Transesterification of a Tertiary Alcohol by Engineered Candida antarctica Lipase A

Tertiary alcohols are known to be challenging substrates for applications in asymmetric synthesis due to their complexity and steric hinderance. The occurrence of tertiary alcohols and their esters in nature indicates the presence of natural biocatalytic synthetic routes for their preparation. Lipase A from Candida antarctica (CalA) is a hydrolase that has previously been shown to catalyze the transesterification of racemic 2-phenylbut-3-yn-2-ol at a low rate. In this work, the activity of that enzyme was improved by protein engineering through a semi-rational design strategy. An enzyme library was created and screened for transesterification activity towards racemic 2-phenylbut-3-yn-2-ol in an organic solvent. One successful enzyme variant (L367G) showed a tenfold increased reaction rate compared to the wild-type enzyme, while maintaining a high enantioselectivity.     

Oxidation of Aliphatic and Benzylic Alcohols by Oxone®, Catalysed by 12-Tungstocobaltate (II)

$R_1 R_2 CH_2 OH\xrightarrow[{50\% {\text{ }}Aqueous{\text{ }}acetonitrile}]{{[Co^{II} (W_{12} O_{40} )]^{6 - } /Oxone}}R_1 R_2 CHO$ A Keggin-type polyoxometalate (POM) 12-tungstocobaltate (II) ([Co^II(W₁₂O₄₀)]^6?) has been used as a catalyst for the oxidation of aliphatic and benzylic alcohols to the corresponding carbonyl compounds. The reduced (POM) formed in the oxidation of alcohols is re-oxidized by potassium peroxomonopersulphate.     

Adsorption Behavior of Azo Dye Eriochrome Black T from Aqueous Solution by β-Cyclodextrins/Polyurethane Foam Material

β-cyclodextrin/polyurethane (β-CD/PU) materials were prepared by foaming technique. The adsorption behavior of EBT on β-CD/PU material and the influences on the adsorption efficiency were investigated. Under the optimal experimental conditions, the maximum adsorption efficiency of EBT was 93.14%. The kinetics characteristic and thermodynamic parameters were analyzed. The experimental isotherms data were analyzed using Langmuir and Freundlich isotherm equations and the results indicated that the Langmuir isotherm showed a better fit for EBT adsorption. The experimental results suggest that the β-CD/PU foam materials have potential application for the wastewater treatment containing EBT dye.     

Direct Determination of MCPD Fatty Acid Esters and Glycidyl Fatty Acid Esters in Vegetable Oils by LC–TOFMS

Analysis of MCPD esters and glycidyl esters in vegetable oils using the indirect method proposed by the DGF gave inconsistent results when salting out conditions were varied. Subsequent investigation showed that the method was destroying and reforming MCPD during the analysis. An LC time of flight MS method was developed for direct analysis of both MCPD esters and glycidyl esters in vegetable oils. The results of the LC–TOFMS method were compared with the DGF method. The DGF method consistently gave results that were greater than the LC–TOFMS method. The levels of MCPD esters and glycidyl esters found in a variety of vegetable oils are reported. MCPD monoesters were not found in any oil samples. MCPD diesters were found only in samples containing palm oil, and were not present in all palm oil samples. Glycidyl esters were found in a wide variety of oils. Some processing conditions that influence the concentration of MCPD esters and glycidyl esters are discussed.     

Transesterification of β ‐keto esters catalysed by transition metal complexes in a novel heterogeneous way

β‐keto esters have been successfully transesterified with primary, secondary, tertiary, allyl and alkynic alcohols by recyclable Mn(III) salen or vanadyl(IV) acetate catalysts realised while conducting the reaction deliberately for the first time in a novel heterogeneous media to afford good to excellent yields. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct Determination of Glycidyl Esters of Fatty Acids in Vegetable Oils by LC–MS

An LC–MS method using a single quadrupole mass spectrometer was developed for direct analysis of glycidyl esters of fatty acids in vegetable oils. Without any sample clean-up, this method provided acceptable recovery of seven glycidyl esters, comparable results to a previously-published method utilizing two solid-phase extraction steps, and consistent detection parameters after greater than 200 injections without any cleaning operations performed. This method could readily be implemented as a screening assay for glycidyl esters in most oil laboratories.     

Enhancing thermostability of β-mannanase by protective additives

The effects of some sugars (glucose, mannose, fructose, sucrose and chitosan) and polyols (glycol, glycerol and sorbitol) as protective additive on the thermostability of β-mannanase were studied. The optimal reaction temperatures of β-mannanase and the thermodynamics and the deactivation kinetics with or without additives were also investigated. The experimental results show that sucrose, chitosan and sorbitol could apparently improve the thermal stability of β-mannanase when their concentration was kept at 2 g/L. The optimal combination additive proportion was sucrose: chitosan : sorbitol = 1 : 2 : 2 (molar ratio) using the orthogonal experimental design. The sucrose, chitosan, glycerol, sorbitol and the combination additive might increase the optimal reaction temperature from 50°C to about 60°C due to their good protection effect. The thermal deactivationcurves of β-mannanase accorded with the kinetic rules of first order reaction, and the corresponding kinetic and thermodynamic parameters were calculated. Meanwhile, the protective mechanism of the additives against deactivation of enzyme was also discussed. __________ Translated from Journal of Tianjin University, 2007, 41(1): 114–118 [译自: 天津大学学报]     

Bulk Synthesis of Monodisperse and Highly Biocompatible Poly(ɛ-caprolactone)-diol by Transesterification Side-Reactions

Ring-opening polymerization of ε-caprolactone was performed at 130°C, under partial vacuum in the presence of stannous octoate as the catalyst and 1,4-butanediol as the initiator. After the termination of polymerization by deionized water, a hydroxyl group formed at the end of the polymer chains. Structure of the synthetic poly(ε-caprolactone)-diols (PCL-diol), molecular weight, polydispersity index, and Cell viability were evaluated. Very narrow distribution in the molecular weight obtained for PCL-diols is due to a new method for synthesis. It was shown that by the increase in PCL-diols, the compatibility of human mesenchymal stem cells grew up.     

Joining of β-SiC by spark plasma sintering

Spark plasma sintering (SPS) was employed to join monolithic β-SiC with or without titanium as intermediate joining material. Both the localized and rapid heating contributed to the inherent energy saving of electric current assisted joining technique. The effects of uniaxial pressure and surface preparation were analyzed independently with respect to the flexural strength and the morphology of the joints. In particular samples polished down to 1 μm and joined at 1900 °C for 5 min achieved the strength of the as received material. The failure occurred outside the joining interface, confirming the optimum quality of the joint. Pressure in combination with surface preparation was necessary to achieve perfect adhesion and pore free direct joining of SiC. The use of Ti foil as a joining material and pressure allowed joining of unpolished SiC.     

Transesterification of soybean oil to biodiesel by tin-based Brønsted-Lewis acidic ionic liquid catalysts

A series of Brønsted-Lewis acidic ionic liquid (BLAIL) catalysts consisting of sulfonated ionic liquid [SO₃H-pmim]Cl and Sn(II) chloride have been synthesized and exploited for catalytic transesterification of soybean oil with methanol to biodiesel. The structural and chemical properties of these [SO₃H-pmim]Cl-xSnCl₂ (x=0-0.8) catalysts were characterized by different analytical and spectroscopic techniques, such as FT-IR, TGA, and NMR. In particular, their acid properties were studied by solid-state ³¹P NMR using trimethylphosphine oxide as the probe molecule. The BLAIL catalysts were found highly efficient for transesterification reaction due to the introduction of Lewis acidity by SnCl₂ in the initially Brønsted acidic [SO₃H-pmim]Cl catalyst. The effects of three independent process variables on biodiesel yield were optimized by response surface methodology (RSM). Consequently, an excellent biodiesel yield of 98.6% was achieved under optimized reaction conditions over the BLAIL catalyst with SnCl₂ loading (x) of 0.7.     

An Efficient and Recyclable Silica Based Inorganic–Organic Hybrid Zinc Catalyst for Transesterification of β-Ketoesters

A new silica based inorganic–organic hybrid zinc catalyst was synthesized and its catalytic activity was investigated for transesterification of β-ketoesters. Polymer supported catalyst was characterized by various techniques such as surface area (BET), elemental and thermogravimetric analyses, FTIR, ¹³C CPMAS spectral studies and atomic absorption spectroscopy (AAS). The reaction proceeded smoothly in the presence of 0.04 mmol of catalyst in toluene at refluxing conditions. The catalyst revealed higher catalytic activity compared to homogeneous catalyst and was reused without appreciable loss in catalytic activity.     

Synthesis of Vitamin A Esters by Immobilized Candida sp. Lipase in Organic Media

Vitamin A ester was synthesized in organic solvents with immobilized lipase from Candida sp. The types of lipases, influences of solvent, the molar ratio of substrates, the reaction temperature and the water activity in the reaction were studied in detail in order to obtain the optimum conditions for Vitamin A palmitate synthesis. In a system of hexane, 100mg immobilized Candida sp. lipase was used in the presence of 1.2mmol vitamin A acetate and 3.6mmol palmitic acid. The yield of vitamin A palmitate reached 81% in 12h at 25℃. The immobilized Candida sp. lipase was prepared by adsorbing Cand/da sp. fermentation broth on pretreated textile and could be reused for at least six batches.     

Adsorption of Basic Dyes on β-Cyclodextrin Functionalized Poly (Styrene-Alt-Maleic Anhydride)

A new [#x003B2]-cyclodextrin functionalized poly (styrene-alt-maleic anhydride) was synthesized for removal of basic fuchsin (BF) and methylene blue (MB) from water via grafting reaction of [#x003B2]-cyclodextrin onto poly (styrene-alt-maleic anhydride) and then acylation with chloroacetyl chloride. Its structure was characterized. At a dosage of 0.25 g[#x000B7]L^[#x02212]1, pH 6, and 25[#x000B0]C, adsorption equilibrium was reached in 600 min and maximum adsorption quantities to BF and MB were 295 mg[#x000B7]g^[#x02212]1 and 528 mg[#x000B7]g^[#x02212]1, respectively. The equilibrium data fitted the Langmuir isotherm and the adsorption kinetics data followed the pseudo-second-order model. Adsorption processes were endothermic, entropy gained, and spontaneous in nature within 288-308 K.     

Densification of additive-free polycrystalline β-SiC by spark-plasma sintering

Additive-free β-SiC nanopowders were densified by spark-plasma sintering in the temperature range 1650-2200 °C, holding time 1-30 min, and pressure 50-150 MPa. The starting nanopowder was further refined and mechanically activated by ball milling in order to promote densification. In a detailed parametric study, temperature, holding time, and/or pressure were varied to investigate their effect on the densification and grain growth during sintering. High densifications were obtained for temperatures greater than 1800 °C. Full densification (98.0 ± 0.6%) was reached at a sintering temperature of 2100 °C. Depending on the sintering conditions, nanostructured materials can be produced with grain sizes between 90 and 100 nm, and microstructured materials with grain sizes between 0.22 and 2.39 μm. Pressure has a major effect on the grain size, it being necessary to use a pressure of 150 MPa to obtain nanostructured materials.     

Thionation of β-lactams to β-thiolactams by silica-supported P2S5

In this paper, an improved method for the thionation of β-lactams is described. Using a solid-supported P₂S₅ reagent and heating under reflux conditions, β-thiolactams were obtained in good to excellent yields. Also the reaction time reduced significantly compared with that achieved under the more conventional method using P₂S₅ alone. Furthermore, inexpensive and easily available starting materials simple reaction conditions and a simple purification process are some other advantages of this method.