Computational study of solvation free energy, dipole moment, polarizability, hyperpolarizability and molecular properties of betulin, a constituent of corypha taliera (Roxb.)

Mohammad Firoz Khan, Ridwan Bin Rashid, Md. Aslam Hossain, Mohammad A. Rashid

Abstract


Ab initio calculations were carried out to studysolvation free energy, dipole moment, molecular
electrostatic potential (MESP), Mulliken charge distribution, polarizability, hyperpolarizability and different
molecular properties like global reactivity descriptors (chemical hardness, softness, chemical potential,
electronegativity, electrophilicity index) of betulin. B3LYP/6-31G(d,p) level of theory was used to optimize the
structure both in gas phase and in solution. The solvation free energy, dipole moment and molecular properties were
calculated by applying the Solvation Model on Density (SMD) in six solvent systems namely water, dimethyl
sulfoxide (DMSO), acetonitrile, n-octanol, chloroform and carbontetrachloride. The solvation free energy of betulin
increases with decreasing polarity of the solvent. No systematic trend of hyperpolarizability with solvent polarity is
found. Molecular electrostatic potential (MESP) and Mulliken population analysis (MPA) reveal that the most
possible sites for nucleophilic attack are C30, H76 and H77 and electrophilic attack are O1 and O2 among the atoms
in betulin. However, the dipole moment, polarizability, chemical potential, electronegativity and electrophilicity index
of betulin increase on going from non-polar to polar solvents. Chemical hardness was also increased with decreasing
polarity of the solvent and opposite relation was found in the case of softness. These results provide better
understanding of the stability and reactivity of betulin in different solvent systems.


Keywords


Betulin, Solvation free energy, Dipole moment, Polarizability, Solvation model.

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The Dhaka University Journal of Pharmaceutical Sciences
ISSN 1816-1820 (Print) 1816-1839 (Online)