Amphiphilic conetworks as activating carriers for the enhancement of enzymatic activity in supercritical CO2

Enzymatic reactions in supercritical carbon dioxide (scCO2) represent a way of combining the advantages of biocatalysis with the environmental benign nature of scCO2 as a solvent. Here we demonstrate that activities of enzymes in scCO2 can be greatly enhanced by incorporating them into amphiphilic conetworks (APCNs), a novel type of enzyme support. Two sets of hydrophilic/scCO2-philic APCNs, poly(2-hydroxyethyl acrylate)-linked by-poly(dimethylsiloxane) (PHEA-l-PDMS) and poly(2-hydroxyethyl acrylate)-linked by-perfluoropolyether (PHEA-l-PFPE), were prepared and loaded with the synthetically relevant lipase from Rhizomucor miehei. The effect of the APCNs' composition on the amount of the absorbed lipase was studied. It is observed that both sets of lipase-loaded APCNs enhance the catalytic activity of the enzyme in scCO2. The chemical nature of the scCO2-philic phase as well as the conetworkscomposition greatly influences the activity of the lipase in the conetworks. Activities obtained with PFPE-basedAPCNS were up to 10-fold higher than those obtained with PDMS-based conetworks. The highest specific activity measured corresponds to a 2,000-fold activation compared to the lyophilized enzyme powder. This activity is 10 times higher than the specific activity of the lipase immobilized on an optimized commercial carrier.     

Stoichiometric and catalytic hydrogenation of the [Co2(CO)6(μ2-η2-alkyne)] complexes

The [Co₂(CO)₆(RC₂R′)] complexes (R, R′ = H, Me, Et, Prⁿ) react with molecular hydrogen under mild conditions of temperature and pressure, at low but appreciable rates. The effect of the steric hindrance of the substituents and the strength of the metalcarbon bonds are discussed. The kinetic data measured for [Co₂(CO)₆(HC₂H)], suggest that both H₂-coordination and CO-dissociation are involved in the rate-determining step of the overall hydrogenation process.The catalytic activity of [Co₂(CO)₆(HC₂H)] in the homogeneous hydrogenation of acetylene is described. At low substrate/catalyst ratio the initial hydrogenation rate is equal, within experimental error, to that found for the stoichiometric reaction; on increasing the acetylene concentration, cyclotrimerization to benzene becomes the dominant process. Interestingly C₄ hydrocarbons (mainly butadiene and 1-butene) are produced in measurable yield (?8%). The formation of these products is interpreted as the result of the hydrogenation of the elusive [Co₂(CO)₅(HC₂H)₂] complex, an unstable intermediate in the cyclotrimerization chain.     

Supercritical carbon dioxide generated vascular endothelial growth factor encapsulated poly(DL-lactic acid) scaffolds induce angiogenesis in vitro

The ability to deliver, over time, biologically active vascular endothelial growth factor-165 (VEGF) through tailored designed scaffolds offers tremendous therapeutic opportunities to tissue-engineered therapies. Porous biodegradable poly(DL-lactic) acid (PLA) scaffolds encapsulating VEGF have been generated using supercritical CO2 (scCO2) and the kinetic release and angiogenic activity of these scaffolds examined in vitro and in an ex vivo chick chorioallantoic membrane (CAM) angiogenesis model. After processing through scCO2, VEGF maintained its angiogenic activity as assessed by increased tubule formation of human umbilical vein endothelial cells (HUVEC) cultured on Matrigel (VEGF = 1937 +/- 205 microm; scCO2-VEGF = 2085 +/- 234 microm; control = 1237 +/- 179 microm). VEGF release kinetics from scCO2-VEGF incorporated PLA monolith scaffolds showed a cumulative release of VEGF (2837 +/- 761 rhog/ml) over a 21 day period in culture. In addition, VEGF encapsulated PLA scaffolds increased the blood vessel network in the CAM compared to controls; control, 24.8 +/- 9.6; VEGF/PLA, 44.1 +/- 12.1 (vessels/field). These studies demonstrate that the controlled release of growth factors encapsulated into three-dimensional PLA scaffolds can actively stimulate the rapid development of therapeutic neovascularisation to regenerate or engineer tissues.     

Tuning of Catalytic Activity by Thermoelectric Materials for Carbon Dioxide Hydrogenation

An innovative use of a thermoelectric material (BiCuSeO) as a support and promoter of catalysis for CO₂ hydrogenation is reported here. It is proposed that the capability of thermoelectric materials to shift the Fermi level and work function of a catalyst lead to an exponential increase of catalytic activity for catalyst particles deposited on its surface. Experimental results show that the CO₂ conversion and CO selectivity are increased significantly by a thermoelectric Seebeck voltage. This suggests that the thermoelectric effect can not only increase the reaction rate but also change chemical equilibrium, which leads to the change of thermodynamic equilibrium for the conversion of CO₂ in its hydrogenation reactions. It is also shown that this thermoelectric promotion of catalysis enables BiCuSeO oxide itself to have a high catalytic activity for CO₂ hydrogenation. The generic nature of the mechanism suggests the possibility that many catalytic chemical reactions can be tuned in situ to achieve much higher reaction rates, or at lower temperatures, or have better desired selectivity through changing the backside temperature of the thermoelectric support.     

Terminal sterilization of BisGMA-TEGDMA thermoset materials and their bioactive surfaces by supercritical CO2

The development of biomaterials endowed with bioactive features relies on a simultaneous insight into a proper terminal sterilization process. FDA recommendations on sterility of biomaterials are very strict: a sterility assurance level (SAL) of 10(-6) must be guaranteed for biomaterials to be used in human implants. In the present work, we have explored the potential of supercritical CO(2) (scCO(2)) in the presence of H(2)O(2) as a low-temperature sterilization process for thermoset materials and their bioactive surfaces. Different conditions allowing for terminal sterilization have been screened and a treatment time-amount of H(2)O(2) relationship proposed. The selected terminal sterilization conditions did not notably modify the mechanical properties of the thermoset nor of their fiber-reinforced composites. This was confirmed by μCT analyses performed prior to and after the treatment. On the contrary, terminal sterilization in the presence of H(2)O(2) induced a slight decrease in the surface hardness. The treatment of the thermoset material with scCO(2) led to a reduction in the residual unreacted monomers content, as determined by means of high performance liquid chromatography (HPLC) analyses. Finally, it was found that a thermoset coated with a polysaccharide layer containing silver nanoparticles maintained a very high antimicrobial efficacy even after the scCO(2)-based terminal sterilization.     

Probing the nature of H2 activation in catalytic asymmetric hydrogenation

Despite many years of intensive study, the natures of turnover-limiting and enantio-determining steps in catalytic asymmetric hydrogenation of prochiral enamides are poorly understood. An intriguing set of studies involving isotopic labeling distributions in catalytic enamide hydrogenation reactions were reported by Brown and Parker (Organometallics, 1 (1982) 950–956) more than a decade ago. In this paper we report the results of studies re-examining the application of isotopic probes to the catalytic hydrogenation enamides. These results provide some insights into the nature of the H₂ activation step in enamide hydrogenation.     

Catalytic activity of dihydride ruthenium complexes in the hydrogenation of nitrogen containing heterocycles

The catalytic activity of the dihydride ruthenium complexes, RuH₂(CO)₂(PⁿBu₃)₂, RuH₂(CO)₂(PPh₃)₂ and RuH₂(PPh₃)₄, in the hydrogenation of nitrogen containing heterocycles has been tested by analyzing the influence of reaction parameters such as temperature, hydrogen pressure, catalyst concentration, on the rate and regioselectivity of the reaction.RuH₂(PPh₃)₄ shows a better catalytic activity with an 86.7% conversion of quinoline after 24 h at 100 °C under a hydrogen pressure of 25 bar, while RuH₂(CO)₂(PPh₃)₂ and RuH₂(CO)₂(PⁿBu₃)₂ in the same conditions give a conversion of 37.1% and 35.6%, respectively. These results are confirmed by the reaction rate of the hydrogenation of quinoline, since the K_c in the presence of RuH₂(PPh₃)₄ (1.46 × 10⁻⁵ s⁻¹) is higher than others (6.37 × 10⁻⁶ s⁻¹ for RuH₂(CO)₂(PPh₃)₂ and 6.36 × 10⁻⁶ s⁻¹ for RuH₂(CO)₂(PⁿBu₃)₂).Noteworthy is the selectivity of these catalytic systems in the hydrogenation of quinoline: in all tests the three catalysts lead to 1,2,3,4-tetrahydroquinoline as the major product, furthermore this compound is the only formed in the presence of RuH₂(CO)₂(PPh₃)₂. The selectivity is affected by the presence of an acid (CH₃COOH) or a base (NⁿBu₃) in the reaction media.The complex RuH₂(PPh₃)₄ is catalytically active, even if in a minor extent, in the hydrogenation of isoquinoline, pyridine and 2-methylpyridine.The basicity of the substrate and steric hindrance around the nitrogen atom show a great influence on the conversion.The results obtained suggest that the catalytic system activates a heterocyclic ring through the coordination of the heteroatom to the metal centre of the complexes.     

Criteria to design green enzymatic processes in ionic liquid/supercritical carbon dioxide systems

Five different ionic liquids (ILs) based on quaternary ammonium cations, with functional side chains ((3-hydroxypropyl)-trimethyl-, (3-cyanopropyl)-trimethyl-, butyl-trimethyl-, (5-cyanopentyl)-trimethyl- and hexyl-trimethyl-) associated with the same anion (bis(trifluoromethane)sulfonyl amide)), were synthesized, and their suitability for Candida antarctica lipase B (CALB)-catalyzed ester synthesis in IL/supercritical carbon dioxide (scCO(2)) biphasic systems was assayed. Catalytic efficiency of the system has been analyzed as a function of both enzyme properties and mass-transfer phenomena criteria. First, the suitability of these ILs as enzymic reaction media was tested for the kinetic resolution of rac-phenylethanol. All ILs were found to be suitable media for enzyme catalysis, the best catalytic parameter (5.3 U/mg specific activity, 94.9% selectivity) being obtained for the (5-cyanopentyl)-trimethylammonium. Second, enzyme stability in all of the ILs was studied at 50 degrees C over a period of 50 days, and data were analyzed by a two-step kinetic deactivation model. All of the ILs were shown to act as stabilizing agents with respect to hexane, producing an increase in the free energy of deactivation (to 25 kJ/mol protein) and an improvement in the half-life time of the enzyme (2000-fold), which agrees with the observed increased hydrophobicity of the cation alkyl side chain (measured by Hansen's solubility parameter, delta). By using two different CALB-IL systems with different hydrophobicity in the cation, continuous processes to synthesize six different short chain alkyl esters (butyl acetate, butyl propionate, butyl butyrate, hexyl propionate, hexyl butyrate, and octyl propionate) in scCO(2) at 10 MPa and 50 degrees C were carried out. Both rate-limiting parameters (synthetic activity and scCO(2)-ILs mass-transfer phenomena) were related with the delta-parameter of the ILs-alkyl chain and reagents.     

Quinoline transfer hydrogenation by a rhodium bipyridine catalyst

The catalytic activity of the rhodium complex cis-[Rh(bipy)₂Cl₂]Cl · 2H₂O in the transfer hydrogenation of different unsaturated substrates is reported. This complex, if pre-activated, is very active in the transfer hydrogenation of ketones (i.e., cyclohexanone is reduced with a 38.1% conversion at 283 K and 100% at 313 K) while in the case of hex-1-ene, a 36.8% conversion was reached at 293 K. A cyclic olefin (cyclohexene) was also reduced with a lower, but still significant, conversion.It is interesting to note the catalytic activity of this complex in the transfer hydrogenation of a CN double bond belonging to imides or nitrogen-containing heterocycles. For instance, N-benzylidenaniline was hydrogenated to N-benzylaniline at 303 K with a conversion of 27.3%. Increasing the temperature to 353 K, the conversion rised to 91.8%. A nitrogen containing heterocycle, quinoline, was also reduced by transfer hydrogenation at 353 K with a 11.7% conversion giving 1,2,3,4-tetrahydroquinoline (selectivity of 96.6%). The conversion rised up to 54.2% with a still high selectivity (84.5%) when the temperature was 383 K. Almost the same activity was shown in the reduction of pyridine to pyperidine (conversion, 51.1% at 383 K), while 2-methylpyridine was hydrogenated with a 24.7% conversion.     

Regulation of CO production in cerebral microvessels of newborn pigs

Carbon monoxide (CO) is produced from heme by heme oxygenase-2 (HO-2) in cerebral blood vessels. Gas chromatography-mass spectrometry was used on piglet cerebral microvessels to address the hypothesis that CO production is regulated by heme delivery and HO-2 catalytic activity. CO production appears to be substrate limited because heme and its precursor aminolevulinate increase CO production. Ionomycin also increases CO production. However, CO production from exogenous heme was the same in Ca-replete medium, Ca-free medium with ionomycin, and Ca-replete medium with ionomycin. Phorbol myristate acetate increases CO production but does not change the catalytic activity of HO-2. Also, the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine has no effect on the HO-2 catalytic activity. Protein tyrosine kinase inhibition reduces HO-2 catalytic activity. Inhibition of protein tyrosine phosphatases increased HO-2 catalytic activity. Therefore, regulation of CO production by cerebral microvessels can include changing heme availability and HO-2 catalytic activity. HO-2 catalytic activity is stimulated by tyrosine phosphorylation.     

Development of a slow non-viral DNA release system from PDLLA scaffolds fabricated using a supercritical CO2 technique

Polyamidoamine polymers (PAA) comprising methylene-bisacrylamide/dimethylethylene-diamine monomers were synthesized, complexed with DNA and incorporated into porous P(DL)LA scaffolds by using a supercritical CO(2) (scCO(2)) technique. Scaffolds were made in a dry state consequently there was a need to lyophilize the complexes. A statistically significant reduction of the transfection efficiency was observed in the absence of trehalose when compared to the original complex after freeze-drying. Increasing concentrations (0-10% w/v) of trehalose were added to the complex prior to freeze-drying. Structure dependent differences in DNA binding were evaluated by gel electrophoresis and thermal transition analysis. TEM and PCS showed aggregate formation after freeze-drying without trehalose. Scaffolds were characterized by pore sizes of 173 +/- 73 microm and a porosity of 71%. The transfection potential of the released DNA was investigated by seeding scaffolds with A549 cells and following firefly luciferase as a marker gene after 48 h exposure. Low but continuous levels of transfection were observed for PAA complexes during a 60-day study. Complexes made with Lipofectaminetrade mark gave initially higher levels of DNA release but no further expression was seen after 40 days. Uncomplexed DNA showed background levels of transfection. Culturing cells on 3D scaffolds showed a benefit in retention of transfection activity with time compared to 2D controls. Transfection levels could be increased when cells were grown in OptiMEM. This study demonstrated that PAA/DNA complexes incorporated into a P(DL)LA scaffold made by using scCO(2) processing exhibited a slow release and extended gene expression profile.     

Synthesis of modified tuftsins containing monosaccharides or monosaccharide derivatives

Synthesis of some modified tuftsins is described in which a monosaccharide or a monosaccharide derivative was incorporated in the molecule. Acylation of H-Thr-Lys(Z)-Pro-Arg(NO2)-OBzl with D(+)-gluco-1,5-lactone followed by catalytic hydrogenation gave N alpha-gluconyl-tuftsin. Glycosylation of the carboxyl function of the C-terminal arginine has been achieved by reacting, through the mixed anhydride procedure, Boc-Thr-Lys(Z)-Pro-OH with 2-deoxy-2-(NG-nitroargininamido)-D-glucopyranose followed by catalytic hydrogenation and trifluoroacetic acid treatment. O-Glucosyl-tuftsin has been prepared by reacting o-nitrophenyl N-benzyloxycarbonyl-O-[(alpha + beta) 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl]-threoninate with H-Lys(Z)-Pro-Arg(NO2)-OBzl in the presence of 1-hydroxybenzotriazole. Flash chromatography on silica gel allowed a partial separation of the diastereoisomers, one of which has been isolated in a reasonable yield. The single diastereoisomer and the alpha + beta anomeric mixture were separately deblocked by catalytic hydrogenation and purified by RP-HPLC.     

A novel procedure for the isolation of glycolipids from Bifidobacterium adolescentis 94 BIM using supercritical carbon dioxide

This study describes a novel isolation procedure for major glycolipids from Bifidobacterium adolescentis 94 BIM. The procedure consists of the use of supercritical carbon dioxide (scCO(2)) with hydro-methanolic solution as co-solvent. The major glycolipids were isolated using the following operating conditions: pressure, 30 MPa, co-solvent concentration, 10% (9:1, methanol/water, v/v), CO(2) flow rate, 5 g/min, extraction time and temperature, 2h and 55 degrees C, respectively. The reference glycolipids sample was prepared by classical organic solvent extraction followed by chromatographic purification. All isolates were characterized by TLC and the major glycolipids additionally by enzyme linked immunosorbent (ELISA). Sixty milligrams of glycolipids with similar immunoreactivity as the reference glycolipids were isolated from 1g of freeze-dried biomass (6% of yield).     

Tripodal oxygen and tripodal nitrogen ligands in hydroformylation reactions: formation of novel rhodium(III) carbonyl bis(acyl) complexes

The rhodium(I) complexes TpmsRh(CO)₂ (1) and TpmsRh(cod) (2) of the tripodal nitrogen ligand tris(pyrazolyl)methanesulfonate, Tpms⁻=[(pz)₃CSO₃]⁻, catalyze the hydroformylation of 1-hexene. Addition of phosphine has a negative effect on the activity. The hydroformylation activity reaches a maximum at about 60 °C. At temperatures above 80 °C hydrogenation becomes an important secondary reaction. When the catalysis is performed at 60 °C in acetone with 1 or 2 as catalyst precursor all of the rhodium is recovered in the form of the rhodium(III) bis(acyl) complex TpmsRh(CO)(COC₆H₁₃)₂ (9). A similar behaviour is observed with rhodium(I) complexes bearing the tripodal oxygen ligand L_OMe⁻=[(cyclopentadienyl)tris(dimethylphosphito-P) cobalt O,O^′,O″]⁻. In this case all of the rhodium is transformed into L_OMeRh(CO)(COC₆H₁₃)₂ (10). These hitherto unknown bis(acyl) rhodium(III) complexes show the same catalytic activity as the rhodium(I) starting compounds.     

A hydrothermally precipitated catalytic iron sulphide membrane as a first step toward life

We propose that life emerged from growing aggregates of iron sulphide bubbles containing alkaline and highly reduced hydrothermal solution. These bubbles were inflated hydrostatically at sulphidic submarine hot springs sited some distance from oceanic spreading centers four billion years ago. The membrane enclosing the bubbles was precipitated in response to contact between the spring waters and the mildly oxidized, acidic and iron-bearing Hadean ocean water. As the gelatinous sulphide bubbles aged and were inflated beyond their strength they budded, producing contiguous daughter bubbles by the precipitation of new membrane. [Fe₂S₂]^+/0 or [Fe₄S₄]^2+/+ clusters, possibly bonded by hydrothermal thiolate ligands as proferredoxins, could have catalyzed oxidation of thiolates to disulphides, thereby modifying membrane properties.We envisage the earliest iron sulphide bubbles (pro botryoids) first growing by hydrostatic inflation with hydrothermal fluid, but evolving to grow mainly by osmosis (the protocellular stage), driven by (1) catabolism of hydrothermal abiogenic organics trapped on the inner walls of the membrane, catalyzed by the iron sulphide clusters; and (2) cleavage of hydrophobic compounds dissolved in the membrane to hydrophilic moieties which were translocated, by the proton motive force inherent in the acidic Hadean ocean, to the alkaline interior of the protocell. The organics were generated first within the hydrothermal convective system feeding the hot springs operating in the oceanic crust and later in the pyritizing mound developing on the sea floor, as a consequence of the reduction of CO, CO₂, and formaldehyde by Fe²⁺- and S^2–-bearing minerals.We imagine the physicochemical interactions in and on the membrane to have been sufficiently complex to have engendered auto- and cross-catalytic replication. The membrane may have been constructed in such a way that a successful parent could have informed the daughters of membrane characteristics functional for the then-current level of evolution.Correspondence to: M. J. RussellGlossary: Hollow pyrite botryoids: hollow hemispheres of cryptocrystalline pyrite (FeS₂) 0.1–1 mm across. Fischer-Tropsch syntheses: the highly exothermic catalytic hydrogenation of CO to hydrocarbons and aliphatic oxygenated compounds using finely divided iron. Greigite (Fe₃S₄): metastable iron sulphide precipitated from aqueous solution in a gel at 100°C and containing two-thirds of its iron as the high-spin ferric ion. Haber-Bosch process: the exothermic catalytic hydrogenation of nitrogen to yield ammonia. Probotryoid: a hydrostatically inflated colloidal iron monosulphide bubble; precursor to hollow botryoids and the progenitor to protocells. Proferredoxins: [Fe₂S₂] and [Fe₃MS₄] clusters (M = Fe, Mo, W, Ni, etc.) ligated by abiogenic thiols and thiolates. Protocell: a cell comprised mainly of abiogenic organics including thiols with subordinate iron sulphides, partly as proferredoxins; growth results from catabolism and osmotic pressure     

Bis-N-heterocyclic carbene ruthenium(II) carbonyl complexes: Synthesis, structural characterization and catalytic activities in transfer hydrogenation of ketones

In this contribution, the synthesis and characterization of eight ruthenium(II) carbonyl complexes supported by chelating alkane-bridged bis-N-heterocyclic carbene ligands are reported. The products obtained are analyzed using infrared and NMR spectroscopies. The molecular structures of four metal complexes were determined by X-ray crystallography, which exhibit the six-coordinate octahedral geometry with two carbene carbon atoms from the bidentate Bi-NHCs, two carbonyl groups and two chlorine atoms in the trans(Cl)-cis(CO) configuration. All these complexes show catalytic activities in transfer hydrogenation of ketones.     

The hydrogenation and hydroformylation of alkenes as catalyzed by polymer-anchored rhodium trichloride under water gas shift reaction conditions

The ‘heterogenized’ water gas shift catalyst Rh/P4VP, prepared from the reaction of RhCl₃ with poly(4-vinylpyridine), is also active for hydrogenation and hydroformylation of 1-hexene and cyclohexene in aqueous ethoxyethanol under mild shift reaction conditions (typically 0.9 atm. P_CO at 100°C). The catalytic activities for these systems were studied as functions of several experimental variables. Hydroformylation rates increased with the P_CO but exhibited saturation behavior in the 1.5 atm. range. Rates for cyclohexane and hexane production were inhibited by CO at higher pressures. Cyclohexene hydroformylation and hydrogenation turnover frequencies were independent of the polymer-loading (50–150 μM RhCl₃/1.0 g P4VP) indicating that the active species are of the same nuclearity as the principal species present. The temperature dependence did not follow simple Arrhenius behavior, but appeared segmented. These data are discussed in terms of possible mechanisms.     

Characterization of the carboxysomal carbonic anhydrase CsoSCA from Halothiobacillus neapolitanus

In cyanobacteria and many chemolithotrophic bacteria, the CO(2)-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) is sequestered into polyhedral protein bodies called carboxysomes. The carboxysome is believed to function as a microcompartment that enhances the catalytic efficacy of RubisCO by providing the enzyme with its substrate, CO(2), through the action of the shell protein CsoSCA, which is a novel carbonic anhydrase. In the work reported here, the biochemical properties of purified, recombinant CsoSCA were studied, and the catalytic characteristics of the carbonic anhydrase for the CO(2) hydration and bicarbonate dehydration reactions were compared with those of intact and ruptured carboxysomes. The low apparent catalytic rates measured for CsoSCA in intact carboxysomes suggest that the protein shell acts as a barrier for the CO(2) that has been produced by CsoSCA through directional dehydration of cytoplasmic bicarbonate. This CO(2) trap provides the sequestered RubisCO with ample substrate for efficient fixation and constitutes a means by which microcompartmentalization enhances the catalytic efficiency of this enzyme.     

Selective hydrogenolysis of raw glycerol to 1,2-propanediol over Cu–ZnO catalysts in fixed-bed reactor

The catalytic properties of Cu–ZnO catalysts for glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) were tested in a fixed-bed reactor at 250 °C and 2.0 MPa H₂. The relation between composition, surface properties, and catalytic performance of glycerol hydrogenation of Cu–ZnO catalysts was studied using nitrogen adsorption (BET methods), XRD, H₂ temperature-programmed reduction, and N₂O chemisorptions. It was found that there was a close link between the surface CuO amount of Cu–ZnO catalyst and the reactivity for glycerol hydrogenation. The Cu–ZnO catalyst (Cu/Zn = 1.86) which had the highest surface Cu amount showed the best catalytic activity for glycerol hydrogenolysis. Furthermore, Cu–ZnO catalyst presented good stability and remarkable catalytic activity for glycerol hydrogenolysis to 1,2-PDO using raw glycerol derived from the fat saponification as feedstock.     

Cooperative catalysis of a trinuclear ruthenium(II) complex in transfer hydrogenation of ketones by formic acid

A novel TPA derivative (TPA = tris(2-pyridylmethyl)amine) having two 1,10-phenanthroline (phen) moieties via amide linkage was synthesized and this ligand reacted with [Ru(hmb)Cl₂]₂ (hmb: hexamethylbenzene) to give a trinuclear Ru(II) complex, [RuCl(TPA-{phenRuCl(hmb)}₂-H⁺)](PF₆)₂ (1-Cl), in a moderate yield. The complex involves a deprotonated and oxygen-coordinated amide linkage, which exhibits reversible protonation-deprotonation equilibrium. The chlorido complex was converted to be an aqua complex, [Ru(H₂O)(TPA-{phenRu(H₂O)₂(hmb)}₂-H⁺)](SO₄)_5/2 (1-H₂O), by the reaction of 1-Cl with Ag₂SO₄ in H₂O. Transfer hydrogenation of ketones was examined by using 1-Cl as a catalyst and HCOONa as a hydride source in H₂O/CH₃OH (1:1 v/v) at 50 °C under Ar. The time-course of the transfer hydrogenation of cyclohexanone to give cyclohexanol revealed that 1-Cl showed a cooperative effect on the catalytic reactivity as compared with that of mononuclear [RuCl(hmb)(phen)] (3-Cl) and [RuCl((1-Naph)₂-TPA)]PF₆ in H₂O/CH₃OH (1:2 v/v) under the same conditions. The detailed kinetic study has revealed that the catalytic transfer hydrogenation proceeds via the formato complex, which interacts with a substrate rather than via the hydrido complex. The two Ru centers placed at close proximity in 1-H₂O enhanced the interaction of the formato complex with a substrate, resulting in an increase in the catalytic reactivity as compared with the mononuclear complex.