aDepartment of Physics, Lucknow University, Lucknow, 226007, India.
bMolecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India.
*Corresponding Author E-mail: neerajmisralu@rediffmail.com.
The combination of Quantum Mechanics (QM) and Molecular Mechanics (MM) methods has become an alternative tool for many applications for which pure QM and MM are not suitable. The QM/MM method has been used for different types of problems, for example: structural biology, surface phenomena, and liquid phase. In this paper we have used this method on the molecular structure of cinnamoyl shikonin. The equilibrium geometry, harmonic vibrational frequencies and infrared intensities were calculated by QM/MM method with B3LYP/6–31G(d,p) and universal force field combination (UFF) using ONIOM code. We found the geometry obtained by the QM/MM method to be very accurate, and we can use this rapid method in place of time consuming ab initio methods for large molecules. A detailed interpretation of the infrared spectra of cinnamoyl shikonin is reported in the present work. The scaled theoretical wave numbers are in perfect agreement with the experimental values. The FT-IR spectra of cinnamoyl shikonin in the region (4000-500) cm-1 was recorded in solid phase.
QM/MM method, FT-IR Spectra, Cinnamoyl shikonin
