Theoretical study of the kojic acid structure in gas phase and aqueous solution

Density functional calculations at the B3LYP/6‐311++G** level have been performed to determine the ground‐state conformational preference for kojic acid, a widely used skin‐whitening, antibrowning, and antibacterial agent. It is found that the gas phase consists almost entirely of the 5‐hydroxy‐2‐(hydroxymethyl)‐4H‐pyran‐4‐one tautomer, although several rotamers of this are prevalent. In aqueous solution, however, other tautomers are also present. The validity of the calculations is confirmed by the observed FTIR, NMR, and UV–vis spectra, which show good correspondence with the theoretical spectra. The electronic interactions are interpreted in terms of charge and bond order analysis as well as the composition of the HOMO and LUMO. The calculations show that kojic acid has partial aromatic character and is a good nucleophile. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011