Laboratoire de Chimie et Biologie des Métaux

The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable, and efficient systems for the conversion and storage of renewable energy sources, such as solar energy. The production of hydrogen, a fuel with remarkable properties, through sunlight-driven water splitting appears to be a promising and appealing solution. While the active sites of enzymes involved in the overall water-splitting process in natural systems, namely hydrogenases and photosystem II, use iron, nickel, and manganese ions, cobalt has emerged in the past five years as the most versatile non-noble metal for the development of synthetic H(2)- and O(2)-evolving catalysts. Such catalysts can be further coupled with photosensitizers to generate photocatalytic systems for light-induced hydrogen evolution from water.

Molecular-based magnets with high magnetic-ordering temperatures, T(c), can be obtained by mild chemistry methods by focusing on the bimetallic and mixed-valence transition metal micro-cyanide of the Prussian blue family. A simple orbital model was used to predict the electronic structure of the metal ions required to achieve a high ordering temperature. The synthesis and magnetic properties of two compounds, [Cr(5)(CN)(12)].10H(2)O and Cs(0.75) [Cr(2.125)(CN)(6)].5H(2)O, which exhibited magnetic-ordering temperatures of 240 and 190 kelvin, respectively, are reported, together with the strategy for further work.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMain-Group Element, Organic, and Organometallic Derivatives of PolyoxometalatesPierre Gouzerh and Anna ProustView Author Information Laboratoire de Chimie des Métaux de Transition, URA CNRS No. 419, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris Cedex 05, France Cite this: Chem. Rev. 1998, 98, 1, 77–112Publication Date (Web):February 5, 1998Publication History Received28 May 1997Revised28 November 1997Published online5 February 1998Published inissue 1 February 1998https://pubs.acs.org/doi/10.1021/cr960393dhttps://doi.org/10.1021/cr960393dresearch-articleACS PublicationsCopyright © 1998 American Chemical SocietyRequest reuse permissionsArticle Views5750Altmetric-Citations702LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Anions,Chemical structure,Cluster chemistry,Ligands,Reaction products Get e-Alerts

BACKGROUND: The availability of hundreds of bacterial genomes allowed a comparative genomic study of the Type VI Secretion System (T6SS), recently discovered as being involved in pathogenesis. By combining comparative and phylogenetic approaches using more than 500 prokaryotic genomes, we characterized the global T6SS genetic structure in terms of conservation, evolution and genomic organization. RESULTS: This genome wide analysis allowed the identification of a set of 13 proteins constituting the T6SS protein core and a set of conserved accessory proteins. 176 T6SS loci (encompassing 92 different bacteria) were identified and their comparison revealed that T6SS-encoded genes have a specific conserved genetic organization. Phylogenetic reconstruction based on the core genes showed that lateral transfer of the T6SS is probably its major way of dissemination among pathogenic and non-pathogenic bacteria. Furthermore, the sequence analysis of the VgrG proteins, proposed to be exported in a T6SS-dependent way, confirmed that some C-terminal regions possess domains showing similarities with adhesins or proteins with enzymatic functions. CONCLUSION: The core of T6SS is composed of 13 proteins, conserved in both pathogenic and non-pathogenic bacteria. Subclasses of T6SS differ in regulatory and accessory protein content suggesting that T6SS has evolved to adapt to various microenvironments and specialized functions. Based on these results, new functional hypotheses concerning the assembly and function of T6SS proteins are proposed.

Catalysis is a key enabling technology for solar fuel generation. A number of catalytic systems, either molecular/homogeneous or solid/heterogeneous, have been developed during the last few decades for both the reductive and oxidative multi-electron reactions required for fuel production from water or CO(2) as renewable raw materials. While allowing for a fine tuning of the catalytic properties through ligand design, molecular approaches are frequently criticized because of the inherent fragility of the resulting catalysts, when exposed to extreme redox potentials. In a number of cases, it has been clearly established that the true catalytic species is heterogeneous in nature, arising from the transformation of the initial molecular species, which should rather be considered as a pre-catalyst. Whether such a situation is general or not is a matter of debate in the community. In this review, covering water oxidation and reduction catalysts, involving noble and non-noble metal ions, we limit our discussion to the cases in which this issue has been directly and properly addressed as well as those requiring more confirmation. The methodologies proposed for discriminating homogeneous and heterogeneous catalysis are inspired in part by those previously discussed by Finke in the case of homogeneous hydrogenation reaction in organometallic chemistry [J. A. Widegren and R. G. Finke, J. Mol. Catal. A, 2003, 198, 317-341].

In an effort to standardize the determination of overpotential values for H(2)-evolving catalysts in non-aqueous solvents and allow a reliable comparison of catalysts prepared and assayed by different groups, we propose to adopt the half-wave potential as reference potential. We provide a simple method for measuring it from usual stationary cyclic voltammograms, and we derive the formulas to which the measured potential should be compared, taking into account the effect of homoconjugation. We also revisit tabulated values of the standard reduction potential of protons in nonaqueous solvents, E(H+/H(2))°.

Membrane and nuclear proteins of poor solubility have been separated by high resolution two-dimensional (2-D) gel electrophoresis. Isoelectric focusing with immobilized pH gradients leads to severe quantitative losses of proteins in the resulting 2-D map, although the resolution is usually high. Protein solubility could be improved by using denaturing solutions containing various detergents and chaotropes. Best results were obtained with a denaturing solution containing urea, thiourea, and detergents (both nonionic and zwitterionic). The usefulness of thiourea-containing denaturing mixtures is shown for microsomal and nuclear proteins as well as for tubulin, a protein highly prone to aggregation.

Hydrogen production through the reduction of water appears to be a convenient solution for the long-run storage of renewable energies. However, economically viable hydrogen production requests platinum-free catalysts, because this expensive and scarce (only 37 ppb in the Earth's crust) metal is not a sustainable resource [Gordon RB, Bertram M, Graedel TE (2006) Proc Natl Acad Sci USA 103:1209-1214]. Here, we report on a new family of cobalt and nickel diimine-dioxime complexes as efficient and stable electrocatalysts for hydrogen evolution from acidic nonaqueous solutions with slightly lower overvoltages and much larger stabilities towards hydrolysis as compared to previously reported cobaloxime catalysts. A mechanistic study allowed us to determine that hydrogen evolution likely proceeds through a bimetallic homolytic pathway. The presence of a proton-exchanging site in the ligand, furthermore, provides an exquisite mechanism for tuning the electrocatalytic potential for hydrogen evolution of these compounds in response to variations of the acidity of the solution, a feature only reported for native hydrogenase enzymes so far.

It is the dawning of the age of supramolecular photocatalysts for H2 production using first-row transition-metal catalytic centers. These catalysts consist of a ruthenium tris(diimine) light-harvesting unit covalently linked to various catalytic cobaloxime centers (see picture). The catalyst stability, CoII/CoI redox potential, and nucleophilicity of the cobaloxime moiety all affect the photocatalytic properties.

Abstract A series of ferrocene derivatives based upon the structure of the antiestrogenic drug tamoxifen or of its active metabolite hydroxytamoxifen has been prepared and named by analogy ferrocifens and hydroxyferrocifens. This series includes 1‐[4‐(O(CH 2 ) n NMe 2 )phenyl]‐1‐phenyl‐2‐ferrocenyl‐but‐1‐ene and 1‐[4‐(O(CH 2 ) n NMe 2 )phenyl]‐1‐(4‐hydroxyphenyl)‐2‐ferrocenyl‐but‐1‐ene, with n =2, 3, 5 and 8, and 1‐[4‐(O(CH 2 ) 2 NMe 2 )phenyl]‐1‐(4‐hydroxyphenyl)‐2‐ferrocenylethene. Most of these molecules have been synthesised by McMurry cross‐coupling of the appropriate ketones, except for the ethene complexes, which were prepared by a four‐step reaction sequence starting from the ferrocenylacetic acid. All these compounds were obtained as mixtures of Z and E isomers. The isomers were separated in the cases of the ferrocenyl derivatives of tamoxifen and hydroxytamoxifen ( n =2). No isomerisation of the Z and E isomers occurred in DMSO after one day, while a 50:50 mixture of the isomers was obtained within one hour in chloroform. The X‐ray structure of ( E )‐1‐[4‐(O(CH 2 ) 2 NMe 2 )phenyl]‐1‐(4‐hydroxyphenyl)‐2‐ferrocenyl‐but‐1‐ene has been determined. The relative binding affinity (RBA) values of the hydroxyferrocifens for the estrogen receptor alpha (ERα) was good to moderate, with values decreasing progressively with the length of the basic chain. The RBA values found for the estrogen receptor beta (ERβ) are equal to or slightly less than those found for the alpha form. The lipophilicity of the hydroxyferrocifens are superior to the values found for estradiol and increase with lengthening of the chain. The antiproliferative effects of the four hydroxyferrocifens with n =2, 3, 5 and 8 were studied on four breast cancer cell lines (MCF7, MDA‐MB231, RTx6 and TD5) possessing different levels of ERα. On MCF7 cells containing high levels of ERα, hydroxyferrocifens behave as antiestrogens. At a molarity of 1 μ M the effect is close to that of hydroxytamoxifen (used for reference) when n =2 or 5, more marked when n =3, and weaker when n =8. Ferrocene alone has no effect. For the MDA‐MB231 cells, classed as a hormone‐independent breast cancer cell line, on the other hand, the hydroxyferrocifens show remarkable antiproliferative behaviour while the hydroxytamoxifen is completely inactive. Hydroxyferrocifens therefore show the unique property of being active both on hormone‐dependent and on hormone‐independent breast cancer cell lines. The molecular modelling study provides some clues for understanding of the antagonist effect of these molecules, while an additional cytotoxic effect due to the vectorised ferrocenyl unit is revealed in some occasions.

Resveratrol, a natural phytoalexin found in grapes, is well known for its presumed role in the prevention of heart disease, associated with red wine consumption. We show here that it is a remarkable inhibitor of ribonucleotide reductase and DNA synthesis in mammalian cells, which might have further applications as an antiproliferative or a cancer chemopreventive agent in humans.

Cobaloximes are effective electrocatalysts for hydrogen evolution and thus functional models for hydrogenases. Among them, difluoroboryl-bridged complexes appear both to mediate proton electroreduction with low overpotentials and to be quite stable in acidic conditions. We report here a mechanistic study of [Co(dmgBF2)2L] (dmg2- = dimethylglyoximato dianion; L = CH3CN or N,N-dimethylformamide) catalyzed proton electroreduction in organic solvents. Depending on the applied potential and the strength of the acid used, three different pathways for hydrogen production were identified and a unified mechanistic scheme involving cobalt(II) or cobalt(III) hydride species is proposed. As far as working potential and turnover frequency are concerned, [Co(dmgBF2)2(CH3CN)2], in the presence of p-cyanoanilinium cation in acetonitrile, is one of the best synthetic catalysts of the first-row transition-metal series for hydrogen evolution.

We report here on a new series of CO2-reducing molecular catalysts based on Earth-abundant elements that are very selective for the production of formic acid in dimethylformamide (DMF)/water mixtures (Faradaic efficiency of 90 ± 10%) at moderate overpotentials (500–700 mV in DMF measured at the middle of the catalytic wave). The [CpCo(PR2NR′2)I]+ compounds contain diphosphine ligands, PR2NR′2, with two pendant amine residues that act as proton relays during CO2-reduction catalysis and tune their activity. Four different PR2NR′2 ligands with cyclohexyl or phenyl substituents on phosphorus and benzyl or phenyl substituents on nitrogen were employed, and the compound with the most electron-donating phosphine ligand and the most basic amine functions performs best among the series, with turnover frequency >1000 s–1. State-of-the-art benchmarking of catalytic performances ranks this new class of cobalt-based complexes among the most promising CO2-to-formic acid reducing catalysts developed to date; addressing the stability issues would allow further improvement. Mechanistic studies and density functional theory simulations confirmed the role of amine groups for stabilizing key intermediates through hydrogen bonding with water molecules during hydride transfer from the Co center to the CO2 molecule.

Several application fields can benefit from solar-hydrogen technologies <italic>via</italic> specific short-term and long-term pathways.

Severe quantitative loss of protein is often observed in high-resolution two-dimensional electrophoresis of membrane proteins, while the resolution is usually not affected. To improve the solubility of proteins in this technique, we tested denaturing cocktails containing various detergents and chaotropes. Best results were obtained with a denaturing solution containing urea, thiourea, and zwitterionic detergents, synthesized for this purpose. Among the dozen detergents synthesized and tested, amidosulfobetaines with an alkyl tail containing 14-16 carbons proved most efficient, solubilizing previously undetected membrane proteins.

A new inorganic solid state electrocatalyst for the hydrogen evolution reaction (HER) is reported. Highly crystalline layered ternary sulfide copper-molybdenum-sulfide (Cu2MoS4) was prepared by a simple precipitation method from CuI and [MoS4]2− precursors. In aqueous solution and over a wide pH range (pH 0 to 7), this Cu2MoS4 showed very good catalytic activity for HER with an overvoltage requirement of only ca. 135 mV and an apparent exchange current density of 0.040 mA cm−2 (Tafel slope of ca. 95 mV per decade was found irrespective of the pH value). This Cu2MoS4 catalyst was found to be stable during electrocatalytic hydrogen generation. Therefore, it represents an attractive alternative to platinum.

Molecular electronics—the storage and processing of data on individual molecules—may be one path toward increased storage density and speed. In his Perspective, Verdaguer discusses work reported by Sato et al. ( p. 704 ) in this issue on light-induced changes in the magnetic properties of various preparations of Prussian blue. This leads to switching of the long-range magnetic ordering of the compound and may point the way to molecular information processing.

BACKGROUND: TiO2 particles are commonly used as dietary supplements and may contain up to 36% of nano-sized particles (TiO2-NPs). Still impact and translocation of NPs through the gut epithelium is poorly documented. RESULTS: We show that, in vivo and ex vivo, agglomerates of TiO2-NPs cross both the regular ileum epithelium and the follicle-associated epithelium (FAE) and alter the paracellular permeability of the ileum and colon epithelia. In vitro, they accumulate in M-cells and mucus-secreting cells, much less in enterocytes. They do not cause overt cytotoxicity or apoptosis. They translocate through a model of FAE only, but induce tight junctions remodeling in the regular ileum epithelium, which is a sign of integrity alteration and suggests paracellular passage of NPs. Finally we prove that TiO2-NPs do not dissolve when sequestered up to 24 h in gut cells. CONCLUSIONS: Taken together these data prove that TiO2-NPs would possibly translocate through both the regular epithelium lining the ileum and through Peyer's patches, would induce epithelium impairment, and would persist in gut cells where they would possibly induce chronic damage.

Abstract Photosynthesis has been for many years a fascinating source of inspiration for the development of model systems able to achieve efficient light‐to‐chemical energetic transduction. This field of research, called “artificial photosynthesis,” is currently the subject of intense interest, driven by the aim of converting solar energy into the carbon‐free fuel hydrogen through the light‐driven water splitting. In this review, we highlight the recent achievements on light‐driven water oxidation and hydrogen production by molecular catalysts and we shed light on the perspectives in terms of implementation into water splitting technological devices.

reduction using water as a reductant.