Primary photoreactions of phylloquinone (vitamin K1) and plastoquinone-1 in solution

Abstract

The photoreactions of electron transport quinones vitamin K1 (1) and plastoquinone-1 (2) were studied by picosecond pump-probe spectroscopy, nanosecond flash photolysis, step-scan FTIR spectroscopy, and by irradiation in glassy solvents at 77 K with optical and EPR detection. In polar solvents, charge transfer from the beta,gamma-double bond to the quinone moiety initiates intramolecular proton transfer from the side chain, k = 2.7 x 10(11) s-1, yielding 1,3-quinone methide diradicals, which establish a metastable equilibrium between the singlet and the triplet state. Subsequent proton transfer through the solvent forms 1,2-quinone methides. In apolar solvents the predominant primary photoreaction is formation of cyclic 'preoxetane' diradicals (kform > 3 x 10(11) s-1, kdecay approximately 1 x 10(9) s-1), which revert to a photostationary E/Z mixture of the starting materials, unless they are trapped by oxygen. The beta,gamma-double bond in the isoprenoid side chain thus provides two efficient deactivation processes, which prevent the intermolecular photoreactions commonly observed with the parent quinones. A combined mechanistic scheme rationalizes the known photoreactions of 1, 2 and related compounds in solution.

Conformational analysis of vitamin K1 model molecule: a theoretical study

“…Mechanism of action of vitamin K (see [7] and references therein, and [8][9][10][11]) and its photophysical and photobiological properties [12][13][14][15][16][17][18] have been studied extensively. Structure and vibrational spectra of the model molecule of both vitamin K 1 and K 2 having an allyl group instead of a phytyl side chain (designated further as model 1, see Fig.…”

Investigation of the photostability properties of memoquin, a quinone derivative for the treatment of Alzheimer's disease

“…Quinones are known to be photoreactive compounds, acting as cofactors in photosynthetic reaction centers of photo system II and I or as electron carriers through cell membranes [6,7]. The presence of side chains may change a quinone's photochemistry, as is the case with phylloquinones [8] and other similar quinones [9][10][11]. In memoquin's structure there are two long and symmetric polyamine side chains that might increase quinone stability and determine a protective effect against photoinduced reactions.…”

Quenching dynamics study on photoinduced excited triplet duroquinone by TEMPO in 1,2-propandiol

“…Some quinones, such as duroquinone (DQ) and ubiquionones (UQ), are widely distributed in biological systems and play important roles as redox carriers of various proteins and enzymes in biological processes, such as photosynthesis, oxidative phosphorylation, and mitochondrial electron transport [1,2]. Nevertheless, triplet excited states of quinines, formed by UV light irradiation or enzymatic X.…”