Showing papers by "University of Madras published in 1969"

Stereochemistry of nucleic acids and polynucleotides. IV. Conformational energy of base-sugar units

Abstract: In this paper, the preferred conformations of the bases with respect to the sugar in various base-sugar units are worked out using criteria of potential energy. The van der Waals type of intercations between nonbonded atoms is represented by a 6-12 function and the electrostatic interactions have been calculated in the monopole approximation using Coulomb's law. The torsional contributions to the total energy have been neglected. It is found that in general the pyrimidines have preferred anti contributions (as described by Donohue and Trueblood) and purines have both syn and anti and conformations. Certain differences between differently puckered riboses in regard to the above general tendency are discussed. The conclusions, in general, conform with the results obtained by us earlier with the use of hard-sphere potential and are also supported by observations on conformations of nucleotides and nucleotides in crystal structure.

Stereochemistry of nucleic acids and polynucleotides. VI. Minimum energy conformations of dimethyl phosphate

Abstract: As part of a study on the conformation of polynucleotides and nucleic acids the preferred conformations of the model conpound dimethyl phosphate are worked out using potential energy functions. In calculating the total potential energy associated with the conformation, nonbonded, torsional, and electrostatic terms have been considered. The variation of the total conformational energy is represented as a function of two torsion angles #x03D5; and Ψ which are the rotations about the two phosphoester bonds. The most stable conformations are found to be the gauche-gauche conformations about these bonds. The conformations observed for phosphodiesters in the solid state and in the proposed structures of polynucleotides and nucleic acids cluster around the minimum. Also, regions of minimum energy correspond well with the typical allowed regions of a representative dinucleotide.

Stereochemistry of nucleic acids and polynucleotides. V. Conformational energy of a ribose-phosphale unit

Abstract: The potential energy calculations on the sugar-phosphate unit for different puckerings of the sugar are reported in this paper. The results obtained here essentially confirm our earlier predictions made by using criteria of contact distances (hard-sphere potential) and are also supported by observed conformation in crystal structures. The minimum energy conformations of the sugar phosphate unit, along with the preferred orientations of the base with respect to the sugar given in the previous paper, determine the probable conformations of the monomer unit of a polynucleotide (or nucleic acid) chain.

Configurational statistics of polysaccharide chains. Part II. Cellulose

Abstract: The characteristic ratio of unperturbed cellulose chain was computed as a function of the angle τ at, the bridge oxygen atom and the degree of polymerization. Very high values of the order of 40 or more, depending on the angle at the bridge oxygen atom, have been obtained for this ratio, indicating that cellulose chains are highly extended. The average dimensions of cellulose chains are found to be sensitive even for small changes in the angle at the bridge oxygen, and these chains attain the character of a random coil in very high molecular weight range (degree of polymerization greater than 2000). The large differences in the unperturbed dimensions of cellulosic chains observed in different solvents have been attributed to the possible small changes in the angle τ caused by specific solvent, interactions.

Conformational studies of β-D-1,4′-xylan†

Abstract: The nonbonded interaction energy was computed for xylobiose and xylan as a function of the dihedral angles (ϕ,ψ). The energy maps indicate that interactions higher than the second neighbor are negligible. Of the four possibilities, the left-handed helical conformation with (ϕ,ψ) = (63°,25°) is of the lowest energy. The hydrogen bond search and the energy maps reveal that the xylan helix is stabilized mainly by van der Waals forces. The allowed region map shows that the freedom of rotation of the monomer units in cellulose is more restricted than that of the monomer units in xylan, because of the presence of the CH2OH group in the former. The intramolecular hydrogen bond of the O5 O3′ type is stronger in cellulose.

Studies on the helical conformational of amylose and possible interconversions

Abstract: The nonbonded energy (van der Waals) was computed for isolated helical amylose chains as a function of the dihedral angles (ϕ,ψ), i.e., the relative orientations of the glucose residues in the polysaccharide chain. In conformity with x-ray data, different helical conformations have been proposed for different crystalline modifications of amylose. Right-handed helical conformations were preferred for 71.13, 61.33, and 42.65-type helices from minimum energy considerations. The hydrogen bond search reveals the possibility of formation of strong OH O type hydrogen bonds between contiguous residues in the polymer chain for 61.33 and 71.13 helices. Smooth transition from a 71.13 to a 61.13 helix is possible with small changes in the values of (ϕ,ψ) and without the loss of intramolecular hydrogen bonds, whereas all the intramolecular hydrogen bonds will be broken during the conversion from 61.33 to 42.65 helix.

Polymerization of acrylonitrile by V5+–lactic acid system in aqueous sulfuric acid

Abstract: Kinetics of polymerization of acrylonitrile by the redox system V 5+ -lactic acid in sulfuric acid at 20-35°C was studied. Oxidation of lactic acid by V 5+ in the absence of monomer was also carried out under identical conditions. The rates of polymerization, V 5+ disappearance and the chainlengths of polyacrylonitrile were measured. From the results it is concluded that the polymerization reaction is initiated by an organic free radical arising from the V 5+ -lactic acid reaction with termination by V 5+ ions. Mutual termination of active polymer radicals does not appear to operate under the conditions studied. The various rate parameters were evaluated.

Vinyl polymerization photosensitized by anthraquinone sulfonates in aqueous solutions

Abstract: The kinetics of the photopolymerization of the vinyl monomers MMA and MA sensitized by anthraquinone sulfonate-NaCl-HClO 4 systems have been studied systematically. The wavelength 365 mμ was used for irradiation. Sodium anthraquinone-2-sulfonate and disodium anthraquinone-2,6-disulfonate were used as sensitizers, and all experiments were conducted in deaerated conditions. The polymerization was followed by the measurement of monomer disappearance (gravimetrically), rate of sensitizer disappearance (spectrophotometrically) and the chainlength of the polymer formed (viscometrically). Monomer concentration, k e , [NaCl], and I were varied. In the light of the experimental results a prima facie kinetic scheme was proposed. The specific rate constants for the various steps have been evaluated.

Nature of the cuticle protein of the branchiopod crustacean Streptocephalus dichotomus.

Abstract: Der einzige Proteinbestandteil des BranchiopodenkrebsesStreptocephalus dichotomus zeigt ahnliche chemische Eigenschaften wie kollagene Eiweissverbindungen. Merkmal der Aminosaurezusammensetzung ist eine relativ grosse Menge von Glyzin (etwa 1/3 des Gesamtresiduums), zusatzlich zu Hydroxyprolin und Prolin. Dies wird als Kriterium zur Unterscheidung von kollagenem Protein von den ubrigen Eiweissen (K-mef-Gruppe) benutzt.

Occurrence of Asexual Reproduction by Budding in Sipunculida

Abstract: SIPUNCULID worms are unisexual or hermaphroditic and they only reproduce sexually1,2. Asexual reproduction by budding, which is common among the annelids3,4, has not so far been recorded for sipunculids5, but we have recently observed asexual reproduction by budding in Sipunculus robustus.

Self-Image, Information Exchange and Social Character

Abstract: On interroge des individus sur l'image qu'ils se font d'eux-měmes, l'image qu'ils desireraient dormer d'eux-měmes dans deux situations sociales distinctes (reunion amicale — entretien professionnel) et les traits d'autrui sur lesquels Us chercheraient, dans ces měmes situations, a s'informer. Les AA. ont choisi des sujets qui sont representatifs des types psycho-sociologiques de Riesman: etudiants de l'Inde meridionale (orientation traditionnelle); etudiants americains d'un college exclusivement noir (orientation vers soi); etudiants americains d'un college exclusivement blanc (orientation vers autrui). Pour se decrire eux-měmes, les sujets indiens ont mis l'accent sur les origines demographiques, les noirs americains sur les traits de personnalite et les americains blancs sur les attitudes et opinions, ce qui est conforme aux hypotheses tirees du caractere dominant qu'ils representent. On constate egalement que les Indiens changent de criteres selon le type de situation evoquee, tandis que les A...

Estimates of Growth for Certain Convex and Close-to-Convex Functions in the Unit DISC

Abstract: Let S denote the class of all univalent analytic functions f defined in the unit disc and normalised by the conditions f(0) = 0,f'(0) = 1. For a fixed α, 0 α for |z| <1.

A note on the decay rates of3HΛ and4HΛ

Abstract: The decay rates and two-body decay mode branching ratios of the khypernuclei3HΛ and4HΛ are calculated using separable potential model wave functions.

Analysis of the decay rates of3HΛ and4HΛ

Abstract: The decay rates and two-body decay mode branching ratios of the hypernuclei3HΛ and4HΛ are calculated using separable-potential model wave functions.

Oxidation studies. VII. Oxidation of hydrazine sulphate and hydroxylamine by cobalt (III)

Abstract: Kinetics of oxidation of hydrazine sulphate and hydroxylamine by Co3+ in nitric and sulphuric acid media at 10–15° C. were studied. In H2SO4 medium, kinetic evidence was obtained for complex formation between Co3+-Substrate for both substrates whereas no such evidence was found in HNO3 medium. The effects of [H+], μ [HSO4 −], [SO4=], [Co2+] and temperature on the reaction rates were studied. An inverse dependence of the rates on [H+] was noticed in both media with both substrates but decreasing effect of [HSO4 −] was observed only with NH2OH in H2SO4 medium. Conclusions were drawn as to the nature of the active species: In H2SO4 medium for hydrazine sulphate, Co3+ (aq.) was concluded to be the active species; similarly for NH2OH, CoOH2+ was the active species. In HNO3 medium for both substrates CoOH2+ was the active oxidant. Nitrogen and Ammonia were found to be the products of oxidation with both substrates in both media. Stoichiometries were established and suitable mechanisms were proposed. The rate laws were formulated and the various equilibria and rate constants were evaluated.

Oxidation studies. VI. Oxidation of some mono- and Di-basic acids by peroxy disulphate

Abstract: Uncatalysed oxidation of malonic, maleic, succinic, malic, mandelic and lactic acids by peroxydisulphate have been studied at 60°–80°C. Rates of oxidation and E values are reported. Probable mechanisms are proposed.