Enzymatic synthesis of medium chain monoglycerides in a solvent-free system

The synthesis of monocaprin, monolaurin, and monomyristin in a solvent-free system was conducted by mixing a commercial immobilized lipase with the organic reactants (glycerol and fatty acids) in a 20-mL batch reactor with constant stirring. The effects of temperature, fatty acid/glycerol molar ratio, and enzyme concentration on the reaction conversion were determined. The addition of molecular sieves in the assays of monomyristin synthesis was also evaluated. The reactions were carried out for 5 to 6 h and the nonpolar phase was analyzed by gas chromatography. The best results in terms of selectivity and conversion (defined as the percentage of fatty acid consumed) were achieved when the stoichiometric amount of reagents (molar ratio=1) and 9% (w/w) commercial enzyme were used and the reaction was performed at 60°C. The addition of molecular sieves did not improve the synthesis of monomyristin. Conversions as high as 80%, with monoglycerides being the major products, were attained. After 5 h of reaction, the concentration of monoglyceride was about twice that of diglyceride, and only trace amounts of triglyceride were found. The results illustrate the technical possibility of producing medium chain monoglycerides in a solvent-free medium using a simple batch reactor.     

Highly Enantioselective Phenylacetylene Addition to Benzaldehyde Catalyzed by Chiral Tridentate Ligand

Development of new or improved methods for the asymmetric preparation of chiral propargylic alcohols has gained considerable significance during the past years because they are useful building blocks for the synthesis of many biologically active compounds and natural products.[1] A series of chiral tridentate ligands were conveniently synthesized from amino acids with good yields (Scheme 1).[2] A preliminary study of the enantioselective alkynylation of benzaldehyde catalyzed by this chiral tridentate ligand was carried out and up to 83% ee of chiral propargyl alcohols was obtained (Table 1 ). A further investigation of the tridentate ligand is currently underway.     

β-环糊精键合改性介孔硅胶的表征和吸附性能评价

β-环糊精键合改性介孔硅胶的表征和吸附性能评价;酚类化合物     

天然磷脂的色谱法分离、纯化研究进展

天然磷脂是一类含磷酸根的类脂化合物的总称,在医药学、营养学、化妆品和生命科学领域等有重要的应用价值。本文综述了不同原料样品中磷脂种类和其各分子的色谱法分离、纯化。着重讨论高效液相色谱法分离技术及其影响因素。最后概述了有助于提高分离选择性、检测灵敏度的化学衍生化方法。     

Validation of a digestion system using a digester block/cold finger system for the determination of lead in vegetable foods by electrothermal atomic absorption spectrometry

This paper presents the validation of a system for sample digestion using a digester block/cold finger to determine the lead content in vegetables by electrothermal atomic absorption spectrometry (ETAAS). After mineralization, lead contents were determined by ETAAS using a calibration curve based on aqueous standards prepared in 2.60 M nitric acid solutions containing 5 microg ammonium phosphate as chemical modifier. A pyrolysis temperature of 900 degrees C and atomization temperature of 2000 degrees C were used. This method allowed the determination of lead with a characteristic mass of 35 pg; LOD and LOQ of 0.6 and 2 nglg, respectively, were found. The precision was investigated in terms of reproducibility and repeatability. Reproducibility was estimated by analysis of nine different portions of a certified reference material (CRM) of spinach leaves, and the repeatability was determined through the analysis of nine aliquots of the same solution. The reproducibility and repeatability were found to be 4.27 and 2.94% RSD, respectively. The accuracy was confirmed by analysis of whole meal flour, spinach leaves, and orchard leaves CRMs, all furnished by the National Institute of Standards and Technology. Lead contents were measured using the newly developed technique in 11 different potato samples. The lead contents ranged from 12.80 to 69.27 ng/g, with an average value of 28.59 ng/g. These values were in agreement with data reported in the literature.     

Influence of the incorporated metal on template removal from MCM-41 type mesoporous materials

Al-modified MCM-41, La-modified MCM-41, and Ce-modified MCM-41 mesoporous materials were prepared with different molar ratios (Si/M = 10; 25; 50; 100 and 200) at room temperature. The materials were characterized using XRD, BET–BJH, and TG–DTA. The XRD showed four peaks, due to the ordered hexagonal array of parallel silica tubes, which could be indexed as (100), (110), (200), and (210), assuming a hexagonal unit cell. The surface area decreased as the concentration of the metal incorporated in the material increased. The thermal stability of the materials was around 650 °C. The CeO₂ phase made the mass transfer process more difficult, hindering Hofmann degradation and favoring oxidation.     

New di‐ and triorganotin(IV) carboxylates derived from a Schiff base: synthesis,characterization and in vitro antimicrobial activities

A new carboxylic acid, 2‐{[5‐(2‐nitrophenyl)furan‐2‐yl]methyleneamino}benzoic acid (HOBZ), has been produced by reacting 5‐(2‐nitrophenyl)furfural with 2‐aminobenzoic acid. Reactions of NaOBZ with organotin chlorides led to formation of [Me₃Sn(OBZ)] ( 1 ), [Bu₃Sn(OBZ)] ( 2 ), [Me₂Sn(OBZ)₂] ( 3 ) and [Bu₂Sn(OBZ)₂] ( 4 ). Complexes 1 , 2 , 3 , 4 have been characterized using elemental analyses and infrared, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR and ¹¹⁹Sn Mössbauer spectroscopies. In the solid state, the OBZ ligands might coordinate to tin in an anisobidentate fashion via the carboxylate group. The in vitro antimicrobial activity of all compounds has been screened against the following fungi: Aspergillus niger, A. flavus, A. parasiticus, Penicillium citrinum, Candida dubliniensis, C. lusitaniae, C. albicans, C. tropicalis, C. parapsilosis and C. glabrata; and against the following bacteria: Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, Streptococcus sanguinis, Escherichia coli, Citrobacter frendii, Salmonella typhimurium and Pseudomonas aeruginosa. Complexes 2 and 4 exhibited higher biocide activity in comparison to 1 and 3 and to the control drugs nystatin and miconazole nitrate for the yeasts, and chloramphenicol and ampicillin for the bacteria. The biological activity of 2 was superior to that of 4 . In addition, the toxicity of HOBZ, NaOBz and 1 , 2 , 3 , 4 were determined using Chlorella vulgaris, revealing low toxicity of the complexes at MIC₅₀ concentrations. We also performed cell viability studies, using XTT assay, displaying no change in the mitochondrial function after 2–4 h of exposure of the microorganism to the complexes at MIC₅₀ concentrations. The butyl‐containing complexes 2 and 4 display greater lipophilicities than do the methyl analogues 1 and 3 , thereby endowing 2 and 4 with superior abilities to cross the microbe cell membrane, the possible mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd.     

Growth under Visible Light Increases Conidia and Mucilage Production and Tolerance to UV‐B Radiation in the Plant Pathogenic Fungus Colletotrichum acutatum

Light conditions can influence fungal development. Some spectral wavebands can induce conidial production, whereas others can kill the conidia, reducing the population size and limiting dispersal. The plant pathogenic fungus Colletotrichum acutatum causes anthracnose in several crops. During the asexual stage on the host plant, Colletototrichum produces acervuli with abundant mucilage‐embedded conidia. These conidia are responsible for fungal dispersal and host infection. This study examined the effect of visible light during C. acutatum growth on the production of conidia and mucilage and also on the UV tolerance of these conidia. Conidial tolerance to an environmentally realistic UV irradiance was determined both in conidia surrounded by mucilage on sporulating colonies and in conidial suspension. Exposures to visible light during fungal growth increased production of conidia and mucilage as well as conidial tolerance to UV. Colonies exposed to light produced 1.7 times more conidia than colonies grown in continuous darkness. The UV tolerances of conidia produced under light were at least two times higher than conidia produced in the dark. Conidia embedded in the mucilage on sporulating colonies were more tolerant of UV than conidia in suspension that were washed free of mucilage. Conidial tolerance to UV radiation varied among five selected isolates.     

Removal of Mn(II) and Cd(II) from wastewaters by natural and modified clays

The adsorption capacities of commercial and Brazilian natural clays were evaluated to test their applications in wastewater control. We investigated the process of sorption of manganese(II) and cadmium(II) present in synthetic aqueous effluents, by calculating the adsorption isotherms at 298 K using batch experiments. The influence of temperature and pH on the adsorption process was also studied. Adsorption of metals was best described by a Langmuir isotherm, with values of Q ₀ parameter, which is related to the sorption capacity, corresponding to 6.3 mg g^{− 1} for K-10/Cd(II), 4.8 mg g^{− 1} for K-10/Mn(II), 11.2 mg g^{− 1} for NT-25/Cd(II) and 6.0 mg g^{− 1} for NT-25/Mn(II). We observed two distinct adsorption mechanisms that may influence adsorption. At the first 5 min of interaction, a cation exchange mechanism that takes place at exchange sites located on (001) basal planes is predominant. This process is inhibited by low pH values. After this first and fast step, a second sorption mechanism can be related to formation of inner-sphere surface complexes, which is formed at edges of the clay. The rate constants and the initial sorption rates correlate positively with temperature in all studied systems, denoting the predominance of a physisorption process. The addition of complexing agents that are incorporated within the K10 structure, enhance metal uptake by the adsorbent. The results have shown that both Cd(II) and Mn(II) were totally retained from a 50 mg L^{− 1} solution when K10 grafted with ammonium pyrrolidinedithiocarbamate (APDC) was used as adsorbent.     

对-叔丁基杯[8]芳烃键合硅胶制备及其毛细管电色谱性能研究

以γ-(环氧丙氧)丙基键合硅胶为前体,于硅胶表面键合环氧基,在催化剂存在下以杯芳烃钠盐开环制备杯芳烃键合硅胶固定相.该方法反应条件温和,适用性强.将这个新方法首次用于制备对-叔丁基杯[8]芳烃电色谱键合固定相(C8BS),采用加压电色谱初步评价其电色谱性能.研究结果表明,C8BS电渗流(Electrosmoticflow,EOF)较小,但通过控制键合反应及使用压力辅助电色谱可部分弥补上述不足.该固定相的EOF受流动相pH影响小(pH=3-8),同时大环配体屏蔽效应能有效地克服硅羟基引起的碱性化合物拖尾现象,这对电色谱分离具有重要意义.通过分步封尾研究EOF的来源发现,杯芳烃酚羟基对EOF有弱的贡献,这与报道的杯芳烃涂层具有径向电渗流调控能力相一致.