title: Contrasting reactions of hydrated electron and formate radical with 2-thio analogues of cytosine and uracil.
abstract: 2-Thiocytosine (TC) and 2-thiouracil (TU) were subjected to hydrated electron (eaq-), formate radical (CO2˙-) and 2-hydroxypropan-2-yl radical ((CH3)2˙COH) reactions in aqueous medium. Transients were characterized by absorption spectroscopy and the experimental findings were rationalized by DFT calculations at LC-ωPBE and M06-2X levels using a 6-311+G(d,p) basis set and SMD solvation. In eaq-reactions, a ring N-atom protonated radical of TC and an exocyclic O-atom protonated radical of TU were observed via addition of eaq-and subsequent protonation by solvent molecules. However, two competing but simultaneous mechanisms are operative in CO2˙-reactions with TC and TU. The first one corresponds to formations of N(O)-atom protonated radicals (similar to eaq-reactions); the second mechanism led to 2 center-3 electron, sulfur-sulfur bonded neutral dimer radicals, TCdim˙ and TUdim˙. DFT calculations demonstrated that H-abstraction by CO2˙-from TC(TU) results in S-centered radical which upon combination with TC(TU) provide the dimer radical. In some cases, DFT energy profiles were further validated by CBS-QB3//M06-2X calculations. This is the first time report for a contradictory behavior in the mechanisms of eaq-and CO2˙-reactions with any pyrimidines or their thio analogues.
authors.affiliation: Department of Chemistry, Government Engineering College, Thrissur 680 009, India. prasanthkumarkp@gmail.com.
authors.forename: Kavanal P
authors.initials: KP
authors.lastname: Prasanthkumar
authors.affiliation: Departamento de Física y Química Teórica, Facultad de Química, Universidad Nacional Autónoma de México, México D. F., 04510, Mexico.
authors.forename: Juan R
authors.identifier: http://orcid.org/0000-0002-2901-5412
authors.initials: JR
authors.lastname: Alvarez-Idaboy
authors.affiliation: Radiation and Photochemistry Division, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400085, India. beenam@barc.gov.in.
authors.forename: Pavitra V
authors.initials: PV
authors.lastname: Kumar
authors.affiliation: Radiation and Photochemistry Division, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400085, India. beenam@barc.gov.in.
authors.forename: Beena G
authors.initials: BG
authors.lastname: Singh
authors.affiliation: Radiation and Photochemistry Division, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400085, India. beenam@barc.gov.in.
authors.forename: K Indira
authors.initials: KI
authors.lastname: Priyadarsini