The effect of ultraviolet light (PRK-2) on pentoses in the presence of various minerals.
4.0 X 10(-2) M solutions (pH 5.8) of ribose, arabinose and xylose were irradiated in UV light (1.84 X 10(9) erg cm-2 to 6.12 X 10(9) erg cm-2) in the presence of 5 mg/ml of Al2O3, SiO2, TiO2, V2O5, Cr2O3, Fe2O3, CuO, ZnO, schist and feldspar oxides. The resulting substance had an absorption spectrum with lambda max 245 nm and lambda min 288 nm. In the presence of all the oxides except that of V2O5 lambda max shifted to 265-268 nm. When irradiation was carried out in an alkaline medium (pH 10.0-11.0) containing no oxides the absorption band showed lambda max 265 nm as well. The photolysis was followed by the oxidative breakdown of pentoses resulting in the formation of H2CO, carbonyl substances, organic peroxides and acids. The quantum yield (phi) during photolysis without sensitizers for ribose, arabinose and xylose respectivelywas: phi (H2CO) - 2.32 X 10(-3), 1.99 X 10(-3), 1.69 X 10(-3) and phi (C=O) -1.58 X 10(-3), 1.46 X 10(-3), 1.43 X 10(-3). By the ability to sensitize formation of oxydation products of pentoses, the oxides are arranged as follows: Fe2O3 > or = V2O5 > or = TiO2 > or = SiO2 > Cr2O3 > CuO > pentose > or = ZnO. By their effect on phi (-m) of pentoses the oxides make up the sequence: Fe2O3 > or = TiO2 > or = V2O5 > or = SiO2 > feldspar > schist > Al2O3 > Cr2O3 > pentose > ZnO. By the increase of phi (-m) pentoses are arranged in a row: ribose (6.4 X 10(-3) > arabinose (2.5 X 10(-3)) > xylose (2.1 X 10(-3)). Photolysis in various gases has shown that oxidative destruction of pentoses increases according to: air > N2 > Ar. The results show that in the prebiological period on Earth, and possibly even at present on some other planets, various minerals could produce a photosensitizing effect on the breakdown of pentoses synthesized abiogenically from formaldehyde. Ribose proved to be the least resistant to photolysis. This fact is of interest in relation to studying the chemical evolution of carbohydrates and their interaction with purine and pyrimidine bases.
Khenokh
M A
MA
Academy of Sciences, Moscow, USSR.
Nikolayeva
M V
MV
D001089:Arabinose / Q000737:chemistry / Q000528:radiation effects*; D019418:Evolution, Chemical; D008903:Minerals / Q000737:chemistry*; D010777:Photochemistry; D010782:Photolysis; D012266:Ribose / Q000737:chemistry / Q000528:radiation effects*; D013057:Spectrum Analysis; D014466:Ultraviolet Rays; D014994:Xylose / Q000737:chemistry / Q000528:radiation effects*
D008903:Minerals; D012266:Ribose; D014994:Xylose; D001089:Arabinose