Selective catalytic reduction of NOx with propene over CeO2-ferrierite.

CeO2-HFerrierite catalysts, prepared by physically mixing the components, showed very high conversions of NO under dry and wet conditions and excellent regeneration properties of the coked catalyst in the presence of water.

Relaxivity and water exchange studies of a cationic macrocyclic gadolinium(III) complex.

We conducted relaxometric and water exchange studies of the cationic [Gd((S,S,S,S)-THP)(H2O)]3+ complex (THP 1,4,7,10-tetrakis(2-hydroxy-propyl)-1,4,7,10-tetraazacyclododecane). While the NMRD profiles obtained are typical for DOTA-like complexes (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), variable-temperature 7O NMR investigations revealed a relatively high water exchange rate (k(298)(ex) = 1.89 x 10(7) s(-1)). These results differ from those reported for other cationic tetraamide macrocyclic Gd(III) complexes, which exhibit characteristically low exchange rates. Since the low exchange rates are attributed partially to the geometry of the M isomer (square antiprismatic) in the tetraamide derivatives, the atypical water exchange rate observed in [Gd((S,S,S,S)-THP-(H2O)]3+ may result from a twisted square antiprismatic structure in this complex and from the relatively high steric strain at the water coordination site as a result of the presence of methyl groups at the alpha-position with respect to the Gd(III)-bound O atoms of THP.

The combined hydrolysis and hydrogenation of inulin catalyzed by bifunctional Ru/C.

A one-pot process for hydrolysis and hydrogenation of inulin to D-mannitol and D-glucitol over a bifunctional Ru/C catalyst was developed. The hydrolysis is catalyzed by the carbon support, onto which acidity was introduced by pre-oxidation. The effect of different carbon treatments on the hydrolysis of inulin was studied. Oxidation with ammonium peroxydisulfate resulted in a carbon with the highest hydrolysis activity. On this carbon, long chain inulin is hydrolyzed faster than inulin rich in short chains. The application of high pressure (up to 100 bar) increased the hydrolysis rate substantially. The combined process was successfully conducted with a Ru-catalyst supported on this oxidized carbon.

Inulin as a carrier for contrast agents in magnetic resonance imaging.

Magnetic resonance angiography (MRA) has put forth an impetus for the development of macromolecular GdIII complexes that have a prolonged lifetime in the vascular system. Herein, we report the synthesis and GdIII complexation of a new sugar conjugate based on inulin and the DO3A ligand (DO3A = 1,4,7,10-tetraazacyclododecan-1,4,7-triacetic acid). Two API-DO3ASQ conjugates (API = O-(aminopropyl)inulin, SQ = squaric acid = 3,4-dihydroxy-3-cyclobutene-1,2-dione) with different degrees of substitution (ds = 0.7 and ds = 1.5) were prepared from API by using the diethyl ester of squaric acid as a linking agent for the DO3A chelate. The efficacies of the resulting GdIII compounds were evaluated by investigation of their water 1H longitudinal-relaxation-rate enhancements at variable field (NMRD). A dramatic increase in relaxivity was observed in the more highly substituted conjugate (ds = 1.5); this prompted us to do a variable-temperature (17)O study in order to further characterize the relaxation parameters involved in this system. [Gd(API-DO3ASQ)] shows promising properties for application as a contrast agent for MRI.

Bromide-free TEMPO-mediated oxidation of primary alcohol groups in starch and methyl alpha-D-glucopyranoside.

TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-mediated oxidation of potato starch and methyl alpha-D-glucopyranoside (MGP) was performed in the absence of sodium bromide (NaBr) as co-catalyst, solely using sodium hypochlorite (NaOCl) as the primary oxidant. The low reaction rate associated with a bromide-free process was increased by performing the oxidation at increased temperatures. The reaction proceeded stoichiometrically and with high selectivity and with only minor depolymerisation, provided that temperature and pH were kept < or = 20 degrees C and < 9.0, respectively. At 20 degrees C and pH 8.5, the reaction rate was comparable to that of a corresponding oxidation catalysed by NaBr at 2 degrees C. Consequently, this is a simple approach to raise the TEMPO/NaOCl reaction rate under bromide-free conditions while still maintaining good product properties. At higher oxidation temperatures (> or = 25 degrees C) and under more alkaline conditions (pH > or = 9.0) degradation of the starch skeleton occurred. Simultaneously, side-reactions of the nitrosonium ion lowered the yield of the oxidation. Despite the absence of the NaBr catalyst, the reaction rate-controlling step was found to be the oxidation of the primary hydroxyl groups with the nitrosonium ion. The reaction was first-order in MGP and in TEMPO.

Hydrogenation of fructose on Ru/C catalysts.

The hydrogenation of D-fructose on Ru/C catalysts was studied. Under the conditions applied (1 bar H2, 72 degrees C), the furanose forms of D-fructose react, while the pyranose forms do not. However, all anomers adsorb with comparable strength on the surface. The reaction rate is controlled by product inhibition. The selectivity to D-mannitol can be increased from 47 to 63% by promotion of Pd/C and Pt/C catalysts with Sn.

Ion-pair interactions of lanthanide(III) complexes in aqueous solutions.

The formation of ion-pair adducts between the cationic complex La(THP)3+ (THP = 1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane) and the anionic complexes Tm(DOTA)- (DOTA = 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetate), Tm(DTPA)2- (DTPA = diethylenetriamine-N,N,N',N",N"-pentaacetate), Tm(TTHA)3- (TTHA = triethylenetetraamine-N,N,N',N",N"',N"'-hexaacetate), and Tm(DOTP)5- (DOTP = 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetrakis(methylenephosphonate)) is examined by 13C NMR spectroscopy. The induced 13C shifts of the La(THP)3+ complex are followed by titration of the Tm(III) complexes of DOTA, DTPA, and TTHA at pH 7. From these data, the stability constants are calculated to be beta 1 = 64 M-1 (1:1), beta 1 = 296 M-1 (1:1), and beta 2 = 26,000 M-2 (2:1) for the ion pairs of La(THP)3+, with Tm(DOTA)-, Tm(DTPA)2-, and Tm(TTHA)3-, respectively. The La(THP)3+,Tm(DOTP)5- system elicits chiral resolution of the rapidly interconverting Tm(DOTP)5- isomers.

Preparation of O-(Aminopropyl)inulin.

Inulin ethers carrying primary amino groups have many potential applications. O-(Aminopropyl)inulin is obtained from O-(cyanoethyl)inulin by reduction of the nitrile groups. Heterogeneously catalyzed hydrogenation using Raney-cobalt as the catalyst resulted in only partial conversion of the O-cyanoethyl into O-aminopropyl groups. Complete conversion of the nitriles to primary amines was achieved by a homogeneous reduction with an excess of sodium borohydride and cobaltous chloride or with metals in liquid ammonia-methanol. Optimal results were obtained with the latter method; 83% of the substituents were converted into primary amines and 17% were lost by dealkylation.

The platinum-catalyzed oxidation of inulin.

The oxidation of inulin with Pt/C as catalyst was studied. Methyl alpha-D-fructofuranoside was used as a model compound for the monomeric unit of inulin. Oxidation occurred selectively at the C-6 position in a high yield (79%). The rate of oxidation and the degree of oxidation obtained for inulin oligosaccharides decreased upon increase of the chain length of the substrate. Inulin could only be oxidized partially: the oxidation degree obtained was 20% of the primary hydroxy groups for inulin with an average dp 30. Possible explanations for these relatively low conversions are discussed. Adsorption and desorption phenomena appear to play and important role during the oxidation process.

The role of deoxyhexonic acids in the hydrothermal decarboxylation of carbohydrates.

Hydrothermolysis of D-glucose, cellobiose, and beta-cyclodextrin leads to the formation of small amounts of 3-deoxyhexonic acids. These acids are known to be produced by the alkaline degradation of carbohydrates. The formation under neutral hydrothermal conditions of the 3-deoxyhexonic acids provides evidence for the formation of 3-deoxy-D-erythro-hex-2-ulose, a compound that has been reported to play a role in both alkaline and acidic conversion of carbohydrates. Hydrothermolysis of 2- and 3-deoxy-D-arabino-hexonic acid does not lead to significant decarboxylation, and therefore these compounds cannot be considered to play a major role in the initial hydrothermal decarboxylation of biomass.

Carboxymethylation of inulin.

Inulin was carboxymethylated in aqueous alkaline medium with monochloroacetic acid as the reagent. The degree of substitution of the reaction product was determined by titration, LC analysis and 13C NMR spectroscopy. Carboxymethylinulin with a degree of substitution between 0.2 and 1 was obtained depending on the molar ratio of inulin-monochloroacetic acid. Increasing the concentration of the reaction mixture and lowering the reaction temperature resulted in higher selectivities towards carboxymethylinulin. Determination of the molecular weight distribution was performed by GPC and by multi-angle laser light scattering. Carboxymethylation caused little or no degradation of the chain length of the starting material.

Selective alkaline oxidative degradation of mono- and di-saccharides by hydrogen peroxide using borate as catalyst and protecting group.

Lactose, maltose, cellobiose, and galactose can be degraded selectively in one step and in high yield into the corresponding next lower aldose and formic acid by H2O2 in the presence of borate. The selectivity further improves when a small amount of EDTA is added, in order to suppress the influence of transition metal ions which catalyze the decomposition of H2O2 via radical pathways, leading to non-selective oxidative degradation of aldoses. The function of borate in the selective oxidative degradation of aldoses is two-fold: catalysis of the degradation of the starting aldose and protection of the next lower aldose against oxidation.

The structure and (local) stability constants of borate esters of mono- and di-saccharides as studied by 11B and 13C NMR spectroscopy.

The formation of borate esters of various mono- and di-saccharides in aqueous solution was studied by 11B and 13C NMR spectroscopy. Association constants K(B-L) at a carbohydrate-borate molar ratio of 1:1, pH 7, and 25 degrees C were determined and compared with literature values obtained from potentiometry. The association constants K(B-L) were converted into local association constants Kloc(B-L) by using the distribution of the various anomeric forms in D2O. In this way, values of Kloc(B-L) were obtained, which appear to be characteristic of the configuration concerned. They explain the favourable effect of borate in the alkaline isomerisation of lactose into lactulose. At a low molar ratio (1:3) of carbohydrate-borate, predominantly diborate esters (B-)2L were formed.