Photochemistry of Potassium Ferrocyanide and its Reaction with Uridine 5′-monophosphate in Aqueous Solution under Ultraviolet Irradiation

The photochemical reaction of potassium ferrocyanide (K _4 Fe(CN) _6 ) exhibits excitation wavelength dependence and non-Kasha rule behavior. In this study, the excited-state dynamics of K _4 Fe(CN) _6 were studied by transient absorption spectroscopy. Excited state electron detachment (ESED) and photoaquation reactions were clarified by comparing the results of 260, 320, 340, and 350 nm excitations. ESED is the path to generate a hydrated electron (e _\rmaq^- ). ESED energy barrier varies with the excited state, and it occurs even at the first singlet excited state ( ^1 T _\rm1g ). The ^1 T _\rm1g state shows \sim 0.2 ps lifetime and converts into triplet Fe(CN) _6 ^4- by intersystem crossing. Subsequently, ^3 Fe(CN) _5 ^3- appears after one CN ^- ligand is ejected. In sequence, H _2 O attacks Fe(CN) _5 ^3- to generate Fe(CN) _5 H _2 O ^3- with a time constant of approximately 20 ps. The ^1 T _\rm1g state and e _\rmaq^- exhibit strong reducing power. The addition of uridine 5 ' -monophosphate (UMP) to the K _4 Fe(CN) _6 solution decrease the yield of e _\rmaq^- and reduce the lifetimes of the e _\rmaq^- and ^1 T _\rm1g state. The obtained reaction rate constant of ^1 T _\rm1g state and UMP is 1.7 \times 10 ^14 (mol/L) ^-1\cdot s ^-1 , and the e _\rmaq^- attachment to UMP is \sim 8 \times 10 ^9 (mol/L) ^-1\cdot s ^-1 . Our results indicate that the reductive damage of K _4 Fe(CN) _6 solution to nucleic acids under ultraviolet irradiation cannot be neglected.