A Combined Experimental and Density Functional Theory Computational Studies on Curcumin: A Bio-Active Ingredient of Rhizome Turmeric

摘要

In the present work, we have presented a combined experimental and Density Functional Theory (DFT) computational studies on curcumin molecule which is a bio-active ingredient of Rhizome turmeric to describe its molecular structure, complete vibrational spectra, electronic transition and thermal stability of the compound. We have characterized the titled molecule using the experimental techniques Fourier-transform infrared (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, and Thermogravimetric analysis (TGA). FTIR and UV-Vis spectra were recorded in the range of 400-4000 cm~(-1) with spectral resolution 1 cm~(-1) and 190-800 nm, respectively. Hartree Fock (HF) and Density functional theory (DFT) using 6-311G(d,p) basis set were used to get the optimized molecular geometry, atomic charges (Mulliken and NBO), harmonic vibrational frequencies, temperature dependence of thermodynamic properties, HOMO-LUMO and related molecular properties of curcumin. The calculated vibrational wavenumbers are in good agreement with the experimental results obtained using FTIR spectroscopy. The correlation between experimental and calculated scaled wavenumbers are in very good agreement with each other. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution (PED). The calculated Highest occupied molecular orbital (HOMO) and Lowest unoccupied molecular orbital (LUMO) energies show that charge transfer occurs within the molecule. The HOMO-LUMO study was extended to calculate molecular parameters like ionization potential, electron affinity, global hardness, electron chemical potential, electronegativity and global electrophilicity of the curcumin. UV-Vis spectrum of curcumin was calculated using time dependent density functional theory (TD-DFT) method and the results are compared with the experimental results.