This work describes a novel method of urinary oxalate determination based on a catalase model compound MnL(H2O)2(ClO4)2 (L ? bis(2-pyridylmethyl)amino)propionic acid). Urinary oxalate is first decomposed by the oxalate oxidase into carbon dioxide and hydrogen peroxide. The later is then disproportionated into water and oxygen by the catalase model compound forming a color compound, which can be spectrophotometrically monitored. The oxalate concentration of the sample is quantified according to the UV-vis absorbance of the formed color compound. This model compound method maintains the specificity and sensitivity of the conventional enzymatic assay. It has several advantages over the traditional enzymatic method, including low cost, simplicity, large linear range, and adjustable assay time. The model compound method showed a very good linearity in the range of 0.002-20 mmol L-1 oxalate, with a detection limit of 2 mmol L-1 oxalate. The mean urinary oxalate determined by this method was 28.6 mg mL-1, standard deviation (SD) was 1.07 mg mL 1, and variation coefficient (CV) is less than 4%. The results are consistent with that acquired from the enzymatic and HPLC methods. The model compound method also showed that the model compounds of the corresponding enzymes can be an alternative to the enzymes, thus the cost of the methods or assays using the enzymes can be greatly decreased.

We report herein a facile method for the preparation of sodium tungsten bronzes hollow nanospheres using hydrogen gas bubbles as reactant for chemical reduction of tungstate to tungsten and as template for the formation of hollow nanospheres at the same time. The chemical composition and the crystalline state of the as-prepared hollow Na0.15WO3 nanospheres were characterized complementarily, and the hollow structure formation mechanism was proposed. The hollow Na0.15WO3 nanospheres showed large Brunauer-Emment-Teller specific area (33.8 m2 g-1), strong resistance to acids, and excellent ability to remove organic molecules such as dye and proteins from aqueous solutions. These illustrate that the hollow nanospheres of Na0.15WO3 should be a useful adsorbent.

Biological systems activate O2 using many mechanisms, but in nearly all cases, the activation process is regulated to assure specificity. The nature of these regulatory aspects of the reaction must be understood before the true nature of the underlying chemistry can be described with certainty. Most metal-containing oxygenases utilize amino acids in the second sphere and beyond to regulate the O2 activation reaction. One example of this is seen in the mechanism of substrate selectivity by methane monooxygenase. The regulatory protein MMOB binds to the active site-containing MMOH and appears to create a pore sized for methane into the active site. This controls access and therefore the preferred substrate. Also, the complex appears to cause quantum tunneling to dominate in C–H bond cleavage reaction for methane, selectively increasing the rate for this substrate. Both effects can be altered by mutagenesis of MMOB, potentially broadening the substrate range of the enzyme. Second sphere effects are also important in determining the position of ring cleavage for catecholic ring cleaving dioxygenases. Intermediates throughout the catalytic cycle of homoprotocatechuate 2,3-dioxygenase can be detected by using the chromophoric substrate 4-nitrocatechol (4NC). Upon mutation of the second sphere residue histidine 200 to asparagine (H200N), the rate of reaction of the Fe-oxy intermediate is greatly slowed, allowing its detection for the first time when using either 4NC or the natural substrate 3,4-dihydroxyphenylacetate (HPCA). HPCA cleavage occurs in the usual proximal extradiol position by this mutant, but 4NC is oxidized to the quinone without ring cleavage. Use of the alternative substrate 2,3-dihydroxybenzoate results in distal extradiol cleavage for the wild type enzyme, but intradiol cleavage for the H200-phenylalanine mutant. Thus, control of the second sphere allows the enzyme to design a specific catalyst that gives only one of the four potential types of products. This insight can be used to design specific enzyme oxidation catalysts.

EPR spin-trapping experiments were carried out using the three-component soluble methane monooxygenase (MMO). Spin-traps 5, 5-dimethyl-1-pyrroline N-oxide (DMPO), a-4-pyridyl-1-oxide N-tert-butylnitrone (POBN), and nitrosobenzene (NOB) were used to investigate the possible formation of substrate radical intermediates during catalysis. In contrast to a previous report, the NADH-coupled oxidations of various substrates did not produce any trapped radical species when DMPO or POBN was present. However, radicals were detected by these traps when only the MMO reductase component and NADH were present. DMPO and POBN were found to be weak inhibitors of the MMO reaction. In contrast, NOB is a strong inhibitor for the MMO-catalyzed nitrobenzene oxidation reaction. When NOB was used as a spin-trap in the complete MMO system with or without substrate, EPR signals from an NOB radical were detected. We propose that a molecule of NOB acts simultaneously as a substrate and a spin-trap for MMO, yielding the long-lived radical and supporting a stepwise mechanism for MMO.

In this work we examine the effect of the pH and the Si/surfactant ratio on the rate of formation of MCM-41 at room temperature. The methodology applied is in situ EPR where minute amounts of the spin probe 5-doxyl stearic acid are added to the reaction gel and the EPR spectrum is followed during the course of the reaction. Within the basic pH range where MCM-41 can be obtained, the pH increase leads to a faster rate of formation while in the acid pH range, a decrease of the pH leads to faster reaction. This is consistent with the hydrolysis of the tetraethyl-orthosilicate being a rate determining step. However, when the pH values are slightly above or below the basic pH range which generates MCM-41 (keeping all other components constant) the reaction is considerably slower. Comparison of reactions with different Si/surfactant ratios showed that the polymerization of the silicate oligomers occurs at the interface of the surfactant aggregate and that its rate is determined by the density of oligomers at the interface. Finally, in situ EPR was also used to determine the factors that control the incorporation of Mn(Ⅱ) into the silica matrix under acidic condi-tions.