4-Dimethylaminochalcone as a f luorescent probe: Quantum chemical calculations of its interaction with the environment

Abstract

Ground-state RHF/6-311G(d,p) and density functional B3LYP/6-311G(d,p) quantum chemical calculations of 4-dimethylaminochalcone (DMAC), a sensitive fluorescent probe, were carried out for vacuum and for solvents of different polarity. The effect of the medium was included by the SCRF method in the framework of the polarization continuum model. The DMAC fragment comprising the aniline and propenone groups has a nearly planar conformation. The phenyl group can lie in the same plane or rotate by an angle within the limits of ±20° with a low barrier at 293 K. The results of calculations were confirmed by the data of X-ray study, according to which the phenyl group in the crystal is rotated by 20°. Calculations with allowance for solvation effects predict charge transfer from the dimethylamino group to the oxygen atom; the higher the medium polarity, the larger the degree of charge transfer (atomic charge of oxygen increases by 0.07 e in acetone). The calculated dipole moment of the DMAC molecule increases from 5.2 D (vacuum) to 5.9 D (heptane) and 6.9 D (acetone), which is in agreement with spectroscopic data. The energy of the DMAC—environment interaction was calculated. Due to large dipole moment of the DMAC molecule, the electrostatic component of this energy strongly depends on the environment polarity, which can be related to redistribution of the probe between the aqueous phase and cells and lipid structures of lipoproteins. The electronic absorption spectra of DMAC in solvents of different polarity were calculated; differences between the calculated and experimentally measured values are at most 15 nm.