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91.
W. Habchi C. Matta L. Joly-Pottuz M. I. De Barros J. M. Martin P. Vergne 《Tribology Letters》2011,42(3):351-358
In this article, the lubricating properties of pure glycerol are investigated under both mild and severe EHL regimes. Amazingly
low friction coefficients (about 0.01) are reported by experiments in thick film regimes compared to traditional base oils.
EHL calculations of film thickness and friction (including thermal effects) predict friction coefficients that are twice those
actually found for glycerol. Chemical analysis of glycerol before and after the friction tests were performed by NMR and Karl
Fischer methods, and they reveal that water is produced by tribochemical reaction as well as other species like aldehydes.
This finding is in agreement with a corrosion pattern observed inside the wear scars of the steel samples. This study provides
an explanation to the anomalously low friction observed in the thick film regime. In fact, water produced in the lubricant
decreases traction forces due to the drastic decrease of the viscosity of glycerol with water addition. 相似文献
92.
Márcio de Barros Gabriela Alves Macedo 《Journal of the American Oil Chemists' Society》2015,92(1):37-45
Alkaline esterase (carboxylic‐ester hydrolases; EC 3.1.1.1) extracted from germinated soybean seeds (Glycine max) was purified approximately 3.6 times by chromatography in a DEAE‐cellulose anion exchange column and filtration in Sephadex G100 gel. The molecular mass of the enzyme was estimated at 45 kDa by gel electrophoresis (SDS‐PAGE). The purified enzyme showed a specific activity of 5.6 U mg?1 using p‐nitrophenyl butyrate as substrate. The esterase showed optimal activity at 47 °C in moderately alkaline pH, low stability in temperatures higher than 50 °C, and high stability at pH values between 6 and 9.5. The Ca2+ and Co2+ ions proved to have a positive effect on enzyme activity; however, Hg2+ completely inhibited esterase activity. Using p‐nitrophenyl butyrate as substrate, the enzyme showed a Km of 0.39 mM, Vmax of 31.5 mM mg?1 min?1 and kcat 7.60 × 106 s?1. Regarding substrate affinity, the enzyme showed greater activity for substrates containing short‐chain fatty acids, especially p‐nitrophenyl acetate. Such characteristics give the enzyme great potential for application in the production of low molecular weight esters, in the food industry, and in chemical products. This enzyme is another new member of the family of lipases and esterases from vegetable seeds with high activity and stability in alkaline pH. 相似文献
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96.
Synthesis of poly(ester amide)s composed of lactic acid and glycolic acid units by the bulk polycondensation of metal halide salts 下载免费PDF全文
Thermal polycondensation of the potassium salt of N‐methylchloroacetyl‐6‐aminohexanoic acid (LAHK) was found to be effective in the preparation of a new poly(ester amide) based on lactic acid units with a high yield and a moderate molecular weight. The reaction started in the solid state and proceeded through the formation of potassium chloride salt as the driving force. The use of a monomer having an amide linkage diminished the secondary reactions previously found in the synthesis of polylactide from 2‐halogenopropionates. The polymerization of potassium salt of N‐chloroacetyl‐6‐aminohexanoic acid (GAHK) took place in a similar temperature range as that of the 2‐chloropropionyl derivative; in this way, it was possible to conduct the copolymerization processes. The polymerization kinetics of LAHK and its mixture with GAHK was studied by Fourier transform infrared spectroscopy. The bulk polycondensation reaction was faster for GAHK than for LAHK, but the kinetic differences were not significant enough to prevent copolymerization at a temperature close to 160°C. Therefore, new degradable materials with tuned properties according to the glycolic acid/lactic acid content were obtained. 1H‐NMR spectroscopy was useful for following the time evolution of the copolymerization process and for determining the final composition. Calorimetric data showed that all of the samples were thermally stable and that decreases in the melting temperature and enthalpy were observed at intermediate compositions. The existence of an eutectic point became proof that effective copolymerization was achieved in the thermal polycondensation process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43197. 相似文献
97.
Roseli de Souza Santos da Costa Flavia da Silva Santos Daniela de Barros Mucci Tânia Vignuda de Souza Fátima Lucia de Carvalho Sardinha Célia Regina Moutinho de Miranda Chaves Maria das Graças Tavares do Carmo 《Lipids》2016,51(12):1363-1373
The purpose of this study was to investigate the trans fatty acids (TFA) content and distribution in colostrum, mature milk, and diet of adolescent mothers, after TFA declaration in food labels became mandatory in Brazil. Participants were healthy adolescents (n 54, 15–19 years, 1–90 days postpartum) practicing exclusive breastfeeding. Milk samples were collected 3 days after delivery (colostrum) and in the third month postpartum (mature milk) by hand expression. The fatty acid composition of the milk samples was determined by gas chromatography. TFA intake corresponded to 1.23 % of total energy value. Total 18:2 TFA accounted for less than 0.5 % of the energy intake. The amount of total 18:1 TFA (mean ± SEM) was 1.9 % ± 0.14 in colostrum and 1.5 % ± 0.2 in mature milk. The total content of n‐3 PUFA was inversely correlated with the total content of 18:1 TFA in colostrum. Both in colostrum and in mature milk, vaccenic acid (11t‐18:1) was found to be the most abundant 18:1 trans isomer, followed by elaidic acid (9t‐18:1), whereas rumenic acid (9c,11t‐18:2 CLA) was the predominant 18:2 trans isomer. In conclusion, the levels of TFA of industrial sources found in the mother's diet and breast milk (colostrum and mature milk) showed a decrease in relation to those observed in studies conducted prior to the TFA labeling resolution in Brazil. However, the current low intake levels of n‐3 LCPUFA and DHA content in the milk of lactating adolescents may be insufficient for supporting adequate neurological development of the infants. 相似文献
98.
J. Saúl García-Pérez Sara P. Cuéllar-Bermúdez Alejandra Arévalo-Gallegos José Rodríguez-Rodríguez Hafiz M. N. Iqbal Roberto Parra-Saldivar 《International journal of molecular sciences》2016,17(9)
Supercritical fluid extraction (SFE) is a sustainable technique used for the extraction of lipophilic metabolites such as pigments and fatty acids. Arnica plant is considered a potential candidate material with high antioxidant and antimicrobial activities. Therefore, in this study, a locally available Heterotheca inuloides, also known as Mexican arnica, was analyzed for the extraction of high-value compounds. Based on different pressure (P), temperature (T), and co-solvent (CoS), four treatments (T) were prepared. A maximum 7.13% yield was recovered from T2 (T = 60 °C, P = 10 MPa, CoS = 8 g/min), followed by 6.69% from T4 (T = 60 °C, P = 30 MPa, CoS = 4 g/min). Some bioactive sesquiterpenoids such as 7-hydroxycadalene, caryophyllene and δ-cadinene were identified in the extracts by GC/MS. The fatty acid profile revealed that the main components were palmitic acid (C16:0), followed by linoleic acid (C18:2ω6c), α-linolenic acid (C18:3ω3) and stearic acid (C18:0) differing in percent yield per treatment. Antibacterial activities were determined by the agar diffusion method, indicating that all the treatments exerted strong antibacterial activity against S. aureus, C. albicans, and E. coli strains. The antioxidant capacity of the extracts was also measured by three in vitro assays, DPPH, TEAC and FRAP, using Trolox as a standard. Results showed high antioxidant capacity enabling pharmaceutical applications of Mexican arnica. 相似文献
99.
Sara Izadyar Mohammad Reza Hantehzadeh Mahmood Ghoranneviss Seyed Mohammad Elahi Arash Boochani 《Protection of Metals and Physical Chemistry of Surfaces》2016,52(6):1043-1045
Cu–Ni nanoparticles (NPs) thin films were prepared by Direct Current (DC) magnetron sputtering with Cu and Ni targets. The products were used as catalysts for Thermal CVD (TCVD) growing of carbon nanotubes (CNTs) from acetylene gas at 825°C. In order to characterize the nano catalysts, X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM) and to study the synthesized CNTs Scanning Electron Microscopy (SEM) and Raman Spectroscopy were applied. A remarkable CNT grown on the sub-surface of catalyst layer compared to its top is deduced from SEM images. Despite the poor catalytic activity of the top-surface, these considerations led us to conclude more catalytic activity of the sub-surface. 相似文献
100.