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Biomedical subjects

S Bhattacharjee

Publications and source records attributed to S Bhattacharjee.

At least 37 records · Page 2Linked to original sources
PubMed1999

Concentration Polarization of Interacting Solute Particles in Cross-Flow Membrane Filtration.

A theoretical approach for predicting the influence of interparticle interactions on concentration polarization and the ensuing permeate flux decline during cross-flow membrane filtration of charged solute particles is presented. The Ornstein-Zernike integral equation is solved using appropriate closures corresponding to hard-spherical and long-range solute-solute interactions to predict the radial distribution function of the solute particles in a concentrated solution (dispersion). Two properties of the solution, namely the osmotic pressure and the diffusion coefficient, are determined on the basis of the radial distribution function at different solute concentrations. Incorporation of the concentration dependence of these two properties in the concentration polarization model comprising the convective-diffusion equation and the osmotic-pressure governed permeate flux equation leads to the coupled prediction of the solute concentration profile and the local permeate flux. The approach leads to a direct quantitative incorporation of solute-solute interactions in the framework of a standard theory of concentration polarization. The developed model is used to study the effects of ionic strength and electrostatic potential on the variations of solute diffusivity and osmotic pressure. Finally, the combined influence of these two properties on the permeate flux decline behavior during cross-flow membrane filtration of charged solute particles is predicted. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Estimation of .OH radical reaction rate constants for phenol and chlorinated phenols using UV/H2O2 photo-oxidation.

A detailed investigation on UV/H2O2 photooxidation has been carried out in order to determine the kinetics of the oxidative degradation of phenol and 2- and 4-chlorophenols in dilute aqueous solutions. Effects of different process parameters, such as initial substrate and H2O2 concentrations, substrate to H2O2 ratio on the degradation kinetics of the phenolic substrates, have been studied. Degradation rates of phenol and chlorophenols are insignificantly small with ultraviolet radiation only and also with hydrogen peroxide (in the absence of UV radiation), but the synergistic effect of UV/H2O2 results in a marked enhancement of the rates of degradation. A mechanistic model for UV/H2O2 photooxidation has been developed. Room temperature (27 degrees C) rate constants for the reaction of .OH radical (formed by absorption of photons) with the substrates have been estimated by using the model equation. The calculated rate constants are of the same order of magnitude as reported for other similar aromatic compounds.

Absorption↗
PubMed1998

HIV, hepatitis B and sexual practices in the street-recruited injecting drug users of Calcutta: risk perception versus observed risks.

Injecting drug users (IDUs) were recruited from the streets of Calcutta to obtain a baseline biological and behavioural data on risk practices. One-fifth of them (mostly using buprenorphine) tested positive for hepatitis B surface antigen (HBsAg); 4% were reactive to serologic test for syphilis (VDRL: Venereal Disease Research Laboratory). Condom use was insignificant while 74% reported sex with female sex workers and 15% of male IDUs also reported having sex with men. Although, sharing of injecting equipment ('works') was perceived as dangerous by the IDUs, majority of them (90/103) reportedly shared it; cleaning of works before sharing was a concern for intravenous but not for intramuscular drug injecting. Half of the IDUs reported suffering ever from abscess; a proportion (12%) of which had had superadded attack of maggots in it. They were also found to be infected with HIV (1%, 95% CI 0.028-5.97%) at a low prevalence that prompted subsequent launching of needle syringe exchange programme, establishment of cleaning norms before sharing of works, cleaning of injecting site on the body and condom promotion.

Abscess↗
PubMed1997

Betidamino acid scan of the GnRH antagonist acyline.

Strong clinical evidence suggests that GnRH antagonists will replace GnRH agonists in a number of indications because of their ability to inhibit gonadotropin secretion as long as an adequate concentration of the analogue is present in the circulation whereas superagonists will take approximately 2 weeks to desensitize the gonadotrophs. Until recently, antagonists were either too weak and/or would release histamine. Azaline B {[Ac-D2Nal1,D4Cpa2,D3Pal3, 4Aph5(atz),D4Aph6(atz),ILys8,DAla10] GnRH} and long-acting members of the azaline family {Ac-D2Nal-D4Cpa-D3Pal-Ser-4Aph(X)-D4Aph(Y) -Leu-ILys-Pro-DAla-NH2}, however, appear to be promising drug candidates. Because these antagonists tend to form gels (due to the formation of beta-sheet structures) and, as a result, are not readily amenable to formulation for long-term delivery, we have investigated ways of increasing hydrophilicity while retaining high potency and lack of histamine releasing activity. Betidamino acids (a contraction of "beta" position and "amide") are N'-monoacylated (optionally, N'-monoacylated and N-mono- or N,N'-dialkylated) aminoglycine derivatives in which each N'-acyl/alkyl group may mimic naturally occurring amino acid side chains or introduce novel functionalities. We have used unresolved N alpha-Boc,N'alpha-Fmoc-aminoglycine, and N alpha-Boc,N'alpha-(CH3)Fmoc-aminoglycine as templates for the introduction of betidamino acids in acyline (Ac-D2Nal-D4Cpa-D3Pal-Ser-4Aph(Ac)-D4Aph(A c)-Leu-Ilys-Pro-DAla-NH2), a long acting member of the azaline B family, to test biocompatibility of these betide derivatives. Diastereomeric peptides could be separated using RP-HPLC in most cases. Biological results obtained in vitro (binding affinity to rat pituitary gland membranes) and in vivo (rat antiovulatory assay, AOA) indicate in most cases small differences in relative potencies (< 5-fold) between the D- and L-nonalkylated betidamino acid-containing acylines. Importantly, most betide diastereomers have high affinity for the GnRH receptor and were equipotent with acyline in the AOA. Greater differences in affinity and potency between diastereomers were observed after introduction of a methyl group on the side chain nitrogen ("beta" position) of the same analogues, with one of the diastereomer having an affinity and a potency in the AOA equivalent to that of acyline. These results suggest that chirality at the alpha-carbon coupled to side chain orientation is important for receptor recognition. The duration of action of some of the most potent analogues was also determined in the castrated male rat in order to measure the extent (efficacy and duration of action) of inhibition of luteinizing hormone release. Data suggest that introduction of a betidamino acid results in reduction of duration of action. Also, introduction of betidamino acids results in peptides with increased hydrophilicity (as determined by elution times on C18 silicas at pH 7.3) compared to that of the parent compound. N'-Methyl substitution results in parallel increase in retention times on C18 silicas as expected.

Amides↗
PubMed1997

Surface Element Integration: A Novel Technique for Evaluation of DLVO Interaction between a Particle and a Flat Plate

A novel method, the surface element integration (SEI), is developed to determine the van der Waals and electrostatic double layer interactions between a particle and an infinite flat plate from the corresponding interactions per unit area between two infinite flat plates. Comparison with the Hamaker expression for nonretarded van der Waals interaction reveals that the new technique gives the exact interaction energy between a spherical particle and a flat plate. Available analytical expressions for the electrostatic double layer interaction energy between two infinite flat plates, based on the linearized Poisson-Boltzmann equation, are used in SEI to obtain the sphere-flat plate interaction energy. These sphere-flat plate interaction energies determined using SEI are compared with the corresponding interaction energies obtained from a detailed numerical solution of the Poisson-Boltzmann equation based on finite element analysis. The comparisons reveal that SEI scales the flat plate interaction to the corresponding sphere-flat plate geometry exactly, while the scaling based on the conventional Derjaguin approximation technique grossly overpredicts the interaction energy for small particles and low electrolyte concentrations. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1997

Apolar, Polar, and Electrostatic Interactions of Spherical Particles in Cylindrical Pores

A new Surface Element Integration (SEI) technique is developed for determination of the interaction energy of a spherical particle in a cylindrical pore based on the knowledge of the corresponding interaction energy per unit area between plane-parallel half spaces. Like the celebrated Deryaguin's approximation, the SEI can be used for any component of the interaction energy (e.g., apolar Lifshitz-van der Waals, electrostatic, polar) whenever interaction between corresponding half-spaces is known theoretically or experimentally. Accuracy of the SEI is assessed based on its comparison with the exact results for the van der Waals interaction energy. Results of the SEI are also compared with the approximate series solution for the electrostatic interaction in the Debye-Huckel approximation. While Deryaguin's approximation fails for the particle-pore geometry for small pores (<10 nm), the SEI is accurate for all realistic combinations of particle and pore radii, radial position of the particle, and decay length of interactions. Based on the SEI, the role of polar repulsion (hydration pressure) on the partitioning behavior of macromolecules across small pores is also studied. The hydration force in aqueous hydrophilic systems can lead to a significant lowering of the distribution coefficient in small pores characteristic of ultrafiltration.

Journal Article↗
PubMed1996

Interaction of aldehydes with glyoxalase I and the status of several aldehyde metabolizing enzymes of Ehrlich ascites carcinoma cells.

The possible effect of several physiologically important aldehydes has been tested on partially purified glyoxalase I of Ehrlich ascites carcinoma (EAC) cells. The results indicate that D, and L-lactaldehyde are strong non-competitive inhibitors of glyoxalase I and the effect with the D-isomer is more pronounced, whereas both D,L-glyceraldehyde and acetaldehyde are moderately inhibitory and the nature of inhibition is strictly competitive. Moreover, D,L-glyceraldehyde strongly inhibits the utilization of methylglyoxal by intact EAC cells. A search for the presence of several aldehyde metabolizing enzymes in EAC cells indicates that non-specific aldehyde reductase, methylglyoxal reductase, aldehyde dehydrogenase and alcohol dehydrogenase are apparently absent in this rapidly growing, highly de-differentiated malignant cell.

Acetaldehyde↗
PubMed1994

Reconstruction of the quadriceps apparatus following open injuries to the knee joint using pedicled gastrocnemius musculotendinous unit as bridge graft.

The objectives of treating open knee joint injuries with disruption of the distal quadriceps mechanism are to ensure rapid wound healing and to restore joint function. For this it is necessary to provide soft tissue cover, control infection, restore full extension of the knee by reconstruction of the extensor apparatus and prevent joint stiffness by early mobilisation. Two cases are presented where the gastrocnemius (medial half) musculotendinous unit has been used to reconstruct, in one stage, the extensor apparatus and at the same time to provide soft tissue cover.

Child↗
PubMed1992

Three-dimensional structure of a cloning vector. X-ray diffraction studies of filamentous bacteriophage M13 at 7 A resolution.

Filamentous bacteriophage M13 is a single-stranded DNA phage about 65 A in diameter and 9300 A long. X-ray diffraction studies of magnetically oriented fibers of native, mercury and iodine-labeled phage particles have been used to determine the arrangement of the major coat protein, the gene 8 product, in the virion. The coat protein is made up of a single gently curving alpha-helix extending from approximately Pro6 to near the carboxyl terminus. The axis of the alpha-helix is tilted about 20 degrees from the viral axis and wraps around the axis in a right-handed helical sense. The surface of the virus is made up largely of polar residues in the amino-terminal half of the protein including the segment of alpha-helix extending from Pro6 to Tyr24. The interior surface of the protein coat faces the DNA and consists of an amphipathic helical segment extending from Thr36 to Ser50. The alpha-helices form a tightly packed 15 to 20 A thick cylindrical coat around the DNA. This structural model provides insight into the potential sites for incorporating foreign protein domains that may act as functional binding sites on the surface of M13.

Amino Acid Sequence↗
PubMed1992

Structural polymorphism correlated to surface charge in filamentous bacteriophages.

Fiber diffraction studies are used to demonstrate that changes in the helical symmetry of the protein coat of filamentous bacterial viruses fd and M13 are correlated with changes in the surface charge. Comparison of the structure of M13 and fd at pH 2 and 8 indicate that surface charge affects both the helical symmetry and flexibility of the virions. The changes in helical symmetry are similar in magnitude to that observed in the Pseudomanas phage Pf1 and probably reflect an inocuous side effect of the particle flexibility required for protection of the virus particles from damage due to shear. The magnitude of the observed changes in helical symmetry appears to be limited to that which can occur without repacking of the interfaces between the alpha-helices making up the viral protein coat.

Bacteriophages↗
PubMed1991

Prevalence of hepatitis C in transfusion dependent thalassaemics & haemophilics.

Seventy thalassaemics (B = 37, EB = 33) and 20 haemophilics (A = 18, B = 1, C = 1) were tested for antibodies to hepatitis C virus (anti-HCV) and markers for hepatitis B virus (HBV). The seropositivity for anti-HCV in thalassaemics and haemophilics was 14.3 and 25 per cent respectively. The subjects who were sero-positive to anti-HCV had had additional exposure to HBV. Anti-HCV positivity was not related to the age of the subject nor the number of units of blood and blood components transfused. Screening of blood donors for anti-HCV, apart from HBV, may minimise the hazards of post transfusion hepatitis in high risk recipients like transfusion dependent thalassaemics and haemophilics.

Hemophilia A↗