A new route for the functionalisation of wood through transesterification reactions

A novel transesterification reaction between acetylated maritime pine sapwood (Pinus pinaster Soland) and methyl benzoate (MB), in the presence of dibutyltin oxide (DBTO) as a catalyst, was performed. Reaction was confirmed by Fourier-transform infrared spectroscopy (FTIR) and ¹³C nuclear magnetic resonance cross-polarisation with magic-angle spinning (NMR CP MAS) analysis: signals corresponding to benzoylated wood were identified and, when transesterification was performed with ethyl trimethylsilylacetate (ETMSA), characteristic trimethylsilyl groups were detected. The acetyl/benzoyl exchange rate was found to increase with increasing amount of DBTO, temperature and reaction time and a concurrent deterioration of the woody material was evidenced.     

Development of electrospun poly(vinyl alcohol) fibers immobilizing lipase highly activated by alkyl-silicate for flow-through reactors

Electrospun fibrous membranes composed of poly(vinyl alcohol) (PVA) fibers of approximately 1 μm in diameter, and immobilizing highly activated lipase entrapped in silicate cages with smaller dimensions than the fibers, were developed; and their feasibility as a component of flow-through reactors was studied. The electrospun PVA fibers were prepared from a mixture of PVA solution and a sol obtained from silicon alkoxide(s)—either tetramethoxysilane (TMOS) or dimethyldimethoxysilane (DMDMOS), or both, containing lipase. The fastest initial transesterification rate converting (s)-glycidol to glycidyl n-butyrate with vinyl n-butyrate in batchwise reactions was accomplished by treatment of lipase using the sol obtained from DMDMOS and TMOS together. The values were 4.5-, 21.8-, and 1.8-fold faster than those of systems using lipases that were either non-modified or modified using TMOS alone or DMDMOS alone, respectively. The higher activity of the lipase modified using both DMDMOS and TMOS and immobilized in PVA fibers resulted in a flow-through reactor having a higher degree of conversion at the same retention time compared with that using immobilized non-modified lipase. These results show the feasibility of flow-through reactors composed of electrospun PVA fibers immobilizing lipase highly activated by alkyl-silicate.     

Fluorescent response of sol-gel derived ormosils for optical ammonia sensing film

Optical sensing films for ammonia have been investigated based on a fluorescent indicator aminofluorescein (AF). AF was immobilized in diverse organically modified silicates (ORMOSILSs) obtained by copolymerizing various proportions of methyltrimethoxysilane (Me-TriMOS), phenyltrimethoxysilane (Ph-TriMOS), dimethyldimethoxysilane (DiMe-DiMOS), and diphenyldimethoxysilane (DiPh-DiMOS) with tetramethoxysilane (TMOS). The effective polarities of ormosils were probed by using the solvatochromic dye E_T (30) [2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)]phenolate. Compared with the fluorescent responses of fluorescein and fluorescein isothiocyanate, the fluorescent intensity enhancement of AF for ammonia was caused by the reaction between ammonia and the NH₂ group on AF. The reaction may cause the reduction of the intermolecular self-quenching of AF to make a fluorescence enhancement of sensing film in NH₃ solution. The ammonia sensing range and rate of response were found to highly depend on the type and content of organosilicon precursors employed. Films prepared with a 1:3, 1:1.5, 1:1.2, or 1:1 mole ratio (TMOS:Me-TriMOS, TMOS:Ph-TriMOS, TMOS:DiMe-DiMOS, or TMOS:DiPh-DiMOS) was found to be the best in terms of stability and response. Their detection limits for ammonia in water was 0.01, 0.5, 0.2, and 0.5 μg ml⁻¹, respectively.     

Preparation of (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate via Novozym-435® catalyzed desymmetrization of cis-3,5-Diacetoxy-1-cyclopentene

Photooxidation of cyclopentadiene has been carried out in methanol using white light of LED lamp, rose bengal as photo initiator, and compressed air at 0?°C. Under conditions of [thiourea] ? [cyclopentadiene], the consumption of thiourea follows a pseudo-first-order reaction kinetics with half life of 75?±?10?min; corr. coeff. r?=?0.989. Slow addition of the monomer and maintaining excess thiourea concentration in reaction mass improves the yield. cis-3,5-Dihydroxy-1-cyclopentene is acetylated without isolation to obtain cis-3,5-Diacetoxy-1-cyclopentene of high purity (>99%) with overall isolated yield of 30%. Desymmetrization of the diacetate to (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate has been carried out via enzymatic transesterification with methanol in methyl tert-butyl ether (MTBE) at 5?°C using Novozym-435^®. The enantiomerically pure monoacetate (e.e. >99%) was obtained in 95% isolated yield. The recovered enzyme was reused for more than 10 times without loss in yield and selectivity. The entire protocol does not require purification of final product by chromatography.     

Study of acetylated EGCG synthesis by enzymatic transesterification in organic media

(-)-Epigallocatechin-3-O-gallate (EGCG), the most abundant polyphenolic compound in catechins, exerts excellent physiological effects including antioxidant. However, with its high hydrophilicity and poor lipophilicity, the application of EGCG in oil products is limited. In this study, EGCG acetylated derivatives were prepared by transesterification of EGCG with vinyl ester in acetonitrile/isopropanol (1:1 v/v). Lipase Lipozyme RM IM was found to be the optimum catalyst at concentration of 12 U/g EGCG, with a molar ratio of 1:5 of EGCG to vinyl acetate as the substrates. And 83.2% conversion was obtained after 10 h reaction at 50 °C. Based on the ping-pong model, the kinetic equation was constructed to determine the reaction kinetic parameters. The analysis of the initial rate and progress curve indicated that the transesterification of EGCG and vinyl acetate was kinetically regulated. Two major acetylated derivatives were identified as 5″-O-acetyl-EGCG and 3″, 5″-di-O-acetyl-EGCG by LC-MS/MS and NMR. Their enhanced lipophilicity was confirmed by transmittance test and octanol–water partition coefficient. The antioxidant activity of di-acetylated EGCG was superior to mono-acetylated EGCG and EGCG, but slightly lower than tert-butyl hydroquinone (TBHQ) as determined by peroxide values (POV) and Rancimat test. Acetylated EGCG might be used as a potent antioxidant for controlling oxidation of oil.     

Preparation of sol�Cgel hybrid materials from ��-methacryloxypropyltrimethoxysilane and tetramethyl orthosilicate: study of the hydrolysis and condensation reactions

Organic?Cinorganic hybrid materials suitable for the development of sol?Cgel coatings for metallic surfaces were prepared by hydrolysis and condensation of ??-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethyl orthosilicate (TMOS). The hydrolysis of MAPTMS/TMOS was carried out in an ethanol/water solution. The prehydrolysis stage of MAPTMS/TMOS system was monitored by Fourier transform infrared spectroscopy (FTIR) and liquid-state ²⁹Si and ¹³C nuclear magnetic resonance (²⁹Si and ¹³C NMR). FTIR analysis indicated that the hydrolysis of MAPTMS/TMOS was accomplished as far as the (SiOMe) band corresponding to unhydrolyzed silane disappeared. The concentration of the alkoxy groups and the extent of self-condensation of mono-, di-, and trisubstituted siloxanes (T species) in the sol were estimated by using liquid-state ²⁹Si NMR spectroscopy. The hydrolysis of the prepared sol was also evaluated by liquid-state ¹³C NMR spectroscopy. The results indicated that under the adopted synthesis strategy conditions, the hydrolysis process requires 4?h to be completed.     

Photophysical and Photochemical Properties of Ru(bpy)3 2+ in Si-Ti Mixed Oxides Xerogels Prepared by the Sol-Gel Process

The luminescence spectra and lifetime of tris(2,2-bipyridine)ruthenium(II), Ru(bpy)₃ ²⁺, were studied in sol-gel reaction systems of tetramethoxysilane (TMOS) and titanium(IV) isopropoxide (TTIP) with HCl. Luminescence lifetime in the TMOS system increased as the sol-gel reaction proceeded, because diffusion-controlled luminescence quenching such as oxygen and collisional quenching with solvent molecules were suppressed in the rigid matrices. On the other hand, luminescence lifetime in the TTIP system decreased during the sol-gel reaction. The decrease in lifetime was ascribed to electron transfer from photoexcited Ru(bpy)₃ ²⁺ to the conduction band of the TiO₂ xerogels. Extended X-ray absorption fine structure (EXAFS) measurements were done to associate lifetime in the Si-Ti xerogels with the structures of Ti⁴⁺ sites in the xerogels.     

Desymmetrization of meso-cyclopenten-cis-1,4-diol to 4-(R)-hydroxycyclopent-2-en-1-(S)-acetate by irreversible transesterification using Chirazyme®

The parameter optimization study for the desymmetrization of meso-cyclopenten-1,4-diol 1 through irreversible transesterification using an immobilized lipase from Mucor meihei, i.e., Lipozyme^®/Chirazyme^® is presented. The enzyme was studied for the transesterification of 1 in various organic solvents by varying reaction parameters such as the nature of acyl donor, temperature, enzyme quantity etc., to afford optically active 4-(R)-hydroxycyclopent-2-en-1-(S)-acetate 2 of >98% enantiomeric excess in >60% yield.     

Characterization of Biocatalysts Prepared with Thermomyces lanuginosus Lipase and Different Silica Precursors,Dried using Aerogel and Xerogel Techniques

The use of lipases in industrial processes can result in products with high levels of purity and at the same time reduce pollutant generation and improve both selectivity and yields. In this work, lipase from Thermomyces lanuginosus was immobilized using two different techniques. The first involves the hydrolysis/polycondensation of a silica precursor (tetramethoxysilane (TMOS)) at neutral pH and ambient temperature, and the second one uses tetraethoxysilane (TEOS) as the silica precursor, involving the hydrolysis and polycondensation of the alkoxide in appropriate solvents. After immobilization, the enzymatic preparations were dried using the aerogel and xerogel techniques and then characterized in terms of their hydrolytic activities using a titrimetric method with olive oil and by the formation of 2-phenylethyl acetate in a transesterification reaction. The morphological properties of the materials were characterized using scanning electron microscopy, measurements of the surface area and pore size and volume, thermogravimetric analysis, and exploratory differential calorimetry. The results of the work indicate that the use of different silica precursors (TEOS or TMOS) and different drying techniques (aerogel or xerogel) can significantly affect the properties of the resulting biocatalyst. Drying with supercritical CO₂ provided higher enzymatic activities and pore sizes and was therefore preferable to drying, using the xerogel technique. Thermogravimetric analysis and differential scanning calorimetry analyses revealed differences in behavior between the two biocatalyst preparations due to the compounds present.     

Transesterification kinetics in the reactive blends of liquid crystalline copolyesters and poly(ethylene terephthalate)

The transesterification kinetics of poly(ethylene terephthalate) (PET)/copoly(oxybenzoate-p-terephthalate) (liquid crystalline polymer, LCP) (70/30 by weight) in the presence of small amount of bis(2-oxazoline) (BOZ) as chain extender was studied by using 1H nuclear magnetic resonance. The kinetic data was treated as a second-order reversible reaction, and it was found that the rate constants of transesterification at 270, 280 and 290 °C were 1.55×10⁻², 2.20×10⁻² and 3.01×10⁻² min⁻¹, respectively, the value of which was higher than the blend without addition of BOZ, 1.26×10⁻² min⁻¹, and the activation energy of PET/LCP transesterification was 84.4 kJ mol⁻¹.     

Products of hydrolysis of C,N-chelated triorganotin(IV) chlorides and use of products as catalysts in transesterification reactions

Triorganotin(IV) chlorides containing one L^CN chelating ligand were hydrolyzed with an excess of sodium hydroxide. The composition of the products is strongly dependent on the nature of the organic groups bound to the tin atom. Di(n-butyl)tin, dimethyltin as well as the diphenyl derivative exhibits an equilibrium between hydroxide and stannoxane forms (oxide), whereas alkyltin species react spontaneously and reversibly with carbon dioxide present in the air to form carbonate species. On the other hand, diphenyl derivatives display virtually no reaction with CO₂ towards carbonates, while the di-t-butyl-substituted tin derivative is stable under the same experimental condition and remains as a tin hydroxide. In the case of the dimethyltin derivative, a methyl group migration was observed with displacement of one L^CN chelating ligand during the reaction on the air. The coordination geometry of the tin central atom(s) of all studied compounds can be described as trigonal bipyramidal with a dative bonded dimethylamino group occupying one coordination site. The catalytic activity of these compounds in transesterification reactions is generally lower compared to the systems reported in the literature, with the exception of the transesterification of ethyl acetate by cyclohexanol which displays a remarkable activity.     

Synthesis of syndiotactic-polystyrene-graft-poly(methyl methacrylate) and syndiotactic-polystyrene-graft-atactic-polystyrene by atom transfer radical polymerization

Syndiotactic polystyrene graft copolymers, including syndiotactic-polystyrene-graft-poly(methyl methacrylate) and syndiotactic-polystyrene-graft-atactic-polystyrene, were synthesized by atom transfer radical polymerization (ATRP) using bromoacetylated syndiotactic polystyrene as macroinitiator and copper bromide combined with 2,2′-bipyridine as catalyst. The macroinitiator was prepared from the acid-catalyzed halogenation reaction of partially acetylated syndiotactic polystyrene, which was synthesized in a heterogeneous process with acetyl chloride and anhydrous aluminum chloride in carbon disulfide. The graft copolymers were characterized by ¹H- and ¹³C-NMR spectra.     

Towards high molecular weight poly(bisphenol a carbonate) with excellent thermal stability and mechanical properties by solid-state polymerization

Poly(bisphenol A carbonate) (BPA-PC) was post-polymerized by solid-state polymerization (SSP) after supercritical CO₂-induced crystallization in low molecular weight particles prepolymerized via melt transesterification reaction. The effects of the crystallization conditions on melting behavior and SSP of BPA-PC were investigated with differential scanning calorimetry (DSC), Ubbelohde viscosity method and gel permeation chromatography (GPC). The reaction kinetics of the SSP of crystallized prepolymers was studied as a function of reaction temperatures for various reaction periods. As a result, the viscosity average molecular weight of BPA-PC particles (2 mm) increased from 1.9 × 10⁴ g/mol to 2.8 × 10⁴ g/mol after SSP. More importantly, the significantly enhanced thermal stability and mechanical properties of solid-state polymerized BPA-PC, compared with those of melt transesterification polymerized BPA-PC with the same molecular weight, can be ascribed to the substantial avoidance of undergoing high temperature during polymerization. Our work provides a useful method to obtain practical product of BPA-PC with high quality and high molecular weight.     

Influence of molar ratios of precursor,catalyst, solvent and water on monolithicity and physical properties of TMOS silica aerogels

In continuation to our earlier work on aerogels, the experimental results on the monolithicity and physical properties of silica aerogels as a function of the molar ratios of tetramethoxysilane (TMOS) precursor, catalyst (NH₄OH), methanol (MeOH) solvent and water, are reported. The molar ratios of NH₄OH/TMOS, MeOH/TMOS and H₂O/TMOS were varied from 7.1 × 10^–6 to 9.6 × 10^–1, 1 to 90 and 1 to 18 respectively. It has been found that larger molar ratios of NH₄OH/TMOS (10^–2), MeOH/TMOS (13 to 60) and H₂O/TMOS (>10) resulted in transparent but cracked aerogels, and very low molar ratios of these combinations gave monolithic but less transparent or opaque aerogels. The best quality silica aerogels, in terms of monolithicity, transparency and low density, have been obtained with TMOS:MeOH:H₂O:NH₄OH in the molar ratio of 1:12:4:3.7 × 10^–3 respectively. The aerogels have been characterized by density, optical transmission, surface area and porosity measurements. The results have been discussed by taking into account the hydrolysis and condensation reactions, and syneresis effects.     

The effect of vinyl esters on the enantioselectivity of the lipase-catalysed transesterification of alcohols

The enantioselectivity of the lipase from Pseudomonas cepacia (PCL) in the transesterification of 2-phenyl-1-propanol 1 was studied using a series of vinyl 3-arylpropanoates as acyl donors. The most enantioselective transesterification reaction of the alcohol was attained by using vinyl 3-(p-iodophenyl)- or 3-(p-trifluoromethylphenyl)propanoates, with enantiomer ratios, E, of 116 and 138, respectively. Vinyl 3-phenylpropanoate was also effective for the resolution of 1 mediated by lipases from P. fluorescens and porcine pancreas and for the PCL-catalysed transesterification of several 2-phenyl-1-alkanols. The enantiomeric resolution of 1 was practically carried out by the first enantioselective transesterification using PCL and vinyl 3-(p-iodophenyl)propanoate to afford (R)-1 and then the enantioselective hydrolysis of the resultant ester to afford (S)-1.     

A facile synthesis of (S)-felodipine

A short and facile synthesis of (S)-felodipine was developed starting from (R)-glycidol as the source of the chiral auxiliary. 2-Hydroxyethyl esters were found to undergo selective transesterification reactions in the presence of other esters. This selective transesterification reaction was applied to the synthesis of (S)-felodipine through selective substitution of the 2-hydroxyethyl group possessing chiral ester with sodium methoxide.     

Synthesis of a (B12H11S) containing glucuronoside as potential prodrug for BNCT

A B₁₂H₁₁SH²⁻ containing glycoside of glucuronic acid has been prepared, for possible use as prodrug in BNCT. The synthesis was carried out by the Koenigs-Knorr reaction of the acetylated glucopyranosyluronate bromide with the nucleophile cyanoethylthioundecahydro-closo-dodecaborate(2−). After removal of the cyanoethyl-group, deacetylation and saponification of the reaction product tris(tetramethylammonium)-[S-(β-d-glucuronate)-thio] undecahydro-closo-dodecaborate(3−) could be prepared.     

Enantioselective transesterification of (RS)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol using Pseudomonas aeruginosa lipases

Lipases from the bacterial strain, Pseudomonas aeruginosa, isolated from the soil by enrichment techniques, are assessed for the enantioselective transesterification of (RS)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol (rac-CDPP) to (R)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol, a key intermediate in the synthesis of the chiral drug (S)-Lubeluzole. The lipases produced by the organism yielded the (S)-ester and the (R)-alcohol as the remaining substrate with an excellent yield (>49.9%) and almost complete enantioselectivity (ee >99.9%) in the presence of vinyl butyrate as an acyl donor in an organic medium. In contrast, purified and expensive commercially available lipases of Candida rugosa and porcine pancreas achieved much lower conversion with enantioselectivities of 15% and 5%, respectively. A well-mixed (∼1000 rev min⁻¹) batch reactor having the aqueous phase finally dispersed in hexane was used in these studies. The parameters of the transesterification reaction were optimized and the optimal concentrations of rac-CDPP and vinyl butyrate were found to be 5 and 150 mM at 30 °C. A preparative-scale reaction yielded the (S)-ester at 42% conversion and ee >99%.     

溶胶-凝胶伴随相分离制备SiO2多孔块体

以正硅酸甲酯(TMOS)为前驱体, 0.01 mol·L^-1盐酸(HCl)为催化剂, 环氧丙烷(PO)为凝胶促进剂, 粘均分子量(M_v)为10000的聚氧化乙烯(PEO)为相分离诱导剂, 采用溶胶-凝胶伴随相分离制备SiO₂多孔块体材料,利用差热分析(DTA)、傅里叶变换红外(FT-IR)光谱、扫描电镜(SEM)、X射线衍射(XRD)、汞压、N₂吸附/脱附等测试技术对所制得的SiO₂多孔块体进行了表征, 探讨了环氧化物调控溶胶-凝胶以及PEO诱导相分离机理. 结果表明, 加入PEO能诱导SiO₂凝胶发生相分离, 当PEO/TMOS摩尔比为0.0018时, 可以获得共连续多孔结构的SiO₂块体材料, 其大孔孔径分布在1-3 μm之间, 比表面积达719 m²·g^-1, 孔体积为0.48 m³·g^-1. 环氧丙烷因其环氧原子的强亲核性和不可逆的开环反应, 促进溶胶-凝胶转换, 同时借助吸附在SiO₂低聚物上的PEO诱导SiO₂凝胶相分离, 从而制备共连续大孔及骨架结构的多孔块体.     

Monitoring of the Viability of Cells Immobilized by Sol-Gel Process

Three different types of cells, Pseudomonas fluorescens HK44, Saccharomyces cerevisiae strain SP4 and plant cells Nicotiana tabacum L. BY-2, were immobilized by entrapment in tetramethoxysilane prepolymer (TMOS) gel or in composite gel containing prepolymer TMOS and alginate in various ratios. Their growth and viability were monitored by bioluminescence and 2-D fluorescence spectra, which are fast and do not need the dissolution of a matrix. The resulting biocomposite gels were obtained by gelation of the mixtures of TMOS prep. or TMOS/alginate sols and the particular cells in proper media on glass supports to provide films ～1 mm thick. The effect of the following parameters on the growth and viability of the cells was studied: (a) the composition of the biocomposites, (b) the preparation conditions of TMOS and (c) the conditions of the procedure of entrapment. All three types of cells were tested in TMOS gel and the composite TMOS/alginate = 1:1 (v/v). The sensitivity of the cells to the changes of conditions increased in the sequence: P. fluorescence HK44 < S. cerevisiae strain SP4 < N. tabacum L. BY-2. Cell viability decreased with the increasing content of Si in biocomposites. The entrapment into alginate–silica composites resulted in the leakage of microbial and yeast cells. However, it had positive effects on the growth and metabolic activity of plant cells.