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The affinity of irbesartan (IRB) to form inclusion complexes with β-cyclodextrin (β-CD), hydroxypropylβ-cyclodextrin (HPβ-CD), and γ-cyclodextrin (γ-CD) was investigated in aqueous buffered solutions at pH 1.7, 4.1, and 7.0. Analysis of the UV absorption-pH profiles revealed that IRB has two p Ka values: p Ka1 = 3.60 (imidazolinone ring moiety) and p Ka2 = 4.70 (tetrazole moiety). In the presence of 5.0 mmol L −1 β-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, HPβ-CD, and γ-CD at pH 4.1 (zwitterionic IRB), pH 1.7 (protonated IRB), and pH 7.0 (deprotonated IRB). Rigorous nonlinear regression analysis of IRB/CD PSDs at pH 4.1, where IRB is poorly soluble, yielded estimates of complex formation constants (K11) that followed the decreasing order of HPβ-CD > γ-CD > β-CD. The highest solubility enhancement of IRB was achieved by complexation with HPβ-CD at pH 4.1. The formation of the IRB/ β-CD inclusion complex in solution and in the solid state has been proven through NMR, DSC, FT-IR, and XRD studies. Analysis of 1 H and 13 C-NMR spectra indicated the inclusion of the tetrazole-biphenyl moiety within the β-CD cavity.

Abstract:Photophysical properties of lamotrigine (LMT) were investigated at different pH values. Lamotrigine exhibited a broad absorption band at 308 nm that was shifted to 268 nm at pH 2.0 due to protonation (HLMT +) . Emission spectra of LMT at different pH values showed a single band at 483 nm except for at pH 2.0, where a second band at 502 nm was observed due to the deprotonation from the singlet excited state. LMT pH profile was used to calculate that LMT is preferentially included within the β -CD cavity through its diamino-1,2,4-triazine moiety.

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Investigation of Solvent Effect and H-Bonding on SpectroscopicProperties of 1-(3-Amino-6-(2,5-dichlorothiophen-3-yl)-4-phenylfuro[2,3-b]pyridin-2-yl) ethenone: Experimental and Computational Study.

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