Synthesis of branched tri- to pentasaccharides representative of fragments of Shigella flexneri serotypes 3a and/or X O-antigens

Fragments of the {2)-[α-d-Glcp-(1→3)]-α-l-Rhap-(1→2)-α-l-Rhap-(1→3)-[Ac→2]-α-l-Rhap-(1→3)-β-d-GlcpNAc-(1→}_n ((E)AB_AcCD)_n polymer were synthesized. D(E)A, CD(E)A, _AcCD(E)A were obtained according to a linear strategy, whereas BCD(E)A and B_AcCD(E)A were derived from the condensation of appropriate BC and D(E)A building blocks. Oligosaccharides were synthesized as their propyl glycoside, relying on (i) the efficient trichloroacetimidate chemistry, (ii) a common EA allyl glycoside, and (iii) a 2-trichloroacetamido-d-glucopyranose precursor to residue D. Final Pd/C-mediated deprotection, run under a high pressure of hydrogen, ensured O-acetyl stability. All targets are parts of the O-antigen of Shigella flexneri 3a, a prevalent serotype. Non-O-acetylated oligosaccharides are shared by the S. flexneri serotype X O-antigen.     

Synthesis, crystal chemistry and physical properties of the Ruddlesden-Popper phases Sr3Fe2−xNixO7−δ (0?x?1.0)

The crystal chemistry, electronic structure, and electrical and magnetic properties of the novel perovskite-related nickel oxides Sr₃Fe_2−xNi_xO_7−δ with 0?x?1.0 have been studied. X-ray diffraction and selected area electron diffraction (ED) data indicate that the samples have a tetragonal (Space group I4/mmm) structure. ED patterns and high-resolution images reveal the presence of a regular stacking along the c-axis for the x=1.0 sample. The lattice parameters, oxygen content, and average oxidation state of iron and nickel decrease with increasing Ni content. The electronic structure of the x=1.0 sample was studied by M 2p X-ray photoelectron spectroscopy (XPS). An analysis of the spectra using the cluster model indicates that this material is in the negative charge-transfer regime and the ground state is dominated by the 3dⁿ⁺¹L configuration with 2p holes (L) in the oxygen band. The insulator states are stabilized due to a p-p type band gap that arises because the p-d transfer integral T_σ dominates over the O 2p bandwith. Although magnetic measurements reveal the presence of ferromagnetic interactions that lead to magnetic frustration at , no long-range magnetic order was observed for the samples with x?0.3. The electrical resistivity decreases with increasing Ni content as the p-p band gap tend to close due to the reduction of the T_σ value. Negative magnetoresistance (∼−24% for x=0.6 and −7% for x=1.0 at 20 K and 9 T) was observed for the Ni containing samples.     

Acid dissociation constants of uridine-5′-diphosphate compounds determined by phosphorus nuclear magnetic resonance spectroscopy and internal pH referencing

The acid dissociation constant (pK_a) of small, biological molecules is an important physical property used for investigating enzyme mechanisms and inhibitor design. For phosphorus-containing molecules, the ³¹P nuclear magnetic resonance (NMR) chemical shift is sensitive to the local chemical environment, particularly to changes in the electronic state of the molecule. Taking advantage of this property, we present a ³¹P NMR approach that uses inorganic phosphate buffer as an internal pH reference to determine the pK_a values of the imide and second diphosphate of uridine-5′-diphosphate compounds, including the first reported values for UDP-GlcNAc and UDP-S-GlcNAc. New methods for using inorganic phosphate buffer as an internal pH reference, involving mathematical correction factors and careful control of the chemical shift reference sample, are illustrated. A comparison of the newly determined imide and diphosphate pK_a values of UDP, UDP-GlcNAc, and UDP-S-GlcNAc with other nucleotide phosphate and thio-analogs reveals the significance of the monosaccharide and sulfur position on the pK_a values.     

p(O2)-stability of LaFe1−xNixO3−δ solid solutions at 1100 °C

LaFe_1−xNi_xO_3−δ (x=0.1−1.0) perovskites were synthesized via citrate route. The p(O₂)-stability of the perovskite phases LaFe_1−xNi_xO_3−δ has been evaluated at 1100 °C based on the results of XRD analysis of powder samples annealed at various p(O₂) and quenched to room temperature. The isothermal LaFeO_3−δ-“LaNiO_3−δ” cross-section of the phase diagram of the La-Fe-Ni-O system has been proposed in the range of oxygen partial pressure −15<log p(O₂)/atm≤0.68. The unit cell parameters of orthorhombic perovskites O-LaFe_1−xNi_xO_3−δ increase with decrease in p(O₂) at fixed composition x. This behavior is explained on the basis of size factor. The decomposition temperatures of rhombohedral phases R-LaFe_1−xNi_xO_3−δ for x=0.7, 0.8, 0.9 and 1.0 in air were determined as 1137, 1086, 1060 and 995 °C, respectively.     

Preparation and reactivity of p-cymene complexes of ruthenium and osmium incorporating 1,3-triazenide ligands

p-Cymene complexes MCl₂(η⁶-p-cymene)L [M = Ru, Os; L = P(OEt)₃, PPh(OEt)₂, (CH₃)₃CNC] were prepared by allowing [MCl(μ-Cl)(η⁶-p-cymene)]₂ to react with phosphites or tert-butyl isocyanide. Treatment of MCl₂(η⁶-p-cymene)L complexes with 1,3-ArNNN(H)Ar triazene and an excess of NEt₃ gave the cationic triazenide derivatives [M(η²-1,3-ArNNNAr)(η⁶-p-cymene)L]BPh₄ (Ar = Ph, p-tolyl). Neutral triazenide complexes MCl(η²-1,3-ArNNNAr)(η⁶-p-cymene) (M = Ru, Os) were also prepared by allowing [MCl(μ-Cl)(η⁶-p-cymene)]₂ to react with 1,3-diaryltriazene in the presence of triethylamine. p-Cymene complexes MCl₂(η⁶-p-cymene)L reacted with equimolar amounts of 1,3-ArNNN(H)Ar triazene to give both triazenide complexes [M(η²-1,3-ArNNNAr)(η⁶-p-cymene)L]BPh₄ and amine derivatives [MCl(ArNH₂)(η⁶-p-cymene)L]BPh₄. A reaction path for the formation of the amine complex is also reported. The complexes were characterised by spectroscopy and X-ray crystallography of RuCl₂(η⁶-p-cymene)[PPh(OEt)₂] and [Ru(η²-1,3-p-tolyl-NNN-p-tolyl)(η⁶-p-cymene){CNC(CH₃)₃}]BPh₄. Selected triazenide complexes were studied as catalysts in the hydrogenation of 2-cyclohexen-1-one and cinnamaldehyde.     

What are the pKa values of organophosphorus compounds?

A first-principle theoretical protocol was developed, which could successfully predict the pK_a values of a number of amines and thiols in DMSO with a precision of about 1.1 pK_a unit. Using this protocol we calculated the pK_a values of diverse types of organophosphorus compounds in DMSO. The accuracy of these predicted values was estimated to be about 1.1 pK_a because phosphorus is in the same group as nitrogen and in the same period as sulfur. The theoretical predictions were also consistent with all the available experimental data. Thus, a scale of reliable pK_a values was constructed for the first time for organophosphorus. These pK_a values would be helpful to synthetic chemists who need to design the experimental conditions for handling deprotonated organophosphorus. On the basis of these pK_a values we also studied, for the first time, some interesting topics such as the substituent effects on the pK_a values of various types of organophosphorus, and the differences between the pK_a values of organophosphorus and organic amines.     

Acidity of several polyprotic acids, amiodarone and quetiapine hemifumarate in pure methanol

Methanol is the organic solvent closest to water and able to dissolve a huge amount of organic compounds. Therefore, it is a good candidate for pK_a determination of drugs sparingly soluble in water or a basic drug presented as a salt which pK_a is close to that of its counter-acid. In this work, the acidic dissociation constants in pure methanol of the most common acids used in pharmaceutical preparations (lactic, tartaric, fumaric, maleic and citric) were determined. In addition, the pK_a values of the antipsychotic quetiapine presented as hemifumarate (Seroquel) and the very insoluble antiarrhythmic amiodarone were also determined by potentiometry. From these values, the aqueous pK_a of these drugs were estimated by means of previously established equations. Estimated values are consistent with those from literature and show the interest of methanol for drug discovery pK_a measurements.     

Hydrolytic and transglycosylation reactions of N-acyl modified substrates catalysed by β-N-acetylhexosaminidases

The hydrolytic and transglycosylation capabilities of 35 fungal β-N-acetylhexosaminidases with p-nitrophenyl 2-amino-2-deoxy-β-d-glucopyranoside and its four N-acyl derivatives (CHO, COCH₂OH, COCH₂CH₃, COCF₃) as substrates were tested. The preparation of four novel p-nitrophenyl disaccharides from these unnatural substrates catalysed by enzymes from Aspergillus oryzae, Penicillium oxalicum and Talaromyces flavus represents a considerable extension of the synthetic potential of glycosidases.     

Charge equilibria and pK values of 5-carboxypyranomalvidin-3-glucoside (vitisin A) by electrophoresis and absorption spectroscopy

Apparent pK values of the wine pigment, 5-carboxypyranomalvidin-3-glucoside (vitisin A), were determined using UV-vis spectroscopy, viz. pK_a1=0.98 (±0.10), pK_H1=4.51 (±0.03) and pK_H2=7.57 (±0.02). An additional ionisation constant at high pH (pK_a4=8.84±0.06) was established by high-voltage paper electrophoresis. These data in conjunction with previously published pK_a values determined by high-voltage electrophoresis suggest that in wine (pH 3.2-3.8), 5-carboxypyranomalvidin-3-glucoside exists as a complex mixture of hydrated and non-hydrated, partially ionised species with the predominant species being the quinonoidal base (λ_max 498 nm).     

Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.     

Synthesis, structural and larvicidal studies of some triorganotin 2-(p-chlorophenyl)-3-methylbutyrates

A series of triorganotin 2-(p-chlorophenyl)-3-methylbutyrates, (R₃SnO₂CCH(CH(CH₃)₂)C₆H₄Cl-4), where R = methyl, ethyl, n-propyl, n-butyl, phenyl and cyclo-hexyl, have been synthesized. Elemental analyses, Mössbauer, Infrared and NMR spectroscopies have been used to characterize their structures. Based on the spectroscopic results, all the complexes with the exception of the tricyclohexyl compound were found to be five-coordinated in the solid state while the tricyclohexyltin derivative was determined to be four-coordinated. Structural assignments based on spectroscopic data are supported by the crystallographic results of four of the triorganotin butyrates (trimethyl-, tri-n-propyl-, tri-n-butyl- and tricyclohexyltin 2-(p-chlorophenyl)-3-methylbutyrate). Multinuclear NMR spectroscopy studies indicated that all the complexes were tetrahedral in solution. Larvicidal activities of the complexes were evaluated against the 2nd instar stage of the Anopheles stephensi, Aedes aegypti and Culex pipiens quinquefasciatus mosquitoes. The toxicity data indicate that there does not appear to be any significant differences of the compounds towards the different mosquito species based on their averaged toxicity values. In addition, the toxicity of the triorganotin compounds towards the mosquito larvae was concluded to be dependent on both the compound and the species of mosquito larvae.     

Phase equilibria of the Ba-Sm-Y-Cu-O system for coated conductor applications

The complex phase relationships near the BaO-poor region of the quaternary Ba-Sm-Y-Cu-O oxide system prepared in pure air (O₂p=22 kPa, 950 °C) and in 0.1% O₂ (O₂p=100 Pa, 810 °C) have been determined. This investigation also included the subsolidus compatibilities in ten subsystems (Ba-Sm-Y-O, Ba-Sm-Cu-O, Ba-Y-Cu-O, Sm-Y-Cu-O, Ba-Sm-O, Ba-Y-O, Ba-Cu-O, Sm-Y-O, Sm-Cu-O, and Y-Cu-O), and the homogeneity range of five solid solutions (Ba(Sm_xY_2−x)CuO₅, (Sm,Y)₂O₃, (Sm,Y)₂CuO₄, (Y,Sm)₂Cu₂O₅, and Ba(Sm,Y)₂O₄). The single phase range of the superconductor solid solution, (Ba_2−xSm_x)(Sm_1−yY_y)Cu₃O_6+z, and the phase compatibilities in its vicinity, which are particularly important for processing, are described in detail. The phase equilibrium data of the Ba-Sm-Y-Cu-O system will enable the improvement of the intrinsic superconducting properties of second-generation wires, and facilitate the flux-pinning process.     

Synthesis and crystal structure of the Sr2MnGa(O,F)6 oxyfluorides

The fluorine-containing derivatives of Sr₂MnGaO_5.5 were prepared by treatment with XeF₂ at temperatures ranging from 300°C to 600°C. The compounds crystallize in a tetragonal unit cell with a_t≈a_p, c_t≈2a_p (a_p—the parameter of the perovskite subcell). An increase in fluorine content is accompanied by a reduction of the Mn oxidation state due to a partial replacement of oxygen by fluorine. The crystal structure of Sr₂MnGaO_4.78F_1.22 was determined by electron diffraction and X-ray powder diffraction (a=3.85559(2) Å, c=7.78289(6) Å, S.G. P4/mmm, R_I=0.012, R_P=0.019). The structure consists of alternating (MnO₂), (SrO) and (GaO_0.78F_1.22) layers. The Ga atoms are situated in slightly elongated octahedra, the MnO₆ octahedra are characterized by two short apical Mn-O distances of 1.876(8) Å and four long equatorial ones of 1.9278(1) Å. This is interpreted as an “apically compressed” type of Jahn-Teller distortion, in contrast to the “apically elongated” one in the Sr₂MnGaO_5+δ brownmillerites with different oxygen content. Possible structural reasons for the reversed Jahn-Teller effect are discussed.     

Synthesis and optical properties of conjugated N,N-dimethyl and thienyl end-capped 2,5-(arylethynyl)thiophene oligomer structures

End-capped (N,N-dimethylaminophenyl) and 2′-thienylethynyl 2,5-thiophene oligomer structures were synthesized by heterocoupling between the terminal acetylenes such as: p-(N,N-dimethylaminophenyl)ethyne (3) [or 1-(p-(N,N-dimethylaminophenyl)-2-p-(ethynylphenyl)ethyne, 4]; p-(β-ethenyl-2′-thienyl)phenylethyne (E-9) [or p-(β-ethynyl-2′-thienyl)phenylethyne, 11], and 2,5-diiodothiophene, catalyzed by the Cl₂Pd(PPh₃)₂/CuI system, in good to excellent yields. The 2,5-di[(3′,5′-di(trimethylsilylethynyl)phenyl]_x-1-ethynyl]thiophene oligomers were prepared by heterocoupling between 3′,5′-di[(trimethylsilylethynyl)phenyl]_x-1-ethyne (n = 0-2) terminal acetylenes and 2,5-diiodothiophene, in excellent yields. The terminal acetylenes were efficiently prepared by a specific protection-deprotection methodology. All the ethynylphenyl compounds obtained show fluorescence radiation emission, with a bathochromic shift of the wavelength that increases with the chain conjugation.     

Synthesis and characterization of n=5, 6 members of the La4Srn−4TinO3n+2 series with layered structure based upon perovskite

Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La₄Sr_n−4Ti_nO_3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)₅Ti₅O₁₇] and [(La,Sr)₆Ti₆O₂₀] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]_p. The n=5 member is similar to the previously reported n=5 member of other A_nB_nO_3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this A_nB_nO_3n+2 series.     

Uptake of weathered p,p′-DDE by plant species effective at accumulating soil elements

Ten plant species previously shown to accumulate inorganic elements effectively from natural solids were grown under field conditions in p,p′-dichlorodiphenyldichloroethane (p,p′-DDE) contaminated soil. The plant species, which included rye, mustard, canola, vetch, pigeonpea, clover, peanut, and 3 cultivars of white lupin, represented both monocots and dicots, as well as two major families within the dicots: the Brassicaceae and the Fabaceae. The plants varied widely in their ability to phytoextract and translocate weathered p,p′-DDE. The percentage of contaminant phytoextracted ranged from 0.06% (white lupin) to 0.22% (clover, vetch), and the translocation factors (TF; contaminant concentration ratio of stems to roots) ranged from 0.04 (clover, white lupin) to 0.37 (canola). An inverse relationship exists between the amount of contaminant in the roots as measured by the root BCF (bioconcentration factor; dry weight contaminant concentration ratio of root to soil) and the TF. Duplicate mounds of each species were periodically amended with nitrogen (N), phosphorus (P), nitrogen and phosphorus together (N/P); a minus phosphorus treatment involved the addition of AlSO₄ to the soil prior to planting. The effect of nutrient regime on plant biomass, p,p′-DDE uptake and translocation, and inorganic element content varied greatly among the 10 plant species. For some species (rye, vetch, pigeonpea, clover, white lupin), reductions or non-significant changes in p,p′-DDE uptake were observed under the nutrient treatments and were not correlated with plant biomass effects. For mustard, canola, and peanut, the percentage of p,p′-DDE phytoextracted in the various treatments was more than doubled and was directly correlated with a two-fold increase in total plant biomass. Although it is generally assumed that fertilizer amendments will enhance the phytoremediation of organic and inorganic pollutants, the data here suggest that such effects are highly species specific and in some cases may actually decrease remediation potential.     

Synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)nfluoren-9-one and 9-(p-methoxyphenyl)-9-methyl derivatives: optical properties

2,7-Substituted 9-fluorenones and 9,9-disubstituted fluorene have been synthesized and their fluorescence properties analyzed. The synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluoren-9-one (or the 9-(p-methoxyphenyl)-9-methyl) structures was carried out by the heterocoupling reaction between the 2,7-di(halo)fluoren-9-one (or 2,7-dibromo-9-(p-methoxyphenyl)-9-methylfluorene) and p-trimethylsilylethynyl(phenylethynyl)_n (n=1,2), catalyzed by the dichloro bis(triphenylphosphine)palladium and cuprous iodide system, in a divergent synthesis.The π-extended conjugated compounds exhibit fluorescence radiation emission (blue light-emitting), with important quantum yield for the 9-(p-methoxyphenyl)-9-methyl-2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluorenes which increases with the conjugation.     

Diels-Alder reaction of optically active (E)-γ-keto-α,β-unsaturated p-tolylsulfoxides with cyclopentadiene

The Diels-Alder reaction of enantiomerically pure (E)-γ-keto-α,β-unsaturated p-tolylsulphoxides 3 with cyclopentadiene give four easily separable diastereomers. The effect of several Lewis acids on the reaction was studied, finding a high endo selectivity with respect to the carbonyl group and moderate π-diastereoselectivity using BF₃·Et₂O as catalyst. The reactivity of compounds 3 as well as their endo selectivity are both higher than those observed for the corresponding (E)-3-sulfinylacrylates.     

Combined microwave-assisted isolation and solid-phase purification procedures prior to the chromatographic determination of phenolic compounds in plant materials

A fast, sensitive and selective procedure employing a combination of microwave-assisted extraction (MAE) and solid phase extraction (SPE) was applied prior to liquid chromatographic identification and quantification of phenolic compounds in plant materials. MAE has been tested and optimized for the isolation of phenolic acids (gallic, protocatechuic, p-hydroxybenzoic, chlorogenic, vanilic, caffeic, syringic, p-coumaric, ferulic, sinapic, benzoic, m-coumaric, o-coumaric, rosmarinic, cinnamic acids) and 3,4-dihydroxybenzaldehyde, syringaldehyde, p-hydroxybenzaldehyde, and vanillin in various plants. The effects of experimental conditions on MAE efficiency, such as solvent composition, temperature, extraction time, have been studied. The extraction efficiencies were compared with those obtained by computer-controlled, two-step Soxhlet-like extractions. Plant extracts were purified and phenolic compounds were pre-concentrated using SPE on polymeric RP-105 SPE sorbent prior to HPLC analysis. Chromatographic separation was carried out on a Hypersil BDS C₁₈ column using a mobile phase consisted of 0.3% (v/v) acetic acid in water (solvent A) and methanol (solvent B) at flow rate 0.6 ml min⁻¹ and column temperature 30 °C with gradient elution.     

Preparation of p-nitrocalix[n]arene methyl ethers via ipso-nitration and crystal structure of tetramethoxytetra-p-nitrocalix[4]arene

Nitration of p-tert-butylcalix[n]arene methyl ethers under a variety of reaction conditions has been examined. It has been determined that amongst different nitration procedures adopted (AlCl₃/KNO₃, HNO₃/CH₃COOH, HNO₃/(CH₃CO)₂O, cerium(IV) ammonium nitrate/CH₃COOH), ipso-nitration with CH₃COOH/HNO₃ gives best yields of p-nitrocalixarenes and work up conditions. ipso-Nitration of tetramethoxytetra-p-tert-butylcalix[4]arene gives tetramethoxytetra-p-nitrocalix[4]arene as triclinic crystals with space group with a=9.102(3) Å, b=11.623(3) Å, c=18.368(3) Å and α=77.99(2)°, β=81.10(2)°, γ=73.37(2)°. Its conformation is partial cone and it forms an exocylic 1:1 complex with DMF.