bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conformations and interactions of excited stales. I. Model compounds for polymers
Authors: Longworth J. W. , Bovey F. A. 
Published: December 2004

AbstractFrom observations on model compounds having two or more benzene rings and structures analogous to high polymers of interest (polystyrene and aromatic polypeptides), we conclude that interactions of pairs of benzene rings sufficiently strong to cause observable excimer emission requires that these rings be separated by no more than 2–3 A. and that they be in an approximately parallel‐stacked, face‐to‐face arrangement. If a molecule does not have such a configuration of its aromatic rings in its ground‐state conformation, strong excimer emission can still occur provided there is a conformation with the appropriate ring configuration which can be attained within the radiative lifetime of the excited state.
Temperature‐dependent properties of dinucleoside phosphates
Authors: Davis Robert C. , Tinoco Ignacio 
Published: December 2004

AbstractThe optical rotatory dispersion, hypochromism, and proton magnetic resonance were measured for a number of dinucleoside phosphates in both dilute salt solutions and in 25.2% LiCl (which freezes below −70°C.) as a function of temperature. Two models for the “disordering” of dinucleoside phosphates: the two‐state model and the oscillating dimer model, are used to analyze the data. Both models fit some of the data, but neither are completely satisfactory. Evidence is given for a dynamic structure of dinucleoside phosphates, in which the bases oscillate with respect to one another, remaining parallel to one another with no solvent in between, even at high temperatures. Implications of this model to the structures of single‐strand sections of RNA's are discussed.
Low temperature infrared spectra of polyglycines and C—H …︁ OC hydrogen bonding in polyglycine II
Authors: Krimm S. , Kuroiwa K. 
Published: December 2004

AbstractInfrared spectra of polyglycines I and II obtained at −170°C. have been compared with those obtained at room temperature. The changes in frequency of some of the C—H stretching bands are consistent with the earlier suggestion that C—H …︁ OC hydrogen bonds are present in the structure of polyglycine II.
Temperature dependence of the hydrogen ion equilibria in poly(riboadenylic acid)
Authors: Holcomb D. N. , Timasheff Serge N. 
Published: December 2004

AbstractHydrogen ion titration curves have been obtained for poly (riboadenylic acid) (poly A) at temperatures of 0–40°C, and ionic strengths of 0.001, 0.01, and 0.15. Where comparable, the data are in general agreement with those previously reported by other investigators. Correlations between the titration data and thermal denaturation curves have been obtained. Formation of a two‐stranded helix is catalyzed by the uptake of protons by the adenine base. Partial protonation of the base is required for formation of the two‐stranded helix, but under appropriate conditions it is stable at degrees of ionization less than 0.2. The degree of ionization required for formation of the two‐stranded helix increases with temperature and decreases with ionic strength.
Molecular weight of T7 and calf thymus DNA by low‐angle light scattering
Authors: Harpst J. A. , Krasna Alvin I. , Zimm B. H. 
Published: December 2004

AbstractA low‐angle light‐scattering instrument has been used to measure molecular weights of native calf‐thymus and T7 DNA. Molecular weights obtained by extrapolation of angular data to 0° from measurements above 30° are less than molecular weights from extrapolation of data taken at low angles (below 30°). The low‐angle molecular weights determined for calf‐thymus DNA and for T7 DNA agree well with estimates of weight‐average molecular weight obtained with other techniques. The low‐angle light‐scattering molecular weight for calf‐thymus DNA is higher than previously reported values by light scattering at angles above 30°. A concentration dependence in the scattering from DNA solutions is also observed.
The ultrasonic degradation of biological macromolecules under conditions of stable cavitation. II. Degradation of deoxyribonucleic acid
Authors: Peacocke A. R. , Pritchard N. J. 
Published: December 2004

AbstractSolutions of T7 bacteriophage or calf thymus DNA arc degraded in solution by ultrasonic fields of low intensity in the presence of vibrating air bubbles but are not degraded at these low intensities when such bubbles are absent. Evidence is presented for the hydrodynamic nature of the observed degradation and theoretical simulation of a plausible degradation mechanism is compared with experimental degradation studies. It is concluded that degradation of such linear macromolecules as DNA may occur as a result of stresses induced in the macromolecule; these stresses are the result of a relative movement of solvent molecules and the macromolecules in the time‐independent flow of solvent near the vibrating bubbles.
Conformational studies of polymers and copolymers of L‐aspartate esters. I. Preparation and solution studies
Authors: Bradbury E. M. , Carpenter B. G. , Goldman H. 
Published: December 2004

AbstractAn alcoholysis method is described for the modification of high molecular weight poly(β‐benzyl L‐asparatate); by this method the benzyl groups in the polypeptide have been replaced by methyl, ethyl, isopropyl, n‐propyl, and phenethyl groups to give a series of copolymers of each of the corresponding aspartate esters with benzyl L‐aspartate. By repeating the reactions, replacement of better than 99% has been achieved in some cases to give in effect the homopolymer. Optical rotatory dispersion studies show that of all the systems studied only poly(β‐methyl L‐aspartate) has the left‐handed helix sense, the others are right‐handed. It is shown further that the helix sense is not an intrinsic property of the nature of the aspartate side chain. Raising the temperature of chloroform solutions of the right‐handed form of the copolymers of benzyl L‐aspartate and ethyl L‐aspartate results in a transition to the left‐handed helix, the temperature of the transition being dependent on the composition of the copolymer. Also poly(β‐n‐propyl L‐aspartate) undergoes a transition from the right‐ to the left‐handed helix form at 59°C. These results suggest a general pattern of behavior of poly(aspartate esters) and that with suitable conditions of solvent and temperature they may be in either the right‐ or left‐handed helical form.
Conformations of poly‐L‐valine in solution
Authors: Epand Raquel F. , Scheraga Harold A. 
Published: December 2004

AbstractIn order to test theoretical predictions that poly‐L‐valine can exist in an α‐helical conformation, water‐soluble block copolymers of L‐valine and D, L‐lysine were prepared. By carrying out the synthesis on a resin support (with the use of N‐carboxyanhydrides) contamination of the individual blocks by any unreacted monomer from the previous block was avoided. A single glycine residue was incorporated at the C‐terminus of the chain for use in amino acid analyses. Using optical rotatory dispersion and circular dichroism criteria, about 50% of the short valine block of (D, L‐lysine HCl)18‐(L‐valine)15‐(D, L‐lysine‐HCl)16‐glycine was found to be in the right‐handed α‐helical conformation in 98% aqueous methanol, in water, the polymer appears to be a dimer, with the valine block being involved in the formation of an intermolecular β‐structure.
Interaction of heat‐denatured HeLa cell DNA with synthetic and natural polysaccharides
Authors: Graves I. L. 
Published: December 2004

AbstractHeat‐denatured DNA from HeLa cells interacts with natural as well as synthetic polysaccharides. Glucose does not inhibit the interaction nor will it produce it. Polysaccharides with a molecular weight of 10000 or greater are required before the interaction takes place.
Ultraviolet dichroic ratio of DNA from T2 and T5 bacteriophages
Authors: Gray Donald M. , Rubenstein Irwin 
Published: December 2004

AbstractThe dichroic ratios of T5st‐O and T2H bacteriophage DNA molecules were measured throughout the ultraviolet region of the spectrum. Two methods of DNA orientation were studied: (1) orientation in solution in a Shimadzu flow dichroism instrument attached to a Beckman DU spectrophotometer, and (2) alcohol precipitation of the DNA from solution and orientation in a thin film on the quartz face of a humidity chamber. Spectra in the latter case were recorded using a Gary Model 14 spectrophotomcter fitted with Glan prisms. The lower wavelength limit was 215 mμ in both systems. The DNA preparations were carefully characterized as to spectral purity, sedimentation coefficient, hyperchromicity, protein content, and DNA content. In addition, the structure of the DNA oriented in films was inferred from x‐ray diffraction patterns of fibers of the precipitated DXA. The A and B configurations of DNA in films could not be distinguished by the dichroic ratio measuiements. The dichroic ratio obtained for the film‐oriented DNA at high relative humidity shows the same wavelength dependence as for the flow‐oriented DNA. The same wavelength dependence for DNA in the fibrous state and in solution, when considered together with the x‐ray diffract ion results, indicates that DNA in solution maintains an orientation of bases which is similar to that in fibers. I1Or both solutions and films of DNA, the dichroic ratio is constant from 290mμ to 240 mμ and increases at wavelengths below 240 mμ. The increased parallel absorption below 240 mμ is consistent with the existence of an n→π* transition. The inherent molecular dichroic ratio is found to be the same for T5st‐O DNA and T2H DNA in solution, and is a maximum of 0.09 ± 0.02 at 260 mμ.
Conformational changes in histone IV
Authors: Li H. J. , Wickett R. , Craig A. Morrie , Isenberg I. 
Published: December 2004

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 reversible.
Lysine oligopeptides. Preparation by ion‐exchange chromatography
Authors: Yaron A. , Otey M. C. , Sober H. A. , Katchalski E. , Ehrlich‐Rogozinski S. , Berger A. 
Published: December 2004

AbstractThe preparation of L‐lysine peptides (Lysn, n = 2–14) from polyL‐lysine is described. Fractionation by ion‐exchange column chromatography of poly‐L‐lysine hydrolysates on a preparative scale resulted in 0.2–1.0 g quantities of individual members of the poly‐L‐lysine series. The peptides isolated proved to be analytically pure and the optical configuration was fully retained, as demonstrated by complete enzymic digestion. Peptides higher than n = 14 were also prepared. They consisted of oligolysine groups of narrow and accurately determined size distribution. Potentiometric titrations were used both to characterize the products and to demonstrate the characteristic dependence of the dissociation constants on size of the peptide.
Proof of the charging of polypeptides and polyamides in organic acids
Authors: Bradbury J. H. , Yuan H. H. H. 
Published: December 2004

AbstractThe electrophoresis of poly‐γ‐benzyl‐L‐glutamate (PBLG), poly‐L‐alanine (PLA) and nylon dissolved in various solvents was studied in a glass cell containing three sintered glass partitions. After the passage of a measured amount of charge the concentration of PBLG remained constant in all four chambers when the helicogenic solvents dimethylformamide and ethylene dichloride were used, but in mixtures of ethylene dichloride and dichloroacetic acid and in trifluoroacetic acid, polypeptide migrated to the cathode. Electrophoresis also occurred with PLA in trifluoroacetic acid and with nylon in formic acid. Although the total charge on the polyion could not be determined, the results show beyond reasonable doubt that polypeptides and polyamides are protonated in the presence of moderately strong organic acids.
Small‐angle x‐ray scattering by poly‐L‐alanine solutions
Authors: Brumberger H. , Anderson L. C. 
Published: December 2004

AbstractThe radius of gyration and “persistence length” of poly‐L‐alanine, calculated from small‐angle x‐ray scattering data, have values of 56 Å and 44 Å, respectively, in dichloroacetic acid, and 78 Å and ∼30 Å in a 1:1 v/v mixture of trifluoroacetic acid and trifluoroethanol. This can be interpreted to mean that poly‐L‐alanine exists in a relatively rigid, predominantly α‐helical conformation in dichloroacetic acid and in an extended, more flexible form in the mixed solvent system.
A Calorimetric Investigation of the Heats of Binding of Mg++ to Poly A, to Poly U, and to Their Complexes
Authors: Krakauer H. 
Published: December 2004

AbstractThe heats of binding of Mg++ ions to poly A, poly U, and to their complexes, in the presence of Na+ ions, have been measurd calorimetrically. In all cases the heat, ΔH(θ), exhibitis a distinct dependence on the extent of binding, θ, and in the cases of poly A and poly U also on the Na+ concentration. The values of ΔH(θ) range from +2 to +3 kcal/mole of Mg++ bound at θ = 0 to 1.3 kcal/mole at θ = 0.5 except in poly A where at θ = 0 ΔH(θ) = −2 to −3 kcal/mole. This is interpreted as being due to a facilitation of base stacking by the binding of Mg++. The extent of facilitation is consistent with current estimates of base stacking. A similar effect but of much smaller magnitude is believed to obtain in poly A poly U. An interpretation of the dependence of ΔH(θ) on θ in terms of simple electrostatic interactions, but neglecting solvent effects, was attempted and found to be inadequate.
The ultraviolet circular dichroism of some natural DNAs and an analysis of the spectra for sequence information
Authors: Allen F. S. , Gray Donald M. , Roberts Gary P. , Tinoco Ignacio 
Published: December 2004

AbstractThe circular dichroism spectra of many natural DNAs and double‐stranded synthetic polynucleotides were obtained. The eight first‐neighbor contributions to the CD spectra of a DNA have been extracted from these data. Therefore, the CD spectrum for any DNA with known first‐neighbor frequencies may be easily calculated. For a natural DNA the CD spectrum may be approximated by assuming the first‐neighbor frequencies have the most probable values consistent with the base composition. Under favorable conditions, the measured CD spectrum can be used to determine thirteen of the sixteen first‐neighbor frequencies of a DNA to ± 0.02 mole percent. The TG, CA, and TA first‐neighbor cannot be unambiguously resolved by our method. The accuracy of the first‐neighbor frequency analysis depends on the number of different first‐neighbors present in the DNA and the extent to which they differ from the most probable value.The extinction coefficient at 260 nm and the base composition can also be calculated from the CD spectrum.
On the Application of Polyelectrolyte “Limiting Laws” to the Helix‐Coil Transition of DNA. II. The Effect of Mg++ Counterions
Authors: Manning Gerald S. 
Published: December 2004

AbstractThe techniques of the previous article are here applied to the case for which the solution contains, in addition to excess uni–univalent salt, one equivalent of divalent counterions per mole nucleotide. In agreement with the melting temperature measurements of Dove and Davidson for Mg++, it is predicted that a region of uni–univalent salt concentration then exists in which (dT m/d log m A+) is negative. It is further predicted, in accord with experiment, that in the presence of divalent counterions, the helical form of DNA is much more stable than in their absence.
Optical properties and base pairing of E. coil 5S RNA
Authors: Richards E. G. , Geroch M. E. , Simpkins H. , Lecanidou R. 
Published: December 2004

AbstractThe ultraviolet absorption, optical rotatory dispersion, circular dichroism, and infrared absorption spectra of renatured 5S RNA have been measured at pH 7.0 in 0.1M NaCl at 25° and used to obtain four independent estimates of the number of base pairs. These four estimations are in reaonable agreement and average values of 28 ± 4 G.C and 13 ± 4 A.U. base pairs.
Optical activity of polypeptides and proteins
Authors: Madison Vincent , Schellman John 
Published: December 2004

AbstractUsing methods described in a previous publication the optical activity of a number of polypeptides and proteins has been calculated. The systems included the α‐helix, the two β‐structures, polyproline I, polyproline II, collagen and collagen models, and poly‐N‐methylalanine. In addition to these orderded structures, calculations were also performed on the α, β and nonperiodic regions of myoglobin, lysozyme, ribonuclease‐S and β‐chymotrypsin. The α and β structures in prteins differ from the polypeptide models by being very short and partially disordered. It is concluded that the 222‐nm band of the α‐helix is a good method for detecting helices in proteins but that the 207‐and 191‐nm bands of the helix will not fit a linear superposition model. The circular dichroism of the so‐called β regions of proteins differs markedly from that for ideal β structure because of breakdownin symmetry. As a result estimates of β‐structure in proteins based on polypeptide models are not likely to be quantitative.The theoretical methods give an adequate account of the optical activity of all the ordered polypeptides except polyproline II and collagen and (by inference) the nonperiodic chains in the various proteins. This difficulty is the remaining barrier to a complete theory of the optical activity of the polypeptide backbone in globular proteins.
Electro‐optic decay analysis for polydisperse systems
Authors: Schweitzer J. , Jennings B. R. 
Published: December 2004

AbstractThe decay curves of electro‐optic transients are generally used to measure the rotary diffusion contants (D) of colloidal particles in suspension or biopolymers in solution. Analysis usually is made by plotting the logarithm of the decay as a function of time, t. Curvature in such plots the presence of several values of D and hence a distribution of particle sizes. In this case, analysis of the complete curve to yield the distribution is severely restricted by lack of precision in the experimental data. The most reliable and reproducible part of the decay curve is the initial (t =0)slope.This paper develops theory for the initial slope for dilute suspensions of long thin cylinders with various electrical properties. It is shown that the inital slope depends not only on the particle‐size distribution and electric field strength, but also on the nature of the electrical properties of the molecules. Futhermore, for an identical polydisperse system. transient electric birefringence, electric optical rotation, and electric dichroism on the one hand, and transient electric light scattering on the other, yield different initial slopes and hence apperently different values for D. These important conclusions have not been appereciated in previous studies and indicate the need for caution when comparing data from different experimental methods. I11ustrative calculations are presented for a polydisperse system of long thin cylinders having a normal distribution in lengths, but of uniform diameter. Some preliminary measurement support the theory.
Synthesis and conformational study of poly(Nϵ‐benzyl‐L‐lysine) and its benzyloxycarbonyl derivative
Authors: Yamamoto Hiroyuki , Hayakawa Tadao 
Published: December 2004

AbstractThe solvent‐and pH‐induced conformational changes are examined in order to investigate the influence of benzyl group. Polymer was prepared via Nϵ‐benzyloxycarbonyl, Nϵ‐benzyl‐Nα‐carboxy‐L‐lysine anhydride. The resulting poly (Nϵ‐benzyloxycarbonyl, Nϵ‐benzyl‐L‐lysine) was obtained in high yield and had a high molecular weight. The protected polymer was removed into poly (Nϵ‐benzyl‐L‐lysine) by treating it with hydrogen bromide. From the results of the ORD and CD, the protected polymer has a righthanded α‐helix, showing [m′]233 = –10,300, [θ]220 = –27,600 and [θ]207 = –25,100 in dioxane. The breakdown of the helical conformation is found to occur at 8% dichloroacetic acid in chloroform‐dichloroacetic acid mixture. In the pH range 3.35–6.90, poly (Nϵ‐benzyl‐L‐lysine) is in a random coil structure. In the pH range 7.50–13.0, the polypeptide has a right‐handed α‐helix structure; [m′]233 = –12,000, [0]220 = –27,200, and [0]207 = –27,000. In comparison with poly‐L‐lysine, the coil‐to‐helix transition is observed at lower pH range in 50% n‐propanol. Above pH 8 by heating, the α ⇀ β transition of poly (Nϵ‐benzyl‐L‐lysine) is not observed in an aqueous media.
Phase relationships of an equivalent mixture of sulfated polyvinyl alcohol and aminoacetalyzed polyvinyl alcohol in microsalt aqueous solution
Authors: Nakajima Akio , Sato Hiroko 
Published: December 2004

AbstractA new type of polymer salt was prepared from an equivalent mixture of partly sulfated polyvinyl alcohol (polyanion, Q−) and partly aminoacetalyzed polyvinyl alcohol (polycation, P+). With respect to a three‐component system composed of this polymer salt (P+Q−), water, and a microsalt (K+A−), phase relationships, as represented by complex coacervation, were investigated. Experimental results were discussed according to a theoretical equation for the free energy of mixing derived by taking into account the entropy and enthalpy contributions as ascribed for non‐ionic polymer solution, and the electrostatic free energy expression as derived by Voorn.
Conformational studies of α‐glucans
Authors: Sathyanarayana B. K. , Rao V. S. R. 
Published: December 2004

AbstractA study of the effect of linkage on the possible conformations of di‐and polysaccharides of α‐D‐glucose and also the probable intramolecular hydrogen bonds has been made. The differences in the nature of linkage is shown to effect the energetically preferred conformations; (1 → 2) linkages lead only to righthanded helical conformations, (1 → 3) linkages lead to extended as well as both left and righthanded helical conformations; (1 → 4) linkages lead to both right‐and lefthanded wide helical conformations. The possible hydrogen bonds between adjacent residues are also dependent on the nature of the linkage. A comparison of the conformational data of α‐D‐glucans with those of β‐D‐glucans has indicated that the favored conformations and hydrogen bonds between contiguous residues in the chain are influenced by the configuration at the anomeric carbon atom in all the three types of polysaccharides. From the energy calculations a probable conformation (ϕM = −10°, ψM = −30°, ϕN = −23°, ψN = −19°) has also been proposed for crystalline mycodextran in conformity with x‐ray data. This conformation contains two types of hydrogen bonds between contiguous residues one between 0–2 and 0–3 atoms at (1 → 4) linkage and the other between 0−2 and 0–4 atoms at (1 → 3) linkage in the chain. The conformation of maltose unit (−10°,−30°) that is likely to occur in the crystalline mycodextran coincides with the minimum energy conformation of maltose.