摘要:

AbstractMeasurements of optical rotatory dispersion (ORD) and circular dichroism (CD) were made in the range of 400–205 nm for polysaccharide tribenzoates such as 2,3,6‐tri‐O‐benzoyl amylose (I), 2,3,4‐tri‐O‐benzoyl dextran (II), tri‐O‐benzoyl pullulan (III), 2,3,6‐tri‐O‐benzoyl cellulose (IV), 2,3,6‐tri‐O‐benzoyl mannan (V), and polyglycan dibenzoates such as 2,3,‐di‐O‐benzoyl amylose (VI), cellulose (VII), and mannan (VIII). All compounds exhibit Cotton effects in the region of their UV absorption bands (206–285 nm).Comparison of the corresponding di‐ and tribenzoyl polysaccharides shows a qualitative agreement in number, position and sign of the CD bands but differences in ellipticity magnitude. The disubstituted derivatives exhibit smaller amplitudes than the trisubstituted ones. The contribution of the C(6) chromophore (linked by a CH2‐group to the asymmetric C(5) atom) was determined to be of the same sign as the combined contribution of the C(2) and C(3) substituents.The CD bonds of the individual polysaccharide derivatives, which differ in number, sign, and position, were discussed in terms of the steric position of the single chromophores and the steric arrangement and interaction caused by the configuration of the polysaccharides. The optical behavior of these polysaccharide derivatives was found to be not strongly influenced by

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111002

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe frequency dependence of dynamic mechanical properties of rat tail tendon (RTT), enzyme‐solubilized collagen membranes (ESC), AKM‐23 dialysis membranes, and gelatin film have been measured at 110, 11, and 3.5 Hz from ‐ 160 to 220°C. RTT and AKM‐23 are devoid of a rubbery region; there are as many as six mechanical loss transitions. Gelatin and ESC membranes behave as rubbery materials above room temperature; only three tan δEpeaks can be resolved for these materials. Strain birefringence was used to measure the crystalline and amorphous contribution of orientation induced by strain. Both the birefringence and the strain optical coefficient are sensitive to the amount of water in a sample. The effect of chemical swelling agents and of annealing on birefringence are described. Stress relaxation data on gelatin film were analyzed with the rubber elasticity theory to give the average number of chains per unit volume, the specific polarizability, the stress‐birefringence ratio and the average molecular weight between hydrogen bonds were calculated. The intrinsic amorphous birefringence for “wet” gelatin film is 1.25 × 10−2; it is estimated to be about 6 × 10−2f

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111003

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe use of a simple chemical equilibrium and of the law of mass action leads to correct prediction when applied to the study of the role of the counterions in the process of acid melting of the DNA molecule. This approach allows an estimate to be given of the enthalpy variation per base pair associated with this process. Experiments have been carried out to test (a) the linearity of the dependence of pHmvs. 1/T; (b) the stabilizing effect of Na+concentration. The enthalphy variation per base pair, deduced from the slope of the pHmvs. 1/Tplot, and from the number of H+bound per base pair, is in agreement with direct measurement.6,8

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111004

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractHigh‐resolution NMR is used to study two series of benzyl‐L‐ orD‐glutamate: benzyl‐L‐aspartate random copolymers. The helix sense of theL‐aspartate residues determined from the αCHand NHchemical shifts agrees with that obtained from ORD. The stability of the helical copolymers to TFA addition shows a minimum at the composition of helix‐sense inversion for theL‐glutamate:L‐aspartate copolymers but no minimum for the lefthandedD‐glutamate:L‐aspartate series. The helix‐coil transition of the glutamate and aspartate residues in each polymer is compared. For theD‐glutamate:L‐aspartate series no differences are found, indicating random copolymerization. In theL‐glutamate:L‐aspartate series significant differences between the transition midpoints are interpreted as resulting from irregular distribution of

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111005

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractpK's of trinucleotides are calculated according to the theory of Kirkwood and Westheimer for ellipsoids. In order to compare the calculated values with some experimental results, a number of trimers were prepared and their pK's were measured. The question ofsynandanticonformations for monomers are discussed in light of the above considerations.

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111006

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe influence of the substituents upon the Amide I and νNH frequencies has been analyzed for ten amides substituted by aliphatic side chains. By considering the aliphatic chain field effect, some data are obtained as to the conformation of the NCαbond. In two amides, the presence of an equilibrium between two conformers is shown and a semiquantitative estimation of the energies involved is obtained. The consequences for polypeptides conformation, especially for poly‐L‐valine, are di

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111007

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe effect of dielectric constant (D) of the solvent on the viscosity of heparin was examined using the relation\documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{{\rm sp}} /c = [\eta ]_\infty (1 + k/\sqrt c) $\end{document}, where [η]∞is the shielded intrinsic viscosity obtained by extrapolating\documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{{\rm sp}} /c\,{\rm vs}{\rm . }\,1/\sqrt c ) $\end{document}to infinite concentration, andkis an interaction parameter independent of the dielectric constant of the solvent. This equation was previously reported by the authors9for describing the reduced viscosities of strong polyelectrolytes in salt‐free polar solvents. It was found that the [η]∞of heparin increases linearly with increasing dielectric constant of the solvent whereas thekvalues were, within experimental error, independent ofDin the range 54.7

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111008

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractA complete normal coordinate analysis, infrared absorption, and inelastic neutron scattering studies on α‐glycylglycine are reported. A Urey‐Bradley force field which is also valid for N‐deuterated sample is obtained. Assignments in the low‐frequency region are based on inelastic neutron spectrum obtained in one phonon and cubic appro

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111009

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractA normal coordinate analysis for cyclic tetra‐L‐alanine molecule is reported. A comparison of amide modes and other low‐frequency vibrations sensitive to conformational changes is made with those in poly‐L‐alanine. Intramolecular coupling coefficients are calculated using perturbation

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111010

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractWe have studied the dichroism of various samples of calf thymus DNA (of molecular weight from 3 × 105to 7 × 106) in pulsed electric fields. The results may be summarized as follows:1We find that calf thymus DNA behaves in electrical orientation as if it possessed a large permanent dipole moment. This apparent moment is sensitive to such effects as Mg++binding which lower the net charge on DNA.2The limiting dichroism at infinite field corresponds to an angle of at least 80% between the transition moments at 265 nm and the helix axis, and could be consistant with a number of known forms of DNA. This result is independent of DNA molecular weight. There is evidence that the conformation may be different in 80% ethanol.3The dichroism relaxation curves contain a component with a relaxation time of about 8 μsec, which is nearly independent of molecular weight, and a longest component which behaves either according to the Broersma theory for low‐molecular‐weight samples, or the Zimm‐Rouse theory at high molecular

ISSN:0006-3525    

DOI:10.1002/bip.1972.360111011

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY