Nonplanar property study of antifungal agent tolnaftate-spectroscopic approach

Vibrational analysis of the thionocarbamate fungicide tolnaftate which is antidermatophytic, antitrichophytic and antimycotic agent, primarily inhibits the ergosterol biosynthesis in the fungus, was carried out using NIR FT-Raman and FTIR spectroscopic techniques. The equilibrium geometry, various bonding features, harmonic vibrational wavenumbers and torsional potential energy surface (PES) scan studies have been computed using density functional theory method. The detailed interpretation of the vibrational spectra has been carried out with the aid of VEDA.4 program. Vibrational spectra, natural bonding orbital (NBO) analysis and optimized molecular structure show the clear evidence for electronic interaction of thionocarbamate group with aromatic ring. Predicted electronic absorption spectrum from TD-DFT calculation has been compared with the UV–vis spectrum. The Mulliken population analysis on atomic charges and the HOMO–LUMO energy were also calculated. Vibrational analysis reveals that the simultaneous IR and Raman activation of the C–C stretching mode in the phenyl and naphthalene ring provide evidence for the charge transfer interaction between the donor and acceptor groups and is responsible for its bioactivity as a fungicide.

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► We have analysed the structure property relationship and bioactivity of the topical antifungal drug Tolnaftate.
► HOMO orbitals predominantly localize on the thionocarbamate group and LUMO orbitals on the naphthalene ring.
► The fungicidal activity of tolnaftate is enhanced by the two electron-withdrawing substituent groups, benzene and naphthalene.