摘要:

AbstractThe synthesis of poly[(S)‐thiazolidine‐4‐carboxylic acid] is described. The polymer is obtained by the polymerization of theN‐carboxyanhydride of (S)‐thiazolidine‐4‐carboxylic acid in pyridine or nitrobenzene using triethylamine as an initiator. The amino acid is prepared by the condensation of cysteine and formaldehyde.N‐Acetyl‐(S)‐thiazolidine‐4‐carboxylic acid methyl ester is also prepared as a model compound by standard acetylation and e

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110902

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe helical structures of poly[(S)‐thiazolidine‐4‐carboxylic acid], in thecisandtransforms, were redetermined by using the new sets of bond angles and bond lengths established by X‐ray diffraction analysis ofL‐thioproline. Calculations of the helical structures of poly‐L‐proline and poly[(S)‐oxazolidine‐4‐carboxylic acid] were also repeated. As a result of these energy calculations, it is suggested that, in contrast to poly‐L‐proline and poly[(S)‐oxazolidine‐4‐carboxylic acid], poly[(S)‐thiazolidine‐4‐carboxylic acid] should not mutarotate from thetransto thecisform. This result is due to the fact that the energy barrier for the conversion is most likely too high. Previous experimental w

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110903

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

年代:1972

数据来源: WILEY

摘要:

AbstractInteraction of poly U (polyuridylic acid) and adenosine is studied by following the changes in ultraviolet absorbance in the wavelength region near the isochromic wave‐length for the complex formation. The interaction is studied as a function of temperature, concentration of adenosine, and ionic strength, while the concentration of poly U was held constant. It is confirmed that only the three‐stranded complex with the stoichiometry 1A to 2U is formed and that it dissociates directly into free poly U and adenosine. No discontinuity of any kind was apparent in the melting curves, and poly U was found to possess no ordered structure above 10°C under the conditions used. The results were, therefore, analyzed in terms of an exact helix–coil equilibrium theory using the mismatching model, i.e., assuming that either completely formed base triplet or completely free unbonded bases only exist, and that the two sections of the polymer chains forming closed loops need not contain the same number of unbonded bases. Self‐association of free adenosine was taken into consideration. (Base triplet is analog of base pair for a three‐stranded helical complex. It refers to a unit of three coplanar bases, in this case two uracils and one adenine, hydrogen bonded to one another to form a triplet. Such triplets may stack over one another along the helical axis, and when they are so stacked the bases of two triplets next to each other may have stacking interactions between them.)The values for enthalpy and entropy changes, both per mole of base triplets, were obtained for the following processes at neutral pH and moderate to high salt concentrations. (1)Growfh: Binding of one adenosine molecule to two uracil residues (one from each poly U strand) to form a base triplet next to an already formed base triplet with which it has stacking interactions, a process that involves both hydrogen bonding and base stacking interactions, ΔHs, = −19 ± 2 kcal, ΔSs= −55 ± 6 clausius; (2)Initiation:Binding of one adenosine molecule to two uracil residues (one from each poly U strand) to form an isolated base triplet, a process that involves only hydrogen bonding interactions, ΔHb*= 4.5 ± 2 kcal, ΔSb*= 6.6 ± 3 clausius; and (3)Interruption:Unstacking of two stacked base triplets initially next to each other by formation of an interruption (viz. a closed loop) between them, a process that involves only base stacking interactions, ΔHb= 23.5 ± 3 kcal, ΔSb= 61.6 ± 7 clausius, where the entropy changes include contributions other than the configurational entropy of closed loops. The discrepancy between our results and the calorimetric ΔHsof −13 kcal is attributed to (i) the possible effects of salt arid polymer on the self‐association of free adenosine, (ii) the uncertainty in the value of the parameter for the probability of ring closure, and (iii) the contributions due to the partial molal enthalpy of the solvent and the unstacking of any poly U structu

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110904

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

年代:1972

数据来源: WILEY

摘要:

AbstractA valence force field has been refined for crystalline polyglycine I using its known antiparallel chain pleated‐sheet structure and without replacing the CH2group by a point mass. Polyglycine I and four of its isotopic derivatives were used in the refinement. The calculated frequencies are in good agreement with the observed, except for the amide I modes. It is shown that this is a consequence of the fact that no reasonable force field predicts a largeD10term of the Miyazawa perturbation treatment. The amide I splittings can, however, be satisfactorily accounted for by introducing a direct interaction force constant between adjacent CO groups in neighboring chains. This can reasonably arise from transition dipole coupling and corresponds to the heretofore neglectedD11t

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110905

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

年代:1972

数据来源: WILEY

摘要:

AbstractA valence force field has been refined for single‐chain polyglycine II using the known structure and four isotopic derivatives. The calculated frequencies are in good agreement with the observed. The force field is compared with that derived from polyglycine I and for the nylon

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110906

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe Raman spectra of the double helical complexes of poly C–poly G and poly I–poly C at neutral pHare presented and compared with the spectra of the constituent homopolymers.When a completely double‐helical structure is formed in solution a strong sharp band at 810–814 cm−1appears which has previously been shown to be due to the A‐type conformation of the sugar–phosphate backbone chain. By taking the ratio of the intensity of the 810–814 cm−1band to the intensity of the 1090–1100 cm−1phosphate vibration, one can obtain an estimate of the fraction of the backbone chain in the A‐type conformation for both double‐stranded helices and self‐stacked single chains. This type of information can apparently only be obtained by Raman spectroscopy.In addition, other significant changes in Raman intensities and frequencies have been observed and tabulated: (1) the Raman intensity of certain of the ring vibrations of guanine and hypoxanthine bases decrease as these bases become increasingly stacked (Raman hypochromism), (2) the Raman band at 1464 cm−1in poly I is asigned to the amide II band of thecis‐amide group of the hypoxanthine base. It shifts in frequency upon base pairing to 1484 cm−1, thus permitting the determination of

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110907

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe conformational transitions in water and in the solid state of poly‐L‐glutamic acid (PGA) and poly‐L‐ornithine (PO) have been studied by Raman spectroscopy. The Raman spectra of PGA, PO, and the monomer, dimer, and trimer of PGA in aqueous solutions and solid state are presented. The Raman spectral changes of PGA and PO were followed through the helix‐to‐coil transition induced by pH, temperature, and solvent composition. A hyperchromic shift in the intensity of the amide III line accompanying the helix‐to‐coil transition was observed. This hyperchromic intensity shift occurs abruptly as a function of pHbut more slowly with heat denaturation of the alpha helix indicating that the Raman spectrum is sensitive to the transition mechanism. The high‐temperature coil and the charged coil may have different conformations as evidenced by different amide III frequencies but similar intensities in these

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110908

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

年代:1972

数据来源: WILEY

摘要:

AbstractA power series method was applied to solve the Poisson‐Boltzmann equation for the spherical polyelectrolyte model and numerical calculation with an electronic computer was performed to obtain surface electric potential on rigid globular proteins. Deviation from the ideal linear relationship in Linderstrom‐Lang's plot was found to become noticeable as the surface charge density and the radius of protein increases and ionic strength decreases. The calculated surface potential was compared with potentiometric titration data of several proteins whose radii have been analyzed. Assuming the radius of the counterions to be equal to about 1.0 Å, the data for phenolic groups in ribonuclease and for carboxyl groups in conalbumin were interpreted. Reversible intramolecular transformation was found for α‐lactalbumin by comparing the present results with the potentiometric titration data for carboxyl groups. The molecular size of each protein was di

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110909

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

年代:1972

数据来源: WILEY

摘要:

AbstractAn approximateab‐initiovalence bond calculation of hydrogen bond energy was carried out and the results are discussed. The total bond energy of a simplified NH…O structure is calculated for various NH and N…O distances and the potential energy profiles are obtained. The hydrogen bond energy, ie, the delocalization energy gained by the formation of one hydrogen bond is found to be 8.7–12.0 kcal/mole. The potential energy is characterized by a deep minimum at 1.6–1.8 a.u. from the nitrogen and the second trough is found to be considerably higher t

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110910

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe problem of determining the molecular weight of DNA samples by sedimentation equilibrium in a buoyant‐density gradient is considered for the case of DNA samples with density heterogeneity. By determining apparent molecular weights in two or more buoyant mediums, quantitative measure of the amount of density heterogeneity can be determined. This method may be employed to determine both the true molecular weight and the extent of base composition heterogeneit

ISSN:0006-3525    

DOI:10.1002/bip.1972.360110911

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

年代:1972

数据来源: WILEY