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At least 19 recordsLinked to original sources
PubMed1968

2-deoxyribose gene-enzyme complex in Salmonella typhimurium. I. Isolation and enzymatic characterization of 2-deoxyribose-negative mutants.

Salmonella typhimurium was found to utilize 2-deoxyribose as a sole carbon and energy source. Cells grown in the presence of deoxyribose contained increased levels of deoxyribose kinase, thymidine phosphorylase, and two forms of deoxyribose-5-phosphate aldolase (DR5P aldolase). One form of DR5P aldolase was induced by deoxyribose and coordinately regulated with deoxyribose kinase. The second form of DR5P aldolase was induced by deoxyribose-5-phosphate and coordinately regulated with thymidine phosphorylase. Mutants unable to ferment deoxyribose have been isolated and shown to be lacking either deoxyribose kinase or deoxyribose permease, but none has been found from which DR5P aldolase is missing. Thymine-requiring mutants which are able to grow on low levels of thymine have been isolated and shown, in some cases, to be lacking one or both DR5P aldolases.

Aldehyde-Lyases↗
PubMed2000

The iron chelator pyridoxal isonicotinoyl hydrazone (PIH) and its analogues prevent damage to 2-deoxyribose mediated by ferric iron plus ascorbate.

Iron chelating agents are essential for treating iron overload in diseases such as beta-thalassemia and are potentially useful for therapy in non-iron overload conditions, including free radical mediated tissue injury. Deferoxamine (DFO), the only drug available for iron chelation therapy, has a number of disadvantages (e.g., lack of intestinal absorption and high cost). The tridentate chelator pyridoxal isonicotinoyl hydrazone (PIH) has high iron chelation efficacy in vitro and in vivo with high selectivity and affinity for iron. It is relatively non-toxic, economical to synthesize and orally effective. We previously demonstrated that submillimolar levels of PIH and some of its analogues inhibit lipid peroxidation, ascorbate oxidation, 2-deoxyribose degradation, plasmid DNA strand breaks and 5,5-dimethylpyrroline-N-oxide (DMPO) hydroxylation mediated by either Fe(II) plus H(2)O(2) or Fe(III)-EDTA plus ascorbate. To further characterize the mechanism of PIH action, we studied the effects of PIH and some of its analogues on the degradation of 2-deoxyribose induced by Fe(III)-EDTA plus ascorbate. Compared with hydroxyl radical scavengers (DMSO, salicylate and mannitol), PIH was about two orders of magnitude more active in protecting 2-deoxyribose from degradation, which was comparable with some of its analogues and DFO. Competition experiments using two different concentrations of 2-deoxyribose (15 vs. 1.5 mM) revealed that hydroxyl radical scavengers (at 20 or 60 mM) were significantly less effective in preventing degradation of 2-deoxyribose at 15 mM than 2-deoxyribose at 1.5 mM. In contrast, 400 microM PIH was equally effective in preventing degradation of both 15 mM and 1.5 mM 2-deoxyribose. At a fixed Fe(III) concentration, increasing the concentration of ligands (either EDTA or NTA) caused a significant reduction in the protective effect of PIH towards 2-deoxyribose degradation. We also observed that PIH and DFO prevent 2-deoxyribose degradation induced by hypoxanthine, xanthine oxidase and Fe(III)-EDTA. The efficacy of PIH or DFO was inversely related to the EDTA concentration. Taken together, these results indicate that PIH (and its analogues) works by a mechanism different than the hydroxyl radical scavengers. It is likely that PIH removes Fe(III) from the chelates (either Fe(III)-EDTA or Fe(III)-NTA) and forms a Fe(III)-PIH(2) complex that does not catalyze oxyradical formation.

Ascorbic Acid↗
PubMed2003

Thymidine phosphorylase and 2-deoxyribose stimulate human endothelial cell migration by specific activation of the integrins alpha 5 beta 1 and alpha V beta 3.

Thymidine phosphorylase is an angiogenic factor that is frequently overexpressed in solid tumors, in rheumatoid arthritis, and in response to inflammatory cytokines. Our previous studies showed that cells expressing thymidine phosphorylase stimulated endothelial cell migration in vitro. This was a consequence of the intracellular metabolism of thymidine by thymidine phosphorylase and subsequent extracellular release of 2-deoxyribose. The mechanisms by which 2-deoxyribose might mediate thymidine phosphorylase-induced cell migration in vitro, however, are obscure. Here we show that both thymidine phosphorylase and 2-deoxyribose stimulated the formation of focal adhesions and the tyrosine 397 phosphorylation of focal adhesion kinase in human umbilical vein endothelial cells. Although similar actions occurred upon treatment with the angiogenic factor vascular endothelial growth factor (VEGF), thymidine phosphorylase differed from VEGF in that its effect on endothelial cell migration was blocked by antibodies to either integrin alpha 5 beta 1 or alpha v beta 3, whereas VEGF-induced endothelial cell migration was only blocked by the alpha v beta 3 antibody. Further, thymidine phosphorylase and 2-deoxyribose, but not VEGF, increased the association of both focal adhesion kinase and the focal adhesion-associated protein vinculin with integrin alpha 5 beta 1 and, in intact cells, increased the co-localization of focal adhesion kinase with alpha 5 beta 1. Thymidine phosphorylase and 2-deoxyribose-induced focal adhesion kinase phosphorylation was blocked by the antibodies to alpha 5 beta 1 and alpha v beta 3, directly linking the migration and signaling components of thymidine phosphorylase and 2-deoxyribose action. Cell surface expression of alpha 5 beta 1 was also increased by thymidine phosphorylase and 2-deoxyribose. These experiments are the first to demonstrate a direct effect of thymidine phosphorylase and 2-deoxyribose on signaling pathways associated with endothelial cell migration.

Antibodies↗
PubMed1984

Deoxyribose 1-phosphate: radioenzymatic and spectrophotometric assays.

A method has been developed to measure deoxyribose 1-phosphate in the presence of ribose 1-phosphate and other sugar phosphates. The specificity of the method is based on the observation that only deoxyribose 1-phosphate is hydrolyzed by heating at pH 7.4, while both deoxyribose 1-phosphate and ribose 1-phosphate remain unchanged when heated at pH 10. A tissue extract is heated at pH 10. The amount of deoxyribose 1-phosphate plus ribose 1-phosphate is determined from that of deoxyinosine plus inosine formed in a coupled enzymatic reaction, based on the following two-stage transformation: deoxyribose 1-phosphate (ribose 1-phosphate) + adenine in equilibrium deoxyadenosine (adenosine) + inorganic phosphate, catalyzed by adenosine phosphorylase; deoxyadenosine (adenosine) + H2O----deoxyinosine (inosine), catalyzed by adenosine deaminase. By taking advantage of its unique heat lability, deoxyribose 1-phosphate is eliminated by heating the tissue extract at pH 7.4, and ribose 1-phosphate is determined as above. The amount of deoxyribose 1-phosphate stems from the difference between the amount of deoxyinosine plus inosine measured in the tissue extract heated at pH 10 and that of inosine measured in the tissue extract heated at pH 7.4. Free deoxyribose 1-phosphate has been found in rat tissues, as well as in Bacillus cereus during stationary phase of growth.

Animals↗
PubMed1990

The influence of pH on OH. scavenger inhibition of damage to deoxyribose by Fenton reaction.

Hydroxyl radicals (OH.) can be formed in aqueous solution by direct reaction of hydrogen peroxide (H2O2) with ferrous salt (Fenton reaction). OH. damage to deoxyribose, measured as formation of thiobarbituric acid-reactive material, was evaluated at different pHs to study the mechanism of action of classical OH. scavengers. OH. scavenger effect on Fe2+ oxidation was also evaluated in the same experimental conditions. In the absence of OH. scavengers, OH. damage to deoxyribose is higher at acidic compared to neutral and moderately basic pH. At acidic pH deoxiribose is per se able to inhibit Fe2+ oxidation by H2O2. Most of OH. scavengers tested inhibit deoxyribose damage and Fe2+ oxidation in a similar manner: both inhibitions are most relevant at acidic pH and decrease by increasing the pH. These results are not due to OH. scavenger inhibition of Fenton reaction. The influence of pH on the parameters studied appears to be due to the competition of deoxyribose and OH. scavengers for iron. These results suggest the prominent role of iron binding in the degradation of deoxyribose and in the OH. scavenging ability of different compounds. Results obtained with triethylenetetramine, a iron chelator with a low rate constant with OH., confirm that both deoxyribose and the OH. scavengers interact with iron bringing about a site specific Fenton reaction; that the OH. formed at these sites oxidize these molecules to their radical forms which in turn reduce the Fe3+ produced by Fenton reaction. The results presented indicate that most of classical OH. scavengers exert their effect predominantly by preventing the site specific reaction between Fe2+ and H2O2 on the deoxyribose molecule.

Copper↗
PubMed1991

Factors that influence the deoxyribose oxidation assay for Fenton reaction products.

The mechanism of oxidation of deoxyribose to thiobarbituric acid-reactive products by Fenton systems consisting of H2O2 and either Fe2+ or Fe2+ (EDTA) has been studied. With Fe2+ (EDTA), dependences of product yield on reactant concentrations are consistent with a reaction involving OH.. With Fe2+ in 5-50 mM phosphate buffer, yields of oxidation products were much higher and increased with increasing deoxyribose concentration up to 30 mM. The product yield varied with H2O2 and Fe2+ concentrations in a way to suggest competition between deoxyribose and both reactants. Deoxyribose oxidation by Fe2+ and H2O2 was enhanced 1.5-fold by adding superoxide dismutase, even though superoxide generated by xanthine oxidase increased deoxyribose oxidation. These results are not as expected for a reaction involving free OH. or site localized OH. product on the deoxyribose. They can be accommodated by a mechanism of deoxyribose oxidation involving an iron(IV) species formed from H2O2 and Fe2+, but the overall conclusion is that the system is too complex for definitive identification of the Fenton oxidant.

Deoxyribose↗
PubMed2001

Thiols alter the partitioning of calicheamicin-induced deoxyribose 4'-oxidation reactions in the absence of DNA radical repair.

Cellular thiols have been proposed to play a protective role in oxidative DNA damage by quenching radical species in solution and by repairing deoxyribose and nucleobase radicals. There is also evidence for participation of thiols in reactions after formation of the DNA radical. Previous studies with neocarzinostatin, a thiol-dependent DNA-cleaving enediyne, revealed that the structure and charge of the activating thiol influence the partitioning of deoxyribose 4'-oxidation reactions between a 3'-phosphoglycolate residue and the alternative 4'-keto-1'-aldehyde abasic site [Kappen, L. S., et al. (1991) Biochemistry 30, 2034-2042; Dedon, P. C., et al. (1992) Biochemistry 31, 1917-1927]. However, interpretation of these results is confounded by the formation of a neocarzinostatin-thiol conjugate that could alter the position of the activated drug in the minor groove and quench drug radicals. Using the DNA-cleaving enediynes calicheamicin gamma(1)(I) and Ø, which are identical except for their trigger moieties, we now present a more definitive study of the role of thiol structure in the partitioning of the deoxyribose 4'-oxidation reaction. In the absence of thiols, calicheamicin Ø, which can undergo hydrolytic or reductive activation, generated 4'-oxidation products consisting of 26% 3'-phosphoglycolate residues, 33% 3'-phosphate-ended fragments, and 41% abasic sites (determined as the 3'-phosphopyridazine derivative). Using a series of thiols of varying size and charge, we found that, at concentrations that do not quench drug or DNA radicals, the negatively charged thiols glutathione and thioglycolate did not significantly affect the baseline proportions of the 4'-oxidation products. However, neutral thiols (O-ethylglutathione, methyl thioglycolate, 2-mercaptoethanol, and dithiothreitol) and, to a greater extent, the positively charged aminoethanethiol inhibited the production of 3'-phosphoglycolate residues with a proportional increase in the number of abasic sites. The effect of the thiols on the quantities of single- and double-stranded DNA lesions produced by calicheamicin gamma(1)(I) was also investigated since 3'-phosphoglycolate residues produced by calicheamicin exist only in double-stranded DNA lesions, and the thiol effects could have resulted from quenching of drug or DNA radicals. These studies revealed that, at thiol concentrations found to alter deoxyribose 4'-oxidation reactions, there was no apparent quenching of drug radicals or repair of DNA radicals. Thus, the effects of the thiols on the deoxyribose 4'-oxidation chemistry are due to reactions with a key intermediate in the phosphoglycolate- and abasic site-generating pathways. These results also suggest that cellular glutathione plays a relatively minor role in the chemistry of deoxyribose 4'-oxidation, which has implications for other oxidative reactions occurring in the minor groove of DNA (e.g., deoxyribose 5'- and 1'-oxidation).

Aminoglycosides↗
PubMed1994

Deoxyribose degradation catalyzed by Fe(III)-EDTA: kinetic aspects and potential usefulness for submicromolar iron measurements.

Iron ions play a central role in .OH radicals formation and induction of oxidative stress in living organisms. Iron-catalyzed .OH radical formation degrades deoxyribose to thiobarbituric acid reactive substances (TBA-RS). This paper analyzes kinetic properties of the Fe(III)-EDTA-catalyzed deoxyribose degradation in the presence of ascorbate. The yield of TBA-RS formation in the presence of EDTA was 4-fold higher than in its absence, contrasting with results reported elsewhere, Cu(II)-EDTA and Fe(III)-citrate were unable to catalyze deoxyribose degradation. The dependence on deoxyribose concentration was fitted to a Lineweaver Burk-like plot and it was calculated that approximately 4.5 mM deoxyribose scavenged half of the .OH radicals formed. The data for Fe(III)-EDTA concentration dependence could also be fitted to a rectangular hyperbolic function. This function was linear up to 1 microM added FeCl3 and this property could be utilized as an assay for the estimation of submicromolar iron concentrations. Submicromolar concentrations of iron could induce measurable yields of TBA-RS. Differences of as little as 0.1 microM Fe(III)-EDTA could be reproducibly detected under optimum experimental conditions, above a consistent background absorbance that was equivalent to 0.35 +/- 0.05 microM Fe(III)-EDTA and represented contaminating iron in the reactants that could not be removed with Chelex-100. The low method determination limit makes the deoxyribose degradation reaction potentially useful as a new, highly sensitive and cost effective assay for iron quantification.

Ascorbic Acid↗
PubMed2001

Differences between cysteine and homocysteine in the induction of deoxyribose degradation and DNA damage.

The effect of two naturally occurring thiols, such as cysteine and homocysteine, has been examined for their ability to induce deoxyribose degradation and DNA damage. Copper(II) ions have been added to incubation mixtures and oxygen consumption measurements have been performed in order to correlate the observed damaging effects with the rate of metal catalyzed thiol oxidation. Ascorbic acid plus copper has been used as a positive control of deoxyribose and DNA oxidation due to reactive oxygen species. Cysteine or homocysteine in the presence of copper ions induce the degradation of deoxyribose and the yield of 8-hydroxy-2'-deoxyguanosine (8-OHdG), although important differences are observed between the two thiols tested, homocysteine being less reactive than cysteine. DNA cleavage is induced by cysteine in the presence of copper(II) ions but not by homocysteine. Catalase and thiourea, but not superoxide dismutase (SOD), were shown to inhibit the damaging effects of cysteine on deoxyribose or DNA suggesting that H(2)O(2) and *OH radicals are responsible for the observed induced damage. The results indicate that there are differences between the damaging effects of the two thiols tested towards deoxyribose and DNA damage. The pathophysiological importance will be discussed.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1997

DNA synthesis arrest at C4'-modified deoxyribose residues.

Many genotoxic agents form base lesions that inhibit DNA polymerases. To study the mechanism underlying termination of DNA synthesis on defective templates, we tested the capacity of a model enzyme (Klenow fragment of Escherichia coli DNA polymerase I) to catalyze primer elongation across a series of C4' deoxyribose derivatives. A site with inverted C4' configuration or two different C4' deoxyribose adducts were introduced into the backbone of synthetic templates without modifying the chemistry of the corresponding bases. Inverted deoxyribose moieties may arise in cellular DNA as a product of C4' radical attack. We found that DNA synthesis by the Klenow polymerase was arrested transiently at the C4' inversion and was essentially blocked at C4' deoxyribose adducts. Major termination sites were located one position downstream of a C4' selenophenyl adduct and immediately 3' to or opposite a C4' pivaloyl adduct. Primer extension studies in the presence of single deoxyribonucleotides showed intact base pairing fidelity opposite all three C4' variants regardless of whether the Klenow fragment or its proofreading-deficient mutant was tested. These results imply that the coding ability of template bases is maintained at altered C4' deoxyribose moieties. However, their capacity to impede DNA polymerase progression indicates that backbone distortion and steric hindrance are important determinants of DNA synthesis arrest on damaged templates. The strong inhibition by C4' adducts suggests a potential target for new chemotherapeutic strategies.

DNA Polymerase I↗
PubMed2000

Optical spectroscopic study of the effects of a single deoxyribose substitution in a ribose backbone: implications in RNA-RNA interaction.

The 2'-OH group in the ribose sugars of an RNA molecule plays an important role in guiding tertiary interactions that stabilize different RNA structural motifs. Deoxyribose, or 2'-OH by 2'-H, substitution in both the single-stranded and the duplex part of an RNA backbone has been routinely used to evaluate what role the 2'-OH plays in different tertiary interactions that guide an RNA-RNA contact. A deoxyribose substitution not only has the effect of removing a hydrogen bond donating group, but also introduces a sugar moiety with a preference for C2'-endo pucker in a backbone of predominantly C3'-endo sugars. This study evaluates the effects of a single deoxyribose substitution in both single-stranded and double-helical forms of RNA oligomers. A single-stranded, nonrepetitive 7-mer oligoribonucleotide (7-mer RNA) and four different variants having the same base sequence but with a single deoxyribose sugar at different positions in the strands have been studied by ultraviolet (UV) absorption, circular dichroism (CD), and Fourier transform infrared (FTIR) spectroscopy. Duplexes were formed by association with the complementary strand of the 7-mer RNA. The results show that both RNA and DNA single strands have preorganized conformations with spectral properties resembling those of A- and B-form helices, respectively, with RNA being more heterogeneous than its DNA counterpart. A single deoxyribose substitution perturbs the structure of the RNA backbone, with the effect being more pronounced in the single-stranded than in the duplex structure. The perturbation depends on the position of the 2'-H substitution in the strand.

Base Composition↗
PubMed1969

2-Deoxyribose gene-enzyme complex in Salmonella typhimurium: regulation of phosphodeoxyribomutase.

Phosphodeoxyribomutase, the enzyme which catalyzes the interconversion of 2-deoxyribose-1-phosphate to 2-deoxyribose-5-phosphate, has been partially purified from Salmonella typhimurium. The enzyme had an absolute requirement for manganese ion and was stimulated by glucose-1, 6-diphosphate. Phosphodeoxyribomutase was induced by deoxyribose-5-phosphate and was coordinately regulated with the enzymes thymidine phosphorylase and deoxyribose-5-phosphate aldolase, type II. Mutants deficient in these three enzymes were isolated and mapped close to the threonine locus in S. typhimurium. The three enzymes thymidine phosphorylase, deoxyribose-5-phosphate aldolase, type II, and phosphodeoxyribomutase are controlled by a series of linked genes and appear to constitute an operon.

Aldehyde-Lyases↗
PubMed2001

NMR evidence for mechanical coupling of phosphate B(I)-B(II) transitions with deoxyribose conformational exchange in DNA.

The conformational exchange of the phosphate and deoxyribose groups of the DNA oligomers d(GCGTACGC)(2) and d(CGCTAGCG)(2) have been investigated using a combination of homonuclear and heteronuclear NMR techniques. Two-state exchange between phosphate B(I) and B(II) conformations and deoxyribose N and S conformations was expressed as percent population of the major conformer, %B(I) or %S. Sequence context-dependent variations in %B(I) and %S were observed. The positions of the phosphate and deoxyribose equilibria provide a quantitative measure of the ps to ns timescale dynamic exchange processes in the DNA backbone. Linear correlations between %B(I), %S, and previously calculated model free (13)C order parameters (S(2)) were observed. The %B(I) of the phosphates were found to be correlated to the S(2) of the flanking C3' and C4' atoms. The %B(I) was also found to be correlated with the %S and C1' S(2) of the deoxyribose ring 5' of the phosphates. The %B(I) of opposing phosphates is correlated, while the %B(I) of sequential phosphates is anti-correlated. These correlations suggest that conformational exchange processes in DNA are coupled to each other and are modulated by DNA base sequence, which may have important implications for DNA-protein interactions.

Base Sequence↗
PubMed1982

Deoxyribose breakdown by the adriamycin semiquinone and H2O2: evidence for hydroxyl radical participation.

We report our finding that the reaction between the adriamycin semiquinone (produced by reduction of the drug by xanthine oxidase) and H2O2 in N2 causes deoxyribose degradation to a thiobarbituric acid-reactive chromogen. Deoxyribose breakdown was inhibited by scavengers of hydroxyl radicals, providing evidence for the participation of hydroxyl radicals. The reaction was detected in air, but was less efficient in air than in N2. Deoxyribose degradation did not require a metal catalyst, and was inhibited by superoxide dismutase in air, but not N2. A similar reaction with deoxyribose in DNA may be of major importance in the antitumour action of adriamycin.

Air↗
PubMed2003

Structure-based mutagenesis approaches toward expanding the substrate specificity of D-2-deoxyribose-5-phosphate aldolase.

2-Deoxyribose-5-phosphate aldolase (DERA, EC 4.1.2.4) catalyzes the reversible aldol reaction between acetaldehyde and D-glyceraldehyde-3-phosphate to generate D-2-deoxyribose-5-phosphate. It is unique among the aldolases as it catalyzes the reversible asymmetric aldol addition reaction of two aldehydes. In order to expand the substrate scope and stereoselectivity of DERA, structure-based substrate design as well as site-specific mutation has been investigated. Using the 1.05 A crystal structure of DERA in complex with its natural substrate as a guide, five site-directed mutants were designed in order to improve its activity with the unnatural nonphosphorylated substrate, D-2-deoxyribose. Of these, the S238D variant exhibited a 2.5-fold improvement over the wild-type enzyme in the retroaldol reaction of 2-deoxyribose. Interestingly, this S238D mutant enzyme was shown to accept 3-azidopropinaldehyde as a substrate in a sequential asymmetric aldol reaction to form a deoxy-azidoethyl pyranose, which is a precursor to the corresponding lactone and the cholesterol-lowering agent Lipitor. This azidoaldehyde is not a substrate for the wild-type enzyme. Another structure-based design of new nonphosphorylated substrates was focused on the aldol reaction with inversion in enantioselectivity using the wild type or the S238D variant as the catalyst and 2-methyl-substituted aldehydes as substrates. An example was demonstrated in the asymmetric synthesis of a deoxypyranose as a new effective synthon for the total synthesis of epothilones. In addition, to facilitate the discovery of new enzymatic reactions, the engineered E. coli strain SELECT (Deltaace, adhC, DE3) was developed to be used in the future for selection of DERA variants with novel nonphosphorylated acceptor specificity.

Aldehyde-Lyases↗
PubMed1986

Copper + zinc and manganese superoxide dismutases inhibit deoxyribose degradation by the superoxide-driven Fenton reaction at two different stages. Implications for the redox states of copper and manganese.

When OH. radicals are formed in a superoxide-driven Fenton reaction, in which O2.- is generated enzymically, deoxyribose degradation is effectively inhibited by CuZn- and Mn-superoxide dismutases. The products of this reaction are H2O2 and a Fe3+-EDTA chelate. The mixing of H2O2 and a Fe3+-EDTA chelate also generates OH. radicals able to degrade deoxyribose with the release of thiobarbituric acid-reactive material. This reaction too is inhibited by CuZn- and Mn-superoxide dismutases, suggesting that most of the OH. is formed by a non-enzymic O2.--dependent reduction of the Fe3+-EDTA chelate. Since the reaction between the Fe3+-EDTA chelate and H2O2 leads to a superoxide dismutase-inhibitable formation of OH. radicals, it could suggest a much wider protective role for the superoxide dismutase enzymes in biological systems. Urate produced during the reaction of xanthine oxidase and hypoxanthine limits deoxyribose degradation as well as the effectiveness of the superoxide dismutase enzymes to inhibit damage to deoxyribose by H2O2 and the Fe3+-EDTA chelate. Some of this damage may result from an O2.--independent pathway to OH. formation in which urate reduces the ferric complex.

Cations, Divalent↗
PubMedDate not supplied

Photochemical production of hydroxyl radical from aqueous iron(III)-hydroxy complex: determination of its reaction rate constants with some substituted benzenes using deoxyribose-thiobartituric acid assay.

Hydroxyl radical (OH) production, mediated by UV light, from aqueous ferric perchlorate was investigated at low pH using a deoxyribose-thiobarbituric acid (-TBA) assay. The rate of production of OH was found to be dependent on the irradiation time. Addition of suitable substrates such as substituted benzenes can compete for the reaction of OH with deoxyribose, leading to a decreased yield of TBA chromogen formed from the deoxyribose-TBA assay. The second-order rate constants of the added substrates can be determined from such a simple competition kinetic method. The second-order rate constants for the reaction of OH with a number of substituted benzenes were determined using this method and the values were compared with the reported rate constants using pulse radiolysis technique. The values determined using the present method (1 to 8 x 10(9) dm3/mols) are in good agreement with those reported by use of the pulse radiolysis technique. It is proposed that the photoproduction of OH from aqueous ferric perchlorate coupled with deoxyribose-TBA assay is a simple and efficient method for determination of rate constants for the reaction of OH with a variety of substituted benzenes that are known to be organic water contaminants.

Benzene↗