Shiga Toxin and Shiga–Like Toxin (SLT) Time-Resolved Absorption and Resonance FT–IR and Raman Biospectroscopy and Density Functional Theory (DFT) Investigation of Vibronic–Mode Coupling Structure in Vibrational Spectra Analysis

Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, expressed by genes considered to be part of the genome of lambdoid prophages. The toxins are named after Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. Shiga–like toxin (SLT) is a historical term for similar or identical toxins produced by Escherichia coli [1-3]. The most common sources for Shiga toxin are the bacteria S. Dysenteriae and some serotypes of Escherichia coli (STEC), which includes serotypes O157:H7, and O104:H4. Parameters such as FT–IR and Raman vibrational wavelengths and intensities for single crystal Shiga Toxin and Shiga–Like Toxin (SLT) are calculated using density functional theory and were compared with empirical results. The investigation about vibrational spectrum of cycle dimers in crystal with carboxyl groups from each molecule of acid was shown that it leads to create Hydrogen bounds for adjacent molecules. The current study aimed to investigate the possibility of simulating the empirical values. Analysis of vibrational spectrum of Shiga Toxin and Shiga–Like Toxin (SLT) is performed based on theoretical simulation and FT–IR empirical spectrum and Raman empirical spectrum using density functional theory in levels of F/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 are separately investigated. The obtained values confirm high accuracy and validity of results obtained from calculations.