bluuebunny/crossref_metadata_2025_split huggingface dataset:
Poly‐α‐Acide‐L‐Glutamique en Solution Aqueuse. Agrégation Spécifique et Phénomènes d'Hystérésis. II. Agrégation et Précipitation. Analyse Chromalographique
Authors: Spach G. , Constantin D. 
Published: December 2004

AbstractThe aggregated form of poly(L‐glutamic acid) can be isolated by gel permeation chromatography, whereby it was found that in a polydispersed sample the lower molecular weight fractions precipitate preferentially and the higher fractions tend instead to aggregate. In addition, aggregation has the effect of retarding or inhibiting precipitation.
Interaction of antibodies specific towards the 2,4‐dinitrophenyl group and of their fragments with hapten
Authors: Zikán J. , Kotýnek O. 
Published: December 2004

AbstractThe interaction of hapten (ε‐DNP lys) with native and S‐sulfonated antibodies specific towards the 2,4‐dinitrophenyl group, as well as the interaction with isolated chains and a complex obtained by mixing light, (L) and heavy (H) chains of these antibodies, were followed both by polarography and by equilibrium dialysis. With the S‐sulfonated antibodies and with the mixture of H and L chains the binding heterogeneity observed in the original antibodies was much lowered or entirely removed. At the same time, the amount of active proteins in the sample decreased approximately by half. The association constants of modified antibodies were of the same order as the average association constants of the original antibodies. A slow increase of the amounts of hapten bound with proteins was observed on mixing the H and L chains and adding hapten. This slow reactivation was not obtained with the original or S‐sulfonated antibodies and with isolated chains. It was shown that the reaction determining the kinetics of this reactivation (the slowest reaction) was not the association of H and L chains but the interaction of complexes of the H and L chains with hapten. It was reported previously that H chains were nonspecifically reactivated by binding L chains. The amount of hapten bound by the complex of H and L chains increased with increasing excess of L chains following a curve resembling the Langmuir isotherm. The limiting value of the amount of hapten bound when using antibody L chains was higher than in the case of nonspecific L chains.
Viscosity and optical activity of chondroitin sulfate C
Authors: Eyring Edward J. , Yang Jen Tsi 
Published: December 2004

AbstractChondroitin sulfate C (CSC), isolated from shark vertebral mucoprotein, has a molecular weight of 0.2 × 104–5.5 × 104 in both NaCl and CaCl2 solutions. Optical rotatory dispersion and circular dichroism of CSC reveal a strong, negative, optically active band near 210 mμ, arising from the carboxylate and N‐acetyl groups. Results of similar studies of glucuronic acid and N‐acetyl‐D‐galactosamine suggest that the N‐acetyl group contributes more to the rotations of CSC than does the carboxylate group, but the acidification of the carboxylate groups largely accounts for the change in magnitude and position of the circular dichroic bands of CSC at low pH.
Induced optical activity of chondroitin sulfate c–acridine orange complexes
Authors: Eyring Edward J. , Kraus Howard , Yang Jen Tsi 
Published: December 2004

AbstractChondroitin sulfate C (CSC) and acrdiine orange (AO) formed two types of complexes at neutral pH, depending upon the order of mixing. The induced optical activity of AO was much more pronounced when the polysaccharide was added to dye than the dye to polymer (final concentration of dye was 5 × 105M). The difference in aggregation of the dye molecules is believed to be responsible for the observed peculiarities. The Cotton effects of the CSC‐to‐dye solution displayed a sharp inversion near 59°C. and the profile at 76°C. was almost a mirror image of that at room temperature. At pH 1.3, however, the order of mixing became unimportant, suggesting that the carboxylate on the polysaccharide way involved more intimately than were sulfates in the peculiarities of the Cotton effects.
Statistics of branching and hairpin helices for the dAT copolymer
Authors: de Gennes P.‐G. 
Published: December 2004

AbstractAt low temperatures a single strand of dAT copolymer tends to form a double helix with a loop at one end (hairpin). At slightly higher temperatures a branched structure (consisting of many hairpins connected by coiled regions) appears. The equilibrium properties of this branched structure are studied here by a propagator method. In particular the radius of gyration RG is calculated; under typical conditions, RG is expected to show a minimum at a temperature slightly below melting, in agreement with viscosity measurements. The present calculation is restricted to rather sharp transitions, for which the size of each helical region is large, even at the melting point. Then, in a rather broad range of molecular weights, M, RG is proportional to M1/4(as in the Zimm‐Stockmayer theory of simple branched polymers).
Radiationless energy transfer through a polypeptide chain
Authors: Gabor Gavriella 
Published: December 2004

AbstractElectronic excitation spectra were measured on a donor‐acceptor pair which was separated by oligomers of L‐proline of gradually increasing lengths. The logarithmic plot of the transfer efficiency versus the donor‐acceptor separation, for (pro)n oligomers with n⩾5, yielded a slope of 5.8 ± 0.3 in good agreement with the theoretical value of 6, predicted by Forster. The above method is suggested as a tool for the estimation of distances between certain chromophoric groups, covalently bound to macromolecules. The use of any stereoregular polymer for calibrating a certain energy donor‐acceptor pair is discussed.
Comparison of several calculations of helix–coil transitions in hetergeneous polymers
Authors: Fink Thomas R. , Crothers Donald M. 
Published: December 2004

AbstractRandom number methods are used to calculate helix—coil transition curves for the model of a heterogeneous polypeptide of random sequence. These curves are compared with several other calculations. The random number computations confirm the exact calculation of Lehman; among the several approximate calculations examined only that of Fixman and Zeroka agrees closely with results of the random number method over the whole range of conditions considered. Calculations are also reported of the average length of helix and coil sections in a heterogeneous molecule of random sequence which is undergoing the helix‐coil transition.
General theoretical approach to the thermodynamic and kinetic properties of cooperative intramolecular transformations of linear biopolymers
Authors: Schwarz Gerhard 
Published: December 2004

AbstractA general method to calculate experimentally accessible thermodynamic and kinetic quantities for any type of cooperative transitions is developed. Special attention has been directed to transition curves and mean relaxation times. The procedure is applied to the most general case of nearest‐neighbor cooperativity by using the linear Ising model and the matrix method of evaluation. The various potential types of end effects arid the resulting chain length dependences are discussed in detail. The significance of the theory with respect to the helix‐coil transition of polypeptides as well as to the polyproline I‐II transition is indicated.
Ionic polysaccharides. II. Comparison of polyelectrolyte behavior of hyaluronatc with that of carboxymethyl cellulose
Authors: Cleland Robert L. 
Published: December 2004

AbstractSodium hyaluronate (NaHy) and sodium carboxymethyl cellulose (NaCMC) behave similarly with respect to concentration.N 3 of an added 1 : 1 electrolyte. The second virial coefficient A2 (light scattering) is identical within experimental error at a given.N 3. The limiting viscosity number [η] also varies with N3−1/2in similar fashion for samples of similar [η] of the two polymers. Differences in Na+ activity in salt‐free solutions are interpreted on the basis of weaker Na+ binding in NaHy, presumably due to the greater charge separation along its chain backbone. Added electrolyte is excluded in dialysis more strongly by NaHy (or its acid form) than by NaCMC. The Flory parameter Φ is smaller in good solvents for NaHy, as for many other polyelectrolytes, than for nonionic polymers.
Effect of side chains on the conformational energy and rotational strength of the n–π*transition for some α‐helical poly‐α‐amino acids
Authors: Vournakis John N. , Yan Johnson F. , Scheraga Harold A. 
Published: December 2004

AbstractCalculations of the dependence of the conformational energy and the rotational strength of the amide n–π* electronic transition (in a series of α‐helical polyhel‐α‐ amino acids with different side chains) on conformation have been carried out. The conformational energies were computed by procedures developed in this laboratory; the computation of rotational strengths was carried out by the method of Schellman and Oriel, with a slight modification. Polyamino acids with both nonpolar and polar side chains were considered; in the latter case, it was assumed that the only influence of the polar side chain was on the backbone conformation and on the electrostatic field which perturbs the amide chromophore of the backbone. Only conformations in the range of backbone dihedral angles of the right‐ and left‐handed a‐helices were considered, and the assumption of regularity (i.e., uniformity of dihedral angles in every residue) was made. The rotational strength per residue was found to vary markedly with chain length (in oligomers of up to 40 residues long); both the conformational energy per residue and the rotational strength per residue were found to vary significantly with the backbone conformation, which in turn depends on the nature of the side chain. The geometry of the hydrogen bond in the α‐helical backbone is the most important factor which influences the dependence of the rotational strength on conformation. The implications of these results, for the interpretation of experimental circular dichroism and optical rotatory dispersion data, are discussed.
Interchain hydrogen bonds via bound water molecules in the collagen triple helix
Authors: Ramachandran G. X. , Chandrasekharan R. 
Published: December 2004

AbstractIf the collagen triple helix is so built as to have one set of NH ⃛ O hydrogen bonds of the type N3H3(A) ⃛ O2(B), then it is possible to have a linkage between N1H1(B) and O1(A) through the intermediary of a water molecule with an oxygen O leading to the formation of the hydrogen bonds N1(B) ⃛ O and O (A). In the same configuration, another water molecule with an oxygen O can link two earbonyl oxygens of chains A and B forming the hydrogen bonds O O1(A) and O O0 (B). The two water oxygens also become receptors at the same time for CH ⃛ O hydrogen bonds. Thus, the neighboring chains in the triple helix are held together by secondary valence bond linkages occurring regularly sit intervals of about 3 Å along the length of the protofibril. The additional water molecules occur on the periphery of the proto‐fibril and will contribute their full share towards stabilizing the structure in the solid state. In solution, they will be disturbed by the medium unless they are protected by long side groups. It appears that this type of two‐bonded structure, in which one NH ⃛ O bond is to a water molecule, can explain several observations on the stability and hydrogen exchange properties of collagen itself and related synthetic polypeptides. The nature of the water bonds and their strength are found to be better in the one‐bonded structure proposed from Madras than in the one having the coordinates of Rich and Crick.
Crystalline structure in oriented fibers of KBr–amylose
Authors: Jackobs John J. , Bumb Robert R. , Zaslow Bert 
Published: December 2004

AbstractThe study of the structure of KBr–amylose begun by Senti and Witnauer has been extended by a three‐dimensional crystallographic analysis and by stereochemical considerations. Location of Br− at (0.200, 0.200, 0.000) and K+ at (0.540, 0.540, 0.000) was obtained from the three‐dimensional map of vector interactions. By using known parameters for the D‐glucose residue and accurate space‐filling models, an amylose helix was constructed to meet the fiber repeat spacing of 16.1 Å. The helix was determined to be left‐handed, and the correct space group for KBr–amylose is P43 212. Placement of the helix in the unit cell resulted from structure factor calculations; minima in the grid of R values were checked with space‐filling models to establish the final structure. Both ions are located in a waterlike environment. The oxygen atoms O(2), O(3), and O(4) from glucose residues on adjacent chains coordinate around K+.
Conformational aspects of polypeptides. XXIX. Conformationl assignments for some aromatic polypeptides by far‐uv cotton effects. New results
Authors: Goodman Murray , Toniolo Claudio , Peggion Evaristo 
Published: December 2004

AbstractRecent improvements in apparatus permit the examination of circular dichroism (CD) and optical rotatory dispersion (ORD) spectra to 185 mμ. In addition, new solvents which are transparent to 185 mμ have become available for synthetic polypeptides. The spectral region 185–250 mμ is extremely important for the amide (peptide) chromophore, because of the presence at these wavelengths of the n–π* and π–π* bands,1 and of another transition, the assignment of which remains unsettled.2
Enthalpy change of the coil–helix transition of poly(γ‐benzyl L‐glutamate) in dichloroacetic acid–1,2‐dichloroethane mixtures
Authors: Kagemoto Akihiro , Fujishiro Ryoichi 
Published: December 2004

AbstractBy combining the heat of dilution of a poly(γ‐benzyl L‐glutamate)–dichloroacetic acid–1, 2‐dichloroethane solution with the corresponding heat of mixing of two solvents, the integrated heat of the coil–helix transition of poly(γ‐benzyl L‐glutamate) in the solution was estimated to be about 750 cal/mole.
Far‐infrared spectra of polyalanines with α‐helical and β‐form structures
Authors: Itoh K. , Nakahara T. , Shimanouchi T. , Oya M. , Uno K. , Iwakura Y. 
Published: December 2004

AbstractFar‐infrared spectra of poly‐L‐alanines having the α‐helical conformation and the β‐form structure were measured. The spectra of glycine–L‐alanine copolymer, silk fibroin, and copoly‐D,L‐alanines with different D:L compositions were also measured. In addition to the bands so far reported, four bands at 190, 107, 120, and 90 cm−1were found for the α‐helix conformation and the two bands at 442 and 247 cm−1 were found for the β form. The 442 cm−1 band consists of the parallel 432 cm−1 and perpendicular 445 cm−1 bands. The 247 cm−1 band is well defined and has strong dichroism parallel to the direction of stretching. These two bands appear also for silk fibroin and glycine–L‐alanine copolymer. All the far‐infrared bands of copoly‐D,L‐alanines can be interpreted as α‐helix bands, the three peaks at 580, 478, and 420 cm−1 being ascribed to the D‐residue incorporated into the right‐handed α‐helix or to the L‐residue in the left‐handed α‐helix.
Dielectric properties of polyelectrolytes. I. A study on tetra‐n‐butyl ammonium polyacrylate
Authors: Minakata Akira , Imai Nobuhisa 
Published: December 2004

AbstractDielectric constant and loss of aqueous solutions of tetra‐n‐butyl ammonium polyacrylate ((Bu)4NPA) were measured in the frequency range from 300 Hz to 6 MHz as compared with sodium and other salts at various conditions. Our results show that there are two dispersions observed in the low‐frequency range (LFD, several ten kHz to MHz), respectively, both of which are roughly expressed as the Cole‐Cole dispersion formula with Cole parameters about 0.3. The large values of dielectric increment, its nonlinear concentration dependence, and other features suggest that both dispersions are explained by relaxations of two different ionic processes. For HFD, experimental results were qualitatively similar to those have been reported and compared with theories of the Maxwell‐Wagner‐type effect. On the other hand, LFD may be attributable to the polarization of loosely bound counterions. A model available for LFD was presented on the basis of counterion fluctuation.
Dielectric properties of polyelectrolytes. II. A theory of dielectric increment due to ion fluctuation by a matrix method
Authors: Minakata Akira , Imai Nobuhisa , Oosawa Fumio 
Published: December 2004

AbstractThe mean square of dipole moment of a linear macromolecule which is responsible for dielectric increment of aqueous polyelectrolyte solutions is calculated by means of a matrix method in which ion binding at discrete sites and the nearest‐neighbor interaction are taken into account. On the basis of the relationship between polarization of poly‐ion and fluctuation of bound counterions the present theory indicates that the loosely bound ions result in larger increment and otherwise smaller increment. Also, the theory predicts that the dielectric increment has a maximum at an intermediate monovalent–divalent ion ratio when both species coexist. These results are consistent with experiments on polyacrylic acid neutralized with NaOH and Ca(OH)2. At large contents of divalent ions the effect of chelation is also discussed.
Nuclear magnetic resonance spectra of poly(N‐alkylamino acid)s
Authors: Sisido Masahiko , Imanishi Yukio , Higashimura Toshinobu 
Published: December 2004

Abstract220‐MHz NMR spectra of various poly (N‐alkylamino acid)s are investigated. Spectra of polysarcosine recorded in various solvents showed fine splittings of the methyl and methylene bands. Comparing the spectrum with that of its model compound, the fine structure of the methyl band of polysarcosine was assigned to four dyad sequences of the cis–trans isomeric state of the main chain amide bonds. Also the methylene band was roughly divided into cis and trans bands. From the temperature dependence of the spectra of polysarcosine, a double coalescence phenomenon was observed, in which the four dyad peaks coalesced into two peaks corresponding to cis and trans, then the two peaks coalesced into one peak. Further, the approximate value of the free energy for the internal rotation of the main chain amide bond was estimated. NMR spectra of various poly(N‐alkylglycine)s in methylene chloride solution were also obtained. From the comparsion of their methylene bands, the introduction of the bulky N‐alkyl groups was found to increase the cis content of the amide bond.
Steady‐state and pulsed NMR studies of gelation in aqueous agarose
Authors: Child T. F. , Pryce N. G. 
Published: December 2004

AbstractSteady‐state and pulsed NMR techniques have been used to investigate molecular motion in sols and gels of agarose. In passing through the sol–gel transition, the molecular mobility of water molecules is reduced only by a small amount, whereas motion of the polymer chains is greatly attenuated. The results are discused in terms of the network theory of gelation, with references to the role of water in the process and the nature of the “junction zones” between polymer chains. T2 and line‐width measurements are dominated by exchange broadening. The effects of exchange rate and differences in relaxation time between the exchanging sites are discussed. The temperature hysteresis behavior of agarose gels has been investigated and the effects of “ageing” correlated with changes in nuclear relaxation times. The synergistic increase in gel strength obtained on adding locust bean gum (LBG) to agarose has been investigated. The results indicate that LBG does not form double‐helix junctions and may decrease rates of gelation by steric effects. At high agarose concentration, the LBG remains mainly in solution in interstitial water, but at low agarose concentration, it is suggested that the LBG can link gel aggregates together into a self‐supporting structure, producing a synergistic increase in gel strength. Comparisons have been made between the nature of the agarose–LBG interaction and agarose–cellulose interactions in biological systems.
A cross‐linked copolypeptide with increased affinity for cations
Authors: Kim Yung D. , Klotz Irving M. 
Published: December 2004

AbstractThe copolymer poly Glu42Lys28Ala30 was crosslinked by S–S bridges by reaction with butyrothiolactone followed by air oxidation of the mercaptan covalent adduct. The modified copolypeptide was more compact hydrodynamically, more resistant to the structurally disruptive effects of urea, and able to bind dye cations with much increased avidity.
The effect of charges on the melting of DNA
Authors: Nagasawa Mitsuru , Muroga Yoshio 
Published: December 2004

AbstractA method of calculating both the electrostatic free energy and en tlpy changes for melting of DNA is proposed. The nonelectrostatic parts of free energy and enthalpy changes for melting of DNA are obtained by subtracting these electrostatic free‐energy and enthalpy changes from the total free‐energy and enthalpy changes of melting reported by Privalov, Ptitsyn, and Birshtein, respectively. The ionic strength dependence of the melting temperature of DNA is computed using these thermodynamic functions.
Rate studies of the amylose–iodine reaction in unfractionated starch samples of various plant origin
Authors: Hamori Eugene , Kallay Michael C. 
Published: December 2004

AbstractThe initial rate of the fast reaction among amylose, iodine, and iodide ions was studied in unfractionated corn, potato, rice, wheat, and arrowroot starches. It was found that the reaction followed the same rate equation as the one established in a previous study using pure amylose fractions containing no amylopectin. There were significant differences, however, among the rate constants of the various starches investigated. These variations were explained in terms of the different average molecular weights of the amylose fractions of these starches. Since whole potato starch indicated a rate constant well within the fange of those of pure amylose fraction (obtained from the same potato starch samples), it was concluded, that amylopectin did not interfere significantly with the rate of the complexation reaction.
Macromolecule‐small molecule interactions; introduction of additional binding sites in polyethyleneimine by disulfide cross–linkages
Authors: Takagishi Toru , Klotz Irving M. 
Published: December 2004

AbstractPolyethyleneimine and its acyl derivatives have been thiolated with thiobutyrolactone and the SH groups introduced have been crosslinked in the presence of and in the absence of methyl orange, respectively. After crosslinking of the polymers, the bound methyl orange was removed. The resultant two kinds of crosslinked polymers have been examined for their ability to bind methyl orange. The polymer crosslinked in the presence of methyl orange shows more binding sites and stronger binding than does the polymer crosslinked in the absence of methyl orange. It seems, therefore, that the conformation of the polymer may be molded to provide sites that can accommodate a specific small molecule.
Rotatory dispersion and circular dichroism of low‐molecular‐weight poly‐γ‐benzyl‐L‐glutamate
Authors: Imae Toyoko , Ikeda Shoichi 
Published: December 2004

AbstractRotatory dispersion and circular dichroism of low‐molecular‐weight poly‐γ‐benzyl‐L‐glutamate, which was prepared from the N‐carboxyanhydride by n‐hexylamine initiation at [A]/[I] 3, 4, and 8, have been measured in ethylene dichloride and dioxane at different concentrations. The rotatory properties of the polypeptides are all characterized by a trough at 233 mμ of a negative Cotton effect or by a negative circular dichroic band at 223 mμ. With increasing A/I value or concentration, dextrorotation increases and the negative dichroic band becomes deeper. Both the trough magnitude and the negative ellipticity are linearly dependent on the content of β‐structure, and the rotatory parameters for the pure β‐structure are estimated by extrapolation of the linear relations. Circular dichroism and infrared spectra of the polypeptides have also been measured in trifluoroethanol, and the effect of solvents on the polypeptide conformation is discussed.