Quinone methides (QM) are important reactive intermediates in synthetic chemistry and molecular biology, but little is known regarding the mechanism(s) for the generation of short-lived reactive QM intermediates from relevant precursors in aqueous solutions. In this study, several time-resolved spectroscopy methods were used to directly examine the photophysics and photochemical pathways of 1,1′-(2,2′-Dihydroxy-1,1′-binaphthyl-6,6′-diyl)bis(N,N,N-trimethylmethanaminium) bromide (BQMP-b) from initial photoexcitation to the formation of the key reactive binol quinone methide intermediate (BQM) in aqueous solution. The fluorescence of BQMP-b is effectively quenched with a small amount of water suggesting that a water-assisted excited state intramolecular proton transfer (ESIPT) process takes place. The kinetics isotope effects observed in femtosecond and nanosecond time-resolved transient absorption experiments provide evidence for the participation of water molecules in the BQMP-b singlet excited state ESIPT process and in the subsequent release of the –HNMe3+ group and ground state intramolecular proton transfer processes that lead to formation of the reactive BQM intermediate. Nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy was also used to study the structure and properties of several intermediates including the key reactive BQM in aqueous solution. Comparison of the ns-TR3 results to results from density functional theory calculations indicate that both the binol moiety and water molecules play important roles in the structure and properties of the key reactive BQM intermediate produced from BQMP-b. The results presented here also provide new benchmark characterization of bifunctional quinone methides intermediates that can be utilized to guide direct time-resolved spectroscopic investigation of the alkylation and interstrand cross-linking reactions of quinone methides with DNA in the future.

Insight into the role of water in the photogeneration and properties of bifunctional quinone methides: A time-resolved spectroscopic study of a binol quinone methide

253rd National Meeting (2017)

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