A Study on Host–Guest Complexation of 5-Amino-2-Mercaptobenzimidazole with β-Cyclodextrin
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Spectral characteristics of 5-amino-2-mercaptobenzimidazole (AMBZ) have been investigated in aqueous β-cyclodextrin (β-CDx) solutions. The absorbance and fluorescence intensity of the neutral and monocationic forms of AMBZ are enhanced due to the formation of an inclusion complex with β-CDx. The stoichiometry and binding constants of the complex were calculated using the Benesi–Hildebrand equation. Formation of an inclusion complex between AMBZ and β-CDx was also confirmed by steady state and time-resolved fluorescence spectroscopy. FT-IR spectral data and SEM images of the solid complex provide supporting evidence for complex formation. The effect of acidity on the ground and excited state equilibrium between neutral and monocationic forms of AMBZ was analyzed in aqueous and β-CDx environments. The ground and excited state acidity constants in β-CDx solutions were found to be different from those in aqueous solution. Based on these results, the structure of the 1:1 complex is proposed.
Keywords5-Amino-2-mercaptobenzimidazole Cyclodextrin Fluorescence spectroscopy Inclusion complex Acidity constant
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