Theoretical study of solvent effect on NMR shielding tensors of luciferin derivatives

Luciferins as the substrates of protein enzyme luciferase are oxidised in the presence of the enzyme luciferase to produce oxyluciferin and energy in the form of light. The solvent effect in biological media and interactions between solvents and luciferin are major points to explain bioluminescence reaction. In this study, we have focussed on the Hartree-Fock calculations of solvent-induced effects on the structural changes of keto and enolate and twisted intra-molecular charge transfer forms of oxyluciferin in different solvent media including water, dimethyl sulphoxide, acetonitryl, ethanol, aniline and cyclohexane using 6-311++G** basis set considering Onsager continuum solvation model, frequency analysis and nuclear magnetic resonance shielding calculation with gauge-included atomic orbital method. The polarity of the environment imposed a significant effect on the relative atomic charge distribution on the selected atoms of luciferin and its derivatives. So, this fact motivated us to report the changes of the relative CHELP - charges from electrostatic potentials - atomic charges of each luciferin derivatives. Among different employed solvents, water as a protic solvent could be suggested as the most suitable solvent. All solvents had no effect on the geometry conformation of luciferin; however, the results have shown that the case of keto luciferin was obviously different and ethanol could affect more the keto luciferin form. This investigation has given useful information about the improved potential activity of luciferin derivatives and its dependence on the environment that are known as the remarkable factors in colour shift.