bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of concentration on the aggregation of poly(γ‐benzyl‐L‐glutamate) in dioxane: Critical concentration and maximum length for linear head to tail aggregates
Authors: Gupta Avadhesh K. 
Published: December 2004

AbstractDielectric relaxation studies in the frequency range 100 Hz to 2 MHz of poly(γ‐benzyl‐L‐glutamate) in dioxane have been carried out over a range of concentration 10−4–10−2g/g. The structure of aggregates is analyzed in terms of dipole moment and relaxation time. A critical concentration (≃ 10−3 g/g for the studied molecular weights) has been determined below which the aggregates are found to have linear head to tail type structure. Above the critical concentration a different structure of aggregates is apparent which could not be fully analyzed by these measurements alone. Possible forms of aggregation above the critical concentration are discussed. Formation of long range order which would lead to nematic liquid crystalline phase at higher concentrations has been discussed as one of the possible explanations for the observed behavior above the critical concentration.Maximum length of linear head to tail type aggregates for poly(γ‐benzyl‐L‐glutamate) in dioxane as determined from these results correspond to an α‐helix of molecular weight 210,000. A slight difference in the purity of dioxane has been shown to have an influence on the reproducibility of the state of aggregation as well as on the rate of disaggregation on dilution.
Racemization in the synthesis of sequential polypeptides using N‐hydroxysuccinimide esters
Authors: Rapaka Rao S. , Bhatnagar R. S. , Nitecki D. E. 
Published: December 2004

AbstractRacemization in the synthesis of peptide intermediates and their polymers was investigated, using L‐amino acid oxidase. The formation of N‐hydroxysuccinimide esters from N‐protected peptide acids yielded optically pure products in contrast to p‐nitrophenyl and pentachlorophenyl active esters. The racemization in the polymerization step was found to be base sensitive. Partially racemized polymer can result from optically homogeneous monomer. Thus, the optical integrity of active monomer species carries no guarantee for that of the polymer.
A study of DNA denaturation in the ultracentrifuge
Authors: Wiesehahn Gary , Cech Thomas R. , Hearst John E. 
Published: December 2004

AbstractThe melting transition of DNA in alkaline CsCl can be followed in the analytical ultracentrifuge. Equilibrium partially denatured states can be observed. These partially denatured DNA bands have bandwidths of up to several times those of native DNA. Less stable molecules melt early and are found at heavier densities in the melting region.An idealized ultracentrifuge melting transition is described. The melting transition of singly nicked PM‐2 DNA resembles the idealized curve. The DNA profile is a Gaussian band at all points in the melt. DNA's from mouse, D. Melanogaster, M. lysodeikticus, T4, and T7 also show equilibrium bands at partially denatured densities, some of which are highly asymmetric. Simple sequence satellite DNA shows an all‐or‐none transition with no equilibrium bands at partially denatured densities.The temperature at which a DNA denatures is an increasing function of the (G + C) content of the DNA. The Tm does not show a molecular‐weight dependence in the range 1.2 × 106–1.5 × 107 daltons (single strand) for mouse, M. lysodeikticus, or T4 DNA. The mouse DNA partially denatured bands do not change shape as a function of molecular weight. The T4 DNA intermediate band develops a late‐melting tail at low molecular weight. M. lysodeikticus DNA bands at partially denatured densities become broader as the molecular weight is decreased. Mouse DNA is resolved into six Gaussian components at each point in the melting transition.
Effect of ligands on the optical rotatory dispersion of hemoglobin. I. Ferrihemoglobin cyanide, ferrihemoglobin azide, ferrihemoglobin hydroxide, and carbonmonoxyhemoglobin
Authors: Beychok Sherman 
Published: December 2004

AbstractThe optical rotatory dispersion curves of ferrihemoglobin at pH 6 and 9.5, ferrihemoglobin cyanide, ferrihemoglobin azide, and carbon monoxyhemoglobin have been measured over the wavelength interval 500–190 mμ. Helix contents, based on the measured rotations at 233 and 200 mμ are estimated for the ferrihemoglobin derivatives on the basis of comparison with the rotations of the helical poly‐α,L‐glutamic acid. For the latter, a mean value of −14,200° is found for [m′]233 and 65,000° for [m′]200. Within experimental error, all the ferrihemoglobins examined have the same helix content, the value of which is 65% based on rotations at 233 mμ and 72% based on rotations at 200 mμ. Thus, the addition of ligands to ferrihemoglobin which enormously stabilize the molecule to acid denaturation and involve heme–heme interaction has no effect on the number of amino acid residues which are in α‐helical segments. Change of pH from 6.8 to 5.0, through which interval the molecular weight decreases to that of the dimer, also leaves the helix content essentially unchanged, although at pH 5 heme–heme interaction in the binding of cyanide ion to ferrihemoglobin is absent. In addition to the Soret band Cotton effect observed for all the hemoglobin derivatives examined, there is at least one (and possibly two) other heme Cotton effects at wavelengths intermediate tot he Soret Cotton effect near 400 mμ and the n‐π* peptide bond transition near 225 mμ. The Soret band Cotton effect is different in magnitude in all the derivatives examined, the most notable difference being in the pronounced intensification of this Cotton effect in CO‐hemoglobin relative to the ferrihemoglobin derivatives. Similar differences have been observed by others in different myoglobin derivatives as well. While the changes are not so large as observed with hemoglobin, this indicates that these altered magnitudes are not directly related to the specific details of heme environment which give rise to differences in affinity for oxygen in the two proteins and result in a Bohr effect in hemoglobin but not in myoglogin.
Polarographic studies of ion binding in solutions of pepsin. I. Binding of cadmium ions
Authors: Lapanje Savo 
Published: December 2004

AbstractThe results of the application of the modified polarographic method to the study of binding of cadmium ions in solutions of pepsin are reported. Isoionic solutions of pepsin were converted by suitable treatment with a cation‐exchange resin to solutions of cadmium pepsin. As in previous cases, i.e., in solutions of synthetic polyelectrolytes, the extent of ion binding was obtained by assuming that only free, i.e., unbound, ions contribute to the diffusion and migration currents, respectively. It has been furthermore shown that cadmium ions are bound to pepsin ionically as well as covalently, and the relative amounts of cadmium in either state of binding have been determined.
Stabilizing effectiveness of alkali metals toward ribonucleic acid from the bacterial virus R17
Authors: Gordon Julius A. 
Published: December 2004

AbstractThe addition of alkali metal cations (0.10–1.00M) stabilizes the macromolecular structure of R17‐RNA as evidenced by a shift of the optical density–temperature profiles to higher temperature. This effectiveness is found to decrease in the order Li+ > Na+ > K+ > Rb+ > Cs+ and the midpoints of each profile (Tm) are found to increase linearly for each salt with the log of the salt concentration. The differences in effectiveness in this series can be best interpreted as a decreasing specific interaction of Li+, Na+, K+, and Rb+ with the phosphate groups of RNA as suggested by known binding constants to phosphate groups and the failure of adenine, adenosine, adenine monophosphoric acid, and uracil to show specific solubility differences in these salts. The importance of this feature is that the thermal stability of RNA in the presence of alkali metals shows specific ion requirements in addition to general electrostatic interactions. Furthermore, the more nonspecific, ionic strength‐dependent stabilization of native RNA also involves a decrease in adenine solubility (e.g., increased activity) and an increase in phosphate solubility in the aqueous salt solutions in addition to the well recognized Coulombic shielding of the negatively charged phosphates.
Studies on amylose and its derivatives. Part VI. Estimation of cohesive energy densities of some amylose derivatives
Authors: Cowie J. M. G. 
Published: December 2004

AbstractThe cohesive energy densities (CED) of three amylose derivatives have been estimated from viscosity measurements in a range of solvents, by using methods proposed by Mangaraj and Bristow and Watson. The values assigned to the triacetate, (2.5) nitrate, and tricarbanilate are 92 ± 2, 90 ± 2, and 87 ± 2 cal./cc., respectively. The CED of unsubstituted amylose has been measured and found to be 154 ± 4 cal./cc. The results are discussed in relation to solvent power, structure, and possible correlation with the internal pressure of the polymer.
Effect of temperature on the buoyant density of bacterial and viral DNA in CsCl solutions in the ultracentrifuge
Authors: Vinograd Jerome , Greenwald Robert , Hearst John E. 
Published: December 2004

AbstractThe effect of temperature on the buoyant density of CsDNA in CsCl at equilibrium in the ultracentrifuge has been measured between 5 and 60°C. The temperature coefficients of the byoyant density for three DNA's of varying guanine‐cytosine (G‐C) contents were, within experimental error, +4.2 ± 0.3 × 10−4 g./ml.°C. This coefficient may be used to normalize results obtained between 5 and 60°C. to 25°C. The results are explained in terms of a loss of water from the hydrated CsDNA complex. It is estimated that about one‐third per cent of the water preferentially hydrated by the DNA is liberated per degree elevation in temperature. Significant errors in buoyant density determinations are made if the thermal expansion coefficient of CsCl solutions is ignored.
Ultraviolet light‐induced change in collagen macromolecules
Authors: Fujimori Eiji 
Published: December 2004

AbstractViscosity measurements and calculated rotary diffusion constants show that collagen undergoes photopolymerization when irradiated with ultraviolet light of 2537 A. Fibril formation at the same time is inhibited. The results are correlated with the aromatic amino acid content of the dangling peptides protruding from the rigid portion of the macromolecule.
Studies of the conformation of carboxymethyl amylose in aqueous solutions
Authors: Rao V. S. R. , Foster Joseph F. 
Published: December 2004

AbstractIn an attempt to clarify certain questions of the configuration of amylose in aqueous solution, carboxymethyl groups were introduced into corn amylose (degree of substitution ca. 0.8) and certain properties of the derivative (CMA) studied. The intrinsic viscosity exhibits a strong increase between pH 2 and 6 but remains constant at higher pH. A pH 6 and above, CMA exhibits typical polyelectrolyte behavior. CMA does not form a complex with iodine at pH 6 or above but does form a violet‐colored complex at low pH. The absorption maximum of the CMA complex lies at a somewhat lower wavelength (550 mμ) than that of the complex formed by the parent amylose. The reduced viscosity and specific optical rotation of the CMA–iodine complex remains constant up to a concentration of 1.2 mg. iodine/100 mg. CMA, then both properties decrease with further increases of iodine content. All of the above results and hydrogen ion titration behavior are in agreement with the hypothesis that CMA exists as a coil of short helical segments in acid solution and that these helical segments break down on ionization of the carboxyl groups. The specific optical rotation of CMA increases between pH 2 and 6, remains constant between pH 6 and 12, and decreases above pH 12. This later result shows that the similar decrease in rotation seen in amylose cannot be attributed, at least entirely, to a helix–coil transition. There must be another effect on optical rotation, direct or indirect, of the ionization of hydroxyl groups.
Dependence of the melting temperature of DNA on salt concentration
Authors: Schildkraut Carl , Lifson Shneior 
Published: December 2004

AbstractData on the decrease of the DNA melting temperature Tm with the salt concentration M are reported and discussed. The electrostatic free energy change in the helix–coil transition, ΔFe is related to the potential, ψ, which represents the electrostatic repulsion between the phosphate charges; ψ is calculated as a function of M and of the distances between the charges of the two strands. The Debye‐Hückel approximation is shown to overestimate ψ. It is suggested that the high local concentration of the counterions in the immediate vicinity of the fixed charges screen these charges from interacting with other fixed charges, to the extent that the system behaves as if the fixed ions carry a reduced charge. The notion of a reduced charge represents in a single parameter the deviation of the Debye‐Hückel approximation from the true potential. A plot of Tm versus ΔFe gives a straight line as predicted. ΔH0 is calculated from the slope and found to be consistent with experimentally determined values. Our calculations support the hypothesis that the change of Tm with salt concentration is due to changes in the screened interactions between the fixed phosphate charges. In analyzing the results of these calculations, we are able on the one hand to indicate some of the limitations of the theoretical model and, on the other hand, draw some conclusions about the order of magnitude of the nonelectrostatic interaction energy of formation of the double helix.
Helix–coil transition in poly‐ε‐carbobenzoxy‐L‐lysine
Authors: Karasz F. E. , O'Reilly J. M. , Bair H. E. 
Published: December 2004

AbstractThe reversible helix‐to‐random coil conformational change which occurs in solvated poly‐ϵ‐carbobenzosy‐L‐lysine, a synthetic polypeptide, has been studied. The course of this cooperative transition, which in many ways resembles a first‐order phase transition, was followed both by measuring changes in optical rotation as a function of temperature, and calorimetrically by determining the heat capacity of the solution through the transition region. From the latter measurements, the enthalpy of transition was calculated. From the results it has been shown directly, for the first time, that in a statistical thermodynamical sense, the transition in this system is significantly more cooperative than that undergone by poly‐γ‐benzyl‐L‐glutamate, a closely analogous polypeptide. Thus a previously held concept that the degree of cooperation might be quantitatively similar for a wide range of such systems has been shown, for at least one important example, not to be tenable.
Magnesium binding to poly(L‐aspartic acid)
Authors: Jacobson A. L. 
Published: December 2004

AbstractThe optical rotatory dispersion of poly(L‐aspartic acid) in magnesium chloride and tetramethylammonium chloride solutions has been measured to determine helix content. At pH 4, helix content estimated by using the Moffitt bo coefficient is about 20%. Optical rotation has been used to determine changes in conformation with polymer ionization. The changes in rotation are very sensitive to the relative concentration of added salt. At very low salt concentrations no ordered structure appears to be present. The effect of magnesium ion binding on the dissociation of side‐chain carboxyl groups in poly(L‐aspartic acid) has been measured by a modified titration technique. The changes in ionization of the carboxylic acid side chains were measured as a function of both the degree of polymer preionization and of added magnesium chloride. These changes have been related to possible changes in the polymer conformation as a function of degree of polymer ionization. The effect of ionization on magnesium ion binding to poly(L‐aspartic acid) and to poly(L‐glutamic acid) have been compared with essentially equivalent polymer concentrations at equivalent salt additions. pH titrations have been used to compare ionization in the two polyacids. The pH titration method proposed by Wada has been used to determine the extent of the helix‐‐coil transition region in this polymer concentration range. Poly(L‐aspartic acid) appears to be more easily ionized than poly(L‐glutamic acid). For both polyacids, a helical conformation appears to favor ion binding. However, in this region, binding to poly(L‐aspartic acid) is approximately double that observed with poly(L‐glutamic acid) at a corresponding degree of ionization. In the coil region the trends observed with magnesium binding are similar to those observed with other extended polyelectrolytes.
Optical rotatory dispersion of mucopolysaccharides and mucopolysaccharide–dye complexes
Authors: Stone Audrey Larack 
Published: December 2004

AbstractAnomalous optical rotatory dispersion (ORD) is induced in symmetric dyes when bound in metachromatic complexes with chondroitin sulfates (ChS) and kerato sulfate (KS) from mammalian and shark origin as well as with heparin (H) providing inference that secondary structures exist in these biopolymers. The induced rotation occurs in the absorption band of the bound dye and differs in shape and/or spectral position from the classical Cotton effect seen with single optically active chromophores. The AO:ChS complex has an induced ORD curve similar to that of the exciton band of a helical polymer. Strength of the induced rotations with methylene blue increases with the degree of metachromasy of the 1:1 complex. The sense of the MB Cotton effects may depend upon the conformations of the repeating dimeric units, since MB complexes with ChS (alternating 1‐3,1‐4 β‐glycosides) give (+) effects while MB:H (1‐4 α‐glycosides) have (−) effects in the γ band region. Preliminary evidence for the occurrence of Cotton effects with the mucopolysaccharides themselves in the ultraviolet region was obtained. The sign of the Cotton effect for ChS‐C is (−), trough about 45.9 kK., crossover about 48.8 kK. whereas that for H is (+), peak about 50.4 kK.
Kinetics of polypeptide denaturation
Authors: McQuarrie D. A. , McTague J. P. , Reiss H. 
Published: December 2004

AbstractThe irreversible kinetics of polypeptide denaturation and renaturation is discussed in terms of the Zimm‐Bragg equilibrium model. An exact solution is presented for situations in which the back reaction is negligible. The solution is given in terms of parameters which are rate constants for the elementary processes in denaturation or renaturation. The formalism is also applicable to reactions of linear polymers in which the reactivity of a given site depends on the state of reaction of its neighbors.
Cyclodextrin–polyethylenimine conjugates for targeted in vitro gene delivery
Authors: Forrest M. Laird , Gabrielson Nathan , Pack Daniel W. 
Published: December 2004

AbstractMany human gene therapies will require cell‐specific targeting. Though recombinant viruses are much more efficient than nonviral vectors, the latter, especially polymers, have the advantage of being targetable via conjugation of cell‐specific ligands, including sugars, peptides, and antibodies, which can be covalently attached to the polymer using a variety of chemistries. Cyclodextrin, which forms inclusion complexes with small hydrophobic molecules, has been incorporated into a gene‐delivery polymer and may provide a facile and versatile attachment site for targeting ligands. Polyethylenimine (PEI) was derivatized with β‐cyclodextrin on ∼10% of the polymer's amines (termed CD‐PEI). Human insulin was also derivatized with a hydrophobic palmitate group (pal‐HI), which could anchor the protein to CD‐PEI/DNA polyplexes. CD‐PEI was essentially nontoxic to HEK293 cells at concentrations optimal for gene delivery and mediated nearly 4‐fold higher gene expression than unmodified PEI, which is relatively toxic to these cells. More importantly, addition of the pal‐HI to CD‐PEI enhanced gene expression by more than an order of magnitude compared to unmodified PEI, either with or without the pal‐HI. Because of the relative ease with which CD‐binding moieties may be attached to various types of ligands, CD‐PEI may be a generally useful material for testing novel cell‐specific targeting compounds. © 2004 Wiley Periodicals, Inc.
Synthesis of galacto‐oligosaccharide from lactose using β‐galactosidase from Kluyveromyces lactis: Studies on batch and continuous UF membrane‐fitted bioreactors
Authors: Chockchaisawasdee Suwimol , Athanasopoulos Vasileios I. , Niranjan Keshavan , Rastall Robert A. 
Published: December 2004

AbstractA study of galacto‐oligosaccharides (GOS) synthesis from lactose with β‐galactosidase from Kluyveromyces lactis (Maxilact® L2000) was carried out. The synthesis was performed using various initial lactose concentrations ranging from 220 to 400 mg/mL and enzyme concentrations ranging from 3 to 9 U/mL, and was investigated at 40°C and pH 7, in a stirred‐tank reactor. In the experimental range examined, the results showed the amount of GOS formed depended on lactose concentration but not on enzyme concentration. Galactose was a competitive inhibitor, while glucose was a non‐competitive inhibitor. In a further study, a laboratory‐scale reactor system, fitted with a 10‐kDa NMWCO composite regenerated cellulose membrane, was used in a continuous process. The reactor was operated in cross‐flow mode. The effect of operating pressures on flux and productivity was investigated by applying different transmembrane pressures to the system. The continuous process showed better production performance compared to the batch synthesis with the same lactose and enzyme concentrations at 40°C, pH 7. Comparison of product structures from batch and continuous processes, analyzed by HPAE‐PAD and methylation analysis, showed similarities but differed from the structures found in a commercial GOS product (Vivinal®GOS). © 2004 Wiley Periodicals, Inc.
Studies on the response of activated sludge to shock–loadings
Authors: Krishnan P. , Gaudy A. F. 
Published: December 2004

AbstractThe response of heterogeneous populations to shockloading was studied under a variety of operational conditions using synthetic wastes consisting of glycerol, glucose, and a mixture of glucose and glycerol. In all experiments, the cells were acclimated to glycerol. The addition of glucose as a shockloading at various times during the aeration period caused an immediate cessation of glycerol metabolism, and glycerol was not again actively metabolized until all glucose had been assimilated. Experiments conducted at various initial sludge concentrations showed that this effect was not dependent upon biological solids level. Glycerol metabolism was also blocked when glucose was applied as a shockloading to a system operating under severe nitrogen deficiency, further reenforcing the conclusion that there is a blockage mechanism for catabolic pathways which operates to suppress enzyme function rather than enzyme synthesis. It was also found that considerable amounts of metabolic intermediates or end products were released during glucose metabolism regardless of the presence or absence of glycerol. In systems containing a source of nitrogen, these products were metabolized after dissimilation of glucose. In resting cell suspensions, the metabolic intermediates were not subsequently removed, indicating that their metabolism depended upon the synthesis of new enzymes. Using old cell sludge, concurrent rather than sequential removal of glycerol and glucose was observed. The results using two component (C6C3) carbon sources were in general the same as for C6C6 synthetic wastes. The results provide further evidence for the generality of sequential substrate removal, and suggest that the metabolite suppressing catabolism of glycerol lies below the triose level.