摘要:

AbstractThe electric birefringence of collagen solutions has been measured over a wide range of field strength with the pulse technique. The soluble collagen was from rat tail tendon. The solvent used was dilute acetic acid. Very pronounced saturation of the electric birefringence was observed, permitting calculation of the optical anisotropy factor. The Kerr constant was determined by extrapolation to zero field strength. From the dependence on field strength of the birefringence, the permanent dipole moment and the anisotropy of polarizability were separately determined. The contribution of the former to the Kerr constant was found to be twice as large as that of the latter. The same conclusion was obtained from the initial slope of the rise curves of the birefringence at low fields. The permanent dipole moment was 1.5 × 104Debye, and the anisotropy of polarizability was about 3 × 10−15cm.3. The magnitude of the latter indicates that the ion atmosphere polarization is important. Effects of added salt and thermal denaturation on the electric birefringence were explo

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040502

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

年代:1966

数据来源: WILEY

摘要:

AbstractPoly‐O‐acetyl‐hydroxy‐L‐proline, forms I and II have been studied by optical rotatory dispersion (ORD) and ultraviolet spectrophotometry in solution and in the solid state. Cotton effects of opposite sign, but not mirror images, were observed in the 250 mμ region for the two forms (Form I, peak 278 mμ; crossover, 254 mμ; trough, 244 mμ: Form II, trough 270 mμ; crossover, 248 mμ; peak, 238 mμ). Thus, the Cotton effects for a right‐handed and left‐handed helix have been shown to be opposite for the proline type helices I and II. The ORD of films of form I was found to have a positive Cotton effect further into the ultraviolet region with peak at 218 mμ. Absorption spectra showed a shift of 8 mμ in the absorption peak in the 200 mμ region for the two forms (form. I, 211 mμ; form II, 203 mμ). A shoulder was demonstrated in the film absorption spectra in the 250 mμ region where the Cotton effects are found. The mixing of then, π* and π, π* states of the amide chromophore andn, π* state of the ester chromophore was suggested as being responsible for the Cotto

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040503

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe electrophoretic mobility of calf thymus DNA has been measured in aqueous buffered solutions as a function of pH. In the pH range 3.7–3.0, two electrophoretic species appear. The faster one migrates with the mobility of native DNA, the slower one migrates with a mobility close to that of thermally denatured DNA. The ratio of the two species varies with pH. Decreasing the pH increase the relative amount of the slower‐moving component. These results may be interpreted by assuming that the DNA used in these experiments has a broad heterogeneity of base composition and that the conformational stability with respect to pH increases with increasing G + C cont

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040504

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

年代:1966

数据来源: WILEY

摘要:

AbstractFurther direct evidences are given that a clear correlation exists between potentiometric and spectroscopic measurements in monitoring the poly(L‐glutamic, acid) helix+coil transtition. Specific Li+ion poly (L‐glUtamic acid) interactions have been observed, suresting that Li+ions may exert a distinct destabilizing action on the helical conformation of the polyelectrol

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040505

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

年代:1966

数据来源: WILEY

摘要:

AbstractA number of basic features of the infrared spectrum of keratin have been confirmed and some new features have been found. In the 3‐μ region, the amide A frequency of helical material in α‐keratin at 3286 cm.−1is close to the expected value, but that of the crystalline phase in α‐keratin, near 3270 cm.−1, is lower than had previously been reported. The noncrystalline phase absorbs in the vicinity of 3300 cm.−1or above, and this causes the low‐intensity component of the amide A band in both α‐ and β‐keratin to occur at higher frequencies than those of the high‐intensity component. In the 6‐μ region, the amide II frequency of noncrystalline material is below 1525 cm.−1. Keratin denatured in lithium bromide, after washing out the reagent, appears to have a considerable helix content, possibly as much as that of the original protein. Hydration causes significant spectral changes. In the 6‐mu; region, the frequency of the amide I band of crystalline material is lowered, while that of the amide II band is increased, both by a few wavenumbers; the amide II frequency of noncrystaline material is also increased by a few wavenumbers. In the 3‐μ region, no significant change is observed in the amide A frequency of crystalline material, while the frequency of the noncrystaline material is reduced. These spectral changes are interpreted in terms of a weak association of water with main‐chain carbonyl groups in the crystalline phase, while in the noncrystaline phase it is thought likely that water molecules form hydrogen‐bond bridges between polypetide chains. The absorption coefficient of the amide A band and the integrated absorption intensities of the amide A, I, and II bands do not vary appreciably in t

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040506

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

年代:1966

数据来源: WILEY

摘要:

AbstractA number of new bands have been found in the spectra of deuterated α‐ and β‐keratin. In particular, the deuteration difference spectrum has been useful for the determination of frequencies of previously unsuspected bands. Thus it is found that the amide A and II frequencies of the nonhelical component in α‐keratin occur at 3310–3320 and 1520 cm.−1, respectively, and that both bands exhibit dichroism consistent with polypeptide chains which have a measure of alignment parallel to the fiber axis. The parallel dichroism of the amide II′ band of this phase at about 1435 cm.−lalso indicates some alignment. A nondichroic residual band at 1513 cm.−1in highly deuterated α‐keratin is assigned to the tyrosine residue, as a sharp band near this frequency is found in the spectrum of polytyrosine. The ν‖(o) component of the α‐helix is weak or absent in α‐keratin, and the relatively sharp band observed near this frequency is thought to be due to the tyrosine residue, while its dichroism is caused by the presence of dichroic nonhelical material. A band near 1575 cm.−1in deuterated α‐ and β‐keratin is tentatively assigned to the deuterated guanidinium group of arginine. This band becomes progressively more prominent during deuteration, which indicates that some arginine side chains arc slow to exchange, possibly because their environment prevents interaction with D2O. The deuteration difference spectrum also shows that, contrary to earlier views, helical material in α‐keratin exchanges significantly during the early stages of deuteration, although at a slower rate than the nonhelical material, while part of the nonhelical phase does not exchange as rapidly as had been thought and makes a c

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040507

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

年代:1966

数据来源: WILEY

摘要:

AbstractIntegral expressions for concentration as a function of time and distance are derived from the continuity equation for centrifugation in a sector‐shaped cell for a macro‐molecular solute initially contained in a finite upper layer and a solute of low molecular weight in the supporting liquid. Computer patterns based on the sedimentation and diffusion coefficients of sucrose and of spherical and randomly coiled model solutes illustrate:(1)the time course of redistribution of both banded and supporting solutes from initial uniform concentrations;(2)the influence of the initial concentration, width, and solute concentration of the upper band; and(3)the effect of restricted diffusion at the meniscus on subsequent band shape. A Gaussian, approximation to band shape is derived and graphically tested. Rapid methods, not requiring computers, are out lined for the estimation of sedimentation and diffusion coefficients, where their concentration dependence is negligible, by band centrifugtion. The theoretical resolution of mixtures attainable by this technique is compared with moving‐boundary centrifugation, with the use of both integral (interferotmetric or absorption) and derivative (schlieren) o

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040508

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

年代:1966

数据来源: WILEY

摘要:

AbstractThe γ‐benzyl‐L‐glutamateN‐carboxyanhydride (NCA) polymerization initialed by diisopropylamine was studied in dimethylformamide (DMF)‐dioxane mixtures of different compositions. It was found that the shape of the conversion versus time plots and the molecular weights of the polymers depend on the solvent composition. Auto‐catalysis is present only when dioxane predominates in the solvent mixtures. Moreover, the molecular weight of the final polymer depends strongly on the precipitation conditions when the polymerization is carrie

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040509

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

年代:1966

数据来源: WILEY

摘要:

AbstractWhen solutions of poly‐L‐lysine and poly(acrylic acid) in salt solutions at neutral pH are mixed, complexes are formed. Optical rotatory dispersion studies of these complexes away from the equivalence point reveals the formation of α‐helices. The α‐helix content of the polylysine never rises above about 50%. On addition of 25% by volume of dioxane, the turbidity of the complex solutions disappears, and there is some enhancement of the α‐helix content. Poly(phosphoric acid) behaves essentially in the same way as poly(acrylic acid). Poly(uridylic acid) forms complexes with polylysine but with no detectable formation of α‐helix. The same is true of ribosomal RNA and native and denatured DNA. A number of other polyacid polybase systems involving basic proteins have been examined, but again no α‐helix formation is induced. The results are related to the case of biological nucleoproitein complexes, and the conformational specificity of these systems is discussed. The effect of scattering on measured optical rotation has been investigated and is shown to be unimportant up to

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040510

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

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040501

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

年代:1966

数据来源: WILEY