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B Ganguly

Publications and source records attributed to B Ganguly.

10 recordsLinked to original sources
PubMed2001

Relevance of torsional effects to the conformational equilibria of 1,5-diaza-cis-decalins: a theoretical and experimental study.

1,5-Diaza-cis-decalin populates two conformations in which the nitrogen atoms are either gauche (N-in) or anti (N-out) to one another. The equilibrium mixture of the two conformers depends on the substituents at the nitrogen atom, as well as the reaction conditions. Ab initio (HF/6-31G, B3LYP/6-31+G) and molecular mechanics (Amber) calculations have been performed to examine the possible role of stereoelectronics and steric effects in controlling the equilibrium of substituted 1,5-diaza-cis-decalins. In the present study, N,N'-diethyl- and N,N'-bistrifluoroethyl-1,5-diaza-cis-decalins have been synthesized, and the equilibrium mixtures have been measured using 1H and 13C NMR experiments. Steric effects appear to control the equilibria between the two conformational isomers of 1,5-diaza-cis-decalin while torsional effects appear to dominate the equilibria for the N,N'-dialkyl derivatives.

Journal Article↗
PubMed2000

Stereoelectronic effects in negatively and positively (Protonated) charged species. Ab initio studies of the gauche effect in 1,4-dioxa systems

A computational study ab initio of the conformational dependence of proton affinities of 2-methoxyethoxide (MEO), dimethoxyethane (DME), and 1,4-dioxane has been carried out at the MP2/6-31+G level of theory. The results were discussed in comparison with reference systems, from simple alkoxides and ethers to anomeric moieties, in open, cyclic, and bicyclic molecules. The COCCOC species are stronger bases than the COCOC (anomeric) ones and approach regular ethers in their strength. The gauche forms in MEO and DME are altogether stronger bases than the anti forms, and anti (equatorial) protonation is preferred over gauche (axial), unless ditopic protonation is possible, like in aga-DME or cis-tetraoxadecalin. The gauche effect plays a significant role in the formation, relative stability, and reactivity of the charged species.

Journal Article↗
PubMed1996

Regulation of cholinomimetic action of pyrantel pamoate by calcium channels in Setaria cervi.

Nerve muscle preparation of Setaria cervi (Nematoda:Filarioidea) exhibits spontaneous rhythmical movements when suspended in isolated organ bath containing modified Ringer's solution. Pyrantel pamoate (50 ng/ml) when applied caused initial short lasting stimulation followed by irreversible paralysis. When suspended in calcium free bathing fluid the movements of n.m. preparation showed a gradual decrease both in amplitude and rate of contraction til the movements ceased completely. The effect was similar when EDTA was added to the bath fluid. The stimulant effect of Pyrantel pamoate was blocked in calcium free solution and in bath applied EDTA. Calcium channel blocker Nifedipine in a concentration of 500 ng/ml blocked the effect of Pyrantel pamoate (50 ng/ml). Neither stimulation nor depression of movements was evident with higher concentration of PP (250 mg/ml) the stimulant effect of Pyrantel pamoate was blocked while the depressant effect characterized by decrease in amplitude of calcium is essential for the stimulant effect of Pyrantel pamoate and its response on n.m. preparation is similar to Acetylcholine.

Acetylcholine↗
PubMed1995

Identification of voltage-sensitive calcium channels in Setaria cervi (Nematoda: Filarioidea) and their role in regulation of spontaneous motility.

Whole worm of Setaria cervi and its nerve muscle preparation exhibit rhythmical movements when suspended in modified Ringer's solution in an isolated organ bath. Deprivation of calcium from the bathing fluid results in gradual reduction in the amplitude and rate of contraction till the movements ceased completely. Similar results were obtained by adding EDTA (5 micrograms/ml) to the bath. The effect was concentration related and was evident early with higher concentration of EDTA. Acetylcholine which increases spontaneous movements of the whole worm as well as N.M. preparation failed to do so when the movements were inhibited either in calcium free solution or in the presence of EDTA. Addition of calcium channel blocker, Nifedipine to the bathing fluid also resulted in concentration related reduction of movements of the preparation of Setaria. Further, the stimulant response of Ach was also reduced by Nifedipine and this too was related to the concentration of calcium channel blocker in the bath. The evidence clearly indicates that presence of calcium is essential for the stimulant response of Ach on S. cervi, which like mammalian tissues contain calcium channels that can be blocked by specific blocking agents.

Acetylcholine↗
PubMed1993

Proteolysis results in altered leak channel kinetics and elevated free calcium in mdx muscle.

Resting free calcium levels ([Ca2+]i) are elevated in Duchenne human myotubes and mdx mouse muscle and myotubes which lack the gene product dystrophin at the sarcolemma. Increased net muscle protein degradation has been directly related to this elevated [Ca2+]i. The [Ca2+]i rise may result from increased calcium influx via leak channels, which have increased opening probabilities (Po) in dystrophic cells. Dystrophin, therefore, might directly regulate leak channel activity. In intact mdx soleus muscles, protein degradation was reduced to normal levels by leupeptin, a thiol protease inhibitor. In muscle homogenates, leupeptin also abolished calcium-induced increases in protein degradation. When mouse myotubes were cultured in the continuous presence of leupeptin (50 microM), the elevation in mdx resting [Ca2+]i was prevented. Leak channel Po increased with age in mdx myotubes, whereas leupeptin-treated mdx leak channel opening probabilities were always lower or equal to the Po for untreated normal myotubes. These results indicate that increased leak channel activity in dystrophic muscle results in elevated [Ca2+]i levels, but also suggest that dystrophin does not directly regulate channel activity. Instead the results suggest that proteolysis may be responsible for the altered gating of calcium leak channels. The resultant increased channel Po in turn elevates [Ca2+]i, which further increases proteolytic activity in a positive feedback loop, leading to the eventual necrosis of the muscle fibers.

Animals↗