Differential Pulse Polarographic and UV‐Vis Spectrophotometric Study of Inclusion Complexes Formed by 1,4‐Dihydropyridine Calcium Antagonists, Nifedipine and Nicardipine with β‐Cyclodextrin

The formation of inclusion complexes of well‐known 1,4‐dihydropyridine calcium antagonists, such as nifedipine (NF) and nicardipine (NC), with β‐cyclodextrin (βCD) was investigated by differential pulse polarography (DPP) and UV‐vis spectrophotometry. The equimolar variation method indicated the formation of the NF‐βCD (1 : 1, M : M) and a NC‐βCD (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‐βCD and NC‐βCD, 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‐βCD and NC‐βCD, respectively. According to the DPP studies, we can postulate that the inclusion moiety were the nitroaromatic group, in the case of NF‐βCD, and the phenyl group on 3‐position of the 1,4‐DHP, in the case of NC‐βCD. The solubility of NF in water was increased about three times due to the formation of an inclusion complex with βCD. For NC the solubility was increased almost seven times.