Molecular structure and vibrational spectra of Irinotecan: A density functional theoretical study

The solid phase FTIR and FT-Raman spectra of Irinotecan have been recorded in the regions 400–4000 and 50–4000 cm−1, respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(d) as basis set. The vibrational frequencies were calculated for Irinotecan by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared spectrum was also simulated from the calculated intensities. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations.

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► The FTIR and FT-Raman spectra of Irinotecan were recorded.
► The vibrational frequencies were calculated by DFT method and compared.
► HOMO–LUMO and MEP analysis were also made.