Michael E. Deary

Determination of peracids in the presence of a large excess of hydrogen peroxide using a rapid and convenient spectrophotometric method

Peracids can be determined in the presence of up to a 1000-fold excess of hydrogen peroxide by taking advantage of the much greater rate of reaction of the peracid with iodide. A fast, convenient and accurate spectrophotometric method is described that involves a simple linear extrapolation. The effects of a number of experimental variables on the accuracy, precision, sensitivity and selectivity of the method are described. The method has been applied to the determination of the peracetic acid formed during the perhydrolysis of p-nitrophenyl acetate.

Development and application of an inhalation bioaccessibility method (IBM) for lead in the PM10 size fraction of soil

An approach for assessing the inhalation bioaccessibility of Pb in the PM10 size fraction is presented, using an in vitro simulated epithelial lung fluid to represent the extracellular environment of the lung. The developed inhalation bioaccessibility method (IBM) is applied to a range of urban surface soils and mining wastes obtained from Mitrovica, Kosovo, a site where impacts upon human health following exposure to Pb have been internationally publicised. All Pb determinations were undertaken by inductively coupled plasma mass spectrometry (ICP-MS). The pseudo-total concentration of Pb (microwave acid digestion using aqua-regia) varied between matrices: smelter (20,900-72,800mgkg(-1)), topsoil (274-13,700mgkg(-1)), and tailings (2990mgkg(-1)-25,300mgkg(-1)). The in vitro inhalation bioaccessibility was typically several orders of magnitude lower: smelter (7.0-965mgkg(-1)), topsoil (9.8-1060mgkg(-1)), and tailings (0.7mgkg(-1)-49.2mgkg(-1)). The % inhalation bioaccessibility ranged from 0.02 to 11.0%, with the higher inhalation bioaccessible Pb concentrations being observed for samples from the Bosniak Mahalla area of Mitrovica (an area proposed for the relocation of internally displaced peoples). The estimated inhalation dose (for adults) calculated from the PM10 pseudo-total Pb concentration ranged from 0.369 to 1.284μgkg(-1)BWday(-1) (smelter), 0.005-0.242μgkg(-1)BWday(-1) (topsoil), and 0.053-0.446μgkg(-1)BWday(-1) (tailings). When daily inhalation doses were calculated using the bioaccessible Pb concentration the modelled exposure doses were much lower: smelter (0.0001-0.0170μgkg(-1)BWday(-1)), topsoil (0.0002-0.0187μgkg(-1)BWday(-1)) and tailings (0.0001-0.0009μgkg(-1)BWday(-1)). Modelled for the neutral pH conditions of the interstitial lung environment, the results indicate a low potential inhalation bioaccessibility for Pb in these samples. Given the already elevated environmental Pb burden experienced by the local population, where significant prolonged dust or particulate generating activities are taking place, or where the inhaled particles are phagocytized, then inhalation exposure has the potential to significantly add to the overall Pb burden. Such data are important for local policy makers to better enable them to assess risk, especially in areas where soils/dusts have elevated levels of contamination.

Kinetics of the hydrolysis and perhydrolysis of tetraacetylethylenediamine, a peroxide bleach activator

Hydrogen peroxide and water react with tetraacetylethylenediamine (TAED) to form consecutively triacetylethylenediamine and diacetylethylenediamine with the release of two molecules of peracetic acid or acetic acid. The effect of pH, specific buffers and temperature on the rates of hydrolysis and perhydrolysis are compared. Peracetic acid reacts with TAED very slowly. The ratio of the second-order rate constants for the reaction of TAED with hydroperoxide and peracetate anions is exceptionally large after taking into account the difference in pKa values of their conjugate acids. The relative reactivity of various nucleophiles with TAED is discussed in terms of its performance as a bleach activator.

Evidence for cyclodextrin dioxiranes

Abstract α -Cyclodextrin, β -cyclodextrin, 2,6-di- O -methyl- β -cyclodextrin, methyl- β -cyclodextrin and sucrose have been oxidised by aqueous bromine solution at neutral pH. Both ketone and carboxylic acid containing materials are among the products of the oxidations. For α -cyclodextrin there is clear 13 C NMR evidence for the presence of a ketone group and its hydrate form. This together with the continued ability of the product to complex p -nitrophenol indicates that the ketone is present at the secondary rim of an intact cyclodextrin ring. A pH dependence for the reaction of bromine with cyclodextrin shows that the maximum rate of bromine loss roughly coincides with the maximum concentration of hypobromous acid, HOBr, indicating that this is the reactive species in these oxidations. The results are consistent with a mechanism involving attack by one of the secondary hydroxyls of cyclodextrin on HOBr, with Br - leaving to yield an intermediate dehydroxy hydroperoxy cyclodextrin that subsequently decomposes to a keto-cyclodextrin via a Kornblum–De La Mare-type reaction. An alternative pathway prevails when the reaction is carried out under alkaline conditions, where carboxylic acids are the principle products. The keto derivatives produced by bromine oxidation at neutral pH are capable of catalysing the oxidation of p -nitrophenol and aryl–alkyl sulfoxides by peroxomono-sulfate in an analogous way to cyclohexanone, which is known to form a dioxirane upon reaction with peroxomonosulfate. It is likely that dioxirane formation is responsible for the observed catalysis in the present case also.

Cooperativity and steric hindrance: important factors in the binding of α-cyclodextrin with para-substituted aryl alkyl sulfides, sulfoxides and sulfones

Binding constants for 22 para-substituted aryl alkyl sulfides, sulfoxides and sulfones have been determined spectrophotometrically. It was found that the presence of sulfur containing substituents generally results in destabilisation of complex formation, and it is postulated that the angle of the sulfur bond in these compounds results in steric hindrance with the 5-H protons at the rear of the cyclodextrin cavity, causing it to be displaced from its optimal position or orientation. Additionally, the observation, for several sulfides, of cooperativity in the binding of a second molecule of cyclodextrin is discussed in terms of binding induced changes in electrical potential within the cyclodextrin cavity.

Dioxaborirane: a highly reactive peroxide that is the likely intermediate in borate catalysed electrophilic reactions of hydrogen peroxide in alkaline aqueous solution

This paper reports on a kinetic and theoretical study into the borate mediated reaction of dimethyl sulfide with hydrogen peroxide in both acid and alkaline conditions. At high pH, whilst the kinetic data is consistent with the catalytic species being monoperoxoborate, formed from the rapid equilibrium between hydrogen peroxide and boric acid, DFT calculations show that this species is in fact less reactive than hydrogen peroxide, requiring us to seek an alternative catalytic mechanism. DFT provides an important insight for this, showing that although boric acid and peroxoboric acid are primarily Lewis acids, they can exhibit a small degree of Brønsted acidity, allowing, respectively, the B(O)(OH)(2)(-) and HOOB(OH)(O)(-) anions to exist in small concentrations. Whilst the peroxoborate anion, HOOB(OH)(O)(-), is predicted to have only marginal catalytic activity, its tautomer, dioxaborirane, (HO)(2)BO(2)(-), a three membered cyclic peroxide, has a very low activation barrier of 2.8 kcal/mol. Hence, even though dioxaborirane is likely to be present in very low concentrations, it is still sufficiently reactive for overall rate enhancements to be observed for this system. This is the first literature report of this species. The observed low selectivity observed for borate catalysed reactions of hydrogen peroxide with a range of substituted phenyl methyl sulfides in our previous study (D. M. Davies, M. E. Deary, K. Quill and R. A. Smith, Chem.-Eur. J. 2005, 11, 3552-3558) is further evidence in favour of a highly reactive catalytic species. At low pH, kinetic data shows that borate catalyses the reaction between hydrogen peroxide and dimethyl sulfide; this is supported by DFT calculations that predict peroxoboric acid to be an effective catalytic intermediate, with an energy barrier of 7.4 kcal mol(-1) compared to 10.1 kcal mol(-1) for the uncatalysed system. Nevertheless, the overall contribution of this pathway is small because of the unfavourable equilibrium between hydrogen peroxide and boric acid to form peroxoboric acid.

Practicalities of mapping PM10 and PM2.5 concentrations on city-wide scales using a portable particulate monitor

Fine particulate matter is considered to be the most significant ambient air pollutant in terms of potential health impacts. Therefore, it is important that regulators are able to accurately assess the exposure of populations to PM10 and PM2.5 across municipal areas. We report on the practicalities of using a laser light scattering portable particulate monitor (Turnkey Instruments DustMate), in combination with a GPS, to map PM10 and PM2.5 concentrations on city-wide scales in Newcastle upon Tyne/Gateshead (UK), during a series of walking surveys. A heated inlet is necessary to remove moisture droplets from the sampled air prior to analysis by the instrument, though this also results in the loss of volatile particulate components, particularly from the PM2.5 fraction. A co-location calibration study was carried out with a reference urban background Tapered Element Oscillating Micro-Balance/Filter Dynamics Measuring System (TEOM-FDMS) system in Newcastle that is part of the UK’s Automatic Urban and Rural Network (AURN) of air quality monitoring stations. For PM10, orthogonal regression of the DustMate against TEOM-FDMS data gave a slope and intercept of 1.02 ± 0.06 and −3.7 ± 1.2, respectively (R2 = 0.73), whereas for PM2.5, the respective values were 0.78 ± 0.06 and −0.63 ± 0.55 (R2 = 0.79). These parameters are comparable to literature calibration studies using this technology. There was good agreement between simultaneous samples taken using two DustMate instruments: for PM10, a slope and intercept of 1.05 ± 0.03 and 0.36 ± 0.5, respectively (R2 = 0.73), were obtained, whereas for the PM2.5, the respective values were 0.79 ± 0.01 and 0.19 ± 0.06 (R2 = 0.86). Correction factors based on the slope and intercepts obtained from the calibration exercise were applied to raw data collected from the DustMate. An annually-normalised correction procedure was then used to account for different background particulate concentrations on different sampling days. These corrected PM10 and PM2.5 concentrations and corresponding GPS coordinates were displayed on a base map using Google Fusion Tables and Google Earth Professional. Almost all areas surveyed in Newcastle/Gateshead were well below the EU Air Quality Standards for PM10 and PM2.5.

Evidence for cyclodextrin dioxiranes. Part 2. Catalytic and enantioselective properties of cyclodextrin dioxiranes formed from keto-derivatised hydroxypropyl-cyclodextrins

Abstract Following our recent study of the bromine oxidation, at neutral pH, of α-cyclodextrin, β-cyclodextrin, O-methylated β-cyclodextrins and sucrose, which yield ketone and carboxylic acid-containing materials in the oxidation products (M.E. Deary, D.M. Davies, Carbohydr. Res., 309 (1998) 17), we have extended the work to hydroxypropyl-α-cyclodextrin and hydroxypropyl-β-cyclodextrin. 13C NMR analysis confirms the presence of ketone groups (δ 207) in the oxidation products of both of these compounds. The continued ability of the products of these oxidations to complex p-nitrophenol demonstrates that ring integrity is maintained. The ketone-containing products are capable of catalysing the peroxomonosulfate (PMS) oxidation of a range of substrates including aryl alkyl sulfoxides, pyridine, 4-bromopyridine, aniline, 4-aminobenzoate, 4-bromoaniline and several amino acids, most probably by the formation of a more reactive cyclodextrin–dioxirane intermediate. A small degree of enantioselectivity is observed in the oxidation of (R)-(+)- and (S)-(−)-methyl p-tolyl sulfoxide by PMS in the presence of the keto derivative of hydroxypropyl-α-cyclodextrin, though not for the β analogue.

Effect of α-cyclodextrin on the oxidation of aryl alkyl sulfides by peracids

Substituent and leaving group effects on the uncatalysed reaction were in good agreement with literature studies. The effect of α-cyclodextrin on the kinetics of aryl alkyl sulfide oxidation by peracids was investigated by studying the following reaction series: (a) a range of aryl alkyl sulfides with three different perbenzoic acids and (b) a range of alkyl peracids and perbenzoic acids with five different aryl alkyl sulfides. For peracids which bind strongly to α-cyclodextrin, the observed second-order rate constant increases to a maximum with increasing cyclodextrin concentration and thereafter non-productive binding of the sulfide causes a decline in rate. Weakly binding peracids, such as peracetic acid show only a decline in rate constant with increasing cyclodextrin concentration. Linear free energy relationships reveal that transition state stabilisation by one molecule of cyclodextrin shows a far greater dependence on the stability of the peracid-cyclodextrin complex than on the stability of the sulfide-cyclodextrin complex, indicating that the principle pathway for the cyclodextrin mediated reaction is that between the peracidcyclodextrin complex and uncomplexed sulfide. Additionally, a linear free energy relationship comparing transition state stabilisation for the α-cyclodextrin mediated oxidation of iodide and methyl 4-nitrophenyl sulfide by peracids indicates a common mechanism of catalysis for both substrates, although the catalysis of sulfide oxidation is more effective. Several possible mechanisms of catalysis are discussed. Transition state stabilisation by two molecules of α-cyclodextrin was observed for those peracids which demonstrate significant 2:1 complex formation. Here the principal pathway is the reaction of the 2:1 cyclodextrin–peracid complex with the unbound sulfide, although the extent of transition state stabilisation by the second cyclodextrin molecule is only about the same as its stabilisation of peracid in the ground state.

Development of a novel kinetic model for the analysis of PAH biodegradation in the presence of lead and cadmium co-contaminants.

We report on the results of a 40 week study in which the biodegradation of 16 US EPA polycyclic aromatic hydrocarbons (PAHs) was followed in microcosms containing soil of high organic carbon content (11%) in the presence and absence of lead and cadmium co-contaminants. The total spiked PAH concentration was 2166mg/kg. Mercury amendment was also made to give an abiotic control. A novel kinetic model has been developed to explain the observed biphasic nature of PAH degradation. The model assumes that PAHs are distributed across soil phases of varying degrees of bioaccessibility. The results of the analysis suggest that overall percentage PAH loss is dependent on the respective rates at which the PAHs (a) are biodegraded by soil microorganisms in pore water and bioaccessible soil phases and (b) migrate from bioaccessible to non-bioaccessible soil phases. In addition, migration of PAHs to non-bioaccessible and non-Soxhlet-extractable soil phases associated with the humin pores gives rise to an apparent removal process. The presence of metal co-contaminants shows a concentration dependent inhibition of the biological degradation processes that results in a reduction in overall degradation. Lead appears to have a marginally greater inhibitory effect than cadmium.