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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]

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]

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]

Calcium is a ubiquitous second messenger regulating numbers of cellular processes in living organisms. It encodes and transmits information perceived by cells to downstream sensors, including calmodulin (CaM), that initiate cellular responses. In plants, CaM has been involved in the regulation of plant responses to biotic and abiotic environmental cues. Plant CaMs possess a cysteine residue in their first calcium-binding motif EF-hand, which is not conserved in other eucaryotic organisms. In this work, we report the near-complete backbone chemical shift assignment of tobacco CaM2 with calcium. These results will be useful to study the impact of this particular EF-hand domain regarding CaM interaction with partners involved in stress responses. [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]

(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]

Phosphorylation of the neuronal microtubule-associated Tau protein plays a critical role in the aggregation process leading to the formation of insoluble intraneuronal fibrils within Alzheimer's disease (AD) brains. In recent years, other posttranslational modifications (PTMs) have been highlighted in the regulation of Tau (dys)functions. Among these PTMs, the O -β-linked N-acetylglucosaminylation (O -GlcNAcylation) modulates Tau phosphorylation and aggregation. We here focus on the role of the PHF-1 phospho-epitope of Tau C-terminal domain that is hyperphosphorylated in AD (at pS396/pS404) and encompasses S400 as the major O -GlcNAc site of Tau while two additional O -GlcNAc sites were found in the extreme C-terminus at S412 and S413. Using high resolution NMR spectroscopy, we showed that the O -GlcNAc glycosylation reduces phosphorylation of PHF-1 epitope by GSK3β alone or after priming by CDK2/cyclin A. Furthermore, investigations of the impact of PTMs on local conformation performed in small peptides highlight the role of S404 phosphorylation in inducing helical propensity in the region downstream pS404 that is exacerbated by other phosphorylations of PHF-1 epitope at S396 and S400, or O -GlcNAcylation of S400. Finally, the role of phosphorylation and O -GlcNAcylation of PHF-1 epitope was probed in in-vitro fibrillization assays in which O -GlcNAcylation slows down the rate of fibrillar assembly while GSK3β phosphorylation stimulates aggregation counteracting the effect of glycosylation. [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]

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]

The structure-to-function relationships of the elusive-end-product, lipo-oligosaccharide (LOS-IV), of the LOS biosynthetic pathway in Mycobacterium marinum are analyzed. The studies have shown that the terminal monosaccharide has granted to LOS-IV important biological functions, including macrophage activating properties.

The neuronal Tau protein phosphorylation by the cAMP dependent protein kinase (PKA) and the kinetic data for each of the PKA generated phosphorylation sites are presented. The results show that NMR spectroscopy can be used to evaluate potential kinase inhibitors in a straightforward manner.

A combined X-ray and nuclear magnetic resonance (NMR) study of a plant peroxiredoxin (Prx) that belongs to the D-Prx (type II) subfamily is presented. The study conducted provides an insight into the Prx oligomerism and the basis for protein-protein and enzyme-enzyme interaction studies by NMR.

Nuclear magnetic resonance studies reveal that Saccharomyces cerevisiae alkylhydroperoxide reductase (Ahp1) peroxiredoxin behaves mainly as a homodimer in solution and in an inactive form its cysteine is overoxidized into sulfonate. Data indicate that yeast Ahp1 belongs to the D-type peroxiredoxins and forms an intermolecular disulfide.

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]

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]

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]

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]

The catalytic conversion of alcohols into carboxylic acid salts in water was performed in the presence of ruthenium complexes supported by aliphatic PNP pincer ligands preformed or formed in situ. High activity toward a wide substrate scope was achieved with turnover number values of up to 4000. The air-stable catalytic system can be recycled by using toluene as a catalyst-immobilizing phase; the activity is maintained after five consecutive runs. Finally, mechanistic studies allowed some fundamental aspects related to water activation to be unveiled and to the mechanism postulated. [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]

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]

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]

Molecular dynamics simulations describing the solvation process of native and modified cyclodextrins (per-substituted α-, β-, and γ-cyclodextrins, as well as an amino-acid derived β-cyclodextrin) have been performed. A homogeneous force field, namely “q4md-CD”, has been built from the development of a new force field topology database and from a combination of the GLYCAM04 and Amber99SB force fields to correctly describe the geometrical, structural, dynamical and hydrogen bonding aspects of heterogeneous cyclodextrin based systems. These include native, organo- and peptidic-linked cyclodextrins. q4md-CD features: (i) geometrical parameters from Amber99SB to describe the protein parts, (ii) geometrical parameters from GLYCAM04 for the carbohydrate and organic parts when available or those of Amber99SB otherwise, (iii) partial atomic charges, embedded in force field libraries for the carbohydrate and organic fragments, were derived using the R.E.D. tools according to the “Amber” strategy and (iv) scaling factors of 1.2 and 2.0 were imposed for the 1–4 electrostatic and 1–4 van der Waals interactions, respectively. Results given by q4md-CD on native cyclodextrins have been compared to those obtained with reference to force fields like GLYCAM04, GLYCAM06 and Amber99SB as well as with experimental data. This work not only gives a global view of the performances of the aforementioned force fields towards a correct description of solvated cyclodextrins, but also extends the capabilities of current force fields by addressing some issues concerning hydrogen bonding and opens new possibilities towards studies of glycoconjugates by molecular dynamics. [ABSTRACT FROM AUTHOR]

The role of the BclA domains of B. cereus ATCC 14579 was investigated in order to understand the phenomena involved in the interfacial processes occurring between spores and inert surfaces. This was done by (i) creating deletions in the collagen-like region (CLR) and the C-terminal domain (CTD) of BclA, (ii) building BclA proteins with various lengths in the CLR and (iii) modifying the hydrophobic upper surface in the CTD. First, it was demonstrated that the CLR was substituted by three residues already reported in the CLR of B. anthracis, viz. rhamnose, 3-O-methyl-rhamnose, and GalNH2 residues, while the CTD was also substituted by two additional glycosyl residues, viz. 2-O-methyl-rhamnose and 2,4-O-methyl-rhamnose. Regarding the properties of the spores, both CLR and CTD contributed to the adhesion of the spores, which was estimated by measuring the resistance to detachment of spores adhered to stainless steel plates). CLR and CTD also impacted the hydrophobic character and isoelectric point of the spores. It was then shown that the resistance to detachment of the spores was not affected by the physicochemical properties, but by the CLR length and the presence of hydrophobic amino acids on the CTD. [ABSTRACT FROM PUBLISHER]