Journal of Environmental Science and Health A, 2012, 47, 149. 

Hg2+ and CH3Hg+ are frequently encountered in the environment either as free ions or complexed with organic matter, such as humic acids. The majority of the reported HPLC-based separations of environmental mercury species, however, separate Hg2+ from CH3Hg+ in which the former species elutes close to the void volume. To detect mercury-species in environmental waters that may have so far escaped detection, a separation method is needed that sufficiently retains both Hg2+ and CH3Hg+. One way to develop such a method is to increase the retention of Hg2+ and CH3Hg+ using existing HPLC separations. We here report on the improvement of a previously reported RP-HPLC-based separation of Hg2+ and CH3Hg+ that employed a 100 % aqueous mobile phase [10 mM L-cysteine (Cys) in 50 mM phosphate buffer (pH 7.5)]. To increase the retention of Hg2+, Cys was replaced by the comparatively more hydrophobic N-acetylcysteine (N-Cys). To achieve a c...

Angew. Chem. Int. Ed. 2011, 50, 12214. 

To dye for: Three related families of fluorescent dyes, rigidified by boron difluoride and based on bidentate anilido-pyridyl donor ligands, are reported (see picture). The dyes show quantum yields up to 0.75 and improved Stokes shifts of >100 nm relative to the widely employed BODIPY family of dyes. Furthermore, the new dyes are exceptionally photostable and membrane-specific.

Photochem. Photobiol. Sci. 2011, 10, 1701. 

Aflatoxins are mycotoxins produced by fungi of the genus Aspergillus, which is widely spread in the tropics and subtropics. To date, aflatoxin phototoxicity has been recognized, but the mechanism responsible for this phototoxicity has not been fully characterized. In the present paper, nanosecond laser flash photolysis studies allowed us to elucidate the photochemical processes undergone by two mycotoxins, namely aflatoxin B-1 and B-2, upon UV irradiation. In brief, photolysis (308 nm) of the aflatoxins leads to intersystem crossing, giving rise to their triplet excited state. The triplet state can readily be quenched by indole and hydroquinone, and also by molecular oxygen yielding singlet oxygen (singlet oxygen quantum yields of 0.51 and 0.59 were found for aflatoxin B-1 and B-2, respectively). In addition, our data indicate the ability of the two aflatoxins to photoionize upon 248 nm excitation. The photoionization quantum yield for aflatox...

ChemBioChem 2010, 11, 2384. 

Lights out at two: The oxidation of avGFP and EGFP by singlet oxygen not only diminishes their fluorescence emission and changes their absorption properties, but also generates undesired protein aggregation. This could have important consequences in studies in which pairs of fluorescent proteins are used, such as in FRET experiments. 

J. Biol. Chem. 2010, 285, 25731. 

We have previously established that the anti-cancer lysophospholipid edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine, Et-18-OCH3) induces cell death in yeast by selective modification of lipid raft composition at the plasma membrane. In this study we determined that α-tocopherol protects cells from the edelfosine cytotoxic effect, preventing the internalization of sterols and the plasma membrane proton pump ATPase, Pma1p. Two non-mutually exclusive hypotheses were considered to explain the protective effect of α-tocopherol: (i) its classical antioxidant activity is necessary to break progression of lipid peroxidation, despite the fact Saccharomyces cerevisiae does not possess polyunsaturated fatty acids and (ii) due to its complementary cone shape, insertion of α-tocopherol could correct membrane curvature stress imposed by edelfosine (inverted cone shape). We then developed tools to distinguish between these two hypotheses and dissect...

March 18, 2010

Chem. Commun. 2010, 46, 3595. 

The unexpected interaction between thiazole orange (TO) and calix[4]arene sulfonate is reported herein. H-Aggregates of TO switching on their fluorescence in solution are observed. Surprisingly, fluorescence enhancement is not linked to host–guest inclusion, but rather to calix[4]arene sulfonate serving as a template for several TO molecules.

Environ. Microbiol. 2009, 11, 2491. 

Microbiological metal toxicity involves redox reactions between metal species and cellular molecules, and therefore, we hypothesized that antioxidant systems might be chromosomal determinants affecting the susceptibility of bacteria to metal toxicity. Here, survival was quantified in metal ion-exposed planktonic cultures of several Escherichia coli strains, each bearing a mutation in a gene important for redox homeostasis. This characterized approximately 250 gene-metal combinations and identified that sodA, sodB, gor, trxA, gshA, grxA and marR have distinct roles in safeguarding or sensitizing cells to different toxic metal ions (Cr(2)O(7)(2-), Co(2+), Cu(2+), Ag(+), Zn(2+), AsO(2)(-), SeO(3)(2-) or TeO(3)(2-)). To shed light on these observations, fluorescent sensors for reactive oxygen species (ROS) and reduced thiol (RSH) quantification were used to ascertain that different metal ions exert oxidative toxicity through disparate modes-of-action. Th...

April 6, 2009

Photochem. Photobiol. 2009, 85, 1110. 

Singlet oxygen is known to be a potent mutagenic agent and several biologically relevant molecules have been proposed to act as scavengers for this noxious species. However, numerous studies have been conducted in homogenous solution and the reactivity of singlet oxygen scavengers known to bind DNA has never been investigated in double-stranded DNA. In the following paper, we present the results obtained regarding the interaction between 4',6-diamidino-2-phenylindole (DAPI) and singlet oxygen. We show the molecule to be a potent scavenger of singlet oxygen in aqueous solution with an absolute rate constant (chemical and physical quenching of singlet oxygen) of (1.7 +/- 0.3) x 10(7) m(-1) s(-1). In addition, we demonstrate that the binding mode of a singlet oxygen scavenger to DNA can strongly influence its reactivity toward singlet oxygen. In the case of DAPI, while the molecule exhibits a chemical reaction with singlet oxygen when the molecule is...

Org. Biomol. Chem. 2008, 6, 354. 

Two new sensors for the detection of reactive oxygen species have been synthesized and characterized; they contain the 4-amino-7-nitrobenzofurazan (ABF) moiety covalently tethered to a phenol. Comparison of sensors ABFhd and dABFhd (the latter containing two ortho-methyl groups) shows that introduction of steric bulk leads to an improvement of fluorescent sensor performance, thus confirming our previous predictions based on computational chemistry. ABFhdand dABFhd are new tools for biological applications involving reactive oxygen species, in particular oxygen-centered radicals.

Biomaterials, 2008, 29, 1147. 

We successfully fabricated transparent, robust hydrogels as corneal substitutes from concentrated recombinant human type I and type III collagen solutions crosslinked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). White light transmission through these gels is comparable or superior to that of human corneas. Hydrogels from both type I and type III collagens supported in vitro epithelium and nerve over-growth. While both these biocompatible hydrogels have adequate tensile strength and elasticity for surgical manipulation, type III collagen hydrogels tended to be mechanically superior. Twelve-month post-implantation results of type I recombinant collagen-based corneal substitutes into mini-pigs showed retention of optical clarity, along with regeneration of corneal cells, nerves and tear film. For clinical use, implants based on fully characterized, recombinant human collagen eliminate the risk of pathogen transfer...

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