ISSN:0006-3525    

DOI:10.1002/bip.1970.360091102

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

年代:1970

数据来源: WILEY

摘要:

AbstractThe electric birefringence of poly(L‐glutamic acid) (PLGA) in methanol, dimethyl sulfoxide, dimethylformamide,N‐methylacetamide, trifluoroacetic acid, dioxane–water mixtures (3:1 and 4:1 by volume), and dioxane–formamide mixture (1:1 by volume) has been measured by the use of the rectangular pulse technique at 30 °C. The intrinsic viscosity has also been measured at the same temperature. The magnitude of the specific Kerr constant and the intrinsic viscosity suggests that PLGA is helical and has a large dipole moment in methanol, dimethyl sulfoxide, dimelhylformamide,N‐methylacetamide, and dioxane–water mixtures. In this case we have obtained the length distribution curve and the mean length of PLGA molecules from the decay of the electric birefringence, by applying the method recently developed for helical polypeptides. Furthermore, we have proposed and applied a method of obtaining the mean dipole moment and the optical anisotropy factor from the field strength dependence of the electric birefringence for polydisperse systems on the basis of the knowledge on the length distribution. The results show that PLGA may have a different helical conformation in dimethyl sulfoxide. The specific Kerr constant of PLGA in trifluoroacetic acid is very small, which suggests that PLGA is a random coil in

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091103

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

年代:1970

数据来源: WILEY

摘要:

AbstractThe optical activity and the conformational energy of the amino acids tyrosine,o‐tyrosine, andm‐tyrosine have been calculated as a function of molecular conformation. A new graphic technique, rotatory strength–conformational energy maps, was developed for the presentation of these calculations. Experimental circular dichroism spectra were determined by utilization of a new experimental technique that involves complete computer control of a Cary spectropolarimeter. This permitted repetitive scanning with signal averaging over extended time periods and resulted in a greatly enhanced signal to noise ratio. On the basis of these calculations, it, was concluded that the Kirkwood “coupled oscillator” mechanism is capable of explaining the observed optical activity of the aromatic chromophores of the molecules that were inv

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091104

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

年代:1970

数据来源: WILEY

摘要:

AbstractThe influence of single‐strand breaks on the kinetics of the relaxation of DNA in a solution of low ionic strength has been investigated by a temperature jump method. The relaxation of DNA after a jump of 0.7 °C in the melting region has been monitored by measuring the extinction at 260 nm. For essentially monodisperse T4 DNA (M= 130 × 106) two distinct relaxation times have been observed, that depend markedly on the initial extent of denaturation 1 − θ. The larger relaxation time decreases from 450 sec to about 300 sec, the smaller one from 55 see to 30 when 1 − θ increases from 0.03 to about 0.8. The dependence of these relaxation times on the average number of single‐strand breaks per molecule (p) appears to be very small up top= 100. However, the relative contribution of the slow process decreases sharply whenpincreases from 0.6 to 30 and remains nearly constant for largerp. The observations are discussed in the light recent theories of the kinetics of d

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091105

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

年代:1970

数据来源: WILEY

摘要:

AbstractMeasurements have been made of the intensity of light scattered from aqueous solutions of calf thymus DNA with and without the application of electric fields. For fields approaching 150 V/cm and frequencies below 2.5 KHz, changes (ΔI) of up to 10% in the residual scattered intensity were observed. In agreement with previous dielectric and electric birefringence measurements, a low frequency dispersion of ΔIwas observed, from which a rotary diffusion constant (D) of 1200 s−1was determined. Interpreting the electric field data in terms of the classical dipolar orientation theory led to values of 2.4 × 10−25cm (7.4 × 10−14esu) and 4.3 × 10−25cm (13 × 10−14esu) for the permanent dipole moment and the anisotropy of the electric polarisabilities respectively. Furthermore the permanent dipole moment was along the major molecular axis and the particles orientated in the field as rigid entities. The zero field data indicated a molecular shape which was not rodlike but corresponded to the Kratky‐Porod “stiffness” parameter ofx= 24 for the wormlike coil model. Although curved, the molecules appeared to orientate in low‐intensity electric fields as rigid, but not rodlike molecules. The implications of this on recent discrepancies inDdetermined by two or more dynamic relaxation metho

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091106

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

年代:1970

数据来源: WILEY

摘要:

AbstractReaction of 27 SMS2 RNA with formaldehyde normally results in an unfolded, 13.4 S form. At acidic pH, however, and under the proper ionic conditions, a compact component sedimenting at 36–40 S was obtained. The molecular weight of this species corresponds to a dinner. The formaldehyde concentration was not critical, and approximately the same number of base pairs had been opened in the compact and in the unfolded form. Presumably dimers, which had been specifically formed under defined conditions, were stabilized by formaldehyde‐induced crosslinks. Similar dimers were formed by 16 S and by 23 S ribosomal RNA, but not by t

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091107

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

年代:1970

数据来源: WILEY

摘要:

AbstractThe buoyant density of T‐4 DNA was determined by equilibrium sedimentation in a density gradient, of mixed solutions of cesium and magnesium chlorides and bromides. The preferential hydration was calculated from these data, allowing appropriately for the exchange equilibrium of DNA with Cs+and Mg++ions. The charge and intrinsic solvation of the counterions were found to have no appreciable effect on the hydration of the DNA, the extent of solvation depending only on the thermodynamic, activity of the water. Various reasonable hypotheses are discussed to account for these result

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091108

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

年代:1970

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091109

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

年代:1970

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091110

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

年代:1970

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1970.360091112

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

年代:1970

数据来源: WILEY