DFT Study on 4(5)-Imidazole-carbaldehyde-N(5)- phenylthiosemicarbazone (ImTPh): NMR Shielding Tensors, Thermodynamic Parameters, NBO Analysis, Molecular Electrostatic Potential (MEP), HOMO and LUMO Studies

The density functional theory (DFT) calculations at the level of B3LYP/6-31G was carried out on the structure 4(5)-Imidazole-carbaldehyde-N(5)-phenylthiosemicarbazone (ImTPh) in gas phase using Gaussian 03. Dipole moment (Debye), energy of structure formation (HF; kcal/mol) and point group, NMR parameters such as isotropic shielding (σiso) and anisotropic shielding (σaniso), σ11, σ22 and σ33 obtained. Also thermodynamic properties and natural bond orbitals (NBO) were calculated. Besides, the frontier molecular orbital (FMO) analysis and the molecular electrostatic potential (MEP) of the compound were investigated by theoretical calculations. key words: DFT; ImTPh; NMR parameter; Thermodynamic parameter; NBO; FMO; MEP. such as antifungal and anti-bacterial activity1, anti inflammatory activity and analgesic activity2, antitubercular activity3, anti depressant activity, anti cancer activity4, antiviral activity5 and antileishmanial activity. Due to their antifungal properties imidazolederived compounds have been used in agriculture as effective ingredients for controlling plants pests. Imidazole derivatives are employed in the control of spoilage microorganisms or organisms potentially harmful to man, in the protection of wood against fungi and also in food storage6. Thiosemicarbazones7,8 and hydrazones9 are reported as compounds which 346 SHEIkHI et al., Orient. J. Chem., Vol. 30(1), 345-350 (2014) present significant antifungal activity. The imidazolederived thiosemicarbazones were prepared by reacting of 4(5)-imidazole-carboxaldehyde, 4-(1Himidazole-1-yl)-benzaldehyde or 4-(1H-imidazole-1yl)acetophenone with the suitable thiosemicarbazide using methanol as solvent10. In the present work we carried out theoretical calculations on one of the imidazole-derived thiosemicarbazones, that is named 4(5)-Imidazole-carbaldehyde-N(5)phenylthiosemicarbazone (ImTPh). Theoretical calculations We have carried out quantum theoretical calculations of ImTPh using DFT (B3LYP) method with 6-31G basis set by the Gaussian 03 program11. We calculated 1H and 13C NMR chemical shifts of ImTPh using B3LYP/6-31G level within GIAO approach. Moreover was studied thermodynamic parameters of ImTPh using methods listed, and obtained the energy (DE), enthalpies (DH), Gibbs free energy (DG), entropies (S) and constant volume molar heat capacity (Cv) of derivatives 12. Some electronic properties such as energy of the highest occupied molecular orbital (EHOMO), energy of the lowest unoccupied molecular orbital (ELUMO), energy gap (Eg; D) between LUMO and HOMO, atomic charges, dipole moment (μ) and Point group were determined. The optimized molecular structures, HOMO and LUMO surfaces were visualized using GaussView 03 program13. We also studied electronic structures of ImTPh using Natural Bond Orbital (NBO) analysis using level of B3LYP/6-31G. The main listing of NBOs, displaying the form and occupancy of the complete set of NBOs that span the input AO space and for each orbital gives the type of orbital and the occupancy14.