Substrate and intensity dependent photoenhanced transamination reactions of pyridoxal 5′-phosphate in solution

The proposed mechanisms underlying the photoenhanced transamination of pyridoxal-5′-phosphate (PLP) Schiff bases in solution were explored via substrate dependent photoactivity and ultrafast transient absorption spectroscopy. The observed substrate-independent transamination activity under incident blue-light with a linear power-dependent up to 1 W is indicative of a single-photon enhancement mechanism, in contrast to a previously proposed multi-transition ‘triplet photoacid’ model. Significant differences in the relative phototransamination efficiencies for different PLP-substrates Schiff bases were argued to originate from slower (>10 ns) triplet-state photochemistry including excite-state proton transfer and back intersystem crossing dynamics back to the singlet manifold.