboxyls which interact with the amine groups of the polypeptide.Elevation of the temperature leads to disruption of the interactions between the polypeptide and polysaccharide species. A sharp melting transition occurs at 47.0 ± 1.0°C, when the poly-L-lysine reverts to the “charged-coil” conformation. The sharp transition suggests that regular ionic bonds are formed between the polypeptide and polysaccharide. These results suggest that a conformation-directing interaction may occur between sulfated mucopolysaccharides and the polar regions of collagen and other fibrous proteins.
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    Biopolymers 12 (1973), S. 627-636 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A coupling constant-dihedral angle correlation for the H—Cα—Cβ—H system of amino acid residues in peptides has been derived from a set of model compounds covering the full range of dihedral angles. The expression obtained, J = 11.0 cos2 θ -1.4 cos θ + 1.6 sin2θ, is close to those already used in pmr studies of peptide conformation, and provides a firmer foundation for them. A factor limiting the precision of this and other “Karplus relations” is illustrated.
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    Biopolymers 12 (1973), S. 655-674 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The ultraviolet absorption, linear dichroism, circular dichroism, and oriented circular dichroism of collagen are reported and the spectra are resolved into a self-consistent set of bands in accord with exciton theory. The parallel band at 200 nm has 40% of the π → π* intensity; the perpendicular band is placed at 189 nm yielding a splitting of 2700 cm-1. The circular dichroism is resolved into two Gaussians at λ∥ and λτ (rotational strengths +14 × 10-40 and -32 × 10-40 esu2. cm2) plus a large non-Gaussian (“helix”) band with ampplitude -25,000° at 201 nm. These data appear to be in reasonably good accord with recent calculations.Measurements of the absorption, linear dichroism and circular dichroism of polyproline I and II are also reported and are resolved into their component bands. Polyproline I is in good accord with exciton theory, whereas polyproline II remains unsatisfactory.
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  • 42
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    Topics: Chemistry and Pharmacology
    Notes: The synthesis is described of the N-benzyloxycarbonylundecapeptide tert-butoxycarbonylhydrazide corresponding to the sequence 82-92 of baker's yeast iso-I-cytochrome c.
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    Notes: The synthesis is described of the protected hexadecapeptide corresponding to the C-terminal sequence 93-108 of baker's yeast iso-I-cytochrome c. The cysteine residue in position 107 of the natural sequence has been substituted by a threonine residue. The rationale of this substitution as well as the synthetic route to the preparation of the hexadecapeptide derivative is discussed.
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    Biopolymers 12 (1973), S. 825-834 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The geometrical properties of collagen molecules place certain restrictions on possible three-dimensional packing models. With certain reasonable assumptions involving the macromolecular structure of collagen, a model for the surface topography of the monomeric unit is developed and two possible models for molecular packing, one hexagonal and the other non-hexagonal, are inferred. The non-hexagonal packing model is identical to the pentagonal unit fibril first postulated by J. W. Smith on different grounds, while the hexagonal model is one of three previously suggested by us on more general assumptions. The two models are compared to available data on collagen packing, and the bulk of the evidence would seem to favor the pentagonal model.
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    Biopolymers 12 (1973), S. 869-876 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: Zones of T2 DNA were sedimented through uniform solutions of T7 DNA to determine if the smaller DNA molecules would become entangled in the larger. No entanglement could be demonstrated even at high DNA concentrations. It is suggested that molecular entanglement is not responsible for the sudden loss of DNA from solution which occurs in high centrifugal fields. This communication also includes observations on the effects of rotor speed on the sedimentation behavior of DNA in high centrifugal fields, distortion of zone shape at high concentrations, and hydrodynamic interactions between DNA and MS2 bacteriophage particles.
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    Biopolymers 12 (1973), S. 1161-1169 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: A new method is proposed for determining chemical rate contants in dimerization reactions of globular proteins. Light scattering from a solution of charged macromolecules in and applied electric field gives a series of bands whose widths can be used to deduce the reaction rate contants. This method should be applicable to other types of peactions. First order reactions are also considered.
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    Biopolymers 12 (1973), S. 1197-1202 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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    Biopolymers 12 (1973), S. 1177-1195 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: Measurements of light scatting, sedimentation equilibrium, sedimentation velocity, and viscosity were carried out on fractions of native amylose in dimethylsulfoxide at 25°C. The data for statistical radius as a function of weight-average molecular weight Mw suggested a stiff nature of this biopolymer in the solvent studied when interpreted in terms of Kirste's recent calculations with a stiff chain model. The data for sedimentation coefficient were consistent with this suggestion, and when analyzed in terms of the theory Hearst and Stockmayer for wormlike chain, a value of 233 Å2 was obtainedd for a/λ, where a is the length of a monomer unit projected on the chain axis and (2λ)-1is the persistence length of the wormlike chain. The intrinsic viscosity data gave a high a value as 0.91 for the exoponent in the Houwink-Mark-Sakuarada equation, in Substantial agreement with Cowie's prenious work.We attempted to interpret these data by use of the Eizner-Ptitsyn equation for wormlike chains, with omission of the free-drainage term and introduction of the a/λ value obtained from sedimentation data. It was found that, except in the region of Mw above one million, the observed values were fitted well by the E-P theory with a = 1.4 Å and (2λ)-1 = 87 Å. The disagreement in the high-molecular-weight region was tentatively attributed to excluded volume effect. The a value obtained suggests that the molecular conformation of amylose in dimethylsulfoxide is predominantly helical, in contrast to that of the same polymer in aqueous solutions of simple electrolyte. It was also found that a similar value of a was derived from our data for the second virial coefficient and partial specific volume if the molecule was assumed to be essentially rodlike.
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    Biopolymers 12 (1973), S. 1247-1257 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: Melting curves of tRNAfMet and two fragments derived from this molecule by limited ribonuclease T1 digestion (i.e., the anticodon arm and loop [K fragment] and the larger fragment representing three-fourths of the tRNA chain from the 3′ terminus including two potential limbs of the cloverleaf structure [L fragment]) are presented. The profiles observed are consistent with the presence of base paired structures in all those molecules. At low salt concentration (0.02M Na+) the stabilities of these molecules measured by the apparent midpoints of the denaturation profiles are in the order K 〉 L 〉 tRNA. The relative stabilities approach each other at 0.2M Na+ (the tRNA profile being biphasic), while at high salt (2M) the L fragment seems to be more stable than either K or t-RNA fMet. Estimation of the enthalpy of denaturing the K structure in 0.02M Na+ gives a value of 40 ± 3 kcal/mole corresponding to an enthalpy per effective G.C. base pair disrupted of 10 ± 1 kcal/mole.
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    Notes: The far ultraviolet absorptions of aliphatic amino acids such as glycine, alanine, aminobutyric acid, valine, and leucine were measured with their solid thin films down to 120 nm. Four absorption bands arising from the carboxyl group were observed in the 200-140 nm region. It was found that the band positions and intensities vary systematically according to the number of carbon atoms in the aliphatic side chain. This result may be interpreted as a phenomenon similar to the hyper-and hypochromisms of aliphatic homopolypeptides in far ultraviolet region.
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    Biopolymers 12 (1973), S. 1377-1385 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: Using Wilson's GF-matrix method as modified by Higgs for infinite helical polymers, dispersion curves and the frequency distribution function have been calculated for poly-L-proline II chain. Infrared spectrum is obtained and a Urey-Bradley force field, which provides best fit with the observed frequencies, is evaluated. The result are discussed from the viewpoint of the conformational characteristics of forms I and II.
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    Biopolymers 12 (1973) 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Biopolymers 12 (1973), S. 1493-1503 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: Studies of the d. c. conductive behavior of solid gels of DNA under high vacuum have shown that a reproducible energy gap of 2.4 eV and a photoelectric effect may be obtained following extensive evacuation procedures. Admission of air for short periods has a reversible effect on this photoelectirc effect and semiconductive behavior. After prolonged illumination in air the sample becomes permanently affected and will not reproduce the photoelectric effect or give rise to a semiconduction energy gap of 2.4 eV but give rise to a permanently lower energy gap of 1.6 eV. The effect of ultraviolet irradiation on the thermal denaturation of DNA in the presence of six aromatic hydrocarbons has been examined in order to determine the extent to which the presence of the hydrocarbon protects the DNA against ultraviolet damage.
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    Biopolymers 12 (1973), S. 1565-1574 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: A new method of computing the geometry of a cyclic polymer from internal coordinates is discussed, which is particularly useful if the molecule has a center of inversion symmetry. When applied to the structure of valinomycin, the calculation is reduced to solving one transcendental equation in one variable.
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    Notes: The double-helical complex formed from m6m9A and poly U has been characterized by circular dichroism and u.v. spectrophotometry. The circular dichroism of the complex is similar to that of the double-helical poly A poly U complex both in shape and in magnitude and thus indicates a quite similar structure. The double Helix-coil transition has been studied at various nucleotide concentrations and at three different ionic strengths. As expected for the binding of a base to a polymer, the Helix-coil transition is shifted to higher temperatures by increasing nucleotide concentrations, but is not affected by changes of the ionic strength. The melting curves are analyzed according to a linear Ising model taking the stacking of the monomers into account. At 0°C the equilibrium constant for nucleation is found to be 2-5 M-1 and that for chain growth is 500 M-1. The enthalpy change associated with chain growth is -11.2 ± 1 kcal M-1.
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    Biopolymers 12 (1973), S. 1479-1491 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: A molecular field theory, taking into account long-range electrostatic forces is used to study helix-coil transitions of polynucleotides. The theory predicts the existence of hysteresis when the electrostatic interaction parameter is large compared to the thermal energy. The theory is applied to the acid-base titration of poly(A)·2 poly(U).
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  • 57
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    Notes: Helix-coil transition of polypeptides in solution involves two elementary processes: unfolding of an α-helical polypeptide chain and interaction of the unfolded chain with solvent molecules which are capable of forming hydrogen bonds. Optical rotation data for poly(β-benzyl L-aspartate) in mixtures of dichloroacetic acid and carbon tetrachloride are analyzed according to the procedure developed by Sayama et al., who explicitly took these processes into theoretical account; and the enthalpy changes, ΔH0 = -650 ± 200 cal/mole and ΔHa = -5.2 ± 1.6 kcal/mole. The latter value is favorably compared with heats of association (per hydrogen bond) of various amides and lactams in CCl4. There is excellent agreement with -5.15 kcal/mole for δ-valerolactam in CCl4. In analogy with amides in non-polar solvents, the difference between ΔH0 and ΔHa may be attributed to the fact that the former is associated with intramolecular hydrogen bonding, whereas the latter is associated with intermolecular hydrogen bonding.
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    Biopolymers 12 (1973), S. 1451-1458 
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    Topics: Chemistry and Pharmacology
    Notes: The coil to helix conformational transitions undergone by poly-γ-benzyl-L-glutamate in solutions of haloacetic acids and various cosolvents were studied by means of proton magnetic resonance. The results indicate a very small solvent dependence of the α-CH Helix-coil chemical shift difference. The helical stabilities of PBLG in different solvent mixtures were interpreted in terms of modifications of the “solvent structure.”
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    Biopolymers 12 (1973), S. 1781-1786 
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    Topics: Chemistry and Pharmacology
    Notes: By X-ray diffraction method, an originally almost dry oriented fiber of sodium poly-L-glutamate was shown to undergo transconformation from β-structure to α-helices when its water content was gradually increased by equilibrating with the helium gas of 64% relative humidity. The observation is correlated to the corresponding infrared spectroscopical study made by Blout et al.
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    Biopolymers 12 (1973), S. 1837-1852 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: An analytic cyclization procedure has allowed the complete specification of c-(Pro-Gly)3 conformation by three dihedral angles. Utilizing this simplification, the intramolecular potential energy of c-(Pro-Gly)3 has been computed over all of conformational space. Conformers with all peptide bonds trans have the lowest total potential energy. Circular dichroism spectra calculated for the low-energy regions provide the basis for the interpretation of experimental CD spectra.
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    Biopolymers 12 (1973), S. 1905-1915 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The storage and loss shear moduli, G, and G˝, have been measured for solutions of three samples of poly-γ-benzyl-L-glutamate with molecular weights from 16 to 57 × 104, by use of the Birnboim-Schrag multiple-lumped resonator. The frequency range was 106 to 6060 Hz, the concentration range 0.0015-0.005 g/ml, and the temperature 25°C. Two helicogenic solvents with widely different viscosities, dimethylformamide and m-cresol, were used to provide a broader effective frequency range. The intrinsic moduli, extrapolated to infinite dilution, were compared with the predictions of the theory of Ullman for rigid rods; agreement was rather good at the lowest frequencies, but unsatisfactory at high frequencies. The data over the entire frequency range of three of logarithmic decades could be described closely by a relaxation spectrum consisting of one terminal relaxation time separated by a gap from a sequence of relaxtion times spaced as in the Zimm theory. The terminal time agrees approximately with that calculated for end-over-end rotation of a rigid rod. The additional relaxation mechanisms are tentatively attributed to modes of flexural deformation of the helix.
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    Biopolymers 12 (1973), S. 1931-1935 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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  • 63
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The change in surface tension of solutions of poly-L-lysine in water has been studied as a function of temperature at various pH values. The changes at various temperatures have been correlated with changes in the circular dichroic spectra reflecting conformational change. In addition to the major transition at 50°C attributed to the conversion of the α-helical → β conformation, two other transitions have been observed at 30°C and 80°C.A minimum in the surface tension value was observed at pH 10, near the pK value for poly-L-lysine. It was concluded that at this pH the concentration of hydrophobic groups at the surface was a maximum.
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  • 64
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    Biopolymers 12 (1973), S. 2007-2021 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MS2 RNA, which sediments at 27S in a neutral buffer, can be converted to a compact 57S conformation at pH 3.8. Requirements for this conversion, besides protonation, are small concentrations of Mg++ ions and a low ionic strength. On the other hand, after heating in the presence of EDTA and at low ionic strength, the RNA can be unfolded to an 11.7S form at pH 6.8 and to 10.5S at pH 3.8. The compact 57S form has lost at least 50% of its secondary structure, as determined by its hypochromicity. It corresponds to a monomer species, as will be shown in a following paper (XXIV). Comparative studies with the homopolymers poly A and poly C and with the heteropolymers poly A,U, poly A,C, and poly A,G indicate that the interactions involved in the acid RNA conformation are not simply explainable by the known interactions of the A-A+, C-C+, and/or A-C+ type.
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  • 65
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    Biopolymers 12 (1973), S. 2329-2334 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of two salts, MgCl2 and MgSO4 on the wide-line nmr spectrum of D2O in oriented, undernatured collagen fibers have been examined at four different D2O contents. MgCl2 was found to decrease the nmr doublet splitting, as compared with equal quantities of pure D2O while the major effect of MgSO4 was to inhibit the adsorption of D2O without significantly affecting its nmr spectrum. The results, together with a few observations of KCl and LiCl solutions, indicate that even fairly high concentrations of salt have only small effects on the nmr spectrum of D2O in fibrous collagen. It is considered unlikely that either “two-state” or “structured-water” models can satisfactorily account for the D2O-nmr doublet spectrum or the effects of salts on it, over the entire range of observed D2O content.
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  • 66
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    Biopolymers 12 (1973), S. 2359-2373 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligopeptides containing glycine and one or two L-alanyl or L-glutamyl residues have been studied by circular dichroism (CD) and optical rotatory dispersion (ORD) in aqueous solution at pH 1.0, pH 6.0, and pH 10.0 and in aqueous ethanol. Two glycyl residues are required to remove effects of α-carboxyl or amino titration on the optical activity of the internal alanyl or glutamyl residues. The CD spectra of the alanyl and protonated glutamyl residues are similar, having two regions of negative ellipticity around 215 nm resulting in a spectrum reassembling that of poly-α-L-glutamic acid (PGA) at high pH. Another large positive band below 190 nm was observed for gly2-glu2-gly2 in water at pH 6 and 10 and for several peptides in aqueous ethanol. Residue ellipticities were approximately additive in every case except for peptides containing intrenal glutamyl residu at pH 6.0.
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    Biopolymers 12 (1973), S. 2431-2434 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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    Biopolymers 12 (1973), S. 2439-2441 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 69
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    Biopolymers 12 (1973), S. 2443-2458 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To attempt to resolve the controversy over “fast” and “slow” helix-coil transition rates in polypeptides, nuclear magnetic resonance spectra were measured for monodisperse poly-γ-benzyl-L-glutamate (PBLG). These results were compared with simulated line spectra which were computed by taking the molecular-weight distribution into consideration. Broad but single peaks have been observed in 220 mHz nmr for the α-CH and NH proton resonance spectra in the transition region. The shape of the line changes with the extent of polydispersity. Assuming a fast conversion rate, a molecular model of the helix-coil transition simulates these results. Consequently, the double peak which has been observed in the nmr of polypeptides at the helix-coil transition region is shown to result from the polydispersity in molecular weight.
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    Biopolymers 12 (1973), S. 2513-2519 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved method for the preparation of Merrifield resin esters is presented. This method is rapid, is free of racemization, and is not complicated by a quaternization side reaction. Chloromethylated resin beads, t-butoxycarbonyl amino acid, and potassium t-butoxide are heated at 80 °C in dimethylsulfoxide for one-half hour to yield resin esters of suitable substitution for solid-phase petide synthesis. All twenty of the BOC protected common amino acids were esterified to the resin by this method. Resin substitution values lie in the range of 0.13 meq/g (BOC-Glu (NH2)) to 0.66 meq/g (BOC/Pro), with most of the amino acids yielding 0.3-0.4 meq/g (on a resin containing 0.8 meq Cl/g).
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    Biopolymers 12 (1973), S. 2177-2183 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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    Biopolymers 12 (1973), S. 2185-2188 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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  • 73
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    Biopolymers 12 (1973) 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 74
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    Biopolymers 12 (1973), S. 2279-2288 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of hemoglobin deoxygenation is measured as a function of inorganic phosphate concentration, pH, and temperature. Isokinetic relationships (enthalpy-entropy compensation) are searched for by applying the method of O. Exner and, for comparative purposes, the conventional method of plotting the energy of activation (E*) versus the natural log of the pre-exponentional factor of the Arrhenious equation (In A). Both plots indicate compensation between the activation parameters. However, unlike the conventional plot, the Exner treatment is able to distinguish between two types of compensation. Furthermore, when extrapolated rate constants based on all the data in an Exner plot are transposed into E* vs. In A plots, so-called “turn-around” behavior is predicted for the effect of increasing phosphate concentration at constant pH. Such “turn-around” behavior in E* vs. In A plots has been observed experimentally by Beetlestone and co-workers for anion binding to human hemoglobin as a functin of pH. Lastly, the compensation temperatures obtained from these data all fall within the Vaslow-Doherty compensation range (250-350°K) which is thought to indicate that the solvent, water, is involved in the reaction mechanism. Thus, Exner plots appear to further resolve isokinetic temperatures of the Vaslow-Doherty type. Differences in the electrostriction of solvent in the activated state is suggested as one possible physical source for the Vaslow-Doherty type compensation observed in this work.
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    Biopolymers 12 (1973), S. 2303-2307 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Determinations of the amount of bound water in hydrated proteins yield strongly diverging values. The cause of this is the continuity of the transition from bound to free water, and the diffeernt sensitivities to water structure of the measuring techniques. Only the methods that aim at the determination of the amount of water, whose phase remians unchanged duing freezing, yield similar values. The value for collagen as deduced from conductivity data is about 50% water of the dry weight. It is believed that this water interacts with adsorptive groups on the macromolecules, whereas the freezable water occurs in capillaries.
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    Biopolymers 12 (1973), S. 2375-2380 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cis-trans isomerism was investigated with N-acetyl and N-propionyl, N-alkylglycine dimethylamides as model compounds for poly(N-alkylglycine dimethlamides as model compounds for (N-alkylglycine)s using n.m.r. spectroscopy. The population of the cis isomer measured in benzene and methylene chloride solutions did not show any marked dependence on the bulkiness of N-alkyl substituents. This contrasts with polyN-alkylglycine)s, whose cis isomer population increased with the introduction of bulky N-alkyl groups. Kinetics of the Cis-trans isomerization was also investigated with N-acetyldimethylamides of sacrosine, N-n-propylglycine, and N-isopropylglycine in tetrachloroethane solution. The δG
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    Biopolymers 12 (1973), S. 2477-2490 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possibility of convection in velocity sedimentation studies on pressure dependent associating systems is known both experimentally and theoretically. We present accurate numerical solutions to the Lamm equation to illustrate this phenomenon for monomer-polymer systems. An approximate theory based on the absence of diffusion is then developed to predict the onset of convection. Comparison of the theory with the numerical solutions shows it to be quite accurate.
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  • 78
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    Biopolymers 12 (1973), S. 2539-2548 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The induced Cotton effect of some acid polysaccharide-thiazine dye complexes were studied at various temperatures. When the equivalent ratio of the anionic site of the polymer to the cationic dye was near unity, all the complexes examined showed remarkable Cotton effects corresponding to their absorption bands in the visible and ultraviolet regions, at neutral pH and room temperature. Although the structure of the hyaluronate complex resembles the carbohydrate backbone, the sign of the Cotton effects was opposite that of chondroitin sulfate complexes.When the temperature was raised, the hyaluronate-toluidine blue complex decreased the metachromatic shift in the absorption spectrum gradually; the amplitude of the Cotton effects of this complex decreased also. With a polysaccharide which has a carboxylate group as its only anionic site (such as carboxymethylcellulose or pectic acid), a similar effect of temperature was observed on its induced Cotton effects.With the chondroitin 4-sulfate-toluidine blue complex, some reverse of the metachromatic shift was observed at higher temperature. However, the amplitude of its Cotton effects decreased up to 70 °C, then the sign of the effects reversed and the amplitude subsequently increased. A similar inversion of the sign of the Cotton effects was found with the chondroitin 6-sulfate-toluidine blue complex, but at a lower temperature (about 40 °C).Charonin sulfate, a highly sulfated cellulose-like glucan from a marine mollusca, showed a marked metachromatic effect on methylene blue even at the elevated temperature. The induced Cotton effects of this complex were also affected by temperature and the inversion of the sign was observed.When the pH was lowered, the amplitude of the Cotton effects of the hyaluronate-toluidine blue complex decreased and diminished at pH 3, at room temperature. With chondroitin 4-sulfate, the induced Cotton effects were remarkable at such a low pH; however, the amplitude of the effects decreased with elevated temperature and no inversion was observed. The optical rotatory dispersion of the chondroitin 6-sulfate-toluidine blue complex was reversed by acidifying to pH 3, and the amplitude of the Cotton effects decreased by elevating the temperature.
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    Biopolymers 12 (1973), S. 2491-2512 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dilute solutions of rigid helical macromolecules with permanent dipole moments have been studied with dielectrophoresis. The polymers used were poly-γ-benzyl-L-glutmate and poly-n-butyl isocyanate, both fractions of average molecular weight 120,000. In this phenomenon dipolar molecules migrate in an inhomogeneous electric field towards the region of maximum field strength. The field gradient is produced by a 10-μm diameter Pt wire serving as the inner electrode of a cell, and a 2.5-mm diameter cylinder as the outer electrode. An equilibrium exponential concentration gradient is achieved within a few wire radii of the inner electrode in a matter of minutes, making both kinetic and equilibrium measurements feasible. The concentration gradient is monitored by measuring the change in capacitance ΔC of the cell from its value for a uniform solute concentration. The time dependences of ΔC for the build-up of the concentration gradient towards the equilibrium value, and the decay to a uniform concentration after the field is removed have been calculated, using a frictional coefficient and a Boltzmann factor, β1, as the sole adjustable parameters.For low voltages (β1 small), the measured build-up and decay are completely symmetrical, in agreement with theory, and yield the same frictional coefficient. For larger β1, the build-up is faster, reflecting a reduced frictional coefficient due to partial alignment of the long axes of the polymers in the direction of migration. In either case, the decay determines a diffusion constant of randomly aligned molecules, identical to classical diffusion measurement.The value of ΔC at equilibrium, for β1 small, determines μ2F2, where μ is the dipole moment and F is the internal field at the polymer. Combined with a classical dielectric constant measurement, which gives μ2F, both μ and F may be determined, independent of assumptions about cavity shapes.Dielectrophoresis works in alternating as well as constant fields, provided the dipolar orientation can follow the field reversals. The dispersion of dielectrophoresis with frequency is a sensitive measure of the molecular-weight distribution of a given sample.
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    Biopolymers 12 (1973), S. 2589-2598 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature-dependent conformations of poly(U) in 0.5M CsC1 have been studied by carbon-13 nuclear magnetic resonance. The transition from random coil to an ordered structure results in broadening of lines in the 13C spectra, due to intramolecular 1H-13C dipolar interactions and restricted motions in the ordered state. Changes in the chemical shifts suggest that the bases are interacting below the transition temperature. The random coil form shows conformation preferences for internal rotation about C4′-C5′, C5′-O5′, and C3′-O 3′ bonds. The statistical randomness of the coil arises mainly because of flexibility about O-P bonds. The results are analyzed in conjunction with theoretical calculations and light-scattering data.
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    Biopolymers 12 (1973), S. 2607-2622 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements of the electric birefringence of suspensions of T4B in the absence of tryptophan and of fiberless T4 particles show that both kinds of particles are hydrodynamically equivalent. Their rotational diffusion coefficients corrected to 25°C and water viscosity (D25,w) are 280 ± 9 sec-1 and 295 ± 10 sec-1, respectively. These corrected rotational diffusion coefficients are almost independent of buffer concentration and temperature. The sedimentation coefficient (s20,w) of T4 B is equal to 1023 ± 12 S, a value which is likewise independent of buffer concentration.By analysis of the field strength dependence of the steady-state birefringence and by reversing pulse experiments it could be shown that the orientation in an electric field is largely due to a permanent dipole moment. This dipole moment is somewhat dependent on buffer concentration and amounts to about 24,000 debye for T4B and 95,000 debye for fiberless T4. An approximate calculation shows that the difference in dipole moment may be ascribed to positive charges on the fiber tip (at least ten per fiber), to negative charges along the fiber or (and) positive charges on the fiberless particle at those places where the fibers are attached in normal particles.
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electric birefringence of poly-L-lysine hydrobromide in methanol-water mixtures has been measured at 25 °C over a wide range of field strengths by use of the rectangular pulse technique. An abrupt change in the specific Kerr constant was observed between 87 and 90 vol % methanol, corresponding to the solvent-induced helix-coil transition. The specific Kerr constant increased rapidly with dilution in the random coil form, and more slowly in the helical conformation. The field strength dependence of the bire fringence at various concentrations, for both the helical and coil conformations, can be described by a common orientation function, which resembles the theoretical one for the case of permanent dipole moment orientation. This is interpreted in terms of the saturation of ion-atmosphere polarization. The optical anisotropy for the helical conformation was much larger than that for the coil form.Anomalous birefringence signals were observed above a critical field strength (about 5 kV/cm) in 90 vol % methanol. The birefringence passed through a maximum and began to decrease slowly before the pulse terminated, reaching a steady-state value. This steady-state value was closer to that of the coil in the coil in the limit of very high fields. The results indicate that a transition from the charged helix to the charged coil is induced by high electric fields in the transition region. This effect can be explained on the basis of the polarization mechanism proposed by Neumann and Katchalasky.
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  • 84
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The buoyant density and potentiometric titrations of six ionizable homopolypeptides in concentrated CsCI solutions have been studied. These six homopolypeptides were chosen as models of the behavior of ionizable residues in proteins. Their buoyant and potentiometric results will be of value in interpreting the buoyant and potentiometric results observed for proteins.The buoyant densities for all six homopolypeptides were found to increase sigmoidally as the pH is increased. These density changes are interpreted in terms of changes in the hydrations and ion binding which are associated with the titration of the residues. Preferential hydrations for the homopolypeptides are calculated. The buoyant density titrations are combined with the potentiometric titrations to determine the relationship between the buoyant density and the degree of ionization.A better method of computing buoyant densities of proteins is described. The slope of β(ρ) has been computed for CsCl using least-squares curve fitting and this is used in calculating the isoconcentration position. This method has been found to be more accurate than calculating the isoconcentration position from the normalized isoconcentration ratio, which is known only under limited conditions.
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    Biopolymers 12 (1973), S. 2853-2883 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pH titration behavior of E. coli rRNA in the acid range has been analyzed by combining spectrophotometric and potentiometric titration data. The “simplest” model for the system, which considers as possible reactions the protonation of adenine (A), cytosine (C), and guanine (G) residues along with the opening of A·U and G·C base pairs, does not adequately account for the titration properties. It is postulated that extra reactions may occur in addition to those in the “simplest” model, and a new analytical method was developed to deal with this situation. Our approach yields the ultraviolet spectral changes which accompany the extra reactions, from which the nature of these reactions can in principle be deduced. The calculations also give, at each pH, the extents of the extra reactions as well as the extents of those reactions which comprise the “simplest” model.We infer that in acidic RNA solutions of 0.1M ionic strength there occur at least two extra reactions, each of which involves G residues. We propose that in the pH range 6.0 ≥ pH ≥ 3.8 triple-stranded helical sequences, presumably protonated G·C·G, are formed. These regions are replaced at lower pH by acid-stable structures involving G·G and A·A base pairs. In solutions of lower ionic strength (I = 0.01M) no triple strands are formed, but G·G and A·A regions seem to develop even at pH values as high as 6.0. At I = 0.1M, an acid-base titration cycle between pH 7 and 2.8 is not reversible; rRNA shows true hysteresis behavior. We conclude that in ribosomal RNA's, which are generally G-rich, guanine residues may participate in hitherto unpredicted conformations, some of which may be metastable while others are equilibrium structures.
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  • 86
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Directed Synthesis of Sulfinato-O and -S Complexes of some Transition Metals, VII. Sulfinato Complexes of Chromium(II), Manganese(II), Iron(II), Cobalt(II) and Nickel(II) with Mono- and Bidentate Nitrogen Ligands.The hitherto unknown, pseudooctahedral configurated bis(organosulfinato-O,O')dipyridine compounds of manganese(II), iron(II), cobalt(II) and nickel(II) 5a, b and 6a-8a are obtained by the reaction of the complexes (p-R-C6h4SO2)2M(OH2)2 1a, b and 2a-4a with pyridine according to equation (1). Linkage or stereo isomers cannot be detected.  -  White (p-CH3C6H4SO2)2Cr(OH2)2 (9) reacts with 2 moles of 2,2′-bipyridyl in water according to equation (2) to form the sulfinato-O complex 10, the corresponding manganese compound 1a adds only 1 mole of 2,2′-bipyridyl according to equation (3), yielding the sulfinato complex 11O,O'. In the case of 9 other solvents are not leading to linkage isomers. In contrast to this the sulfinato complex 11S, being linkage and structural isomeric to 11O,O' is obtained from 1a and 2,2′-bipyridyl in pyridine according to equation (4). The iron compound 2c reacts only in THF with 2 moles of 2,2-bipyridyl according to equation (5) to give the sulfinato complex 12O, which is in pyridine irreversibly converted into the S-isomer 12S according to equation (6). 12S can also be isolated from 2c and 2 moles of 2,2′-bipyridyl in pyridine according to equation (7). The newly prepared compounds are characterized on the basis of their i.r. and their electronic spectra as well as by magnetochemical investigations.
    Notes: Bei der Umsetzung der Komplexe (p-R C6H4SO2)2M(OH2)2 1a,b und 2a-4a mit Pyridin erhält man gemäß Gl. (1) die bisher unbekannten, pseudooktaedrisch konfigurierten Bis(organosulfinato-O,O')-dipyridin-Verbindungen von Mangan(II), Eisen(II), Kobalt(II) und Nickel(II) 5a, b und 6a-8a. Bindungs- oder Stereoisomere lassen sich nicht nachweisen.  -  Während (p-CH3C6H4SO2)2Cr(OH2)2 (9) in Wasser gemäß Gl. (2) 2 mol 2,2′-Bipyridyl unter Bildung des Sulfinato-O-Komplexes 10 aufnimmt, addiert die entsprechende Mangen-Verbindung 1a gemäß Gl. (3) nur 1 mol 2,2′-Bipyridyl, wobei der Sulfinato-Komplex 11O,O' entsteht. Andere Lösungsmittel führen bei 9 zu keinen Bindungsisomeren. Dagegen erhält man aus 1a und 2,2′-Bipyridyl in Pyridin entsprechend Gl. (4) den zu 11O,O' bindungs- und strukturisomeren Sulfinato-Komplex 11S. Die Eisen-Verbindung 2c setzt sich nur in THF mit 2 mol 2,2′-Bipyridyl gemäß Gl. (5) zum Sulfinato-O-Komplex 12O um, welcher in Pyridin irreversibel entsprechend Gl. (6) in das S-Isomere 12S übergeht 12S läßt sich gemäß Gl. (7) auch aus 2c und 2 mol 2,2′-Bipyridyl in Pyridin isolieren., Die neu dargestellten Verbindungen werden anhand ihrer IR- und Elektronenspektren, sowie durch magnetochemische Untersuchungen charakterisiert.
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  • 87
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 288-311 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: X-Ray Structure Analysis of the 2 : 1-Cycloaddition Product of Diazomethane and 4-Methyl-1,1-bis(trifluormethyl)-2-aza-1,3t-butadieneThe structure of 1-(4-methyl-1-pyrazolin-3-yl)-5,5-bis(trifluormethyl)-Δ2-1,2,3-triazoline (C8H9F6N5) (4a), which is the 2 : 1-cycloaddition product of diazomethane and 4-methyl-1,1-bis(trifluormethyl)-2-aza-1,3t-butadiene, was solved by direct methods. Space group: Pbca; a = 19.839 Å, b = 12.985 Å, c = 8.826 Å 8 molecules per unit cell. The refinement by least squares methods yielded a final R index of 5.5% (for 1900 observed reflexions). The hydrogen atoms have been included into the refinement.The constitution of the molecule, which on chemical and physical ways could not unambigously be determined, has been evaluated. The binding situation is discussed and including hydrogen atoms a detailed conformational analysis is carried out. The crystal structure is discussed, too. It contains an interesting type of a hydrogen-bridge system.
    Notes: Die Lösung der Struktur des 1-(4-Methyl-1-pyrazolin-3-yl)-5,5-bis(trifluormethyl)-Δ2-1,2,3-triazolins (C8H9F6N5) (4a), dem 2 : 1-Cycloadditionsprodukt von Diazomethan und 4-Methyl-1,1-bis(trifluormethyl)-2-aza-1,3t-butadien erfolgte mit direkten Methoden. Raumgruppe: Pbca; a = 19.839 Å, b = 12.985 Å, c = 8.826 Å, mit 8 Molekülen pro Elementarzelle. Die Verfeinerung nach der Methode der kleinsten Quadrate konvergierte unter Einschluß der H-Atome bei einem R-Wert von 5.5% (für 1900 beobachtete Reflexe).DIE KONSTITUTION der Molekel, die auf chemisch-physikalischem Wege nicht eindeutig bestimmt werden konnte, wurde festgelegt. Es werden die Bindungsverhältnisse diskutiert und unter Einbeziehung der Wasserstoffatome eine detaillierte Konformationsanalyse durchgeführt. Gleichfalls wird auf die Kristallstruktur, die einen interessanten Typ eines Wasserstoffbrückensystems enthält, eingegangen.
    Additional Material: 11 Ill.
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  • 88
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 332-338 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: On the Hydrogenation of Δ2-5-IsoxazolonesThe Δ2-5-isoxazolones 1, 5, 8a-c, and 11a, b are opened under conditions of the catalytic reduction to yield β-enamino-β'-ketocarboxylic acids 6a, b. In a second step, the derivatives 8a-c, 11a, b form diazepines 10a-c and pyrazoles 12, 13 by intramolecular cyclization. The structures are elucidated on the basis of the n.m.r. and i.r. spectra.
    Notes: Die Δ2-5-Isoxazolone 1, 5, 8a-c und 11a, b werden bei der katalytischen Hydrierung unter reduktiver Ringöffnung zu β-Enamino-β'-ketocarbonsäuren 6a, b gespalten Dabei cyclisieren die Derivate 8a-c, 11a, b intramolekular zu den Diazepinen 10a-c und Pyrazolen 12, 13. Die Strukturen werden durch NMR- und IR-Spektren bewiesen.
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  • 89
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973) 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 90
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactions of Short-Life Radicals, IX1) Radical-Induced Decomposition of Esters of Peroxycarboxylic Acids: SH2 Reaction and Radical-Catalysed Fragmentation as Competing MechanismsThe radical decomposition of peresters RC(O)—O—OC(CH3,)3 R = C6H5, CH3, C(CH3)3 (1a-c) is induced very strongly by triethyltin hydride. A SH2 reaction and a radicalcatalysed fragmentation (a new type of reaction) are found to be competing mechanisms here. In both cases the stannyl radical is the attacking species. In the former reaction, splitting of the O—O bridge occurs with formation of the stannyl esters 3a-c. In the latter R· +CO2 ·OC(CH3) are formed, while the attacking radical is recovered. All products have been identified and quantitatively determined. From hall-life times and rate constants in the range of 21 -3O°, the following values have been calculated for the two competing reactions at 25° in the case of 1c: for the SH2 reaction ΔG+ = 22.7 kcal/mole, ΔS≠ = -19 e. u.; for the fragmentation ΔG≠ = -22.4 kcal/mole, ΔS+ = - 12 e. u. With 1a, the SH2 reaction dominates under all conditions. The importance of the competing catalysed fragmentation, however, increases greatly in the sequence 1a 〈 1b 〈 1c, and can become the main reaction. Dissociation energies and inductive effects of R, stereochemistry of transition states, temperature, and polarity of solvents are found to be of considerable influence.
    Notes: Der radikalische Zerfall von Perestern RC(O)—O—OC(CH3)3, R = C6H5, CH3, C(CH3)3 (1a-c) wird durch Triäthylzinnhydrid sehr stark induziert. Als konkurrierende Mechanismen werden eine SH2-Reaktion und, als neuartiger Reaktionstyp, eine radikal-katalysierte Fragmentierung beobachtet. In beiden ist das Stannyl-Radikal angreifendes Agens, in einem Fall unter Spaltung der O—O-Brücke und Bildung der Stannylester 3a-c, im anderen unter Bildung von R· +CO2 + ·OC(CH3)3 und Rückgewinnung des angreifenden Radikals. Entstehende Produkte werden qualitativ und quantitativ bestimmt. Für 1c ergibt sich aus Halbwertszeiten und Geschwindigkeitskonstanten im Bereich 21-30° für SH2-Reaktion bzw. Fragmentierung bei 25°: ΔG≠ = 22.7 kcal/mol, ΔS≠ = -19 e. u. bzw. 22.4 kcal/mol, -12 e. u. - Bei 1a überwiegt stets die SH2-Reaktion. In der Reihe 1a 〈 1b 〈 1c tritt jedoch die konkurrierende katalysierte Fragmentierung immer stärker hervor und kann zur Hauptreaktion werden. Dissoziationsenergien und induktive Effekte von R, die Stereochemie der Übergangszustände, Temperatur und Polarität des Lösungsmittels haben hierauf beträchtlichen Einfluß.
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  • 91
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 471-483 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Tautomerism of Heterocyclic Compounds, I. The Prototropic Tautomerism of “4-Quinazolylthioureas” and Related CompoundsThe prototropic tautomerism and hydrogen-bonding interactions of 4-quinazolylthioureas, -thioamides and a thiocarbamic acid ester are studied by spectroscopic methods (i. r. and n. m. r.). In case of thiocarbamic acid ester both tautomeric forms (10 and 11) can be isolated as crystalline solids.
    Notes: Die Tautomerieerscheinungen und Wasserstoffbrückenbeziehungen bei 4-Chinazolylthioharnstoffen, -thioamiden und einem -thiourethan werden IR- und NMR-spektroskopisch untersucht. Im Falle des Thiourethans können beide Tautomeren (10 und 11) in Substanz isoliert werden.
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  • 92
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 497-504 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Polyacetylenic Compounds, 2131) Novel Natural Sulphur Acetylenic CompoundsThe structures and configurations of four sulphur compounds isolated from Berkheya barbata (L. f.) Hutch. are established by synthesis of the two possible structure type (1 and 17)
    Notes: Die Konstitutionen und Konfigurationen von vier aus Berkheya barbata (L. f ) Hutch. isolierten Schwefel-Verbindungen werden durch Synthese der beiden möglichen Strukturtypen geklärt (1 und 17).
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  • 93
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973) 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 94
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 1-7 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: On a [3 + 1] Cycloaddition, II. Reactions of 4,5-Dihydro-1,3,5-oxazaphosph(V)olen, VI4,5-Dihydro-1,3,5-oxazaphosph(V)oles 1 react with isonitriles to yield disubstituted 3-imino-4,4-bis(trifluoromethyl)-1-azetines 2 with elimination of phosphoric acid esters. The reaction should proceed via nitrile ylides.
    Notes: 4,5-Dihydro-1,3,5-oxazaphosph(V)ole 1 reagieren mit Isonitrilen zu disubstituierten 3-Imino-4,4-bis(trifluormethyl)-1-azetinen 2 unter Ehmmierung von Phosphorsäureester Eine Nitrilylid-Zwischenstufe wird angenommen.
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  • 95
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 882-887 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 17β-CyclobutenylsteroidsThe 21-mesylate derivative 1c of 3β,21-diacetoxy-5α-pregnan-20-one (1a) reacts with dimethyl(methylene)sulfonium oxide to give the aldehyde 2. Reduction of the aldehyde leads to the corresponding alcohol 3, which is easily dehydrated with ring expansion to the cyclobutenyl derivative 4a. After saponification and oxidation 17β-(1-cyclobuten-1-yl)-5α-androstan-3-one (5) is obtained.
    Notes: Ausgehend vom 3β,21-Diacetoxy-5α-pregnan-20-on (1a) gelangt man durch Umsetzung des 21-Mesylats 1c mit Dimethyl(methylen)sulfoniumoxid zum Aldehyd 2. Nach Reduktion zum Alkohol 3 erfolgt leicht Dehydratisierung unter Ringerweiterung zum Cyclobutenyl-Derivat 4a. Nach Verseifung und Oxidation erhält man das 17β-(1-Cyclobuten-1-yl)-5α-androstan-3-on (5).
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  • 96
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 893-901 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Mechanism of the Formation of 4-Amino-5-aminomethyl-2-methylpyrimidine from 2-(Diethoxymethyl)-3-ethoxypropionitrile and AcetamidineThe mechanism of the formation of 4-amino-5-aminomethyl-2-methylpyrimidine (3) from 2-(diethoxymethyl)-3-ethoxypropionitrile (5) and acetamidine has been investigated by means of labelled compounds 5 which contained the C ≡ 15N, 14C ≡ N, and 14CH(OC2H5)2, respectively. The labelled 3 was subjected to a series of degradation reactions. From the distribution of the isotopes it has been proved as follows: The nitrogen of the C ≡ N group is incorporated either into the 3-position or into the amino group at the 4-position of 3 in a ratio of ca. 1 : 1. The carbon atom at 6-position originates from HCO2R. The formation of 3 probably proceeds through the routes c and d.
    Notes: Der Bildungsmechanismus von 4-Amino-5-aminomethyl-2-methylpyrimidin (3) aus 3-Äthoxy-2-(diäthoxymethyl)propionitril (5) und Acetamidin wurde mittels markiertem 5, das die C ≡ 15N-, 14C ≡ N- bzw. die 14CH(OC2H5)2-Gruppe enthielt, untersucht. Das markierte 3 wurde einer Reihe von Abbaureaktionen unterworfen. Aus der Verteilung der Isotope ergibt sich, daß der Stickstoff der C ≡ N-Gruppe in 3-Stellung oder in die 4-Aminogruppe von 3 mit einer Wahrscheinlichkeit von ca. 1 : 1 eingebaut wird. Der Kohlenstoff in 6-Stellung leitet sich aus HCO2R ab. Die Bildung von 3 verläuft wahrscheinlich auf den Wegen c und d.
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  • 97
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 69-77 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Tris(chloromethyl)amine and Bis(chloromethyl)methylamine. Synthesis and Chemical ReactionsThe title compounds (1, 8) were synthesized by reaction of PCl5 with hexamethylenetetramine or 1,3,5-trimethylhexahydro-s-triazine, respectively. The reactions of 1 and/or 8 with SbCI5, SnCl4, sodium methylate, sodium acetate, phenyllithium, Grignard compounds, sec. amines and ethanethiol are described. The reaction products, tertiary amines, partially unknown as yet, are characterized.
    Notes: Die Titel-Verbindungen (1,8) wurden durch Umsetzung von PCl5 mit Hexamethylentetramin bzw. 1,3,5-Trimethylhexahydro-s-triazin dargestellt. Die Reaktionen von 1 und/oder 8 mit SbCl5. SnCl4, Natriummethylat, Natriumacetat, Phenyllithium, Grignard-Verbindungen, sek. Aminen und Äthanthiol werden beschrieben. Die Reaktionsprodukte, teilweise bislang nicht beschriebene tertiäre Amine, werden charakterisiert.
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  • 98
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Fragmentation Reactions of Carbonyl Compounds with Electronegative ß-Substituents, XXIII cis- and trans-4.4.8.8-Tetraalkyl-2.6-dioxabicyclo[3.3.0]octanes from 1.6-Bis(tosyloxy)-2.2.5.5-tetraalkyl-3.hexandionesDiketoditosylates 8 and 9a-c are prepared and reduced with NaBH4. 8 yields 16a and a cis-trans mixture of 23; 9a-c afford the tetrahydrofuranols 14a-c and the cis-2.6-dioxabicyclo[3.3.0]octanes 21a-c. 14a-c and 16a react with NaOH in methanol to form the pure trans-compounds 21a-c and 23. Solvolysis of 9a with excess NaOH in methanol leads to the tetrahydrofuranone 13a and to the bicyclo acetal 22a. Solvolysis of 9b with only 2 equivalents of NaOH yields thc intermediate 12, which can be isolated and converted to 13b and 22b.The trispiro compound 27 is isolated as an unexpected side product from the NaBH4-reduction of 9b.
    Notes: Die Diketo-ditosylate 8 und 9a-c werden dargestellt und mit NaBH4 reduziert. 8 liefert 16a und ein cis-trans-23-Gemisch, aus 9a-c werden die Tetrahydrofuranole 14a-c und die cis-2.6-Dioxa-bicyclo[3.3.0]octane 21a-c erhalten. 14a-c und 16a reagieren mit NaOH in Methanol zu den reinen trans-Verbindungen 21a-c und 23. Die Solvolyse von 9a mit überschüssigem NaOH in Methanol führt zu dem Tetrahydrofuranon 13a und dem bicyclischen Acetal 22a. Mit 2 Äquivv. NaOH kann aus 9b die Zwischenstufe 12 isoliert und erneut zu 13b und 22b umgesetzt werden.Als ungewöhnliches Nebenprodukt tritt bei der NaBH4-Reduktion von 9b die Trispiroverbindung 27 auf.
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  • 99
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 150-156 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Asteranes, IX. Synthesis and Structure of Tetramethyltetraasteranes1,2,7,8- and 1,4,5,8-tetramethylpentacyclo[6.4.0.02.7.04.11.05.10.]dodecane (3 and 6) are obtained by Wolff-Kishner reduction of the cage dimers from 2,3- and 2,5-dimethyl-p-benzoquinone via the tetrahydrazones 2 and 5. The structure of 6 is confirmed by X-ray-diffraction analysis.
    Notes: Wolff-Kishner-Reduktion überführt die Käfigdimeren aus 2,3- und 2,5-Dimethyl-p-benzochinon in 1,2,7,8- und 1,4,5,8-Tetramethylpentacyclo[6.4.0.02.7.04.11.05.10]dodecan (3 und 6), wobei es notwendig ist, die Tetrahydrazone 2 und 5 zu isolieren. Die Struktur von 6 wird durch Röntgenanalyse bestätigt.
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  • 100
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    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 106 (1973), S. 382-387 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Naturally Occuring Coumarin Derivatives, IX1) On the Constituents of the Genus GerberaThe roots of several Gerbera species contain the known polyynes 1 and 2. In addition from Gerbera crocea the acetophenon derivative 3 and two new coumarins (4 and 7) were isolated, the structures being elucidated by spectroscopic data as well as by synthesis.
    Notes: Die Wurzeln mehrerer Gerbera-Arten enthalten die bekannten Polyine 1 und 2. Aus Gerbera crocea wurden zusätzlich das Acetophenon-Derivat 3 und zwei neue Cumarine (4 und 7) isoliert, deren Strukturen durch spektroskopische Daten sowie durch Synthese geklärt werden.
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