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  • Articles: DFG German National Licenses  (7,211)
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  • 101
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 961-972 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A previous equilibrium model is generalized to study time-dependent behavior of hemoglobin and allosteric enzymes. An exact solution for two interacting subunits (e.g., diheme) is given, and a general method for solving the resulting set of differential equations is outlined. At half saturation (equilibrium) concentration, the model takes a particularly simple form which suggests an experiment to determine the number of subunits of an allosteric enzyme, or in particular to distinguish diheme from ordinary hemoglobin. The relation between the present model and other kinetic models is also discussed.
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  • 102
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 973-989 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper a microscopic model is developed which considers conformational changes in polypeptides. The model applied here to diglycine involves calculation of torques due to pairwise interatomic forces acting about the two single bonds (N—C and C—C′) of the peptide unit. Account is taken of Brownian motion and rotational frictional resistance in addition to a van der Waals 6-12 potential, a classical electrostatic potential and a torsional potential. The rates of the conformational transition from an initial α-helical position are computed. The mechanism of Conformational change is a random walk within the minimum well followed by a jump out of the minimum into another portion of the energy surface. The latter process occurs when a fluctuation carries the dipeptide into a high energy region of the potential surface. Correlation times for the process are computed. Estimates are made for the relaxation times for the process. A first passage-time treatment is developed and used to compute internal diffusion coefficients for the relaxation process.
    Additional Material: 5 Ill.
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  • 103
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 991-1001 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sedimentation coefficient of calf thymus and of T7 DNA was determined at several concentrations up to saturation in solutions of each of the following salts: MgCl2, MgBr2, and MgSO4. Under certain conditions, a plot of the product of the relative viscosity and sedimentation coefficient against the density of the solution has been found to be linear and to extrapolate to zero at a density corresponding to that of the solvated molecule. This behavior was realized in MgSO4 solutions, the zero intercept occurring at a density of 1.41 g/cc, corresponding to a wafer activity of 0.89. The preferential solvation of DNA in MgSO4 solutions calculated for this value is 10.5 moles water/mole of nucleotide, in good agreement with published values of solvation of DNA at the same water activity in univalent salt solutions. Since linear plots were not obtained in MgCl2 and MgBr2 solutions, buoyant densities could not be determined in these cases. The nonlinear behavior observed in MgCl2 and MgBr2 solutions may be due to a change in shape of the DNA molecule at the lower water activities reached in these solutions. The possibility of increased DNA-solute interactions in MgBr2 and MgCl2 solutions is also considered as an explanation for the difference in behavior between MgSO4 and the two magnesium halides.
    Additional Material: 5 Ill.
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  • 104
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction between acridine orange (AO) and deoxyribonucleic acid (DNA) was studied by the stopped-flow method. The spectral change of AO due to interaction with DNA was followed over the wavelength range 350-600 nm at various concentration ratios of DNA phosphate to dye. The spectral change observed by the stopped-flow method was found distinctly different from that, during the dead-time, leading to a conclusion that the binding of AO to the outside of DNA occurs much faster than the intercalation into base pairs of DNA. The dependence of the rate of reaction on the reactant concentration and on the salt, concentration of the solution was also studied. The results are consistent with the mechanism that the intercalation proceeds via the outside bound state.
    Additional Material: 8 Ill.
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  • 105
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1013-1019 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strong magnetic field has been utilized to orient the liquid crystalline phase of concentrated polypeptide solutions enabeling the preparation of nematic solid films. The uniaxially oriented nematic films are suitable for x-ray studies of the polypeptide backbone chain conformation. A distorted α-helix with 3.5 residues per turn is observed in nematic films of the L-isomer of poly (benzyl glutamate) when the film is cast from chloroform. The normal α-helix (3.6 residues per turn) is found in similarly prepared films cast from dichloromethane.
    Additional Material: 2 Ill.
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  • 106
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Infrared spectra of homo- and co-oligopeptides containing glutamate residues were studied in both solution and solid state. Conformational analyses of these oligomers were carried out by using amide I and II band frequencies. Trimethyl phosphate supports the folded structure of oligomers above the heptamer. In chloroform solution, these oligomers assume the β-extended structures above the pentamer.
    Additional Material: 5 Ill.
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  • 107
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ultraviolet absorption and circular dichroism spectra of azlactones derived from N-acetoacetyl amino acids are examined. A number of model compounds of the isomeric forms possibly present in the equilibrium mixtures of these azlactones have also been prepared and their spectral properties compared. The reported data permit, structural and stereochemical assignments on these amide compounds.
    Additional Material: 8 Ill.
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  • 108
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 2377-2386 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The far-infrared absorption spectrum (40-400 cm-1) of solid pellets and films of several globular proteins (lysozyme, myoglobin, hemoglobin, serum albumin, ribonuclease, chymotrypsinogen, subtilisin) and of some representative polypeptides [nylon 66, poly (γ-benzyl L-glutamate)] have been investigated by using a Michelson interferometer. While polypeptides are known to present several peaks which can be assigned mostly to hydrogen-bond modes, all the investigated globular proteins display only one broad, intense baud in the 100-200 cm-1 region. The origin of this band, which persists even after denaturation or partial digestion, is discussed.
    Additional Material: 6 Ill.
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  • 109
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 2435-2443 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of rotation of the peptide (amide) bond in dimethylacetamide, glycine dimethylamide, N-acetylsarcosine, and glycylsarcosine have been studied in basic, neutral, and acidic aqueous solutions by proton magnetic resonance spectroscopy. The data indicate that the presence of nearby negative or positive charges do not greatly perturb the energetics of conformational equilibration about the amide carbon-nitrogen bond. In N-acetylsarcosine and glycylsarcosine two distinguishabe conformers are present; their relative abundance is essentially 50%/50% except at low pH. It is suggested that intramolecular hydrogen bonding is responsible for deviations from this population ratio. The activation enthalpies (ΔH
    Additional Material: 1 Tab.
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  • 110
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971) 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 111
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 9-18 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Bedeutung der Abgase aus Verbrennungsmotoren wie auch aus Düsenstrahltriebwerken spielt mit wachsender Motorisierung eine immer größere Rolle für die Luflverunreinigung. In den USA beträgt der Anteil auf diese Art entstandener Schadstoffe an der Gesamtbelastung heute schon mehr als 60%, in der Bundesrepublik liegt er über 40%.
    Additional Material: 10 Ill.
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  • 112
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 27-28 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
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  • 113
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 33-40 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Ill.
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  • 114
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 43-49 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
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  • 115
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 63-64 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 116
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 61-62 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 117
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 107-113 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 118
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    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 5 (1971), S. 114-124 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 23 Ill.
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  • 119
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1039-1048 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dielectric dispersion and viscosity measurement, s were performed on apotransferrin and transferrin monomers in aqueous solutions so as to check the influence of iron binding on the overall conformation of the molecule. Iron saturation by two iron atoms per transferrin molecule modifies the parameters of the equivalent ellipsoid. The molecule becomes more spherical while its hydration value remains high.
    Additional Material: 7 Ill.
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  • 120
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Acetyl-amino acid methylamides CH3CONHCHRCONHCH3 were prepared from L- and DL-alanine, L and DL-α-amino-n-butyric acid, L- and DL-norvaline, DL-norleucine, L- and DL-methionine, L- and DL-leucine, L-aspartic acid and DL-phenylalanine. The deuterium homologs of the type CH3CONDCHRCONDCH3, CD3CONHCHRCONHCH3, and CH3CONHCHRCONHCD3 were also prepared. The infrared spectra of these compounds were measured down to 300 cm-1 in the crystalline state. The infrared spectra of N-isopropylacetamide CH3CONHCH(CH3)2, N-methylisobutyramide (CH3)2CHCONHCH3 and their deuterium homologs were also measured. The C=O in-plane and out-of-plane bending vibration bands of the CH3CONHCα group (amide IVa and VIa) and those of the -CαCONHCH3 group (amide IVb and VIb) were assigned from these data. Two crystalline modifications, form I and form II, were found for the compounds prepared from L-alanine, DL-leucine, L-aspartic acid and DL-phenylalanine. The two forms show quite different skeletal vibrations, which suggest, rotational isomerism. Two distinct patterns were found as to the positions of the amide IVa and VIa bands for the above compounds. The two amide bands were found near 630 and 600 cm-1 in form I, whereas they were found near 600 cm-1 in form II. The crystals of the remaining compounds were also classified into form I or form II on the basis of the arrangement of the amide bands. The X-ray structure analyses suggest that these two forms have different hydrogen-bond structures.
    Additional Material: 9 Ill.
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  • 121
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1153-1157 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Double stranded RNA from CPV and RDV have been studied by the flow-dichroism technique. The flow orientation and dichroic spectra have shown that the molecular chain is flexible and has bases tilted slightly against the helix axis. It has been shown also that the wavelength dependency is similar to that of DNA, which strongly suggests the existence of an n - π* transition of bases around the 230 nm region.
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  • 122
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method was developed that allowed comparison of the stiffness of the chain in different polyelectrolyte from measurements of the intrinsic viscosity at different concentrations of added monovalent (sodium) salt. The response to salt was quantitatively expressed as the slope of straight lines relating the intrinsic viscosity to the reciprocal of the square-root of the ionic strength. This slope increased considerably with increasing molecular weight of the polyelectrolyte, and could serve to characterize the response to salt of different substances only when comparison was made at a constant molecular weight. An empirical parameter, B, which is the slope corresponding to an intrinsic viscosity of 1.0 at an ionic strength of 0.1 M could be correlated to the unperturbed dimensions of the molecules. A method of extrapolation, enabling the determination of B from measurements of viscosity on only one sample of unknown molecular weight, was evaluated. The empirically found correlation between Band some well established parameters of stiffness did not contrast predictions from the “fuzzy-sphere model” of Fixman, provided that reasonable assumptions regarding ion-binding and the interaction between polymer and solvent were made.
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  • 123
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 124
    Electronic Resource
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1277-1298 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vibrational frequencies of α-helical poly-L-alanine and its N-deuterated analog have been assigned by normal coordinate analyses. The phonon dispersion curves and frequency distribution of α-poly-L-alanine have been calculated by using a model which includes hydrogen bonding. The frequency distribution was used to interpret the inelastic neutron scattering data and to calculate the heat capacity. The low-frequency chain modes involving accordian-like motions of the whole helix have been calculated and their dispersion investigated by means of a simplified model.
    Additional Material: 4 Ill.
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  • 125
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1351-1364 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The swelling behavior of gelatin gels containing proteoglycans (sulphated proteoglycans from bovine intervertebral discs and a hyaluronate proteoglycan from bovine synovial fluid) when immersed in osmotically active solutions of dextran have been measured. The presence of the proteoglycans markedly affects the internal osmotic contribution to the swelling pressure of the gel. These internal osmotic pressures are considerably in excess of the sum of the osmotic activities of the individual components. This behavior is understood in terms of an entropic interaction between the gelatin and the proteoglycan molecules. By use of the “dilute solution” treatment of Flory, the osmotic pressure excesses are related to the volumes and hence dimensions of the interact acting species. A comparison of these values with those calculated by other means shows good agreement. The osmotic behavior of the complex gels can be understood on a mechanistic basis, if we regard the gelatin and sulphated proteoglycans as spheres and the hyaluronate proteoglycan as a rod.
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  • 126
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 127
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Raman spectra are presented on ordered and presumably helical structures of DNA and RNA as well as the poly A·poly U helical complex, polydAT, and the helical aggregates of 5′-GMP and 3′-GMP. The changes in the frequency and the intensity of the Raman bands as these structures undergo order-disorder transitions have been measured. In general the changes we have found can be placed into three categories: (1) A reduction in the intensities of certain ring vibrations of the polynucleotide bases is observed when stacking or ordering occurs (Raman hypochromism). Since the ring vibrational frequencies are different for each type of base, we have been able to obtain some estimate of average amount of order of each type of base in partially ordered helical systems. (2) A very large increase in the intensity of a sharp, strongly polarized band at about 815 cm-1 is observed when polyriboA and polyriboU are formed into a helical complex. Although this band is not present in the separated chains at high temperature, a broad diffuse band at about 800 cm-1 is present. The 815 cm-1 band undoubtedly arises from the vibrations of the phosphate-sugar portions of the molecule and provides a sensitive handle to the back-bone conformation of the polymer. This band also appears upon ordering of RNA, formation of the helical aggregate of 5′-riboGMP, and to some extent in the selfstacking of the polyribonucleotides polyA, polyU in the presence of Mg++, PolyC, and polyG. No such intense, polarized band is found, however, in ordered DNA, polydAT, or the 3′-riboGMP aggregate, although there is a conformationally independent band at about 795 cm-1 in DNA and polydAT. (3) Numerous frequency changes occur during Conformational changes. In particular the 1600-1700 cm-1 region in D2O shows significant conformationally dependent changes in the C=O stretching region analogous to the changes in this region which have been observed in these substances in the infrared. Thus, Raman scattering appears to provide a technique for simultaneously observing the effects of base stacking, backbone conformation and carbonyl hydrogen bonding in nucleic acids in moderately dilute (10-25 mg/ml) aqueous solutions.
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  • 128
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1525-1531 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Circular dichroism (CD) spectra of histone, DNA and native, partial and reconstituted nucleohistone complexes in 0.01 M Tris buffer in which nucleohistone complexes appear to be intact and in 2 M NaCl, in which complexes are mostly dissociated, have been compared. The CD spectra in the longwave region, where the protein contribution is negigible, reveal differences in the spectra for DNA in nucleohistone complexes as compared with that of free DNA, the difference being roughly proportional to the protein DNA ratio. An analysis of the shape of the first positive CD maximum suggests that we are probably dealing here with slight conformational changes on DNA. Minor differences between the behavior of native and reconstituted complexes may be due to the effect of different conformational states of the protein component.
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  • 129
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1543-1557 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A dielectric method is presented to measure the ejection of counterion during the thermal fusion of Na DNA solutions. The dielectric conductivity behavior at fixed frequency versus temperature is a measure of the molar concentration of counterfoils formed from the macromolecules. A linear dependence between Na+ cations released and DNA concentration was verified. We consider the variation of sodium activity coefficient ΔγNa+ during thermal transconformation to be in good agreement with other experimental data.
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  • 130
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    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1597-1604 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The infrared spectra of undenatured bovine tendon collagen were investigated at 25°C and relative humidities from 0 to 95%. Suitable samples were prepared by forcing frozen suspensions of the material in distilled water through a stainless steel capillary. The samples were investigated by electron microscopy before and after the spectra were obtained to ascertain that no denaturation had taken place while the sample was exposed to infrared radiation. Temperature controlled absorption cells were constructed which permitted the passing of air with a known water content over the sample film. Gradual changes were observed in the frequencies and intensities of characteristic amide bands over the relative humidity range of 0 to 75%. These changes are particularly pronounced for the amide II band, associated with bending motions of peptide NH bonds. They lead to the conclusion that water molecules are gradually attached to peptide NH bonds within the triple helix over a wide range of relative humidity. Changes in CH deformation bands suggest that CH to O hydrogen bonding does occur and that it is more pronounced in collagen exposed to high relative humidity.
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  • 131
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Steric and energy contour diagrams have been plotted for disaccharide-like and for helical structures of linear β-D-glucans having (1 → 2), (1 → 3) and (1 → 4) linkages. The allowed conformations constitute only about. 4% of the total conformations, indicating that the freedom of rotation of glucose residues is highly restricted in all the three polysaccharides. The additional restrictions of the monomer unit, as one passes from disaccharide to polysaccaride structures, are severe in the case of (1 → 2) and (1 → 3) linked polysaccharides but not in (1 → 4) linked polysaccharide. The difference in the nature of linkages also has shown to affect the energetically preferred conformations: (1 → 2) linkages lead only to left handed helical conformations; (1 → 3) linkages lead to both right and left handed wide and extended helical conformations, (1 → 4) linkages lead to both right and left handed extended helical conformations. The possible hydrogen bonds between adjacent residues are also dependent on the nature of linkage.
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  • 132
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    Biopolymers 10 (1971), S. 1583-1596 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sequential polypeptides of L-alanine(A) and glycine(G), which were incorporated between two blocks of poly(D,L-glutamic acid) (DL), were synthesized by applying Merri-field's solid-phase method. On the basis of optical rotatory dispersion criteria, DL(A)38-DL was found to assume the α-helix in the whole range of the water-methanol system; whereas other block sequential polypeptides were found to assume the random-coiled conformation in water and partly the α-helix at the high methanol content. The stability of the α-helix decreased in the order: DL(A)38DL, DL(A2G)10DL, DL(A2G)6DL, and DL(A3G)7DL. This phenomenon may be explained in terms of the dependence of hydrophobic bonding between the C3H group of the ith L-alanine regularly arranged on the surface of the α-helix and the C2H group of the (i + 3)th residue on whether the residue is alanine or glycine. The role which the methanol plays in stabilizing the α-helix is also discussed.
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  • 133
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    Biopolymers 10 (1971), S. 1625-1634 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To elucidate the role of the bases in single-strand polynucleolide conformation, we have studied apurinic acid, a single-strand polydeoxyribonucleotide from which almost half the bases have been removed. The conformation of apurinic acid in aqueous solution near θ condition has been investigated by sedimentation velocity and sedimentation equilibrium measurements. The unperturbed coil dimensions of apurinic acid are essentially identical to those of poly rU of the same degree of polymerization. The dimensions are also similar to those of poly rA at high temperature, where the adenine residues are not stacked upon one another. We conclude that the considerable rigidity of these polynuclotides is conferred not by residual, undetected base stacking, but by restrictions in rotation about the bonds of the backbone. Furthermore, the rigidity of the ribose-phosphate backbone cannot be attributed to interactions involving the 2' - OH group.
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  • 134
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    Biopolymers 10 (1971), S. 2387-2404 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aqueous solutions of poly-L-tyrosine were studied by potentiometric titrations, light-scattering measurements, and infrared spectroscopy in order to characterize the conformational changes the macromolecules exhibit when the hydrogen-ion concentration of the solutions is varied. It was found that when the pH of the system at 25°C is lowered from a value of about 13 the poly-L-tyrosine molecules undergo a random-coil to β-structure conformation change at pH 11.5. It appears, that under the experimental conditions used, the formation of the β structure is an intramolecular process which involves the folding of the polymer backbone into several hairpins of antiparallel β structure. On further lowering of the pH of the solutions aggregation (pH 11.35) and subsequently precipitation (pH 11.2) takes place. Since the apparent pK of the polymer does not show a drastic change during the random-coil to β-structure conformation change, it was concluded, that the therinodynamic driving force for this conformation change is mainly due to the electrostatic effect of the partially charged side chains of the poly-L-tyrosine molecules.
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  • 135
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    Biopolymers 10 (1971), S. 2491-2498 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complex formation of polyadenylic acid (poly A) and polyuridylic acid (poly U) in 0.1M NaCl solution containing 0.01M sodium cacodylate was followed by dilatometric measurements at various mixing ratios of poly A and poly U. The volume changes, ΔV, accompanying the formation of poly A. poly U and poly A.2poly U were + l.5 and + 2.5 ml per mole of the nucleotide residue, respectively. This increase in volume was probably due to the increased counterion binding when the single-stranded polynucleotides were converted into the double- and triple-stranded helices, since depletion of charged species from the solvent proper would lessen the effect of electrostriction, thus resulting in a positive ΔV. The conversion of a single-stranded poly A to a double-stranded helix in acidic solution led to a ΔV of + 3.8 ml per mole of the nucleotide residue. This increase in volume was attributed to the charge neutralization as a result of protonation of the adenine bases.
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  • 136
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    Biopolymers 10 (1971), S. 2525-2536 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potentiometric titration curves have been determined for aqueous solutions of poly-S-carboxyethyl-L-cysteine, which is subject to the β-coil transition by a change in pH. Reversibility and time dependence of the titration curves are examined by different methods in order to establish the conditions for obtaining equilibrium curves. The β-coil transition is manifest, at some region on the equilibrium titration curve, if pH - log (α/1 - α) is plotted against α. Assuming a value, 4.00, for pKint, the free-energy change for the β-coil transition of uncharged polymer has been evaluated from the extrapolation of the observed titration curves and is found to depend on the ionic strength and polymer concentration. The Henderson-Hasselbach plot of the titration curve yields clearer distinction between the β-form and random coil, and it permits estimation of the content of β-form at, a given pH. Comparison of the conformational titration curve with the circular dichroic measurements leads to a value of -10,000° for [θ]223 for the pure β-structure. Precipitation which occurs at low degrees of ionization and, especially, at high ionic strength does not reveal any discontinuous change of the titration curve, which suggests that, the degree of ionization of the precipitated β-form is not very different from that in solution.
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  • 137
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a study of A-B type block copolymers of γ benzyl-L-gultamate and β-benzyl-L-aspartate use has been made of the observations: (1) that for poly aspartate esters the chemical shifts of the α-CH and NH resonances are sensitive to the helix sense, (2) that in both helical and random coil conformations the same resonances of poly-γ-benzyl-L-glutamate are well separated from those of poly aspartates. Since the sense of poly-β-benzyl-L-aspartate is very sensitive to the inclusion of γ-benzyl-L-glutamate residues, the degree of overlap between the blocks can be studied by monitoring the helix sense of the aspartate. The ability of the NMR method to make separate observation of the two blocks removes the necessity of relying on an overall ORD parameter such as b0. The copolymers studied include those having lefthanded, righthanded, and mixed-sense aspartate, corresponding to differing degrees of overlap.
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  • 138
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    Biopolymers 10 (1971), S. 2615-2617 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 139
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    Biopolymers 10 (1971), S. 2629-2634 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
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  • 140
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    Biopolymers 10 (1971), S. 2649-2649 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 141
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    Biopolymers 10 (1971), S. 11-20 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper describes a theoretical and experimental analysis of the binding of magnesium ions to yeast, ribosomes. In the theoretical considerations the interactions between charges located on a macroion are included. In the calculations these interactions result in a term, in which both the charge and the radius of the macroion are accounted for. It appears that on dissociation of the ribosomes both the charge and the radius change, but in such a way, that the term, which accounts for the electrostatic interactions, remains constant. As a consequence the dissociation can lie neglected in the analyses of the binding experiments. Our experiments indicate that two binding reactions between ribosomes and magnesium ions occur. The endpoints of these reactions correspond to about 0.40 and 1.0 equivalent magnesium per ribosomal phosphate, respectively. The pK values are about 3.8 and 2.2, respectively. The experimental results indicate that the effect, of monovalent cations can be explained as a pure ionic strength effect, though the binding of monovalent cations could not be excluded completely.
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  • 142
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    Biopolymers 10 (1971), S. 89-106 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Raman spectra of poly-γ-benzyl-L-glutamate, poly-L-leucine, poly-L-valine, and poly-L-serine are reported. For the α-helical polymers, the conformationally sensitive amide I, II, and III modes are observed in the Raman as, well as the infrared. For the β form, the Raman effect, supplies the infrared inactive inphase motion which is useful for the determination of a parallel or antiparallel chain alignment. Modes characteristic of the specific polypeptide are also observed which are insensitive to conformation.
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  • 143
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    Biopolymers 10 (1971), S. 47-68 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The helical stability of a variety of DNA samples, ranging in base composition from 0 to 72 mole-% GC, has been studied by heat denaturation at neutral pH in increasing concentrations of LiCl, NaCl, KCl, CsCl, Li2SO4, and K2SO4. The variation of melting temperature with average base composition, dTm/dXGC, was found to decrease drastically in the concentrated salt media, e.g., from 41°C in 0.006M LiCl to 29°C in 3.2M LiCl, and from 39°C in 0.003M Li2SO4 to 18°C in 1.6M Li2SO4. At the same time, the thermal transition is much more cooperative in the concentrated salt solutions than at low ionic strength. Indeed, at limiting salt concentrations, the transition breadth seems to reach a minimum value irrespective of the compositional heterogeneity of the DNA samples. Attempts to correlate the observed decrease of dTm/dXGC with predicted changes in the enthalpy of melting, deduced from a simple theoretical treatment, experimental data on the binding of counterions and water to DNA, and experimental data on thermal denaturation, were unsuccessful. However, the strongly reduced composition dependence of the melting temperature can be understood in terms of a destabilizing effect of the concentrated salt media on GC-base pairs. It is suggested, though not proven, that the destabilization involves the displacement of water molecules from the DNA helix.
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  • 144
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    Biopolymers 10 (1971), S. 329-336 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal helix-coil transition of poly(γ-benzyl L-glutamate-co-ε-carbobenzoxy-L-lysine) copolypeptides was studied in solvent mixtures of different compositions. The cooperativity parameter v changes linearly with polymer (and solvent) composition, whereas the heat of the transition shows a very pronounced minimum as a function of polymer composition. This minimum cannot be due only or mainly to the solvent changes and must be attributed to the effect on the transition of the side chains of the polypeptides.
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  • 145
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: β-(l)-Menthyl D- and L-aspartates were prepared by a fusion reaction of N-phthalyl D- and L-aspartic anhydrides with l-menthol, followed by hydrazinolysis. The monomers were then polymerized to poly[β-(l)-menthyl D- and L-aspartates] by the N-carboxyanhydride method. These polymers were soluble in many organic solvents, such as diethyl ether, tetrahydrofuran, chloroform, n-bexane, and dioxane. From the results obtained by a study of the optical rotatory dispersions and circular dichroisms, poly [β-(l)-menthyl D-aspartate] was found to be a β form structure in solution. On the other hand, poly[β-(l)-menthyl L-aspartate] was a random-coil structure. These results suggest that the asymmetry of the l-menthyl chromophore in the side chain interacts with the polypeptide main chain and causes an extraordinary optical rotation.
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  • 146
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The diffusion, sedimentation, and viscosity behavior of native DNA has been studied as a function of molecular weight absolutely determined by diffusion and sedimentation measurements between 106 and 20 × 106 Daltons. Only data for monodisperse subfractions of the polydisperse DNA samples investigated have been compared. They were derived by means of calculations based on individual sedimentation constant distribution and polymer parameters. The inconstancy of these parameters for the semi-rigid DNA molecules over the range of different sub-fractions of the polydisperse samples has been taken into account. A detailed description of the corresponding mathematical background as well as of the diffusion measurements has been given in the two preceding papers. For the homologous series of monodisperse native DNA molecules, three-parameter equations have been determined representing the s0-[η], s0-M, and [η]-M relations as well as the D0-s0 and D0-M interdependence over the entire molecular weight range of interest. Furthermore a simple equation is given describing the molecular weight dependence of the Mandelkern-Flory-Scheraga parameter β in terms of s0 and [η]. The asymptotic value β∞ has been determined, primarily by measurements at finite molecular weights, to be 2.39 × 106, resulting in β values near 2.50 × 106 at M = 108 Daltons. The hydrodynamic properties of our two calf thymus DNA samples of highest molecular weight proved to be influenced by residual protein interactions resulting in a more compact conformation. Further data are given demonstrating the influence of the individual polydispersity of the investigated samples on diffusion constant and molecular weight averages.
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  • 147
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titration of an aqueous solution of sodium poly-L-glutamate with a strong acid usually produces turbidity and precipitation before the equivalence point is reached. In 1M sodium p-toluenesulfonate and 1M sodium methylcyclohexanesulfonate aggregation was delayed for days to months. In very concentrated tetra-n-butylammonium chloride and bromide the polymeric acid dissolved and could be titrated with NaOH. However, potentiometric titration curves in these solutions did not yield information (by way of plots of apparent pK versus the degree of neutralization) about the helix-to-coil transition of the polymer. It was argued in addition that the apparent pK of a weak polyelectrolyte should not be calculated from titrations in concentrated salt solutions since it is a mixed or composite quantity. It contains not only the effect of the salt on the dissociation of the weak electrolyte but its effect on the activity coefficient of hydrogen ions as well.Circular dichroic spectra were therefore measured a t various degrees of neutralization of poly(L-glutamic acid) in a number of aqueous salt solutions and mixtures of organic solvents with water. It was found that the undissociated polymer in the concentrated methylcyclohexanesulfonate and quaternary ammonium halide solutions had the spectrum of a right-handed α helix. The n → π* band at 222 mμ was used as a measure of the fraction of polymer in the helical conformation. The value of - Δε for the undissociated polyacid in these organic electrolyte solutions was 11.4. By means of this value and a number of assumptions, the fraction of helix (fh) as a function of α, the degree of polyacid neutralization, was calculated for the different solvent mixtures. An empirical equation was used to describe the variation of fh with α, fh = 1/(1 + e-a+bα), in which b represents the degree of cooperativeness of the transition, and a is a measure of the effect of the medium on the onset of the transition. The values of b did not differ very much from one another, suggesting that the cooperativeness of the transition was not sensitive to changes in the medium. On the other hand, the value of a (or its equivalent, the value of α at the halfway point in the transition) was more dependent on the solvent. Comparisons of these results with those of some other workers were made by means of the empirical equation.
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  • 148
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    Biopolymers 10 (1971), S. 411-416 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 149
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    Biopolymers 10 (1971), S. 417-419 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 150
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    Biopolymers 10 (1971), S. 399-410 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of temperature on the binding of 9-aminoacridine and of proflavine to E. coli DNA in 10-3M NaCl solution has been determined by a spectrophotometric technique. The inadequacy of the expression normally used for the determination of the extent of binding is discussed with reference to measurements at temperatures above which dissociation of the double helix occurs. A method of determining the relative extents of binding to native and denatured DNA at elevated temperatures is described.
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  • 151
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    Biopolymers 10 (1971), S. 421-421 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 152
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    Biopolymers 10 (1971), S. 423-423 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 153
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quantum-mechanical calculations by the PCILO method on the conformation of amino acid residues of proteins have been extended to the valyl, leucyl, and isoleucyl residues. In distinction to the earlier “empirical” computations, the quantum-mechanical results indicate very similar energy contours for the stable conformations of the three residues. Their general outline is also similar to that of the alanyl residue, although reduced by about 25%. Contrary to the “empirical” computations, the present results predict that the region corresponding to the α-helix should be one of great stability for the three residues and in particular for the valyl residue. The quantum-mechanical results are in excellent agreement with the experimental conformations of the aliphatic residues in lysozyme and myoglobin. Their prediction as to the ready availability of the valyl residue in the α-helical conformation agrees moreover with Ptitsyn's statistical evaluation of the participation of this residue in the inner turns of the helical regions in six globular proteins. The maximum conformational space allowed for the aliphatic residues is somewhat smaller than that allowed for the aromatic ones, while the minimum conformational space (region of stability common to all the residues) is similar in both groups.
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  • 154
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    Biopolymers 10 (1971), S. 513-522 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The helix-coil transition of DNA of various base compositions has been followed by measuring the heat capacity and the ultraviolet absorption as a function of temperature through the transition region. The results of these measurements indicate that the transition enthalphy ΔH for a given pH value and salt concentration depends considerably on the base composition of the various DNA samples. The values of the transition enthalpies vary from ΔH = 7.73 kcal/mole base pair (MBP) for 31% GC base pairs to ΔH = 8.52 kcal/MBP for 72% GC base pairs. The results of the heat capacity measurements are discussed in relationship to the theoretical models suggested by various authors. Some peculiarities of the measured heat capacity versus temperature curves are reported. The correlation between these peculiarities and the results of the transcription experiments of DNA is discussed.
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  • 155
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    Biopolymers 10 (1971), S. 711-719 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly-L-histidine (PLH) films at different degrees of protonation were produced mid subjected to infrared spectroscopic investigation (range 4000-650 cm-1). In addition, the N-deuterated film spectra were plotted. The amide II and III bands show that the peptide group is present in the trans form. The amide I and II bands show that at 0% and 50% protonation the PLH occurs as an α-helix and at 100% protonation as a random coil with some ranges in β structure. At 0% and 50% protonation, no hydration water is bound to the backbone. At 0% protonation all NH groups are linked to each other or to water molecules via hydrogen bonds. At 50% protonation NH+ċN bonds form between the imidazole rings. These protons are present in continuous energy level distribution. Such bonds with tunneling protons are extremely polarizable and between these bonds may act proton dispersion forces. The Cl- ions are bonded to the NH groups of the imidazole groups. The hydration water is bonded to the Cl-- ions and to the NH groups. At 100% protonation, hydration water is bonded also to the CO groups of the backbone. The NH groups of the backbone, like those of the rings, endeavor especially in the dry state to bond to the Cl- ions. This leads to a strong steric constraint of the random coil.
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  • 156
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    Biopolymers 10 (1971), S. 721-737 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational transition between the two helical forms I and II of poly-L-proline serves as an experimental model for the study of the kinetic, behavior of cooperative systems. The slow I ⇌ II conversion after a sudden perturbation of the solvent composition was followed polarimetrically. The dependence of the mean relaxation times on chain length and the degree of conversion was compared with Schwarz's theory. In addition, a description of the entire relaxation curves was possible in three special cases: all-or-nothing, small perturbations of the I ⇌ II equilibrium in long chains, and conversions which start off with molecules completely in one or the other conformational state. The mathematical model on which the theory is based contains only one more adjustable parameter than the equilibrium model, but it adapts to the experimental results surprisingly well. The present kinetic results and equilibrium measurements on this system are described by the same values of those parameters which are common to both models. The found value of the rate constant of the propagation step, i.e. the cis ⇌ trans isomerization of a peptide bond at an existing I-II junction, agrees with the rate of isomerization in N,N-dimethylacetamide reported in the literature. The rate of nucleation is up to 105 times smaller than the rate of propagation.
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  • 157
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    Biopolymers 10 (1971), S. 739-751 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism of glycosaminoglycans and ganglioside in distilled water are described, showing two bands in the region of amide and carboxyl transitions. The first, negative hand is common to all polymers and the amino sugar derivatives. The characteristics of the second band depend upon polymer structure. Those containing 4-1-linked amino sugars show a second, positive, resolved band about 190 mμ, while those with 3-1-linked amino sugars show a second, negative band less resolved from the first usually ≤185mμ, but clearly centered at 188mμ for dermatan sulfate. Ultraviolet optical absorption from 300 to ∼183 mμ showed inflection regions around 190 mμ for most compounds.
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  • 158
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization of γ-benzyl glutamate NCAs has been investigated. The results indicate that a coil-to-helix transformation is not responsible for the kinetic data. The results were rationalized by assuming formation of polymer aggregates coupled with the stereoselective adsorption of monomer onto growing polymer prior to reaction. From kinetic data a ratio of equilibrium constants for adsorption was determined. Independent data confirmed the assumption that adsorption of monomer onto polymer occurred. Equilibrium constants were evaluated, and their ratio was found to be comparable with that obtained from the kinetic data.
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  • 159
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    Biopolymers 10 (1971), S. 849-863 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A preliminary neutron-scattering study of wet-spun oriented NaDNA samples with various contents of H2O or D2O has been performed to obtain information about the hydration of NaDNA. The preferred orientation was in the direction of the crystallographic c axis. Perpendicular to this direction the samples could be regarded as poly-crystalline. It has been found that the preferred crystallite orientation was also reflected in the water structure. This fact, taken together with the small energy widths of the measured near-elastic peaks indicates that water molecules in the sample are relatively strongly bound to the DNA helix either directly or via other water molecules. Angular distribution measurements of elastically scattered neutrons were performed with the momentum transfer vector directed along and perpendicular to the DNA helix axis. Different Debye-Waller factors were obtained, indicating different water dynamics in the two directions. Comparison between the H2O and D2O measurements suggests that the difference is caused by motions of rotational nature. The shape of the frequency distribution function for the H2O molecules in the NaDNA sample was somewhat similar to that which has been measured in ice.
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  • 160
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    Biopolymers 10 (1971), S. 865-882 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The linear dichroism induced in a solution of electrically anisotropic molecules by a pulsed electric field has been studied. Equations have been obtained which express the dichroism as a function of dipole moment, excess polarizability, field strength, and the angle α between the dipole moment and the transition moment for the absorption band. These expressions have been related to the experimentally observed difference signal in such a way that when the dichroism is measured as a function of field strength the permanent moment, excess polarizability and angle a can be determined.Experiments have been carried out on tobacco mosaic virus (TMV), which is similar in its properties to the theoretical model. The polarizability anisotropy and rotary diffusion constant for the monomer and dimer of TMV have been obtained from these experiments. In addition to the molecular parameters mentioned above, the saturated electric dichroism of the virus was measured as a function of wave length and the presence of an n-π* transition in the tryptophan spectrum was indicated.Further experiments measuring dichroism as a function of pH demonstrated the general denaturation of the virus at high pH (10-11) but also the existence of a stable fraction which is not fragmented even at the high pH involved.
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  • 161
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    Biopolymers 10 (1971), S. 2459-2490 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of Mg ++ to polyadenylate (poly A), Polyuridylate(poly U), and their complexes, poly (A + U) and poly (A + 2U), was studied by means of a technique in which the dye eriochrome black T is used to measure the concentration of free Mg-. The apparent binding constant KX = [MgN]/[Mg++][N], N = site for Mg++ binding (the phosphate group of the nucleotide), was found to decrease rapidly as the extent of binding increased and, at low extents of binding, as the concentration of Na- increased in poly A, poly (A + U), and poly (A + 2U), and somewhat less so in poly U. Kx is generally in the range 104 〉 KX 〉 102. The cause of these dependences is apparently, primarily, the displacement of Na+ by Mg++ in poly U and poly (A + U) on the basis of the similarity of extents of displacement measured in this work and those measured potentiometrically. \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta H'{\rm v}.{\rm H}. = - R(\partial {\rm }\ln Kx/\partial 1/T)_\theta,\theta = \frac{{{\rm Mg}N}}{{N_t }} $$\end{document} was calculated and was found to approach zero as the concentration of Na+ increased. In poly U, poly (A + U), and poly (A + 2U) at low ΔH′ v.H. 〉 0, about + 2 kcal/“mole.” In poly A, also at low salt, ΔH′ v.H. ≈ -4 kcal/“mol” for the initial binding of Mg++, and increases to +2 kcal/“mol” at saturation. This enthalpic variation probably accounts for the anticooperativity in the binding of Mg++ not ascribable to the displacement of Na++.
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  • 162
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    Biopolymers 10 (1971), S. 2581-2590 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-resolution nuclear magnetic resonance spectra at 100 MHz have been obtained on poly-N-methyl-L-alanine in the chloroform-trifluoroacetic acid system under various conditions of solvent composition. Different spectra are observed for the CH3-Cα, Cα-H, and N-CH3 protons. On the basis of conformational analysis an interpretation of the NMR results was attempted.
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  • 163
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    Biopolymers 10 (1971), S. 2607-2614 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An analysis of optical rotatory dispersion and circular dichroism of RNA is described which leads to an estimate of the degree of base pairing. By the use of new standards for the double-helical parts of the molecule, based on data for two-stranded viral RNA species, a good fit between calculated and observed curves can be achieved. Where data are available the results of analyses of optical rotatory dispersion and circular dichroism in general show satisfactory consistency.
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  • 164
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    Biopolymers 10 (1971), S. 2625-2628 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 165
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    Biopolymers 10 (1971), S. 2645-2648 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 166
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    Chemie in unserer Zeit 5 (1971), S. 19-23 
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Ill.
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  • 167
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    Chemie in unserer Zeit 5 (1971), S. 30-30 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 168
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  • 169
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  • 170
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    Chemie in unserer Zeit 5 (1971), S. 50-56 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Ill.
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  • 171
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    Chemie in unserer Zeit 5 (1971), S. 57-60 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
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  • 172
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    Chemie in unserer Zeit 5 (1971), S. 65-77 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 19 Ill.
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  • 173
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    Chemie in unserer Zeit 5 (1971), S. 78-81 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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  • 174
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    Chemie in unserer Zeit 5 (1971), S. 125-127 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 7 Ill.
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  • 175
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    Chemie in unserer Zeit 5 (1971), S. 129-130 
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    Keywords: Chemistry ; Chemistry
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  • 176
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    Chemie in unserer Zeit 5 (1971) 
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  • 177
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    Chemie in unserer Zeit 5 (1971), S. 128-128 
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    Keywords: Chemistry ; Chemistry
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  • 178
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    Chemie in unserer Zeit 5 (1971), S. 131-141 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 14 Ill.
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  • 179
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    Chemie in unserer Zeit 5 (1971), S. 142-146 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 180
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    Chemie in unserer Zeit 5 (1971), S. 147-153 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 6 Ill.
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  • 181
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    Chemie in unserer Zeit 5 (1971), S. 154-159 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
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  • 182
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  • 183
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    Chemie in unserer Zeit 5 (1971), S. 161-162 
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    Keywords: Chemistry ; Chemistry
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  • 184
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    Chemie in unserer Zeit 5 (1971) 
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  • 185
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    Chemie in unserer Zeit 5 (1971), S. 163-169 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 9 Ill.
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  • 186
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    Chemie in unserer Zeit 5 (1971), S. 170-177 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 187
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    Chemie in unserer Zeit 5 (1971), S. 179-184 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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  • 188
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    Chemie in unserer Zeit 5 (1971), S. 185-190 
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    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 8 Ill.
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  • 189
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    Chemie in unserer Zeit 5 (1971), S. 191-191 
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    Keywords: Chemistry ; Chemistry
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  • 190
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    Chemie in unserer Zeit 5 (1971), S. 192-194 
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    Keywords: Chemistry ; Chemistry
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  • 191
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    Berichte der deutschen chemischen Gesellschaft 104 (1971) 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 192
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    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 21-30 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Diastereomers of Nonactin Acid and Epimers of 2-Desmethylnonactin AcidNonactin acid 8a was prepared in only four reaction steps starting from the furan 3a. - In an attempt to prepare nonactin acid by intramolecular cyclisation of 13, the tetrahydropyran 15 was obtained in addition to the desired tetrahydrofuran 14. Treatment of 14 + 15 with sodium cyanide under the conditions of the Kolbe reaction led to the formation of the isomeric acids 16 + 17.
    Notes: Ausgehend von dem Furan 3a gelangt man in vier Reaktionsschritten zur Nonactinsäure 8a, einem 2.5-disubstituierten Tetrahydrofuran. - Beim Versuch der Darstellung von Nonactinsäure durch intramolekulare Cyclisierung von 13 entstand neben dem gewünschten Tetrahydrofuran 14 durch Ringerweiterung auch das Tetrahydropyran 15. Die Umwandlung von 14 + 15 mit Natriumcyanid nach Kolbe führte zu den stellungsisomeren Säuren 16 + 17.
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  • 193
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    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 40-49 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Aromatic Solvent Induced Shifts (ASIS) in the N.M.R. Spectra of tert-Butyl-, tert-Butoxy-and Nitro(tert-butyl)benzene DerivativesThe n.m.r. spectra of aromatic tert-butyl and tert-butoxy groups which are not separated in CCl4 may always be resolved in benzene and pyridine solution. In some cases (e. g. 15) assignements for these signals are obtained empirically from their solvent shifts. The signals of the aromatic protons in 2.6- and 3.4-dinitro-1-tert-butylbenzene show remarkable solvent effects (CCl4→C6D6) which cannot be explained by the 1:1 complex models. The shifts induced by aromatic solvents must originate rather from the time average over all orientations of the anisotropic molecules in the nearest solvent schell. The interpretation of such solvent shifts should be based on values derived from an absolute standard.
    Notes: In CCl4 nicht getrennte NMR-Signale für aromatisch gebundene tert.-Butyl- und tert.-Butyloxygruppen werden in Benzol und Pyridin stets aufgelöst und können in bestimmten Fällen (z. B. 15) an Hand der Lösungsmittelabhängigkeit empirisch zugeordnet werden. Die Ringprotonensignale bei 2.6- und 3.4-Dinitro-1-tert.-butyl-benzol zeigen beim Lösungsmittelwechsel CCl4→C6D6 sehr unterschiedliche und z. T. sehr starke Verschiebungen, die nicht mit dem Modell spezifischer 1:1-Komplexe erklärt werden können. Die Wirkung des aromatischen Lösungsmittels muß vielmehr durch das Zeitmittel über alle Orientierungen aller anisotroper Moleküle in der engsten Solvathülle zustandekommen. Auf die Verwendung eines absoluten Standards bei der Deutung von Lösungsmitteleffekten in der NMR-Spektroskopie wird hingewiesen.
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    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 473-478 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of 7-β-Neohesperidosyl-4′-(β-D-glucopyranosyl)naringenin, a Flavanone Triglycoside from Citrus FruitsThe glycoside 7-β-neohesperidosyl-4′-(β-D-glucopyranosyl)naringenin (3), isolated from the segments of Citrus paradisi Macf, by Mizelle et al., was synthesized by condensation of phloracetophenone 4-β-neohesperidoside (1) with 4-hydroxybenzaldehyde 4-β-D-glucopyranoside (2) and by cyclisation of the resulting chalkone glykoside. Dehydrogenation of the flavanone triglykoside undecaacetate and subsequent saponification leads to the formation of 7-β-neohesperidosyl-4′-(β-D-glucopyranosyl)apigenin (7), the first synthetic apigenin triglycoside.
    Notes: Das von Mizelle und Mitarbb. aus Citrus paradisi Macf. isolierte 7-β-Neohesperidosyl-4′-β-D-glucopyranosyl-naringenin (3) wurde durch Kondensation von Phloracetophenon-4-β-neohesperidosid (1) mit 4-Hydroxy-benzaldehyd-4-β-D-glucopyranosid (2) und Cyclisierung des entstandenen Chalkonglykosids synthetisiert. Durch Dehydrierung des Flavanontriglykosid-undecaacetats (3a) wurde nach Verseifen das 7-β-Neohesperidosyl-4′-β-D-glucopyranosyl-apigenin (7) als erstes synthetisches Apigenintriglykosid dargestellt.
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  • 195
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    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Theoretical and Spectroscopic Investigations of Indigo Dyes, XI. Compounds with the Basic Chromophore of Thioindigo: Preparation and Properties of 3.4-Bis(alkylthio)hex-3-ene-2.5-dionesThe nucleophilic exchange of halogen in trans-3.4-dibromo- and -3.4-dichlorohex-3-ene-2.5-dione (4 and 5) with alkanethiols is studied. With bromine as leaving group substitution and reductive debromination leads to the formation of trans-3-methylthiohex-3-ene-2.5-dione (7a). With chlorine the expected trans-3.4-bis(alkylthio)hex-3-ene-2.5-diones (6a-c) are formed. These have the same structure and geometry as the basic chromophore of thioindigo, but they do not show the corresponding typical chemical and spectroscopic properties. They rather behave spectroscopically like β-alkylthio-α,β-unsaturated ketones. Conformation and spectroscopic properties of 6a-e are discussed with respect to the sterical requirements of the different groups at the sulfur atoms.
    Notes: Der Austausch der beiden Halogenatome von trans-3.4-Dibrom- und -3.4-Dichlor-hexen-(3)-dion-(2.5) (4 und 5) gegen Alkylmercaptane wird untersucht. Mit Brom als Abgangsgruppe erfolgt neben einfachem Austausch quantitativ eine reduktive Entbromierung zu trans-3-Methylmercapto-hexen-(3)-dion-(2.5) (7a), während mit Chlor als Abgangsgruppe zweifacher Austausch zu trans-3.4-Bis-alkylmercapto-hexen-(3)-dionen-(2.5) (6a-e) stattfindet. Diese zeigen nicht die spektroskopischen und chemischen Eigenschaften, die man für dieses - in der Verknüpfung ihrer funktionellen Gruppen dem Thioindigogrundchromophor entsprechende - System erwartet, sondern sie verhalten sich wie einfache β-alkylmercapto-α,β-ungesättigte Ketone. Die Abhängigkeit der Konformation und der spektroskopischen Eigenschaften von der Größe der Alkylreste am Schwefel wird diskutiert.
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    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 549-557 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Chemistry of Boron, LIV. Chemical Properties of Tris(2.2-dimethylhydrazino)boraneIn contrast to the ready cleavage of BN-bonds in tris(dialkylamino)boranes by BCl3, (BH3)2, HCl or CH3J the prefered reactions of these acids with tris(2.2-dimethylhydrazino)borane (1) are additions. Due to the greater basicity of the dimethylamino group as compared to the NH moiety, additions occur at the group (CH3)2N before the group NH is attacked. Solvolysis of B[NH—N(CH3)2]3 (1) by H2O or C2H5OH yields (CH3)2 N—NH2 and B(OH)3 or B(OC2H5)3, respectively, but no mixed compounds XnB[NH—N(CH3)2]3 n are formed in these reactions or by ligand exchange with B(OCH3)3 or B[N(CH3)2]3. 1 is stable up to 280° at higher temperature condensation with formation of N.N-dimethylhydrazine occurs.
    Notes: Während die Verbindungen BCl3, (BH3)2, HCl und CH3J die B N-Bindungen von Tris(dialkylamino)-boranen spalten, lagern sie sich an Tris(2.2-dimethyl-hydrazino)-boran (1) an. Dabei erfolgt zunächst Addition an die stärker basische Dimethylaminogruppe, danach reagiert auch die schwächer basische NH-Gruppe. Solvolysen von 1 mit H2O und C2H5OH oder Komproportionierungen mit B(OCH3)3 oder B[N(CH3)2]3 führen nicht zu gemischten Verbindungen XnB[NH—N(CH3)2]3 n(X—OH, OR, N(CH3)2). Im Vergleich zu Tris(alkylamino)-boranen ist 1 thermisch sehr stabil. Erst oberhalb 280° spaltet sich N,N-Dimethylhydrazin ab.
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    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 605-638 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: o- and p-(Dicyanomethylene)quinocyclopropenes. Synthesis, Mechanisms of Formation and Propertieso- and p-quinocyclopropenes of the benzene, naphthalene, anthracene, phenanthrene, and fluorene series (9, 12-15, 29, 30b, 37, 38) are prepared a) by thermolysis of 1:1 adducts of 3-ethoxy-1.2-diaryl-cyclopropenylium cations 6 and arylmalodinitrile anions, b) by reaction of diarylcyclopropenones with arylmalodinitriles in acetic anhydride. The reaction mechanisms suggested by isolation of intermediates are discussed. - Polarography of the quinocyclopropenes shows reversible formation of a radical cation in a one-electron step. This is in agreement with calculations according to the simple HMO model, which give satisfactory correlations with polarography, u. v. and i. r. spectroscopical data.
    Notes: o- und p-Chinocyclopropene der Benzol-, Naphthalin-, Anthracen-, Phenanthren- und Fluorenreihe (9, 12-15, 29, 30b, 37, 38) werden dargestellt a) durch Thermolyse von 1:1-Addukten aus 3-Äthoxy-1.2-diaryl-cyclopropenylium-Kationen 6 und Arylmalodinitril-Anionen, b) durch Reaktion von Diarylcyclopropenonen und Arylmalodinitrilen in Acetanhydrid. Die sich aus der Isolierung von Zwischenprodukten ergebenden Reaktionsmechanismen werden diskutiert. - Durch polarographische Untersuchungen wird festgestellt, daß die Chinocyclopropene reversibel im Einelektronenschritt in ein Radikal-Kation übergehen. Dies wird durch Rechnungen nach dem einfachen HMO-Modell bestätigt, die befriedigende Korrelationen mit den polarographischen sowie UV- und IR-spektroskopischen Daten ergeben.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 198
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 665-667 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 199
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 668-670 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 200
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 71-74 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Studies on the Bromination of Hydrocarbons in Liquid BromineThe bromination of aliphatic hydrocarbons in liquid bromine in the presence of catalytic amounts of hydrobromic acid is described. Hydrocarbons with neighbouring tertiary carbon atoms and tetraalkylated ethylenes give definite bromination products. From the corresponding hydrocarbons were obtained 1.4-Dibromo-2.3-bis(bromomethyl)but-2-ene (1), 1.4.5-Tribromo-2.3-bis(bromomethyl)pent-2-ene (2), 1.4.5-Tribromo-2.3-bis(bromomethyl)-hex-2-ene (3), 1.4.5-Tribromo-2-bromomethyl-3-(α.β-dibromoethyl)pent-2-ene (4), and 1.4.5.8-Tetrabromo-Δ4a(8a)-octalin (5).
    Notes: Bei der Bromierung in flüssigem Brom in Gegenwart katalytischer Mengen Bromwasserstoffsäure bilden aliphatische Kohlenwasserstoffe mit benachbarten tertiären Kohlenstoffatomen und tetraalkylierte Äthylene definierte Bromierungsprodukte. Im einzelnen werden 1.4-Dibrom-2.3-bis-brommethyl-buten-(2) (1), 1.4.5-Tribrom-2.3-bis-brommethyl-penten-(2) (2), 1.4.5-Tribrom-2.3-bis-brommethyl-hexen-(2) (3), 1.4.5-Tribrom-2-brommethyl-3-[α.β-dibromäthyl]-penten-(2) (4) und 1.4.5.8-Tetrabrom-Δ4a(8a)-octalin (5) aus den entsprechenden Kohlenwasserstoffen erhalten.
    Type of Medium: Electronic Resource
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