Differential pulse polarographic and UV-vis spectrophotometric study of inclusion complexes formed by 1,4-dihydropyridine calcium antagonists, nifedipine and nicardipine with beta-cyclodextrin

Abstract

The formation of inclusion complexes of well-known 1,4-dihydropyridine calcium antagonists, such as nifedipine (NF) and nicardipine (NC), with beta-cyclodextrin (betaCD) was investigated by differential pulse polarography (DPP) and UV-vis spectrophotometry. The equimolar variation method indicated the formation of the NF-betaCD (1:1, M:M) and a NC-betaCD (1:1, M:M) inclusion complexes. Titrations using the DPP peak currents for NF and NC permitted one to determine formation constant values of (135 +/- 20) M-1 and (357 41) M-1 for NF-betaCD and NC-betaCD, respectively. For comparative purposes we have also applied phase solubility studies with spectrophotometric detection obtaining formation constant values of (129 +/- 5) M-1 and (385 +/- 19) M-1 for NF-betaCD and NC-betaCD, respectively. According to the DPP studies, we can postulate that the inclusion moiety were the nitroaromatic group, in the case of NF-betaCD, and the phenyl group on 3-position of the 1,4-DHP, in the case of NC-betaCD. The solubility of NF in water was increased about three times due to the formation of an inclusion complex with betaCD. For NC the solubility was increased almost seven times.