Synthesis of Silver–3,5-dimethylphenol –Cyclodextrin Nanomaterials and pH-Dependent Characteristics of 3,5-Dimethylphenol –Cyclodextrin Inclusion Complexes

Absorption, emission, and time-resolved fluorescence maxima of 3,5-dimethylphenol (35DMP) were examined in various solvents, as well as in α-CD and β-CD solutions at pH ~2, pH ~7, and pH ~11. The corresponding nanomaterials were synthesized and characterized using SEM, DSC, FTIR, XRD, and ¹H NMR analyses. In CD solutions, the absorption and emission spectra of 35DMP are similar at pH ~2 and pH ~7 but differ at pH ~11. At higher β-CD concentrations, the spectral maxima and shapes are similar in all the pH, suggesting the formation of a same type of inclusion complex. But, α-CD shows distinct absorption and emission maxima at different pH values, indicating the formation of different inclusion. 35DMP is more deeply encapsulated in the nonpolar interior of β-CD than in α-CD, as reflected by the increase in fluorescence lifetime in the order: pH < α-CD < β-CD. The calculated HOMO–LUMO energy gap, total energy, free energy, enthalpy, entropy, dipole moment, and zero-point vibrational energy of the CD: 35DMPcomplex differed significantly from those of the isolated 35DMP, α-CD and β-CD molecules, and both the vertical and horizontal bond lengths between the methyl and hydroxy groups are smaller than the β-CD cavity size confirming the formation of an inclusion complex. SEM-EDX analysis confirmed the presence of silver in the nanomaterials. DSC thermograms of Ag: 35DMP: CD complexes show new thermal peaks distinct from those of pure 35DMP, α-CD, and β-CD. FTIR spectra of the nanomaterials indicate substantial decreases or absence of most characteristic peaks, confirming strong interactions between 35DMP, the CD cavity, and the silver nanoparticles.