bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solution properties and structure of brain proteolipids
Authors: Zand Robert 
Published: December 2004

AbstractBovine white matter proteolipids have been studied by several physical methods and have been found to exist as micelles in 2 : 1 (v/v) chloroform–methanol solution. The data would indicate the existence of a critical micelle concentration at 0.017–0.022 g/100 ml. The curve appears linear in the range 0.017–0.2 g/100 ml, but from the data at higher concentrations it would appear that a change in slope is occurring in the region 0.2–0.3 g/100 ml. Light‐scattering measurements on 2 : 1 (v/v) chloroform–methanol solutions containing more than 0.2 g/100 ml of proteolipid yielded a weight‐average aggregate weight of 2.9 × 106and a radius of gyration of 64.5 Å. The intrinsic viscosity of the solutions was 0.32 dl/g and the Huggins constant was 1.085. Light‐scattering measurements in 88.5% formic acid–0.5M sodium formate yielded a weight‐average aggregate weight of 7.1 × 106 and a radius of gyration of 241 Å. The intrinsic viscosity observed for this solvent system is 0.14 dl/g and the Huggins constant is 1.005. Osmotic pressure measurements in 2 : 1 (v/v) chloroform–methanol containing less than 0.2 g/ 100 ml of proteolipid yielded a number‐average aggregate weight of 7.2 × 104 Ultracentrifugal analysis in 1.5:1 (v/v) methylene chloride–methanol showed two broad peaks with, s values of s1.5% = 20.05 S, s2% = 19.79 S for the minor peak and s1.5%,2% = 1.86 S for the major peak. Optical rotatory dispersion studies revealed large changes in b0 with change in solvent and proteolipid concentration. The present data suggest that the mode of attachment of protein to lipid is primarily of a noncovalent type. The results of this investigation also suggest that the proteolipid micelle above 0.2 g/100 ml is cylindrical (prolate ellipsoid) in 2:1 (v/v) chloroform‐methanol and approaches a more spherical shape in 88.5% formic acid. A structure for the proteolipid micellar complex above concentrations of 0.2 g/100 ml is proposed.
Dynamic‐elastic investigation of the chemical denaturation of collagen fibers
Authors: Reich S. , Katchalsky A. , Oplatka A. 
Published: December 2004

AbstractThe dynamic elastic behavior of collagen fibers treated by LiBr solutions was studied by the method of free longitudinal vibrations. The frequency response functions and the stress–strain relationship were evaluated for fibers denatured to different extents by various concentrations of the salt solution. The James and Guth model for rubber elasticity was applied to the experimental data. The elastometric parameter β, which is a measure of the degree of folding of the macromolecular chains, was found to decrease on increasing the salt concentration. It might thus serve as a characteristic of the degree of denaturation of fibrillar proteins.
On the triplet states of polynucleotide–acridine complexes. I. Triplet energy delocalization in the 9‐aminoacridine–DNA complex
Authors: Galley W. C. 
Published: December 2004

AbstractPhosphorescence and fluorescence from the dye in complexes of DNA with 9‐amino‐acridine and acridine orange in a glycerol‐H2O glass have been measured at 77°K. The dependence of the p/fratio for 9‐aminoacridine on the exciting wavelength demonstrates triplet–triplet energy transfer from DNA to dye. The result provides evidence for π electron overlap between the dye and the bases of native DNA. The observation that the magnitude of the enhancement in ultraviolet‐excited dye phosphorescence increases with the base to dye ratio indicates triplet delocalization in the polymer. Preliminary flash experiments provide evidence that this delocalization is not limited by slow diffusion of the triplet exciton. The inability to detect transfer on denaturation of the DNA illustrates the sensitivity of triplet–triplet energy transfer to the conformation of the macromolecular complex.
Studies on the myosin molecule from smooth muscle
Authors: Kotera Akira , Yokoyama Masao , Yamaguchi Masahiro , Miyazawa Yuji 
Published: December 2004

AbstractThe myosin molecule was extracted from the smooth muscle parts of horse esophagus and purified by ammonium sulfate fractionation. The schlieren pattern of the sedimentation velocity run showed a very sharp single peak of.5.9. S (s20,w). Molecular weight of the protein was measured by means of the Archibald and sedimentation equilibrium methods, both in 0.5M KCI buffered by 1/150 M phosphate at pH 7.5 and at 5°C. The values obtained were 6.25 × 105 and 5.81 × 105respectively, for the two methods. The second virial coefficients were 1.1 × 104 and 1.2 × 10−4 ml/g. Denatured smooth muscle myosin was prepared in a solution of 5M guanidine HC1 containing 0.4 M KC1 and 0.2 M β‐mercaptoet hanol buffered at pH 8.0. The weight‐average molecular weight of the denatured smooth muscle myosin was 2.24 × 105 and the second virial coefficient was 7.6 × 10−4 ml/g. The values described above are in good agreement with those reported for rabbit skeletal myosin with ammonium sulfate fractionation. The molecular dimension of the molecule is estimated as the value for an axial ratio of 100, assuming a rigid rod molecular model for this molecule, both the thermodynamical and hydrodynamical treatment being in a good agreement with this estimation.
Optical rotatory dispersion of mucopolysaccharides and mucopolysaccharide–dye complexes. II. Ultraviolet cotton effects in the amide transition bands
Authors: Stone A. L. 
Published: December 2004

AbstractUltraviolet optical rotatory dispersion curves of mucopolysaccharides exhibit particular Cotton effects in the spectral region of the n–π and π–π amide transitions. Two general patterns emerge: (1) enhancement of negative rotation and of the first negative Cotton effect (troughs 217–220 mμ) and (2) relative dominance of the positive Cotton effect in the π–π transition region (peak ∼198 mμ). Groups (1) and (2) can be correlated with a structural difference in the linkages of the amino sugars: (1) occurs with polymers containing 3‐1‐linked glycosamino sugars and (2) with glycosamino moieties linked 4–1 by either α‐ or β‐glycosidie bonds. Measurements of the circular dichroic absorption bands support the qualitative conclusions from optical rotation. All mucopolysaccharides exhibit a first, negative band centered at 208–211 mμ, while only those in group (2) show, in addition, a positive band centered at 189–192 mμ. A suggested unifying model considers that difference in kind and/or degree of preferred geometry of the amide groups obtains from two forms of secondary order: (1) having a linear hydrogen bond from the N (acceptor) to the (C2)O—H of the preceding uronic acid and (2) having a linear hydrogen bond from the N (acceptor) to the (C2 or 3) O—H of the following sugar. The hydrogen bonds would have similar strength but opposite directions in two systems towards the nonreducing end (1) or towards the reducing end (2)], closing eight‐membered rings magnified image
Quantum mechanical approach to the conformational analysis of macromolecules in ground and excited states
Authors: Hoffmann Roald , Imamura Akira 
Published: December 2004

AbstractMolecular orbital calculations of the extended Hückel type have been used to study the conformations of glycyl and alanyl residues in ground and excited states. The ground‐state surfaces show features similar to those obtained with the standard calculational methods in which the total energy is partitioned into components such as torsions, nonbonded and electrostatic interactions. The molecular orbital calculations provide the first independent theoretical check on such calculations. The excited‐state surfaces, Uniquely available from the molecular orbital calculations, exhibit a better definition and sharpening of potential minima in the sterically allowed regions.
Formation of a streaming convective disturbance which may occur at one gravity during preparation of samples for zone centrifugation
Authors: Nason Paul , Schumaker Verne , Halsall Brian , Schwedes Jean 
Published: December 2004

AbstractZone centrifugation experiments are occasionally ruined by convective processes which occur at one gravity subsequent to layering a solution of macromolecules on a supporting density gradient. The factors which contribute to this convection have been little understood. In most of the experiments described in this communication, Blue Dextran 2000 is used as the macromolecular component. The convective disturbance may be clearly seen and accurately measured. The effects of macromolecular concentration, composition and density of the supporting gradient, diffusion coefficient of the solute, and several other variables are studied, and an empirical equation constructed to describe the phenomenon. This convective disturbance appears to be minimized or prevented by layering and fractionating in the presence of a centrifugal field.
Dependence of polynucleotide helix–coil transition theory on the ring closure exponent
Authors: Klotz L. C. 
Published: December 2004

AbstractFormulas are derived which relate the maximum slope of the helix‐coil transition in synthetic polynucleotides to the stacking free energy and to the exponent k in the expression for the probability of ring closure for polymer chains. The exact value of k has not yet been determined. By use of the derived formulas, it is then shown that estimates of the stacking free energy are sensitive enough to the value chosen for k, so that exact values of these energies must await a precise determination of k.
Hydrogen‐tritium exchange of the random chain polypeptide
Authors: Englander S. W. , Poulsen A. 
Published: December 2004

AbstractThe Hydrogen–tritium exchange character of poly‐D,L‐alanine was studied in detail as a model for the hydrogen exchange behavior of the unhindered, polymeric peptide group. The random chain nature of poly‐D,L‐alanine was evident in the uniformity of exchange rate of all its hydrogens and in the similarity between this rate and that of random chain poly‐D,L‐lysine and other known, unhindered secondary amide groups. An equilibrium isotope effect favoring the binding of tritium over protium to the extent of 21% was measured. Specific acid and base catalysis of the exchange and the absence of detectable general catalysis were demonstrated. Apparent energy of activation is 17 kcal/mole for deprotonation, largely due to dependence of Kw on temperature, and 15 kcal/mole for protonation, which correlates with the extreme apparent pK. The hydrogen –tritium exchange half‐time rate; of poly‐D,L‐alamine at any pH and temperature (T: °C) is given by the equation:
Synthesis of poly‐L‐asparagine and poly‐L‐glutamine
Authors: Ariely S. , Fridkin M. , Patchornik A. 
Published: December 2004

AbstractPoly‐β‐N‐diphenylmethyl‐L‐asparagine and poly‐γ‐N‐diphenylmethyl‐L‐glutamine were prepared from the corresponding N‐carboxyanhydrides. Poly‐L‐aspuragine and poly‐L‐glutamine were obtained by removal of the diphenylmethyl protecting groups with liquid anhydrous hydrofluoric acid.
Spatial configurations of polynucleotide chains. I. Steric interactions in polyribonucleotides: A virtual bond model
Authors: Olson Wilma K. , Flory Paul J. 
Published: December 2004

AbstractA simplified scheme for treating the spatial configurations of polynucleotide chains is developed using the rotational isomeric state approximation and statistical methods applicable to linear systems of interacting subunits. As a consequence of geometric constraints imposed by the skeletal structure and of the severity of certain steric interactions, it is possible to represent the repeat unit comprising six skeletal bonds by two virtual bonds of fixed length. The configuration of the polynucleotide chain as a whole may be conveniently described by an alternating succession of these two virtual bonds. Moreover, analysis of steric interactions suggests that bond rotations governing the mutual orientation of a given pair of successive virtual bonds should be sensibly independent of the rotations affecting the mutual orientation of other pairs. The statistical mechanical treatment of configuration‐dependent properties is much simplified in consequence of this mutual independence. Mean‐square dimensions calculated by giving equal weights to all sterically allowed conformations are much smaller than values determined by Felsenfeld and co‐workers. The calculated dimensions are markedly increased, however, by placing certain arbitrary restrictions on the rotations about selected pairs of skeletal bonds. It is thus demonstrated that steric interactions alone are insufficient to account for the spatial characteristics of polynucleotide chains. The dimensions are also found to be sensitive to the conformation of the ribose ring of each nucleotide unit, but, insofar as the influences of steric interactions are concerned, the dimensions do not depend on the heterocyclic base attached to the ribose ring.
“Active monomer” polymerization of δ‐benzyl L‐α‐aminoadipate
Authors: Choi Nam S. , Goodman Murray 
Published: December 2004

AbstractThe N‐carboxyanhydride of δ‐benzyl L‐α‐aminoadipate polymerizes when initiated by strong base through an “active monomer” mechanism. This is shown by the isolation of 6‐oxo‐L‐pipecolic acid from the product mixture, since this byproduct could only arise from an “active monomer” pathway. This study also specifies conditions for preparing high molecular weight poly(δ‐benzyl L‐α‐aminoadipate) in high yield.
X‐Ray and stereochemical studies on xylan diacetate
Authors: Gabbay S. M. , Sundararajan P. R. , Marchessault R. H. 
Published: December 2004

AbstractBy means of x‐ray fiber diffraction, it has been found that xylan diacetate crystallizes with two chains or four residues in a monoclinic cell (space group P21): a = 7.64, b = 12.44, c (fiber axis) = 10.31 Å, and γ = 85°. Pairs of residues are related by a twofold screw axis in the c direction. Based on the observed fiber repeat and chain symmetry, the probable conformation of a pair of xylose diacetate residues joined via a β‐1,4′ linkage has been obtained by energy minimization methods. The conformations corresponding to a threefold screw axis and a twofold screw axis along the chain have been compared and the reason why xylan diacetate assumes a twofold screw axis seems to be due to intermolecular packing effects rather than intramolecular non‐bonded interactions.
Sodium counter ion activity of poly‐S‐carboxyethyl‐L‐cysteine
Authors: Maeda Hiroshi 
Published: December 2004

AbstractCounterion activity of poly‐S‐carboxyethyl‐L‐cysteine in salt‐free solutions neutralized to various degrees with sodium hydroxide was determined either directly from the e.m.f measurements of concentration cells formed across a Na–glass electrode, or from the potentiometric titrations at different sodium chloride concentrations assuming the additivity rule.From e.m.f. measurements, the activity coefficient of counterions was confirmed to display the β‐structure random coil transition of the polymer.For random coil state, both methods gave identical results. Observed values of the activity coefficient was generally smaller than those for other randomly coiled polypeptides. The activity coefficient was found to decrease with the increase of the polymer concentration.The activity coefficient of counterions for β‐structure was extremely small as compared with that for random coil at the same degree of neutralization. The activity coefficient obtained from titrations was almost independent of degree of neutralization and increased with the increase of the polymer concentration.
Determination of pK's of trinucleotides
Authors: Javaherian K. 
Published: December 2004

AbstractpK's of trinucleotides are calculated according to the theory of Kirkwood and Westheimer for ellipsoids. In order to compare the calculated values with some experimental results, a number of trimers were prepared and their pK's were measured. The question of syn and anti conformations for monomers are discussed in light of the above considerations.
Viscosity of heparin as a function of dielectric constant and of desulfation
Authors: Yuan L. , Stivala S. S. 
Published: December 2004

AbstractThe effect of dielectric constant (D) of the solvent on the viscosity of heparin was examined using the relation \documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{{\rm sp}} /c = [\eta ]_\infty (1 + k/\sqrt c) $\end{document}, where [η]∞ is the shielded intrinsic viscosity obtained by extrapolating \documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{{\rm sp}} /c\,{\rm vs}{\rm . }\,1/\sqrt c ) $\end{document} to infinite concentration, and k is an interaction parameter independent of the dielectric constant of the solvent. This equation was previously reported by the authors9 for describing the reduced viscosities of strong polyelectrolytes in salt‐free polar solvents. It was found that the [η]∞ of heparin increases linearly with increasing dielectric constant of the solvent whereas the k values were, within experimental error, independent of D in the range 54.7 < D < 93.2 examined. Graded hydrolysis of heparin from its acid form (heparinic acid) at 57°C resulted in samples of varying degree of desulfation with corresponding decrease in biological activity. It was found that both [η]∞ and k decrease with increasing desulfation.
Normal vibrations of α‐glycylglycine
Authors: Dwivedi A. M. , Gupta V. D. 
Published: December 2004

AbstractA complete normal coordinate analysis, infrared absorption, and inelastic neutron scattering studies on α‐glycylglycine are reported. A Urey‐Bradley force field which is also valid for N‐deuterated sample is obtained. Assignments in the low‐frequency region are based on inelastic neutron spectrum obtained in one phonon and cubic approximation.
Magnitude of a finite equilibration effect in analytical gel chromatography
Authors: Weiss George H. , Ackers Gary K. 
Published: December 2004

AbstractPrevious analyses of solute behavior in analytical gel chromatography1,2 have allowed for a finite equilibration time between stationary and mobile phases in estimating the magnitude of axial dispersion coefficients, but have ignored these effects in formulating the continuity equations for solute transport. We develop a more accurate theory including the equilibration effect, and show experimentally that it can be disregarded after approximately two minutes from the start of a small‐zone experiment.
On the conformation change attending the hydration of lyophilized cytochrome c
Authors: Aviram Irit , Schejter Abel 
Published: December 2004

AbstractWhen lyophilized cytochrome c is disolved in pH 5 to 9 buffers, a spectroscopic change can be detected with a first‐order rate constant of 0.016 sec−1 at 23°, activation energy of 24.2 kcal/mole and entropy of activation of 11 e.u. The difference spectrum obtained by extrapolating the kinetic plots to zero time indicates that the form obtained by dissolving cytochrome c is in the low spin state and lacks the 695 nm band. It is proposed that the rate process observed corresponds to a conformation change in which the lysyl‐79 residue is displaced from iron coordination by the methionyl‐80 residue.
New banding species, with densities of phage‐ghost clusters, produced from lambda phage particles on storage
Authors: Costello R. C. , Baldwin R. L. 
Published: December 2004

AbstractDensity gradient analysis of purified lambda phage particles after storage reveals that minor species with new banding desities arise during storage. These have densities expected for phage‐ghost clusters containing integra rations of ghosts to phage particles. A lage numbersof new banding species has been observed.
The pH dependence of tyrosine cyanuration in proteins
Authors: Gorbunoff Marina J. 
Published: December 2004

AbstractThe pH, temperature, and reagent concentration dependences of the cyanuration of tyrosines within proteins are compared with those of the free amino acid. The results indicate that the mechanism of the cyanuration reaction is a nucleophilic aromatic substitution of the SN2 type, where the tyrosine oxygen acts as a nucleophile and the displacement takes places at a carbon atom which is part of the six‐membered ring of the s‐triazene. This reaction must compete with the hydrolysis of cyanuric fluoride in aqueous media. These competing reactions generate curves for the pH dependence of the reactivity of tyrosine with cyanuric fluoride whihc vary in a predictable manner with the extent of ionization of tyrosine and the concentration of cyanuric fluoride. In the case of proteins, the dependence of the degree of tyrosine reactivity on pH and temperature within the pH range of full reactivity of the free amino acid reflects constraints imposed by the microenvironment of these groups within the three‐dimensional structure of the macromolecule.
Study of the interaction of DNA and acridine orange by various optical methods
Authors: Fredericq E. , Houssier C. 
Published: December 2004

AbstractThe degree of binding of acridine orange to DNA, native or denatured, has been determined by equilibrium dialysis in 0.1M and 0.001M NaCl at 20°. The nature of the binding process has been investigated by studying various optical properties of the dye–DNA complexes and by relating them to the binding ratio. All these properties were found to vary quantitatively and qualitatively according to the successive stages of the process. These stages were assumed to be a strong binding of intercalated monomers followed by formation of bound dimers and finally by external binding of aggregates of native DNA.Absorption spectra of the complexes could be interpreted on that basis.Circular dichroism spectra were resolved into components: one band for intercalated monomers without interactions, two excition splittings for interacting monomers and bound dimers, respectively, weak bands and exciton splitting for external aggregates.The fluorescence intensity was greatly enhanced in intercallated monomers; its quenching at higher binding ratio was quantitatively related to dimer fixation. The value of the anisotropy of fluorescence at low binding ratio suggested a limited mobility of intercalated monomers; the decrease of polarization at higher binding was attributed to energy transfer between monomers.Electric dichroism displayed by the complexes in the dye absorption bands indicated an orientation of the bound molecules quite parallel to the base rings at low binding. In the range of fixation of dimers and external molecules, the dichroism was lower but still indicated an important degree of ordering.
Complexes of histone F1 with DNA in 0.15M NaCl. Circular dichroism and structure of the complexes
Authors: Šponar J. , Frič I. 
Published: December 2004

AbstractConditions were studied under which aggregated complexes of histone F1 with DNA display a circular dichroic spectrum of nonconservative type characterized by two intense negative maxima at 269 nm and 209 nm. It was found that the intensity of the longwave band depends directly on the content of guanine plus cytosine and inversely on the molecular weight of DNA. The same type of dependence was found for DNA's of eukaryotic and bacterial origin. It appears that the formation of the nonconservative spectrum which can be ascribed to a certain structural form of DNA is caused by orientation of the DNA molecules in the aggregated complex and by specific interactions of the bases of the guanine–cytosine pair. The possible mechanism of formation of nonconservative dichroic spectrum is discussed with respect to special properties of guanine.