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Biomedical subjects

S V Bhat

Publications and source records attributed to S V Bhat.

17 recordsLinked to original sources
PubMed2005

Vitrification and glass transition of water: insights from spin probe ESR.

Three long-standing problems related to the physics of water, viz., the possibility of vitrifying bulk water by rapid quenching, its glass transition, and the supposed impossibility of obtaining supercooled water between 150 and 233 K, the so-called "no man's land" of its phase diagram, are studied using the highly sensitive technique of spin probe ESR. Our results suggest that water can indeed be vitrified by rapid quenching; it undergoes a glass transition at approximately 135 K, and the relaxation behavior studied using this method between 165 K and 233 K closely follows the predictions of the Adam-Gibbs model.

Journal Article↗
PubMed2004

Rapid screening for HIV-1 protease inhibitor leads through X-ray diffraction.

Knowledge of the three-dimensional structures of HIV-1 protease and of its complexes with various inhibitors has played a key role in development of drugs against AIDS. Hexagonal crystals of unliganded tethered HIV-1 protease in which the enzyme conformation is identical to its ligand-bound state can be used in combination with the soaking method in order to identify potential inhibitor leads via X-ray diffraction. The advantages of the soaking method are the generality of application and the rapidity of structure determination for iterative structure-based drug design. Structures of two ligand complexes with HIV-1 protease determined using this method are shown to be very similar to the structures obtained earlier via co-crystallization.

Amino Acid Substitution↗
PubMed2004

On the analysis of broad Dysonian electron paramagnetic resonance spectra.

We analyze the equation used for simulating the lineshapes of broad electron paramagnetic resonance spectra in conducting samples (i.e., broad Dysonian lineshapes) where it becomes necessary to include the effects of both clockwise and counterclockwise rotating components of the microwave magnetic field. Using symmetry arguments, we propose a modification to the equation. We show that the modified equation fits the experimental results better than the equation used in literature.

Journal Article↗
PubMed2003

Optical and magnetic properties of manganese-doped zinc sulfide nanoclusters.

We report the synthesis of fixed-size ZnS nanoclusters approximately 24 A in diameter with varying manganese concentrations. Various samples of Zn1-x MnxS, with x = 0, 0.02, 0.055, 0.09, and 0.13, have been prepared and characterized using X-ray diffraction, energy-dispersive analysis of X-rays, UV absorption, fluorescence emission and excitation, electron paramagnetic resonance (EPR), and magnetic susceptibility measurements. The manganese ions are found to substitute Zn randomly without giving rise to any clustering of Mn sites, as seen from EPR and magnetic susceptibility results. Our studies reveal that the band gap of the doped nanoclusters passes through a maximum as the manganese concentration is varied. Also, we observe orange emission from Mn2+ ions in the doped ZnS nanoclusters, apart from the blue emission characteristic of the ZnS defect states. The relative intensity of the orange emission compared with the blue varies with the manganese concentration in a nonmonotonic way. The inverse of susceptibility temperature plots can be plotted onto a universal curve by simple multiplicative constants, thus showing that the magnetic interactions between Mn2+ ions are weak.

Crystallization↗
PubMed2001

Antimalarial t-butylperoxyamines.

Twelve t-butylperoxyamines (6-17) were synthesized as targeted antimalarials and evaluated for antimalarial activity in vivo against Plasmodium berghei in mice and in vitro against both chloroquine sensitive and chloroquine resistant strains of Plasmodium falciparum. Compound 8 was found to have highest potency with activity at 80 and 160mg/kg dose in vivo and compound 11 exhibited highest efficacy in vitro.

Animals↗
PubMed2001

Properties of polyvinyl pyrrolidone/beta-chitosan hydrogel membranes and their biocompatibility evaluation by haemorheological method.

The semi-IPN hydrogel membranes of polyvinyl pyrrolidone (PVP) and beta-chitosan were synthesized by crosslinking beta-chitosan with glutaraldehyde. Hydrogel membranes were characterized by spectroscopic, swelling, thermal and mechanical properties. The in vitro biocompatibility of hydrogel membranes was studied by haemorheological method. These hydrogels have water contents in the range of 60-70% with a high fraction contributed by free water (> 45%). The gel composition, amount of cross-linking agent and swelling temperature plays an important role in swelling kinetics of these semi-IPN membranes. Melting temperature (Tm) of membranes increased with a decrease in endothermic peak with increasing beta-chitosan content. The tensile strength of membranes in the dry state was found to be high (29-43 MPa) and it increased with increasing beta-chitosan content. The in vitro haemorheological studies indicated the biocompatible nature of membranes with no significant changes in whole blood and plasma viscosity and red blood cell rigidity.

Journal Article↗
PubMed2000

pH-sensitive freeze-dried chitosan-polyvinyl pyrrolidone hydrogels as controlled release system for antibiotic delivery.

The aim of this study was to develop a pH-sensitive chitosan/polyvinyl pyrrolidone (PVP) based controlled drug release system for antibiotic delivery. The hydrogels were synthesised by crosslinking chitosan and PVP blend with glutaraldehyde to form a semi-interpenetrating polymer network (semi-IPN). The semi-IPN formation was confirmed by Fourier transform infrared spectroscopic (FTIR) analysis. Semi-IPNs, viz, air-dried and freeze-dried, were compared for their surface morphology, wettability, swelling properties and pH-dependent swelling. Air- and freeze-dried membranes were also incorporated with amoxicillin and antibiotic release was studied. Porous freeze-dried hydrogels (pore diameter, 39.20+/-2.66 microm) exhibited superior pH-dependent swelling properties over non-porous air-dried hydrogels. A high octane contact angle (144.20+/-0.580) of hydrogel was indicative of its hydrophilic nature. Increased swelling of hydrogels, under acidic conditions, was due to the protonation of a primary amino group on chitosan, as confirmed by FTIR analysis. Freeze-dried membranes released around 73% of the amoxicillin (33% by air-dried) in 3 h at pH 1.0 and, thus, had superior drug-release properties to air-dried hydrogels. Freeze-dried membranes could serve as potent candidates for antibiotic delivery in an acidic environment.

Anti-Infective Agents↗
PubMed2000

Neuromuscular blocking effects of an alkaloidal extract from Inula royleana: contractile and electrical studies on amphibian skeletal muscle in vitro.

The neuromuscular blocking properties of an alkaloidal extract from the root of Inula royleana have been investigated in vitro using a combination of mechanical and electrophysiological approaches. Neurogenic twitches of the frog sartorius were profoundly inhibited by concentrations of the extract > or = 20 micrograms/ml, being reduced to 50% of control amplitude in approximately 90 s at a concentration of > or = 20 micrograms/ml. They were partially reversed by neostigmine (6 micrograms/ml), and by prolonged washout of the extract. Muscle surface action potentials, recorded with extracellular electrodes, also declined rapidly in amplitude in the presence of the extract. Direct muscle stimulation during inhibition by the extract elicited contractions and action potentials whose magnitudes were similar to control responses. Resting membrane potentials, and the intracellular input impedance of the skeletal muscle cells, were not significantly changed by the alkaloids. These results indicate that the extract has significant neuromuscular blocking activity of a partially or slowly reversible nature. The block appears to be exerted at the postjunctional end-plate nicotine receptors, thus offering promise for the identification of novel cholinergic receptor antagonist(s).

Action Potentials↗
PubMed1999

Antimalarial activity of 3-hydroxyalkyl-2-methylene-propionic acid derivatives.

Several Baylis-Hillman adducts and their derivatives were synthesized and evaluated as targeted potential anti-malarials. The compounds 4, 7 and 9 were found to have highest potency against P. falciparum in vitro. The in vivo test result of compound 4 and 9 against P. berghei demonstrated activity at 80 mg/Kg dose level.

Animals↗
PubMed1995

In vitro antimalarial activity of monoterpenic fragment analogues of aplasmomycin.

Synthetic analogues of a monoterpenic fragment of aplasmomycin were tested for their antimalarial activity in Plasmodium falciparum culture in vitro. The antimalarial activities of these agents were evaluated in chloroquine sensitive strains. Parasite growth was inhibited in a dose dependent manner in the presence of the synthetic compounds (3-9).

Animals↗
PubMed1992

Non-Newtonian rheology of leukemic blood and plasma: are n and k parameters of power law model diagnostic?

When discussing the rheological properties of normal and leukemic blood it must be considered that blood is a suspension of cells in aqueous solution which is also known as plasma. Whole blood viscosity and plasma viscosity were determined by Rheometer LS30 which allows measuring whole blood and plasma viscosity in the middle and low shear rate ranges. The measurements of the viscosity showed that whole blood and plasma behave as non-Newtonian power law fluid. The values of n (non-Newtonian index) and k (consistency index) of power law fluid were calculated for both leukemic blood and plasma samples. The importance of this phenomenon for the micro-circulation is discussed.

Adolescent↗
PubMed1992

Blood viscosity parameter correlation with types of leukemia.

We investigated the hemorheological, hematological and biochemical parameters in 30 cases of acute lymphocytic leukemia (ALL), 21 cases of acute myelogenous leukemia (AML) and 30 cases of chronic myelogenous leukemia (CML). The parameters studied include whole blood viscosity, plasma viscosity, erythrocyte sedimentation rate (ESR), red cell filterability, hematocrit, platelet count and aggregation, fibrinogen, hemoglobin, leucocyte count, bleeding time and lactate dehydrogenase activity (LDH). In the cases of ALL we observed significant decrease in whole blood viscosity, hemoglobin, hematocrit and platelet count but an increase in plasma viscosity, fibrinogen, bleeding time and LDH activity. In the cases of AML, we observed increase in whole blood viscosity, plasma viscosity, ESR, fibrinogen, leucocyte count, bleeding time and LDH activity but decrease in the hemoglobin, hematocrit and platelet count. In the cases of CML, we observed an increase of whole blood viscosity, plasma viscosity, ESR, fibrinogen elevation but decreases in bleeding time. In all cases, red cell filterability was unaffected.

Blood Sedimentation↗
PubMed1991

Effect of hydroxyurea on blood viscosity in chronic myelogenous leukemia with hyperleukocytosis.

The effect of hydroxyurea on blood viscosity was studied in 10 patients with Philadelphia chromosome positive chronic myelogenous leukemia (CML) and hyperleukocytosis (white blood cell counts over 200 x 10(9)/l). All the patients had visible manifestations of leukostasis such as headache, blurred vision, retinal hemorrhage, pulmonary infiltrates, etc. Contraves LS 30 viscometer was used to measure the blood viscosity at 37 degrees C and at different shear rates on paired leukemic blood samples obtained before and after the hydroxyurea treatment. The blood viscosity was significantly higher in CML patients then normal subjects and decreased after treatment with hydroxyurea. In all the cases plasma viscosity was unaffected by the treatment.

Adolescent↗
PubMed1983

The antihypertensive and positive inotropic diterpene forskolin: effects of structural modifications on its activity.

Four naturally occurring analogues of forskolin were isolated. Forty-nine semisynthetic derivatives were prepared, incorporating structural alterations at the 1-, 6-, 7-, 9-, 11-, and 14/15-positions. Blood pressure lowering properties of 53 compounds were assessed in anesthetized normotensive cats and of 31 compounds in conscious spontaneously hypertensive (SH) rats. The positive inotropic properties of 25 compounds were investigated in an isolated guinea pig atrial preparation. Forskolin was unique among the compounds in its hypotensive activity in cats and in its positive inotropic properties. Although several derivatives displayed oral antihypertensive activity in the SH rats, none was significantly more potent than forskolin. The optimal structural requirements for activity are apparent, since they are found in forskolin itself.

Animals↗