bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impurity study of CdZnTe substrates used for LPE HgCdTe
Authors: Bollong A. B. , Feldewerth G. , Tower J. P. , Tobin S. P. , Kestigian M. , Norton P. W. , Schaake H. F. , Ard C. K. 
Published: December 2004

AbstractImpurites were tracked from raw material purification through to CdZnTe processing in an effort to identify the sources of elements which impact on IR photodetector performance. Chemical analyses by GDMS and ZCGFAA effectively showed the levels of impurities introduced into CdZnTe substrate material from the manufacturing processes. A new purification process (ISDZR) for raw materials was developed, resulting in improved CdZnTe substrate purity. Substrate CU contamination was found to have detrimental effects on LPE layer and device electrical properties for lightly doped HgCdTe.
Essential language function of the right hemisphere in brain tumor patients
Authors: Thiel Alexander , Habedank Birgit , Winhuisen Lutz , Herholz Karl , Kessler Josef , Haupt Walter F. , Heiss Wolf‐Dieter 
Published: December 2004

AbstractNeuroimaging studies of language networks in patients with brain lesions of the left language‐dominant hemisphere have shown activation in the right inferior frontal gyrus (IFG). We tested the functional relevance of right IFG activation using neuroimaging‐guided repetitive transcranial magnetic stimulation (rTMS) to disturb language function over bilateral IFG in right‐handed patients with brain tumors and controls. All subjects were susceptible to TMS over the left IFG. In patients, this susceptibility correlated with left‐sided the degree of language lateralization to the left. Those patients with lowest dominance were also susceptible to right‐sided TMS proving relevant language function of the right IFG. Ann Neurol 2005;57:128–131
Einfach koordinierte Palladiumspezies als Katalysatoren in Kreuzkupplungen
Authors: Christmann Ute , Vilar Ramón 
Published: December 2004

AbstractPalladiumvermittelte Kreuzkupplungen sind nützliche metallorganische Transformationen zur Knüpfung von C‐C‐, C‐N‐, C‐O‐ und C‐S‐Bindungen. Obgleich sie bei Laborsynthesen häufig eingesetzt werden, haben sie keine bedeutende industrielle Anwendung gefunden, denn bis vor kurzem waren nur Verfahren für die reaktiven Arylbromide und ‐iodide bekannt, die teurer und weniger leicht erhältlich sind als die entsprechenden Arylchloride. In den letzten Jahren wurden neue Katalysatoren entwickelt, die auch weniger reaktive und sterisch gehinderte Arylchloride aktivieren. Diese Systeme beruhen auf Palladiumkomplexen mit elektronenreichen und sperrigen Phosphin‐ oder Carbenliganden. Die erhöhte Reaktivität dieser Systeme wurde dem Vorliegen von ungesättigten und reaktiven [PdL]‐Spezies zugeschrieben, die Ar‐X bereitwillig unter Bildung von [Pd(Ar)X(L)] oxidativ addieren.
Studies on dextran and dextran derivatives. II. Acid hydrolysis of native dextran
Authors: Antonini E. , Bellelli L. , Bonacci M. L. , Bruzzesi M. R. , Caputo A. , Chiancone E. , Rossi‐Fanelli A. 
Published: December 2004

AbstractThe kinetics of the depolymerization of native dextran in dilute hydrochloric acid at different temperatures has been followed by measurements of M̄w, M̄n, [η], 〈ρ2〉1/2, and S. The data allow the correlation of the various parameters of the total hydrolyzate at various degrees of depolymerization. At a first approximation the results conform to a random splitting of a statistical, branched polymer.
Polymerization of α‐amino acid N‐carboxy anhydrides in N,N‐dimethylformamide
Authors: Nylund Robert E. , Miller Wilmer G. 
Published: December 2004

AbstractThe polymerization of γ‐benzyl‐L‐glutamate NCA initiated by n‐hexylamine in DMF proceeds with two successive propagation rates whose ratio is about 1.5. The onset of the increase in rate of propagation occurred at a DPn of 7–14, which was independent of initiator to anhydride ratio and anhydride concentration and not a result of anhydride impurities. The increase in rate is likely a result of a conformational change in the polymer at a DPn of 7–14.
Synthesis and polymerization of N‐carboxyanhydrides of N‐benzyl‐β‐amino acids
Authors: Zilkha Albert , Burstein Yigal 
Published: December 2004

AbstractThe NCAs of the N‐benzyl derivatives of β‐alanine, β‐DL‐aminobutyric acid, and β‐DL‐aminoisobutyric acid (nonplanar six‐membered rings) were prepared by reacting the corresponding N‐chloroformyl derivatives, obtained on reaction of the N‐benzyl amino acids with phosgene, with triethylamine. Contrary to the others, the NCA of N‐benzyl‐β‐alanine polymerized readily on heating in vacuo or in solution, using n‐hexylamine or methanolic sodium methoxide as initiators. With n‐hexylamine the molecular weights of the polymers obtained in benzene, dioxan, and dimethylsulfoxide, were in accordance with DP = [NCA]/[Initiator], as was found with conventional five‐membered ring NCAs of α‐amino acids. With sodium methoxide initiation, DPs of the polymers obtained were smaller than the (NCA)/[Initiator] ratio, contrary to what was found previously with α‐amino acid NCAs. The possibility that stereochemical factors are responsible for the differences in polymerization activity of various. N‐alkyl β as well as α amino acid NCAs is discussed.
Helix‐coil transition of polo‐L‐glutamic acid film
Authors: Noguchi Hajime , Yang Jen Tsi 
Published: December 2004

AbstractWater‐insoluble films (ca. 0.04 × 3 × 30 mm. in dried state) of poly‐L‐glutamic acid (PGA), crosslinked with glycerol or polyvinyl alcohol at pH 4.8, were suspended in aqueous media and their relative lengths measured as a function of pH. The films elongate in alkaline pH and contract in acidic pH; the process is completely reversible, although the equilibration time usually takes several days at each pH. A sharp transition of the polymer was observed in the pH range which corresponded with that observed in PGA solutions by other physical methods.In NaCl, KCl, and KF solution the coiled from of the PGA film shrinks with increasing salt concentration. A notable exception is LiBr, which extends the film after a broef, rapid contraction and eventually causes it to disintegrate. Eight molar urea also caused a small elongation of film.Curpic ion has a drastic effect on the stability of the PGA helices. As low as 0.001M Cu(CH3COO)2 at pH 6.6 converted the coiled from the of the film into the helical form. On the other hand, calcium and magnesium ions only reduced the film length, probably without coil‐to‐helix transition.
Infrared spectra of isotopic polyglycines
Authors: Suzuki S. , Iwashita Y. , Shimanouchi T. , Tsuboi M. 
Published: December 2004

AbstractFor infrared absorption measurements, the following five isotopic polyglycines have been prepared: ordinary polyglycine (—NHCH2CO—)n, N‐deuterated polyglycine (—NDCH2CO—)n, C‐deuterated polyglycine (—NHCD2CO—)n, completely deuterated polyglycine (—NDCD2CO—)n, and N15‐substituted polyglycine (—15NHCH2CO—)n. Infrared spectra have been observed both in the I and II forms of each of these five isotopic polyglycines in the spectral region of 4000–300 cm.−1. On the basis of the comparison of these spectra with each other, a nearly complete set of assignments of the observed bands of polyglycines has been given.
Study of biological activity regenerated by the oxidation of fully reduced insulin
Authors: Pruitt Kenneth M. , Robison Bonnie S. , Gibbs Julian H. 
Published: December 2004

AbstractVarious techniques for recombining the fully reduced A and H chains of insulin were studied. Best results were obtained from water solutions of the reduced chains allowed to oxidize by standing in air at 3 °C. and from metal‐catalyzed oxidation under the same conditions but in 7.6M urea solutions. Average net regeneration of insulin was 6% by weight, based on rat hemidiaphragm analysis for insulin activity. The theoretical yield for a random recombination of the A and B chains was calculated to be 3%. The 50% yield of insulin (from the oxidation of reduced insulin thiosulfate) reported by Jiang et al. could not. be confirmed.
Solvent effects on the helix–coil transition in polypeptides
Authors: Bixon Mordechai , Lifson Shneior 
Published: December 2004

AbstractA simple way to incorporate the solvent–peptide interaction in any available theory of the helix–coil transition is developed. The competition between the intramolecular hydrogen bonding and the solvent–polymer hydrogen bonding is considered in multi‐component solvents where some of the components have hydrogen‐bonding capacity. Molecular averages are computed by using the theory of Lifson and Roig. The experimental data of Yang are analyzed, and the range of acceptable values of the equilibrium constants of hydrogen bond formation is deduced. The enthalpy of the transition in multicomponent solvents is calculated.
Interaction of poly‐L‐lysine with nucleic acids. II. Poly(A + U), poly(A + 2U), and rice dwarf virus RNA
Authors: Higuchi Shigesada , Tsuboi Masamichi 
Published: December 2004

AbstractThe optical density–temperature profile of double‐stranded poly(A + U), triple stranded poly(A + 2U), and double‐stranded RNA from rice dwarf virus in solutions with and without poly‐L‐lysine has been examined. When poly‐L‐lysine is added, more than one melting temperature Tm is observed for poly(A + U) and poly(A + 2U). One of them is considered to correspond to the melting of the polynucleotide molecule free from poly‐L‐lysine, and another to the melting of a polynucleotide–poly‐L‐lysine complex. For rice dwarf virus RNA, the Tm assignable to the complex is not found to be lower than 99°C. In every case, however, the hyperchromicity observed at the Tm of the free poly‐nucleotide molecule is lowered linearly as the amount of poly‐L‐lysine added to the solution increases. This fact is taken as indicating that there is a stoichiometric complex formed. The stoichiometric ratio lysine/nucleotide in each complex is determined by examining the relation between the amount of poly‐L‐lysine added to the solution and the percentage of hyperchromicity remaining at Tm of the free polynucleotide molecule. The ratio is found to be 2/3 for all of the three complexes. A discussion is given on the molecular conformations of four types of polynucleotide–polylysine complex hitherto found: (A) double‐stranded DNA plus poly‐L‐lysine in which the lyslne/nucleotide ratio is 1, (B) three‐stranded RNA [poly(A + 2U)] plus poly‐L‐lysine in which the ratio is 2/3, (C) double‐stranded RNA [poly (A + U) or rice dwarf virus RNA] plus poly‐L‐lysine in which the ratio is 2/3, and (D) double‐stranded RNA [poly(I + C)] plus poly‐L‐lysine in which the ratio is 1/2.
Low‐sulfur proteins from α‐keratins. Interrelationships between their amino acid compositions, α‐helix contents, and the supercontraction of the parent keratin
Authors: Crewther W. G. , Gillespie J. M. , Harrap B. S. , Inglis A. S. 
Published: December 2004

AbstractS‐Carboxymethyl (SCM) kerateine preparations from a range of keratins were fractionated by acid precipitation into low‐sulfur (SCMKA) and high‐sulfur (SCMKB) fractions. Amiono acid analyses and optical rotatory dispersion measurements on the SCMKA fractions from different keratins indicated that the proportion of α‐helical material (30–64%) increased with increasing leucine and glutamic acid contents and decreased with increasing SCM‐cysteine and proline contents. It is shown that these variations in α‐helix contents are due mainly to differences in the conformations of the principal components of the SCMKA fractions, although there is also a smaller contribution arising from contamination with varying amounts of non helical components. The thiol + disulfide contents for the parent keratins were measured and compared with the SCM ‐cysteine contents of the solubilized fractions. In general the SCM‐cysteine contents of the SCMKA fractions increased with increasing thiol + disulfide content of the parent keratin, but these values were not directly proportional. The extent of total supercontraction in 8M LiBr solution was measured for the parent keratins and shown to bear no significant relationship to their disulfide contents. From the extents of first‐stage and total supercontractions the disulfide contents of the contractile structures in the fibers were calculated according to a model described previously and compared with the analytical values for the SCM ‐cysteine contents of the SCMKA and SCMKB fraction. Data for both fractions were consistent with the model in that they were in each case related to the calculated values by a constant factor. However, because of simplifying assumptions in the model, it was not possible to identity positively one or other of these protein fractions with the contractile elements in the fiber.
Collagen aggregation phenomena
Authors: Cassel James M. 
Published: December 2004

AbstractThree processes by which tropocollagen units associate to yield highly specific aggregates have been examined. From the temperature coefficients of the amounts aggregated it is concluded that the complex “native” aggregation is endothermic, whereas both end‐to‐end and lateral aggregation are exothermic. These results combined with additional information lead to the conclusion that “native” aggregation is an entropy‐driven process in which hydrophobic bonding plays the dominant role. In contrast the reactions producing the lateral aggregate and the aggregate in which end‐to‐end bonding is dominant are electrostatically governed.
Frictional coefficients of multisubunit structures. I. Theory
Authors: Bloomfield V. , Dalton W. O. , Van Holde K. E. 
Published: December 2004

AbstractThe theory of Kirkwood for the translational frictional coefficients of structures composed of subunits has been generalized in two ways in order to consider aggregates of nonidentical subunits. One of these generalizations fails when the sizes of subunits are too disparate; the other, derived from a surface shell distribution of frictional elements, is effective over the whole range of relative sizes. It is shown that, in the limit of a continuous surface distribution, a shell model reproduces Stoke's law for a sphere. Comparison is made between the frictional coefficients of spheres, ellipsoids, and rods modeled by finite numbers of subunits and by continuous shells of frictional elements, and those calculated from other theories. Agreement is generally good, though the shell model for prolate ellipsoids of revolution deviates by a few per cent from the Perrin value.
Polarographic investigation of binding of Cu++ and Cd++ by DNA
Authors: Bach D. , Miller I. R. 
Published: December 2004

AbstractThe equilibrium binding constants of Cd++ and Cu++ to native and denatured calf thymus DNA were determined polarographically. The binding constants are an exponential function of the potential at the binding site and as such they vary with ionic strength and with the charge on the DNA molecule. The correlation between the fraction of sites occupied by heavy metal ions and between the thermal stability of DNA in solution is discussed.
Étude, par diffusion centrale des Rayons X, des polyelectrolytes rigides en solution. Cas des sels de Li, Na et Cs du DNA
Authors: Luzzati Vittorio , Masson F. , Mathis A. , Saludjian P. 
Published: December 2004

AbstractThe study of polyelectrolytes in solution by small‐angle x‐ray scattering techniques involves special problems, raised by the presence of several species: solvent, macroions, counterions, and possibly the ions of an additional electrolyte. A theoretical treatment of this problem is developed, based upon geometric concepts; the treatment applies to globular and to rodlike particles for the case of x‐ray experiments carried out on an absolute scale. The equation obtained involves several parameters: mass and radius of gyration for globular particles; mass per unit length and axial radius of gyration for rodlike particles; partial specific volumes of the neutral macromolecular component of the counterions and of the added electrolyte; solvation of the macromolecular species; fraction of the counterions osmotically free. The equation is used to interpret a series of experiments performed with the Li, Na, and Cs salts of DNA in solution in water containing variable amounts of the chlorides of each cation. The effects of concentration are first eliminated by extrapolating to infinite dilution the experiments carried out at different concentrations; then the effects of the solvation are eliminated by extrapolating to pure water the results obtained at different electrolyte concentration. The parameters still involved at this stage are the mass per unit length, the partial specific volumes of the DNA and of the counterions, and the fraction of the counterions osmotically free. If the partial specific volumes are chosen in agreement with other data of the literature, and if the fraction of the counterions osmotically free is assumed to be 0.30 for the three salts, as suggested by other workers, the structure of the DNA molecules turns out to be the same for three cations, and to agree with the Watson‐Crick model. These results are confirmed by the study of the liquid–crystalline gels, obtained at higher concentration, that lead to a direct determination of the mass per unit length of the rods. Moreover the solvation of the DNA molecules is determined as is shown to be different for each of the three cations. These results are in excellent agreement with those obtained by other techniques.
Derivatives of proteins. II. Coupling of α‐chymotrypsin to carboxyl‐containing polymers by use of N‐ethyl‐5‐phenylisoxazolium‐3′‐sulfonate
Authors: Patel R. P. , Lopiekes D. V. , Brown S. P. , Price S. 
Published: December 2004

AbstractA method for covalently binding proteins to carboxyl‐containing polymers is described. N‐Ethyl‐5‐pheriylisoxazolium‐3′‐sulfonate is used to form active esters of the carboxyls, which then condense with amine groups on the protein to yield amides. Conjugates of α‐chymotrypsin with such polymers have been obtained, with nearly full retention of enzymatic activity in some preparations.
Viscosity and temperature effects on the rate of DNA strand separation in alkali
Authors: Davison Peter F. 
Published: December 2004

AbstractThe time required for the completion of the process of strand separation in λ bacteriophage DNA preparations exposed to strongly alkaline conditions in aqueous glycerol solutions was directly proportional to the viscosity of the solvent. This finding supports the idea that the rate‐limiting step in the denaturation of high molecular weight DNA is the uncoiling of the strands and in the course of this uncoiling the forces arising from electrostatic and entropic factors must overcome the hydrodynamic viscous drag of the solvent resisting the translation of the polynucleotide strands.
Helix‐with‐loops structure of polynucleotide. II. Poly(I + CU)
Authors: Tsuboi Masamichi , Matsuo Kimiko , Nakanishi Mamoru 
Published: December 2004

AbstractCopolymers of ribocytidylic acid (C) and ribouridylic acid (U) with C contents of 66.5 and 43 mole‐% have been prepared. Ultraviolet, absorption measurements were made of aqueous solutions of the mixtures of these copolymers (poly CU) and polyriboinosinic acid (poly I). In every set of examinations, a maximum hypochromicity (at 230, 248, or 260 mμ) was observed when the solution contained equal moles of C residue in the copolymer and I residue in the homopolymer. This fact was interpreted as indicating that a helix‐with‐loops structure, similar to that proposed by Fresco and Alberts7, is formed. It was shown that this structure is formed more rapidly and melts more sharply than that observed by Fresco and Alberts. An infrared examination was also made of this “helix‐with‐loops” structure. It was found that a few absorption bands are assignable to the helix part and a few other bands to the loop part of the structure.
Conformations of model compounds of proteins. I. Acetylglycine N‐methylamide
Authors: Koyama Yasushi , Shimanouchi Takehiko 
Published: December 2004

AbstractInfrared spectra in the region 4000–60 cm−1 have been measured for acetylglycine N‐methylamide and its deuterium homologs, CD3CONHCH2CONHCH3, CH3‐CONHCD2CONHCH3, CH2CONHCH2CONHCD3, and CH3CONDCH2CONDCH3. Normal frequencies have also been calculated for these molecules with various conformations. The spectra show that this compound has two crystalline modifications, form A and form B. The frequencies and their isotope shifts show that the molecular conformation (Ψ, ϕ) of form B is near (0, 120) and that of form A near (180, 120). The short‐range factors determining the conformation of peptide backbone having glycine residues are discussed.
Kinetic properties and the electric field effect of life helix–coil transition of poly(γ‐benzyl L‐glutamate) determined from dielectric relaxation measurements
Authors: Schwarz Gerhard , Seelig Joachim 
Published: December 2004

AbstractDielectric relaxation of poly(γ‐benzyl L‐glutamate) in solution has been studied in the 5 kcps‐10 Mcps range for various values of the helix content. The results give first experimental evidence for three effects of major significance. (1) The system exhibits dielectric relaxation due to a chemical rate process (namely helix formation). This confirms recent theoretical predictions. (2) The mean relaxation time τ* of the helix–coil transition could be evaluated as a function of the degree of transition. The results are in excellent agreement with a previously developed theory. At the midpoint of transition it is found τ*max = 5 × 10−7 sec. The elementary process of helical growth turns out to be practically diffusion‐controlled (with a rate constant of hydrogen bond formation of 1.3 × 1010 sec−1). (3) There is a considerable electric field effect of the helix–coil transition. This indicates that conformation changes in biological systems could be potentially caused by direct action of an electric field.
Influence of the tritium labeling of calf thymus DNA by the Wilzbach method on its physical properties
Authors: Frommer M. A. , Miller I. R. 
Published: December 2004

AbstractThe adsorption at the air‐water interface of calf thymus H3‐DNA labeled in the dry state by the Wilzbach method was studied by measuring surface concentration, surface tension, and surface potential. It was found that, correspondingly to the behavior of E. coli H3‐DNA labeled by incorporation of thymine H3 and described in another paper, both the rate of adsorption and the amount of material adsorbed increased with increase in DNA concentration, salt concentration, or in the valency of the counterion. Surface pressure and potential did not change in the course of adsorption, and this is also in accordance with the properties found for E. coli DNA. However, while the surface concentration of the E. coli DNA corresponds approximately to monomolecular layer adsorption, the radiation from the adsorbed layer of the calf thymus H3‐DNA indicated apparently multilayer adsorption. On comparing the physical properties of the H3‐DNA labeled by the Wilzbach method to those of nonlabeled DNA, it is found that while the chemical composition and the bihelical structure is essentially maintained in the labeled material, exposure to tritium gas results in a reduction in molecular weight and produces random breaks in the strands of the bihelix. The H3‐DNA produced by Wilzbach's method is not labeled homogeneously. The more the molecule is exposed to the gaseous tritium, the more efficient is the isotopic, exchange and the greater the alteration in physical properties. The defects in the labeled H3‐DNA molecule make it more surface active, thus H3‐DNA of higher specific radioactivity concentrates at the interface, conveying the impression of multilayer formation although actually the adsorbed layer is approximately monomolecular.