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

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

“…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.…”

“…After recording the EPR spectra, the irradiated samples were stored for 24 h in liquid nitrogen (77 K) before the determination of H 2 O 2 . The determination of Н 2 О 2 was done via spectral iodometry [9], as in the works cited above [1][2][3][4][5][6]. Samples were defrosted at room temperature after photolysis, with each sample being placed in a separate 5-mL tube.…”

“…1, Tables 1 and 2). Possible means of the photoinduced formation of radicals were considered in [1,2,[5][6][7].…”

“…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]. It is therefore likely that among the derivatives of different nucleobases, AX can serve as the main photoinduced sources of H 2 O 2 formation.…”

“…(A high proportion of these peroxyl radicals in the total EPR signals photoinduced in our systems at 77 K was found in [7]). It is assumed that this pathway can apparently consist of the interaction between and radicals and the participation of water, possibly when defrosting the samples [1,2]. Pathway II is observed at low Int S of EPR signals (low AX concentrations, 2 × 10 −4 M), the absence of NaCl, limited intensity of irradiation (I hν ), and minimum excitation wavelength λ min (~260 to ~290 nm).…”