Carboxymethylation of hemicelluloses isolated from sugarcane bagasse

Hemicelluloses isolated from sugarcane bagasse were converted to carboxymethyl hemicelluloses (CMH) by carboxymethylation using sodium monochloroacetate and sodium hydroxide in ethanol/water medium. The reaction was performed under various temperatures, times, times of alkaline activation, the ways of the addition of alkali, and the amounts of sodium hydroxide and sodium monochloroacetate. The product had the maximum degree of substitution (DS) of 0.56. The structure of the resulting polymers was characterized with Fourier transform infrared (FT-IR) and ¹³C nuclear magnetic resonance (NMR) spectroscopies. Destructive methods such as thermal analysis and non-destructive techniques such as gel permeation chromatography (GPC) were used to characterize the carboxymethyl hemicellulose preparations. It was found that a significant degradation of the polymers occurred during carboxymethylation. The thermal stability of carboxymethyl hemicelluloses was higher than that of the native hemicelluloses.     

海藻酸钠/羧甲基淀粉共混膜

用溶液共混法成功制备出海藻酸钠／羧甲基淀粉共混膜，IR、XRD、SEM结构表征以及力学性能、吸水性和水蒸汽透过率测定结果表明：共混膜中海藻酸钠和羧甲基淀粉间存在强烈的分子间氢键等相互作用及良好的相容性；随羧甲基淀粉含量的增加，共混膜的吸水率显著降低；当羧甲基淀粉含量(wCMS)=0．20时，共混膜的抗张强度和断裂伸长率分别为53．1MPa和5．3％，比海藻酸钠膜分别提高了97．4％和60．6％，水蒸汽透过率达最小值，是一种具有潜在应用前景的可食性包装膜材料。     

Synthesis and evaluation of new chiral nonracemic C2-symmetric and unsymmetric 2,2'-bipyridyl ligands

The synthesis of a series of chiral nonracemic and C2-symmetric 2,2'-bipyridyl ligands (R = Me, i-Pr and Ph) as well as the syntheses of the corresponding unsymmetric 2,2'-bipyridyl ligands (R = Me and Ph) is described. These bipyridyl ligands were prepared, in a notably direct and modular fashion, from the readily available and corresponding 2-chloropyridine acetals (R = Me, i-Pr and Ph). The bipyridyl ligands were evaluated in copper(I)-catalyzed cyclopropanation reactions of styrene with the ethyl and t-butyl esters of diazoacetic acid. The stereoselectivities, as well as the yields of the cyclopropanation reactions, were dependant on the ratio of the bipyridyl ligands and copper triflate that was employed. The best result was obtained in the asymmetric cyclopropanation reaction of styrene and tert-butyl diazoacetate with the C2-symmetric bipyridyl ligand (R = i-Pr). This afforded the corresponding trans-cyclopropane in good diastereoselectivity (4 : 1) and in moderate enantioselectivity (44% ee). The X-ray structure determination of a complex formed between the C2-symmetric 2,2'-bipyridyl ligand (R = Ph) and copper(I) chloride showed that two bipyridyl ligands had coordinated to the copper(I) ion. This information, along with the results of a series of cyclopropanation reactions and NMR data, led to the conclusion that the 2,2'-bipyridyl ligands had the propensity to form catalytically inactive bis-ligated copper(I) species in solution that were in equilibrium with catalytically active copper(i) triflate and the desired mono-ligated copper(I) species. Moreover, it was observed that the complex of the bipyridyl ligand (R = Ph) and copper(I) chloride had a particularly large optical rotation (sodium D-line). The maximum positive optical rotation was subsequently found to be +1.1 x 10(4) at 304 nm and the maximum negative optical rotation was -1.3 x 10(4) at 329 nm.     

The standard enthalpies of formation of crystalline N-(carboxymethyl)aspartic acid and its aqueous solutions

The energy of combustion of N-(carboxymethyl)aspartic acid (CMAA) was determined by bomb calorimetry in oxygen. The standard enthalpies of combustion and formation of crystalline N-(carboxymethyl)aspartic acid were calculated. The heat effects of solution of crystalline CMAA in water and a solution of sodium hydroxide were measured at 298.15 K by direct calorimetry. The standard enthalpies of formation of CMAA and its dissociation products in aqueous solution were determined.     

Luminescent properties of water-soluble conjugated metallopolymers and their application to fluorescent nitric oxide detection

Water-soluble pi-conjugated polymers (CPs) incorporating 5,5'-(2,2'-dipyridyl) (CP1) or 6,6'-(2,2'-dipyridyl) (CP2) units within the pi-conjugated backbone were prepared as scaffolds for macromolecular metal complexation. The response of CP emission to a range of metal ions was investigated in water, 10 mM aqueous sodium dodecyl sulfate, and acetonitrile/water (95:5). Cupric ions are the most efficient quenchers of CP emission, with K(SV) = 1.1 x 10(5) and 5.2 x 10(4) M(-1) in water for CP1a (40% bipyridyl monomer units) and CP1b (20% bipyridyl monomer units), respectively. Quenching is approximately twice as effective in acetonitrile/water (95:5) (K(SV) = 3.1 x 10(5) M(-1) for CP1a and 1.1 x 10(5) M(-1) for CP1b). Partial restoration of emission was observed upon exposure of Cu(II)-CP solutions to excess NO(g) in acetonitrile/water (95:5) or 10 mM SDS(aq).     

Heat-resistant polymers containing bipyridyl units. I. Polyimides

Polyimides containing bipyridyl units were synthesized. The bipyridyl units were successfully incorporated by polymerization of various bipyridyl diamines with aromatic tetracarboxylic acid dianhydrides. The resulting polyamic acids had inherent viscosities in the range 0.07 to 2.26, and they were converted to the polyimides by thermal cyclization. The polyimides containing the bipyridyl units exhibited varying degrees of solubility in dimethylacetamide and m-cresol and were found to be very soluble in dichloroacetic acid.     

Unexpected dependence of the protonation constant of 2,2'-bipyridyl on ionic strength

The protonation constants of 2,2'-bipyridyl and ammonia have been determined by pH titration at 25 degrees , at ionic strengths of 0.1, 0.2, 0.5, 1.0, 1.5 and 2.0M obtained by using LiNO(3), NaNO(3), KNO(3), LiClO(4) and NaClO(4) as background electrolytes. The protonation constants generally change by about 0.3-0.4 log units for both ligands in nitrate media. A similar change in the protonation constant of ammonia was observed in perchlorate media. There is, however, a change of about 0.8-0.9 log units in the protonation constant of bipyridyl in the perchlorate media. This phenomenon is interpreted by postulating ion-pair formation between perchlorate and the protonated form of bipyridyl, HBp(+) + ClO(4)(-) rlharr2; HBp(+).ClO(4)(-) with formation constants of 0.54 in 2M lithium nitrate and 0.45 in 2M sodium nitrate.     

Synthesis and Characterization of Halo, Cyanato, Thiocyanato and Selenocyanato Molybdenum(VI) Dioxo and Dioxo-μ-oxo Complexes

Ten new 4,4′-bipyridyl molybdenum(VI) dioxo and dioxo-μ-oxo complexes have been synthesized and fully characterized. The substituents on the bipyridyl moiety are: t-butyl, benzyl, carbomethoxy, nitro and methoxy groups, whereas the functional ligands on molybdenum are: chloro, bromo, thiocyanato, cyanato and selenocyanato groups. The molecular structure of three of them have been determined by single crystal X-ray crystallography and showed distortions from an octahedral geometry in accord with the nature of the various substituents.     

A new allosteric bis crown ether ligand containing a 2,2′-bipyridyl fragment

The synthesis of a new allosteric bis crown ether ligand incorporating a 2,2′-bipyridyl function and two benzo-15-crown-5 subunits is described. Chelation of Ru(II) at the bipyridyl nitrogens forces the bipyridyl function towards coplanarity, restricting the conformational freedom of the two benzo-15-crown-5 binding units in such a way as to favour the formation of an intramolecular sandwich complex with sodium. A variety of bimetallic complexes have been isolated resulting from the simultaneous coordination of transition metals at the bipyridyl fragment and alkali metals at the crown ether moieties.     

二氧化碳和水气氛对高钠煤转化过程中钠迁移的影响

对新疆的两种高钠煤（伊犁煤YL、呼图壁煤HTB）进行了N₂、CO₂和H₂O气氛和不同温度下钠迁移的研究。采用逐级萃取和湿法消解法确定了原煤、半焦中钠的赋存形态,定量研究了两种煤中钠的挥发及迁移规律。结果表明,YL煤的形态钠中水溶钠占80.08%,HTB煤的形态钠中不溶钠占61.54%。不同气氛下,升高温度都可促进两种煤中钠的挥发,半焦中水溶钠比例减小,醋酸铵可溶钠比例会出现先增加后减少现象,盐酸可溶钠比例呈增加趋势。对于YL煤,CO₂气氛可抑制钠的挥发,H₂O蒸气可促进钠的挥发;900℃时,YL煤CO₂气氛下钠挥发仅为N₂气氛下的50.25%,而H₂O气氛钠挥发为N₂气氛下的111.45%。对于HTB煤,CO₂气氛也可抑制钠的挥发,900℃时CO₂气氛下钠挥发为N₂气氛的80.91%;HTB煤在H₂O蒸气下,800℃之前钠挥发高于N₂,当900℃时,钠挥发略低于N₂气氛。YL煤形态钠中以水溶钠为主,其挥发的同时会向盐酸可溶钠及不溶钠转变。而HTB煤形态钠中以不溶钠为主,其次是水溶钠,CO₂和H₂O气氛能促进不溶钠向其他可溶态钠转变。     

Lipase-catalyzed kinetic resolution of β-borylated carboxylic esters

The kinetic resolution of chiral β-borylated carboxylic esters via lipase-catalyzed hydrolysis and transesterification reactions was studied. The enantioselective hydrolysis catalyzed by CAL-B furnished the β-borylated carboxylic acid with reasonable enantiomeric excess (62% ee), while both methyl and ethyl β-borylated carboxylic esters were recovered with excellent ee (>99%). Meanwhile, the transesterification reaction of β-borylated carboxylic esters and several alcohols, catalyzed by CAL-B, only indicated a high selectivity when ethanol and methyl-(β-pinacolylboronate)-butanoate were used as substrates, which gave ethyl-(β-pinacolylboronate)-butanoate with >99% ee.     

Coordination polymers and hydrogen‐bonded assemblies of 2,2′‐[2,5‐bis(carboxymethoxy)‐1,4‐phenylene]diacetic acid with ammonium,lanthanum and zinc cations

We report the synthesis of the 2,2′‐[2,5‐bis(carboxymethoxy)‐1,4‐phenylene]diacetic acid (TALH₄) ligand and the structures of its adducts with ammonium, namely diammonium 2,2′‐[2,5‐bis(carboxymethyl)‐1,4‐phenylenedioxy]diacetate, 2NH₄⁺·C₁₄H₁₂O₁₀²⁻, (I), lanthanum, namely poly[[aquabis[μ₄‐2,2′‐(2‐carboxylatomethyl‐5‐carboxymethyl‐1,4‐phenylenedioxy)diacetato]dilanthanum(III)] monohydrate], {[La₂(C₁₄H₁₁O₁₀)₂(H₂O)]·H₂O}_n, (II), and zinc cations, namely poly[[{μ₄‐2,2′‐[2,5‐bis(carboxymethyl)‐1,4‐phenylenedioxy]diacetato}zinc(II)] trihydrate], {[Zn(C₁₄H₁₂O₁₀)]·3H₂O}_n, (III), and poly[[diaqua(μ₂‐4,4′‐bipyridyl){μ₄‐2,2′‐[2,5‐bis(carboxymethyl)‐1,4‐phenylenedioxy]diacetato}dizinc(II)] dihydrate], {[Zn₂(C₁₄H₁₀O₁₀)(C₁₀H₈N₂)(H₂O)₂]·2H₂O}_n, (IV), the formation of all four being associated with deprotonation of TALH₄. Adduct (I) is a diammonium salt of TALH₂²⁻, with the ions located on centres of crystallographic inversion. Its crystal structure reveals a three‐dimensional hydrogen‐bonded assembly of the component species. Reaction of TALH₄ with lanthanum trinitrate hexahydrate yielded a two‐dimensional double‐layer coordination polymer, (II), in which the La^III cations are nine‐coordinate. With zinc dinitrate hexahydrate, TALH₄ forms 1:1 two‐dimensional coordination polymers, in which every Zn^II cation is linked to four neighbouring TALH₂²⁻ anions and each unit of the organic ligand is coordinated to four different tetrahedral Zn^II cation connectors. The crystal structure of this compound accommodates molecules of disordered water at the interface between adjacent polymeric layers to give (III), and it has been determined with low precision. Another polymer assembly, (IV), was obtained when zinc dinitrate hexahydrate was reacted with TALH₄ in the presence of an additional 4,4′‐bipyridyl ligand. In the crystal structure of (IV), the bipyridyl and TAL⁴⁻ entities are located on two different inversion centres. The ternary coordination polymers form layered arrays with corrugated surfaces, with the Zn^II cation connectors revealing a tetrahedral coordination environment. The two‐dimensional polymers in (II)–(IV) are interconnected with each other by hydrogen bonds involving the metal‐coordinated and noncoordinated molecules of water. TALH₄ is doubly deprotonated, TALH₂²⁻, in (I) and (III), triply deprotonated, viz. TALH³⁻, in (II), and quadruply deprotonated, viz. TAL⁴⁻, in (IV). This report provides the first structural characterization of TALH₄ (in deprotonated form) and its various supramolecular adducts. It also confirms the potential utility of this tetraacid ligand in the formulation of coordination polymers with metal cations.     

Water-Soluble Magnetic Nanocomposites Based on Carboxymethyl Cellulose and Iron(III) Oxide

The one-step synthesis of water-soluble composites from maghemite (γ-Fe₂O₃) nanoparticles with a diameter of 12 ± 4 nm and a biocompatible polysaccharide, namely, sodium salt of carboxymethyl cellulose, is described. The role of the polymer matrix consists in stabilization of the resulting nanoparticles by the electrostatic interaction of polymer carboxyl groups with the surface atoms of iron in the (3+) oxidation state. The dissolution of the composites in water affords aggregatively stable dispersions responding to the external magnetic field. The content of the magnetic phase (iron oxide) in the formulation of the maghemite–carboxymethyl cellulose composite is defined by the ratio of components during the synthesis.     

A highly water-soluble disulfonated tetrazolium salt as a chromogenic indicator for NADH as well as cell viability

A highly water soluble disulfonated tetrazolium salt, 4-[3-(2-methoxy-4-nitrophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate sodium salt, was synthesized. The compound is reduced by NADH in good yields at neutral pHs in the presence of 1-methoxy PMS to produce the corresponding formazan dye that absorbs at 460 nm. The formazan is soluble to water at concentrations higher than 0.1 M. The tetrazolium salt thus proved to be useful as a sensitive chromogenic indicator for NADH. It is also applicable to cell proliferation assays as a cell viability indicator.     

Einwirkung der natriumzitrate auf das berlinerblau

1. Prussian blue is soluble in the sodium citrates to form sodium ferrocyanide and sodium ferric citrate. It is much less soluble in disodium citrate than in trisodium citrate, and nearly insoluble in monosodium citrate. 2. Colloidal solutions are formed when the sodium citrates are added to Prussian blue in much smaller quantities than is required to produce a complete solution. 3. The peptizing action of the sodium citrates is explained by the formation of water soluble colloidal sodium ferric ferrocyanide NaFe[Fe(CN)₆]. 4. The peptizing action of the potassium oxalates and of the neutral alkali tartrates is also explained by the formation of KFe[Fe(CN)₆].     

五彩湾煤中钠在热解过程中的形态变迁

采用不同萃取液进行了新疆准东五彩湾高钠煤萃取实验,并利用微波消解仪和电感耦合等离子体原子发射光谱仪,分析了原煤和不同萃取过程下制得的煤样中的钠元素,确定了五彩湾煤中钠的存在形式。在氮气氛围下进行了原煤及不同萃取过程下煤样的热解实验,分析了热解半焦中钠的存在形式并确定煤中不同存在形式钠在热解过程中的演变规律。结果表明,五彩湾煤中钠主要为水溶钠,有机钠主要以羧酸盐形式存在。450~650℃时,实验煤样热解过程中部分水溶钠和盐酸溶钠会转化为醋酸铵溶钠。在热解过程中,实验煤样中水溶钠和醋酸铵溶钠的析出主要集中于650~850℃,1050℃时则有部分盐酸溶钠析出,此时,在实验条件下钠的挥发达到最大值。煤样半焦中的钠主要以不可溶钠形式存在。     

Catalytic mechanism of water oxidation with single-site ruthenium-heteropolytungstate complexes

Catalytic water oxidation to generate oxygen was achieved using all-inorganic mononuclear ruthenium complexes bearing Keggin-type lacunary heteropolytungstate, [Ru(III)(H(2)O)SiW(11)O(39)](5-) (1) and [Ru(III)(H(2)O)GeW(11)O(39)](5-) (2), as catalysts with (NH(4))(2)[Ce(IV)(NO(3))(6)] (CAN) as a one-electron oxidant in water. The oxygen atoms of evolved oxygen come from water as confirmed by isotope-labeled experiments. Cyclic voltammetric measurements of 1 and 2 at various pH's indicate that both complexes 1 and 2 exhibit three one-electron redox couples based on ruthenium center. The Pourbaix diagrams (plots of E(1/2) vs pH) support that the Ru(III) complexes are oxidized to the Ru(V)-oxo complexes with CAN. The Ru(V)-oxo complex derived from 1 was detected by UV-visible absorption, EPR, and resonance Raman measurements in situ as an active species during the water oxidation reaction. This indicates that the Ru(V)-oxo complex is involved in the rate-determining step of the catalytic cycle of water oxidation. The overall catalytic mechanism of water oxidation was revealed on the basis of the kinetic analysis and detection of the catalytic intermediates. Complex 2 exhibited a higher catalytic reactivity for the water oxidation with CAN than did complex 1.     

Synthesis,Characterization, and Antimicrobial Activity of Carboxymethyl Chitosan-Graft-Poly(N-acryloyl,N′-cyanoacetohydrazide) Copolymers

Carboxymethyl chitosan was grafted with N-acryloyl,N′-cyanoacetohydrazide in homogenous aqueous phase using potassium persulfate initiator. The maximum grafting yield achieved was 448% at 0.03 mol/L potassium persulfate, 0.75 mol/L N-acryloyl,N′-cyanoacetohydrazide, and 60°C within 2 h. The grafted copolymers showed better thermal stability than that of carboxymethyl chitosan. The samples with percent grafting values up to 98% were soluble in water, but a higher grafting extent resulted in insoluble copolymers. The grafted copolymers are nontoxic materials and showed an inhibition effect on both Escherichia coli and Staphylococcus aureus bacteria and Aspergillus flavus and Candida albicans fungi better than those of chitosan and carboxymethyl chitosan themselves.     

Structure and properties of biodegradable carboxymethyl cellulose films containing silver nanoparticles

Silver nanoparticles stabilized in a solution of sodium carboxymethyl cellulose with a degree of substitution of 0.85 and a degree of polymerization of 600 have been synthesized. The structuring; physical, chemical, and mechanical properties; and antimicrobial activities of films prepared from sodium carboxymethyl cellulose solutions containing silver nanoparticles have been studied. The shapes, quantities, and sizes of the silver nanoparticles occurring in the sodium carboxymethyl cellulose films were determined with the use of transmission electron microscopy, atomic force microscopy, and UV spectroscopy. It was found that an increase in the concentration of silver nitrate in sodium carboxymethyl cellulose solutions, as well as photoirradiation of the films, leads to the changes in the sizes and shapes of silver nanoparticles. The shapes, sizes, and quantities of silver nanoparticles determine their biological activity. An increase in the quantity of 5- to 25-nm silver nanoparticles was found to enhance the microbicidal activities of the carboxymethyl cellulose films.     

Synthesis of 2-Oxo amide triacylglycerol analogues and study of their inhibition effect on pancreatic and gastric lipases

A general method for the synthesis of chiral 2-oxo amide triacylglycerol analogues, from (R)- or (S)-3-aminopropane-1,2-diol, was developed. These novel inhibitors of digestive lipases are analogues of the triacylglycerol molecule, a natural substrate of lipases, and they were designed to contain the 2-oxo amide functionality in place of the scissile ester bond at the sn-1 or sn-3 position and nonhydrolysable ether bonds instead of ester bonds at the other two remaining positions. The 2-oxo amide derivatives synthesised were tested for their ability to form stable monomolecular films at the air/water interface by recording their surface pressure/molecular area compression isotherms. The inhibition of porcine pancreatic and human gastric lipases by the 2-oxo amides was studied by means of the monolayer technique with mixed films of 1,2-dicaprin and with variable proportions of each inhibitor. The alpha50 values of these triacylglycerol analogues for PPL and HGL varied between 4.4 to 7.0% and 5.6 to 15.9%, respectively. The chirality at the sn-2 position of 2-oxo amide triacylglycerol analogues affected the alpha50 value for HGL, but not for PPL.