Properties of the OH Adducts of Hydroxy-, Methyl-, Methoxy-, and Amino-Substituted Pyrimidines: Their Dehydration Reactions and End-Product Analysis

Reaction mechanism of the cation radicals of thymine and thymine derivatives in aqueous solution: A theoretical study

Mechanisms of decomposition reaction of thymine cation radicals (T[Formula: see text]), 1-methyl substituted T[Formula: see text] (1-MeT[Formula: see text]), and 1,3-dimethyl substituted T[Formula: see text] (1,3-Me2T[Formula: see text]) generated by ionizing radiation or one-electron oxidation to thymine, 1-methylthymine and 1,3-dimethylthymine in aqueous solution have been investigated by theoretical calculations. Seven reaction paths including H2O or OH[Formula: see text] addition, and deprotonation were considered. The most likely reaction for T[Formula: see text] decomposition is N1 deprotonation forming T(-N1H)[Formula: see text]. When N1 hydrogen is replaced by methyl, T[Formula: see text] would deprotonate from C5 methyl group generating 1-methyl substituted UCH[Formula: see text] in neutral solution, and reaction with OH[Formula: see text] producing 1-methyl substituted T6OH[Formula: see text] in basic solution. When N1 and N3 hydrogens are both replaced by methyl, T[Formula: see text] decomposition reaction is similar to 1-MeT[Formula: see text], indicating that N3 hydrogen barely influences the subsequent reaction of 1-MeT[Formula: see text]. These results can provide theoretical support for experimental observations.

Hydroxyl radical induced oxidation of theophylline in water: a kinetic and mechanistic study

Oxidative destruction and mineralization of emerging organic pollutants by hydroxyl radicals (˙OH) is a well established area of research. The possibility of generating hazardous by-products in the case of ˙OH reaction demands extensive investigations on the degradation mechanism. A combination of pulse radiolysis and steady state photolysis (H2O2/UV photolysis) followed by high resolution mass spectrometric (HRMS) analysis have been employed to explicate the kinetic and mechanistic features of the destruction of theophylline, a model pharmaceutical compound and an identified pollutant, by ˙OH in the present study. The oxidative destruction of this molecule, for intermediate product studies, was initially achieved by H2O2/UV photolysis. The transient absorption spectrum corresponding to the reaction of ˙OH with theophylline at pH 6, primarily caused by the generation of (T8-OH)˙, was characterised by an absorption band at 330 nm (k2 = (8.22 ± 0.03) × 10(9) dm(3) mol(-1) s(-1)). A significantly different spectrum (λmax: 340 nm) was observed at highly alkaline pH (10.2) due to the deprotonation of this radical (pKa∼ 10.0). Specific one electron oxidants such as sulphate radical anions (SO4˙(-)) and azide radicals (N3˙) produce the deprotonated form (T(-H)˙) of the radical cation (T˙(+)) of theophylline (pKa 3.1) with k2 values of (7.51 ± 0.04) × 10(9) dm(3) mol(-1) s(-1) and (7.61 ± 0.02) × 10(9) dm(3) mol(-1) s(-1) respectively. Conversely, oxide radicals (O˙(-)) react with theophylline via a hydrogen abstraction protocol with a rather slow k2 value of (1.95 ± 0.02) × 10(9) dm(3) mol(-1) s(-1). The transient spectral studies were complemented by the end product profile acquired by HRMS analysis. Various transformation products of theophylline induced by ˙OH were identified by this technique which include derivatives of uric acids (i, iv & v) and xanthines (ii, iii & vi). Further breakdown of the early formed product due to ˙OH attack leads to ring opened compounds (ix-xiv). The kinetic and mechanistic data furnished in the present study serve as a basic frame work for the construction of ˙OH induced water treatment systems as well as to understand the biological implications of compounds of this kind.

Theoretical study of the reaction of hydroxyl radicals with uridine: the influence of ribose and solvent

The reaction of ˙OH with uridine has been investigated. The influence of ribose and the solvent effect are presented.