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Biomedical subjects

R Chandrasekaran

Publications and source records attributed to R Chandrasekaran.

At least 37 records · Page 2Linked to original sources
PubMed1998

X-ray diffraction of food polysaccharides.

The morphologies of food polysaccharides described in this chapter illustrate the power of x-ray fiber diffraction in conjunction with computer modeling and sophisticated refinement techniques. On the other hand, the lack of information on structures such as xanthan reflects the inadequacy of the experimental techniques used to date. But the demands from academic and industrial sectors to investigate the molecular interactions in multicomponent systems, including protein-protein, protein-polysaccharide, polysaccharide-polysaccharide, and other complexes, are high and growing, because they have important food applications. These complexes are structurally more difficult than those solved in the past 40 years and it is improbable that any chosen system will be amenable for crystallographic investigation, crystals or fibers. Modern research facilities that include two-dimensional area detectors, millisecond exposures with synchrotron x-ray radiation, interactive computer graphics, sophisticated molecular dynamics calculations, unbelievably fast and inexpensive computers, and our own intellectual abilities are indispensable tools for the future of structural science in general and food polysaccharides in particular.

Carbohydrate Conformation↗
PubMed1997

X-ray and conformational analysis of arabinan.

Fibers prepared from the enzymically debranched plant polysaccharide arabinan, containing (1-->5)-linked alpha-L-arabinofuranose residues, produce X-ray diffraction patterns containing concentric rings indicative of a high degree of structural organization. The measured unit cell dimensions and fiber density are consistent with a 2-fold helix passing through each unit cell. According to model-building techniques and energy calculations, a total of seven molecular structures (three with C2'-endo and four with C3'-endo sugars), all of pitch 8.74 A, and hence seven different crystal-packing arrangements are the most probable. While intrachain hydrogen bonds are only present in three cases, interhelix association is facilitated by hydrogen bonds in all allomorphs. Small energy differences between them suggest that easy conformational transitions may be made from one form to another. This polymorphism and the tendency to form microcrystals in the solid state might confer upon arabinan the observed fat mimetic properties.

Carbohydrate Conformation↗
PubMed1997

Structure of poly d(AI).poly d(CT) in two different packing arrangements.

X-ray diffraction analysis of poly d(AI).poly d(CT) in oriented and polycrystalline fibers has revealed the DNA structure to be a 10-fold, right-handed, antiparallel, Watson-Crick base paired double helix in two distinct packing arrangements corresponding to one and two helices, respectively, in the unit cell. The helix pitch is 32.1 A and 32.4 A in the two cases, almost 1.5 A shorter than in classical B-DNA. The resulting B'-DNA geometry, described in terms of a tetranucleotide repeat which is conformationally similar to B-DNA, has its minor groove closely shut and major groove correspondingly widened, thus striking a sharp morphological contrast to B-DNA. According to difference electron density maps, a spine of hydration along the minor groove connects both strands and provides structural stability; ordered sodium ions and water molecules are actively involved in bridging the phosphate groups of neighboring helices. The crystallographic R-values for these two allomorphs are 0.26 and 0.20, respectively, for data up to 3.0 A resolution.

Crystallography, X-Ray↗
PubMed1996

Differential scanning calorimetric and X-ray study of the binding of the water of primary hydration to calf-thymus DNA.

Differential scanning calorimetry has been used to study the thermal properties of hydrated films of calf-thymus Na-, K- and CsDNA between 20 and 320 degrees C. A broad endothermic transition near 75 degrees C and a sharp exothermic transition near 240 degrees C are observed. The broad transition is due to the dehydration of the DNA, while the exothermic transition is due to pyrolysis of the sample. the peak temperatures of both transitions increase as the scan rate is increased. Based on a Kissinger analysis, the net activation energy for the desorption of the primary water of hydration is about 0.6 eV while that for the pyrolysis is about 1.9 eV. X-ray diffraction patterns suggest that heating the DNA films to 180 degrees C once does not, but thrice does, destroy their structural ordering.

Calorimetry, Differential Scanning↗
PubMed1996

The structure of B-DNA in oriented fibers.

Native, general sequence B-form DNA in uniaxially oriented fibers is a ten-fold helix with identical antiparallel strands: this is to say the molecular symmetry is 2 2 10(1). The diffraction patterns indicate that local variations, however significant, must be modest. This is true also for the lithium salt of calf thymus DNA in fibers that are polycrystalline as well as oriented. The contents of its orthorhombic unit cells are arranged with P2(1)2(1)2(1) symmetry which permits the molecular symmetry to be merely two-fold. The molecular structure of DNA in such conditions resembles, conformationally and molecularly, that of B-type DNA in oligonucleotide single crystals and in oriented polycrystalline fibers of polyoligonucleotides, and therefore provides a basis for evaluating the variations that may be due to sequence effects in polyoligonucleotides in fibers and oligonucleotides in single crystals.

Base Composition↗
PubMed1996

Increased sister chromatid exchange (SCE) frequencies in lymphocytes from traffic policemen exposed to automobile exhaust pollution.

Sister chromatid exchange (SCE) frequencies were determined in peripheral lymphocytes from traffic policemen drawn from various busy traffic points of Madras metro in India. These policemen were under constant exposure to automobile exhaust pollution during their 8 h work schedule. Analysis of SCE frequencies revealed a significantly greater number of SCE/cell in these policemen as against the matched control population. Sixty percent of these subjects who remained in the service after 5 years showed insignificant but higher values of SCE than in the initial analysis.

Adult↗
PubMed1996

Embryotoxicity and teratogenicity studies of poly (DL-lactide-co-glycolide) microspheres incorporated tetanus toxoid in Wistar rats.

Tetanus Toxoid loaded biodegradable microspheres (MTT) (poly (DL-Lactide-co-Glycolide) were administered intramuscularly to pregnant Wistar rats from Days 6 to 15 of gestation, at 1, 5 and 10-times the human equivalent dose of TT. Developmental defects in relation to soft tissues and skeleton, weight and sex of live pups and early fetal deaths from treated and control rats were analysed. The findings in treatment groups were comparable to those in the controls. These observations show that MTT was safe for pregnant rats and developing pups.

Animals↗
PubMed1996

Molecular abnormalities of bcr gene in some Indian patients with chronic myeloid leukaemia.

The DNAs from 7 unselected Philadelphia chromosome-positive (Ph') chronic myeloid leukaemia (CML) patients were analysed for the distribution of breakpoints in the breakpoint cluster region (bcr) gene by Southern blot. Breakpoints were detected between the regions of exons '2' and '4' of the bcr gene in 5 out of 7 patients. In two patients, breakpoints occurred around exon 4 of the bcr gene. This study presents some information on the nature of breakpoint distribution in the bcr gene of Indian CML patients.

Adult↗
PubMed1995

Sodium ions and water molecules in the structure of poly(dA).poly(dT).

Analysis of X-ray diffraction data from a polycrystalline and well oriented fiber of the sodium salt of poly(dA).poly(dT) shows that this B'-DNA corresponds to a right-handed antiparallel tenfold double-helix of pitch 32.4 A, with C2'-endo furanose rings in both strands. The helix contrasts itself from B-DNA in terms of a very narrow minor groove. Difference electron-density maps have revealed that a continuous spine of water molecules, two per base pair, propagates along this groove with the same symmetry as the DNA and establishes new links between the two strands. In addition to this hydrated DNA helix, the monoclinic unit cell (space group P2(1)) accommodates about 20 sodium ions and 12 water molecules in the vicinity of phosphate groups. These structured guest molecules provide an intricate network of bridges, ranging in size from a single sodium ion to a multiple sodium-water-water-sodium unit, connecting phosphate groups belonging to adjacent DNA helices. The crystallographic R value for this structure is 0.23 for a total of 102 reflections extending out to 3.2 A resolution.

Journal Article↗
PubMed1994

Molecular architecture of a galactoglucan from Rhizobium meliloti.

Rhizobium meliloti mutants produce a linear, acidic exopolysaccharide with alternating galactopyranosyl and glucopyranosyl units having (1-->3) linkages. It has a 4,6-O-pyruvic cyclic acetal group on the alpha-galactosyl and 6-O-acetyl ester group on the beta-glucosyl units. X-ray diffraction patterns from polycrystalline and well oriented specimens of its potassium salt indicate that the polymer forms a 2-fold helix of pitch 15.89 A. The three-dimensional structure has been determined and refined by using the X-ray intensities and the linked-atom least-squares technique. The details of the antiparallel packing arrangement of two helices in an orthorhombic unit cell, a = 14.49, b = 9.79, and c = 15.89 A, reveal that each disaccharide repeating unit is associated with one potassium and three water molecules. The helices are interconnected by a series of ...COO- ...K+ ...W ...COO- ... interactions. Both pyruvyl and acetyl groups, which are on the periphery of the helix, are involved in the association of the polysaccharide chains and thus appear to be an integral component of the galactoglucan in the nodule invasion process.

Carbohydrate Sequence↗
PubMed1994

Structural roles of calcium ions and side chains in welan: an X-ray study.

Welan is the first branched polymer in the gellan family of polysaccharides whose three-dimensional structure has been determined by X-ray diffraction analysis of polycrystalline and well oriented fibers of the calcium salt. The molecule exists as a half-staggered, parallel, double-helix, similar to that of gellan. The side chains fold back on the main chain to form hydrogen bonds with the carboxylate groups. This shielding enhances the stability of the double-helix. Three molecules are organized in a trigonal unit cell of dimensions a = 20.83 and c = 28.69 A with a lateral separation of 12.0 A in each pair; this is 2.9 A larger than in gellan. The double helices are in contact with each other through calcium ions and water molecules via COO-...Ca2+...COO- and COO-...W...Ca2+...COO- interactions, and through side chain-side chain hydrogen bonds. These structural features enable us not only to explain how the side chains in welan are responsible for the enhanced molecular stability relative to gellan, but also to show how essential they are for the associative properties which control the rheology of the polymer.

Calcium↗
PubMed1994

A study of life events in mania.

After clinical recovery, 46 manic patients were screened for evidence of life events during a period of 6 months before the first episode of mania (DSMIIIR criteria) and 6 months after the episode. Within-patient group comparisons showed that patients who reported life events had a significantly higher presumptive mean stress score before manic episode as compared with the period after the illness. When life events were considered in relation to age, sex, marital status and family history of affective disorder, on a logistic regression equation, it was found that life events before mania were significantly associated with males and with a younger age of onset. The implications of these findings are discussed.

Adult↗
PubMed1994

Sequence-dependent conformational variations in the B-DNA double-helix of poly d(AATT).poly d(AATT).

X-ray diffraction data from well oriented and polycrystalline fibers of the lithium salt of poly d(AATT).poly d(AATT) are isomorphous with those from B-DNA. The double-helix consists of conformationally identical antiparallel strands and the molecular symmetry is 2 5(2); the asymmetric unit is a tetranucleotide, AATT, and 5 tetranucleotides span two turns per strand. Two double helices pass through a monoclinic unit cell of dimensions a = 31.05, b = 22.62, c = 33.85 A (fiber axis) and gamma = 90 degrees. In each repeating motif, the four nucleotides have distinct conformations, TpA displays an axial P-O bond and there is shortening of minor groove in the central region.

Base Sequence↗
PubMed1994

Hysterical neurosis--a follow-up study.

Hysterical neurosis, though infrequently diagnosed in the West, is still one of the commonest mental disorders in India. In this study, 38 women with an index diagnosis of hysterical neurosis were evaluated after a period of 5 years; 63% of the patients remained totally asymptomatic. The premorbid hysterical personality alone showed significant relationship with the outcome.

Adolescent↗
PubMed1993

The prevalence of mental disorders in school-age children attending a general paediatric department in southern India.

This study was conducted over a period of 18 months in a medical college hospital in southern India. Of 313 children of age 5 and above referred for detailed psychiatric evaluation, 101 were found to have a mental disorder according to DSM-III-R criteria; the remaining had organic disorders. Children above 8 years (74%) registered higher morbidity. There was no sex difference in overall morbidity. Precipitating factors were discernible in half of these cases, of which school-related problems were found in the majority. Almost two-thirds had multiple stressors, of which chronic family and social adversity (39%) and learning disabilities (28%) were common. Mental disorders were significantly related to urban background, middle-class socioeconomic status and literate parents compared with age- and sex-matched controls. There was no significant relationship with the type of family and number of siblings. Conversion disorder (31%) was the commonest, followed by conduct disorders (16%). The symptoms, stressors, response to treatment and the transcultural aspects are also discussed.

Adolescent↗
PubMed1992

The "pseudo double-helical" structure of the gel-forming capsular polysaccharide from Rhizobium trifolii.

X-ray diffraction analysis of oriented fibers of the gel-forming, neutral, doubly branched, galactoserich capsular polysaccharide from Rhizobium trifolii has been used to determine and refine the molecular structure to a final R value of 0.28. The polysaccharide forms a 2-fold single helix of pitch 20.2 A, is stabilized by a series of hydrogen bonds that involve the side chains, and has the appearance of a double helix. Packing calculations reveal that the short-range ordering of these "pseudo double helices" is brought about by intermolecular hydrogen bonds that involve the side chains. Complete or partial removal of side chains will weaken the molecular association and is detrimental to the gelation process.

Carbohydrate Conformation↗