A simple, sensitive, and rapid RP-HPLC method for analysis of enalapril in the presence of H 2 -receptor antagonists has been developed and validated. Enalapril maleate was separated from H 2 -receptor antagonists by use of a 250 mm × 4.6 mm, 5-µm particle, C 18 column with 86:14 ( υ / υ ) methanol-water, pH adjusted to 3.5, as mobile phase, at a flow rate of 1.5 mL min -1. UV detection was performed at 227 nm. The retention times of enalapril maleate, ranitidine, cimetidine, and famotidine were 3, 5, 7, and 7.5 min, respectively. The detection limit for enalapril was 10 ng mL -1 and the calibration plot was linear in the range 2.5–50 µg mL -1. In-vitro interaction of enalapril with the commonly administered H 2 -receptor antagonists cimetidine, ranitidine, and famotidine in simulated gastric juice at different pH and 37°C was also studied by use of this method. These studies clearly indicated that most of these H 2 -receptor antagonists bind to enalapril causing drastic changes in the availability of the drug. The HPLC method is accurate, selective, sensitive, and reproducible.
The mechanism of interaction of bromocresol purple (BCP) with bovine serum albumin (BSA) has been investigated by spectrofluorometric and circular dichroism methods. Association constant for the BCP-BSA system showed that the interaction is non-covalent in nature and that there occurs only a partial occupation of a binding site. Binding studies in the presence of hydrophobic probe, 8-anilino-1-naphthalene sulphonic acid, sodium salt (ANS) showed that there is hydrophobic interaction between BCP and ANS and they may share common sites in BSA. Stern-Volmer analysis of fluorescence quenching data showed that the fraction of fluorophore (protein) accessible to the quencher (BCP), was close to unity, indicating thereby that both tryptophan residues of BSA are involved in dye-protein interaction. The rate constant for quenching, greater than 1010M-1s-1, indicated that the dye binding site is in close proximity to tryptophan residue of BSA. Thermodynamic parameters, obtained from data at different temperatures, showed that the binding of BCP to BSAinvolves hydrophobic bonds predominantly. Fluorescence intensity data in the presence of additives showed that hydrophobic interaction plays a prominent role. Significant decrease in concentration of free dye was observed for BCP in presence of paracetamol. Circular dichroism studies revealed the change in helicity of BSA, due to binding of BCP to BSA.
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