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Publication Abstract from PubMed

It is theoretically plausible that thiazolium mesomerizes to congeners other than carbene in a low effective dielectric binding site; especially given the energetics and uneven electronegativity of carbene groups. However, such a phenomenon has never been reported. Nine crystal structures of transketolase obtained from Pichia stipitis (TKps) are reported with subatomic resolution, where thiazolium displays an extraordinary ring-bending effect. The bent thiazolium congeners correlate with non-Kekule diradicals because there is no gain or loss of electrons. In conjunction with biophysical and biochemical analyses, it is concluded that ring bending is a result of tautomerization of thiazolium with its non- Kekule diradicals, exclusively in the binding site of TKps. The chemophysical properties of these thiazolium mesomers may account for the great variety of reactivities carried out by thiamine-diphosphate-containing (ThDP) enzymes. The stability of ThDP in living systems can be regulated by the levels of substrates, and hydration and dehydration, as well as diradical-mediated oxidative degradation.

The Mesomeric Effect of Thiazolium on non-Kekule Diradicals in Pichia stipitis Transketolase.,Hsu NS, Wang YL, Lin KH, Chang CF, Lyu SY, Hsu LJ, Liu YC, Chang CY, Wu CJ, Li TL Angew Chem Int Ed Engl. 2018 Feb 12;57(7):1802-1807. doi: 10.1002/anie.201709799., Epub 2018 Jan 15. PMID:29243887^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.