The affinity of irbesartan (IRB) to form inclusion complexes with β-cyclodextrin (β-CD), hydroxypropylβ-cyclodextrin (HP-β -CD), and γ-cyclodextrin (γ-CD) was investigated in aqueous buffered solutions at pH , , and . Analysis of the UV absorption-pH profiles revealed that IRB has two pKa values: pKa1 = (imidazolinone ring moiety) and pKa2 = (tetrazole moiety). In the presence of mmol L−1β-CD, the tetrazole moiety became more acidic, indicating its inclusion within the β-CD cavity. Phase-solubility diagrams (PSDs) were obtained for IRB in aqueous buffered solutions of β-CD, HP-β -CD, and γ-CD at pH (zwitterionic IRB), pH (protonated IRB), and pH (deprotonated IRB). |
