bluuebunny/crossref_metadata_2025_split huggingface dataset:
The solution behavior of poly‐L‐proline: II. Fluorescence behavior of labeled polyproline in water and conentrated aqueous neutral salt solytions
Authors: Lerner D. A. , Schleich Thomas 
Published: December 2004

AbstractFluorescence depolarization experiments performed on labaled poly‐L‐proline Forme II suggest the occurrence of aggrgation in water while 6M guanidinium‐HCl induces dissociation. The solvent 4M CaCl2 results in a reduction of polymer structural orgganization. These findings corroborate suggestion of polyproline aggregation and solution behavior in aqueous neutral salt solytion (see preceding article).
Theory of aggregation in solution. I. General equations and application to the stacking of bases, nucleosides, etc.
Authors: Hill Terrell L. , Chen Yi‐Der 
Published: December 2004

AbstractEarlier theoretical work on aggregation in imperfect gases and in solutions of protein molecules is reformulated here in such a way as to be applicable to a number of aggregation systems in solution. The theory is most easily developed for an “osmotic” solution. It is exact, in principle, and in particular does not treat the aggregates as an ideal mixture as is usually done. If osmotic virial coefficients are diffcult to measure in a particular case, it is then necessary to relate these coefficients to properties of the more conventional “constant pressure” solution. An important special case is used as an example in the last three sections: The stacking of bases, nucleosides, etc., is represented by a statistical mecchanical model in which the aggregates resemble vertical stacks of checkers.
The self‐assembly of collagen molecules
Authors: Yuan Leon , Veis Arthur 
Published: December 2004

AbstractThe aggregation of native acid‐soluble collagen (N‐ASC) and of pronase‐treated acid soluble collagen (P‐ASC) was examined in solution under conditions which varied from those of minimum collagen‐collagen interaction to those leading to incipient fiber formation. Molecular weights and weight distributions were determined in the analytical ultracentrifuge using the Yphantis high speed sedimentation equilibrium and Aarchiblad approach‐to‐equilibrim techniques. The aggregation was pH and ionic strength dependent in each case. Under conditions of minimum aggregation (low pH, low ionic strength), N‐ASC showed the presence of permant aggregates. At higher pH and ionic strength, a higher fraction of aggregate was formed but these were of the same charcter and molecular weight as the permanent aggregates. The aggregates were of a single molecular size, with a weight of 1.5 × 106 daltons, compared with a monomer collagen weight of 3.1 × 105 daltons. The P‐ASC formed aggregates also but to a much lower extent and the maximum aggregate size corresponded to dimers in molecular weight. These data show the major importance of molecular end‐regions in collagen aggregation to form native type fibers and, by virtue of the discrete size of the N‐ASC aggregates, support the microfibrillar hypothesis for the assembly of collagen fibrills.
Observations of self‐aggregation and dissociation of E. coli ribosomes by optical mixing spectroscopy
Authors: Hocker L. , Krupp J. , Benedek G. B. , Vournakis J. 
Published: December 2004

AbstractMeasurements of the diffusion coefficient of E. coli ribosomes by the technique of optical mixing spectroscopy are used to show that these ribosomes, when incubated in a 4°C cold room, undergo a slow aggregation with time. Even in the presence of this aggregation, it was possible to observe the diffusive character of the single 70s ribosome. It was found that at high (≥0.100 molar) KCl concentrations the ribosomes broke into their subunits. At moderate KCl concentrations they were relatively stable and at a very low KCl concentration (0.005 M) they were observed to dimerize. The values of the diffusion coefficients of the 50s subunits, the 70s single ribosome and the ribosome dimer determined in these measurements are consistent with currently accepted values.
Electric and hydrodynamic properties of polypeptides in solution. IV. A new conformational change of poly(L‐glutamic acid) in dimethylsulfoxide–methanol mixtures
Authors: Matsumoto Mitsuhiro , Watanabe Hiroshi , Yoshioka Koshiro 
Published: December 2004

AbstractThe electric birefringence of poly(L‐glutamic acid) (PLGA) in dimethylsulfoxide (DMSO)–methanol mixtures has been measured by use of the rectangular pulse technique. The length distribution curve, the mean molecular length, and the mean apparent permanent dipole moment of PLGA in solution have been obtained from the decaycurve and field strength dependence of the steady‐state birefringence according to the method developed for analyzing the electric birefringence of a polydisperse system. The length distribution curve exhibits one or two peaks. The length corresponding to a high peak and the mean length of PLGA undergo an abrupt change in the vicinity of 50 to 60 vol % DMSO at 30°C. Moreover, a sharp change of the Moffitt b0 parameter with the solvent composition is observed. These results provide evidence for the existence of a solvent‐induced transition from a helical conformation (presumably α‐helix) to another helical conformation with shorter length per amino acid residue. Further, the temperature dependence of the length distribution of PLGA in 50 vol % DMSO suggests the existence of a temperature‐induced helix ⇌ helix transition.
Electroviscous effect of lysozyme in aqueous solutions
Authors: Komatsubara Michiro , Suzuki Kazuo , Nakajima Haruhiko , Wada Yasaku 
Published: December 2004

AbstractReduced viscosity of a dilute aqueous solution of hen egg white lysozyme is measured in the pH range from 1.4 to 12.7 for various NaCI concentrations. The viscosity decreases with increasing pH below the isoelectric point (pH 11) on account of diminution in the electroviscous effect, reaches a minimum at pH 11, and then increases at high pH's because of coagulation. The electroviscous effect is depressed by the increase in the small ion concentration. The dependence of reduced viscosity on small ion concentration and pH is discussed on the basis of Booth's theory and a partial agreement between theory and experiment is obtained. The discrepancy between theory and experiment is attributed to non‐spherical distribution of charges in the protein. The volume of lysozyme obtained through Einstein's equation by extrapolating the reduced viscosity to a sufficiently high ion concentration compares well with the molecular volume in the crystal.
Heats of thermally induced helix–coil transitions of DNA in aqueous solution
Authors: Shiao D. D. F. , Sturtevant J. M. 
Published: December 2004

AbstractThermal denaturation of calf thymus DNA at both alkaline and neutral pH values was studied by differential scanning calorimetry. It was shown that the dependence of the enthalpy of transition on pH and salt concentration could be accounted for on the basis of a heat capacity change of +40 cal deg−1(base pair)−1. In the pH range between 10.3 and 11.3, a release of 0.6 proton per base pair was calculated from the pH dependence of the melting temperature. The heat effect associated with the release of this proton was calculated to be 5 kcal mole−1.
Infinite‐dilution viscoelastic properties of poly‐γ‐benzyl‐L‐glutamate in helicogenic solvents
Authors: Warren Thomas C. , Schrag John L. , Ferry John D. 
Published: December 2004

AbstractThe storage and loss shear moduli, G, and G˝, have been measured for solutions of three samples of poly‐γ‐benzyl‐L‐glutamate with molecular weights from 16 to 57 × 104, by use of the Birnboim‐Schrag multiple‐lumped resonator. The frequency range was 106 to 6060 Hz, the concentration range 0.0015–0.005 g/ml, and the temperature 25°C. Two helicogenic solvents with widely different viscosities, dimethylformamide and m‐cresol, were used to provide a broader effective frequency range. The intrinsic moduli, extrapolated to infinite dilution, were compared with the predictions of the theory of Ullman for rigid rods; agreement was rather good at the lowest frequencies, but unsatisfactory at high frequencies. The data over the entire frequency range of three of logarithmic decades could be described closely by a relaxation spectrum consisting of one terminal relaxation time separated by a gap from a sequence of relaxtion times spaced as in the Zimm theory. The terminal time agrees approximately with that calculated for end‐over‐end rotation of a rigid rod. The additional relaxation mechanisms are tentatively attributed to modes of flexural deformation of the helix.
Synthesis of two sequential polypeptides by dispersion in benzene and their circular dichroism spectra in aqueous solution: Poly(L‐Glu‐L‐Lys‐L‐Ala‐Gly) and Poly(L‐Ala‐D‐Glu‐L‐Lys‐D‐Ala‐Gly)
Authors: Zeiger Allen R. , Lange Armand , Maurer Paul H. 
Published: December 2004

AbstractThe monomers γ‐benzylglutamyl‐ε‐benzyloxycarbonyl‐lysylalanylglycine pentachlorophenyl ester and alanyl‐γ‐benzyl‐D‐glutamyl‐ε‐benzyloxycarbonyllysyl‐D‐alanyl‐glycine pentachlorophenyl ester, were polymerized in dilute solutions of dimethylform‐amide (DMF) or as dispersions in the same volume of benzene. After deprotection with hydrogen bromide, the products were either chromatographed on Sephadex G‐50 or dialyzed. The polymers derived from the polymerization in benzene were considerably larger than those from DMF. The results in benzene indicated that high monomer to solvent ratios are not necessary for the production of high‐molecular‐weight sequential polypeptides. Circular dichroism spectra of the polymers and monomers at neutral and acid pH indicated that poly(L‐Glu‐L‐Lys‐L‐Ala‐Gly) exists in a random coil configuration and poly(L‐Ala‐D‐Glu‐L‐Lys‐D‐Ala‐Gly) exists in a β conformation.
Electric birefringence of poly‐L‐lysine hydrobromide in methanol–water mixtures and helix–coil transition induced by high electric fields
Authors: Kikuchi Kazuo , Yoshioka Koshiro 
Published: December 2004

AbstractThe electric birefringence of poly‐L‐lysine hydrobromide in methanol–water mixtures has been measured at 25 °C over a wide range of field strengths by use of the rectangular pulse technique. An abrupt change in the specific Kerr constant was observed between 87 and 90 vol % methanol, corresponding to the solvent‐induced helix–coil transition. The specific Kerr constant increased rapidly with dilution in the random coil form, and more slowly in the helical conformation. The field strength dependence of the bire fringence at various concentrations, for both the helical and coil conformations, can be described by a common orientation function, which resembles the theoretical one for the case of permanent dipole moment orientation. This is interpreted in terms of the saturation of ion–atmosphere polarization. The optical anisotropy for the helical conformation was much larger than that for the coil form.Anomalous birefringence signals were observed above a critical field strength (about 5 kV/cm) in 90 vol % methanol. The birefringence passed through a maximum and began to decrease slowly before the pulse terminated, reaching a steady‐state value. This steady‐state value was closer to that of the coil in the coil in the limit of very high fields. The results indicate that a transition from the charged helix to the charged coil is induced by high electric fields in the transition region. This effect can be explained on the basis of the polarization mechanism proposed by Neumann and Katchalasky.
The effect of temperature and salt concentration on the circular dichroism exhibited by unionized derivatives of L‐alanine in aqueous solution
Authors: Mattice Wayne L. 
Published: December 2004

AbstractThe circular dichroism of Ac–Ala–NHMe, cyclo(–Ala–Ala–), Ac–Ala–OMe, Ac–Ala–Ala–OMe, and Ac–Ala–Ala–Ala–OMe has been measured in water and in aqueous salt solutions as a function of temperature. Only cyclo(–Ala–Ala–) exhibits circular dichroism which is independent of temperature. Each of the linear derivatives of L‐alanine exhibits a positive circular dichroism in the range 208–218 nm at 15°C in water. Heating reduces the intensity of the positive circular dichroism, and only Ac–Ala–OMe retains positive circular dichroism at 75°C in water. Isothermal addition of salts produces changes in the circular dichroism of linear derivatives of L‐alanine which resemble those seen on heating. The relative effectiveness of the salts tested, at a concentration of 4M, is LiCl ⩽ KCl = NaCl < MgCl2 ⩽ CaCl2 ⩽ NaClO4. The circular dichroism of cyclo(–Ala–Ala–) is also affected by the salts. Extrapolation of the results obtained with Ac–Ala–OMe, Ac–Ala–Ala–OMe, and Ac–Ala–Ala–Ala–OMe to a long polypeptide with a –CH2R side chain in the L‐configuration leads to the conclusion that this polypeptide should exhibit a temperature‐dependent salt‐sensitive positive circular dichroism between 208 and 218 nm when it exists as a statstical coil.
The effects of cations and diamines on the viscosity of T2 DNA
Authors: Baxter‐Gabbard Karen , Fraser Dean 
Published: December 2004

AbstractThe viscosity of the DNA of T2 bacteriophage has been studied with the aim of understanding the folding of the DNA in the phage head. Thus the results of previous workers have been extended into a range of concentrations and mixtures of cations and polyamines simulating the conditions obtaining in actual phage heads. Difficulties in obtaining reproducible results with DNA in 0.001M NaCl have been attributed to the presence of traces of protein, perhaps nulease(s), that can be eliminated by hot‐phenol extraction of the DNA. The results have been negative in the sense that the minimum viscosity obtained (120–140 dl/g) indicates a molecule that is far from tightly folded and in that viscosities in this range can be obtained with a simple mixture of Na+ and Mg++. No specificity of the diamines putrescine and spermidine is seen; they are simply surrogate cations.
Effect of protonation on electronic structure of guanosine and 5′‐guanosine monophosphate and on glycosidic (CN) bond rotations
Authors: Jordan Frank 
Published: December 2004

AbstractSemiempirical molecular orbital studies were performed on 5′‐guanosine monophosphate in its various states of base and phosphate ionization (employing the extended Hückel method) and on guanosine protonated on N‐3 and on N‐7 (employing CNDO/2). Semiempirical potential energy calculations (Lennard–Jones and Coulombic) failed to pinpoint the reasons for the recent experimental suggestion that guanine protonation increases the syn population in 2′‐ and 3′‐guanosine monophosphates. Changes in electron densities upon base protonation are much in evidence and are a very sensitive function of the site of base protonation assumed. It is suggested that the CNDO/2‐type calculations when combined with 13C and 15N pH‐dependent chemical shifts can lead to assignment of the site of protonation in the DNA bases.
A theory of complex multiple equilibria. The effect of polyU concentration on the binding of deoxyadenosine
Authors: Han Helen , Schurr J. Michael 
Published: December 2004

AbstractA grand‐partition function method employed previously for the study of cooperative binding of nucleosides to polynucleotides is generalized to include the effect of changes in the polymer concentration, as well as the effect of changes in the nucleoside concentration. This method is applied to compute isotherms for the binding of deoxyadenosine by polyuridylic acid at various total concentrations of polyuridylic acid. It is found that these isotherms are extremely insensitive to the polymer concentration, as commonly assumed heretofore, and as demonstrated experimentally (to some degree) by Davies and Davidson. However, the conclusion inferred by Davies and Davidson that the complexes must be unimolecular in polyuridylic acid is now seen to be clearly unwarranted, though it remains still a viable possibility, until data over a much wider range of polyuridylic acid concentrations become available.
Raman spectroscopic study of mechanically deformed poly‐L‐alanine
Authors: Frushour Bruce G. , Koenig J. L. 
Published: December 2004

AbstractRaman spectroscopy has been used in investigating the conformational transitions of poly‐L‐alanine (PLA) induced by mechanical deformation. We see evidence of the alpha‐helical, antiparallel beta‐sheet, and a disordered conformation in PLA. The disordered conformation has not been discussed in previous infrared and X‐ray diffraction investigations and may have local order similar to the left‐handed 31 poly glycine helix. The amide III mode in the Raman spectrum of PLA is more sensitive than the amide I and II modes to changes in secondary structure of the polypeptide chain. Several lines below 1200 cm−1 are conformationally sensitive and may generally be useful in the analysis of Raman spectra of proteins. A line at 909 cm−1 decreases in intensity after deformation of PLA. In general only weak scattering is observed around 900 cm−1 in the Raman spectra of antiparallel beta‐sheet polypeptides.The Raman spectra of the amide N–H deuterated PLA and poly‐L‐leucine (PLL) in the alpha‐helical conformation and poly‐L‐valine (PLV) in the beta‐sheet conformation are presented. Splitting is observed in the amide III mode of PLV and the components of this mode are assigned. The Raman spectrum of an alpha‐helical random copolymer of L‐leucine and L‐glutamic acid is shown to be consistent with the spectra of other alphahelical polypeptides.
Sedimentation coefficient and intrinsic viscosity of semiflexible chains
Authors: Noda Ichiro 
Published: December 2004

AbstractPublished theoretical equations for the sedimentation coefficient and intrinsic viscosity of a semiflexible chain are compared, neglecting the excluded volume effect. The theories are extended to the case of a small excluded volume, by applying the perturbation theory, established for flexible chains, to a semiflexible chain. Using the derived equation, the experimental results for the sedimentation coefficient and intrinsic viscosity of DNA and cellulose trinitrate are analyzed.
Raman spectral studies of nucleic acids. XI. Conformations of yeast tRNAPhe and E. coli ribosomal RNA in aqueous solution and in the solid state
Authors: Chen M. C. , Thomas G. J. 
Published: December 2004

AbstractLaser‐excited Raman spectra of tRNAPhe from yeast and of fractionated 16S and 23S rRNA from E. coli are reported for samples in aqueous solution and in the solid state. The Raman scattering spectrum of each RNA is not significantly altered by the change from an aqueous to a solid environment and displays the same characteristic frequencies and intensities associated with ordered polyribonucleotide structures. Unlike DNA, the backbone conformation of RNA thus appears to be largely insensitive to gross changes in the degree of hydration.Raman scattering from the phosphate group vibrations of aqueous tRNAyeastPhe is qualitatively and quantitatively the same as obtained from previously studied tRNA's and is indicative of a highly ordered conformational structure in which some 85% of the nucleotide residues are in ordered configurations. The major differences observed between spectra of tRNA and rRNA are attributed to differences in base composition of these RNA's.
13C nmr study of the helix–coil transition of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine
Authors: Di Blasi R. , Verdini A. S. 
Published: December 2004

AbstractThe helix–coil transition of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine in methanol–water solutions has been observed using 13C nuclear magnetic resonance. Two signals appear in the α‐CH region in the course of the transition; this is in contrast with previous proton magnetic resonance experiments carried out on this polymer in the same solvent system.
The strand‐separation transition of T2 bacteriophage DNA
Authors: Elson Elliot L. , Record M. Thomas 
Published: December 2004

AbstractStrand separation of T2 DNA has been investigated in a helix‐destabilizing solvent. Temperature‐shift experiments in which the conformation of the DNA is monitored by its viscosity, sedimentation behavior, and kinetics of helix formation show that a well‐defined strand‐separation transition follows the helix–coil transition usually observed by changes in absorbance. For T2 DNA, this strand‐separation transition is 70% as broad as the helix–coil transition, and is characterized by extremely slow kinetics of conformational change in the population. Strand separation requires the expansion of the two‐stranded coil observed at the end of the helix–coil transition. This expansion is apparently coupled with the disurption of the last remaining base pairs in the molecule. The expansion process increases the viscosity, and can be readily followed as a function of time and/or temperature. Subsequent separation of the expanded form into complementary strands results in a viscosity decrease, the net result of a reduction in hydrodynamic volume and the halving of the molecular weight. Only under conditions where the driving force for strand separation is large are these events at all synchronous in the population. When the kinetics of conformational change are complete in the strand‐separation transition, a mixture of expanded forms and separate strands is observed; the breadth of the transition reflects differences in stability with respect to strand separation among the molecules in the population. The transition exhibits hysteresis and is not a reversible equilibrium between double‐stranded and single‐stranded forms. It appears that renucleation is kinetically forbidden within the strand‐separation region.
Synthesis of some amino acids, sugars, and peptides in cold plasma abiotic synthesis of some high‐molecular‐weight proteid‐like structures (V)
Authors: Simionescu Cr. , Denes F. , Onac D. , Bloos G. 
Published: December 2004

AbstractThe synthesis of some high‐molecular‐weight protenoid structures in radiofrequency cold plasma conditions are discussed. The fractionation results of the raw product and the spectrum of free and protenoid‐bound amino acids are given. The uv analysis of these compounds is presented.A protein‐forming mechanism that might have existed on the primitive earth is proposed.
The dynamic mechanical, dielectric, and melting behavior of reconstituted collagen
Authors: Nguyen An‐Lac , Vu Ban The , Wilkes Garth L. 
Published: December 2004

AbstractThe dielectric, dynamic mechanical, and melting (denaturation) behavior of reconstituted collagen has been investigated. Dynamic mechanical properties are reported for the range of temperature from −100 to 220°C. Dielectric properties are reported for the range of temperature from −120 to 90°C. Possible origins of dynamic mechanical and dielectric relaxations are discussed. Effect of moisture content on mechanical and dielectric behavior is also presented. The melting process of collagen immersed in diluents as well as that of dry collagen were studied by the techniques of hot‐stage polarizing microscopy, differential thermal analysis, thermal mechanical analysis, and small‐angle light scattering. It was concluded that the melting point of dry collagen is about 217°C.