Experimental and DFT studies on 2′,4′-dihydroxychalcone, a product isolated from Zuccagnia punctata Cav. (Fabaceae) medicinal plant

Abstract

Here, 2′,4′-dihydroxychalcone (DHC) has been isolated from Zuccagnia punctata Cav. (Fabaceae) medicinal plant and, after that, the FT-IR, UV?Visible, 1H and 13C NMR spectroscopies were combined with the hybrid B3LYP/6?311++G** method to characterize this species. Structural, electronic, topological and vibrational properties of two conformers of DHC in gas phase and in aqueous and in ethanol solutions at the same level of theory were investigated. The most stable C2 conformer of DHC shows an intra-molecular O?H⋯O bond, as observed in the experimental structure reported for DHC by using X-ray diffraction. Force fields for both conformers of DHC in the three media at the same level of theory and their complete vibrational assignments of expected 84 vibration modes are reported for first time. The calculations predicted in the IR spectrum of C2 notable shifting of O?H and C[dbnd]O stretching modes due to intra-molecular H bonds formed. Corrected solvation energy of C1 in water and ethanol are respectively of −101.86 and −94.93 kJ/mol while the values for C2 decrease to −81.06 and −75.85 kJ/mol, respectively. Hence, both forms clearly evidence the higher solubility of DHC in water. The evaluation of molecular electrostatic potentials (MEP) surfaces have suggested that nucleophilic and electrophilic sites of higher reactivity in C1 and C2 of DHC are strongly located on the C[dbnd]O and OH groups while the frontier orbital studies reveal that DHC in the three media are most reactive than other species isolated from plants. The two forms of DHC could be present in solid phase and in solutions, as supported by two bands observed in the UV?Visible spectra of DHC in methanol solution.