ISSN:0006-3525    

DOI:10.1002/bip.1972.360110202

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

年代:1972

数据来源: WILEY

摘要:

AbstractDielectric constant and loss of aqueous solutions of tetra‐n‐butyl ammonium polyacrylate ((Bu)4NPA) were measured in the frequency range from 300 Hz to 6 MHz as compared with sodium and other salts at various conditions. Our results show that there are two dispersions observed in the low‐frequency range (LFD, several ten kHz to MHz), respectively, both of which are roughly expressed as the Cole‐Cole dispersion formula with Cole parameters about 0.3. The large values of dielectric increment, its nonlinear concentration dependence, and other features suggest that both dispersions are explained by relaxations of two different ionic processes. For HFD, experimental results were qualitatively similar to those have been reported and compared with theories of the Maxwell‐Wagner‐type effect. On the other hand, LFD may be attributable to the polarization of loosely bound counterions. A model available for LFD was presented on the basis of counterion

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110203

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe mean square of dipole moment of a linear macromolecule which is responsible for dielectric increment of aqueous polyelectrolyte solutions is calculated by means of a matrix method in which ion binding at discrete sites and the nearest‐neighbor interaction are taken into account. On the basis of the relationship between polarization of poly‐ion and fluctuation of bound counterions the present theory indicates that the loosely bound ions result in larger increment and otherwise smaller increment. Also, the theory predicts that the dielectric increment has a maximum at an intermediate monovalent–divalent ion ratio when both species coexist. These results are consistent with experiments on polyacrylic acid neutralized with NaOH and Ca(OH)2. At large contents of divalent ions the effect of chelation is also disc

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110204

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

年代:1972

数据来源: WILEY

摘要:

AbstractProflavine binding experiments were carried out with yeast rRNA, native and “unfolded” ribosomes; the binding constants and the number of binding sites were calculated by a spectroscopic method. The study of the intercalation complexes by fluorescence and electric dichroism shows the intercalation binding sites to involve two subtypes of sites, which could be related to different nucleotide composition and secondary structure of the rRNA regions, i.e., binding sites located in the (A + U)‐rich single strands and binding sites located in the (G + C)‐rich double‐helical strands (fluorescence quenching sites). Electric dichroism of complexed proflavine is interpreted in terms of rRNA conformation within the ribosomes. The conclusions are in agreement with the ribosomal model of Cox and Bonanou and show that, according to this model, the base planes of the nucleotides are not all parallel in the native ribsome, but rather radiate around the folding axis of the ribonucleoprot

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110205

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

年代:1972

数据来源: WILEY

摘要:

AbstractConformational change of histone IV, induced by phosphate, have been investigated by observing the intrinsic fluorescence of tyrosine residues and circular dichroism (CD). There is a fast conformational change upon the addition of phosphate, followed by a slow process with time constants in the range of minutes to hours depending upon both the phosphate and histone concentrations. The CD results indicate α‐helix formation in the fast process, and β‐sheet formation in the slow one, although other secondary and tertiary structural changes also may occur. The histone concentration dependence of the fast process is consistent with dimerization. Divalent phosphate is about ten times more effective than monovalent phosphate in inducing conformational changes. All of the changes are rever

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110206

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

年代:1972

数据来源: WILEY

摘要:

Abstract220‐MHz NMR spectra of various poly (N‐alkylamino acid)s are investigated. Spectra of polysarcosine recorded in various solvents showed fine splittings of the methyl and methylene bands. Comparing the spectrum with that of its model compound, the fine structure of the methyl band of polysarcosine was assigned to four dyad sequences of thecis–transisomeric state of the main chain amide bonds. Also the methylene band was roughly divided intocisandtransbands. From the temperature dependence of the spectra of polysarcosine, a double coalescence phenomenon was observed, in which the four dyad peaks coalesced into two peaks corresponding tocisandtrans, then the two peaks coalesced into one peak. Further, the approximate value of the free energy for the internal rotation of the main chain amide bond was estimated. NMR spectra of various poly(N‐alkylglycine)s in methylene chloride solution were also obtained. From the comparsion of their methylene bands, the introduction of the bulkyN‐alkyl groups was found to increase theciscontent of the a

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110207

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

年代:1972

数据来源: WILEY

摘要:

AbstractSteady‐state and pulsed NMR techniques have been used to investigate molecular motion in sols and gels of agarose. In passing through the sol–gel transition, the molecular mobility of water molecules is reduced only by a small amount, whereas motion of the polymer chains is greatly attenuated. The results are discused in terms of the network theory of gelation, with references to the role of water in the process and the nature of the “junction zones” between polymer chains.T2and line‐width measurements are dominated by exchange broadening. The effects of exchange rate and differences in relaxation time between the exchanging sites are discussed. The temperature hysteresis behavior of agarose gels has been investigated and the effects of “ageing” correlated with changes in nuclear relaxation times. The synergistic increase in gel strength obtained on adding locust bean gum (LBG) to agarose has been investigated. The results indicate that LBG does not form double‐helix junctions and may decrease rates of gelation by steric effects. At high agarose concentration, the LBG remains mainly in solution in interstitial water, but at low agarose concentration, it is suggested that the LBG can link gel aggregates together into a self‐supporting structure, producing a synergistic increase in gel strength. Comparisons have been made between the nature of the agarose–LBG interaction and agarose–cellulose interactions

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110208

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe copolymer poly Glu42Lys28Ala30was crosslinked by S–S bridges by reaction with butyrothiolactone followed by air oxidation of the mercaptan covalent adduct. The modified copolypeptide was more compact hydrodynamically, more resistant to the structurally disruptive effects of urea, and able to bind dye cations with much increased avidit

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110209

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

年代:1972

数据来源: WILEY

摘要:

AbstractWhen exposed to a low pH, in various ionic strength conditions and in sufficiently dilute solutions, DNA undergoes a transition, revealed by an increase in optical density. A careful analysis shows that, associated with this transition, there is an effective decrease in absorbance, overcompensated by an increase in scattering. The conditions for the new transition can be summarized conveniently by a graph in a pH–Na+molarity diagram. If the pH of a DNA solution is progressively lowered at constant Na+concentration, one finds first the melting transition (I), and at lower pH values, the new transition (II). If the same experiment is performed on pre‐denatured DNA, only transition II will be found. If native DNA is brought directly to the low pH conditions, without allowing it to denature irreversibly at intermediate pH values, transition II is reversible (with a small hysteresis effect). DNA, initially native, neutralized after prolonged exposures to the low pH, recovers the buoyant density value of native DNA, along with the absorption and scattering properties of the native state. The experiments are consistent with the interpretation that a new state exists in which DNA, still double stranded, assumes a very compact shape (of the order of 1500 Å in diameter for T2 DNA), with a hyperchromicity value of 10–14% above the native value. Nearly monodisperse suspensions of DNA molecule in this apparent state may be obtained only at very low concentrations (∼0.25 μg/ml). At 1 μg DNA/ml aggregation is noticeable. The possible connection with the condition of intraphage DNA is

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110210

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

年代:1972

数据来源: WILEY

摘要:

AbstractA method of calculating both the electrostatic free energy and en tlpy changes for melting of DNA is proposed. The nonelectrostatic parts of free energy and enthalpy changes for melting of DNA are obtained by subtracting these electrostatic free‐energy and enthalpy changes from the total free‐energy and enthalpy changes of melting reported by Privalov, Ptitsyn, and Birshtein, respectively. The ionic strength dependence of the melting temperature of DNA is computed using these thermodynamic functi

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110211

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

年代:1972

数据来源: WILEY