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An effective method of grafting functionalities onto lignin based on glycerol carbonate has been developed. This biobased grafting reagent reacts with lignin without generating co-products. Alkenyl groups were added to the glycerol carbonate moiety from 1,3-butadiene chemistry using the nickel-catalysed hydroalkoxylation reaction and the newly developed nickel-catalysed telomerisation reaction under solvent-free conditions. The high-atom economical reactions lead to three different sets of glycerol carbonate ethers with various chain lengths that can be separated from the catalyst to avoid lignin contamination with metals. Kraft, organosolv and soda lignins, without prior purification, were grafted via ether functions using these linkers in a clean and efficient procedure. The technical and modified lignins were characterised by NMR, IR and SEC, and their thermal properties were determined by DSC. The glass transition temperatures of the modified lignins are significantly reduced, opening up possibilities of shaping, for example, on hot presses. In addition, these modifications offer the possibility of inserting new reactive functions within the lignin, including unsaturations and alcohols, allowing a new range of lignin-based resins to be developed. [ABSTRACT FROM AUTHOR]

In the present study, we report the first silver-dependent enantiodivergent gold-catalysed reaction. The asymmetric intramolecular hydroamination of alkenes catalysed by the combination of a single chiral binuclear gold(I) chloride complex and silver perchlorate can afford both enantiomers of the products by a simple solvent change from toluene to methanol. Such an enantiodivergent reaction is strictly independent of the reaction temperature or of the nature of the catalyst anion and displays the same first-order kinetic rate law with respect to substrate concentration in both solvents. Beyond a simple solvent effect the enantioinversion is controlled by gold-silver chloride adducts which occur only in methanol and allow a dual activation of the reagent. While one single gold atom activates the alkene moiety, the other gold atom forms an oxophilic gold-silver chloride adduct which is likely to interact with the carbamate function. By comparison with toluene, which affords ( S)-enantiomer, this proximal and bimetallic activation would allow an opposite stereodifferentiation of the two diastereomeric intermediates during the final protodeauration step and lead therefore to the ( R)-enantiomer. [ABSTRACT FROM AUTHOR]

Readily accessible cationic IrIII metallacycles catalyze efficiently the chemoselective hydrosilylation of tertiary and secondary amides to amines. The catalyst described herein operates at low loadings using inexpensive 1,1,3,3-tetramethyldisiloxane and allows fast reactions with high yields, selectivities, and turnover numbers. A transient iminium intermediate has been observed for the first time by using mass spectrometry, and the activation of the catalyst and the silane reagent have been studied by using DFT calculations. These fundamental insights support the present and future improvements of IrIII metallacycles through proper ligand modifications and enable further broad applications of catalysts based on metallacycles. [ABSTRACT FROM AUTHOR]

The reaction of Na10[α-SiW9O34] with 4f tetravalent cerium cations in aqueous solution in the presence of sodium acetate at different pH values leads to the stabilization of three cerium-based polyanionic molecular clusters [Ce3(µ2-OH)3(µ3-O)(SiW9O34)2]13- ( 1), [Ce3(µ2-O)3(SiW9O34)2]14- ( 2), and {[Ce6(µ3-O)4(µ3-OH)4]2(W8O32)(SiW9O34)4}32- ( 3). The condensation behavior of cerium in this kind of association with trivacant polyoxometalates (POMs) when a pH variation occurs is relatively unknown and needed to be explored. Compounds 1 and 2 consist of a trinuclear cerium cluster fragment stabilized by two POM moieties with a variation of the central cerium cluster from [Ce3(µ2-OH)3(µ3-O)] to [Ce3(µ2-O)3]. Compound 3 appears much more condensed with two hexanuclear [Ce6(µ3-O)4(µ3-OH)4] groups that are stabilized by the SiW9O34 moieties and a W8O32 tungsten ring. This evolution in cluster size and composition reflects the pH variation applied during their synthesis. The molecules have been characterized by single-crystal X-ray diffraction, 183W and 29Si NMR spectroscopy, IR spectroscopy, thermogravimetric analysis (TGA), and SEM/energy-dispersive X-ray (EDX) microscopy. The three compounds obtained here exemplify the influence of pH on the condensation of tetravalent cations and open a new route toward the stabilization of polynuclear tetravalent clusters by nucleophilic O-donating POM species. [ABSTRACT FROM AUTHOR]

A selected diphosphine binuclear gold(I) chloride complex was combined with a silver salt to catalyze efficiently, for the first time, the asymmetric intramolecular hydroamination of alkenes with high conversions and enantioselectivities, in mild conditions and in presence of water. Both enantiomers of the products could be obtained by controlling the molecular ion-pairs through the solvent polarity. The gold(I) cationic active species was characterized unambiguously at the solid state by X-ray analysis and in solution by DOSY 1H NMR experiments. No contribution of silver chloride was observed on the bonding mode of the catalyst. [ABSTRACT FROM AUTHOR]

Carbon assimilation in plants is regulated by the reduction of specific protein disulfides by light and their re-oxidation in the dark. The redox switch CP12 is an intrinsically disordered protein that can form two disulfide bridges. In the dark oxidized CP12 forms an inactive supramolecular complex with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase, two enzymes of the carbon assimilation cycle. Here we show that binding of CP12 to GAPDH, the first step of ternary complex formation, follows an integrated mechanism that combines conformational selection with induced folding steps. Initially, a CP12 conformation characterized by a circular structural motif including the C-terminal disulfide is selected by GAPDH. Subsequently, the induced folding of the flexible C-terminal tail of CP12 in the active site of GAPDH stabilizes the binary complex. Formation of several hydrogen bonds compensates the entropic cost of CP12 fixation and terminates the interaction mechanism that contributes to carbon assimilation control. [ABSTRACT FROM AUTHOR]

Mycobacterial species, like other microbes, spontaneously form multicellular drug-tolerant biofilms when grown in vitro in detergent-free liquid media. The structure of Mycobacterium tuberculosis biofilms is formed through genetically programmed pathways and is built upon a large abundance of novel extracellular free mycolic acids (FM), although the mechanism of FM synthesis remained unclear. Here we show that the FM in Mycobacterium smegmatis biofilms is produced through the enzymatic release from constitutively present mycolyl derivatives. One of the precursors for FM is newly synthesized trehalose dimycolate (TDM), which is cleaved by a novel TDM-specific serine esterase, Msmeg_1529. Disruption of Msmeg_1529 leads to undetectable hydrolytic activity, reduced levels of FM in the mutant, and retarded biofilm growth. Furthermore, enzymatic hydrolysis of TDM remains conserved in M. tuberculosis, suggesting the presence of a TDM-specific esterase in this pathogen. Overall, this study provides the first evidence for an enzymatic release of free mycolic acids from cell envelope mycolates during mycobacterial growth. [ABSTRACT FROM AUTHOR]

Peroxiredoxins (Prxs) constitute a family of thiol peroxidases that reduce hydrogen peroxide, peroxinitrite, and hydroperoxides using a strictly conserved cysteine. Very abundant in all organisms, Prxs are produced as diverse isoforms characterized by different catalytic mechanisms and various thiol- containing reducing agents. The oligomeric state of Prxs and the link with their functionality is a subject of intensive research. We present here a combined X-ray and nuclear magnetic resonance (NMR) study of a plant Prx that belongs to the D-Prx (type II) subfamily. The Populus trichocarpa Prx is the first Prx shown to be regenerated in vitro by both the glutaredoxin and thioredoxin systems. The crystal structure and solution NMR provide evidence that the reduced protein is a specific noncovalent homodimer both in the crystal and in solution. The dimer interface is roughly perpendicular to the plane of the central β sheet and differs from the interface of A- and B-Prx dimers, where proteins associate in the plane parallel to the &ebeta; sheet. The homodimer interface involves residues strongly conserved in the D (type II) Prxs, suggesting that all Prxs of this family can homodimerize. The study provides a new insight into the Prx oligomerism and the basis for protein-protein and enzyme-substrate interaction studies by NMR. [ABSTRACT FROM AUTHOR]

Peroxiredoxins (Prx's) are a superfamily of thiol-specific antioxidant proteins present in all organisms and involved in the hydroperoxide detoxification of the cell. The catalytic cysteine of Prx's reduces hydroperoxides and is transformed into a transient sulfenic acid (Cys-SOH). At high hydroperoxide concentration, the sulfenic acid can be overoxidized into a sulfonate, or even a sulfonate. We present here the first peroxiredoxin characterization by solution NMR of the Saccharomyces cerevisiae alkylhydroperoxide reductase (Ahpl) in its reduced and in vitro overoxidized forms. NMR [sup15]N relaxation data and ultracentrifugation experiments indicate that the protein behaves principally as a homodimer (2 × 19 kDa) in solution, regardless of the redox state. In vitro treatment of Ahp 1 by a large excess of tBuOOH leads to an inactive form, with the catalytic cysteine overoxidized into sulfonate, as demonstrated by [sup13]C NMR. Depending on the amino acid sequence of their active site, Prx' s are classified into five different families. In this classification, Ahpl is a member of the scarcely studied D-type Prx' s. Ahpl is unique among the D-type Prx's in its ability to form an intermolecular disulfide. The peptidic sequence of Ahpl was analyzed and compared to other D-type Prx sequences. [ABSTRACT FROM AUTHOR]

Several aryl polycarboxylic ligands (pyromellitic acid, 4,4′-azobenzenedicarboxylic acid and 3,3′,5,5′-azobenzenetetracarboxylic acid) have been used to react with the pentavalent ethoxide niobium(V) precursor Nb(OEt)5. Three new crystalline molecular compounds (1 with pyromellitate, 2 with 4,4′-azobenzenedicarboxylate and 3 with 3,3′,5,5′-azobenzenetetracarboxylate) were isolated from slow crystallization at room temperature from the mother liquid containing the precursor Nb(OEt)5. They are composed of one polycarboxylate ligand fully coordinated to mononuclear or dinuclear octahedrally-coordinated niobium(V) units. For the dimers, the two adjacent niobium centers are bridged by one μ-O and one μ-OEt groups and complexed by only one of the syn–syn bidentate carboxylate function arms from the polytopic ligand. Compounds 1–3 were characterized in solid state by single-crystal and powder X-ray diffraction analysis. Insight into the formation of the three compounds was supported by the help of infrared and liquid 1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Rare actinomycetes are likely treasure troves for bioactive natural products, and it is therefore important that we enrich our understanding of biosynthetic potential of these relatively understudied bacteria. Dactylosporangium are a genus of such rare Actinobacteria that are known to produce a number of important antibacterial compounds, but for which there are still no fully assembled reference genomes, and where the extent of encoded biosynthetic capacity is not defined. Dactylosporangium vinaceum (NRRL B-16297) is known to readily produce a deep wine red-coloured diffusible pigment of unknown origin, and it was decided to define the chemical identity of this natural product pigment, and in parallel use whole genome sequencing and transcriptional analysis to lay a foundation for understanding the biosynthetic capacity of these bacteria. Results show that the produced pigment is made of various rubrolone conjugates, the spontaneous product of the reactive pre-rubrolone, produced by the bacterium. Genome and transcriptome analysis identified the highly expressed biosynthetic gene cluster (BGC) for pre-rubrolone. Further analysis of the fully assembled genome found it to carry 24 additional BGCs, of which the majority were poorly transcribed, confirming the encoded capacity of this bacterium to produce natural products but also illustrating the main bottleneck to exploiting this capacity. Finally, analysis of the potential environmental role of pre-rubrolone found it to react with a number of amine containing antibiotics, antimicrobial peptides and siderophores pointing to its potential role as a "minesweeper" of xenobiotic molecules in the bacterial environment. Key points: • D. vinaceum encodes many BGC, but the majority are transcriptionally silent. • Chemical screening identifies molecules that modulate rubrolone production. • Pre-rubrolone is efficient at binding and inactivating many natural antibiotics. [ABSTRACT FROM AUTHOR]

(E)‐Azobenzene is introduced as a suitable chemical actinometer in the visible spectral range (440–540 nm) for photon flux determination of fluidic microphotoreactors or for assessing efficiency of visible light photo‐induced reactions, its evaluation is straightforward without tedious analytics. Photoisomerization quantum yields (ΦE→Z) of (E)‐azobenzene were accurately determined upon irradiation at several wavelengths and in different solvents based on well‐known diarylethene. [ABSTRACT FROM AUTHOR]

In the background is featured Ginkakuji (Silver Pavilion), a Zen temple along Kyoto′s eastern mountains (Higashiyama) in Japan. In the foreground is featured a chemistry sketch based on the Yin and Yang symbol. As many possible dualities (such as light and dark, fire and water…) are thought of as physical manifestations of the duality symbolised by Yin and Yang, parallels can be drawn with organic chemistry and the gold(I)‐catalysed asymmetric hydroamination of alkenes. An enantiodivergent reaction is possible depending on the presence of silver. Whereas a gold‐catalysed hydroamination reaction afforded (S)‐product in toluene, the use of methanol led to an enantioinversion and the generation of (R)‐product through solvation of silver and bimetallic activation of the amino‐alkene reagent. For more information see the Full Paper by F. Agbossou‐Niedercorn, C. Michon and co‐workers on page 10777 ff. [ABSTRACT FROM AUTHOR]

The industrial fluorination of UO2 to UF4 is based on a complex process involving the manipulation of a large amount of HF, a very toxic and corrosive gas. We present here a safer way to accomplish this reaction utilizing ionic liquid [Bmim][PF6] as a unique reaction medium and fluoride source. [ABSTRACT FROM AUTHOR]

Herein, we report the catalytic activity of a series of platinum(II) pre‐catalysts, bearing N‐heterocyclic carbene (NHC) ligands, in the alkene hydrosilylation reaction. Their structural and electronic properties are fully investigated using X‐ray diffraction analysis and nuclear magnetic resonance spectroscopy (NMR). Next, our study presents a structure‐activity relationship within this group of pre‐catalysts and gives mechanistic insights into the catalyst activation step. An exceptional catalytic performance of one of the complexes is observed, reaching a turnover number (TON) of 970 000 and a turnover frequency (TOF) of 40 417 h−1 at 1 ppm catalyst loading. Finally, an attractive solvent‐free and open‐to‐air alkene hydrosilylation protocol, featuring efficient platinum removal (reduction of residual Pt from 582 ppm to 5.8 ppm), is disclosed. [ABSTRACT FROM AUTHOR]

The reactivity of aryl monocarboxylic acids (benzoic, 1‐ or 2‐naphtoic, 4'‐methylbiphenyl‐4‐carboxylic, and anthracene‐9‐carboxylic acids) as complexing agents for the ethoxide niobium(V) (Nb(OEt)5 precursor has been investigated. A total of eight coordination complexes were isolated with distinct niobium(V) nuclearities as well as carboxylate complexation states. The use of benzoic acid gives a tetranuclear core Nb4(μ2‐O)4(L)4(OEt)8] (L=benzoate (1)) with four Nb−(μ2‐O)−Nb linkages in a square plane configuration. A similar tetramer, 7, was obtained with 2‐naphtoic acid by using a 55 % humid atmosphere synthetic route. Two types of dinuclear brick were identified with one central Nb−(μ2‐O)−Nb linkage; they differ in their complexation state, with one bridging carboxylate ([Nb2(μ2‐O)(μ2‐OEt)(L)(OEt)6], with L=1‐naphtoate (3) or anthracene‐9‐carboxylate (5)) or two bridging carboxylate groups ([Nb2(μ2‐O)(L)2(OEt)6], with L=4'‐methylbiphenyl‐4‐carboxylic (4) or anthracene‐9‐carboxylate (6)). An octanuclear moiety [Nb8(μ2‐O)12(L)8(η1‐L)4−x(OEt)4+x] (with L=2‐naphtoate, x=0 or 2; 8) was obtained by using a solvothermal route in acetonitrile; it has a cubic configuration with niobium centers at each node, linked by 12 μ2‐O groups. The formation of the niobium oxo clusters was characterized by infrared and liquid 1H NMR spectroscopy in order to analyze the esterification reaction, which induces the release of water molecules that further react through oxolation with niobium atoms, in different {Nb2O}, {Nb4O4} and {Nb8O12} nuclearities. [ABSTRACT FROM AUTHOR]

In this contribution, we study the conversion of a bio-sourced unsaturated fatty ester by cross-metathesis with nitrile-functionalized olefinic partners (acrylonitrile and crotonitrile). A switch from terminal to internal olefins leads to higher conversion. This is in part rationalized by involvement of a more stable ruthenium ethylidene species with crotonitrile. A new carbenic complex forms upon reaction with the nitrile-functionalized olefins, that is also catalytically active. [ABSTRACT FROM AUTHOR]

[Mo6X14]2- octahedral molybdenum clusters are the main building blocks of a large range of materials. Although 95Mo nuclear magnetic resonance was proposed to be a powerful tool to characterize their structural and dynamical properties in solution, these measurements have never been complemented by theoretical studies which can limit their interpretation for complex systems. In this Article, we use quantum chemical calculations to evaluate the 95Mo chemical shift of three clusters: [Mo6Cl14]2-, [Mo6Br14]2-, and [Mo6I14]2-. In particular, we test various computational parameters influencing the quality of the results: size of the basis set, treatment of relativistic and solvent effects. Furthermore, to provide quantum chemical calculations that are directly comparable with experimental data, we evaluate for the first time the 95Mo nuclear magnetic shielding of the experimental reference, namely, Mo042- in aqueous solution. This is achieved by combining ab initio molecular dynamics simulations with a periodic approach to evaluate the 95Mo nuclear shielding?. The results demonstrate that, despite the difficulty to obtain accurate 95Mo chemical shifts, relative values for a cluster series can be fairly well-reproduced by DFT calculations. We also show that performing an explicit solvent treatment for the reference compound improves by ~50 ppm the agreement between theory and experiment. Finally, the standard deviation of ~70 ppm that we calculate for the 95Mo nuclear shielding of the reference provides an estimation of the accuracy we can achieve for the calculation of the 95Mo chemical shifts using a static approach. These results demonstrate the growing ability of quantum chemical calculations to complement and interpret complex experimental measurements. [ABSTRACT FROM AUTHOR]

[Mo6X14]2- octahedral molybdenum clusters are the main building blocks of a large range of materials. Although 95Mo nuclear magnetic resonance was proposed to be a powerful tool to characterize their structural and dynamical properties in solution, these measurements have never been complemented by theoretical studies which can limit their interpretation for complex systems. In this Article, we use quantum chemical calculations to evaluate the 95Mo chemical shift of three clusters: [Mo6Cl14]2-, [Mo6Br14]2-, and [Mo6I14]2-. In particular, we test various computational parameters influencing the quality of the results: size of the basis set, treatment of relativistic and solvent effects. Furthermore, to provide quantum chemical calculations that are directly comparable with experimental data, we evaluate for the first time the 95Mo nuclear magnetic shielding of the experimental reference, namely, MoO42- in aqueous solution. This is achieved by combining ab initio molecular dynamics simulations with a periodic approach to evaluate the 95Mo nuclear shieldings. The results demonstrate that, despite the difficulty to obtain accurate 95Mo chemical shifts, relative values for a cluster series can be fairly well-reproduced by DFT calculations. We also show that performing an explicit solvent treatment for the reference compound improves by ~50 ppm the agreement between theory and experiment. Finally, the standard deviation of ~70 ppm that we calculate for the 95Mo nuclear shielding of the reference provides an estimation of the accuracy we can achieve for the calculation of the 95Mo chemical shifts using a static approach. These results demonstrate the growing ability of quantum chemical calculations to complement and interpret complex experimental measurements. [ABSTRACT FROM AUTHOR]

Infection of the zebrafish with Mycobacterium marinum is regarded as a well-established experimental model to study the pathogenicity of Mycobacterium tuberculosis. Herein, a M. marinum transposon mutant library was screened for attenuated M. marinum phenotypes using a Dictyostelium discoideum assay. In one attenuated mutant, the transposon was located within tesA, encoding a putative type II thioesterase . Thin-layer chromatography analyses indicated that the tesA::Tn mutant failed to produce two major cell wall-associated lipids. Mass spectrometry and nuclear magnetic resonance clearly established the nature of missing lipids as phthioglycol diphthioceranates and phenolic glycolipids, respectively, indicating that TesA is required for the synthesis of both lipids. When injected into the zebrafish embryo bloodstream, the mutant was found to be highly attenuated, thus validating the performance and relevance of the Dictyostelium screen. Consistent with these in vivo findings, tesA::Tn exhibited increased permeability defects in vitro, which may explain its failure to survive in host macrophages. Unexpectedly, virulence was retained when bacteria were injected into the notochord. Histological and ultrastructural studies of the infected notochord revealed the presence of actively proliferating mycobacteria, leading to larval death. This work presents for the first time the notochord as a compartment highly susceptible to mycobacterial infection. [ABSTRACT FROM AUTHOR]

The cell envelope is a crucial determinant of virulence and drug resistance in Mycobacterium tuberculosis. Several features of pathogenesis and immunomodulation of host responses are attributable to the structural diversity in cell wall lipids, particularly in the mycolic acids. Structural modification of the α-mycolic acid by introduction of cyclopropane rings as catalyzed by the methyltransferase, PcaA, is essential for a lethal, persistent infection and the cording phenotype in M. tuberculosis. Here, we demonstrate the presence ofcyclopropanated cell wall mycolates in the nonpathogenic strain Mycobacterium smegmatis and identify MSMEG_1351 as a gene encoding a PcaA homologue. Interestingly, α-mycolic acid cyclopropanation was inducible in cultures grown at 25°C. The growth temperature modulation of the cyclopropanating activity was determined by high resolution magic angle spinning NMR analyses on whole cells. In parallel, quantitative reverse transcription-PCR analysis showed that MSMEG_1351 gene expression is up-regulated at 25°C compared with 37 °C. An MSMEG_1351 knock-out strain of M. smegmatis, generated by recombineering, exhibited a deficiency in cyclopropanation of a-mycolates. The functional equivalence of PcaA and MSMEG_1351 was established by cross-complementation in the MSMEG_1351 knock-out mutant and also in a ΔpcaA strain of Mycobacterium boris BCG. Overexpression of MSMEG_1351 restored the wild-type mycolic acid profile and the cording phenotype in BCG. Although the biological significance of mycolic acid cyclopropanation in nonpathogenic mycobacteria remains unclear, it likely represents a mechanism of adaptation of cell wall structure and composition to cope with environmental factors. [ABSTRACT FROM AUTHOR]

Abstract: Based on the prodrug concept as well as the combination of two different classes of antimalarial agents, we designed and synthesized two series of ferrocenic antimalarial dual molecules consisting of a ferroquine analogue conjugated with a glutathione reductase inhibitor (or a glutathione depletor) through a cleavable amide bond in order to target two essential pathways in the malarial parasites. The results showed no enhancement of the antimalarial activity of the dual molecules but evidenced a unique mode of action of ferroquine and ferrocenyl analogues distinct of those of chloroquine and nonferrocenic 4-aminoquinoline analogues. [Copyright &y& Elsevier]

The yeast Candida albicans is an opportunistic pathogen that causes infections in immunocompromised individuals with a high morbidity and mortality levels. Recognition of yeasts by host cells is directly mediated by cell wall components of the yeast, including a wide range of abundantly expressed glycoconjugates. Of particular interest in C. albicans are the β-mannosylated epitopes that show a complex expression pattern on N-glycan moiety of phosphopeptidomannans and are absent in the non-pathogenic species Saccharomyces cerevisiae. Being known as potent antigens for the adaptive immune response and elicitors of specific infection-protective antibodies, the exact delineation of β-mannosides regulation and expression pathways has lately become a major milestone toward the comprehension of host-pathogen interplay. Using the newly developed HR-MAS NMR methodology, we demonstrate the possibility of assessing the general profiles of cell-surface-exposed glycoconjugates from intact living yeast cells without any prior purification step. This technique permitted to directly observe structural modifications of surface expressed phosphodiester-linked β-mannosides on a series of deletion strains in β-mannosyltransferases and phospho-mannosyltransferases compared with their parental strains [ABSTRACT FROM PUBLISHER]

Susceptibility of Mycobacterium tuberculosis to the second-line antitubercular drug thiacetazone (TAC) requires activation by the monoxygenase, EthA. Here, we report isolation of spontaneous mutants in Mycobacterium bovis BCG that are highly resistant to TAC, but carry a functional EthA. Unexpectedly, a majority of the TAC-resistant mutants lacked keto-mycolic acids, which are long-chain fatty acids associated with the cell wall and which contribute significantly to the physiopathology of tuberculosis. Predictably, causative mutations in the above mutants were in the gene encoding methyltransferase MmaA4, which is required for synthesis of keto- and methoxy-mycolic acids. Drug-resistant phenotype of the BCG mutants was reproduced in a mmaA4, but not in a mmaA3 null mutant of M. tuberculosis CDC1551. Susceptibility to TAC could be restored by complementation with a functional mmaA4 gene. Interestingly, overexpression of MmaA4 in M. bovis BCG made it more susceptible to TAC. We provide novel mechanistic insights into antitubercular drug activation by co-ordinated actions of EthA and MmaA4. This study is the first demonstration of the participation of an enzyme linked to the synthesis of oxygenated mycolates in a drug activation process in M. tuberculosis, and highlights the interplay between mycolic acid synthesis, drug activation and mycobacterial virulence. [ABSTRACT FROM AUTHOR]

CP12 is a protein of 8.7 kDa that contributes to Calvin cycle regulation by acting as a scaffold element in the formation of a supramolecular complex with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase (PRK) in photosynthetic organisms. NMR studies of recombinant CP12 (isoform 2) of Arabidopsis thaliana show that CP12-2 is poorly structured. CP12-2 is monomeric in solution and contains four cysteines, which can form two intramolecular disulfides with midpoint redox potentials of -326 and -352 mV, respectively, at pH 7.9. Site-specific mutants indicate that the C-terminal disulfide is involved in the interaction between CP12-2 and GAPDH (isoform A4), whereas the N-terminal disulfide is involved in the interaction between this binary complex and PRK. In the presence of NAD, oxidized CP12-2 interacts with A4-GAPDH (KD = 0.18 μM) to form a binary complex of 170 kDa with (A4-GAPDH)-(CP12-2)2 stoichiometry, as determined by isothermal titration calorimetry and multiangle light scattering analysis. PRK is a dimer and by interacting with this binary complex (KD = 0.17 μM) leads to a 498-kDa ternary complex constituted by two binary complexes and two PRK dimers, i.e. ((A4-GAPDH)-(CP12-2)2-(PRK))2. Thermodynamic parameters indicate that assembly of both binary and ternary complexes is exoergonic although penalized by a decrease in entropy that suggests an induced folding of CP12-2 upon binding to partner proteins. The redox dependence of events leading to supramolecular complexes is consistent with a role of CP12 in coordinating the reversible inactivation of chloroplast enzymes A4-GAPDH and PRK during darkness in photosynthetic tissues. [ABSTRACT FROM AUTHOR]

Neutral and ionic ruthenium and iron aliphatic PNHP-type pincer complexes (PNHP = NH(CH2CH2PiPr2)2) bearing benzyl, n-butyl or tert-butyl isocyanide ancillary ligands have been prepared and characterized. Reaction of [RuCl2(PNHP)]2 with one equivalent CN-R per ruthenium center affords complexes [RuCl2(PNHP)(CNR)] (R = benzyl, 1a, R = n-butyl, 1b, R = t-butyl, 1c), with cationic [RuCl(PNHP)(CNR)2]Cl 2a–c as side-products. Dichloride species 1a–c react with excess NaBH4 to afford [RuH(PNHP)(BH4)(CN-R)] 3a–c, analogues to benchmark Takasago catalyst [RuH(PNHP)(BH4)(CO)]. Reaction of 1a–c with a single equivalent of NaBH4 results in formation of [RuHCl(PNHP) (CN-R)] (4a–c), from which 3a–c can be prepared upon reaction with excess NaBH4. Use of one equivalent of NaHBEt3 with 4a and 4c affords bishydrides [Ru(H)2(PNHP)(CN-R)] 5a and 5c. Deprotonation of 4c by KOtBu generates amido derivative [RuH(PNP)(CN-t-Bu)] (6, PNP = −N(CH2CH2PiPr2)2), unstable in solution. Addition of excess benzylisonitrile to 4a provides cationic hydride [RuH(PNHP) (CN-CH2Ph)2]Cl (7). Concerning iron chemistry, [Fe(PNHP)Br2] reacts with one equivalent of benzylisonitrile to afford [FeBr(PNHP)(CNCH2Ph)2]Br (8). The outer-sphere bromide anion can be exchanged by salt metathesis with NaBPh4 to generate [FeBr(PNHP) (CNCH2Ph)2](BPh4) (9). Cationic hydride species [FeH(PNHP) (CN-t-Bu)2](BH4) (10) is prepared from consecutive addition of excess CN-t-Bu and NaBH4 on [Fe(PNPH)Br2]. Ruthenium complexes 3a–c are active in acceptorless alcohol dehydrogenative coupling into ester under base-free conditions. From kinetic follow-up, the trend in initial activity is 3a ≈ 3b > [RuH(PNHP)(BH4)(CO)] ≫; 3c; for robustness, [RuH(BH4)(CO)(PNHP)] > 3a > 3b ≫; 3c. Hypotheses are given to account for the observed deactivation. Complexes 3b, 3c, 4a, 4c, 5c, 7, cis-8 and 9 were characterized by X-ray crystallography. [ABSTRACT FROM AUTHOR]

A single and accessible cationic iridiumIII metallacycle effectively catalyzes the one‐pot sequential double hydrosilylation of challenging α,β‐unsaturated secondary and tertiary amides to afford, in a controlled and straightforward way, the corresponding reduced products, namely, the related secondary and tertiary amides and amines. The catalytic hydrosilylations of the conjugated amides described herein proceeded in good yields and high chemoselectivities. The critical silyl enolate, in other words silyl ketene aminal intermediate, has been observed and characterized by using control experiments, mass spectrometry and state of the art NMR analyses. The present achievements indicate a promising potential of catalysts based on metallacycles for future significant developments in one‐pot multicatalytic synthesis and therefore the production of highly functionalized and complex organic molecules. [ABSTRACT FROM AUTHOR]

Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications. Reported herein are achiral iron complexes, that are highly active, productive, and stereoselective under mild reaction conditions for the ring‐opening polymerization of lactide. The corresponding catalytic systems enable the production of stereoblock polymers with high molecular weights, allowing the formation of thermally stable and industrially relevant stereocomplexes. [ABSTRACT FROM AUTHOR]

Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications. Reported herein are achiral iron complexes, that are highly active, productive, and stereoselective under mild reaction conditions for the ring‐opening polymerization of lactide. The corresponding catalytic systems enable the production of stereoblock polymers with high molecular weights, allowing the formation of thermally stable and industrially relevant stereocomplexes. [ABSTRACT FROM AUTHOR]

The reaction of Na10[SiW9O34] with the 4f tetravalent cerium cation associated with four different organic O/N-donor ligands at pH = 4–4.5 gives rise to the formation of five anionic polyoxometalates [Ce4(μ3-O)2(SiW9O34)2(C4H5O4)2]10− (1), [Ce4(μ3-O)2(SiW9O34)2(C5H7O4)2]10− (2), [Ce4(μ3-O)2(SiW9O34)2(C5H8O2–NH3)2]8− (3), [Ce4(μ3-O)2(SiW9O34)2(C6H10O2–NH3)2]8− (4) and [(Ce3(μ3-O)(μ2-OH)3)(Ce6(μ3-O)4(μ3-OH)4)(SiW9O34)4]21− (5). Compounds 1–4 consist of one tetranuclear Ce-based cluster fragment stabilized by two [SiW9O34]10− polyanions and two organic linkers. Compound 5 is composed of a hexanuclear core combined with a trinuclear cerium core, stabilized by four [SiW9O34]10− moieties. The molecular species were characterized by single-crystal and powder X-ray diffraction, IR spectroscopy, TGA, SEM/EDX, SAXS and ICP analysis. The solution stability of compounds 1–4 was also assessed by 29Si and 183W NMR. [ABSTRACT FROM AUTHOR]

The catalytic acceptorless dehydrogenative oxidation of biosourced alcohols into carboxylic acid salts was achieved using earth-abundant Fe and Mn complexes that feature aliphatic PNP pincer ligands in good to excellent yields. The Fe derivatives were characterized by using 57Fe NMR spectroscopy. Mn pincer catalysts are catalytically more efficient than their Fe counterparts thanks to their robustness under basic conditions. Attempts to generate aldehydes from alcohols were not successful using the Fe and Mn species, but a commercially available Ru analogue achieves this transformation selectively under very mild conditions in the presence of a large excess of acetone as a hydrogen acceptor. [ABSTRACT FROM AUTHOR]

In a Siberian river, the concentrations of chemical species vary with the hydrological regime. Dissolved Organic Matter (DOM) and aluminum ions show a parallel trend in the course of the hydrological year. However, the speciation of aluminum in this natural environment remains an open question. We propose here a combination of spectroscopic techniques to investigate the proximity between the aluminum atoms and DOM. First, one-dimensional (1D) solid-state Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR) and 1D and 2D solution NMR spectra were acquired, providing a clear overview of the DOM composition. Second, the sensitivity enhancement yielded by Dynamic Nuclear Polarization enabled the NMR detection of proximities between the 27 Al and 13 C nuclei. Hence, we show that 8.3 ± 1.3% of the carboxylate groups observed by NMR are connected to the Al 3 + ions in the DOM sample. We here demonstrate for the first time how advanced solid-state NMR methods can provide key information about the localization of aluminum in such complex natural materials. [ABSTRACT FROM AUTHOR]

AMSH [associated molecule with a Src homology 3 domain of signal transducing adaptor molecule (STAM)] is one of the deubiquitinating enzymes associated in the regulation of endocytic cargo trafficking. It shows an exquisite selectivity for Lys63-linked polyubiquitin chains that are the main chains involved in cargo sorting. The first step requires the ESCRT-0 complex that comprises the STAM and hepatocyte growth factor-regulated substrate (Hrs) proteins. Previous studies have shown that the presence of the STAM protein increases the efficiency of Lys63-linked polyubiquitin chain cleavage by AMSH, one of the deubiquitinating enzyme involved in lysosomal degradation. In the present study, we are seeking to understand if a particular structural organization among these three key players is responsible for the stimulation of the catalytic activity of AMSH. To address this question, we first monitored the interaction between the ubiquitin interacting motif (UIM)-SH3 construct of STAM2 and the Lys63-linked diubiquitin (Lys63-Ub 2 ) chains by means of NMR. We show that Lys63-Ub 2 is able to bind either the UIM or the SH3 domain without any selectivity. We further demonstrate that the SH3 binding motif (SBM) of AMSH (AMSH-SBM) outcompetes Lys63-Ub 2 for binding SH3. Additionally, we show how different AMSH-SBM variants, modified by their sequence and length, exhibit similar equilibrium dissociation constants when binding SH3 but significantly differ in their dissociation rate constants. Finally, we report the solution NMR structure of the AMSH-SBM/SH3 complex and propose a structural organization where the AMSH-SBM interacts with the STAM2-SH3 domain and contributes to the correct positioning of AMSH prior to polyubiquitin chains' cleavage. [ABSTRACT FROM AUTHOR]

Base-free catalytic acceptorless dehydrogenative homo-coupling of alcohols to esters under neat conditions was investigated using a combined organometallic synthesis and kinetic modelling approach. The considered bifunctional ruthenium aliphatic PNP complexes are very active, affording TONs up to 15,000. Notably, gas mass transfer issues were identified, which allowed us to rationalize previous observations. Indeed, the reaction kinetics are limited by the rate of transfer from the liquid phase to the gas phase of the hydrogen co-produced in the reaction. Mechanistically speaking, this relates to the interconverting couple amido monohydride/amino bishydride. Overcoming this by switching into the chemical regime leads to an initial turnover frequency increase from about 2000 up to 6100 h −1 . This has a significant impact when considering assessment of novel or reported catalytic systems in this type of reaction, as overlooking of these engineering aspects can be misleading. [ABSTRACT FROM AUTHOR]

The spores of the Bacillus cereus group (B. cereus, Bacillus anthracis, and Bacillus thuringiensis) are surrounded by a paracrystalline flexible yet resistant layer called exosporium that plays a major role in spore adhesion and virulence. The major constituent of its hairlike surface, the trimerized glycoprotein BclA, is attached to the basal layer through an N-terminal domain. It is then followed by a repetitive collagen-like neck bearing a globular head (C-terminal domain) that promotes glycoprotein trimerization. The collagen-like region of B. anthracis is known to be densely substituted by unusualO-glycans that may be used for developing species-specific diagnostics of B. anthracis spores and thus targeted therapeutic interventions. In the present study, we have explored the species and domain specificity of BclA glycosylation within the B. cereus group. First, we have established that the collagen-like regions of both B. anthracis and B. cereus are similarly substituted by short O-glycans that bear the species-specific deoxyhexose residues anthrose and the newly observed cereose, respectively. Second we have discovered that the C-terminal globular domains of BclA from both species are substituted by polysaccharide-like O-linked glycans whose structures are also species-specific. The presence of large carbohydrate polymers covering the surface of Bacillus spores may have a profound impact on the way that spores regulate their interactions with biotic and abiotic surfaces and represents potential new diagnostic targets. [ABSTRACT FROM AUTHOR]

The reaction of Na10[α-SiW9O34] with tetravalent metallic cations such as 4f ((NH4)2Ce(NO3)6), 5d (HfCl4), or 5f (UCl4 and Th(NO3)4) in a pH 4.7 sodium acetate buffer solution leads to the formation of four sandwich-type polyoxometalates [Ce4(μ³-O)2(SiW9O34)2(CH3COO)2]10- (1), [U4(μ³-O)2(SiW9O34)2(CH3COO)2]10- (2), [Th3(μ³-O)(μ²-OH)3(SiW9O34)2]13- (3), and [Hf3(μ²-OH)3(SiW9O34)2]11- (4). All four compounds consist of a polynuclear cluster fragment stabilized by two [α-SiW9O34]10- polyanions. Compounds 1 and 2 are isostructural with a tetranuclear core (Ce4, U4), while compound 3 presents a trinuclear Th3 core bearing a μ³-O-centered bridge. It is an unprecedented configuration in the case of the thorium(IV) cluster. Compound 4 also possesses a trinuclear Hf3 core but with the absence of the μ³-O bridge. The molecules have been characterized by single-crystal X-ray diffraction, 183W and 29Si nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis. [ABSTRACT FROM AUTHOR]

For the first time, hexanuclear complexes with general chemical formula [Ln6O(OH)8(NO3)6(H2O)n]2+ with n = 12 for Ln = Sm-Lu and Y and n = 14 for Ln = Pr and Nd were stabilized as nanoaggregates in ethylene glycol (EG). These unprecedented nanoaggregates were structurally characterized by 89Y and ¹H NMR spectroscopy, UV-vis absorption and luminescence spectroscopies, electrospray ionization mass spectrometry, diffusion ordered spectroscopy, transmission electron microscopy, and dynamic light scattering. These nanoaggregates present a 200 nm mean solvodynamic diameter. In these nanoaggregates, hexanuclear complexes are isolated and solvated by EG molecules. The replacement of ethylene glycol by 2-hydroxybenzyl alcohol provides new nanoaggregates that present an antenna effect toward lanthanide ions. This results in a significant enhancement of the luminescence properties of the aggregates and demonstrates the suitability of the strategy for obtaining highly tunable luminescent solutions. [ABSTRACT FROM AUTHOR]

Mycobacterium tuberculosis bacilli display two signature features: acid-fast staining and the capacity to induce long-term latent infections in humans. However, the mechanisms governing these two important processes remain largely unknown. Ser/Thr phosphorylation has recently emerged as an important regulatory mechanism allowing mycobacteria to adapt their cell wall structure/composition in response to their environment. Herein, we evaluated whether phosphorylation of KasB, a crucial mycolic acid biosynthetic enzyme, could modulate acid-fast staining and virulence. Tandem mass spectrometry and site-directed mutagenesis revealed that phosphorylation of KasB occurred at Thr334 and Thr336 both in vitro and in mycobacteria. Isogenic strains of M. tuberculosis with either a deletion of the kasB gene or a kasB_T334D/T336D allele, mimicking constitutive phosphorylation of KasB, were constructed by specialized linkage transduction. Biochemical and structural analyses comparing these mutants to the parental strain revealed that both mutant strains had mycolic acids that were shortened by 4–6 carbon atoms and lacked trans-cyclopropanation. Together, these results suggested that in M. tuberculosis, phosphorylation profoundly decreases the condensing activity of KasB. Structural/modeling analyses reveal that Thr334 and Thr336 are located in the vicinity of the catalytic triad, which indicates that phosphorylation of these amino acids would result in loss of enzyme activity. Importantly, the kasB_T334D/T336D phosphomimetic and deletion alleles, in contrast to the kasB_T334A/T336A phosphoablative allele, completely lost acid-fast staining. Moreover, assessing the virulence of these strains indicated that the KasB phosphomimetic mutant was attenuated in both immunodeficient and immunocompetent mice following aerosol infection. This attenuation was characterized by the absence of lung pathology. Overall, these results highlight for the first time the role of Ser/Thr kinase-dependent KasB phosphorylation in regulating the later stages of mycolic acid elongation, with important consequences in terms of acid-fast staining and pathogenicity. [ABSTRACT FROM AUTHOR]

Although lipo-oligosaccharides (LOSs) are recognized as major parietal components in many mycobacterial species, their involvement in the host-pathogen interactions have been scarcely documented. In particular, the biological implications arising from the high degree of structural species-specificity of these glycolipids remain largely unknown. Growing recognition of the Mycobacterium marinum-Danio rerio as a specific host-pathogen model devoted to the study of the physiopathology of mycobacterial infections prompted us to elucidate the structure-to-function relationships of the elusive end-product, LOS-IV, of the LOS biosynthetic pathway in M. marinum. Combination of physicochemical and molecular modeling methods established that LOS-IV resulted from the differential transfer on the caryophyllose-containing LOS-IV of a family of very unusual N-acylated monosaccharides, naturally present as different diastereoisomers. In agreement with the partial loss of pathogenecity previously reported in a LOS-IV-deficient M. marinum mutant, we demonstrated that this terminal monosaccharide conferred to LOS-IV important biological functions, including macrophage activating properties. [ABSTRACT FROM AUTHOR]

Abstract: A series of five new alkyl 4-N-substituted analogues of ferroquine (FQ, SR97193) were designed, synthesized, and characterized. The antimalarial activity of the compounds was measured against twelve strains of Plasmodium falciparum. The compounds were more active than chloroquine (CQ) against all the CQ-resistant clones. For a better understanding of their mechanism of action, their physicochemical properties (lipophilicity and basicity) and their action on the inhibition of β-hematin formation were evaluated. The importance of the intramolecular hydrogen bond in neutral FQ in the antimalarial activity was probed, compared to the methyl analogue 1. Results of additional physicochemical measurements suggested new insights into the mechanism of action of FQ in sharp contrast with CQ. We complement here our understanding on the mechanism of action of FQ with the process of catalysis-mediated hemozoin formation at the interface between vacuolar content and membrane lipids. [Copyright &y& Elsevier]

Successful treatment of human tuberculosis requires 6–9 months' therapy with multiple antibiotics. Incomplete clearance of tubercle bacilli frequently results in disease relapse, presumably as a result of reactivation of persistent drug-tolerant Mycobacterium tuberculosis cells, although the nature and location of these persisters are not known. In other pathogens, antibiotic tolerance is often associated with the formation of biofilms – organized communities of surface-attached cells – but physiologically and genetically defined M. tuberculosis biofilms have not been described. Here, we show that M. tuberculosis forms biofilms with specific environmental and genetic requirements distinct from those for planktonic growth, which contain an extracellular matrix rich in free mycolic acids, and harbour an important drug-tolerant population that persist despite exposure to high levels of antibiotics. [ABSTRACT FROM AUTHOR]

The phosphorylation of the neuronal Tau protein modulates both its physiological role of microtubule binding and its aggregation into paired helical fragments observed in Alzheimer's diseased neurons. However, detailed knowledge of the role of phosphorylation at specific sites has been hampered by the analytical difficulties to evaluate the level of site-specific phosphate incorporation. Even with recombinant kinases, mass spectrometry and immunodetection are not evident for determining the full phosphorylation pattern in a qualitative and quantitative manner. We show here that heteronuclear NMR spectroscopy on a 15N labeled Tau sample modified by the cAMP dependent kinase allows identification of all phosphorylation sites, measures their level of phosphate integration, and yields kinetic data for the enzymatic modification of the individual sites. Filtering through the 15N label discards the necessity of any further sample purification and allows the in situ monitoring of kinase activity at selected sites. We finally demonstrate that the NMR approach can equally be used to evaluate potential kinase inhibitors in a straightforward manner. [ABSTRACT FROM AUTHOR]

The low to excellent product yield strongly depends on the substrates′ substituents. [ABSTRACT FROM AUTHOR]

The crystal structures of compounds (IV), (VII), (X), and (XIII) are determined by single crystal XRD. [ABSTRACT FROM AUTHOR]