UV-activated luminescence/colourimetric O-2 indicator

An oxygen indicator is described, comprising nanoparticles of titania dispersed in hydroxyethyl cellulose (HEC) polymer film containing a sacrificial electron donor, glycerol, and the redox indicator, indigo-tetrasulfonate (ITS). The indicator is blue-coloured in the absence of UV light, however upon exposure to UV light it not only loses its colour but also luminesces, unless and until it is exposed to oxygen, whereupon its original colour is restored. The initial photobleaching spectral ( absorbance and luminescence) response characteristics in air and in vacuum are described and discussed in terms of a simple reaction scheme involving UV activation of the titania photocatalyst particles, which are used to reduce the redox dye, ITS, to its leuco form, whilst simultaneously oxidising the glycerol to glyceraldehye. The response characteristics of the activated, that is, UV photobleached, form of the indicator to oxygen are also reported and the possible uses of such an indicator to measure ambient O-2 levels are discussed. Copyright (C) 2008 Andrew Mills et al.

A rapid method of assessing the photocatalytic activity of thin TiO2 films using an ink based on the redox dye 2,6-dichloroindophenol

An indicator ink based on the redox dye 2,6-dichloroindophenol ( DCIP) is described, which allows the rapid assessment of the activity of thin, commercial photocatalytic films, such as Activ. The ink works via a photoreductive mechanism, DCIP being reduced to dihydro-DCIP within ca. 7.5 minutes exposure to UVA irradiation of moderate intensity ( ca. 4.8mW cm(-2)). The kinetics of photoreduction are found to be independent of the level of dye present in the ink formulation, but are highly sensitive to the level of glycerol. This latter observation may be associated with a solvatochromic effect, whereby the microenvironment in which the dye finds itself and, as a consequence, its reactivity is altered significantly by small changes in the glycerol content. The kinetics of photoreduction also appear linearly dependent on the UVA light intensity with an observed quantum efficiency of ca. 1.8 x 10(-3). Copyright (C) 2008.

A solvent-based intelligence ink for oxygen

A solvent-based, irreversible oxygen indicator ink is described, comprising semiconductor photocatalyst nanoparticles, a solvent-soluble redox dye, mild reducing agent and polymer. Based on such an ink, a film - made of titanium dioxide, a blue, solvent-soluble, coloured ion-paired methylene blue dye, glycerol and the polymer zein - loses its colour rapidly (

Method of rapid assessment of photocatalytic activities of self-cleaning films

An ink, comprising the redox dye resazurin (Rz) and the sacrificial electron donor glycerol, is shown to be capable of the rapid assessment of the photocatalytic activities of self-cleaning films. In the key initial stage of photocatalysis the ink changes from blue to pink. Prolonged irradiation bleaches the ink and eventually mineralizes it. The kinetics of the initial photoinduced color change is studied as a function of UV irradiance, [glycerol], [Rz], and temperature. The results reveal an apparent approximate quantum yield of 3.5 x 10(-3) and an initial rate, r(i), which increases with [glycerol] and decreases with [Rz]. It is proposed that the reduction of Rz, dispersed throughout the thick (ca. 590 nm) indicator film, may take place either via the diffusion of the dye molecules in the ink film to the surface of the underlying semiconductor layer and their subsequent reaction with photogenerated electrons and/or via the diffusion of alpha-hydroxyalkyl radicals, produced by the oxidation of the glycerol by photogenerated holes, or hydroxy radicals, away from the surface of the semiconductor into the ink film and their subsequent reaction with the dye molecules therein. The decrease in r(i) with [Rz] appears to be due to dimer formation, with the latter impeding the reduction process. The activation energy for the initial color-change process is low, ca. 9.1 +/- 0.1 kJ mol(-1) and not unlike many other photocatalytic processes. The initial rate of dye reduction appears to be directly related to the rate of destruction of stearic acid. The ink can be applied by spin-coating, stamping, or writing, using a felt-tip pen. The efficacy of such an ink for assessing the photocatalytic activity of any photocatalytic film, including those employed on commercial self-cleaning glasses, tiles, and paving stones, is discussed briefly.

THE EFFECT OF POWER ULTRASOUND ON THE OXIDATIVE DISSOLUTION OF RUO2.XH2O BY BROMATE IONS

The effects of continuous sonication and presonication on the kinetics of oxidative dissolution of ruthenium dioxide hydrate by bromate ions under acidic conditions are reported. Compared with unsonicated and presonicated dispersions the overall rate of dissolution of continuously sonicated dispersions is significantly greater due to a reduction in the average particle size and, hence, an increase in the specific surface area. Powder dispersions subjected to continuous ultrasound and presonication exhibit an initial induction period in their corrosion kinetics; the length of this induction period increases with increasing presonication. This corrosion feature is retained in the dissolution kinetics of powder samples which have been subjected to pre-ultrasound, but which are then stirred during the dissolution process. It is believed that this apparent permanent change in the nature of the powder particles is due to the ultrasound induced formation of a very thin layer of a largely unreactive form of ruthenium dioxide (possibly due to partial dehydration) on the surface of the powder particles. A kinetic scheme, based on this model, is used to account for the observed kinetics of dissolution of RuO2 . xH2O which have been subjected to both continuous sonication and presonication.

Selective homogeneous snythesis of dimethyl ether from methanol

Selected Bronsted acidic ionic liquids were tested as homogeneous catalysts for the dehydration of methanol to dimethyl ether. Ionic liquids incorporating an alkanesulfonic acid as a part of the cation, a complex acidic anion, [A(2)H](-), or both, proved to be good catalysts for this process, providing high conversions and selectivities. Homogeneous catalysis in the liquid state represents a novel approach to dimethyl ether synthesis.

A minor catalase/peroxidase from Burkholderia cenocepacia is required for normal aconitase activity

The opportunistic bacterium Burkholderia cenocepacia C5424 contains two catalase/peroxidase genes, katA and katB. To investigate the functions of these genes, katA and katB mutants were generated by targeted integration of suicide plasmids into the katA and katB genes. The catalase/peroxidase activity of the katA mutant was not affected as compared with that of the parental strain, while no catalase/peroxidase activity was detected in the katB mutant. However, the katA mutant displayed reduced resistance to hydrogen peroxide under iron limitation, while the katB mutant showed hypersensitivity to hydrogen peroxide, and reduced growth under all conditions tested. The katA mutant displayed reduced growth only in the presence of carbon sources that are metabolized through the tricarboxylic acid (TCA) cycle, as the growth defect was abrogated in cultures supplemented with glucose or glycerol. This phenotype was also correlated with a marked reduction in aconitase activity. In contrast, aconitase activity was not reduced in the katB mutant and parental strains. The authors conclude that the KatA protein is a specialized catalase/peroxidase that has a novel function by contributing to maintain the normal activity of the TCA cycle, while KatB is a classical catalase/peroxidase that plays a global role in cellular protection against oxidative stress.

A universal measure of chaotropicity and kosmotropicity

Diverse parameters, including chaotropicity, can limit the function of cellular systems and thereby determine the extent of Earth's biosphere. Whereas parameters such as temperature, hydrophobicity, pressure, pH, Hofmeister effects, and water activity can be quantified via standard scales of measurement, the chao-/kosmotropic activities of environmentally ubiquitous substances have no widely accepted, universal scale. We developed an assay to determine and quantify chao-/kosmotropicity for 97 chemically diverse substances that can be universally applied to all solutes. This scale is numerically continuous for the solutes assayed (from +361kJkg^-1mol^-1 for chaotropes to -659kJkg^-1mol^-1 for kosmotropes) but there are key points that delineate (i) chaotropic from kosmotropic substances (i.e. chaotropes =+4; kosmotropes =-4kJkg^-1mol^-1); and (ii) chaotropic solutes that are readily water-soluble (log P<1.9) from hydrophobic substances that exert their chaotropic activity, by proxy, from within the hydrophobic domains of macromolecular systems (log P>1.9). Examples of chao-/kosmotropicity values are, for chaotropes: phenol +143, CaCl₂ +92.2, MgCl₂ +54.0, butanol +37.4, guanidine hydrochloride +31.9, urea +16.6, glycerol [>6.5M] +6.34, ethanol +5.93, fructose +4.56; for kosmotropes: proline -5.76, sucrose -6.92, dimethylsulphoxide (DMSO) -9.72, mannitol -6.69, trehalose -10.6, NaCl -11.0, glycine -14.2, ammonium sulfate -66.9, polyethylene glycol- (PEG-)1000 -126; and for relatively neutral solutes: methanol, +3.12, ethylene glycol +1.66, glucose +1.19, glycerol [<5M] +1.06, maltose -1.43 (kJkg^-1mol^-1). The data obtained correlate with solute interactions with, and structure-function changes in, enzymes and membranes. We discuss the implications for diverse fields including microbial ecology, biotechnology and astrobiology.

Minimizing side reactions in chemoenzymatic dynamic kinetic resolution: organometallic and material strategies

Chemoenzymatic dynamic kinetic resolution (DKR) of rac-1-phenyl ethanol into R-1-phenylethanol acetate was investigated with emphasis on the minimization of side reactions. The organometallic hydrogen transfer (racemization) catalyst was varied, and this was observed to alter the rate and extent of oxidation of the alcohol to form ketone side products. The performance of highly active catalyst [(pentamethylcyclopentadienyl) IrCl2(1-benzyl,3-methyl-imidazol-2-ylidene)] was found to depend on the batch of lipase B used. The interaction between the bio- and chemo-catalysts was reduced by employing physical entrapment of the enzyme in silica using a sol-gel process. The nature of the gelation method was found to be important, with an alkaline method preferred, as an acidic method was found to initiate a further side reaction, the acid catalyzed dehydration of the secondary alcohol. The acidic gel was found to be a heterogeneous solid acid.

Activity and deactivation studies for direct dimethyl ether synthesis using CuO-ZnO-Al2O3 with NH(4)ZSM-5, HZSM-5 or gamma-Al2O3

Herein we investigate the use of CuO-ZnO-Al2O3 (CZA) with different solid acid catalysts (NH(4)ZSM-5. HZSM-5 or gamma-Al2O3) for the production of dimethyl ether from syngas. It was found that of the solid acids, which are necessary for the dehydration function of the admixed system, the CZA/HZSM-5 bifunctional catalyst with a 0.25 acid fraction showed high stability over a continuous period of 212 h.

As this particular system was observed to loose around 16.2% of its initial activity over this operating period this study further investigates the CZA/HZSM-5 bifunctional catalyst in terms of its deactivation mechanisms. TPO investigations showed that the catalyst deactivation was related to coke deposited on the metallic sites: interface between the metallic sites and the support near the metal-support: and on the support itself. 

On the Mechanism of Lewis Acid Catalyzed Glucose Transformations in Ionic Liquids

A complementary computational and experimental study of the reactivity of Lewis acidic CrCl2, CuCl2 and FeCl2 catalysts towards glucose activation in dialkylimidazolium chloride ionic liquids is performed. The selective dehydration of glucose to 5-hydroxymethylfurfural (HMF) proceeds through the intermediate formation of fructose. Although chromium(II) and copper(II) chlorides are able to dehydrate fructose with high HMF selectivity, reasonable HMF yields from glucose are only obtained with CrCl2 as the catalyst. Glucose conversion by CuCl2 is not selective, while FeCl2 catalyst does not activate sugar molecules. These differences in reactivity are rationalized on the basis of in situ X-ray absorption spectroscopy measurements and the results of density functional theory calculations. The reactivity in glucose dehydration and HMF selectivity are determined by the behavior of the ionic liquid-mediated Lewis acid catalysts towards the initial activation of the sugar molecules. The formation of a coordination complex between the Lewis acidic Cr2+ center and glucose directs glucose transformation into fructose. For Cu2+ the direct coordination of sugar to the copper(II) chloride complex is unfavorable. Glucose deprotonation by a mobile Cl- ligand in the CuCl42- complex initiates the nonselective conversion. In the course of the reaction the Cu2+ ions are reduced to Cu+. Both paths are prohibited for the FeCl2 catalyst.

Redispersion of Gold Supported on Oxides

Although many gold heterogeneous catalysts have been shown to exhibit significant activity and high selectivity for a wide range of reactions in both the liquid and gas phases, they are prone to irreversible deactivation. This is often associated with sintering or loss of the interaction of the gold with the support. Herein, we report on the use of methyl iodide as a method of dispersing gold nanoparticles supported on silica, titania, and alumina supports. In the case of titania- and alumina-based catalysts, the gold was transformed from nanometer particles into small clusters and some atomically dispersed gold. In contrast, although there was a drop in the gold particle size on the silica support following CH3I treatment, the size remained in the submicrometer range. The structural changes were correlated with changes in the selectivity and activity for ethanol dehydration and benzyl alcohol oxidation. From these observations, it is clear that this treatment provides a method by which deactivated gold catalysts can be reactivated via redispersion of the gold.

Effects of alcohols and compatible solutes on the activity of β-galactosidase

During alcoholic fermentation, the products build up and can, ultimately, kill the organism due to their effects on the cell's macromolecular systems. The effects of alcohols on the steady-state kinetic parameters of the model enzyme ß-galactosidase were studied. At modest concentrations (0 to 2 M), there was little effect of methanol, ethanol, propanol and butanol on the kinetic constants. However, above these concentrations, each alcohol caused the maximal rate, V (max), to fall and the Michaelis constant, K (m), to rise. Except in the case of methanol, the chaotropicity of the solute, rather than its precise chemical structure, determined and can, therefore, be used to predict inhibitory activity. Compounds which act as compatible solutes (e.g. glycerol and other polyols) generally reduced enzyme activity in the absence of alcohols at the concentration tested (191 mM). In the case of the ethanol- or propanol-inhibited ß-galactosidase, the addition of compatible solutes was unable to restore the enzyme's kinetic parameters to their uninhibited levels; addition of chaotropic solutes such as urea tended to enhance the effects of these alcohols. It is possible that the compatible solutes caused excessive rigidification of the enzyme's structure, whereas the alcohols disrupt the tertiary and quaternary structure of the protein. From the point of view of protecting enzyme activity, it may be unwise to add compatible solutes in the early stages of industrial fermentations; however, there may be benefits as the alcohol concentration increases.

In Situ Single-Crystal Diffraction Studies of the Structural Transition of Metal-Organic Framework Copper 5-Sulfoisophthalate, Cu-SIP-3

The flexibility of the metal-organic framework Cu-2(OH)(C8H3O7S)(H2O)center dot 2H(2)O (Cu-SIP-3) toward reversible single-crystal to single-crystal transformations is demonstrated using in situ diffraction methods at variable temperature. At temperatures below a dehydration-induced phase transition (T < 370 K) the structure is confirmed as being hydrated. In the temperature range where the transition takes place (370 K < T < 405 K) no discrete, sharp Bragg peaks can be seen in the single-crystal X-ray diffraction pattern, indicating significant loss of long-range order. At temperatures higher than 405 K, the Bragg peaks return and the structure can be refined as dehydrated Cu-SIP-3. The loss of guest water molecules can be followed at temperatures below the phase transition giving insight into the mechanism of the dehydration. Addition of nitric oxide gas to the material above the gating opening pressure of 275 mbar also leads to loss of Bragg scattering in the diffraction pattern.

Temperature and water potential relations of tropical Trametes and other wood-decay fungi from the indigenous forests of Zimbabwe

Three isolates each, of nine different Trametes and five other wood inhabiting basidiomycetes, were collected from the indigenous forests of Zimbabwe, and the impact of temperature (20-60 degrees C), osmotic and matric potential (-0.5 to - 8.0 MPa), and their interactions on in vitro growth compared. Generally, there was no significant difference between growth of isolates of the same species in relation to temperature. Temperature relationships of the species studied correlated well with their geographic distributions. Species occurring in hot, dry regions tolerated a wide temperature range, with some showing unusually high thermotolerance (55 degrees, T. socotrana, T. cingulata and T. cervina). There were significant intra-strain differences for individual species in relation to solute potential on glycerol-modified media. Generally, growth of ail species was better on glycerol- and KCl-modified osmotic media than on a metrically-modified medium (PEG 8000) at 25, 30 and 37 degrees. The limits for growth on the osmotic media were significantly wider than matric medium, being - 4.5 to - 5.0 and - 2.5 to - 4.5 MPa, respectively. An Irpex sp. grew at lower water potentials than all other species, with good growth at - 7.0 MPa. This study suggests that the capacity of these fungi for effective growth over a range of temperatures, osmotic and matric potentials contributes to their rapid wood decay capacities in tropical climates.