bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of oxytetracycline by flow injection with chemiluminescence detection
Authors: Guo Liangqia , Xie Zenghong , Bian Xintong , Lin Xucong , Zhang Weilin , Liu Xiaohua , Chen and Guonan 
Published: May 2005

AbstractA flow‐injection chemiluminescent method for the determination of oxytetracycline was developed. The method is based on an enhancement by oxytetracycline of the chemiluminescence light emission of tris(2,2′‐bipyridine) ruthenium (II), generated by the continuous oxidation of tris(2,2′‐bipyridine) ruthenium (II) by cerium (IV) sulphate in sulphuric acid. Under the optimum conditions, the calibration curve was linear over the range 1.0 × 10−7–1.0 × 10−5 g[sol ]mL for oxytetracycline with the linear equation: ΔINT = 148.77 × C + 0.6637 (R2 = 0.9994). The detection limit was 4.52 × 10−8 g[sol ]mL. The proposed method was also successfully used to determine oxytetracycline in pharmaceutical formulations. The mean recovery of determination of oxytetracycline was 92.73%. A mechanism for the chemiluminescence enhancement by oxytetracycline of tris(2,2′‐bipyridine)–ruthenium (II) and cerium (IV) sulphate system is also proposed. Copyright © 2005 John Wiley & Sons, Ltd.
Determination of ergometrine maleate by fluorescence detection
Authors: Gong Zhengjun , Lv Yi , Huang Yuming , Zhang Zhujun 
Published: May 2005

AbstractA simple, accurate, sensitive and selective fluorescence analysis method for rapid determination of trace amounts of ergometrine maleate has been developed. The method is based on the fluorescence of ergometrine maleate. The calibration graph was linear in the range of 1 × 10−4 to 0.2 µg[sol ]mL and the detection limit was 4 × 10−5 µg[sol ]mL, with a relative standard deviation of 0.32% at 0.05 µg[sol ]mL (n = 11) ergometrine maleate. The influence of foreign compounds was tested. The proposed method was applied successfully to the determination of ergometrine maleate in pharmaceutical preparations and human plasma. Copyright © 2005 John Wiley & Sons, Ltd.
Volume changes accompanying the thermal denaturation of deoxyribonucleic acid. I. Denaturation at neutral pH
Authors: Chapman R. E. , Sturtevant J. M. 
Published: May 2005

AbstractDilatometric measurements were made to determine the change in apparent specific volume φ of DNA resulting from thermal denaturation in neutral solution, φ increased continuously with temperature in the range 10–85°C. No deviations from a monotonically rising curve were observed in the φ versus temperature profile in the region of the melting temperature. The results are interpreted in terms of a partial loss of the preferentially bound DNA hydration shell. The nature of the well known buoyant density difference between native and denatured DNA was investigated by evaluating the densities in a series of cesium salt gradients at constant temperature. Extrapolation of the results to zero water activity indicates that the partial specific volumes of anhydrous native and denatured DNA are equal. The density difference at nonzero water activities is attributed to decreased hydration in the denatured state. The absence of a related change in φ accompanying the denaturation in the dilatometric experiments suggests that the probable volume change associated with loss of bound water during denaturation is accompanied by other compensatory volume effects. The possible nature of these volume effects is discussed.
Optical rotatory dispersion and circular dichroism of carbanilyl polysaccharides
Authors: Bittiger H. , Keilich G. 
Published: May 2005

AbstractMeasurements of optical rotatory dispersion (ORD) and circular dichroism (CD) have been made in the range of 600‐210 mμ for the β‐glycan carbanilates as for instance, 2,3,6‐tricarbanilylcellulose (I), 2,3,6‐tricarbanilylmannan (II), 2,3‐dicarbanilylcellulose (III), and octacarbanilylcellobiose (IV) and also for the α‐glycan carbanilates, such as 2,3,6‐tricarbanilylamylose (V), tricarbanilylpullulan (VI), 2,3‐dicarbanilylamylose (VII), and octacarbanilylmaltose (VIII). Furthermore, the 2,3,4,6‐tetracarbanilyl‐α‐methyl‐glucopyranoside (IX) and the 1,2,3,4,6‐pentacarbanilylglucose (X) have been measured in dioxane at 20°C. For the β‐glycans a small negative CD in the region of 238–240 mμ and nearly symmetrical ORD curve with a crossover point at 238–240 mμ are found; this indicates a simple negative Cotton effect. In the case of α‐glycosides, a strong negative CD with a maximum at 240–242 mμ and a strong positive CD with a maximum at 223–225 mμ were found; the ORD curves are asymmetrical and cross the abscissa in two places, at 241–243 and 220–222 mμ. With 2,3,4,6‐tetracarbanilyl‐α‐methylglucoside (IX) no CD and ORD in the ultraviolet region and with 1,2,3,4,6‐pentacarbanilyl‐glucopyranoside (X) the ORD, but not the CD, could be measured. The ORD curve is nearly symmetrical, like those of the β‐glycans but is of opposite sign. It seems impossible to discuss the striking difference of the CD and ORD spectra between the α‐and the β‐glycans in terms of contributions of single independant chromophores influenced by their individual different steric arrangements and their spatial relation to the glycosidic bond in C1. The exciton theory of Moffitt, which is suitable for explaining the ORD and CD spectra of helical polymers, has been applied to α‐ and β‐glycans. A structure with helical parts is proposed for the α‐glycans while a nearly planar arrangement is assumed for the β‐glycans.
Increasing viscosity of E. coli chromatin with increasing shear
Authors: Thompson Douglas S. , Hays John B. , Gill Stanley J. 
Published: May 2005

AbstractWe have observed that the viscosity of a solution of E. coli chromatin increases as the shear to which the solution is subjected is suddenly increased. This dilatant effect is opposite to the usual thixotropic non‐Newtonian effects that are observed in DNA solutions. We suggest that the observed dilatancy may be explained in terms of shear‐induced aggregation of large DNA molecules. Conditions for aggregation are discussed in the context of the “cluster theory” of condensation.
Optical activity of simple cyclic amides in solution
Authors: Greenfield Norma J. , Fasman Gerald D. 
Published: May 2005

AbstractThe cyclic dipeptide, L‐alanylglycyl anhydride, has been studied by optical rotatory dispersion; both L‐alanylglycyl anhydride and the lactam, L‐3‐aminopyrrolidin‐2‐one, have been studied by circular dichroism. In hydroxylic solvents the circular dichroism spectra of 3‐aminopyrrolidin‐2‐one can be attributed to an n–π* transition near 220 mμ and a π–π* transition near 190 mμ. In these solvents the optical activity of L‐alanylglycyl anhydride can be explained as being due to contributions of n–π* transitions and a split π–π* transition. In acetonitrile, however, the circular dichroism spectrum of 3‐aminopyrrolidin‐2‐one shows an additional apparent minimum near 200 mμ. The CD spectrum of the dipeptide is also quite distinctive in this solvent. The possible nature of the band at 200 mμ and the implications of these findings are discussed.
Interactions des ions métalliques avec le DNA. I. Comportement de polyélectrolyte et liaison des ions compensateurs
Authors: Daune M. 
Published: May 2005

AbstractThe theory of polyelectrolyte solution of Alexandrowicz: and Katchalsky is used to calculate the electrostatic potential of single stranded polynucleotides for different ionic strength. We have considered the potential of double stranded DNA as the superposition of the different potentials produced by each chain, provided the average distance between the strands is higher than an ionic strength‐dependent parameter b. For ionic strength lower than 5 × 10−2M, the assumption is no longer valid, and a cylindrical model with a uniform charge density must be used. The continuity between the two models was tested, and thus we can calculate the electrical potential at the vicinity of a phosphate group in the whole range of ionic‐strength where the double helix is stable. It was therefore possible to determine the theoretical number of ions bound electrostatically to DNA and we found an increase of ion binding with a decrease of ionic strength. Such a model was further applied to the change of specific volume in different salt solutions. Comparison is made with recent pycnometric data on Na− and Cs− salts of DNA. Agreement is good in the case of Cs+, but for Na+, cation binding is likely to be accompanied by a change of the hydration of DNA, which depends on ionic strength. With the same model we can see easily the ion‐trapping properties of DNA which play an important role in any formation of complex between heavy ions and bases.
Circular dichroism of polynucleotides: A simple theory
Authors: Johnson W. C. , Tinoco I. 
Published: May 2005

AbstractA particularly simple theory of circular dichroism is described and applied to the polynucleotides. It works surprisingly well and predicts the conservative spectrum of DNA and the more intense nonconservative spectrum of RNA. The anomalously low intensity of the CD of the nucleic acids is shown to be a natural consequence of the cancellation of the rotational strengths of the many CD bands. The theory's many successes and predictions as well as its weaknesses are discussed.
Crystal and molecular structure of L‐cis‐3,6‐dimethyl‐2,5‐piperazinedione (L‐alanyl‐L‐alanyl‐2,5‐diketopiperazine)
Authors: Benedetti Ettore , Corradini Paolo , Pedone Carlo 
Published: May 2005

AbstractThe crystal structure of L‐cis‐3, 6‐dimethyl‐2,5‐piperazinedione (L‐alanyl‐L‐alanyl‐2,5‐diketopinerazine) has been determined. The unit cell is triclinic with a = 8.05, b = 6.08, c = 5.15 Å, α = 131.7°, β = 82.4°, γ = 106.6°. The space group is P1 with one molecule per unit cell. The six‐membered ring is found to be nonplanar with an angle between the two amide group planes of 26°. One amide group deviates slightly from planarity. The experimental molecular model is discussed in terms of its flexibility.
Intrinsic viscosity of native and single‐stranded T7 DNA and its relationship to sedimentation coefficient
Authors: Rosenberg Alan H. , Studier F. William 
Published: May 2005

AbstractThe intrinsic viscosity and sedimentation coefficient, of native and single‐stranded T7 DNA have been determined at 25°C as a function of ionic strength in neutral and alkaline NaCl. The relationship between [η] and S,w is well represented by the Mandelkern‐Flory equation over the entire range of conditions between 0.0013 and 1M Na+. An apparent discrepancy between the two methods at moderate to high ionic strengths is probably due to a change in V with ionic strength. It appears that [η] is a more sensitive and reliable measure of molecular expansion for native DNA, S,w but is a better index of conformational change in single strands, since [η] becomes too small to measure conveniently at high ionic strengths. At moderate to high ionic strengths, denaturation leads to a decrease in [η], although unfolded single strands retain considerable viscosity. At sufficiently low ionic strength, the intrinsic viscosity of the single strands becomes higher than that of native DNA, and the effective volume of a single strand approaches that of the native molecule.
Stereochemistry of nucleic acids and their constituents. IV. Allowed and preferred conformations of nucleosides, nucleoside mono‐, di‐, tri‐, tetraphosphates, nucleic acids and polynucleotides
Authors: Sundaralingam M. 
Published: May 2005

AbstractA uniform notation and convention is suggested to describe the torsional angles in nucleic acids and their derivatives. The torsional angle χ, relating the stereochemistry of the base with respect to the sugar, shows more variation for the β‐purine glycosides than for the β‐pyrimidine glycosides. This variation is attributed to the fact that the β‐purine derivatives may form intramolecular O(5′)‐H…N(3) hydrogen bonding. The χ values for the α‐purine and α‐pyrimidine glycosides show preference for the –syn‐clinal (or anti) conformation. The mode of puckering of the sugar also influences the χ value. The various possible conformations for the furanose ring are described by the torsional angles τ0 τ1, τ2, τ3, τ4, about the five ring bonds. From an analysis of the torsional angles (ω, ϕ, ψ, ψ′, ϕ′, ω′) about the sugar phosphate bonds in the x‐ray structures of the known nucleosides, nucleotides, phosphodiesters, nucleic acids, and related compounds, and from a consideration of molecular models, it is found that the possible conformations for the backbone of helical nucleic acids is strikingly limited. Most importantly, the preferred conformation of the nucleotide unit in poly nucleotides and nucleic acids turns out to be the same as that found for the nucleotide in the crystal structure. It is observed that base “stacking” is a consequence of the restricted backbone conformation. The torsional angles are illustrated in the form of conformational “wheels”. Interrelation between the torsion angles about successive pairs of sugar‐phosphate bonds are presented in the form of conformational maps: ω,ϕ; ϕ,ψ; ψ.ψ′; ψ′,ϕ′; ϕ′,ω′; ω′,ω. The ω′,ω map shows the perferred conformations about the inter‐nucleotide bonds of right‐ and left‐handed helices and the possible conformations of phosphodiesters. The preferred conformation of the pyrophosphate and triphosphate is that in which the phosphate oxygens display a staggered arrangement when viewed along the P–P axis. A plausible structure and conformation for the ATPM2− backbound complex is presented. This structure differs from that proposed by SzentGyorgi in that the metal (only transition metals are considered here) is not bound to the NH2 nitrogen of adenine, but rather is simultaneously bound to N(7) of the ring and three phosphates (α, β, γ), or N(7) of the ring and two phosphates (β, γ). The remaining metal coordination may be satisfied by solvent–metal or enzyme–metal bonds.
Conformation of dipeptides
Authors: Lande Saul 
Published: May 2005

AbstractThe amide bond in L,L‐ and L,D‐α‐chloropropionylalanine methyl ester is shown to be trans by molar polarization and infrared spectroscopy. In these dipeptide diastereoisomer analogues, therefore, differences in physical properties, i.e., melting points, crystalline forms, gas chromatographic mobilities, etc., depend on preferred molecular conformations and not peptide bond configuration. Nuclear magnetic resonance spectra of both compounds were identical, indicating that no major chemical environment differences exist, which might have resulted from dissimilar side group interactions. Based on the data reported here and those of others, most dipeptide conformations can be eliminated because of contradiction with limits set by experimental or theoretical considerations. Of the remaining conformational possibilities, a single pair accounts for observed physical differences in dipeptide diastereoisomers, free or blocked. The preferred form contains α‐hydrogens trans to each other and in the plane of the peptide bond. In this conformation, R1–R2 and amino–carboxyl distances are minimal in L,D diastereomers and maximal in L,L forms.
Polymerization of amino acid derivatives by polymer catalysts. II. Polymerization by copolymer catalysts containing a tertiary amine as a component
Authors: Suzuoki Kazuhiro , Imanishi Yukio , Higa‐Shimura Toshinobu , Okamura Seizo 
Published: May 2005

AbstractThe polymerizations of D,‐Lβ‐phenylalanine NCA, p–nitro‐D,L‐β‐phenylalanine NCA, and o,p‐dinitro‐D,L‐β‐phenylalanine NCA were investigated, homopolymers and copolymers of N‐vinyl‐2‐ethylimidazole or 2‐Vinylpyridine being used as catalysts. When N‐vinylpyrrolidone and N,N‐diethylacrylamide, which are capable of forming hydrogen bonds with the NCA's, were used as comonomers with N‐vinyl‐2‐ethylimidazole, the copolymer catalysts were found to bring about a faster polymerization than poly‐N‐vinyl‐2‐ethylimidazole. However, when styrene, which has no particular interaction with the NCA's, was used as a comonomer with 2‐vinylpyridine, the copolymer catalyst was found to give a slower polymerization than poly‐2‐vinylpyridine. Electronic spectroscopy showed that the charge‐transfer complex between copolymer catalysts and the NCA's plays an important role in the polymerization. The experimental results are discussed in terms of the effectiveness of the copolymer catalysts for forming hydrogen bonds or charge‐transfer complexes with the NCA's.
Polymerization of amino acid derivatives by polymer catalysts. III. Chain effect polymerization induced by poly(N‐ethylglycine) diethylamide
Authors: Sisido Masahiko , Imanishi Yukio , Okamura Seizo 
Published: May 2005

AbstractThe polymerization of D,L‐β‐phenylalanine NCA induced by preformed polyi(N‐ethylglycine) diethylamide having a terminal secondary amino group was investigated. The polymerization was much faster than the same reaction initiated by a low molecular weight amine of similar base strength. Hence, the chain effect is operative with poly (N‐ethylglycine) diethylamide as well as polysarcosine diethylamide, with which Bamford et al. found the chain‐effect mechanism. The polymerization rate was dependent on the degree of polymerization of the polymer catalyst. The rate enhancement was attributed to adsorption of the NCA onto the amide carbonyl groups of the polymer chain by the formation of hydrogen bond. In going from polysarcosine diethylamide to poly (N‐ethylglycine) diethylamide, the absorptivity of NCA on on the polymer chain was little affected. However, the reaction between an adsorbed NCA and a terminal base was more difficult with poly (N‐ethylglycine) diethylamide than with polysarcosine diethylamide. This may be related to differences in flexibility of the polymer chain.
Partial denaturation of macromolecules by chemical agents
Authors: Cohen‐Addad J. P. 
Published: May 2005

AbstractThe denaturation of a macromolecule such as a polypeptide is considered in the case where the total number of noncovalent internal bonds broken in the binding process of the chemical agent is only a fraction, αs, of the total number of noncovalent internal bonds involved in its helical native conformation. Starting from a two‐parameter (s, σ) model of the helix–random coil transition of polypeptides, the transition temperature is derived as a function of the fraction αs, and of the concentration and the binding constant of the chemical agent. The lower limit of the transition temperature and the corresponding slope of the transition curve are shown to depend on αs. As an illustration, existing data on the partial acid denaturation of the enzymes ribonuclease A and muromidase are analyzed. The resulting average enthalpies of a noncovalent bond in the native ribonuclease A and muromidase are found to be 1.81 kcal/mole and 1.54 kcal/mole, respectively; the corresponding entropies are 5.4 and 4.4 cal/deg./mole, respectively. As a further example, existing data on a partially methylated enzyme ribonuclease A are also considered.
Viscosity and sedimentation study of sonicated DNA–proflavine complexes
Authors: Cohen Gerald , Eisenberg Henryk 
Published: May 2005

AbstractThe intrinsic viscosity of sonicated calf thymus DNA (molecular weight 4–5 × 105) increases and the sedimentation constant decreases, with increasing binding of proflavine at 0. 2 ionic strength and at 25°C. The measurements correspond to a linear increase in length of the almost rodlike DNA molecules with the amount of proflavine bound; independent calculations from viscosity and sedimentation measurements yield almost identical results. Over the range of r (moles of proflavine bound per moles of nucleotides) equal to zero to r = 0.13, the length increases by about 20%. This extension is compatible with the intercalation hypothesis proposed by Lerman. Density increments at various values of r, at constant chemical potential of diffusible solutes, were determined. It was also found that, in addition to the known isosbestic point of DNA‐proflavine complexes at 455.5 mμ, an additional isosbestic point exists at 225.5 mμ; this proved extremely useful for the evaluation of binding studies.
Helix–coil transition for poly(L‐glutamic acid) in water–ethanol solutions
Authors: Conio G. , Patrone E. 
Published: May 2005

AbstractPotentiometric titrations and some complementary optical rotation data are presented for solutions of poly(L‐ glutamic acid) (PGA) in several H2O–ethanol mixtures. The data allow the determination of the intrinsic pK (pK0), slope of the apparent. pK (pKapp), versus degree of ionization curves and of the enthalpy of ionization as a function of ethanol concentration. The variation of the degree of ionization at which the helix–coil transformation occurs with ethanol and temperature is also determined. Finally free energy, enthalpy, and intropy changes associated with the helix–coil transformation for the uncharged conformers are determined from the titration curves. The effect of the ethanol is to increase the stability of the helical conformation of PGA for both the charged and the uncharged forms of the polymer. The stabilization of the uncharged helix is essentially an entropic effect.
Dégradation du DNA par H2O2 en présence d'ions Cu++, Fe++ et Fe+++
Authors: Schweitz H. 
Published: May 2005

AbstractThe mechanism of degradation of calf thymus DNA by H2O2 in dark and light, and in the presence of either Cu++, Fe++, or Fe+++ ions has been investigated by following the decrease of molecular weight M̄w by light scattering. Both in the dark and in light, the rate of degradation decreases in the following order: Cu++>Fe++>Fe+++. In order to exploit quantitatively the variation of M̄w with time, we calculated the probability p(t) of rupture in a double stranded polymer as a function of the occurence at random of both breaks of the “first kind” (single hits) and of the “second kind” (double hits), when there are caused by any degrading agent. The value of p(t) can then be related to M̄w(t) for the present case of a randomly polydisperse sample of DNA molecules. In the dark, and in the presence of Cu++ ions, a degradation of the first kind (which takes place through the simultaneous or successive splitting of both strands of DNA at the same level) is the only one so far observed. The number of degradation sites of the first kind is equivalent to the number of bound Cu++ ions in inner sites of DNA. A model is set up to explain the successive breaks of the two strands of the DNA molecule through the formation of a complex (DNA site–Cu++‐H2O2) which exhibits peroxidative properties. The comparison of the degradation induced under these conditions in a native and a sonicated DNA, shows that the specific sites of attack of ultrasonic waves are not specific sites of H2O2 action in the presence of Cu++ ions. In the dark and in the presence of Fe++ or Fe+++ ions, breaks of the first kind and second kind are superimposed, but the last are predominant. This is ascribed to the low binding of iron ions in inner sites of DNA under these conditions. A large increase in degradation rate of the second kind occurred in the presence of light (with or without added metallic ions and) is ascribed to the action of the free radicals HO· (and HO2·) which arise from the photolysis of H2O2. These results are discussed in relation to those obtained by the action of ionizing radiations on aqueous solutions of DNA.