01987nas a2200193   4500008004100000022001400041245008500055210006900140260000800209300001400217490000800231520133800239100002301577700001901600700002201619700001901641700001801660856011501678       2021                        eng d  a1520-610600aCurious case of aqueous warfarin: structural isomers or distinct excited states?0 aCurious case of aqueous warfarin structural isomers or distinct   cMAR  a2871-28780 v1253 a<p>Warfarin is a potent anti-coagulant drug and is on the World Health Organization's List of Essential Medicines. Additionally, it displays fluorescence enhancement upon binding to human serum albumin, making warfarin a prototype fluorescent probe in biology. Despite its biological significance, the current structural assignment of warfarin in aqueous solution is based on indirect evidence in organic solvents. Warfarin is known to exist in different isomeric forms-open-chain, hemiketal, and anionic forms-based on the solvent and pH. Moreover, warfarin displays a dual absorption feature in several solvents, which has been employed to study the ring-chain isomerism between its open-chain and hemiketal isomers. In this study, our pH-dependent experiments on warfarin and structurally constrained warfarin derivatives in aqueous solution demonstrate that the structural assignment of warfarin solely on the basis of its absorption spectrum is erroneous. Using a combination of steady-state and time-resolved spectroscopic experiments, along with quantum chemical calculations, we assign the observed dual absorption to two distinct pi -&gt;pi* transitions in the 4-hydroxycoumarin moiety of warfarin. Furthermore, we unambiguously identify the isomeric form of warfarin that binds to human serum albumin in aqueous buffer.</p>1 aSakpal, Sushil, S.1 aGhosh, Deborin1 aManae, Meghna, A.1 aHazra, Anirban1 aBagchi, Sayan  uhttps://library.ncl.res.in/content/curious-case-aqueous-warfarin-structural-isomers-or-distinct-excited-states