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The kinetics have been studied over the pH range 8.95–11.0 of the bleaching of the azo dye methyl orange (4-[[(4-dimethylamino)phenyl]-azo]benzenesulfonic acid sodium salt) by hydrogen peroxide catalysed by molybdate and tungstate at 25 °C. A plot of the overall rate constants against pH fell on a bell-shaped curve with molybdate catalyst, but with tungstate the rate constant rose to a plateau as the pH increased. The contributory rate constants for both the peroxometalate catalyst and the singlet oxygen pathways were determined by carrying out experiments both without and with the singlet oxygen trap 2,5-dimethylfuran. The singlet oxygen rate constants correlated well with 1 O 2 generation data in the literature. The results obtained with molybdate were consistent with MoO(O 2 ) 3 2− ion being the active metalate bleaching agent and also the precursor for 1 O 2 generation, but the tungstate results indicated that our knowledge of the peroxotungstate system is still incomplete.

The reaction in perchloric acid solution between Hg 2C and Fe 2C was found to proceed extremely slowly until it suddenly exhibited an autocatalytic surge. In conjunction with this rise, a yellow-green by-product formed and disappeared again when the reaction came to an end. In the related reaction between Hg 2C 2 and Fe 2C , the autocatalytic behaviour started early and the yellow-green by-product again appeared. No metallic mercury or other solid formed in either reaction, but the production of colloidal mercury was demonstrated by the Tyndall effect and by electrophoresis experiments. A five-step mechanism for these reactions is proposed and incorporated into a computer simulation called Mercury. The behaviour predicted by these simulations agrees well with the unusual experimental findings. © 2000 Elsevier Science B.V. All rights reserved.

The rates of transfer of aqueous caffeine through a membrane of teabag paper were measured by means of a modified rotating diffusion cell. The reciprocals of the transfer rates were found to be directly proportional to the inverse square root of the rotation speed. These results are consistent with the rate-controlling step being diffusion of caffeine through the Nernst diffusion layers on each side of the membrane. At both 25 and 80°C the resistance to transfer through the teabag membrane itself was negligible, showing that the material was well suited to the brewing of tea, coffee or other food materials.

The oxidation by Co(NH3)5Cl2+ of N,N,N‘,N‘-tetramethyl-p-phenylenediamine (TMPPD) catalyzed by nanoparticles of palladium in an aqueous buffer/AOT/n-heptane microemulsion has been studied. The init...

The kinetics have been studied of the reaction between p-Me2NC6H4NH2 (DMPPD) and Co(NH3)5Cl2+, a process of relevance in color photography, in a water/AOT/n-heptane microemulsion catalyzed by nanop...

The electrical migration was studied of several cations passing longitudinally through cylindrical samples of green sapwood ofPinus sylvestris L. under the influence of an applied electric field. This led to values for the hindered ionic conductances within the wood of the cations Li+, K+ and CU2+ which were compared with data obtained previously (Simons et al., 1998) for several endogenous cations. There was satisfactory agreement for the conductance of the potassium ion, the only one to be determined by both methods. Copper ions were found to possess a higher conductance within the wood than calcium or magnesium, a factor relevant to its use as a wood preservative. Visual observation of the location of the blue-green colouration produced in the wood by copper ions indicated that they migrated via longitudinal resin ducts and tracheids. Elution and transport experiments were also carried out with sapwood which had been flushed with water, Li2SO4 or CuSO4 solution.

The relative migration of the major endogenous ions (K+, Ca2+ Mg2+, Na+, Cl− in green sapwood ofPinus sylvestris L. was measured in a modified Hittorf transference cell. The transference numbers obtained gave the fractions of the current carried by these ions when an electric field was applied across the wood samples under the conditions used.

A novel technique has been developed for measuring the electrical transport of ions and of water through natural materials when a dc electric field is applied across them. The material studied was green sapwood of Pinussylvestris L. (Scots pine). By means of a special cell the processes at the wood/solution interfaces were separated from those at the solution/electrode interfaces. Analyses of the electrode compartment solutions after the passage of known numbers of coulombs yielded the relative transference numbers of ions in the wood. Horizontal capillaries in the two electrode compartments enabled equal hydrostatic pressure to be maintained across the cell and allowed the simultaneous measurement of the electroosmotic water flow. This provided a value for the zeta potential of the green sapwood.The experiments showed electroosmotic water flow and ionic migration to be independent processes. The endogenous inorganic current carriers in the samples decreased in the sequence K+, Ca2+>Mg2+>Na+>NH4+, Cl-, SO42- and values were obtained for the hindered conductances of the major ionic carriers. The results are consistent with a cation-exchange model for the wood.

The rates of infusion of caffeine into water at 25.5°C were measured for green and medium roast Kenyan arabica coffees in the particle size range 0.85–1.00 mm. Each type of coffee was employed in three forms: dry (as received), water-filled but still containing the original amount of solubles, and water-filled and free of solubles other than caffeine. Intra-bean diffusion coefficients of caffeine were calculated from the rate constants and compared with the known diffusion coefficients of caffeine in water to provide hindrance factors. These were much larger than the corresponding hindrance factors obtained at 80°C (Spiro et al, J Sci Food Agric46, 349–356 (1989)). Examination of these results and of partition constants determined at both temperatures enabled the factors contributing to slow internal diffusion to be separated and identified. Factors which were more pronounced at 25°C were the finite rate of caffeine dissolution within the bean, complexation of caffeine with chlorogenic acid and other coffee solubles, and the adsorption of caffeine molecules within the bean matrix. © 1997 SCI

Dilute (1–10 vol. %) solutions of milk in hot London mains water formed films on the surface which increased with time. No film formed in solutions of milk in distilled water unless calcium chloride had been added. The mass of the surface film depended on the total mass of milk used, not on its concentration. These facts are consistent with an interaction between calcium (and other metal) ions and milk components within the bulk solution, the product then rising to the surface. Surface oxidation did not seem to be involved. This mechanism is quite different from that which forms films on infusions of black tea. The mass of the milk film increased in the order skimmed milk

Added milk greatly increased the mass of film formed on the surface of black tea brewed in hot London mains water. The amounts of film collected after adding different types of milk (skimmed, homogenised full cream, non-homogenised full cream, and UHT single cream) to black tea brews increased in the sequence listed. No film formed when distilled water was used, and very little even in hard water if the tea concentration was large. Chemical microanalysis and Fourier transform infrared examination of the films indicated that they were composed of milk constituents modified by tea polyphenols and aggregated by calcium ions. The role of the tea polyphenols is consistent with their being sequestered in casein micelles as well as bound to the protein membranes of milk fat globules. The presence of milk prevented the formation of most of the dark tea scum observed on black tea infused in hard water.

Experiments carried out on tea infusions with blown-over films of calcium carbonate (CaCO3) have shown that it is the presence of calcium and bicarbonate ions in the water, and not the concomitantly produced CaCO3, which mediates the formation of tea scum. Other experiments have refuted Lewin's (1993) theory that tea scum is mainly composed of epidermal waxes loosened from the tea leaves by hot water. Addition of fresh lemon juice greatly decreased the amount of tea scum formed in temporary hard water. This effect was explained by the resulting drop in pH and by complexation of calcium ions by the citric acid contained in the juice. Addition of sucrose equivalent to two cubes of sugar per cup significantly reduced the mass of scum, far more than could be accounted for by the increase in solution viscosity.

The kinetics of the oxidation of malvin chloride [3,5-bis(glucosyloxy)-4′,7-dihydroxy-3′,5′-dimethoxyflavylium chloride] by hydrogen peroxide have been studied in aqueous solution over the pH range 1.5 to 4.0 and at temperatures from 25 to 45 °C. The rates were found to be first order both in malvin chloride and in hydrogen peroxide and independent of the ionic strength. Use of free radical and singlet oxygen trapping agents ruled out the involvement of these species in the reaction. The variation of the rate constant with pH showed that the reaction took place between molecular hydrogen peroxide and both the flavylium ion I and the carbinol pseudo-base II, with I reacting more rapidly than II. At pH 3.0 the activation energy was 65.7 kJ mol–1 and the entropy of activation –78 J K–1 mol–1.The peroxide bleaching reaction was found to be catalysed by a range of transition-metal salts. Kinetic experiments carried out at 25 °C and pH 3.0 and using up to 10–4 mol dm–3 concentrations of catalyst showed that the catalytic reaction was first order in each of malvin chloride, hydrogen peroxide and metal salt. The third-order catalytic rate constants decreased in the order [Co(NH3)5Cl]2+ > MoVI≈ TiIV > [MoO(O2)2(pyO)2] > WVI≈[WO(O2)2(pyO)2]≈ VV≈ CrVI, somewhat similar to the order found for the catalytic bleaching of phenolphthalein at pH 10. Use of trapping agents showed that neither free radical species nor singlet oxygen were involved in the catalytic process. The way in which the catalytic rate constant of K2[MoO4] decreased with increasing ionic strength showed that the flavylium ion I was reacting much more rapidly than species II. The various metal-peroxo species likely to be the active catalytic agents are discussed.

The rates and extents of extraction have been measured for three major constituents of peppermint oil, namely 1,8-cineole, menthone and menthol, using the leaves of the black mint (Mentha x piperita L.). The solvents used were hexane, ethanol and mixtures of composition 90mol% ethanol + 10mol% hexane and 90mol% hexane + 10 mol% ethanol. The extractions were carried out isothermally at 25, 35 and 45°C as well as in an electrically and mechanically modified domestic microwave oven where the temperature increase varied from c. 10 to 30°C. The rates of both isothermal and microwave extractions were sensitive to the solvent employed and decreased in the order 90mol% hexane > 90 mol% ethanol > hexane > ethanol. The rates of microwave extraction were also affected by the microwave power output and the size of the sample load. The activation energies for the extractions were in the range 30-90 kJ mol -1 , again dependent on the solvent used. Scanning electron microscopy on the spent leaves provided evidence of a link between the kinetics of extraction and structural changes on the glands.

Extraction experiments were carried out at atmospheric pressure in an electrically and mechanically modified domestic microwave oven, with temperature changes monitored by a gas thermometer. The rates of extraction were measured of six essential oil components of rosemary (Rosmarinus officinalis L.) and detailed results are given for α-pinene and for 1,8-cineole. Major differences of behaviour were found according to whether the solvent employed was hexane, ethanol, or a mixture of 10 mol% hexane + 90 mol% ethanol. Simulated microwave extraction plots generated from the data of a series of thermostatted solvent extractions showed faster extraction rates than expected from the temperature changes. The rates of extractions were affected by the intensity of the microwave energy, the dielectric properties, size and composition of the workload, and the shape of the extracting vessel. Scanning electron micrographs showed that the kinetics and mechanism of the extractions were related to structural changes in the oil-containing glands

The rates of infusion into distilled water of caffeine and of Cl − , H 2 PO 4 − , SO 4 2− , C 2 O 4 2− , K + and Mg 2+ ions have been measured at 80 °C, using both black orthodox Bukial and green Chun Mee tea leafs in the size range 1.70–2.00 mm. The analytical techniques employed were HPLC and ion chromatography. The total moles of positive charge extracted per litre of infusion were several times as large as the moles of negative charge of all the anions analysed, pointing to large concentrations of organic anions including polyphenolates. The kinetic data were fitted to first order plots. From the resultant rate constants the diffusion coefficients of the various species within the tea leafs were calculated and compared with the corresponding diffusion coefficients in pure water at 80 °C. The hindrance factors in the leafs were all of the order of 10 2 .

The rates and extents of extraction into hexane, ethanol and two mixtures of hexane + ethanol (10.1 mol% hexane and 89.7 mol% hexane) of six essential oil constituents of the leaves of rosemary (Rosmarinus officinalis L.) have been measured. The data were fitted to a first order kinetic equation to yield rate constants (k) for the extraction of α-pinene, camphene, α-pinene, limonene, 1,8-cineole and camphor. The values of k increased between threefold and fiftyfold in the mixed solvents compared to values obtained in the pure solvents. Experiments carried out over the temperature range 25–45°C yielded activation energies of over 100 kJ mol−1 for every constituent, showing that the extraction of rosemary oil was a hindered process. Scanning electron micrographs showed that the kinetics and mechanism of the extractions are related to structural changes in the oil-containing glands. The partition constants of most of the components were found to be 0.7 for hexane extraction.

The rate of the reaction between titanium(III) chloride and triiodide ions in an acid chloride medium has been studied in the absence and presence of a rotating platinum disk. At low concentrations of triiodide the catalytic rate at platinum was found to be first order in I3–, zero order with respect to TiI I I and H+, and proportional to the square root of the rotation speed of the disk. These results pointed to diffusion-controlled catalysis, as did the low activation energy of 19 kJ mol–1 as compared with 40 kJ mol–1 for the uncatalysed reaction.All these findings are consistent with an electrochemical interpretation of the catalytic mechanism, as was shown by the current–potential curves determined for the two reactants at the same reduced platinum surface. Provided that the voltammograms for TiI I I had been carried out in the presence of the same concentration of Kl as in the reaction mixtures, the rates and mixture potentials determined electrochemically agreed well with the catalytic rates and potentials measured experimentally. The fact that quite different results were obtained when no Kl was present in the TiCl3 solution provides further confirmation for the modified form of the additivity principle.

A detailed study has been made of the rate of scum formation in hard London mains water at 80°C. From a given black tea infusion the scum grew continuously and, in the first hour, proportionately with time. The amount formed depended on the exposed surface area and not on the volume of the tea brew. Longer infusion of a given mass of tea leaf first increased and eventually decreased the mass of scum. Surprisingly, the more tea leaf that was used the less scum was produced, a phenomenon largely caused by the concomitant decrease in pH. Tea scum only formed in water which contained both calcium (or magnesium) ions and bicarbonate ions. No scum developed if the former were removed by complexing agents or the latter by lowering the pH. Boiling the water reduced but did not eliminate scum. More scum formed if the period of scum development took place at a higher temperature and the activation energy of scum formation was found to be 34 kJ mol −1 . This relatively high value, as well as the absence of any effect when the infusion was stirred, showed that the overall process is chemically- and not diffusion-controlled. Decaffeinated tea gave a similar amount of scum as normal black tea while green Chun Mee leaf produced about 80% as much. Moreover, scum formation was inhibited by passing nitrogen over the surface but enhanced by passing oxygen. Taken together, these experiments suggest that scum is produced by oxidation of tea solubles mediated by calcium carbonate formation.

The kinetics of the oxidation of phenolphthalein by hydrogen peroxide catalysed by transition-metal complexes (1–50 µmol dm–3) have been studied in aqueous solution at pH 10 and over a range of temperatures and ionic strengths. The rate laws for the reactions were first order in each of phenolphthalein, hydrogen peroxide and the metal catalyst. Complexes of the early transition metals in their highest oxidation states catalysed the reaction; the order of reactivity was MoVI TiIV > WVI > VV≈ CrVI. Suggestions as to the identities of the active catalytic species are made on the basis of the ionic strength dependence of the reactions. In the MoVI-catalysed reaction the active species is thought to be [Mo(O2)4]2–. The greatest catalytic activity was exhibited by [Co(NH3)5Cl]2+, which is ascribed to an electrostatically favourable reaction between a positively charged peroxocobalt(III) ion with anionic phenolphthalein species. The temperature dependence of the reactions has been investigated over the range 10–30 °C and mechanisms for the reactions are proposed. Use of trapping agents showed that neither singlet oxygen nor radical species were involved in the oxidations.At higher (0.1–4 mmol dm–3) concentrations of MoVI and WVI the rate laws of the reactions included a term in the square of the hydrogen peroxide concentration. Experiments using a singlet oxygen trapping agent showed that here 1O2 was produced in significant quantities and made a major contribution to the overall rates of the oxidations.

An outline is given of the problems and techniques involved in studying the heterogeneous catalysis by noble metals of solution reactions. In the case of oxidation-reduction reactions, the application of electrochemical methods has revealed a common mechanism of electron transfer through the metal. As a result, the catalytic kinetics of many types ofredox reaction can often be correctly predicted from purely electrochemical and hydrodynamic data.

The concentration of l -ascorbic acid (AA) has been measured in aqueous infusions of four different rose-hip teas (Chilean, French, German and Italian) sieved into narrow size ranges. To prevent aerial oxidation the experiments were carried out under anaerobic conditions. The l -ascorbic acid concentrations in the original teas were obtained and correlated with the particle colour, and the AA partition constant was determined at 80°C for the German rose-hip tea. The density of the dry and of the water-swollen German tea was also measured as well as the extent to which it absorbed water. The rate of AA extraction from the various teas was found to decrease with increasing particle size but it showed little variation with temperature from 70 to 90°C or with the pH of the extracting medium. Electron micrographs were taken of several rose-hip tea samples.

The concentrations of sodium, potassium, magnesium, calcium, chloride, phosphate, sulphate, formate and acetate ions in infusions at 80°C of sieved German rose-hip tea have been measured by ion chromatography. From the equilibrium concentrations of the infusion the ionic contents of the rose-hip tea were evaluated and compared with sparse and contradictory information in the literature. The main species present was found to be potassium, followed by calcium. From the rates of increase of the ionic concentrations with time, first order rate constants of infusion were determined and interpreted in terms of slow diffusion of the ions through the rose-hip particles. The resulting internal diffusion coefficients were found to be 30–80 times smaller than the corresponding diffusion coefficients of the ions in water at 80°C.

The kinetics of the oxidation of alizarin (1,2-dihydroxyanthraquinone) and crocetin (8,8-diapo-ψ,ψ-carotenedioic acid) by alkaline hydrogen peroxide have been studied in aqueous solution over a range of pH, ionic strength and temperature. In each case the rates of the reactions were found to be first order both in the organic colourant and in hydrogen peroxide. Use of free radical and singlet oxygen trapping agents have ruled out the involvement of these species in both reactions. Analysis of the kinetics of oxidation of alizarin has shown that over the pH range 10–12 the predominant reaction is that between the mono-ionised form of alizarin and the perhydroxyl anion, HOO–. The kinetic experiments with crocetin, coupled with spectrophotometric determination of its second ionisation constant, showed that the largest rate constant was that for reaction between HOO– and the doubly ionised form of crocetin. Experiments over the temperature range 21.0–45.0 °C led to activation energies of 68.8 and 69.9 kJ mol–1, and entropies of activation of –95 and –92 J K–1 mol–1 for the alizarin and crocetin reactions, respectively, at 298 K in hydrogencarbonate buffers. Mechanisms for both reactions are proposed.

The kinetics of the oxidation of phenolphthalein by alkaline hydrogen peroxide have been studied in aqueous solution over a range of pH, ionic strength and temperature. The rate of reaction was found to be first order in both phenolphthalein and hydrogen peroxide. Use of free radical and singlet oxygen trapping agents have ruled out the involvement of these species in the reaction. The variation of the rate constant with pH and ionic strength has shown that at pH 11 the main reaction is that between the pink bisphenolate form of phenolphthalein and the perhydroxyl anion, HO2–. At pH 9, epoxidation by the hydrogen peroxide molecule contributed most to the overall rate constant. Borate-buffered solutions gave a faster rate of reaction than those in hydrogencarbonate or ammonia buffers. Experiments over the temperature range 21.0–45.0 °C lead to activation energies of 43.3 and 48.4 kJ mol–1 and entropies of activation of –149 and –131 J K–1 mol–1 at 298 K, in carbonate and borate buffers, respectively. A mechanism for the reaction is proposed.

Ten polyoxo-tungstate and -molybdate complexes have been shown to be stronger catalysts than [WO4]2− and [MoO4]2−, respectively, for bleaching by hydrogen peroxide of methyl orange and of crocetin in aqueous solutions at pH 10 and at 25°C. This is the first report of kinetics of polyoxometalate-catalysed bleaching of dyestuffs with H2O2.

An outline is given of the problems and techniques involved in studying the heterogeneous catalysis by noble metals of solution reactions. In the case of oxidation-reduction reactions, the application of electrochemical methods has revealed a common mechanism of electron transfer through the metal. As a result, the catalytic kinetics of many types ofredox reaction can often be correctly predicted from purely electrochemical and hydrodynamic data.

Adsorption of iodide on reduced platinum electrodes has been shown to increase the rate of reduction of Fe 3+ ions and to inhibit the reduction of oxygen. As a result, platinum was found to catalyse the Fe +3 + I − reaction to a greater extent than predicted from the simple Wagner and Traud additivity principle while, contrary to initial expectation, platinum and gold did not catalyse the O 2 +I − reaction at all. However, these facts were quite consistent with the additivity postulate when use was made of current—potential curves for Fe 3+ reduction, and for oxygen reduction, measured in the presence of small concentrations of iodide ion. It follows that the current—potential curve of a mixture of couples can be obtained by algebraically adding the current—potential curves of the couples present provided the latter curves have been determined in circumstances which correspond to those in the mixture.

The reaction between Ce(IV) and Hg22+ in 1 M (M=mol dm−3) HClO4 at 25 °C has been shown to be catalysed by light, glass and metallic mercury. The kinetics were therefore studied in Teflon vessels in the dark. The addition of Hg2+ ions to mercury(I) stock solutions avoided the formation of colloidal mercury through the disproportionation of Hg22+. When these precautions were taken, the reaction was found to be much slower than reported by previous workers. The rate was first order in Ce(IV) but zero order in Hg(I), and the activation energy was 125 kJ mol−1.

The kinetics of the reaction between CeIV and Hg2+2 in 1 mol dm–3 HClO4 have been studied at 25 °C in the presence of a large rotating platinum disc catalyst. When the disc was cathodically preconditioned, the catalytic rate was first order in cerium(IV) and zero order in mercury(I). It was also directly proportional to the square root of the rotation speed and exhibited a low activation energy, which showed that the reaction was mass-transport controlled. There was excellent agreement between the catalytic rate and the limiting current density for CeIV reduction (converted to rate units by Faraday's law), as would be expected from an electrochemical model of the catalysis. Diffusion coefficients of CeIV and Hg2+2 in 1 mol dm–3 HClO4 were determined from the limiting current measurements. Cyclic voltammetric sweeps after the catalytic runs revealed the presence of underpotential-deposited mercury layers on the platinum surface, and the number of mercury monolayers was evaluated.In contrast, when the platinum disc was anodically preconditioned, the catalytic rate was smaller, of fractional order in both reactants, and independent of rotation speed. The catalysis was therefore surface-controlled. Kinetic and cyclic voltammetric experiments pointed to the presence of two types of adsorbed mercury species on the oxidised platinum surface which strongly influenced the catalysis. Exposure of the oxidised disc to a solution of Hg2+2 ions before the addition of CeIV resulted in an increased catalytic rate because the mercury(I) ions had partly reduced the oxidised surface.

The rate of the reaction between Fe3+ and I– ions, in aqueous 0.05 mol dm–3 HClO4 made up to an ionic strength of 0.1 mol dm–3, has been determined from 5 to 20 °C both homogeneously and in the presence of a large reduced platinum rotating disc catalyst. At low iodide concentrations the catalytic rate was first order in iodide and zero order in iron(III), at low iron(III) concentrations it was first order in iron(III) and zero order in iodide, and at intermediate and comparable concentrations of reactants both kinetic orders were fractional. In all three concentration regions the catalytic rate was proportional to the square root of the disc rotation speed, indicative of mass transport control. These results, as well as the variation in the potential adopted by the catalyst and other findings, agreed with the predictions of the electrochemical mechanism of the catalysis and with the current–potential curves measured for each of the two couples at the same platinum disc.

Carbons catalyse a variety of solution reactions, especially substitutions and isomerisations of certain organic and transition metal substrates as well as a wide range of redox reactions. The kinetic and mechanistic studies carried out on these reactions have been reviewed and the opportunities and problems of the field highlighted.

Tracer diffusion coefficients (Di) have been determined by measuring the limiting oxidation or reduction currents at a large platinum rotating-disc electrode. The systems studied at 5 °C were I–, Fe2+ and Fe3+ in an aqueous supporting medium of 0.05 mol dm–3 HClO4 made up to an ionic strength of 0.1 mol dm–3 with NaClO4, and I–3 in 0.05 mol dm–3 HClO4–0.05 mol dm–3 Nal. The last three ions were also studied at 10, 15 and 20 °C. The resulting activation energies were similar to the value expected from the Stokes–Einstein equation. The values of Diη/T, where η is the viscosity of the solution and T the absolute temperature, have been compared with appropriate literature data at 25 °C. The effective hydrodynamic radii of the four ions have been calculated and interpreted in structural terms.

We have assessed photoinduced toxicity of hypericin in PAM 212 murine keratinocytes and the relationship between concentration, incubation time and light fluence to evaluate the effect of intracellular aggregation at high concentrations. Confocal microscopy was used to establish the subcellular localization of hypericin at 5 and 50 μM and incubation times of 1 and 3 h. From fluorescence uptake time course studies, intracellular hypericin was demonstrated to exist predominantly in the monomeric form for up to 26 h incubation at 5 μM. However, there was a pronounced aggregation effect at 50 μM, with intracellular hypericin fluorescence levels initially showing an increase followed by a decrease with incubation time. This effect was subsequently shown to exert an effect on the phototoxicity of hypericin. On irradiation, the photocytotoxicity for 1 and 7 h incubation with 50 μM hypericin was comparable, whereas using 5 μM the photocytotoxicity showed good correlation with the intracellular fluorescence measurements at 1 and 7 h incubation.

The rates of infusion of caffeine from green Chun Mee tea and from black orthodox Assam Bukial tea, using leaf of size 1.70–2.00 mm, were measured over a range of temperatures. The activation energies were found to be 62 and 40 kJ mol−1, respectively. The diffusion coefficients of caffeine within the tea leaves, calculated from the first-order rate constants at 80°C, were respectively 96 and 132 times smaller than the diffusion coefficient of caffeine in water at 80°C. These results show that diffusion of caffeine through the leaf is a greatly hindered process.

Les neutrinos jouent un role cle, a la fois en physique des particules et en astrophysique. Les sources de neutrinos sont multiples dans l'Univers et ceux-ci sont produits en abondance. Sur Terre, les principales sources sont les accelerateurs ou les reacteurs nucleaires. Cette revue se focalise sur la recherche actuelle de la masse des neutrinos, principalement via la recherche du phenomene appele « oscillations des neutrinos », dans l'etude des neutrinos solaires, des neutrinos « atmospheriques » et des neutrinos issus des accelerateurs ou des reacteurs.

In August 2009, during the swine flu pandemic, a 55-year-old male presented to the Emergency Department (ED) with shortness-of-breath and chest pain. He had experienced diarrhoea and vomiting during the 3 weeks preceding admission, and so had sought the advice of his General Practitioner (GP) who had prescribed a course of oseltamivir (Tamiflu). Despite this, his symptoms had worsened, and on arrival in the ED he was found to be tachypnoeic, tachycardic, feverish, anuric and in type I respiratory failure with a compensated metabolic acidosis. He subsequently became hypotensive, and so was transferred to the Intensive Care Unit (ICU) for supportive treatment of three organ failures. Investigation revealed that he was suffering from Legionnaires disease. This required a prolonged inpatient stay owing to both disease and treatment related complications.

A recent area of developing interest is that of low nuclearity polyperoxometallates, especially the “heteropolyperoxo” species, [PO4{WO(O2)2}4]3-, which was isolated and found to have a highly symmetrical structure by Venturello and co-workers 1 . This is an active catalyst for the epoxidation of unactivated alkenes, by H2O2 under phase transfer conditions, notably as salts containing large lipophilic quaternary ammonium cations 2,3 .

Carbons catalyse a variety of solution reactions, especially substitutions and isomerisations of certain organic and transition metal substrates as well as a wide range of redox reactions. The kinetic and mechanistic studies carried out on these reactions have been reviewed and the opportunities and problems of the field highlighted.

The kinetic results obtained by Zanoni el al (J Set Food Agric 58 1992 275–279) for the extraction of solubles from sieved roast arabica coffee at 90°C have been recalculated and re-interpreted. It has been shown that the 85–90% of soluble extracted within the first minute can be accounted for by diffusion of the soluble constituents through the coffee particles rather than by a large washing phase. It is also suggested that the subsequent slower extraction process may be caused by the emergence of different constituents according to the particle size.