Inclusion Complexation of 4-methoxybenzoic Acid: Cyclodextrin at Different pH and Synthesis of Silver: 4-methoxybenzoic Acid: Cyclodextrin Nanomaterials

The inclusion behavior of 4-methoxybenzoic acid (4MBA) with α-cyclodextrin and β-cyclodextrin in buffer solutions of pH ~3, ~7, and ~11 was examined using UV-visible, steady-state and time-resolved fluorescence spectroscopy, along with PM3 computational analysis. Ag: 4MBA: CD nanomaterials were synthesized and characterized by SEM, DSC, FTIR, XRD, and ¹H NMR techniques. Because 4MBA predominantly exists as a carboxylate anion in pH ~7 medium, the spectra of its neutral and monoanion forms were also recorded at pH ~3 and pH ~11, respectively. In both cyclodextrin solutions, smooth emission profiles were obtained at pH ~3, while structured emission bands appeared at pH ~7 and pH ~11, with greater band structure observed in alkaline medium. The CD-induced spectral changes at different pH values indicate that the geometries of the resulting inclusion complexes vary across media. Since the carboxylate group is ionized, ground-state dimer is not formed, however, excimer formed in the excited state. Lifetime measurements reveal that the β-CD: 4MBA complex is more stable than the α-CD counterpart. 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 4MBA, 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 analysis confirms the presence of silver in the composite. FTIR, XRD, and NMR results collectively suggest strong interactions between 4MBA and the silver nanoparticles.