Time‐resolved resonance Raman, time‐resolved UV–visible absorption and DFT calculation study on photo‐oxidation of the reduced form of nicotinamide adenine dinucleotide

Photochemical reaction of the reduced form of nicotinamide adenine dinucleotide (NADH) was studied in aqueous solutions using nanosecond time‐resolved resonance Raman and UV–visible absorption spectroscopies combined with DFT/B3LYP calculations. Four transients were detected. A transient exhibiting absorption bands at 370 and 560 nm was assigned to the cation radical NADH +• . A transient having an absorption band at 394 nm was assigned to the deprotonated neutral radical NAD • . A transient exhibiting an absorption band at 493 nm was considered to be attributable to the anion radical NADH −• . The broad and strong band at about 700 nm was assigned to hydrated electrons. It was concluded that the photo‐oxidation of NADH to NAD + proceeded stepwise via NADH +• and NAD • . The Raman band at 1627 cm −1 of NADH +• was assigned to the CC symmetric stretch of the protonated pyridyl ring of the dihydronicotinamide moiety. It was shown that the CC symmetric stretch of the protonated pyridyl ring exhibited a low‐wavenumber shift from 1688 cm −1 to 1627 cm −1 on going from the ground state to NADH +• . This implies that the protonated pyridyl ring is weakened considerably on ionization in good accord with the DFT calculations. Copyright © 2006 John Wiley & Sons, Ltd.