DFT study of conformation, hydrogen bonds, IR, and Raman spectra of the sodium salt of p-hexasulfonatocalix[6]arene DFT

Abstract

The vibrational spectra of p-hexasulfonatocalix[6]arene hexasodium salt (SC6) and p‑tert-butylcalix[6]arene (TB6) were studied. The comparison of the IR spectra SC6 and TB6 allows to distinguish bands of tert‑butyl and sulfonate groups. The structure and the vibrational spectra of the SC6 molecule were calculated for the conformations of the compressed cone and the double partial cone. For the molecule SC6, the conformation of a compressed cone is the most stable, and the conformation of a double partial cone is 43.6 Kcal/mol less stable. When replacing tert‑butyl groups with sulfonatel groups, the cavity size of calixarene molecules increases from 5.22 (TB6) to 7.80 Ǻ (SC6). In the sodium salt of the SC6 molecule, six sodium ions are coordinated with the oxygen atoms of the sulfonate groups. Under the influence of sodium ions, the electron density is redistributed in the SC6 molecule, and its supramolecular properties change. The transition from TB6 to SC6 increases the ionization energy, electronic affinity, chemical potential and dipole moment. In the SC6 molecule, the frontal orbitals are located on aromatic and sulfonate groups. Due to these orbitals, calixarenes interact with biological objects.