Prediction of the most preferable rotamer of meta-aminophenol in β-cyclodextrin cavity in aqueous medium by using spectroscopic and DFT computational studies

Abstract

Meta-aminophenol (m-AP) was used as a guest molecule to be incorporated into the hydrophobic nano-cavity of the host molecule β-cyclodextrin (β-CD) to form host–guest inclusion complex in aqueous medium. For this, we employed spectrometric titration method, i.e., β-CD was added gradually in an aqueous solution of m-AP maintaining a fixed concentration of m-AP. We investigated the changes in the photophysical properties of m-AP through inclusion complex formation in β-CD in aqueous medium by using steady state and time-resolved spectroscopic techniques as well as density functional theory (DFT) computations. Benesi–Hildebrand method was used to find the stoichiometry and association constant at two concentration ranges of β-CD. The average fluorescence lifetime of m-AP was found to increase from 0.17 ns in absence of β-CD to 3.69 ns in presence of β-CD (highest concentration used). DFT computations carried out in water medium clearly indicate that the inclusion complex is more stable for the cis-rotameric conformation of m-AP rather than trans.