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

Role of an Inorganic Phosphate in the Photogeneration of Hydrogen Peroxide in Aqueous Solutions of Adenine Derivatives at 77 K

“…Irradiation was performed with a DRSh-1000 high-pressure mercury lamp equipped with UFS-5 (standard value, 40% transmittance in the range of 260-400 nm) and FS-6 (standard value, 40% transmittance in the range of 290-470 nm) light filters. The intensity I hν of illumination was limited to ~ 0.6 of the maximum intensity of the irradiation source using meshes calibrated on a spectrophotometer as described in [3][4][5]. This was because the efficiency of the photoproduction of H 2 O 2 (α), defined as the ratio of the amount of formed peroxide [H 2 O 2 ] to Int S , is greatly reduced upon an increase in I hν [3,4].…”

“…The intensity I hν of illumination was limited to ~ 0.6 of the maximum intensity of the irradiation source using meshes calibrated on a spectrophotometer as described in [3][4][5]. This was because the efficiency of the photoproduction of H 2 O 2 (α), defined as the ratio of the amount of formed peroxide [H 2 O 2 ] to Int S , is greatly reduced upon an increase in I hν [3,4].…”

“…Samples were irradiated in a quartz Dewar flask at 77 K. The irradiation time was 16 min. The EPR spectra were recorded at 77 K on a Bruker EMX-8 EPR spectrometer, and in some cases on an EPR spectrometer made in our laboratory (frequency 9.5 GHz) and used in [1][2][3][4][5][6][7]. The power of microwave irradiation was W = 200 μW, and the amplitude of modulation was 2 G. The results obtained on different devices are given with allowance for the conversion to the corresponding parallel measurements in identical samples given in our earlier works.…”

“…It is known that under certain conditions of freezing aqueous solutions of adenine derivatives (AX, where X = H for adenine (A), X = ribose for adenosine (Ado), X = ribose-5'-diphosphate for adenosine-5'diphosphate (ADP)) with near-UV irradiation at 77 K, the fairly intense formation of hydrogen peroxide (H 2 O 2 ) occurs during the defrosting of the samples [1][2][3][4][5][6]. Irradiating solutions of thymine and derivatives of other nucleobases (guanosine-5'-monophosphate and cytidine were studied) under the same conditions does not result in the formation of H 2 O 2 [1,2].…”

“…This pathway increases the yield of H 2 O 2 with a drop in Int S of EPR signals and thus no appreciable release of peroxyl radicals into the environment. We assume this is closely related to the self-associative properties of AX [3][4][5][6]. A comparison of the results from determining the yield of H 2 O 2 in irradiated solutions after † Deceased.…”