bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infrared absorption spectrum of keratin. I. Spectra of α‐, β‐, and supercontracted keratin
Authors: Bendit E. G. 
Published: December 2004

AbstractA number of basic features of the infrared spectrum of keratin have been confirmed and some new features have been found. In the 3‐μ region, the amide A frequency of helical material in α‐keratin at 3286 cm.−1 is close to the expected value, but that of the crystalline phase in α‐keratin, near 3270 cm.−1, is lower than had previously been reported. The noncrystalline phase absorbs in the vicinity of 3300 cm.−1 or above, and this causes the low‐intensity component of the amide A band in both α‐ and β‐keratin to occur at higher frequencies than those of the high‐intensity component. In the 6‐μ region, the amide II frequency of noncrystalline material is below 1525 cm.−1. Keratin denatured in lithium bromide, after washing out the reagent, appears to have a considerable helix content, possibly as much as that of the original protein. Hydration causes significant spectral changes. In the 6‐mu; region, the frequency of the amide I band of crystalline material is lowered, while that of the amide II band is increased, both by a few wavenumbers; the amide II frequency of noncrystaline material is also increased by a few wavenumbers. In the 3‐μ region, no significant change is observed in the amide A frequency of crystalline material, while the frequency of the noncrystaline material is reduced. These spectral changes are interpreted in terms of a weak association of water with main‐chain carbonyl groups in the crystalline phase, while in the noncrystaline phase it is thought likely that water molecules form hydrogen‐bond bridges between polypetide chains. The absorption coefficient of the amide A band and the integrated absorption intensities of the amide A, I, and II bands do not vary appreciably in the three forms of keratin investigated.
Mathematics of band centrifugation: Concentration‐independent sedimentation and diffusion in shallow density gradients
Authors: Rubin Merry M. , Katchalsky Aharon 
Published: December 2004

AbstractIntegral expressions for concentration as a function of time and distance are derived from the continuity equation for centrifugation in a sector‐shaped cell for a macro‐molecular solute initially contained in a finite upper layer and a solute of low molecular weight in the supporting liquid. Computer patterns based on the sedimentation and diffusion coefficients of sucrose and of spherical and randomly coiled model solutes illustrate: (1) the time course of redistribution of both banded and supporting solutes from initial uniform concentrations; (2) the influence of the initial concentration, width, and solute concentration of the upper band; and (3) the effect of restricted diffusion at the meniscus on subsequent band shape. A Gaussian, approximation to band shape is derived and graphically tested. Rapid methods, not requiring computers, are out lined for the estimation of sedimentation and diffusion coefficients, where their concentration dependence is negligible, by band centrifugtion. The theoretical resolution of mixtures attainable by this technique is compared with moving‐boundary centrifugation, with the use of both integral (interferotmetric or absorption) and derivative (schlieren) optics.
Solvent effects in N‐carboxyanhydride (NCA) polymerization initiated by strong base type initiators
Authors: Cosani A. , D'este G. , Peggion E. , Scoefone E. 
Published: December 2004

AbstractThe γ‐benzyl‐L‐glutamate N‐carboxyanhydride (NCA) polymerization initialed by diisopropylamine was studied in dimethylformamide (DMF)‐dioxane mixtures of different compositions. It was found that the shape of the conversion versus time plots and the molecular weights of the polymers depend on the solvent composition. Auto‐catalysis is present only when dioxane predominates in the solvent mixtures. Moreover, the molecular weight of the final polymer depends strongly on the precipitation conditions when the polymerization is carried out in DMF.
Helix–random chain transitions of polyamino acids in organic acid–salt solutions
Authors: Franzen James S. , Bobik Caroline , Harry John B. 
Published: December 2004

AbstractPolyamino acids which are soluble and helical in acetic acid and dichloroacetic acid (DCA) have been observed to undergo a helix to random chain transition upon the addition of lithium salts of strong acids. The transition can be reversed by diluting the salt. Apparently only lithium cations are able to bring about the polycarbobenzoxy‐L‐lysine (PCBL) transition in acetic acid, whereas the anions display a varying degree of effectiveness; ClO4− > Br− > TSA− > Cl− > NO3−. The lithium salts of carboxylate anions such as OAc− and TFA− do not cause polymer unwinding in acetic acid. Neither do the acids, TSA, HCl, TFA, or DCA induce the transformation in acetic acid. Poly‐L‐alanine (PLA) in DCA unfolds as LiBr is added, but does not unfold in the presence of 0.5M (CH3)4NBr, 0.25M CsBr, or 0.32M HCl. These results are explained on the basis of a direct interaction of the lithium salt with the polymer amide groups to form an ion‐pair complex. The extent to which the union of the ion pair can dissociate from the complex in the low dielectric constant, environment determines the degree of unfolding of the polymer. The anion dissociation equilibrium presumably therefore would lie in the same order as given above. Acids such as HCl and TSA are considered to substantially protonate and ion‐pair with the polymer, but do not readily dissociate the anion partner from the complex, and therefore do not produce an unstable positively charged helical structure.
Study of helix–coil transition of DNA by dielectric constant measurement
Authors: Takashima Shiro 
Published: December 2004

AbstractThe thermal helix–coil transition of DNA was studied by means of dielectric constant measurements. The dielectric dispersion of native helical DNA is characterized by a large dielectric increment and a large relaxation time, whereas that of denatured coil DNA is characterized by a small dielectric increment and a small relaxation time. The dielectric dispersion of partially denatured DNA is of particular interest. At the intermediate stage of the helix–coil transition, dispersion curves which are different from either that of helix DNA or that of coil DNA appear. This is particularly pronounced for large DNA. This indicates the presence of an intermediate form of DNA. Flow birefringence measurements were carried out simultaneously. The negative birefringence of helical DNA diminishes as the helix–coil transition proceeds. However, the extinction angle remains constant, as long as it can be measured. These results indicate the absence of intermediate forms during the helix–coil transition. The discrepancy between dielectric and birefringence measurements can be resolved by assuming that the intermediate forms are not birefringent. The size distribution of native DNA and of the indicated intermediate form of DNA was studied. It is found that a logarithmic normal distribution function explains the distribution of size of DNA reasonably well.
Polymerization of γ‐benzyl‐L‐glutamate N‐carboxy‐ anhydride: Effects of conditions of polymer precipitation on the molecular weight distribution
Authors: Peggion Evaristo , Scoffone Ernesto , Cosani Alessandro , Portolan Antonio 
Published: December 2004

AbstractPoly‐γ‐berizyl‐L‐glutamate prepared by polymerization of γ‐benzyl‐L‐glutamate NCA in dimethylformamide (DMF) with the use of diisopropylamine as the initiator was precipitated from the polymerization mixture under different conditions. A portion of the almost completely polymerized solution was treated with an excess of isopropylamine and then precipitated into diethyl ether (sample A). The remaining portion of the polymerization mixture was concentrated in a rotating evaporator, stored at room temperature for a few days, and then diluted with DMF and precipitated into diethyl ether (sample B). The molecular weight distributions of the two polymer samples were determined by the chromatographic procedure of Baker and Williams. The molecular weight of sample B is roughly three times that of sample A. However both samples have the “most probable” distribution of molecular weight. The results are interpreted according to Bamford's polymerization mechanism.
Reconstruction of protein and nucleic acid sequences. V. Computer‐simulated tests of various tactics for reconstructing the sequences of transfer ribonucleic acids
Authors: Merril Carl R. , Shapiro Marvin B. , Bradley Dan F. , Mosimann James E. , Vinton Jay E. 
Published: December 2004

AbstractOne hundred hypothetical polynucleotides of varying chain length and composition and of random sequence were generated and their chemical degradation simulated by a computer. Included in the study were 20 hypothetical polymers with the composition and chain length of a transfer RNA. A second computer program attempted to reconstruct the sequences from the nucleotide composition and the simulated fragments produced. Approximately 700 reconstructions were attempted from various sets of fragments generated from the 100 polymers. The dependence of the probability of reconstructing the original sequences on the methods of producing and isolating the fragments was studied.
Topological considerations in protein structure. I. Disulfide linkage
Authors: Kato Ikunoshin , Narita Kozo , Fuke Ichita 
Published: December 2004

AbstractThe patterns of disulfide bridges in proteins were considered by using the concept of topological information content. It was proposed that the difference between topological informal ion content in the half‐cystine residues of the native state and of the fully reduced form of a protein is related to the problems of the renaturation of the fully reduced and denatured protein. Specifically, when there is no difference between the topological information contents of the two states, the reduced protein is able to recover its native conformation. The concept reported in the present paper is consistent without exception with reported experimental results.
Sedimentation coefficient of T‐even bacteriophage DNA
Authors: Rosenbloom J. , Cox E. C. 
Published: December 2004

AbstractThe sedimentation coefficient of T2 phage DNA has been studied by zone centrifugation in sector‐shaped preparative centrifuge tubes over a concentration range of 0.02–2.0 μg./ml. DNA. These results have been compared to a similar study in the analytical centrifuge of T4 DNA over the range of 0.50–5.75 μg./ml. DNA. A value for the sedimentation coefficient of 60.7 ± 1.8 S. was obtained by the first method and a value of 61.3 ± 1.5 S. by the second.
Solution properties of synthetic polypeptides. I. Light scattering and osmometry of poly‐γ‐benzyl‐L‐glutamate in helicogenic solvents
Authors: Fujita Hiroshi , Teramoto Akio , Okita Koichi , Yamashita Tsuneko , Ikeda Shoichi 
Published: December 2004

AbstractLight‐scattering measurements were performed for a number of poly‐γ‐benzyl‐L‐glutamate (PBLG) samples in dimethylformamide (DMF) and in chloroform‐formamide (C‐F) at 25°C. Osmotic pressure data for some of these polypeptide samples in DMF at 37°C. were also determined. The scattering radii 〈S2〉1/2 in the two solvents were roughly proportional to the sample's weight‐average molecular weight Mw. The lengths per monomeric residue h, calculated from the measured 〈S2〉1/2 and Mw with the assumption of a rigid rod of uniform density, were about 1.2 A. in DMF and about 1.5 A. in C‐F. The measured values for the Mw/Mn ratio indicated that the samples used were quite polydisperse in molecular weight. If this effect is taken into account, the above values for h must be lowered drastically. In fact, application of Holtzer's procedure, which is capable of yielding h free of polydispersity effects, gave 0.85 A. for h in DMF and 1.16 A. for h in C‐F. Since, according to the recent conclusion established by Parry and Elliott, the correct conformation of the PBLG molecule in helicogenic solvents must be the α‐helix for which h is 1.5 A., these results imply that the overall shape of the PBLG helix cannot be a rigid rod, in contradiction to the earlier conclusion of Doty et al.
Denaturation and renaturation of DNA. I. Equilibrium statistics of copolymeric DNA
Authors: Montroll Elliott W. , Goel Narendra S. 
Published: December 2004

AbstractThe one‐dimensional Ising model, with nearest neighbor correlation only, suitably modified, is used to explain the observed linear dependence of melting temperature of copolymeric DNA with GC content. Transition curves are plotted for regular, random, and Markoff distribution of base pairs for various values of a correlation parameter U between nearest neighbor bonds. Exact analytic formulas are given for fraction of bonds intact at a particular temperature for various regular distributions for all U and approximate ones for random and Markoff distributions for small U. A scheme is indicated for further improvement. The model, in principle, makes it possible to estimate the statistical distribution of base pairs from the detailed shape of the transition curve.
Interaction of aminoacridines with deoxyribonucleic acid: Viscosity of the complexes
Authors: Drummond D. S. , Pritchard N. J. , Simpson‐Gildemeister V. F. W. , Peacocke A. R. 
Published: December 2004

AbstractThe intrinsic, viscosities at zero shear rate of defined complexes of proflavine, 9‐aminoacridine, and 9‐amino‐l,2,3,4‐tetrahydroaeridine with calf thymus DNA have been determined at, various ionic strengths by means of rotating cylinder viscometers. By controlled adjustment, of the composition of the mixtures, the amount of bound acridine (r moles/g.‐atom DNA phosphorus) was maintained constant at different dilutions. The intrinsic viscosities of the complexes increased with r up to r values (ca. 0.16–0.20) corresponding to the end of the process of strong binding of the acridinium cations. However, complex formation between the acridines and thermally denatured DNA caused either a marked decrease in viscosity (at the low ionic strengths of 0.0015 and 0.005) or no change at all (ionic strength 0.1). These results are discussed in the light of presently available hydrodynamic theories relating the intrinsic, viscosity of DNA to its molecular extension.
Properties of thyroglobulin. XII. Comparison of the configurational states of reduced and unreduced thyroglobulin
Authors: Edelhoch H. , Steiner R. F. 
Published: December 2004

AbstractThe relaxation time of thyroglobulin has been determined in water at. neutral pH, in concentrated urea and guanidine solutions, at alkaline pH, both before and after reduction with β‐mercaptoethanol. The structure of thyroglobulin in concentrated urea solutions is markedly affected by the pH, Time‐dependent changes occur in thyroglobulin in concentrated urea or guanidine solutions which arc observable by polarization of fluorescence but not by optical rotation or viscosity. The reduction of the disulfide crosslinks of thyroglobulin in urea at high pH or in guanidine produces linear polypeptide chains with few if any permanent contacts between segments.
Mesure de la dispersion diélectrique en très basse fréquence de solutions de DNA
Authors: Hanss Maxime 
Published: December 2004

AbstractBased on the four electrodes technique, an apparatus is described which measures the Very Low Frequency (VLF) conductivity of ionic solutions, all electrode effects being completely eliminated. It is thus possible to measure the conductivity frequency dependence between 0.8 and 500 cps, with a relative error of 10−4. Applying this method to DNA solutions, one always finds a conductivity dispersion in the VLF range, which disappears when the biopolymer is heat‐denatured. The relaxation time is different from one solution to another, but is always greater than 10 msee. approximately, sometimes even greater than 0.1 sec., the upper limit which one can estimate with our apparatus. The different, explanations of the DNA very low frequency polarization, assuming that its relaxation is connected with the rotational diffusion of the biopolymer long axis, is discussed.
Optical rotatory dispersion of E. coli ribosomes and their constituents
Authors: Sarkar P. K. , Yang J. T. , Doty Paul 
Published: December 2004

AbstractInvestigations have been made on the optical rotatory dispersion properties of E. coli ribosomes and their constituent RNA and proteins. The results indicate that (1) no conformational changes are involved in the formation of a 70S particle from the 50S and 308 subunits, (2) the E. coli ribosomal proteins are similar to most globular proteins with little α‐helix content, and (3) the conformation of RNA and proteins inside the ribosome is very similar to that in the free state.
Wechselstrompolarographische kriterien der nucleinsäuredenaturierung
Authors: Berg H. , Bär H. , Gollmick F. A. 
Published: December 2004

AbstractThe electrochemical possibilities for investigation of nucleic acids with high molecular weight are restricted to the determination of the adsorption behavior. According to our experience the alternating current polarography (Breyer‐polarography) is mainly appropriate for the characterization of changes in the secondary structure of DNA. The Breyer‐polarogram shows the alternating current of the dropping electrode in dependence on their potential which varied from 0–2 v. negative against the normal calomel electrode (NCE). By addition of native DNA to the supporting electrolyte (buffer solution) the current drops down in the range of adsorption between 0 and 1 v. At 1.16 v. against NCE the desorption takes place together with the formation of a rounded desorption peak. The investigation was carried out in phosphate buffer solution 0.1m with 0.075m NaCl or in a phosphate buffer 0.18m with 0.03m NaCl. In the pH range above pH 8 NaOH was added to realize the higher pH values. A calf thymus DNA sample having a mean molecular weight of about 18 million was used. The concentration of DNA was 5 × 10−3−1 × 10−1 wt.‐%. The polarographic measurements were performed with an a.c./d.c.‐polarograph “GWP 564” from Akademiewerkstätten für Forschungsbedarf der Deutschen Akademie der Wissenschaften zu Berlin (DAW). The denaturation of the double helix causes a sharp desorption peak at negative potentials of the alternating current polarogram. This new criterion for the helix‐coil transition is due to formation of unpaired bases. These nearly free bases undergo a specific adsorption and the desorption takes place within a narrow potential range. Nevertheless, at present time an electron transfer to particular bases cannot be excluded at special conditions. The increase of the sharp peak permits to estimate: (a) the melting curve of the double helix in agreement with spectroscopic measurements; (b) the photolysis of the double helix; (c) the strand separation in acid and alkaline solution. In the alkaline range the sharp peak increases and reaches its maximum at pH > 12. In the acid range, however, no sharp peak is observed and the rounded desorption peak decreases. Therefore, the best way of following the conformation changes is to measure the current difference between the curves of the solutions with and without DNA at electrocapillary‐zero‐potential. On the classical d.c.‐polarogram one can measure small current steps only, which may be caused mainly by capacity changes. Moreover, the scission of the molecule by ultrasonic action can be followed. In this case the rounded peak of DNA increases but the sharp peak does not appear. Similar alternating current polarograms are obtained with poly‐A in the native state, because helical and unordered regions coexist in the same molecule. The very rapid indication of these structure changes allows one to carry out kinetic measurements at a fixed potential with this method.
Structure of branched poly‐α‐amino acids in dimethylformamide. I. Light scattering
Authors: Eliezer N. , Silberberg A. 
Published: December 2004

AbstractLight scattering of multichain poly‐α‐amino acids was studied in dimethylformamide (DMF). The polymers consisted of a backbone of poly‐L‐lysine of degree of polymerization n with side chains of benzyl L‐glutamate and benzyl L‐aspartate of degree of polymerization, m, on each ε‐amino group. The backbone length n is known and m is obtained by amino acid analysis. The results on a series of such materials confirm this structure and show that the molecules are dissolved in highly compacted conformations. It was found that DMF is a poor solvent for these polymers. In the case of the higher molecular weight polymers, the solutions initially were not molecularly disperse. The aggregates were resistant to dilution in the experimental range. Mild heat treatment, however, disaggregated the solutions irreversibly, and the light‐scattering data indicated that a structural rearrangement of the molecules had occurred.
Dynamic viscoelastic properties of solutions of shear‐degraded deoxyribonucleic acid
Authors: Meyer H. H. , Pfeiffer William F. , Ferry John D. 
Published: December 2004

AbstractCalf thymus and salmon sperm deoxyribouncleie acid were degraded by high‐shear stirring to molecular weights M in the range of 1.3–3.2 × 106 and purified by chromatography on methylated bovine serum albumin. Dynamic viscoelastic properties of the fragmented products, in aqueous glycerol solutions in the concentration range of c = 0.003–0.01 g./ml., were investigated with the apparatus of Birnboim and Ferry. At values of the product cM higher than 4 × 103, the frequency dependence of the components of the complex shear modulus, G′ and G″, displayed a plateau region in which G′ > G″ – ων1ηS, similar to that observed in concentrated solutions of coiling polymers where it is attributed to an entanglement network (ω is radian frequency, ν1 volume fraction of solvent, and η8, solvent viscosity). The width of this plateau region on the logarithmic frequency scale is given by Δ = 3.8 (log cM – 3.56). At lower values of cM, the frequency dependence is intermediate between those predicted by the theory of Zimm for flexible coiled macromolecules and by the theory of Kirkwood and Auer for rods. Fitting to the Zimm theory gives highly discrepant values for molecular weights, while fitting the low‐frequency end of the dispersion to the Kirkwood‐Auer theory gives reasonable agreement for both molecular weight and rotary diffusion coefficient. It is concluded that the helical fragments appear as nearly rigid rods in their behavior at very low frequencies, but at higher frequencies reveal substantial bending flexibility.
Eleclrophoresis of adsorbed DNA
Authors: Chattoraj D. K. , Chowrashi P. , Chakravarti K. 
Published: December 2004

AbstractThe electrophoresis mobilities of native calf thymus DNA adsorbed on the charged solid particles were measured by a micro‐electrophoretic method as functions of pII, ionic strength, and DNA concentration. The mobility data confirm the adsorption of DNA both on the positively charged alumina and negatively charged resin particles at wide range of pH and ionic strength. The mobility data also indicate significant DNA adsorption by negatively charged glass in the acidic range of pH. The electrophoretic mobilities of DNA adsorbed on different substrate particles under identical conditions do not differ widely, indicating the major role of the adsorbed DNA rather than the covered substrate in controlling the charge behavior of the particle. The mobilities of the adsorbed DNA at salt pH are of a comparable order of magnitude to those for the dissolved DNA in solution. The mobility of the adsorbed heat‐denatured and alkali‐denatured DNA is lower than that of the native adsorbed DNA under identical conditions of pH and ionic strength.