Direct Observation of Triplet State Mediated Decarboxylation of the Neutral and Anion Forms of Ketoprofen in Water-Rich, Acidic, and PBS Solutions

Abstract

The decarboxylation reaction of KP in different acetonitrile-water mixtures producing a carbanion or biradical intermediate is investigated by using femtosecond transient absorption and nanosecond time-resolved resonance Raman spectroscopies to unveil the mechanism of the photochemistry of KP. The irradiation of either the neutral or anion forms of KP leads to the excited singlet state KP species transforming into a corresponding triplet state KP species via a highly efficient intersystem crossing, and then, a triplet state mediated decarboxylation reaction occurs to generate a carbanion intermediate in the phosphate buffer solutions or a biradical species in the water-rich or acidic solutions examined here.

Phototriggered Release of a Leaving Group in Ketoprofen Derivatives via a Benzylic Carbanion Pathway, But not via a Biradical Pathway

“…[15] Because CH 3 CN is a relatively inert solvent, the intermediate of KP observed on the nanosecond time-scale in pure CH 3 CN has previously been assigned as a 3 KP on the basis of femtosecond transient absorption (fs-TA) and ns-TR 3 studies. [19] Thus, the first species of KP-OAc at 0 ns observed in pure CH 3 CN can readily be assigned to the 3 KP-OAc intermediate. At later delay times (180 ns), a very weak band appears at 1582 cm À1 , which can be attributed to the formation of a ketyl radical, possibly generated from intramolecular hydrogen abstraction on the side chain in KP-OAc.…”

“…In PB solution, with the dramatic decay of the band intensity at 523 nm, a new band appears around 600 nm that is assigned to the benzylic carbanion species. [12,19] Therefore, in PB solution, 3 KP-OAc cannot be observed in the ns-TR 3 experiment. The observation of the ISC process and 3 KP-OAc in higher water content solution, acidic aqueous solution, and PB solution by the fs-TA experiments suggests that the KP-OAc biradical and carbanion species are formed in the triplet state.…”

“…Fs-TA experiments: The fs-TA experiments were performed by using apparatus and methods discussed in detail previously. [19,26] The fs-TA measurements were performed based on a femtosecond Ti:Sapphire regenerative amplified Ti:sapphire laser system and an automated data acquisition system. At each temporal delay, data were averaged for 2 s. For the present experiments, the sample solution was excited by a 267 nm pump beam (the third harmonic of the fundamental 800 nm from the regenerative amplifier).…”

Dynamics of Oxygen-Independent Photocleavage of Blebbistatin as a One-Photon Blue or Two-Photon Near-Infrared Light-Gated Hydroxyl Radical Photocage

“…Femtosecond transient absorption (fs-TA) experiments. The fs-TA measurements were performed with an apparatus and methods detailed previously 35,36 and details are given in references 45 and 46. Very briefly, fs-TA spectra were obtained by employing the harmonic (400 nm light) for the pump pulse and white-light continuum (350800 nm light) for the probe pulse generated from the 800 nm output of a femtosecond regenerative amplified Ti:sapphire laser system For the measurements here, a solution of 40 mL was passed through a mm thick cell, excited by a 400 nm pump pulse and then interrogated by the white light continuum pulse.…”

“…The RR spectra given here were determined via subtraction of a solvent without sample spectrum from a corresponding RR spectrum of solvent with sample primarily to remove solvent bands. 35 C. Fluorometric analysis of ROS. All fluorescence experiments were acquired at ambient temperature with a Hitachi F-7000 fluorescence apparatus.…”