Xyl II

We recently reported a density functional theory (DFT) analysis of the Nb(V)-C bond in various NbCl5 (L) complexes, discovering that the carbon ligand L receives electronic density from the metal (classical back-donation) and from the chlorides in the cis position (direct interligand interaction). Here we report the synthesis and the structural characterization of two new coordination compounds of niobium pentahalides, i.e., NbX5 (CNXyl) (X = Cl, Br; Xyl = 2,6-C6 H3 Me2 ), and the corresponding DFT analyses of the Nb(V)-C bond using the Natural Orbitals for Chemical Valence-Charge Displacement (NOCV-CD) approach, confirming the presence of a cis-halide → isocyanide direct interligand interaction...

Jambo is a tropical fruit cultivated in Southeast Asia and tropical regions of America and Africa. After extraction, its polysaccharides were structurally characterized. Water soluble polysaccharides (WSP) were composed of GalA:Ara:Gal:Glc:Rha in 51:22:16:5:6 molar ratio, indicating the presence of pectic polysaccharides. Methylation analysis and NMR spectroscopy indicated the presence of homogalacturonan (HG), type II arabinogalactan and type I rhamnogalacturonan (RG-I). The HG/RG-I ratio was 88%, indicating greater amounts of smooth than hairy pectic regions...

Gene regulation at the transcriptional level is a central process in all organisms, and DNA-binding transcription factors, known as TFs, play a fundamental role. This class of proteins usually binds at specific DNA sequences, activating or repressing gene expression. In general, TFs are composed of two domains: the DNA-binding domain (DBD) and an extra domain, which in this work we have named "companion domain" (CD). This latter could be involved in one or more functions such as ligand binding, protein-protein interactions or even with enzymatic activity...

Rich polysaccharides were directly observed in the bulbs of Fritillaria unibracteata var. wabuensis (FUW) using the periodic acid-Schiff (PAS) method and microexamination. An acidic water-soluble heteropolysaccharide (FWPS1-1) was isolated from FUW through ethanol precipitation, decoloration, deproteinization, dialysis and separation using a DE-52 anion-exchange column and a Sepharose G-150 gel filtration column. FWPS1-1 (average molecular weight: ~7.44 kDa) has many branches and long side chains; holds the triple-helix conformation; was composed of mannose (Man), galacturonic acid (GalA), galactose (Gal), xylose (Xyl) and arabinose (Ara) with a molar ratio of 2...

Polysaccharides were extracted from sweet pepper (Capsicum annum) with hot water and named ANW (9% yield). Starch was precipitated by freeze-thaw treatment, while pectic polysaccharides (8% yield) remained soluble and consisted of GalA (67.0%), Rha (1.6%), Ara (6.4%), Xyl (0.3%), Gal (6.7%) and Glc (4.4%). A highly methoxylated homogalacturonan (HG, degree of methylesterification of 85% and degree of acetylation of 5%), and type I and type II arabinogalactans (AG-I and AG-II) were observed in NMR analyses. These were fractionated with Fehling's solution to give HG (5...

The synthesis of novel heteroleptic organomagnesium(ii) amide complexes [IMesMg(Ar){N(SiMe3 )2 }]; (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), Ar = 2,6-Me2 C6 H3 (Xyl) (1) and 2,4,6-Me3 C6 H2 (Mes) (2) is reported. Both compounds 1 and 2 were confirmed by multinuclear (1 H,13 C and29 Si) magnetic resonance spectroscopy, elemental analysis and single crystal X-ray structural analysis. Furthermore, the organomagnesium amide pre-catalyzed cross-dehydrogenative coupling of organosilanes with amines has been investigated...

The reaction of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with various 1,3-thiazol- and 1,3,4-thiadiazol-2-amines in chloroform gives a mixture of two regioisomeric binuclear diaminocarbene complexes. For 1,3-thiazol-2-amines the isomeric ratio depends on the reaction conditions and kinetically (KRs) or thermodynamically (TRs) controlled regioisomers were obtained at room temperature and on heating, respectively. In CHCl3 solutions, the isomers are subject to reversible isomerization accompanied with the cleavage of Pd-N and С-N bonds in the carbene fragment XylNCN(R)Xyl...

BACKGROUND: Transcription of genes coding for xylanolytic and cellulolytic enzymes in Aspergillus niger is controlled by the transactivator XlnR. In this work we analyse and model the transcription dynamics in the XlnR regulon from time-course data of the messenger RNA levels for some XlnR target genes, obtained by reverse transcription quantitative PCR (RT-qPCR). Induction of transcription was achieved using low (1 mM) and high (50 mM) concentrations of D-xylose (Xyl). We investigated the wild type strain (Wt) and a mutant strain with partial loss-of-function of the carbon catabolite repressor CreA (Mt)...

Dioxygen is widely used in nature as oxidant. Nature itself has served as inspiration to use O2 in chemical synthesis. However, the use of dioxygen as an oxidant is not straightforward. Its triplet ground-state electronic structure makes it unreactive toward most organic substrates. In natural systems, metalloenzymes activate O2 by reducing it to more reactive peroxide (O2(2-)) or superoxide (O2(-)) forms. Over the years, the development of model systems containing transition metals has become a convenient tool for unravelling O2-activation mechanistic aspects and reproducing the oxidative activity of enzymes...

This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2 Xyl, PMeXyl2 , and PMe2 Ar Xyl 2 (Xyl=2,6-Me2 C6 H3 and Ar Xyl 2=2,6-(2,6-Me2 C6 H3 )2 -C6 H3 ) as well as reactivity studies of the trans-[Pt(C^P)2 ] bis-metallacyclic complex 1 a derived from PiPr2 Xyl. Protonation of compound 1 a with [H(OEt2 )2 ][BArF ] (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ) forms a cationic δ-agostic structure 4 a, whereas α-hydride abstraction employing [Ph3 C][PF6 ] produces a cationic platinum carbene trans-[Pt{PiPr2 (2,6-CH(Me)C6 H3 }{PiPr2 (2,6-CH2 (Me)C6 H3 }][PF6 ] (8)...

Specific α- l -arabinofuranosidases are involved in the realisation of elongation growth process in cells with type II cell walls. Elongation growth in a plant cell is largely based on modification of the cell wall. In type II cell walls, the Ara/Xyl ratio is known to decrease during elongation due to the partial removal of Ara residues from glucuronoarabinoxylan. We searched within the maize genome for the genes of all predicted α-L-arabinofuranosidases that may be responsible for such a process and related their expression to the activity of the enzyme and the amount of free arabinose measured in six zones of a growing maize root...

Xyloglucan plays an important structural role in primary cell walls, possibly tethering adjacent microfibrils and restraining cell expansion. There is therefore considerable interest in understanding the role of xyloglucan endotransglucosylase/hydrolases (XTHs), which are encoded in Arabidopsis by a 33-member gene family. We compared the key catalytic properties of two very different Arabidopsis XTHs (heterologously produced in Pichia), both of which are aluminium-repressed. Reductively tritiated oligosaccharides of xyloglucan were used as model acceptor substrates...

The bis(μ-oxo)dicopper(III) species [Cu(III) 2 (μ-O)2 (m-XYL(MeAN) )](2+) (1) promotes the electrophilic ortho-hydroxylation-defluorination of 2-fluorophenolates to give the corresponding catechols, a reaction that is not accomplishable with a (η(2) :η(2) -O2 )dicopper(II) complex. Isotopic labeling studies show that the incoming oxygen atom originates from the bis(μ-oxo) unit. Ortho-hydroxylation-defluorination occurs selectively in intramolecular competition with other ortho-substituents such as chlorine or bromine...

A series of γ-hydroxy amides were synthesized with high enantioselectivities (up to 99%) using asymmetric hydrogenation of the corresponding γ-ketoamides in the presence of Ru-Xyl-SunPhos-Daipen catalyst providing key building blocks for a variety of naturally occurring and biologically active compounds.

A thermophilic fungus, Humicola grisea var thermoidea, produced in liquid culture two endoxylanases (1,4-β-D-xylan-xylanohydrolase, EC 3.2.1.8) with M r of 95 (Xyl I) and 13 (Xyl II) kDa. PAGE of the crude culture filtrate and of each fraction obtained by gel filtration produced three and one band, respectively. Cross-reaction of the culture filtrate and each fraction with polyclonal antibodies prepared against Xyl II produced two and one precipitin bands, respectively. Hydrolysis of wheat straw and rice husk xylan was maximal using a combination of Xyl I and Xyl II...

Streptomyces griseus, a well-known industrial producer of streptomycin, is a member of the genus Streptomyces, which shows a complex life cycle resembling that of fungi. A-factor, a C13 γ-butyrolactone compound, was discovered as a self-regulatory factor or a bacterial hormone to induce morphological differentiation and production of secondary metabolites, including streptomycin, in this organism. Accumulating evidence has revealed an A-factor-triggered signal cascade, which is composed of several key steps or components...

BACKGROUND: Wheat and rice are important food crops with enormous biomass residues for biofuels. However, lignocellulosic recalcitrance becomes a crucial factor on biomass process. Plant cell walls greatly determine biomass recalcitrance, thus it is essential to identify their key factors on lignocellulose saccharification. Despite it has been reported about cell wall factors on biomass digestions, little is known in wheat and rice. In this study, we analyzed nine typical pairs of wheat and rice samples that exhibited distinct cell wall compositions, and identified three major factors of wall polymer features that affected biomass digestibility...

Reaction of dimesityliron(II) (Fe2(mes)4) with the N-heterocyclic carbenes 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) and 1,3-bis(2,6-dimethylphenyl)hexahydropyrimidin-2-ylidene (6-Xyl) afforded the novel trigonal planar complexes [Fe(IPr)(mes)2] (1) and [Fe(6-Xyl)(mes)2] (2), respectively. Both species were structurally characterized by single crystal X-ray diffraction and display structures and magnetic responses consistent with a quintet ground state (S = 2). Reaction of 1 with KC8 in THF afforded K(+) salts of the anionic complex [{:C[N(2,6-(i)Pr2C6H3)]2(CH)C}2Fe(mes)](-) (3) and the homoleptic organometallic anion [Fe(mes)3](-) (4)...

The hydroxylation of aromatic substrates catalyzed by coupled binuclear copper enzymes has been observed with side-on-peroxo-dicopper(II) (P) and bis-μ-oxo-dicopper(III) (O) model complexes. The substrate-bound-O intermediate in [Cu(II)2(DBED)2(O)2](2+) (DBED = N,N'-di-tert-butyl-ethylenediamine) was shown to perform aromatic hydroxylation. For the [Cu(II)2(NO2-XYL)(O2)](2+) complex, only a P species was spectroscopically observed. However, it was not clear whether this O-O bond cleaves to proceed through an O-type structure along the reaction coordinate for hydroxylation of the aromatic xylyl linker...

In the present study we report the complete nucleotide sequence of the toluene catabolic plasmid pD2RT of Pseudomonas migulae strain D2RT isolated from Baltic Sea water. The pD2RT is 129,894 base pairs in size with an average G+C content of 53.75%. A total of 135 open reading frames (ORFs) were predicted to encode proteins, among them genes for catabolism of toluene, plasmid replication, maintenance and conjugative transfer. ORFs encoding proteins with putative functions in stress response, transposition and site-specific recombination were also predicted...