A study of the kinetic solvent isotope effect on the destruction of microcystin-LR and geosmin using TiO2 photocatalysis

We have previously reported the effectiveness of TiO₂ photocatalysis in the destruction of species generated by cyanobacteria, specifically geosmin and microcystin-LR. In this paper we report an investigation of factors which influence the rate of the toxin destruction at the catalyst surface. A primary kinetic solvent isotope effect of approximately 1.5 was observed when the destruction was performed in a heavy water solvent. This is in contrast to previous reports of a solvent isotope effect of approximately 3, however, these studies were undertaken with a different photocatalyst material. The solvent isotope effect therefore appears to be dependent on the photocatalyst material used. The results of the study support the theory that the photocatalytic decomposition occurs on the catalyst surface rather than in the bulk of the solution. Furthermore it appears that the rate determining step is not oxygen reduction as previously reported. 

The degradation of microcystin-LR using doped visible light absorbing photocatalysts

Microcystins are one of the primary hepatotoxic cyanotoxins released from cyanobacteria. The presence of these compounds in water has resulted in the death of both humans and domestic and wild animals. Although microcystins are chemically stable titanium dioxide photocatalysis has proven to be an effective process for the removal of these compounds in water. One problem with this process is that it requires UV light and therefore in order to develop effective commercial reactor units that could be powered by solar light it is necessary to utilize a photocatalyst that is active with visible light. In this paper we report on the application of four visible light absorbing photocatalysts for the destruction of microcystin-LR in water. The rhodium doped material proved to be the most effective material followed by a carbon-modified titania. The commercially available materials were both relatively poor photocatalysts under visible radiation while the platinum doped catalyst also displayed a limited activity for toxin destruction. © 2009 Elsevier Ltd. All rights reserved.

The photocatalytic decomposition of microcystin-LR using selected titanium dioxide materials

Microcystins (cyclic heptapeptides) produced by a number of freshwater cyanobacteria are a potential cause for concern in potable water supplies due to their acute and chronic toxicity. TiO₂ photocatalysis is a promising technology for removal of these toxins from drinking water. It is, however, necessary to have a sufficient knowledge of how the catalyst materials cause the degradation of the toxins through the photocatalytic process. The present study reports microcystin degradation products of the photocatalytic oxidation by using a number of commercial TiO₂ powder (P25, PC50, PC500 and UV100) and granular (KO1, KO3, TiCat-C, TiCat-S) materials, so aiding the mechanistic understanding of this process. Liquid chromatography-mass spectrometry analysis demonstrated that the major destruction pathway of microcystin for all the catalysts tested followed almost the same pathway, indicating the physical properties of the catalysts had little effects on the degradation pathway of microcystin-LR. 

Mechanistic studies of the photocatalytic oxidation of microcystin-LR: An investigation of byproducts of the decomposition process

Microcystins (cyclic heptapeptides) are produced by a number of freshwater cyanobacteria and cause concern in potable water supplies due to their acute and chronic toxicity. The present study reports the structural characterization of the degradation products of the photocatalytic oxidation of microcystin-LR, so aiding the mechanistic understanding of this process. TiO₂ photocatalysis is a promising technology for removal of these toxins from drinking water. However, before it can be adopted in any practical application it is necessary to have a sufficient knowledge of degradation byproducts and their potential toxicity. Liquid chromatography-mass spectrometry analysis demonstrated that the major destruction pathway of microcystin appears to be initiated via three mechanisms: UV irradiation, hydroxyl radical attack, and oxidation. UV irradiation caused geometrical isomerization of microcystin converting the (4E), (6E) of the Adda configuration to (4E), 6(Z) or 4(Z), 6(E). Hydroxyl radical attack on the conjugated diene structure of Adda moiety produced dihyroxylated products. Further oxidation cleaved the hydroxylated 4-5 and/or 6-7 bond of Adda to form aldehyde or ketone peptide residues, which then were oxidized into the corresponding carboxylic acids. Photocatalysis also hydrolyzed the peptide bond on the ring structure of microcystin to form linear structures although this appeared to be a minor pathway.

Mechanistic and toxicity studies of the photocatalytic oxidation of microcystin-LR

Cyanobacterial toxins present in drinking water sources pose a considerable threat to human health. Conventional water treatment systems have proven unreliable for the removal of these toxins and hence new techniques have been investigated. Previous work has shown that TiO₂ photocatalysis effectively destroys microcystin-LR in aqueous solutions, however, a variety of by-products were generated. In this paper, we report a mechanistic study of the photocatalytic destruction of microcystin-LR. In particular, the toxicity by-products of the process have been studied using both brine shrimp and protein phosphatase bioassays. 

Hydrogen peroxide enhanced photocatalytic oxidation of microcystin-lR using titanium dioxide

Cyanobacterial toxins present in drinking water sources pose a considerable threat to human health. Conventional water treatment systems have proven unreliable for the removal of these toxins and hence new techniques have been investigated. Previous work has shown that TiO₂ photocatalysis effectively destroys microcystin-LR in aqueous solutions, however non-toxic by-products were detected. It has been shown that photocatalytic reactions are enhanced by utilisation of alternative electron acceptors. We report here enhanced photocatalytic degradation of microcystin-LR following the addition of hydrogen peroxide to the system. It was also found that hydrogen peroxide with UV illumination alone was capable of decomposing microcystin-LR although at a much slower rate than found for TiO₂. No HPLC detectable by-products were found when the TiO₂/UV/H₂O₂ system was used indicating that this method is more effective than TiO₂/UV alone. Results however indicated that only 18% mineralisation occurred with the TiO₂/UV/H₂O₂ system and hence undetectable by-products must still be present. At higher concentrations hydrogen peroxide was found to compete with microcystin-LR for surface sites on the catalyst but at lower peroxide concentrations this competitive adsorption was not observed. Toxicity studies showed that both in the presence and absence of H₂O₂ the microcystin solutions were detoxified. These findings suggest that hydrogen peroxide greatly enhances the photocatalytic oxidation of microcystin-LR.

The Involvement of Phycocyanin Pigment in the Photodecomposition of the Cyanobacterial Toxin, Microcystin-LR

While investigating the destruction of the cyanobacterial hepatotoxin microcystin-LR in the presence of phycocyanin pigment via semiconductor photocatalysis, it became apparent that the pigment was catalysing the toxin decomposition. The mechanism of this process in terms of phycocyanin acting as a photo-oxygenation sensitizer via singlet oxygen and superoxide attack is explored. The absorption and fluorescence spectra of phycocyanin have been obtained and data on the properties of the excited state calculated. The established photo-oxygenation sensitizer rose bengal was also used as a catalyst for the photolytic decomposition of microcystin-LR to help elucidate the decomposition mechanism. 

Processes influencing the destruction of microcystin-LR by TiO2 photocatalysis

We have previously reported the effectiveness of TiO₂ photocatalysis in the destruction of the cyanotoxin microcystin-LR [P.K.J. Robertson, L.A. Lawton, B. Münch, J. Rouzade, J. Chem. Soc., Chem. Commun., 4 (1997) 393; P.K.J. Robertson, L.A. Lawton, B. Münch, B.J.P.A. Cornish, J. Adv. Oxid. Technol., in press]. In this paper we report an investigation of factors which influence the rate of the toxin destruction at the catalyst surface. A primary kinetic isotope effect of approximately 3 was observed when the destruction was performed in a heavy water solvent. Hydroxylated compounds were observed as products of the destruction process. No destruction was observed when the process was investigated under a nitrogen atmosphere.

Label-free Detection of Microcystin-LR in Waters Using Real-Time Potentiometric Biosensors Based on Single-Walled Carbon Nanotubes Imprinted Polymers

Microcystin-LR (MC-LR) is a dangerous toxin found in environmental waters, quantified by high performance liquid chromatography and/or enzyme-linked immunosorbent assays. Quick, low cost and on-site analysis is thus required to ensure human safety and wide screening programs. This work proposes label-free potentiometric sensors made of solid-contact electrodes coated with a surface imprinted polymer on the surface of Multi-Walled Carbon NanoTubes (CNTs) incorporated in a polyvinyl chloride membrane. The imprinting effect was checked by using non-imprinted materials. The MC-LR sensitive sensors were evaluated, characterized and applied successfully in spiked environmental waters. The presented method offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods.

Microcystin-LR detection in water by the Fabry–Pérot interferometer using an optical fibre coated with a sol–gel imprinted sensing membrane

Cyanobacteria deteriorate the water quality and are responsible for emerging outbreaks and epidemics causing harmful diseases in Humans and animals because of their toxins. Microcystin-LR (MCT) is one of the most relevant cyanotoxin, being the most widely studied hepatotoxin. For safety purposes, the World Health Organization recommends a maximum value of 1 μg L−1 of MCT in drinking water. Therefore, there is a great demand for remote and real-time sensing techniques to detect and quantify MCT. In this work a Fabry–Pérot sensing probe based on an optical fibre tip coated with a MCT selective thin film is presented. The membranes were developed by imprinting MCT in a sol–gel matrix that was applied over the tip of the fibre by dip coating. The imprinting effect was obtained by curing the sol–gel membrane, prepared with (3-aminopropyl) trimethoxysilane (APTMS), diphenyl-dimethoxysilane (DPDMS), tetraethoxysilane (TEOS), in the presence of MCT. The imprinting effect was tested by preparing a similar membrane without template. In general, the fibre Fabry–Pérot with a Molecular Imprinted Polymer (MIP) sensor showed low thermal effect, thus avoiding the need of temperature control in field applications. It presented a linear response to MCT concentration within 0.3–1.4 μg L−1 with a sensitivity of −12.4 ± 0.7 nm L μg−1. The corresponding Non-Imprinted Polymer (NIP) displayed linear behaviour for the same MCT concentration range, but with much less sensitivity, of −5.9 ± 0.2 nm L μg−1. The method shows excellent selectivity for MCT against other species co-existing with the analyte in environmental waters. It was successfully applied to the determination of MCT in contaminated samples. The main advantages of the proposed optical sensor include high sensitivity and specificity, low-cost, robustness, easy preparation and preservation.

Decadal predictability of the Atlantic meridional overturning circulation and climate in the IPSL-CM5A-LR model

This study explores the decadal potential predictability of the Atlantic Meridional Overturning Circulation (AMOC) as represented in the IPSL-CM5A-LR model, along with the predictability of associated oceanic and atmospheric fields. Using a 1000-year control run, we analyze the prognostic potential predictability (PPP) of the AMOC through ensembles of simulations with perturbed initial conditions. Based on a measure of the ensemble spread, the modelled AMOC has an average predictive skill of 8 years, with some degree of dependence on the AMOC initial state. Diagnostic potential predictability of surface temperature and precipitation is also identified in the control run and compared to the PPP. Both approaches clearly bring out the same regions exhibiting the highest predictive skill. Generally, surface temperature has the highest skill up to 2 decades in the far North Atlantic ocean. There are also weak signals over a few oceanic areas in the tropics and subtropics. Predictability over land is restricted to the coastal areas bordering oceanic predictable regions. Potential predictability at interannual and longer timescales is largely absent for precipitation in spite of weak signals identified mainly in the Nordic Seas. Regions of weak signals show some dependence on AMOC initial state. All the identified regions are closely linked to decadal AMOC fluctuations suggesting that the potential predictability of climate arises from the mechanisms controlling these fluctuations. Evidence for dependence on AMOC initial state also suggests that studying skills from case studies may prove more useful to understand predictability mechanisms than computing average skill from numerous start dates.

Microcystins -LA, -YR, and -LR action on neutrophil migration

Microcystins (MCs) produced by some freshwater cyanobacterial species possess potent liver toxicity as evidenced by acute neutrophil infiltration. Here, we investigate the ability of three structurally distinct toxins (MC-LA, MC-LR, and MC-YR) to evoke neutrophil recruitment per se and their effects on migration pathways. Intravital Microscopic Studies showed that topical application of only MC-LR enhanced the numbers of rolling and adhered leukocytes in the endothelium of postcapillary mesenteric venules. The latter effects may be dependent upon induction of the synthesis and expression Of L-selectin and beta(2)-integrin in neutrophils, as assessed by flow cytometry and RT-PCR, respectively. Conversely, the three toxins promoted direct locomotion of neutrophils and enhanced their migration in response to NO, as measured by Boyden chamber assays, and increased intracellular calcium, a messenger in the chemotaxic process. In conclusion, our results show that MCs act on specific pathways of neutrophil recruitment, indicating their potential effect on neutrophils activation. (C) 2009 Elsevier Inc. All rights reserved.

Att leva som man lär : Implementering av företagskultur vid företagsförvärv

Så mycket som 83 % av alla företagsförvärv misslyckas med att öka aktieägarvärde och hela 53 % minskar till och med i aktieägarvärde (Daniel & Metcalf, 2001). Det är mycket lättare att göra själva affären, än att få den att fungera menar Nguyen & Kleiner (2003). Misslyckade företagsförvärv beror oftast på kulturella skillnader mellan företag och implementering av företagskultur är en nyckelfaktor för ett framgångsrikt företagsförvärv (Lodofors & Boateng, 2006). Syftet är att undersöka implementering av företagskultur efter ett företagsförvärv och att kartlägga ledningens och mellanchefernas egna upplevelser av framgångsfaktorer och svårigheter under processen. I den teoretiska referensramen definieras företagskultur och beskrivs utifrån ett flertal kulturella nivåer där värderingar får särskild uppmärksamhet då studien fokuserar på värdegrundsarbete. Det görs även en beskrivning av olika sätt att utveckla kulturer på. Vidare beskrivs faktorer som ledning och chefer bör ta hänsyn till vid implementering av företagskultur. Dessa är ledarskap, förtroende och lärande (Schein, 2010, Nguyen & Kleiner, 2003, Lakshman, 2011, Bijlsma-Frankema, 2001 m.fl.). För att undersöka studiens syfte har en kvalitativ metod med semistrukturerade intervjuer genomförts. Undersökningen grundar sig på intervjuer med ledning och mellanchefer på Fastighetsbolaget AB. Resultatet visar att bolagets implementering av värderingar upplevs av de flesta respondenter som väldigt framgångsrik. Framgångsfaktorer i deras värdegrundsarbete sammanfattas med att ta det bästa av två världar, anpassa struktur efter önskad kultur, leva som man lär, ha transparens i information och beslut, skapa en gemensam syn på värderingar och uppföljning av medarbetares upplevelser. Den svårighet som diskuteras är kring att skapa en gemensam värdegrund i hela bolaget. Studiens slutsats är att implementering av företagskultur efter ett företagsförvärv handlar om att ledare måste leva som de lär och att ledningen måste skapa förutsättningar för det och arbeta med uppföljning av medarbetares upplevelser.