Alkaline NaBH4 Research Articles

Electrodeposition of Microporous Co-P Catalysts and Their Hydrogen Generation Characteristics in Alkaline NaBH4 Solution

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Hydrogen generation utilizing alkaline sodium borohydride solution and supported cobalt catalyst

Supported Co catalysts with different supports were prepared for hydrogen generation (HG) from catalytic hydrolysis of alkaline sodium borohydride solution. As a result, we found that a -Al2O3 supported Co catalyst was very effective because of its special structure. A maximum HG rate of 220 mL min −1 g −1 catalyst and approximately 100% efficiency at 303 K were achieved using a Co/-Al2O3 catalyst containing 9 wt.% Co. The catalyst has quick response and good durability to the hydrolysis of alkaline NaBH4 solution. It is feasible to use this catalyst in hydrogen generators with stabilized NaBH4 solutions to provide on-site hydrogen with desired rate for mobile applications, such as proton exchange membrane fuel cell (PEMFC) systems. © 2006 Elsevier B.V. All rights reserved.

A structured Co–B catalyst for hydrogen extraction from NaBH 4 solution

A structured Co–B catalyst has been developed to produce hydrogen from an alkaline NaBH 4 solution. The catalyst was prepared by chemical reduction of Co precursors coated on a Ni foam support. The effects of catalyst preparation conditions on activity of the catalyst were investigated. The active catalyst was amorphous in structure and contains boron with a Co/B molar ratio of 1.5–2.8. With increasing the heat treatment temperature, the catalyst showed a maximum activity to hydrogen generation at approximately 250 °C. Adhesion of the catalyst to the support was also enhanced by heat treatment at 300–400 °C. The catalysts were successfully applied in both a batch reactor and a flow reactor for continuous generation of hydrogen.

Effects of electrodeposited Co and Co–P catalysts on the hydrogen generation properties from hydrolysis of alkaline sodium borohydride solution

Co and Co–P catalysts electroplated on Cu in sulfate based solution without or with an addition of H 2PO 2 − ions were developed for hydrogen generation from alkaline NaBH 4 solution. The microstructures of the Co and Co–P catalysts and their hydrogen generation properties were analyzed as a function of cathodic current density and plating time during the electrodeposition. An amorphous Co–P electrodeposit with micro-cracks was formed by electroplating in the sulfate based solution containing H 2PO 2 − ions. It was found that the amorphous Co–P catalyst formed at 0.01 A/cm 2 exhibited 18 times higher catalytic activity for hydrolysis of NaBH 4 than did the polycrystalline Co catalyst. The catalytic activity of the electrodeposited Co–P catalyst for hydrolysis of NaBH 4 was found to be a function of both cathodic current density and plating time, that is, parameters determining the concentration of P in the Co–P catalyst. Especially, Co–13 at.% P catalyst electroplated on Cu in the Co–P bath at a cathodic current density of 0.01 A/cm 2 for 1080 s showed the best hydrogen generation rate of 954 ml/min g-catalyst in 1 wt.% NaOH + 10 wt.% NaBH 4 solution at 30 °C.

Effects of Electroless Deposited Co-P Catalysts on the Hydrogen Generation Properties from Hydrolysis of Alkaline NaBH4 Solution

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Cobalt boride catalysts for hydrogen generation from alkaline NaBH 4 solution

Cobalt boride precursors were synthesized via chemical reaction of aqueous sodium borohydride with cobalt chloride, and followed by heat-treating at various temperatures. The as-prepared Co–B catalysts were characterized and analyzed by X-ray diffraction (XRD), nitrogen adsorption–desorption and catalytic activity test; and were adopted to help accelerating hydrolysis reaction of NaBH 4 alkaline solution. The Co–B catalyst treated at 500 °C exhibits the best catalytic activity, and achieves an average H 2 generation rate of 2970 ml/min/g, which may give a successive H 2 supply for a 481 W proton exchange membrane fuel cell (PEMFC) at 100% H 2 utilization.

Hydrogen production from catalytic hydrolysis of sodium borohydride solution using nickel boride catalyst

A highly stable and active nickel boride catalyst (Ni x B) was prepared and tested for the catalytic hydrolysis of alkaline NaBH 4 solution. It was found that after heat treatment at 150°C in vacuum the Ni x B catalyst shows greatly enhanced catalytic activity and operational stability. In the experimental conditions, the hydrolysis reaction can produce 6.75 wt% hydrogen at 45°C and >4.0 wt% hydrogen even at room temperatures, exhibiting much higher hydrogen storage capacity than currently used alloys for hydrogen storage. Since the Ni x B catalyst is inexpensive and easy to prepare, it is feasible to use this catalyst in the construction of practical hydrogen generators for portable and in situ applications.

Cold vapour atomic fluorescence studies on the behaviour of mercury(II) and mercury(II)-thiol complexes. An alternative route for characterization of –SH binding groups

The behaviour of Hg II and Hg II -thiol complexes (RSH=L-cysteine, DL-penicillamine, propane-2-thiol, glutathione, thiosalicylic acid) following their reduction with alkaline sodium tetrahydroborate to give Hg 0 has been studied by using a continuous flow reaction system coupled with atomic fluorescence spectrometric (AFS) detection. The quantitative reduction of Hg II to Hg 0 takes place with a specific amount of sodium tetrahydroborate according to the stoichiometric reaction of mercury with alkaline NaBH 4 . The complete reduction of Hg II -thiol complexes to Hg 0 requires a molar excess of NaBH 4 of up to six orders of magnitude, depending on the type of complex. Under an appropriate excess of reductant, Hg II and its thiol complexes are not distinguishable giving the same AF molar response. The method allows the discrimination of Hg II from Hg II -thiol complexes without any preliminary separation. Applications to the indirect titration of thiols and to the determination of the number of accessible }}n1SH groups in pure ovalbumin samples are reported.

Structural variations in the glycosaminoglycan-protein linkage region of recombinant decorin expressed in Chinese hamster ovary cells.

Decorin is a small fibroblast proteoglycan consisting of a core protein and a single chondroitin/dermatan sulfate chain. The structure of the carbohydrate-protein linkage region of the recombinant decorin expressed in Chinese hamster ovary cells was investigated. The decorin was secreted in the culture medium and isolated by anion-exchange chromatography. The glycosaminoglycan chain was released from the decorin by beta-elimination using alkaline NaBH4, and then digested with chondroitinase ABC. These treatments resulted in a major and a few minor hexasaccharide alditols derived from the carbohydrate-protein linkage region. Their structures were analyzed by enzymatic digestion in conjunction with high-performance liquid chromatography. Two of these compounds have the conventional hexasaccharide core, deltaHexA alpha1-3GalNAc beta1-4GlcA beta1-3Gal beta1-3Gal beta1-4Xyl-ol. One is nonsulfated, and the other is monosulfated on C4 of the GalNAc residue. They represent 12% and 60% of the total linkage region, respectively. The other compound has the hexasaccharide alditol with an internal iduronic acid residue deltaHexA alpha1-3GalNAc(4-sulfate)beta1-4IdoA alpha1-3Gal beta1-3Gal beta1-4Xyl-ol, which was previously demonstrated in one of the five linkage hexasaccharide alditols isolated from dermatan sulfate proteoglycans of bovine aorta (Sugahara et al., J. Biol. Chem., 270, 7204-7212, 1995). The compound accounts for 11% of the total linkage region. These structural variations in the linkage hexasaccharide region of the decorin strikingly contrast to the uniformity demonstrated in the linkage hexasaccharide structure of human inter-alpha-trypsin inhibitor (Yamada et al., Glycobiology, 5, 335-341, 1995) and urinary trypsin inhibitor (Yamada et al., Eur. J. Biochem., 233, 687-693, 1995), both of which have a single chondroitin sulfate chain with a uniform linkage hexasaccharide structure, deltaHexA alpha1-3GalNAc(4-sulfate)beta1-4GlcA beta1-3Gal(4-sulfate)beta1-3Gal beta1-4Xyl, containing a 4-O-sulfated Gal residue.

The uniform galactose 4-sulfate structure in the carbohydrate-protein linkage region of human urinary trypsin inhibitor.

The carbohydrate-protein linkage region of a chondroitin 4-sulfate chain attached to urinary trypsin inhibitor (UTI) was isolated from human urine and characterized structurally. The chondroitin 4-sulfate chain was released from UTI by beta-elimination using alkaline NaBH4 then digested with chondroitinase ABC. These treatments resulted in only a single hexasaccharide alditol derived from the carbohydrate-protein linkage region. Chemical and enzymic analyses and 600-MHz 1H-NMR spectroscopy revealed that the hexasaccharide alditol had the following structure: delta HexA alpha 1-3GalNAc(4-sulfate) beta 1-4GlcA beta 1- 3Gal(4-sulfate) beta 1-3Gal beta 1-4Xyl-ol, where delta HexA, GlcA and Xyl-ol represent 4-deoxy-alpha-L-threo-hex-4-enepyranosyluronic acid, D-glucuronic acid and D-xylitol, respectively. This structure contained the novel 4-sulfated Gal residue, which was first demonstrated in one of the three linkage hexasaccharide-serines isolated from chondroitin 4-sulfate of rat chondrosarcoma [Sugahara, K., Yamashina, I., de Waard, P., Van Halbeek, H. & Vliegenhart, J. F. G. (1988) J. Biol. Chem. 263, 10168-10174]. This disulfated structure was recently identified as the sole structural component in the linkage hexasaccharide alditol fraction isolated from inter-alpha-trypsin inhibitor (ITI) in human plasma [Yamada, S., Oyama, M., Kinugasa, H., Nakagawa, T., Kawasaki, T., Nagasawa, S., Khoo, K.-H., Morris, H.R., Dell, A. & Sugahara, K. (1995) Glycobiology 5, 335-341]. The structural uniformity in the linkage hexasaccharide structure of ITI and UTI is in marked contrast to the heterogeneity demonstrated in the linkage hexasaccharides isolated from cartilaginous chondroitin sulfate whose linkage regions are sometimes but not always phosphorylated on the Xyl residue or sulfated on the Gal residue(s). The uniform structure containing the novel 4-sulfated Gal residue in the linkage region of UTI and ITI may imply its significance in the biosynthetic mechanism of chondroitin sulfate.

New Technetium (V) and Rhenium (V)-N-Acetyl Anthranilic Acid (NAA) Complexes

Abstract New N-acetyl anthranilic acid (NAA) -Tc(V) and -Re(V) complexes were prepared by the direct reduction of TcO4 − and ReO4 − with alkaline and acidic NaBH4 respectively and in the presence of an excess of ligand. The complexes were characterized by spectroscopy and elemental analysis. Reversed phase HPLC on Lichrosorb-Rp-18 was used to isolate Tc(V)-NAA complex. Electrophoresis measurements showed them having negative charges. The complexes were H2O soluble.

Characterisation of chondroitin/dermatan sulphate proteoglycans synthesised by rat mammary myoepithelial and fibroblastic cell lines

Chondroitin sulphate proteoglycans were isolated from the culture medium of rat mammary gland fibroblast (Ram 27) and myoepithelial (Rama 401) cell lines which had been labelled with [ 35S]sulphate. Chromatography on Sepharose CL-4B indicated that the Rama 401 proteoglycan was larger than the Rama 27 proteoglycan ( Kav values 0.47 and 0.56, respectively). Treatment of the proteoglycans with alkaline NaBH 4 yielded chondroitin sulphate chains with average M rvalues of 37 000 (Rama 401) and 21 000 (Rama 27). Structural analysis of the glycosaminoglycan chains indicated that both were co-polymers of chondroitin and dermatan sulphate although there were differences in the amounts and distribution of the disaccharide repeating units. The M rvalues of the core proteins, determined by immunoblotting, were about 43 000 and 46 000 (Rama 27) and 44 500 (Rama 401). Using an antibody to chondroitin sulphate proteoglycan in immunofluorescence experiments, the proteoglycan was demonstrated on the surface of both cell lines. Rama 27 cells additionally possessed an extensive fibrous extracellular matrix which also stained with the antibody. Staining of sections of lactating mammary gland suggested that the proteoglycan was present in the basement membrane as well as the stromal connective tissue. The presence of chondroitin sulphate proteoglycan in the basement membrane was confirmed by ultrastructural immunolocalisation.

Heparan sulfate proteoglycan from human tubular basement membrane. Comparison with this component from the glomerular basement membrane

Heparan sulfate proteoglycan (HSPG) was extracted from human tubular basement membrane (TBM) with guanidine and purified by ion-exchange chromatography and gel filtration. The glycoconjugate was sensitive to heparitinase and resistant to chondroitinase ABC, had an apparent molecular mass of 200–400 kDa and consisted of 70% protein and 30% glycosaminoglycan. The amino acid composition was characterized by its high content of glycine, proline, alanine and glutamic acid. Hydrolysis with trifluoromethanesulfonic acid yielded core proteins of 160 and 110 kDa. The heparan sulfate (HS) chains obtained after alkaline NaBH 4 treatment had a molecular mass of about 18 kDa. Results of heparitinase digestion and HNO 2 treatment suggest a clustering of sulfate groups in the distal portion of the HS side chains. These chemical data are comparable to those obtained previously on glomerular basement membrane (GBM) HSPG (Van den Heuvel et al. (1989) Biochem. J. 264, 457–465). Peptide patterns obtained after trypsin, clostripain or V8 protease digestion of TBM and GBM HSPG preparations showed a large similarity. Polyclonal antisera and a panel of monoclonal antibodies raised against both HSPG preparations and directed against the core protein showed complete cross-reactivity in ELISA and on Western blots. They stained all basement membranes in an intense linear fashion in indirect immunofluorescence studies on human kidneys. Based on these biochemical and immunological data we conclude that HSPGs from human GBM and TBM are identical, or at least very closely related, proteins.

Isolation and partial characterization of heparan sulphate proteoglycan from the human glomerular basement membrane

Heparan sulphate proteoglycan was solubilized from human glomerular basement membranes by guanidine extraction and purified by ion-exchange chromatography and gel filtration. The yield of proteoglycan was approx. 2 mg/g of basement membrane. The glycoconjugate had an apparent molecular mass of 200-400 kDa and consisted of about 75% protein and 25% heparan sulphate. The amino acid composition was characterized by a high content of glycine, proline, alanine and glutamic acid. Hydrolysis with trifluoromethanesulphonic acid yielded core proteins of 160 and 110 kDa (and minor bands of 90 and 60 kDa). Alkaline NaBH4 treatment of the proteoglycan released heparan sulphate chains with an average molecular mass of 18 kDa. HNO2 oxidation of these chains yielded oligosaccharides of about 5 kDa, whereas heparitinase digestion resulted in a more complete degradation. The data suggest a clustering of N-sulphate groups in the peripheral regions of the glycosaminoglycan chains. A polyclonal antiserum raised against the intact proteoglycan showed reactivity against the core protein. It stained all basement membranes in an intense linear fashion in immunohistochemical studies on frozen kidney sections from man and various mammalian species.

Carbohydrate moieties of peanut agglutinin receptors isolated from human gastric cancer cells.

Receptors for peanut agglutinin (PNA) were isolated from Kato III human gastric cancer cells by affinity chromatography on PNA agarose, and were labeled by the galactose oxidase-NaB3H4 method. Alkaline NaBH4 treatment of the labeled receptors released two small oligosaccharide alcohols, which were identified as Gal beta 1----3GalNAc-ol and Gal beta 1----4GlcNAc beta 1----6(Gal beta 1----3)GalNAc-ol. Higher oligosaccharides and glycopeptides of both N- and O-linked type were also detected, but they did not appear to bear PNA binding sites. The presence of oligo-N-acetyllactosamine units in the N-linked type sugars was indicated by endo-beta-galactosidase digestion.

Mechanisms in hydride generation AAS

Results of recent studies on the mechanisms playing a role in hydride generation AAS are discussed and compared with results obtained elsewhere. Within 10 ms after mixing the alkaline NaBH4 solution with the acid sample solution, the NaBH4, is decomposed, so hydride formation proceeds even faster. The separation of the hydride from the liquid takes much more time, however. The interference by heavy metal ions is caused by their catalytic action on the NaBH4 decomposition: the reagent is decomposed before it has reacted with the analyte. In the determination of selenium the presence of iodide has a beneficial effect on the interference of heavy metals. This is attributed to a catalytic effect of iodide on the reaction between NaBH4 and Se(IV). The presence of iodide in the NaBH4 solution also has the effect that the concentration of NaBH4 required for complete conversion of Se(IV) to SeH2 is reduced from 0.16 to 0.001%. A discussion is given on some mechanisms that have been proposed for the atom formation in the cuvette. The mechanism may depend on the analyte considered, the temperature and other parameters, and radicals are probably involved. At high analyte concentrations or long residence times of the gas mixture in the cuvette analyte losses may occur by dimerization (As, Se) or condensation (possibly after oxidation). Such effects are promoted by the tube walls. In developing procedures and apparatus, results mentioned should be considered. Several suggestions are discussed.

Distinct properties of receptors for Dolichos biflorus agglutinin (DBA) isolated from small intestine of adult mice and endoderm cells of early embryos and teratocarcinomas

Receptors for Dolichos biflorus agglutinin are only expressed in severely restricted cell populations of the mouse. The receptors were isolated from mouse embryos, teratocarcinoma cells, and the small intestine of adult mice. Upon SDS-polyacrylamide gel electrophoresis, all of the receptor preparations migrated as distinct glycoprotein bands; the apparent molecular weights were more than 150 kilodaltons in all cases. The sizes of the carbohydrate moieties determined by gel filtration after alkaline NaBH 4 treatment appeared to correlate with the status of cell differentiation. Thus, as has previously been reported, the receptors from teratocarcinoma OTT6050 and embryonal carcinoma cells (F9 and N4-1) contained large amounts of high-molecular-weight carbohydrates eluted near the excluded volume of a Sephadex-G-50 column. The receptors from 6.5-day embryos also contained high-molecular-weight carbohydrates, whose average molecular weight was lower than those obtained from OTT6050, F9, or N4-1. The receptors from PYS-2 parietal endoderm cells, END-C-2 visceral endoderm cells, and the small intestine did not contain significant amounts of the large carbohydrates. These results illustrate the complex nature of the cell-surface changes accompanying cell differentiation.

Simple and condensed β-lactams-I : The application of diketene in β-lactam synthesis. The synthesis and functional group manipulations of diethyl 3-acetyl-4-oxoazetidine-2,2-dicarboxylates

Acylation of the N-substituted diethyl aminomalonates 3a– 3d with diketene furnished the ring tautomers 6a– 6d of the expected acetoacetyl derivatives 5. By treatment with iodine and sodium ethoxide compounds 6a– 6d are smoothly converted into the β-lactam derivatives 2a– 2d. Deethoxycarbonylation of the ethylene ketals 7a– 7d of the latter furnishes mixtures of the corresponding diastereomeric monoesters 8 and 10. The ethoxycarbonyl groups of the trans esters 8 are more reactive than those of the cis isomers 10. This permits, under appropriate conditions, selective alkaline hydrolysis and NaBH 4 reduction of the trans esters 8 in the presence of the cis esters 10. Reduction of the cis ester 10c under more forceful conditions furnishes the trans hydroxymethyl derivative 11c.

Isolation of mannan-protein complexes from viable cells of Saccharomyces cerevisiae X2180-1A wild type and Saccharomyces cerevisiae X2180-1 A-5 mutant strains by the action of Zymolyase-60,000

The viable whole cells of Saccharomyces cerevisiae X2180-1A wild type and its mannan mutant strain S. cerevisiae X2180-1A-5, were treated with an Arthrobacter sp. beta-1,3-glucanase in the presence of a serine protease inhibitor, phenyl-methylsulfonyl fluoride. Fractionation of the solubilized materials of each strain with Cetavlon (cetyltrimethylammonium bromide) yielded one mannan-protein complex. Molecular weights of these complexes were almost the same as that of the mannoprotein of the mutant strain prepared by Nakajima and Ballou, which had a molecular weight of 133,000 and were approximately three times larger than those of the mannans isolated from the same cells by hot-water extraction. Each mannan-protein complex contained up to 2% glucose residue, which was not removed by specific precipitation with anti-mannan sera or by affinity chromatography on a column of concanavalin A-Sepharose. Treatment of these complexes with alkaline NaBH4 produced peptide-free mannan containing small amounts of glucose nearly identical to those of the parent complexes. The above findings provide evidence that the glucose residues exist in a covalently linked form to the mannan moiety. Fractionation of the mannan-protein complex of the S. cerevisiae wild-type strain by DEAE-Sephadex chromatography yielded five subfractions of different phosphate content, indicating that these highly intact mannan-protein complexes were of heterogeneous material consisting of many molecular species of different phosphate content.

Populations of herpes simplex virus glycoprotein gC with and without affinity for the N-acetyl-galactosamine specific lectin of Helix pomatia.

SummaryTwo fractions of herpes simplex virus glycoprotein gC were isolated and characterized by means of immunosorbent-purification with monoclonal antibodies against gC and Helix pomatia lectin (HPA) affinity chromatography. About 25 per cent of the glycoprotein gC population demonstrated affinity for the lectin, compatible with presence of N-acetylgalactosamine as terminal sugar of the oligosaccharide. The HPA-binding populations of gC appeared as two electrophoretic bands with lower molecular weights than the non-binding gC.The gC subfraction without affinity for the HPA was subjected to treatments aiming to desialylize the carbohydrate moiety. Only 5 per cent of the initially non-reactive fraction of gC became reactive to HPA after the treatments, suggesting that masking of penultimate N-acetylgalactosamine by sialic acid was not a main reason for lack of HPA affinity. Results of treatment with alkaline Na BH4 demonstrated presence of oligosaccharide-peptide linkages sensitive to β-elimination suggesting O-glycosidic type of linkage.The subfraction of gC demonstrating affinity for HPA as well as gC devoid of HPA binding capacity both revealed affinity for Con A. Therefore N-glycosidically as well as O-glycosidically linked oligosaccharides seemed to be present on the one and same glycoprotein.On the basis of the results presented we assume that the glycosylation of HSV glycoprotein gC may lead to, at least, two populations of the glycoprotein gC, one with terminal N-acetylgalactosamine residues of oligosaccharides 0-glycosidically linked to the polypeptide and the other without affinity for HPA. However, both populations of gC contain similar proportions of oligosaccharides of the high mannose or complex types with N-glycosidic carbohydrate-peptide linkages as indicated by their affinity for Con A.