A quantum mechanical study of bioactive 3-chloro-2,5-dihydroxybenzyl alcohol through substitutions

Electronic structures, vibrational and ionization spectra of 3-chloro-2,5-dihydroxybenzyl alcohol (CHBA), a novel bioactive benzene derivative from marine fungi, are presented in this study using quantum mechanical methods such as density functional theory and outer valence Green function method. A number of related benzene derivatives such as chlorobenzene, 3-chlorobenzyl alcohol, hydroquinone and chlorohydroquinone are also studied, in order to assist our understanding of the structure, properties and interactions of CHBA. Vibrational spectra such as infrared (IR) and Raman spectra reveal signatures of the functional group substitutions and their hydrogen bond interactions in CHBA. Solvent effects on the IR spectra of CHBA with polar and non-polar solvents are simulated using the polarizable continuum model (PCM) and cause redshifts of some of the IR spectral frequencies with respect to the gas phase values at both ends of the 400-4,000 cm-1 region. The inner-shell ionization spectra, in particular the C-K spectra of the benzene derivatives, reveal detailed chemical environmental changes of the carbon and oxygen atoms due to the substitutions. The valence ionization energies of the highest occupied molecular orbital (HOMO) and the 3rd HOMO, (HOMO-2) of the benzene derivatives respond significantly to the substitutions, whereas the charge distributions of the HOMO and 2nd HOMO (HOMO-1) do not change significantly from their benzene counterparts. As a result, the 3rd HOMO changes significantly in both ionization energies and the charge distributions, which can serve as a signature of the substitutions among the benzene derivatives