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Keywords:

  • nicotinamide adenine dinucleotide;
  • photo-oxidation;
  • time-resolved Raman spectroscopy;
  • time-resolved absorption spectroscopy;
  • DFT/B3LYP calculation

Abstract

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 C[DOUBLE BOND]C symmetric stretch of the protonated pyridyl ring of the dihydronicotinamide moiety. It was shown that the C[DOUBLE BOND]C 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.