Metal-Metal Cooperation in the Oxidation of a Flapping Platinum Butterfly by Haloforms: Experimental and Theoretical Evidence

The model 1-DFT for the butterfly complex [{Pt(C¿C*)(µ-pz)}2] (1; HC¿C* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene) shows two minima in the potential energy surface of the ground state in acetone solution: the butterfly-wing-spreading molecules 1-s, (dPt-Pt ˜ 3.20 Å) and the wing-folding molecules 1-f (dPt-Pt = 3.00 Å). Both minima are very close in energy (¿G° = 1.7 kcal/mol) and are connected through a transition state, which lies only 1.9 kcal/mol above 1-s and 0.2 kcal/mol above 1-f. These very low barriers support a fast interconversion process, resembling a butterfly flapping, and the presence of both conformers in acetone solution. However, the 1-f ratio is so low that it is undetectable in the excitation and emission spectra of 1 in 2-MeTHF of diluted solutions (10-5 M) at 77 K, while it is seen in more concentrated solutions (10-3 M). In acetone solution, 1 undergoes a [2c, 2e] oxidation by CHX3 (X = Cl, Br) in the sunlight to render the Pt2(III, III) compounds [{Pt(C¿C*)(µ-pz)X)}2] (X = Cl (2-Cl), Br (2-Br)). In concentrated solutions, 1 can react with CHCl3 under blue light to give 2-Cl and with CHBr3 in the dark, the latter rendering the compound [BrPt(C¿C*)(µ-pz)2Pt(C¿C*)CHBr2] (3-Br) or mixtures of 2-Br and 3-Br if the reaction is performed under an argon atmosphere or in the air, respectively. Mechanistic studies showed that in concentrated solutions the oxidation processes follow a radical mechanism being the MMLCT-based species 1-f, those which trigger the reaction of 1 with CHBr3 and CHCl3. In the ground state (S0f), it promotes the thermal oxidation of 1 by CHBr3 and in the first singlet excited state (S1f) the blue-light-driven photooxidation of 1 by CHCl3. Complexes, 2-Cl, 2-Br, and 3-Br were selectively obtained and fully characterized, showing Pt-Pt distances (ca. 2.6 Å) shorter than that of the starting complex, 1. They are, together with the analogous [{Pt(C¿C*)(µ-pz)I)}2] and [IPt(C¿C*)(µ-pz)2Pt(C¿C*)CHI2], the only dinuclear metal-metal-bonded PtIII(µ-pz)2PtIII compounds reported to date

GlcNAcstatins are nanomolar inhibitors of human O-GlcNAcase inducing cellular hyper-O-GlcNAcylation

O-GlcNAcylation is an essential, dynamic and inducible post-translational glycosylation of cytosolic proteins in metazoa and can show interplay with protein phosphorylation. Inhibition of OGA (O-GlcNAcase), the enzyme that removes O-GlcNAc from O-GlcNAcylated proteins, is a useful strategy to probe the role of this modification in a range of cellular processes. In the present study, we report the rational design and evaluation of GlcNAcstatins, a family of potent, competitive and selective inhibitors of human OGA. Kinetic experiments with recombinant human OGA reveal that the GlcNAcstatins are the most potent human OGA inhibitors reported to date, inhibiting the enzyme in the sub-nanomolar to nanomolar range. Modification of the GlcNAcstatin N-acetyl group leads to up to 160-fold selectivity against the human lysosomal hexosaminidases which employ a similar substrate-assisted catalytic mechanism. Mutagenesis studies in a bacterial OGA, guided by the structure of a GlcNAcstatin complex, provides insight into the role of conserved residues in the human OGA active site. GlcNAcstatins are cell-permeant and, at low nanomolar concentrations, effectively modulate intracellular O-GlcNAc levels through inhibition of OGA, in a range of human cell lines. Thus these compounds are potent selective tools to study the cell biology of O-GlcNAc

Ruthenium molecular complexes immobilized on graphene as active catalysts for the synthesis of carboxylic acids from alcohol dehydrogenation

Ruthenium complexes containing N-heterocyclic carbene ligands functionalized with different polyaromatic groups (pentafluorophenyl, anthracene, and pyrene) are immobilized onto the surface of reduced graphene oxide. The hybrid materials composed of organometallic complexes and graphene are obtained in a single-step process. The hybrid materials are efficient catalysts for the synthesis of carboxylic acids from the dehydrogenation of alcohols in aqueous media. The catalytic materials can be recycled up to ten times without significant loss of activity. The catalytic activity of the pyrene derivative, Pyr-Ru (3) is enhanced when the ruthenium complex is anchored onto the surface of graphene. The carbonaceous material limits the degradation of the ruthenium complex resulting in increased activity and requiring lower catalyst loadings. The catalytic process of the pyrene hybrid material is heterogeneous in nature due to the strong interaction between the pyrene and graphene. The catalytic process of the anthracene and pentafluorophenyl hybrid materials is governed by the so-called ‘boomerang effect’. The ruthenium molecular complex is released from and returned to the graphene surface during the catalytic reaction. Mechanistic insight has been obtained experimentally and theoretically. The energy profile suggests that the rate-determining step is the water nucleophilic attack to a coordinated aldehyde complex to form a gem-diolate complex.The authors thank the financial support from MINECO (CTQ2015-69153-C2-2-R and CTQ2015- 67461-P), Generalitat Valenciana (AICO/2015/039), Universitat Jaume I (P1.1B2015-09) and Universidad de Zaragoza (UZ2014-CIE-01)

Iridium complexes catalysed the selective dehydrogenation of glucose to gluconic acid in water

[EN] We describe an unprecedented catalytic dehydrogenation of glucose by homogeneous catalysts. Iridium(iii) complexes containing the fragment [Cp*Ir(NHC)](2+) (NHC = N-heterocyclic carbene ligand) are shown to be very active and highly selective catalysts for the dehydrogenation of glucose to gluconic acid and molecular hydrogen. Glucose is converted to gluconic acid at a catalyst loading of 2 mol%, at reflux in water, without additives and with a selectivity of over 95%. Experimental evidence obtained by H-1 NMR spectroscopy and mass spectrometry (ESI/MS) reveals the formation of iridium coordinated to glucose and gluconic acid species. A plausible mechanism is proposed, based on the experimental evidence and supported by DFT calculations.The authors thank the MINECO (Severo Ochoa, CTQ2015-69153-C2-1-R, CTQ2015-69153-C2-2-R and CTQ2015-67461-P), Diputacion General de Aragon (Grupo Consolidado E21) and Universitat Jaume I (P1.1B2015-09) for financial support. P. Borja thanks the Universitat Jaume I for a postdoctoral grant. The authors are very grateful to the 'Serveis Centrals d'Instrumentacio Cientifica (SCIC)' of the Universitat Jaume I, S. Fuertes (Universidad of Zaragoza) for data collection of the X-ray structure of 4 and to the Instituto de Biocomputacion y Fisica de Sistemas Complejos (BIFI) and the Centro de Supercomputacion de Galicia (CESGA) for the generous allocation of computational resources.Borja, P.; Vicent, C.; Baya, M.; García Gómez, H.; Mata, JA. (2018). Iridium complexes catalysed the selective dehydrogenation of glucose to gluconic acid in water. Green Chemistry. 20(17):4094-4101. https://doi.org/10.1039/c8gc01933aS409441012017Corma, A., Iborra, S., & Velty, A. (2007). Chemical Routes for the Transformation of Biomass into Chemicals. Chemical Reviews, 107(6), 2411-2502. doi:10.1021/cr050989dBesson, M., Gallezot, P., & Pinel, C. (2013). Conversion of Biomass into Chemicals over Metal Catalysts. 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Differential Responses of Bird Species to Habitat Condition in a Coastal Kenyan Forest Reserve: Implications for Conservation

The management of assemblages of species across many taxa is a common concern in conservation. Consequently, the use of one or a few surrogate or indicator species to represent an entire assemblage has become an increasingly important tool in conservation science. However, conservation schemes based on the needs of one or two focal species often fail to account for individualistic responses of larger assemblages of species. Data from bird point counts along with vegetation characteristics from a coastal tropical dry forest in Kenya that is subject to elephant disturbance were used to explore the differential responses of bird species to environmental conditions in a forest reserve where wildlife management includes both endangered birds and mammals. Results revealed that even birds with similar foraging habits had idiosyncratic responses to both environmental traits and elephant disturbance. While overall species responded to important characteristics such as percent canopy cover and leaf litter depth, individualistic responses of different species trait diversity defied easy characterization of optimal forest management schemes. Taken together, our analyses highlight the difficulty in basing the development of management plans for entire assemblages of species on the response of a single or a few species. Implications for wildlife conservation in Arabuko-Sokoke Forest and similar forest reserves are discussed, emphasizing the need for a better understanding of individual species’ responses to forest conditions

Field Sampling and Necropsy Examination of Fish

This paper presents an overview of observational and fish sampling tech­niques for investigating fish lesions, morbidity and mortality. These sam­pling techniques and investigations are much like detective work and require attention to detail, common sense, technical proficiency and experience. To solve the mystery of a fish kill, the investigator must use available evidence and clues to piece together a series of events that often have long since passed. The cause of these field events may be chemical, biological or physical; more often, it is some combination of these. An initial categorization approach may be used to reduce the great number of possible causes of a fish kill to something more reasonable. Through proper observations, the most probable cause may be placed in one of four broad categories (although additional secondary relationships should also be recognized). These broad categories include oxygen related, toxics or water quality related, disease or population related and trauma related events, and may be based on defined criteria Caution should be taken on making etiologic generaliz.ations since many types of lesions or mortality events may appear similar. This paper provides support for making consistent observations; taking photographs, tissue and water samples; classifying external lesions and choosing appropriate ne­cropsy methods. A bibliography is provided to reference information perti­nent to fish kill investigations and fish disease, anatomy and taxonomy

Catalytic Dehydrogenative Coupling of Hydrosilanes with Alcohols for the Production of Hydrogen On-demand: Application of a Silane/Alcohol Pair as a Liquid Organic Hydrogen Carrier

The compound [Ru(p-cym)(Cl)2(NHC)] is an effective catalyst for the room-temperature coupling of silanes and alcohols with the concomitant formation of molecular hydrogen. High catalyst activity is observed for a variety of substrates affording quantitative yields in minutes at room temperature and with a catalyst loading as low as 0.1 mol %. The coupling reaction is thermodynamically and, in the presence of a Ru complex, kinetically favourable and allows rapid molecular hydrogen generation on-demand at room temperature, under air, and without any additive. The pair silane/alcohol is a potential liquid organic hydrogen carrier (LOHC) for energy storage over long periods in a safe and secure way. Silanes and alcohols are non-toxic compounds and do not require special handling precautions such as high pressure or an inert atmosphere. These properties enhance the practical applications of the pair silane/alcohol as a good LOHC in the automotive industry. The variety and availability of silanes and alcohols permits a pair combination that fulfils the requirements for developing an efficient LOHC

Electrophilicity of neutral square-planar organosilver(III) compounds

Neutral Ag(III) complexes stabilised with just monodentate ligands are here unambiguously established. In a series of square-planar (CF3)3Ag(L) compounds with hard and soft Group 15 donor ligands, L, the metal center has been found to exhibit substantial acidity favouring apical coordination of an additional ligand under no coordination constraints