Hydrogen peroxide formation photoinduced by near-UV radiation in aqueous solutions of adenine derivatives at 77 K

Abstract

An estimate of the content of free radicals in aqueous solutions of adenosine (Ado), adenosine-5′diphosphate (ADP) and guanosine-5′-monophosphate (GMP) irradiated with near-UV radiation at 77 K is obtained by interpreting EPR spectra. It is established that in the presence of NaCl (0.1 M), the total number of peroxyl radicals and in samples of the studied compounds was 15-45% of the total quantity of produced free radicals and was affected by the conditions of exposure. The estimates are compared with the results from hydrogen peroxide (H 2 O 2 ) determination in the same samples after thawing. Although the number of peroxyl radicals in the samples of adenine derivatives (A) and GMP are comparable, the formation of H 2 O 2 is observed only in the case of A derivatives, but not in GMP. Possible reasons for these differences are discussed.

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.…”

“…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).…”

Photocatalyst Bi(OH)SO4 · H2O with High Photocatalytic Performance

“…The ESR spectra can help us to study the types and intensities of active radicals in the catalytic process and then to propose the mechanism of Bi(OH)SO4•H2O photocatalyst for the degradation of pollutants [44,45]. Fig.…”