Molecular structure, electronic properties, and charge transfer analysis of clopenthixol as a nano-drug with quantum chemical calculations

Molecular structure, electronic absorption spectra, electronic and optical properties, spectroscopic characterization, molecular electrostatic potential (MEP) analysis, natural charge distribution, charge transfer analysis, and thermodynamic properties investigations of clopenthixol as an antipsychotic drug have been evaluated with density functional theory and time-dependent density functional theory (TDDFT) methods with the B3LYP hybrid functional and 6-311+G** basis set. Computational results verify that cis structure of clopenthixol is marked as an active drug. Cis structure of clopenthixol is more stable than the trans structure with a small energy difference. The nonlinear optical (NLO) properties and the chemical softness of the trans structure of clopenthixol are smaller than the cis structure, which displays that the chemical reactivity and charge transfer of the trans structure is lower than the cis structure. Charge transfer analysis of the two structures also verifies that the amount of charge transfer in the cis structure is higher than that in the trans structure. Electronic absorption spectra calculated using the TDDFT method shows that the cis structure of clopenthixol shows slightly better absorption properties than the trans structure, which is in agreement with the greater reactivity of the cis structure. The MEP maps and charge distribution analysis of both structures of clopenthixol show that there are preferred sites for electrophilic and nucleophilic reactivity in these structures. The infrared spectra of clopenthixol show that both structures of this molecule have similar modes of vibrations. The thermodynamic parameters show that, because of the enhancement of molecular vibrational intensities with temperature, all these quantities are increasing with increasing temperature. The medicinal properties of the cis structure of clopenthixol are almost confirmed with these quantum quantities. (author)