摘要:

AbstractA uniform notation and convention is suggested to describe the torsional angles in nucleic acids and their derivatives. The torsional angle χ, relating the stereochemistry of the base with respect to the sugar, shows more variation for the β‐purine glycosides than for the β‐pyrimidine glycosides. This variation is attributed to the fact that the β‐purine derivatives may form intramolecular O(5′)‐H…N(3) hydrogen bonding. The χ values for the α‐purine and α‐pyrimidine glycosides show preference for the –syn‐clinal (or anti)conformation. The mode of puckering of the sugar also influences the χ value. The various possible conformations for the furanose ring are described by the torsional angles τ0τ1, τ2, τ3, τ4, about the five ring bonds. From an analysis of the torsional angles (ω, ϕ, ψ, ψ′, ϕ′, ω′) about the sugar phosphate bonds in the x‐ray structures of the known nucleosides, nucleotides, phosphodiesters, nucleic acids, and related compounds, and from a consideration of molecular models, it is found that the possible conformations for the backbone of helical nucleic acids is strikingly limited. Most importantly, the preferred conformation of the nucleotide unit in poly nucleotides and nucleic acids turns out to be the same as that found for the nucleotide in the crystal structure. It is observed that base “stacking” is a consequence of the restricted backbone conformation. The torsional angles are illustrated in the form of conformational “wheels”. Interrelation between the torsion angles about successive pairs of sugar‐phosphate bonds are presented in the form of conformational maps: ω,ϕ; ϕ,ψ; ψ.ψ′; ψ′,ϕ′; ϕ′,ω′; ω′,ω. The ω′,ω map shows the perferred conformations about the inter‐nucleotide bonds of right‐ and left‐handed helices and the possible conformations of phosphodiesters. The preferred conformation of the pyrophosphate and triphosphate is that in which the phosphate oxygens display a staggered arrangement when viewed along the P–P axis. A plausible structure and conformation for the ATPM2−backbound complex is presented. This structure differs from that proposed by SzentGyorgi in that the metal (only transition metals are considered here) is not bound to the NH2nitrogen of adenine, but rather is simultaneously bound to N(7) of the ring and three phosphates (α, β, γ), or N(7) of the ring and two phosphates

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070602

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe effects of various electrolytes on the conformation of poly‐L‐proline II in aqueous and nonaqueous solution have been investigated by optical rotatory techniques. It is shown that these agents induce a linear decrease in the corrected specific levorotaton of poly‐L‐proline with increasing salt concentration, with a molar effectiveness which varies from one salt to another. The salt‐induced rotatory changes may be divided into anion and cation components, and it is shown that the major specific affectors are the anions, which increase in effectiveness in reducing the corrected specific levorotation in the following sequence: Cl−

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070603

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe amide bond inL,L‐ andL,D‐α‐chloropropionylalanine methyl ester is shown to betransby molar polarization and infrared spectroscopy. In these dipeptide diastereoisomer analogues, therefore, differences in physical properties, i.e., melting points, crystalline forms, gas chromatographic mobilities, etc., depend on preferred molecular conformations and not peptide bond configuration. Nuclear magnetic resonance spectra of both compounds were identical, indicating that no major chemical environment differences exist, which might have resulted from dissimilar side group interactions. Based on the data reported here and those of others, most dipeptide conformations can be eliminated because of contradiction with limits set by experimental or theoretical considerations. Of the remaining conformational possibilities, a single pair accounts for observed physical differences in dipeptide diastereoisomers, free or blocked. The preferred form contains α‐hydrogenstransto each other and in the plane of the peptide bond. In this conformation, R1–R2and amino–carboxyl distances are minimal inL,Ddiastereomers and maxim

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070604

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe theories of the helix–coil transition of Lifson, Lifson and Allegra, and Allegra for random copolymers are compared with the exact results of Lehman and McTague, as was done by Fink and Crothers in an earlier test of the approximate theories of Fixman and Zeroka, Reiss et al, and Montroll and Goel. The Fixman‐Zeroka theory is the best approximation to the exact result (under the conditions used), and the Allegra theory is next best, the calculated slope of the transition curve in the Allegra theory being too small by a factor of two. An alternative derivation of the Allegra approximation, using the method of sequence generating functions, is given, and the resulting equations are of very simple form. A hybrid method, based on the work of Lifson and Allegra, is also developed here; it involves a technique of successive approximations, and reduces to the Allegra theory in first order. The fourth‐order approximation gives a slope that is too small by 10%; however, the value of the slope, extrapolated to infinite order of approximation, converges to the exact result‐ of Lehman and Mc‐Tague. By using illustrative calculations of helix–coil transition curves, some physical insight into the behavior of a copolymer in the transition region is provided: it is found that an important feature determining the shape of the transition curve is the variation in composition over the correlation length. The question of the application of copolymer theory to DNA i

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070605

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe infrared absorption spectrum in the 4000–400 cm−region of an oriented film of a DNA–RNA hybrid in its undeuterated and deuterated states was observed with the polarized radiation. Most of the stronger bands found in the double‐helical DNA's and double‐helical RNA's are identified in the spectrum of the hybrid. The absorption band at 1225 cm−1shows a perpendicular dichroism and that at 1085 cm−1shows almost no dichroism. These facts indicate that the orientation of the group with respect to the helix axis in the hybrid structure is not entirely the same as that in the double‐helical Na DNA at, 75% RH., although the x‐ray diffraction pattern of the hybrid is quite similar to that of the DNA A form. The PO2−orientation is not the same as that in the double‐helical RNA either. The observed dichroism is explained, however, by considering that the PO2−group in the RNA moiety takes nearly the same orientation as that in the double‐helical RNA, and the PO2−group in the DNA moiety takes nearly the same as tha

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070606

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

年代:1969

数据来源: WILEY

摘要:

AbstractPolymerizations ofD,L‐β‐phenylalanine,p‐nitro‐D,L‐β‐ phenylalanine, ando,p‐dinitro‐D,L‐β‐phenylalanine NCA's were carried out with the use of α‐picoline or poly‐2‐vinyl‐pyridine as initiator. Polymerizations induced by the polymer catalyst were always faster than those with α‐picoline in the same base concentrations. Furthermore, the polymer effect was more marked when the number of nitro groups in the NCA's increased. It was considered that the polymer catalyst interacts with the NCA's primarily by hydrogen bonding and increases the effective concentration of NCA along the chain. The increase of the NCA concentration in the vicinity of the polymer catalyst wits also achieved through charge‐transfer complexes between nitrophenyl groups in the NCA's and pyridine groups in the polymer catalyst. As the polymer chain is flexible, a collision between an adsorbed NCA and a pyridine unit in the same polymer chain is favored, thu

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070607

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe polymerizations ofD,‐Lβ‐phenylalanine NCA,p–nitro‐D,L‐β‐phenylalanine NCA, ando,p‐dinitro‐D,L‐β‐phenylalanine NCA were investigated, homopolymers and copolymers ofN‐vinyl‐2‐ethylimidazole or 2‐Vinylpyridine being used as catalysts. WhenN‐vinylpyrrolidone andN,N‐diethylacrylamide, which are capable of forming hydrogen bonds with the NCA's, were used as comonomers withN‐vinyl‐2‐ethylimidazole, the copolymer catalysts were found to bring about a faster polymerization than poly‐N‐vinyl‐2‐ethylimidazole. However, when styrene, which has no particular interaction with the NCA's, was used as a comonomer with 2‐vinylpyridine, the copolymer catalyst was found to give a slower polymerization than poly‐2‐vinylpyridine. Electronic spectroscopy showed that the charge‐transfer complex between copolymer catalysts and the NCA's plays an important role in the polymerization. The experimental results are discussed in terms of the effectiveness of the copolymer catalysts for forming hy

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070608

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe polymerization ofD,L‐β‐phenylalanine NCA induced by preformed polyi(N‐ethylglycine) diethylamide having a terminal secondary amino group was investigated. The polymerization was much faster than the same reaction initiated by a low molecular weight amine of similar base strength. Hence, the chain effect is operative with poly (N‐ethylglycine) diethylamide as well as polysarcosine diethylamide, with which Bamford et al. found the chain‐effect mechanism. The polymerization rate was dependent on the degree of polymerization of the polymer catalyst. The rate enhancement was attributed to adsorption of the NCA onto the amide carbonyl groups of the polymer chain by the formation of hydrogen bond. In going from polysarcosine diethylamide to poly (N‐ethylglycine) diethylamide, the absorptivity of NCA on on the polymer chain was little affected. However, the reaction between an adsorbed NCA and a terminal base was more difficult with poly (N‐ethylglycine) diethylamide than with polysarcosine diethylamide. This may be related to differences in flexibility of the

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070609

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

年代:1969

数据来源: WILEY

摘要:

AbstractThe denaturation of a macromolecule such as a polypeptide is considered in the case where the total number of noncovalent internal bonds broken in the binding process of the chemical agent is only a fraction, αs, of the total number of noncovalent internal bonds involved in its helical native conformation. Starting from a two‐parameter (s, σ) model of the helix–random coil transition of polypeptides, the transition temperature is derived as a function of the fraction αs, and of the concentration and the binding constant of the chemical agent. The lower limit of the transition temperature and the corresponding slope of the transition curve are shown to depend on αs. As an illustration, existing data on the partial acid denaturation of the enzymes ribonuclease A and muromidase are analyzed. The resulting average enthalpies of a noncovalent bond in the native ribonuclease A and muromidase are found to be 1.81 kcal/mole and 1.54 kcal/mole, respectively; the corresponding entropies are 5.4 and 4.4 cal/deg./mole, respectively. As a further example, existing data on a partially methylated enzyme ribonuclease A are also con

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070610

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

年代:1969

数据来源: WILEY

摘要:

AbstractDielectric dispersion measurements with aqueous solutions of hemoglobin and myoglobin have been performed in the frequency range from 100 kcps to 15 Mcps. The influence of preparation, particle size, and solvent conditions was studied. The results are analyzed in terms of an orientational polarization mechanism.

ISSN:0006-3525    

DOI:10.1002/bip.1969.360070611

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

年代:1969

数据来源: WILEY