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D S Rawat

Publications and source records attributed to D S Rawat.

15 recordsLinked to original sources
PubMed2002

Possible existence of a higher coverage quasi-one-dimensional phase of argon adsorbed on bundles of single-walled carbon nanotubes.

We present results of Ar adsorption isotherms at very low coverages in the first layer and, beyond monolayer completion, on bundles of close-ended single-walled carbon nanotubes. The low coverage results were used to determine the isosteric heat of adsorption and the binding energy of Ar in the groove sites in the first layer. The higher coverage results show evidence of the possible formation of a second-layer groove phase, beyond monolayer completion. Our results for higher coverages are compared with recent computer simulations for this system.

Adsorption↗
PubMed2001

The contribution of ligand flexibility to metal center geometry modulated thermal cyclization of conjugated pyridine and quinoline metalloenediynes of copper(I) and copper(II).

We report the syntheses, reactivities, and structure evaluations of a series of Cu(I) and Cu(II) metalloenediynes of conjugated 1,6-bis(pyridine-3)hex-3-ene-1,5-diyne (PyED, 7) and 1,6-bis(quinoline-3)hex-3-ene-1,5-diyne (QnED, 8) enediyne ligands, as well as their benzoenediyne analogues. Differential scanning calorimetry demonstrates that the [Cu(PyED)(2)](NO(3))(2) (11) exhibits a Bergman cyclization temperature (156 degrees C) which is dramatically reduced from that of the corresponding [Cu(PyED)(2)](PF(6)) (19) analogue (326 degrees C), indicating that large differences in the reactivities of these metalloenediynes can be accessed by variations in metal oxidation state. The distorted, 4-coordinate dichloride compound Cu(PyED)(Cl)(2) (15) exhibits a cyclization temperature (265 degrees C) between those of 11 and 19, suggesting that variation in geometry of the copper center is responsible for the wide range of reactivities. Similar results are obtained for the benzoenediyne and quinoline analogues. The structures of the Cu(II) systems have also been evaluated by a combination of electronic absorption and EPR spectroscopies which reveal tetragonal, 6-coordinate structures for the bis(enediyne) complexes, and tetrahedrally distorted 4-coordinate Cu(enediyne)Cl(2) species. For the bis(quinoline) enediyne derivatives 12 and 14 the larger g-anisotropy (g( parallel) = 2.27-2.28; g( perpendicular) = 2.06-2.07) indicates strong oxygen coordination from counterion. Molecular mechanics/dynamics calculations reveal that the geometries of these metal centers force the alkyne termini to a wide range of distances (3.85-4.20 A), thereby accounting for the variability in Bergman cyclization temperatures. Overall, the results show that ligand rigidity plays a prominent role in the conformational response of the enediyne to metal center geometry, which results in enhanced variations in the Bergman cyclization temperatures between complexes of different geometries.

Journal Article↗
PubMed2001

Complete nucleotide sequence of the 6 kb element and conserved cytochrome b gene sequences among Indian isolates of Plasmodium falciparum.

The malaria parasite contains a nuclear genome with 14 chromosomes and two extrachromosomal DNA molecules of 6 kb and 35 kb in size. The smallest genome, known as the 6 kb element or mitochondrial DNA, has been sequenced from several Plasmodium falciparum isolates because this is a potential drug target. Here we describe the complete nucleotide sequence of this element from an Indian isolate of P. falciparum. It is 5967 bp in size and shows 99.6% homology with the 6 kb element of other isolates. The element contains three open reading frames for mitochondrial proteins-cytochrome oxidase subunit I (CoI), subunit III (CoIII) and cytochrome b (Cyb) which were found to be expressed during blood stages of the parasite. We have also sequenced the entire cyb gene from several Indian isolates of P. falciparum. The rate of mutation in this gene was very low since 12 of 14 isolates showed the identical sequence. Only one isolate showed a maximum change in five amino acids whereas the other isolate showed only one amino acid change. However, none of the Indian isolates showed any change in those amino acids of cyb which are associated with resistance to various drugs as these drugs are not yet commonly used in India.

Amino Acid Sequence↗
PubMed2000

Disappearance of intramolecular stacking due to one-atom movement or increment of a 'propylene linker' in pyrazolo[3,4-d]pyrimidine-based flexible models.

In the crystal structures of 4,6-dimethylthio-1-[3-(4, 6-dimethylthio-2H-pyrazolo[3, 4-d]pyrimidin-2-yl)propyl]-1H-pyrazolo[3,4-d]pyrimidine, C(17)H(20)N(8)S(4), and 1-[4-(4-methoxy-6-methylthio-1H-pyrazolo[3, 4-d]pyrimidin-1-yl)butyl]-5-methyl-6-methylthio-4, 5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-4-one, C(18)H(22)N(8)O(2)S(2), only intermolecular stacking due to aromatic pi-pi interactions between pyrazolo[3,4-d]pyrimidinerings is present.

Journal Article↗
PubMed1984

Lipid composition of Cryptococcus neoformans.

The lipid composition of Cryptococcus neoformans grown in Sabouraud's dextrose broth (shake culture) was analysed. The organism contained extremely low amounts of lipid (0.96% dry weight basis) of which 86.1% were nonpolaris lipids, 3.4% phospholipids and the rest were glycolipids and pigments. Alkoxylipids (41%), tryglicerides (18%), diglycerides (7.4%), free fatty acids (5.4%), sterols (4.7%), sterol ester (3.9%) and monoglycerides (2.2%) were found in the nonpolar lipid fraction of C. neoformans. The phospholipid composition (expressed as relative abundance) was: phosphatidylinositol (11.5%), lysophosphatidyl ethanolamine (10.9%), cardiolipin (10.1%), a glycophospholipid (9.5%), lysophosphatidyl choline (4.7%), phosphatidic acid (4.1%), phosphatidyl choline (28.1%), phosphatidyl ethanolamine (14.5%) and an unidentified lipid (6.5%). Phosphatidyl serine, sphingolipids and cerebrosides, generally found in yeast-like fungi, were absent. Probable reasons for the abnormally low lipid content are discussed.

Chromatography, Thin Layer↗
PubMed1984

Virulence, capsule size and lipid composition interrelation of Cryptococcus neoformans.

Virulence and lipid composition were studied in three isolates of Cryptococcus neoformans. Virulence was evaluated by injecting mice intraperitoneally with 10(7) cells and recording organ involvement and spontaneous death over a 25 day period. Though the least virulent strain contained the least amount of total lipid and phospholipids, none of the lipids showed any quantitative relation to virulence. There was no major difference in the phospholipid composition among the three strains. Fungal cells with bigger capsules had a lower lipid content. The role of lipid in the defence mechanism of pathogenic fungi during the host invasion process is discussed.

Animals↗
PubMed1982

Lipid composition of Microsporum gypseum.

Lipid composition of Microsporum gypseum grown in Sabouraud's liquid media on a rotary shaker were analyzed. The organism contains 6.07% lipid (dry weight basis), of which 75.88% is neutral lipids, 0.9% phospholipids and the rest are glycolipids and pigments. Phospholipids of M. gypseum contain phosphatidyl choline (44.21%), phosphatidyl ethanolamine (17.8%), polyphospho inositide (12.13%), phosphatidyl inositol (8.24%), phosphatidic acid (4.61%) and cardiolipin. Phosphatidyl serine is absent. The neutral lipid composition (expressed as mg/g dry weight of mycelia) of M. gypseum is monoglycerides (1.35), diglyceride (2.87), triglycerides (35.79), free fatty acids (1.00), sterols (3.95) and sterol esters (1.13).

Glycolipids↗
PubMedDate not supplied

Relationship of Xba1 and EcoR1 polymorphisms of apolipoprotein-B gene to dyslipidemia and obesity in Asian Indians in North India.

BACKGROUND: Genetic investigation of dyslipidemia and obesity prevalent in the Indian population form the basis of this study. METHODS AND RESULTS: The frequency of restriction fragment length polymorphisms (Xba1 and EcoR1) of the apolipoprotein-B gene was investigated in a case-control study of 30 hyperlipidemic and 40 normolipidemic subjects. By univariate analysis, old age, higher body mass index, waist-hip ratio and sum of four skinfolds were found to be significantly associated with hyperlipidemia. The frequencies of X- and E+ alleles of the apolipoprotein-B gene were significantly higher in North Indians in the state of New Delhi (0.83 and 0.91, respectively) as compared to the observations made in Caucasians in previous studies, but was similar to the frequency reported in Indians settled in Singapore and the UK. There were no significant differences in the allele or genotype frequencies of either Xba1 or EcoR1 polymorphisms between the hyperlipidemic and normolipidemic groups. On multiple logistic regression analysis considering body mass index, waist-hip ratio, percentage body fat and genotypes as independent variables, no association was observed between the apolipoprotein-B genotypes and serum lipid components. Further, there were no associations between apolipoprotein-B polymorphisms and generalized obesity (as assessed by body mass index, sum of four skinfolds, and percentage total body fat) and abdominal obesity (as measured by waist circumference and waist-hip ratio). CONCLUSIONS: We conclude that apolipoprotein-B (Xba1 and EcoR1) polymorphisms do not appear to influence serum lipid levels and parameters of generalized andregional obesity in the study sample.

Adult↗