Formation of two centre three electron bond by hydroxyl radical induced reaction of thiocoumarin: evidence from experimental and theoretical studies.

Formation of two centre three electron bond by hydroxyl radical induced reaction of thiocoumarin: evidence from experimental and theoretical studies.
Free Radic Res. 2019 May 09;:1-271
Authors: Shinde RG, Khan AA, Barik A
Abstract
Radiation chemical studies of thioesculetin (1), a thioketone derivative of coumarin, were performed by both pulse radiolysis technique and DFT calculations. Hydroxyl (•OH) radical reaction with 1 resulted transients absorbing at 320, 360 and 500 nm. To identify the nature of the transients, the reaction was studied with specific one-electron oxidant (N3•) radical, where 360 nm band was absent. The transient absorption at 500 nm was concentration-dependent. The overall impression for •OH radical reaction was that the transient absorbing at 320, 360 and 500 nm was due to sulfur centred monomer radical, hydroxysulfuranyl and dimer radical of 1 respectively. The equilibrium constant between the monomer to dimer radical was 3.75 × 104 M-1. From the transients' redox nature, it was observed that 57 and 24% of •OH radical yielded to oxidizing and reducing products respectively. Further the product analysis by HPLC suggested that the dimer radical disproportionate to esculetin and thioesculetin. DFT energy calculation for all the possible transients revealed that dimer radical has the lowest energy. The HOMO of 1 and its monomer radical suggested that the electron density was localized on sulfur ato...

Source: Free Radical Research - May 12, 2019 Category: Research Tags: Free Radic Res Source Type: research