摘要:

AbstractDielectric dispersion measurements on poly‐γ‐benzyl‐L‐glutamate (PBLG) in dioxane and dioxane–dichloroacetic acid (DCA) mixtures in the frequency range 200 Hz–2 MHz were made in order to study the structure of molecular aggregates. The structure of aggregates is explained on the basis of the variation of dipole moment and relaxation time with degree of aggregation. PBLG was found to form linear head‐to‐tail‐type aggregates in dioxane. These aggregates gradually reduce in size without loosing their α‐helical structure during the process of disaggregation obtained by either adding DCA to the solution in dioxane or by heating. It was confirmed that the addition of 30 wt % DCA completely destroys the aggregation of PBLG in dioxane at 30°C. Thermal disaggregation, however, was not complete even at a temperature approaching the boiling point of the solvent.A reaction scheme for aggregation is proposed and equilibrium constants are calculated at various stages of aggregation. The enthalpy of aggregate formation is found to be −3 kcal/mol. Results of optical rotatory dispersion measurements of the helix–coil transition in this

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130702

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe dielectric absorption of poly‐DL‐phenylalanine and poly‐γ‐benzyl‐L‐aspartate (PLAB) was measured in very dilute solutions to determine the type of molecular association and to locate the helix–coil transition. Both polypeptides were present as associated helices in chloroform. The mode of aggregation, which was determined by measuring the dipole moment and the critical frequency, did not depend on the polarity of the side chain but rather on that of the solvent.In both polymers, the dissociation of the aggregates in chloroform was observed on addition of small amounts of dichloroacetic acid; further addition of the acid lead to the helix–coil transition.No second region of dielectric absorption that might be related to the kinetics of the transition was found during the helix–coil

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130703

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe polymerization kinetics and optical rotatory properties of AnBmpolypeptides have been studied, where A =D,L‐Tyr,D,L‐TyrZ,D,L‐LysZ,L‐AspOBzl, orL‐Asp‐ONBzl, and B =D,L‐GluOR (R = Me or Bzl). In most cases where Anand Bmprefer the same helix sense, the polymerization of AN‐carboxyanhydride (initiated by Bmin dioxane) shows first order kinetics and produces a monotonic change in optical rotation, while if opposite helix senses are preferred, the kinetics are multiphasic and the change in rotation reverses direction after the addition of several residues. The rotation change in the latter case is interpreted to mean that the helix in the A block is initially induced to take the nonpreferred sense, as originally suggested by Doty and Lundberg from similar observations on (D‐GluOBzl)n‐(L‐GluOBzl)m. It is found here that the CD spectra for the latter polymer show the sign changes required by this hypothesis. The optical rotation curves and CD spectra for (D,L‐Tyr)n‐(L‐GluOBzl)20suggest, by analogy, that (L‐Tyr)nprefers the same helix sense as (L‐GluOBzl)n. However, it is found that the opposite conclusion is equally consistent with the data if one considers the effects of possible changes in side‐chain conformation on these data in accordance with the calculated CD spectra of Chen and Woody. The optical rotation curves for (D‐GluOBzl)n‐(L‐GluOBzl)20, (D‐Tyr)n‐(L‐GluOBzl)20, and (L‐Tyr)n‐(L‐GluOBzl)20are all found to be consistent with a two‐state equilibrium model in which the A block initially takes on an induced conformation and has an increasing tendency to revert to its preferred conformation asnincreases. It is concluded that in bothD‐Tyr and L‐Tyr the side‐chain and/or the backbone conformation is induced by the neighboringL‐GluOBzl block, and the data do not distinguish which type of change is occurring. These results are discussed in connection w

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130704

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe circular dichroic spectrum of poly(Tyr,TyrBr) in trimethylphosphate from 180 to 320 nm is found to be a linear function of composition from 25 to 68% TyrBr, and the spectra of the Tyr and TyrBr components are resolved. For Tyr the resolved spectrum is in agreement with available CD spectra of poly(Tyr). These results are interpreted to mean that the side‐chain conformations of Tyr and TyrBr are not affected by the other component, and that for Tyr the conformation is the same as in poly(Tyr). It is also concluded that poly(Tyr,TyrBr) is helical with the same helix sense as poly(Tyr). The restrictions on the side‐chain conformations are discussed, and it is suggested that the Tyr and TyrBr side chains are all in the sameχ1 re

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130705

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe Zimm–Bragg parameterssand σ were determined for poly(γ‐benzylL‐glutamate) (PBLG) inm‐cresol and in dimethylformamide (DMF) from ORD data as a function of molecular weight. It was found that, within the temperature range between 10 and 55°C and on the average,s= 1.61± 0.1 and √σ = 0.04 ± 0.01 inm‐cresol ands= 1.65± 0.05 and √σ = 0.045 ± 0.015 in DMF. The values ofsinm‐cresol decreased with increasing temperature, while the values of σ in the same solvent increased. This result forssuggests that PBLG inm‐cresol will undergo a thermal helix–coil transition of normal type. The parameters in DMF showed no appreciable trend to vary with temperature. Aside from the difference between the two solvents, our results are consistent with existing data for various conformation‐dependent properties such as light‐scattering radius, intrinsic viscosity, and dipole moment, each indicating that the polypeptide chain has some fl

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130706

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

年代:1974

数据来源: WILEY

摘要:

AbstractMolecular conformation of some polysaccharides in aqueous solution in evidenced by changes in the optical rotation and in the elution pattern of gel filtration. The changes in the specific rotation against that in water are expressed as a molar conformational value [K] D21: −495° for colominic acid in 1.0NNaOH solution, and −180° for hyaluronate (HA), +85° for corneal keratin sulfate, and +234° for amylose in 8Murea solution. The gel filtration of amylose and HA dissolved in 8Murea solution shows elution patterns distinctly different from those dissolved in water. The phenomena are attributable to a molecular conformational transition of polysaccharide molecules in aqueous

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130707

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

年代:1974

数据来源: WILEY

摘要:

AbstractIntrinsic viscosity [η] is a characteristic of proteins and other molecules related directly to their ability to disturb flow and indirectly to their size and shape. It is usually determined by extrapolating reduced viscosity to zero concentration. Four other methods for deriving [η]have been utilized by previous investigators. Studies of the intrinsic viscosity of bovine serum albumin had been carried out two years apart as a test of viscometry technique; the data obtained were used to compare the five methods. Four of the five produced [η] values ranging from 3.92 to 4.21 ml/g. Agreement was good between the two studies. The five methods were compared to each other using linearity of regression, statistical error of determination, effect of varying solvent time, and result obtained in different concentration ranges. By these four criteria, use of the regression of specific fluidity (1 − 1/ηrel) with concentration was found superior to other methods. Its only deficiency was a requirement that solution density be corrected for at each concentration studied rather than applying a single correction for density after using kinematic viscosity data.All methods for deriving intrinsic viscosity are based on one of three equations; flow is expressed either in terms of reduced viscosity (Huggins), inherent viscosity (Kraemer), or specific fluidity. Of these three equations, specific fluidity is the most closely related both to theoretical analyses and to experimental studies of rigid spheres. There is abundant evidence in past reports that in contrast to rigid spheres, flexible polymers do not produce a linear rise in specific fluidity as their concentration increases, strongly suggesting that their molecular conformation is changing with concentration. A linear relation between fluidity and concentration has been observed for almost all proteins and protein mixtures studied. When this linear relation is present it indicates both that molecular conformation during flow is independent of concentration in the range studied and that the specific fluidity method for deriving intrinsic viscosity is the most approp

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130708

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe circular dichroism of double‐helical nucleic acids was calculated as a function of geometry using the theory of Tinoco and Johnson. This theory does not include contributions of near ultraviolet transitions that are not π → π* in nature. The calculated circular dichroism shows a strong dependence on the distance of base pairs from the helix axis and the tilt of the base pair. Smaller dependences are predicted for the propeller‐like twist of a base pair and for variation of the angular increment per base pair. Moderately good agreement between calculated and many experimentally observed spectra could be ge

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130709

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe circular dichroism of double‐helical nucleic acids was calculated as a function of geometry, including terms involvingn→ π* transitions. The “nonbonding”nor σ orbitals were of the azine type, delocalized, but concentrated at the nitrogen atoms of the purines and pyrimidines. Dynamic coupling of the magnetic moments of then→ π* transitions with the electric moments of π → π* transitions generated important terms. Mixing of electric dipole character inton→ π* transitions by the static electric field perturbation of the molecule is of lesser importance. The largest contributions ofn→ π* transitions to the circular dichroism of double‐helical nucleic acids are comparable in magnitude to the sum of π → π* terms only for geometries where the circular dichroism is weak. Using bothn→ π* and π → π* contributions one is able to match experimental and calculated circular dichroism spectra for DNA's over a much wider range of cond

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130710

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe circular dichroism of double‐helical nucleic acids was calculated using three different sets of wave functions for the purine and pyrimidine chromophores. Different wave functions give qualitatively the same types of spectra. Quantitatively, the differences are very substantial. However, the dependence of calculated circular dichroism spectra on nucleic acid geometry and base composition is very similar for the three different sets of wave functions. Each set of wave functions could be used to reproduce some, but not all experimentally observed spectra. The geometries required to reproduce experimentally observed spectra consistently require double‐helical geometries similar to the B or C forms of

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130711

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

年代:1974

数据来源: WILEY