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R Haran

Publications and source records attributed to R Haran.

11 recordsLinked to original sources
PubMed1991

The effect of aluminum ions and sorbitol on collagen and skin: a thermally stimulated current spectroscopy study.

The influence of aluminum ions introduced either directly or with sorbitol, in collagen and skin, has been investigated by Thermally Stimulated Current/TSC spectroscopy. The intramolecular mobility of collagen has been found to be significantly reduced by aluminum ions. The substitution of water molecules by aluminum ions on intramolecular hydrophilic sites is suggested to be responsible for this evolution. The presence of sorbitol minimizes this effect. The intermolecular mobility of collagen is decreased upon introduction of aluminum ions in presence of sorbitol. This result can be explained by the interaction of sorbitol-aluminum entities with the telopeptidic regions of collagen molecules. In skin samples, the intra- and intermolecular mobilities are restored due to the combined actions of sorbitol and noncollagenous proteins and other macromolecules.

Aluminum↗
PubMed1987

Interaction of cis-Pt(ino)2Cl2 with amino acids.

The reactions of cis-Pt(ino)2Cl2 with the amino acids Gly, L-Ala, L-Val, L-Ileu, L-Phe and L-Pro were studied in methanolic solutions. The (1:1) adducts of the formulas cis-[Pt(ino)2(am-ac)]Cl were isolated from these reactions in the solid state, which in turn produce the cis-[Pt(ino)2(am-acH)Cl]Cl complexes, by treating the former with equivalent amounts of HCl, in aqueous solutions. The complexes were characterized with elemental analysis, conductivity measurements, IR, 1H NMR, and 13C NMR spectra. The results show that the purine ring of inosine interacts with the aliphatic side chain of the amino acids. The platination increases the percentage of the C3'-endo-anti conformation of the sugar part of inosine.

Amino Acids↗
PubMed1986

NMR study of thymulin, a lymphocyte differentiating thymic nonapeptide. Conformational states of free peptide in solution.

The nonapeptide less than Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (formerly called serum thymic factor) is a factor produced by the thymic epithelium, which needs a zinc ion to express its immunoregulatory properties. We report here on 1H and 13C NMR investigation of the conformational properties of the free peptide in aqueous medium and in dimethyl sulfoxide-d6 solution by a combination of homo- and heteronuclear one- and two-dimensional experiments. The various resonances have been assigned in a straightforward manner on the basis of 1H,1H COSY spectroscopy for the recognition of the proton spin systems; two-dimensional NOESY spectra with the correlation peaks across amide bonds and for the amino acid sequence assignment; amide bonds and for the amino acid sequence assignment; 13C,1H COSY experiments using selective polarization transfer from 1H- to 13C-nucleus via the 13C,1H long-range couplings for the attribution of the carboxyl and carbonyl groups; and 13C,1H COSY experiments with selective polarization transfer via the 13C,1H direct couplings for the assignment of all the aliphatic carbons. Other experiments such as pH-dependent chemical shifts, combined use of multiple and selective proton-decoupled 1H and 13C NMR spectra, the temperature and the concentration dependence of the proton shifts of the amide resonances, the solvent dependences of peptide carbonyl carbon resonances, and comparison of the spectra with three different analogues were performed. In aqueous solution, the data are compatible with the assumption of a highly mobile dynamic equilibrium among different conformations, whereas in dimethyl sulfoxide-d6, a more rigid structure is found involving three internal hydrogen bonds. These observations provide an insight into the conformational tendencies of this peptidic hormone in two different media.

Dimethyl Sulfoxide↗
PubMed1983

N.m.r. and e.p.r. investigation of the interaction of copper(II) and glycyl-L-histidyl-L-lysine, a growth-modulating tripeptide from plasma.

Interaction of Cu(II) and Gly-His-Lys, a growth-modulating tripeptide from plasma, was investigated by 13C- and 1H-n.m.r. and e.p.r. spectroscopy. The n.m.r. line-broadening was interpreted in terms of major and minor species formed as a function of pH. The results indicate that the n.m.r. line-broadening is due to the presence of minor species in rapid exchange and not due to the major species in solution, which has a large tau M. It is concluded that the technique of 13C- and 1H-n.m.r. line broadening, caused by paramagnetic Cu(II) ion, should be undertaken with caution, since the method may not be useful for obtaining structural information on the major species. The e.p.r. spectra over a wide pH range are almost entirely due to similarly co-ordinating species. Starting at pH 5.5, the narrowest absorption near 340 mT shows superhyperfine structure, which comes out sharply in the pH region 6.0-9.6. The spectra in this pH range showed the seven lines of nitrogen superhyperfine splitting, indicating clearly the co-ordination of three nitrogen atoms to Cu(II). The e.p.r. parameters in the medium pH range, A parallel = 19.5 mT and g parallel = 2.21, fit well with the contention that Cu(II) is ligated to Gly-His-Lys through one oxygen atom and three nitrogen atoms in a square-planar configuration.

Chemical Phenomena↗
PubMed1982

The binding of aluminium to [Leu5]-enkephalin. An investigation using 1H, 13C and 27Al NMR spectroscopy.

The binding of aluminium ion to [Leu5]-enkephalin has been investigated by 1H, 13C and 27Al NMR spectroscopy in dimethyl sulphoxide solution at different peptide/metal ratio. Analysis of the spectra suggests that Al3+ binds at two metal-binding sites. The binding of Al3+ at the first site involves the Tyr1CO, and Leu5COO- groups to give a 2:1 species in a tetracoordinated structure; whereas the binding of Al3+ at the second site utilizes the NH2 terminal groups of the tyrosine moiety in a 2:2 species. 27Al chemical shift values strongly suggest that the second type of aluminium atom displays an octahedral environment. On this basis, we discuss our data in terms of the coordination of aluminium with [Leu5]-enkephalin.

Aluminum↗
PubMed1982

Metal-peptide interactions: enkephalin rigidifications.

Two enkephalin analogues, Tyr-D-Ala-Gly-Phe-NVal-NH2 and Tyr-D-Ala-Gly-Phe-NVal-OH were studied by n.m.r. spectroscopy. 13C chemical shifts were determined as a function of pH and in water-dimethyl sulfoxide solvent mixtures. The acid and amide forms of the analogues show a marked difference in their n.m.r. features. Complexation with metal ions causes changes in the n.m.r. spectra of the acid form. The temperature dependence of the NH proton resonances of the zinc complex shows striking similarity with that of the amide analogue. The results are discussed in terms of the potential modification of biological activities which may occur following metal ion induced conformation changes.

Calcium↗