Ultrafast Time Resolved Spectroscopic Studies on the Generation of the Ketyl-Sugar Biradical by Intramolecular Hydrogen Abstraction among Ketoprofen and Purine Nucleoside Dyads

Abstract

Intramolecular hydrogen abstraction reactions among ketoprofen (KP) and purine nucleoside dyads have been proposed to form ketyl-sugar biradical intermediates in acetonitrile. Femtosecond transient absorption studies on KP and purine nucleoside dyads reveal that the triplet state of the KP moiety of the dyads with cisoid structure decay faster (due to an intramolecular hydrogen abstraction reaction to produce a ketyl-sugar biradical intermediate) than the triplet state of the KP moiety of the dyads with transoid structure detected in acetonitrile solvent. For the cisoid 5-KP-dG dyad, the triplet state of the KP moiety decays too fast to be observed by ns-TR(3); only the ketyl-sugar biradical intermediates are detected by ns-TR(3) in acetonitrile. For the cisoid 5-KP-dA dyad, the triplet states of the KP moiety could be observed at early nanosecond delay times, and then it quickly undergoes intramolecular hydrogen abstraction to produce a ketyl-sugar biradical intermediate. For the cisoid 5-KPGly-dA and transoid 3-KP-dA dyads, the triplet state of the KP moiety had a longer lifetime due to the long distance chain between the KP moiety and the purine nucleoside (5-KPGly-dA) and the transoid structure (3-KP-dA). The experimental and computational results suggest that the ketyl-sugar biradical intermediate is generated with a higher efficiency for the cisoid dyad. However, the transoid dyad exhibits similar photochemistry behavior as the KP molecule, and no ketyl-sugar biradical intermediate was observed in the ns-TR(3) experiments for the transoid 3-KP-dA dyad.

One‐Step Photochemical Green Synthesis of Water‐Dispersible Ag, Au, and Au@Ag Core–Shell Nanoparticles

“…These results suggest that the triplet state of the BP moiety decays too fast (<50 ns) to be observed with nanosecond laser flash photolysis, due to the very efficient H‐abstraction process. This hypothesis is well supported by a recent work on BP–nucleoside dyads exhibiting a triplet decay in about 1.6 ns, due to fast intramolecular H‐abstraction from the nearby sugar moiety . Notably, in the case of BP encapsulated in SDS micelles, the H‐abstraction process occurred on a time scale about two order of magnitude slower and, as a consequence, 1,4‐cyclohexadiene needed to be added to make the process faster to avoid the triplet quenching by the metal ions .…”

“…This hypothesis is well supported by ar ecent work on BP-nucleoside dyads exhibiting at riplet decay in about 1.6ns, due to fast intramolecular H-abstraction from the nearbysugar moiety. [22] Notably,int he case of BP encapsulated in SDS micelles,t he H-abstraction processo ccurred on at ime scale about two order of magnitude slower and, as ac onsequence, 1,4-cyclohexadienen eededt ob ea dded to make the process faster to avoid the triplet quenching by the metal ions. [12] Therefore, the fast photogeneration of the reducing ketyl radicals observedi no ur case represents the ideal conditions fort he photocontrolled formation of metal NPs without the need of externaladditives.…”

Singlet versus Triplet Excited State Mediated Photoinduced Dehalogenation Reactions of Itraconazole in Acetonitrile and Aqueous Solutions

“…The femtosecond transient absorption (fs-TA) experiments were done with a femtosecond Ti:sapphire regenerative amplifier laser and a transient absorption spectrometer. , For the present experiments, part of these fundamental 800 nm pulses (approximately 95%) were employed to pump a third harmonic generator to obtain the laser of 267 nm, used as the pump pulse, whereas the probe was obtained by utilizing the remaining 5% 800 nm light to produce a white-light continuum (330–700 nm) with a one-dimensional moveable CaF 2 crystal. A flow cell with a 2 mm optical path length was used to hinder the build-up of photoproducts.…”