Towards Reliable Modeling of S-Nitrosothiol Chemistry: Explicitly-Correlated Coupled Cluster and DFT Studies
Date of Award
Master of Science (MS)
In this work, we apply recently proposed explicitly-correlated coupled cluster methods, CCSD(T)-F12x, as well as density functional theory methods, to study the acid-base properties of HSNO molecule in gas phase. Used in this work approach theoretical efficiently alleviates excessive computational cost of the traditional ab initio methods, used in computational chemistry, with identical level of accuracy. Our high-level reference calculations show that protonation of HSNO molecule will most readily occur at the S atom (with energy release ~ 17 kcal/mol), compared to N atom (energy release ~ 5 kcal/mol) or O atom (energy release ~ 7 kcal/mol). S-N bond in HSNO elongates by 0.572 Å and weakens by 11.1 kcal/mol upon protonation at the S at-om, gaining noticeable anharmonic character. Deprotonation of HSNO is thermodynami-cally unfavorable, with energy loss ~ 170 kcal/mol, accompanied with S-N bond shorten-ing by 0.149 Å. Based on generated in this work the reference values, we tested and ranked the performance of total 45 different DFT functionals of various families and rungs of the DFT "Jacob's ladder", applied to HSNO in neutral or protonated and deprotonated forms. Best performing functionals are identified for the future computational studies of the bio-logically relevant reactions involving S-nitrosothiols.