Boosting Effect of Sterically Protected Glucosyl Substituents in Formic Acid Dehydrogenation by Iridium(III) 2-Pyridineamidate Catalysts.

[Cp*Ir(R-pica)Cl] (Cp*=pentamethylcyclopentadienyl anion, pica=2-picolineamidate) complexes bearing carbohydrate substituents on the amide nitrogen atom (R=methyl-ß-D-gluco-pyranosid-2-yl, 1; methyl-3,4,6-tri-O-acetyl-ß-D-glucopyranosid-2-yl, 2) were tested as catalysts for formic acid dehydrogenation in water. TOFMAX values over 12000 h-1 and 50000 h-1 were achieved at 333 K for 1 and 2, respectively, with TON values over 35000 for both catalysts. Comparison with the simpler cyclohexyl-substituted analogue (3) indicated that glucosyl-based complexes are much better performing under the same experimental conditions (TOFMAX=5144 h-1, TON=5000 at pH 2.5 for 3) owing to a lower tendency to isomerize to the less active k2-N,O isomer upon protonation. The 5-fold increase in TOFMAX observed for 2 with respect to 1 is reasonably due to an optimal steric protection by the acetyl substituent, which may prevent unproductive inner-sphere reactivity. These results showcase a powerful strategy for the inhibition of the common deactivation pathways of [Cp*Ir(R-pica)X] catalysts for FA dehydrogenation, paving the way for the development of better performing hydrogen storage systems.

Laccase treatment impairs bisphenol A-induced cancer cell proliferation affecting estrogen receptor alpha-dependent rapid signals.

A wide variety of environmental contaminants exert estrogenic actions in wildlife, laboratory animals, and in human beings through binding to nuclear estrogen receptors (ERs). Here, the mechanism(s) of bisphenol A (BPA) to induce cell proliferation and the occurrence of its bioremediation by treatment with laccase are reported. BPA, highly present in natural world and considered as a model of environmental estrogen action complexity, promotes human cancer cell proliferation via ERalpha-dependent signal transduction pathways. Similar to 17beta-estradiol, BPA increases the phosphorylation of both extracellular regulated kinase and AKT. Specific inhibitors of these kinase completely block the BPA effect on cancer cell proliferation. Notably, high BPA concentrations (i.e., 0.1 and 1 mM) are cytotoxic even in ERalpha-devoid cancer cells, indicating that an ERalpha-independent mechanism participates to BPA-induced cytotoxicity. On the other hand, BPA oxidation by laccase impairs the binding of this environmental estrogen to ERalpha loosing at all ERalpha-dependent effect on cancer cell proliferation. Moreover, the laccase-catalyzed oxidation of BPA reduces the BPA cytotoxic effect. Thus, laccase appears to impair BPA action(s), representing an invaluable bioremediation enzyme.

The reaction of hydrogen atoms with methionine residues: A model of reductive radical stress causing tandem protein-lipid damage.

The occurrence of tandem damage, due to reductive radical stress involving proteins and lipids, is shown by using a biomimetic model. It is made of unsaturated lipid vesicle suspensions in phosphate buffer in the presence of methionine, either as a single amino acid or as part of a protein such as RNase A, which contains four methionine residues. The radical process starts with the formation of H(.) atoms by reaction of solvated electrons with dihydrogen phosphate anions, which selectively attack the thioether function of methionine. The modification of methionine to alpha-aminobutyric acid is accompanied by the formation of thiyl radicals, which in turn cause the isomerization of the cis fatty acid residues to the trans isomers. The relationship between methionine modification and lipid damage and some details of the reductive radical stress obtained by proteomic analysis of irradiated RNase A are presented.

Investigation of radical-based damage of RNase A in aqueous solution and lipid vesicles.

The gamma-irradiation of bovine pancreatic ribonuclease A (RNase A) in aqueous solution were investigated at different doses by vibrational spectroscopy as well as enzymatic assay, electrophoresis, and HPLC analysis. Both functional and structural changes of the protein were caused by attack of H(*) atoms and (*)OH radicals. In particular, Raman spectroscopy was shown to be a useful tool in identifying conformational changes of the protein structure and amino acidic residues that are preferential sites of the radical attack (i.e., tyrosine and methionine). After partial structural changes by the initial radical attack, the internal sulfur-containing amino acid residues were rendered susceptible to transformation. By using the biomimetic model of dioleoyl phosphatidyl choline vesicle suspensions containing RNase A, the damage to methione residues could be connected to a parallel alteration of membrane unsaturated lipids. In fact, thiyl radical species formed from protein degradation can diffuse into the lipid bilayer and cause isomerization of the naturally occurring cis double bonds. As a consequence, trans unsaturated fatty acids are formed in vesicles and can be considered to be markers of this protein damage.

Structural analysis of styrene oxide/haemoglobin adducts by mass spectrometry: identification of suitable biomarkers for human exposure evaluation.

The structural characterisation of adducts formed by the in vitro reaction of haemoglobin (Hb) with styrene oxide (SO), the most reactive metabolite of the industrial reagent styrene, was obtained by liquid chromatography/electrospray ionisation mass spectrometry (LC/ES-MS) analysis of modified tryptic peptides of human Hb chains. The reactive sites of human Hb towards SO were identified through characterisation of alkylated tryptic peptides by matrix-assisted laser desorption/ionisation with tandem mass spectrometry (MALDI-MS/MS). A procedure was set up based on this characterisation, allowing Hb modification to be assessed by monitoring SO/Hb adducts using HPLC with selected ion recording (SIR) mass spectrometry. By this methodology it was also possible to compare advantages and disadvantages of presently available strategies for the measurement of Hb adducts with SO. The results obtained could most plausibly lead to the optimisation of molecular dosimetry of SO adducts, and the analytical procedure described herein could be applied to the biological monitoring of styrene exposure in the workplace.