Search PubMed⌕ Search

Biomedical subjects

V D Gupta

Publications and source records attributed to V D Gupta.

At least 19 recordsLinked to original sources
PubMed1999

Effect of sulphur crosslinking on the stability and transition of triple helical DNA.

In continuation to our work on order-order and order-disorder transition in triple stranded DNA when it is bounded to netropsin, we report in this communication the stabilizing/destabilizing effect of disulphide linkage on the phase dynamics of the triplex using the amended Zimm-Bragg theory. It is observed that in contrast to the sequential triplex-->duplex -->single strand melting of the uncrosslinked triplex, crosslinking causes the triplex state to melt directly to the single stranded state, with no apparent intermediary of a duplex state. Since there is no overall difference in the enthalpy of crosslinked and uncrosslinked triplexes, the transition is entropy driven.

Base Sequence↗
PubMed1994

Normal vibrations and valence charge distribution in relation to bioactivity of gammexane.

Normal coordinate analysis has been made for gammexane using the Wilson's G-F matrix method with Urey-Bradley force field. Molecular orbital calculations using CNDO/2 method have also been carried out for the five isomers of hexachlorocyclohexane to give the valence charge densities on the atoms of the molecules. A toxicity parameter that takes into account a shape factor and the valence charge density on the atoms has been defined. On the toxicity scale so defined the gamma-isomer alone has a significant value.

Electrons↗
PubMed1994

Dynamics of Met5- and Leu5-enkephalin and their receptor binding activity in relation to morphine.

A complete normal coordinate analysis of Met5- and Leu5-enkephalins using Wilson's GF matrix method and Urey Bradley force field has been carried out to understand the dynamical behaviour of enkephalins. In addition, the charge distributions on different atoms of the two enkephalins and morphine using CNDO/2 method are also reported. The similarity in the charge distribution on the part of these two molecules is indicative of the possible interactions at the same receptor site as that of morphine and its derivatives. Apart from the topographical features and charge distribution, binding onto receptor site is not a static but a dynamic process and low frequency modes must play an important role in the recognition process. The significance of the out-of-plane amide VII band and other skeletal modes as characteristic of conformational states of Met5- and Leu5-enkephalins are discussed.

Enkephalin, Leucine↗
PubMed1992

Conformational transitions and specific heat anomaly in poly(dG-dC) and its methylated analogue.

The Zimm and Bragg theory of the helix<-->coil transition has been modified to explain order<-->order transitions in polynucleotides, in particular B<-->Z<-->psi(-)<-->coil transitions in poly(dG-dC) and poly(dG-me5dC). Lambda anomalies in specific heat measurements around the transition point have also been explained by a further modification of the same theory. Theoretical results are found to be in good agreement with the experimental data. The nucleation parameter is consistent with the stabilization/destabilization of the ordered states (Z helix) under various environmental conditions, e.g. methylation of cytosine residue at C5 position or change in the cationic concentration of the solvent.

Calorimetry↗
PubMed1991

Preformulation studies of spironolactone: effect of pH, two buffer species, ionic strength, and temperature on stability.

Using a stability-indicating HPLC assay method, the effect of pH, two buffer species (citrate and phosphate), ionic strength, and temperature on the stability of spironolactone in 20% solution of ethyl alcohol in water has been studied. The optimum pH of stability appears to be approximately 4.5. On increasing the buffer concentration, both species hastened the decomposition of spironolactone. The ionic strength did not affect the stability of the drug. The energy of activation has been estimated to be approximately 78.8 kJ/mol at pH 4.3. The un-ionized spironolactone is subject to general acid-base catalysis. The Kh and Koh values at 40 degrees C have been estimated to be 1.63 and 2.8 x 10(5) day-1, respectively. The HPO4(-2) ion had approximately 10 times more catalytic effect than the H2PO4(-1) ion. This data will be used to develop a stable oral liquid dosage form of the drug.

Buffers↗
PubMed1989

Preformulation studies of acetazolamide: effect of pH, two buffer species, ionic strength, and temperature on its stability.

Using an HPLC method, the effect of pH, two buffer species (phosphate and citrate), ionic strength, and temperature on the stability of acetozolamide has been studied. The optimum pH of stability appears to be 4. The buffers and ionic strength did not affect the decomposition constant. There was a direct relationship between the activation energies and pH values, with an energy of activation (Ea) value of 16.61 kcal/mol at pH 4. The un-ionized acetazolamide is subject to specific acid-base catalysis. The KH and KOH values have been estimated to be 0.23 and 1.56 d-1, respectively. These preformulation studies can be used to develop a stable oral liquid dosage form of acetazolamide.

Acetazolamide↗
PubMed1983

Stability of triamcinolone acetonide solutions as determined by high-performance liquid chromatography.

A stability-indicating assay method based on reverse-phase high-performance liquid chromatography has been developed for the quantitation of triamcinolone acetonide. The method was used to study the stability of triamcinolone acetonide in water--ethanol solutions of varying pH, buffer concentration, and ionic strength. The decomposition of triamcinolone followed pseudo-first-order law and was minimal at pH approximately 3.4. Above pH 5.5, the decomposition increased rapidly and was directly related to phosphate buffer concentration. The decomposition decreased with increasing ionic strength when the pH of the solution was greater than 7. Two new peaks corresponding to decomposition products were noted in the chromatogram; their ratio varied significantly with the composition of the vehicle.

Buffers↗
PubMed1983

Quantitation of amikacin, kanamycin, neomycin, and tobramycin in pharmaceutical dosage forms using the Hantzsch reaction.

A spectrophotometric assay method for the quantitative determination of amikacin, kanamycin, neomycin, and tobramycin in pharmaceutical dosage forms has been developed. The method is based on the Hantzsch reaction, forming dihydrolutidine derivatives which can be measured spectrophotometrically. The excipients EDTA, phenol, sodium bisulfite, and sodium citrate do not interfere, while salts of ammonia do interfere. The relative standard deviations based on seven readings were 1.64, 1.88, 2.10, and 1.93% for amikacin, kanamycin, neomycin, and tobramycin, respectively. Assay results have been compared with microbiological assay results provided by the manufacturers. The assay method appears to be stability indicating.

Amikacin↗
PubMed1983

Stability of mezlocillin sodium as determined by high-performance liquid chromatography.

The stability of mezlocillin sodium solutions in water with either phosphate buffers or other ingredients used in intravenous admixtures (dextrose, fructose, and sodium chloride) has been studied using a stability-indicating high-performance liquid chromatographic method. This assay shows a relative standard deviation of 1.42% based on six injections. The optimum stability was shown at an approximate pH of 4.8, and solutions in dextrose (5%) and sodium chloride (0.9%) were stable for up to 4 days at 25 degrees, 36 days at 5 degrees, and for 60 days at -10 degrees. When refrigerated, the solutions in 5% fructose and 10% dextrose were as stable as those in 5% dextrose.

Chromatography, High Pressure Liquid↗
PubMed1982

Complexation of procainamide with dextrose.

The percent of procainamide complexed with dextrose was determined to be directly related to the concentration per mole fraction of dextrose in the solution. The complexation process was reversible and did not proceed at lower pH (approximately 1.5). The rate of formation of complex was dependent on the initial pH value of the solution and the pH decreased as the concentration of the complex increased. The increase in the concentration of procainamide did not change the equilibrium concentration of the complex. The addition of sodium chloride or edetate disodium did not alter the rate of formation of the complex or its equilibrium concentration. The addition of hydrochloric acid prevented the formation of the complex and on adding hydrochloric acid after the formation of the complex, procainamide was completely freed.

Chemistry, Pharmaceutical↗
PubMed1980

Quantitation of carbenicillin disodium, cefazolin sodium, cephalothin sodium, nafcillin sodium, and ticarcillin disodium by high-pressure liquid chromatography.

High-pressure liquid chromatographic (HPLC) methods for the quantitation of carbenicillin, cefazolin, cephalothin, nafcillin, and ticarcillin were developed. The stability of 2% solutions of the antibiotics in normal saline and in 5% dextrose in water were studied at 24 and 5 degrees. The assays were conducted using a previously reported colorimetric method, and some assays also were performed using HPLC. For discolored solutions of cephalothin, the colorimetric method was not stability indicating. The percent relative standard deviations by HPLC based on six injections were 1.69, 0.94, 1.30, 1.59, and 1.6 for carbenicillin, cefazolin, cephalothin, nafcillin, and ticarcillin, respectively. Both carbenicillin and ticarcillin apparently may be mixtures of two isomers at equilibrium with each other. The shelflives recommended by the manufacturers at 5 degrees may be too conservative.

Carbenicillin↗
PubMed1979

Applications of paired ion high-pressure liquid chromatography: quantitative determination of potassium guaiacolsulfonate and other ingredients in cough syrups.

A method for the quantitative determination of potassium guaiacolsulfonate and phenylephrine hydrochloride in commercial dosage forms was developed. The method is based on paired ion high-pressure liquid chromatography with tetrabutylammonium as the counterion. The method not only separates potassium guaiacolsulfonate from phenylephrine hydrochloride but also from some other ingredients: chlorpheniramine maleate, sodium benzoate, colors, and flavors. Furthermore, two isomers of potassium guaiacolsulfonate, potassium salts of 4- and 5-guaiacolsulfonic acid, also separate from each other. The method was tried on five different commercial dosage forms (all with different colors) with excellent results on three. In the other two samples, which also contained codeine, three may have been a stability problem.

Chromatography, High Pressure Liquid↗
PubMed1979

High-pressure liquid chromatographic evaluation of aqueous vehicles for preparation of prednisolone and prednisone liquid dosage forms.

A high-pressure liquid chromatographic method was developed that separates prednisolone from prednisone, prednisone from methylprednisolone succinate sodium, and hydrocortisone from hydrocortisone acetate or cortisone acetate. The common liquid dosage preservatives methylparaben, propylparaben, and sodium benzoate do not interfere with quantitative prednisolone, prednisone, and hydrocortisone determinations. The method was used to study prednisolone and prednisone stability in five aqueous vehicles (water, citrate buffer USP, 50% glycerin, 50% sorbitol, and 50% sucrose) containing 10% (v/v) ethanol. Prednisone crystallized out in all vehicles except glycerin, in which it appeared to be stable for at least 92 days. Prednisolone did not crystallize in any vehicle but decomposed quickly in citrate buffer. Sorbitol and glycerin appeared to be the best vehicles for prednisolone. The developed method was applied successfully to the quantitative determinations of prednisolone, prednisone, and hydrocortisone in commercial tablets.

Chromatography, High Pressure Liquid↗
PubMed1979

Quantitative dexamethasone and dexamethasone sodium phosphate determinations in pharmaceutical dosage forms by high-pressure liquid chromatography.

A high-pressure liquid chromatographic procedure for quantitative dexamethasone and dexamethasone sodium phosphate determinations in all types of commercially available pharmaceutical dosage forms was developed. The method also separates dexamethasone from its phosphate salt and separates dexamethasone or its salt from a number of inactive ingredients such as benzoic acid, benzyl alcohol, some colors, creatinine, and parabens. Inactive ingredient concentrations may be estimated without additional cost. Part of the parabens present in the commercial injections may be adsorbed by the rubber closures.

Chromatography, High Pressure Liquid↗
PubMed1978

Effect of vehicles and other active ingredients on stability of hydrocortisone.

The stability of hydrocortisone in various types of vehicles, aqueous, water-washable (polyethylene glycol ointment base), and oil in water or water in oil-type emulsified vehicles, and in the presence of other ingredients, iodochlorhydroxyquin, menthol, and phenol, was studied under normal conditions (room temperature and weakly acidic pH). The study was conducted using a stability-indicating assay method, high-pressure liquid chromatography. The hydrocortisone was very unstable in water and water-washable ointment base. The addition of alcohol and glycerin to water had a stabilizing effect. Under drastic conditions (very acidic or very basic pH), hydrocortisone proved to be unstable only on the basic side. The data at higher temperatures confirmed that the decomposition in water and polyethylene glycol was pseudo-first order. The decomposition process appears to be different in the highly basic solution versus weakly acidic media or in water versus polyethylene glycol ointment base.

Chromatography, High Pressure Liquid↗