Synthesis of Silver-2-Aminophenol-Cyclodextrin Nanomaterials and pH Dependent of 2-Aminophenol-Cyclodextrin Inclusion Complexes

The spectral characteristics of 2-aminophenol (2AP) in various solvents, α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) at pH~3, pH~7, and pH~11, were investigated using UV-visible, fluorescence, time-resolved fluorescence measurements, and PM3 computational methods. The Ag: 2AP: CD nanomaterials were synthesized and characterized by SEM, FTIR, and XRD techniques. In all the pH conditions, 2AP exhibited distinct absorption and emission shifts upon complexation with α-CD and β-CD. In various solvents, the absorption and emission maxima of 2AP were similar to those of 2-anisidine. 2AP showed a single broad emission band in all solvents, whereas dual emission observed in CD solutions indicates the presence of an intramolecular proton transfer (IPT) process in the 2AP molecule. The lifetimes of the inclusion complexes were longer than that of the free 2AP molecule. The geometrical restriction of the α-CD cavity likely limits the free rotation of the amino and hydroxyl groups, thereby enhancing the intensity of the IPT emission. The calculated HOMO-LUMO energy gap, total energy, free energy, enthalpy, entropy, dipole moment, and zero-point vibrational energy of the CD: 2AP complex differed significantly from those of the isolated 2AP, α-CD and β-CD molecules, and both the vertical and horizontal bond lengths between the amino and hydroxy groups are smaller than the β-CD cavity size confirming the formation of an inclusion complex. SEM-EDX data confirmed the presence of 5.5% silver in the nanomaterials.