摘要 :
In the present work, 13 p-substituted phenols with different functional groups have been systematically evaluated as metHb substrates by means of HPLC analysis. Non-hyperbolic kinetics were observed and Hill coefficients in the 0....
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In the present work, 13 p-substituted phenols with different functional groups have been systematically evaluated as metHb substrates by means of HPLC analysis. Non-hyperbolic kinetics were observed and Hill coefficients in the 0.37-1.00 range were obtained. The catalytic constants and the Hill coefficients were found to be quantitatively correlated with two independent variables: the energy level of the highest-occupied molecular orbital (Ehomo), which describes the intrinsic redox activity of the substrates and the pK_a-values, which are related to substrate ionization. Oxygen evolution in the presence of each phenol derivative was also measured, and good correlation between peroxidase-like and catalase-like activities of the protein was observed. It is also shown that bovine metHb, although less active than other peroxi-dases, may represent a good alternative from an economical point of view for phenol removal processes. The equations here obtained may serve as a basis to further explore the potential use of metHb-mediated reactions in the treatment of phenols in wastewaters and to predict which phenol will be removed most efficiently under this treatment with satisfactory reliability.
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The alkylating potential of p-nitrostyrene oxide (pNSO)-a compound used as a substrate to study the activity of epoxide hydrolases as well as in polymer production and in the pharmaceutical industry-was investigated kinetically. T...
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The alkylating potential of p-nitrostyrene oxide (pNSO)-a compound used as a substrate to study the activity of epoxide hydrolases as well as in polymer production and in the pharmaceutical industry-was investigated kinetically. The molecule 4-(p-nitrobenzyl)pyridine (NBP), as a model nucleophile for DNA bases, was used as an alkylation substrate. In order to gain insight into the effect of the hydrolysis of pNSO, as well as the hydrolysis of the NBP-pNSO adduct on the pNSO alkylating efficiency, these two competing reactions were studied in parallel with the main NBP-alkylation reaction. The following conclusions were drawn: (ⅰ)pNSO reacts through an S_N2 mechanism, with NBP to form an adduct, pNSO-NBP (AD). The rate equation for the adduct formation is: r = d[AD]/dt = K_(alk)[NBPJ(pNSO]- K_(hyd)~(AD) [AD] (k_(alk), and K_(hyd)~(AD) being the alkylation rate constant and the NBP-pNSO adduct hydrolysis rate constant, respectively); (ⅱ) the alkylating capacity of pNSO, defined as the fraction of initial alkylating agent that forms the adduct, is similar to that of mutagenic agents as effective as β-propiolactone, The instability of the pNSO-NBP adduct formed could be invoked to explain the lower mutagenicity shown by pNSO; (ⅲ) the different stabilities of the α and β-adducts formed between NBP and styrene oxides show that the alkylating capacity/ =K_(alk)[NBP]/(K_(alk)[NBP] + K_(hyd)) (K_(hyd) being the pNSO hydrolysis rate constant) as well as the alkylating effectiveness, AL =K_(hyd)~(AD), are useful tools for correlating the chemical reactivity and mutagenicity of styrene oxides; (ⅳ) a pNSO-guanosine adduct was detected.
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The formation of chemical species with DNA-damaging and mutagenic activity for bacterial test systems was detected in sorbic acid-nitrite mixtures. 1,4-Dinitro-2-methylpyrrole (NMP), one the main products resulting from the reacti...
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The formation of chemical species with DNA-damaging and mutagenic activity for bacterial test systems was detected in sorbic acid-nitrite mixtures. 1,4-Dinitro-2-methylpyrrole (NMP), one the main products resulting from the reaction between sorbic acid and nitrite, has mutagenic properties, and here its alkylating capacity was investigated. The conclusions drawn are as follows: (i) In aqueous medium, after the addition of a hydroxide ion and the subsequent loss of nitrite, NMP affords 5-methyl-3-nitro-1H-pyrrol-2-ol. This species is in equilibrium with 5-methyl-3-nitro-1H-pyrrol- 2(5H)-one, the effective alkylating agent responsible for the genotoxic capacity of NMP; (ii) 5-methyl-3-nitro-1H-pyrrol-2(5H)-one alkylates 4-(p-nitrobenzyl)pyridine (NBP), a molecule with nucleophilic characteristics similar to those of DNA bases, forming an adduct (AD; ε=1.14 104M-1 cm-1); (iii) The calculated energy barrier for the alkylation ofNBPforNMPand the value of the fraction of alkylating agent forming the adduct are consistent with the observed mutagenicity of NMP; (iv) The reactivity of NMP can be explained in terms of the instability of the N-NO2 bond as well as the effect of this group on aromaticity.
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Sorbic acid reacts with nitrite to yield mutagenic products such as 1,4-dinltro-2-methylpyrrole (NMP) and ethylnitrolic acid (ENA). In order to know the stability of these compounds, a kinetic study of their decomposition reaction...
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Sorbic acid reacts with nitrite to yield mutagenic products such as 1,4-dinltro-2-methylpyrrole (NMP) and ethylnitrolic acid (ENA). In order to know the stability of these compounds, a kinetic study of their decomposition reactions was performed in the 6.0-9.5 pH range. The conclusions drawn are as follows: (i) The decomposition of NMP occurs through a nucleophilic attack by OH~- ions, with the rate equation as follows: r=k_(dec)~(NMP)[OH~-][HUP] with k_(dec)~(NMP) (37.5 °C) = 42 ± 1 M~(-1) s~(-1). (ii) The rate law for the decomposition of ENA is as follows: r= k_(dec)~(ENA)[ENA]K_a/(K_a + [H~+]), with K_a being the ENA dissociation constant and k_(dec)~(ENA) (37.5 °C) = (7.11 ± 0.04) x 10~(-5) s~(-1) (iii) The activation energies for NMP and ENA decomposition reactions are, respectively, E_a = 94 ± 3 and 94 ± 1 kJ mol~(-1) (iv) The observed values for the decomposition rate constants of NMP and ENA in the pH range of the stomach lining cells, into which these species can diffuse, are so slow that they could be the slow determining step of the alkylation mechanisms by some of the products resulting from NMP and ENA decomposition. Thus, the current kinetic results are consistent with the low mutagenicity of these species.
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