bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mise en évidence d'une relation entre la longueur el la constante de sédimentation des molécules de DNA en solution
Authors: Nicolaíeff Anatole , Litzler Robert 
Published: May 2005

AbstractA comparative study on sonicated calf thymus DNA was made by using electron microscopy and sedimentation methods. The length distribution, established by electron microscopy by using Kleinschmidt's technique, is related to the sedimentation curve obtained with the same solution. The relation permits a determination of the sedimentation constant corresponding to a given length up to 8000 Å and vice versa.
Helix–coil transition of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine: Thermodynamic and statistical analysis
Authors: Lotan Noah , Bixon Mordechai , Berger Arieh 
Published: May 2005

AbstractThe thermally induced conformational changes of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine in water and in methanol–water (3:7 v/v) have been analyzed in terms of the Lifson‐Roig theory. The transitions in both solvents can be described by using v = 0.017. The thermodynamic parameters for the random coil‐to‐helix transition of one amino acid residue at room temperature were found to be: in water, ΔH = − 130 cal/mole and ΔS = − 0.45 e.u.; in methanol–water (3:7 v/v), ΔH = − 170 cal mole and ΔS = − 0.45 e.u. The size distribution of helical segments is broad, and the results of numerical calculations are presented for three degrees of polymerization (DP = 100, 300, and 750).
Conductivity and photoconductivity of NaDNA in the solid state
Authors: Šubertová E. , Prosser V. , Drobník J. 
Published: May 2005

AbstractThe d. c. conductivity of five samples of NaDNA in dry state was investigated. All specimens show similar behavior, with specific resistivity at 40°C of the order of 1013–1014 ohm‐cm and an energy gap of Ec = 2.04–2.25 eV. Based on the Eley's model for conductivity mechanism, the possibility of conservation of an ordered structure in the dry state (temperature range 20–80°C) is discussed. This is ascribed to the interaction of electron systems of individual bases. From the activation energy values it may be estimated that 17–19 π‐electrons take part in the interaction. Photoconductivity measurements indicated activation energies Ef of 0.88–0.96 eV in the visible region.
Morphological evidence for the folding of polyproline II helices
Authors: Andries J. C. , Walton A. G. 
Published: May 2005

AbstractSpherulites of poly‐L‐proline II were grown by film casting from a dilute formic acid solution. Electron diffraction indicated that the molecular axis was parallel to the surface and essentially normal to the face of the lamellae. The molecular length was five times greater than the width of the lamellae. This is considered to he substantial evidence for the molecular folding of poly‐L‐proline II. A correlation between the molecular conformation of poly‐L‐proline in solution and the observed morphological form in the solid state has been determined. As the solution mutarotates from form I to form II, the solid morphology varies from an indistinetly shaped spherulite with little inner detail to a well formed crystalline spherulite complete with lamellae.
Persistence length of DNA
Authors: Hays John B. , Magar Magar E. , Zimm Bruno H. 
Published: May 2005

AbstractIn the wormlike chain (Kratky‐Porod) model of DNA the stiffness of the chain is determined by the persistence length, a. The persistence length may be evaluated from light‐scattering measurements of the molecular weight and the mean‐square radius if the samples are not polydisperse or if the polydispersity can be quantitatively determined. The persistence length can also be evaluated with the aid of hydro dynamic theory from measurements of intrinsic viscosity and sedimentation coefficient. Data taken from the literature and from other studies by the authors are examined by these methods. The light‐scattering method yields a value of a of 900 ± 200 Å the hydrodynamic data yield 600 ± 100 Å. These values are considerably larger than those obtained by most previous authors.
Interactions of metallic ions with DNA. V. DNA Renaturation Mechanism in the Presence of Cu2+
Authors: Richard Hélène , Schreiber J. P. , Daune M. 
Published: May 2005

AbstractNew experimental data were obtained by means of circular dichroism, melting, renaturation, and kinetic experiments, upon Cu2+ binding to DNA, poly dAT, and poly dGdC. They enable us to propose a model of binding giving a satisfactory explanation to all of the data found in the literature. Two types of binding sites are proposed: (a) a “sandwich” of Cu2+ between two adjacent G‐C pairs giving a charge‐transfer complex, and (b) a chelate between a phosphate group and a nitrogen atom of the bases (N7 of guanine and N3 of cytosine at room temperature, N3 of adenine after thermal opening of A‐T pair). Type (a) stabilizes the helix and keeps the two strands linked. Type (b) destabilizes the helix and explains why the kinetic rate of renaturation is the same as that of copper release.
Ultrasonic absorption studies of poly‐benzyl‐L‐aspartate in mixed solvents, in relation to the helix–coil transition
Authors: Zana R. , Lang J. 
Published: May 2005

AbstractUltrasonic absorption measurements were carried out on solutions of polybenzyl‐L‐aspartate (PBLA) in chloroform–dichloroacetic acid (DCA) and in 1,2‐dichloroethane (DCE)–DCA, in the range 3.9–155 MHZ. The helix–coil transition of PBLA produces an increase of absorption which is larger in CHCl3–DCA than in DCE–DCA solutions. The influence of the solvent on the excess ultrasonic absorption suggests that solvation processes may be involved in these changes of absorption. The plots of the absorption vs. the volume fraction of DCA do not show any absorption maximum. This indicates that the ultrasonic absorption is not sensitive to the helix–coil equilibrium of PBLA in the frequency range investigated. A maximum value of 109 S−1 has been obtained for the rate constant of growth of a helix region.
Different conformations of double‐stranded nucleic acid in solution as revealed by circular dichroism
Authors: Ivanov V. I. , Minchenkova L. E. , Schyolkina A. K. , Poletayev A. I. 
Published: May 2005

AbstractConformation of two‐stranded DNA in H2O–methanol, H2O–ethanol, H2O–isopropanol, and H2O–dioxane solutions at different concentrations of alkaline ions has been studied with the aid of circular dichroism. The following conclusions are drawn:The conformation of DNA in H2O and H2O–methanol belongs to a family of B forms (B, C, T forms are the representatives of the family). The magnitude of the winding angle between adjacent base pairs (θ) is determined by the concentration and type of the cations. In H2O the cation action is nonspecific and leads to an increase in θ value. In 80% methanol the ions act specifically, Cs+ being to stabilize a form with a greater θ value, and Li+ being with a lesser one. The total θ change is likely within the limits of 33° ⩽ θ ⩽ 45°.At high content of ethanol, isopropanol, or dioxane (∼80%), but not with methanol, and in low ionic strength the conformation of DNA belongs to a family of A forms (A form is one of the members of the family) and is specified by the concentration and type of cation involved. The two‐stranded regions of RNA in H2O are also of A type and winds with the rise of cation concentration. The range of θ variation is not narrower than 30° ⩽ θ 33°.The conformational transitions within the families (induced by ions) are of non‐cooperative pattern, wheras the transitions between the families (induced by nonpolar component) are of cooperative pattern. The effect of cations, when specific, is discussed on the basis of steric correspondence between the width of DNA narrow groove and the size of a hydrated cation.
Electric permittivity of alfalfa mosaic virus in aqueous solutions
Authors: Touw F. Van Der , Briedé J. W. H. , Mandel M. 
Published: May 2005

AbstractThe electric permittivity of alfalfa virus particles in buffer solutions of three different concentrations at pH 7 was studied between 10 kHz and 100 MHz. The experimental results could be described with one single dispersion curve of the Cole‐Cole type characterized by a concentration independent specific dielectric increment and mean relaxation time. The results were interpreted semi‐quantitatively in terms of counterions–atmosphere polarizability, neglecting counterion repulsion.
Interaction of the polyelectrolyte heparin with copper(II) and calcium
Authors: Lages Bruce , Stivala S. S. 
Published: May 2005

AbstractThe binding of copper(II) ions by heparin was investigated using equilibrium dialysi techniques, and the effects of this binding on solution properties determined. In neus tral Tris buffer solutions, heparin binds a maximum of twenty‐three to twenty‐four copper ions in two classes of sites, one containing three to four binding sites, the other containing twenty to twenty‐one sites. Cooperative binding is associated with the larger class of sites. In more acidic citrate buffer solution, only one class of sites is observed, containing about four to five binding sites. Association constants are calculated for the classes and the possible chemical nature of the sites is discussed. The binding of calcium ions in neutral buffer is also examined, and these ions appear to be bound by a group of twenty to twenty‐one binding sites, with a larger association constant than that for the copper ions. Definite effects on the solution properties of heparin, such as intrinsic viscosity, sedimentation coefficients, and partial specific volume, can be observed only in the cooperative binding of copper ions in neutral buffer. The interpretation of these solution properties in terms of molecular size and shape is analyzed, and it is concluded that the metal ion interactions cause no major change in the apparently random coil conformation of heparin in buffered solution, although some minor changes can be associated with the cooperative uptake of copper ions.
Proton magnetic resonance studies of the conformational changes of dideoxynucleoside ethyl phosphotriesters
Authors: Kan Lou S. , Barrett James C. , Miller Paul S. , Ts'O Paul O. P. 
Published: May 2005

AbstractPMR investigations on the diastereomeric phosphate methyl protons of the dinucleoside ethyl phosphotriesters Tp(C2H5)T, dA, and dIp(C2H5)dI have been used to study the conformational changes of these dimersin solution. In D2O (273°K), the diastereomeric phosphate‐methly groups of Tp(C2H5)T appear as a triplet. The methyl resonances of dIp(C2H5)dI and dAp(C2H5)dA appear as two sets of triplets and their chemical shift differences (δ1 − δ2), decrease with increasing temperature, finally becoming zero at 292°K and 333°K, respectively. The same phenomenon is observed for dAp(C2H5)dA in CD3OD; in this detacking solvent, the difference (δ1 − δ2) diminishes to zero at a lower temperature (261°K). At room temperature in D2O, the chemical shift of the phosphate methyl of Tp(C2H5)T appears at lower field than those of dIp(C2H5)dI or dAp(C2H5)dA. The differences between the chemical shifts of these groups (δI − δT or δA − δT) increase with increasing temperature, and reach maximal values at 301°K and 333°K, respectively. The results suggest that at low temperature the largest fraction of the dimer population exists in a stacked state, with the phosphate‐ethyl groups outside the stack. Increasing temperature causes an oscillation of the bases and a shift in the dimer population away from the stacked state. Finally at high temperature, the planar bases rorate with respect to one another and in the case of dIp(C2H5)dI and dAp(C2H5)dA, the ethyl groups experience shielding by the anisotropic ring current of the five‐membered ring of the bases. Thus, the current pmr studies and those reported earlier from our laboratory support an “oscillation‐rotation model” for the unstacking process of the dimers. The relationship of this model and the “two‐state model” is discussed.
Etude Phsicochimique des Copolymères Triséquencés Poly(γ‐L‐glutamate de benzyle)/Poly(oxyéthylène)/Poly(γ‐L‐glutamate de benzyle). Rǒle de la Polydispersiteé dans la Détermination de la Conformation des Molécules en Solution Diluée
Authors: Reibel Léonard , Spach Gérard , Dufour Claude 
Published: May 2005

AbstractWe have prepared a series of three‐block copolymers containing the same central block of poly(ethylene oxide) (POE) and two side blocks poly(γ‐L‐glutamate) (PBLG) of variable lengths. These molecules could present an unusual conformational model when dissolved in solvents where PBLG exhibits a helical structure: a helical structure: a gaussian chain connected at each end to a rigid rod. We checked this hypothesis by light scattering, viscosimetry, and dielectric adsorption measurements.In order to take into account the possibility that the orientations of the two rods may not be completely independent, we have introduced in the calculations the angle θ, formed by the two rigid segments. We have mainly considered three types of conformation which can be described by assimilating the lods of PBLG of two vectors having their origin at the juncture with the POE chain: depending whether cos θ (the average value of cos θ) is equals to −1,0, or +1 ( where the two vectors are antiparalles, oriented independently, or parallel, respectively). We have tried to establish a theoretical expression for the molecular size obtained by each method of investigation, as a function of cos θ. We corrected this value to account for the effect of the polydispersity on the molecular size and then compared the theoretical values thus calculated with the experimental results. The measurements of the radius of gyration, R, by light scattering does not permit the unambiguous determination of cos θ. As soon as the system is not perfectly monodisperse, the variation of R as a funciton of cos θ is not very large. The viscosity results are also difficult to interpret because the effect of the polydispersity on the viscosity cannot be established fo each conformational model. However, a clear answer can be obtained by the dielectric absorption technique for two reasons: the variation of the dielectric absorption as a function of cos θ is very important and the influence of the polydispersity on the measurements is weaker than for the two former methods. The results show that cos θ is equal to −1, demonstrating that the two vectors are antiparallel.From the dielectric dispersion, one sees that the total length of the molecule is roughly equals to the sum of the lengths of the two rigid blocks. To explain this result we propose a new conformational model. Since it is known that in some solvents and mixtures of solvents the molecules of PBLG tend to associate, we assume that the two rigid rods are antiparallel and partly associated. The associated part of the molecule is assumed to be surrounded by the mixture of POE and solvent, which acts as a poor solvent (ef. Fig. 2.).
A model for solvent contributions to polypeptide and protein circular dichroism
Authors: Pysh E. S. 
Published: May 2005

AbstractThe possibility of bound solvent contributing directly to the circular dichroism of polypeptides and proteins is discussed. The model presented is based on the requirement of a breakdown in the planar symmetry of the amide environment. This symmetry breakdown is described in terms of the conformational states of the chain, and leads to necessary, but not sufficient, conditions for observable solvent contributions. Application of the model leads to the conclusion that, while some chain conformations are intrinsically incapable of roviding the required breakdown in the symmetry of solvent perturbations, other conformations force such a breakdown, notably poly‐L‐proline II and disordered chains.
Energy transfer in tRNAPhe (Yeast). The solution structure of transfer RNA
Authors: Blumberg W. E. , Dale R. E. , Eisinger J. , Zuckerman D. M. 
Published: May 2005

AbstractIn the preceding paper, the dependence of the dipolar orientation factor κ2, which governs long‐range (Förster) energy transfer, on the relative orientation and reorientational freedom of the donor and acceptor chromophores is examined. The analysis given there is employed to derive minimum and maximum values of 〈κ2〉 for energy transfer from the Y base of tRNAPhe (yeast) to an acriflavine acceptor attached to the 3′ terminus of the tRNA using estimates for the reorientational freedom of the donor derived from a combination of steady‐state and time‐dependent polarized emission measurements. The acceptor motion is estimated from data in the literature. From these limiting values of 〈κ2〉 and Beardsley and Cantor's determination of the long range energy‐transfer efficiency for this donor–acceptor pair, the interchromophore distance R is calculated to be between 34 and 61 Å, this range being independent of the particular model chosen to described the reorientational freedom of the donor and acceptor. While this large range in R is of little help in establishing the solution structure of tRNA, the analysis illustrates the potential of polarized energy‐transfer experiments, particularly when transfer depolarization experiments are possible.
Water sorption on deoxygenated hemoglobins CC, SC, SS, AS, and AA
Authors: Killion Philip J. , Cameron Bruce F. 
Published: May 2005

AbstractFive human hemoglobins whose genetic relationship to one another involves one set of alleles, hemoglobins CC, SC, SS, AS, and AA, were studied in the deoxygenated form within a McBain gravimetric sorption system at 28°C. Water was used as the adsorbate at relative vapor pressures ranging from 0.11 to 0.39. The results of this study are reported and compared with a similar study on the ferric form of these same five hemoglobins. For both forms of hemoglobin studied, a slight increase was measured in the number of polar sites accessible to H2O vapor for those genotypes in which the substituent in the sixth position from the N terminus of the two β chains had a positively charged side chain, i.e., hemoglobin C. Those samples containing hemoglobin S (less soluble in the deoxy form) show an increased BET monolayer coverage in the deoxy as compared to the ferric form. For each genotype, the deoxygenated form had more polar sites accessible to H2O vapor than its ferric form. This finding is in agreement with an increase in the size of the central cavity as shown by crystallographic analysis.
Intensities and other spectral parameters of infrared amide bands of polypeptides in the α‐helical form
Authors: Chirgadze Yu. N. , Brazhnikov E. V. 
Published: May 2005

AbstractIntensities and other spectral parameters of infrared amide I and II bands of α‐helical polypeptides in solutions have been determined for poly(γ‐benzylglutamate), poly(γ‐ethylglutamate), and polymethionine in chloroform, polylysine, poly(glutamic acid), and fibrillar protein tropomyosin from rabbit muscles in heavy water. The majority of spectral parameters are characteristic. The half‐width of the amide I band was found to vary in the range of 15–40 cm−1 for different polypeptides in the different solutions. The correlation between this parameter of the amide I band and the stability of the α‐helix was estimated. A new weak band near 1537 cm−1 of unknown origin was observed for the hydrogen form of polypeptides in the α‐helical state.
Energy bands and electronic delocalization in the sugar‐phosphate backbone of DNA
Authors: Suhai Sándor 
Published: May 2005

AbstractThe results of a CNDO/2 all‐valence electron crystal orbital study are reported for the sugar‐phosphate chain of DNA. The valence and conduction bandwidths are found to be large enough to make electronic delocalization through this backbone possible. Different mechanisms for charge carrier transport in DNA are compared on the basis of the electron and hole effective masses. Conduction along the backbone seems to be at least as probable as through the aperiodic system of the superimposed nucleotide bases.
The state of water on hydrated collagen as studied by pulsed NMR
Authors: Fung B. M. , Witschel John , McAmis Lavon L. 
Published: May 2005

AbstractThe spin‐lattice relaxation time (T1) of water adsorbed on collagen fibers was determined at six frequencies and temperatures varying from 25° to −80°C. Care was taken to eliminate the contributions to the signal of protons other than those in the adsorbed water. Quantitative calculations were made on T1 and the results were compared with the experimental data. It is suggested that a maximum of about 0.50–0.55 g water per g collagen forms a hydration layer, which cannot be frozen down to −90°C and exhibits a distribution of motional correlation times. For collagen samples containing a larger quantity of adsorbed water, the additional water molecules behave like ordinary isotropic water, having a single correlation time and a freezing temperature of about −10°C.
Evaluation of kinetic parameters of thermal decomposition of native collagen by thermogravimetric analysis
Authors: Lim Jong J. , Shamos Morris H. 
Published: May 2005

AbstractThe kinetic parameters associated with the thermal decomposition of native collagen have been obtained by thermogravimetric techniques. In order to achieve this a thermogravimetric analysis was carried out in the temperature range of 25°C to about 1000°C. In this temperature range, it had been found that the differential primary weight loss curve had yielded three distinct peaks for the tendon collagen. The thermal decomposition corresponding to each peak was analyzed to retrieve its kinetic parameters. The peak temperature associated with the first peak decreased as the water content in a sample increased, while that of the second peak was independent of its hydration condition. It is believed that the first and the second peaks are, respectively, results of: (1) dissociation of water from collagen, and (2) of breaking of the collagen molecule itself. The third peak has not been easily identified so far. The activation energy and the order of water decomposition are obtained by various known methods. The results obtained by these different approaches agree reasonably well. The kinetic parameters of second and third peak are also obtained and reported here.
Raman spectroscopic study of tropomyosin denaturation
Authors: Frushour B. G. , Koenig J. L. 
Published: May 2005

AbstractRaman spectra of the pH denaturation of tropomyosin are presented. In the native state tropomyosin has an alpha‐helical content of nearly 90%, but this value drops rapidly as the pH is raised above 9.5. The Raman spectrum of the native state is characterized by a strong amide I line appearing at 1655 cm−1, very weak scattering in the amide III region around 1250 cm−1, and a medium‐intensity line at 940 cm−1. When the protein is pH‐denatured, a strong amide III line appears at 1254 cm−1 and the 940 cm−1 line becomes weak. The intensities of the latter two lines are a sensitive measure of the alpha‐helical and disordered chain content. These results are consistent with the helix‐to‐coil studies of the polypeptides.The Raman spectra of α‐casein and prothrombin, proteins thought to have little or no ordered secondary structure, are investigated. The amide III regions of both spectra display strong lines at 1254 cm−1 and only weak scattering is observed at 940 cm−1, features characteristic of the denatured tropomyosin spectrum. The amide I mode of α‐casein appears at 1668 cm−1, in agreement with the previously reported spectra of disordered polypeptides, poly‐L‐glutamic acid and poly‐L‐lysine at pH 7.0 and mechanically deformed poly‐L‐alanine.