ISSN:0006-3525    

DOI:10.1002/bip.360230402

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

年代:1984

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360230403

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

年代:1984

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360230404

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe effect of salt on the intercalation of acridine dyes and DNA is rather well explained by the Gouy‐Chapman double‐layer theory as applied to a cylinder model of the DNA–dye complex. The free energy of transfer of a dye ion from the bulk solution to the complex is divided into several parts, one of which, ΔF0, accounts for the short‐range, nonelectrostatic interactions. The assumption that ΔF0should not depend on the amount of dye in the complex leads to an internal dielectric constant of the cylinder of aboutDi= 7. The scatter in ΔF0values, as calculated from individual experimental points, is of order 0.5 kT per dye ion. This scatter is large enough to mask possible effects of heterogeneity in DNA sequences. The calculations are made for a long cylinder with radius 10 Å, with the DNA phosphate charges smeared uniformly at the surface, a uniform spacing of dye charges at the cylinder axis, and a length ofb= 3.37 Å per base pair. Each intercalated dye ion also adds a lengthbto the total length of the cylinder. The salt‐dependent part of the electric free energy of intercalation, ΔF1, is tabulated for complexes withr= 0–0.24 dye ions per DNA phosphate in 0.002–0.2Mmonovalent sal

ISSN:0006-3525    

DOI:10.1002/bip.360230405

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

年代:1984

数据来源: WILEY

摘要:

AbstractFractionated samples of sodium hyaluronate of low molecular weight were used to calibrate the carbazole method for glucuronyl analsis and to determine the density increment (based on dry weight) of 0.444 (±0.003) mL/g in water and 0.386 (±0.003) mL/g for samples dialyzed against 0.2MNaCl. Weight‐average molecular weights obtained by high‐speed sedimentation equilibrium were used to calibrate the limiting viscosity number [η] in 0.2MNaCl, which gave [η]/Mw= 0.0028 (±0.0002) mL/g, valid toMw= 0.0028 (±0.0002) mL/g, valid toMw= 105. Experimental data from this work and the literature, including viscosity and light‐ and small‐angle x‐ray scattering measurements, were compared to theoretical chain models of the Kratky‐Porod (KP) wormlike and the helical wormlike (HW) chain, as treated by Yamakawa and collaborators. Although either model could be fitted to experimental data about equally well with consistent parameters, provided those for the HW chain were ofweaklyhelical nature, calculation of the unperturbed meansquare end‐to‐end distance as a function of chain length from a conformational model favored the KP chain alternative. The parameters that provide the best fit to experimental data for the KP wormlike model are a persistence length of 4.5–5 nm and a diameter of 1.1 nm. The latter is resonable for a hydrated hydrodynamic cylinder in view of the approximate unhydrated value of 0.7 nm estimated fro

ISSN:0006-3525    

DOI:10.1002/bip.360230406

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

年代:1984

数据来源: WILEY

摘要:

AbstractCD and nmr studies show that the conformational equilibrium of N(P)‐alkylated adenosine 5′‐phosphorodiamidates2–4and, to a much lesser extent, adenosine 5′‐phosphorodiamidate1differ at two parts from that of adenosine 5′‐phosphate in water. The glycosidic bond conformation is slightly shifted into the direction of thesynrange, and the ribose ring N‐conformer population increases. The conformational changes increase with increasing degree of N(P)‐alkylation and cause a change of the sign of the long‐wavelength CD band for2–4. The new conformation may be characterized by a stacked arrangement for the adenine ring and the 5′‐substituted phosphate group of2–4. Hydrophobic attraction between the head and the tail of the molecules, as well as the entropy effect (which promotes the clustering of apolar faces in water), may be jointly responsible for this stacked arrangement. The intramolecular attractive forces stabilizing the stacked conformation may act at the expense of the solubility decreasing intermolecular attractive forces, and may thus be responsible for the increased water solubility of2–4, which is higher than that of1by mo

ISSN:0006-3525    

DOI:10.1002/bip.360230407

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe diffusion–collision model of protein folding has been solved exactly for a three‐microdomain protein subunit. Numerical analysis shows that the exact kinetics may be excellently approximated in all cases studied by a standard chemical kinetics approach with the forward rate constants calculated from the mean folding time formula found previou

ISSN:0006-3525    

DOI:10.1002/bip.360230408

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

年代:1984

数据来源: WILEY

摘要:

AbstractWe studied films of poly(L‐tyrosine) with hydrogen phosphate (residue/phosphate, 1:1) by ir spectroscopy. The influences of the alkali cations (Li+, Na+, K+) and of the degree of hydration were clarified. If Li+ions are present, the OH ⃛−OP hydrogen bonds formed in the dried films between the tyrosine OH groups and hydrogen phosphate are asymmetrical. The formation of hydrogen phosphate–hydrogen phosphate hydrogen bonds is prevented by the presence of the Li+ions. With an increase in the degree of hydration, the tyrosine–phosphate bonds are not broken but become slightly stronger. Completely different behaviour is found if K+ions are present. In dry films, the OH ⃛−OP ⇌ O−⃛HOP hydrogen bonds formed between tyrosine and hydrogen phosphate show large proton polarizability. The tyrosine proton has a noticeable residence time at the acceptor O atom of the phosphate. The difference in the behaviour of the system with K+ions when compared to the system with Li+ions can be explained, since the hydrogen acceptor O atom of phosphate ions is more negatively charged due to the weaker influence of the K+ions. Furthermore, POH ⃛−OP hydrogen bonds between hydrogen phosphate molecules are formed. With an increase in the degree of hydration, the tyrosine–hydrogen phosphate hydrogen bonds are broken, all tyrosine protons are found at the tyrosine residues, and the ‐PO3−groupings are in a symmetrical environment, indicating that the K+ions are removed from these groupings. If the degree of hydration increases further, hydrogen‐bonded systems such as hydrogen phosphate–water–hydrogen phosphate are formed that show large proton polarizability due to collective proton motion. When Na+ions are present, the OH ⃛−OP ⇌ O−⃛HOP hydrogen bonds formed in dry films still show proton polarizability, but the residence time of the t

ISSN:0006-3525    

DOI:10.1002/bip.360230409

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

年代:1984

数据来源: WILEY

摘要:

AbstractAn electric birefringence study was carried out on aqueous suspensions of the purple membrane ofHalobacterium halobium. In addition to the characterization of both native and modified membrane samples, the dependence of electric birefringence on pH and ionic strength was also investigated. The results indicate that purple membrane shows electric birefringence at a field strength as low as 200 V/cm. The permanent dipole moment and polarizability ranged from 20,500 debyes and 1.01 × 10−14cm3for a purple membrane concentration of 0.40 mg/mL to 41,000 debyes and 2.05 × 10−14cm3for a concentration of 0.80 mg/mL. It was also found that removal of the retinyl group of bacteriorhodopsin substantially decreases but does not eliminate the electric birefringence of the membrane. The solubilization of the membrane by Triton X‐100, however, completely abolishes the electric birefringence. These experiments indicate that there is an interaction between adjacent bacteriorhodopsin molecules within the purple membrane via the retinyl chromophore moiety that builds up the permanent dipole moment. They also suggest that there are two types of response when purple membrane suspensions are placed in an electric field. One is an alignment of the disk‐shaped particles with the field. The other is a stacking of the particles following their alignment by the electric field, which is promoted by the induced dipo

ISSN:0006-3525    

DOI:10.1002/bip.360230410

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe aggregation of poly(γ‐benzyl‐α,L‐glutamate) and its enantiomer in toluene has been investigated by following the viscosity as a function of temperature, concentration, molecular weight, molecular‐weight distribution, helix chirality, and shear rate. The temperature and concentration data for a 138,000‐molecular‐weight sample was fitted to an open, reversible end‐to‐end aggregation model. The aggregation numbers resulting from this fit were consistent with the sudden onset in non‐Newtonian flow resulting from only a 0.2‐wt% increase in concentration. The association equilibrium constant was then used to predict viscosity for comparison with other data, in particular, the effect of molecular weight and molecular‐weight distribution. A mixture of right‐and left‐handed helices showed the aggregation was not chiral selective. The stiffness of end‐to‐end aggregated (hydrogen‐bonded) molecules differed little from their covalent counterparts, at least below a molecular weight of ∼106. We conclude that polybenzylglutamate aggregation in toluene can be described by a

ISSN:0006-3525    

DOI:10.1002/bip.360230411

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

年代:1984

数据来源: WILEY