Photosensitized formation of peroxyl radicals in aqueous solutions of adenine at 77 K

Conditions for the formation of peroxyl radicals photosensitized by near-UV irradiation in frozen aqueous solutions of adenine containing 0.1 M NaCl (pH 4–7) are studied. Analysis of the EPR spectra shows that the systems under study contain two types of peroxyl radicals presumably classified earlier as O ₂ ^?· and HO _2· ^· . The effect of freezing methods on the production of the radicals is shown. The signal from O ₂ ^?· predominates in the spectra of samples with open surfaces and is likely due to the reduction of adsorbed O₂ molecules with photoejected electrons. The signal from HO ₂ ^· could be due to photoinduced interaction between the sensitizer and solvent. Possible mechanisms of these processes are considered.     

Effect of Na+ and Ca2+ ions on the photochemical formation of hydrogen peroxide in frozen aqueous solutions of adenine derivatives

Russian Journal of Physical Chemistry A - The content of hydrogen peroxide is determined in NaCl-containing (0.001–0.1 M) aqueous solutions of adenosine-5'-diphosphate (ADP) and adenosine...     

Effect of the Irradiation Conditions on the Yield of Hydrogen Peroxide in Frozen Aqueous Solutions of Adenine Derivatives

Russian Journal of Physical Chemistry A - Comparative results are presented from detecting hydrogen peroxide (H2O2) in aqueous solutions of adenine derivatives irradiated at 77 K in the near-UV...     

Photoinduced formation of hydrogen peroxide in aqueous solutions of adenine derivatives at 77 K

The amount of hydrogen peroxide in aqueous solutions of adenine (A), adenosine (Ado), cytidine (Cyt), and thymine (T) containing 0.1 M NaCl and irradiated with near-UV light at 77 K is determined. It is established by comparing the results to data obtained earlier that the amount of H₂O₂ detected in the defrosted samples following identical irradiation falls in the order Ado > adenosine-5′-diphosphate (ADP) > A >> Cyt. The formation of H₂O₂ was not detected for T. The formation of H₂O₂ in solutions of adenine derivatives was observed when the samples were irradiated with light having wavelengths in the ranges λ = 240–400 nm and 290–450 nm. The latter covers only the long wave absorption range of these compounds. It is shown that the change in the intensity of irradiation that strongly affected the intensity оf EPR signals of irradiated samples prior to defrosting affected the amount of detected H₂O₂ only slightly, and the effect was not unidirectional. The results from determining H₂O₂ in the samples of adenine derivatives are compared to estimates of the content of free peroxyl radicals, obtained by analyzing EPR spectra. Plausible mechanisms of the processes are discussed.     

Effect of Inorganic Phosphate on the Photoproduction of Hydrogen Peroxide in Frozen Aqueous Solutions of Adenine Derivatives

Russian Journal of Physical Chemistry A - The content of hydrogen peroxide in 2 × 10−4 M aqueous solutions of adenine (A), adenosine (Ado) and adenosine-5'-diphosphate (ADP)...     

Role of inorganic phosphate during electron transfer in the redox system NADH+flavin

We have used ³¹P NMR and EPR to study the effect of inorganic phosphate (P_i) on the process of electron transfer in oxidation of reduced nicotinamide adenine dinucleotide (NADH) by flavin in aqueous solutions. Observation of a significant (up to 40%) drop in the integrated intensity of the ³¹P NMR signal for the inorganic phosphate over the course of the reaction is interpreted as a manifestation of the effect of chemically induced polarization of the phosphorus nuclei during singlet-triplet conversion in charge-transfer complexes [NADH…P_i], and is evidence for a possible catalytic role for P_i in processes involving transfer of an electron (hydrogen atom) from NADH to appropriate acceptors. The results presented support the possibility of direct involvement of P_i in a chain of one-electron conversions in chemical systems. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 392–396, May–June, 2006.