Investigation of the FMOs, Global, and Local Reactivity Descriptors of caffeine based on Density Functional theory

Caffeine (۱,۳,۷-trimethylxanthine) is one of the most commonly consumed dietary ingredients in the world. In the present work, extensive quantum chemical calculations were carried out on caffeine in gas phase and in different solvents, in order to get the insights of its structural, and electronical properties such as (EL-EH) energy gap, global chemical reactivity descriptors, dipole moment, Mulliken population analysis, and Molecular Electrostatic Potential (MEP). The solvent effects have been studied in three different polarity mediums by Using Density Functional Theory (DFT) calculations at the B۳LYP/۶-۳۱++G (d, p) level of theory in the combination with the Polarizable Continuum Model (PCM). The whole theoretical calculations were achieved via using the Gaussian ۰۹ software. The chemical reactivity and stability properties of the investigated molecule was evaluated through global chemical reactivity descriptors using Frontier Molecular Orbitals (FMOs) energies gap; revealing the stability order of the caffeine as gas phase (۵.۱۴۲ eV) > acetone (۵.۰۸۷ eV) > DMSO (۵.۰۸۰ eV) > benzene (۵.۰۶۷ eV). In Mulliken Population Analysis (MPA), atomic charge distribution of the caffeine compound is studied for better understanding of molecular characteristics. Local descriptors such as Fukui Functions (FFs) have been used for determining the active site for this compound. The Molecular Electrostatic Potential (MEP) for a compound has been determined to check their electrophilic and nucleophilic reactivity sites. The thermodynamic parameters were computed in various temperatures and show that with rising temperatures all values were increased. In conclusion, theoretical calculation of quantum chemical parameters has been done for the caffeine compound to deeper understanding of the optimized structure and electronic properties for physical chemistry and biological physics interest.