Microcystin-LR Time-resolved Absorption and Resonance FT-IR and Raman Biospectroscopy and Density Functional Theory Investigation of Vibronic-mode Coupling Structure in Vibrational Spectra Analysis

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria. It is the most toxic of the microcystins. Parameters such as FT-IR and Raman vibrational wavelengths and intensities for single crystal MC-LR are calculated using density functional theory and were compared with empirical results. The investigation about the vibrational spectrum of cycle dimers in crystal with carboxyl groups from each molecule of acid was shown that it led to create hydrogen bonds for adjacent molecules. The current study aimed to investigate the possibility of simulating the empirical values. Analysis of the vibrational spectrum of MC-LR was performed based on theoretical simulation and FT-IR empirical spectrum and Raman empirical spectrum using density functional theory in levels of HF/6–31G*, HF/6–31++G**, MP2/6–31G, MP2/6–31++G**, BLYP/6–31G, BLYP/6–31++G**, B3LYP/6–31G and B3LYP6–31–HEG**. Vibration modes of methylene, carboxyl acid, and phenyl cycle were separately investigated. The obtained values confirmed high accuracy and validity of results obtained from calculations.