Artículos de revistas: "Esters"

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Janin, Yves, Vincent Hervin, Eloi Coutant y Glwadys Gagnot. "Synthesis of α-Amino Esters via α-Nitro or α-Oxime Esters: A Review". Synthesis 49, n.º 18 (9 de agosto de 2017): 4093–110. http://dx.doi.org/10.1055/s-0036-1589506.

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This review is an in-depth survey of the reported synthetic approaches for the preparation of racemic α-amino esters via the reduction of α-nitro or α-oxime ester intermediates. Accordingly, it describes the many pathways that have been designed to prepare such intermediates. This includes synthesis starting with α-nitroacetates, dialkyl malonates, acetoacetates, diethyl oxalates as well as [2+3] or [2+4] cycloadditions using, respectively, alkyl carbonocyanidate N-oxides or alkyl 2-nitrosoacrylates. This review also contains the description of a myriad of side reactions which can occur when working with α-nitro esters.1 Introduction2 α-Amino Esters from α-Nitroacetates via Condensation Reactions3 α-Amino Esters via C-Alkylation or C-Arylation of α-Nitroacetates4 α-Amino Esters from α-Nitroacetates Using Other Reactions5 Synthesis of α-Amino Esters via α-Oxime Esters6 Synthesis of α-Amino Esters via [2+3] Cycloadditions7 Synthesis of α-Amino Esters via [2+4] Cycloadditions8 On the Reduction of α-Oxime Esters9 Conclusion

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Wang, Wenchao, Fashe Li y Ying Li. "Kinetics and the fluidity of the stearic acid esters with different carbon backbones". Green Processing and Synthesis 8, n.º 1 (6 de agosto de 2019): 776–85. http://dx.doi.org/10.1515/gps-2019-0046.

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Abstract In this work, stearic acid esters were prepared using [HPY][HSO4] ionic liquids as catalysts and different kinds of alcohols and stearic acid as reactants in a self-designed reactor. Catalytic esterification, kinetics analysis and low temperature fluidity of the esters were studied. Through single-factor experiment, the optimal reaction conditions were determined for methyl stearate, ethyl ester, propyl ester, butyl ester, and amyl ester. The conversion rates under the optimized conditions were all above 97%. The kinetics of the reaction process of all five esters was analyzed by the integral method, and the activation energy, pre-exponential factor and kinetic model were obtained for the five esters. Finally, the low temperature fluidity of all esters was tested and the best value was observed for amyl alcohol. Therefore, these esters would be useful additives for reducing the condensation and cold filter plugging points of biodiesel, thus improving the cold flow properties of biodiesel.

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Rabinovitch, M., V. Zilberfarb y C. Ramazeilles. "Destruction of Leishmania mexicana amazonensis amastigotes within macrophages by lysosomotropic amino acid esters." Journal of Experimental Medicine 163, n.º 3 (1 de marzo de 1986): 520–35. http://dx.doi.org/10.1084/jem.163.3.520.

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Leishmania amastigotes parasitize almost exclusively the mononuclear phagocytes of mammals. The organisms survive and multiply within acidified vacuoles (parasitophorous vacuoles; p.v.) akin to phagolysosomes. Certain amino acid esters are known to accumulate in and disrupt lysosomes. We postulated that, since Leishmania possess lysosome-like organelles, they may be susceptible to the potentially high ester concentrations attained in the p.v. We report here that L-amino acid esters can rapidly destroy intracellular Leishmania at concentrations that do not appear to damage the host cells. L-leu-OMe, which cured greater than or equal to 90% of infected macrophages at 0.8 mM concentrations, was used in most of the experiments. L-leu-OMe was only active after infection, implying inefficient transfer from secondary lysosomes to the p.v. Parasite destruction had several features in common with lysosomal and leukocyte damage induced by the esters, i.e., inactivity of D-amino acid esters, a marked pH dependence and increased killing after ester pulses at lower temperatures. Killing depended on the amino acid and on the ester substitution. The most active of the methyl esters assayed was that of leucine, followed by those of tryptophan, glutamic acid, methionine, phenylalanine, and tyrosine. Methyl esters of seven other amino acids were inactive when tested at up to 10 mM concentrations. Among leucine esters studied, benzyl ester was sixfold more active than the methyl homolog. The dipeptide L-leu-leu-OMe produced 90% cure at 0.08 mM concentrations. Leishmanicidal activity could be related to penetration of the parasites by the esters or to toxic ester hydrolysis products released in the p.v. The first hypothesis is supported by the pH-dependent destruction of isolated amastigotes by the esters. Furthermore, relatively high concentrations of L-leucine, methanol, or benzyl alcohol were not demonstrably toxic to the amastigotes. We postulate that ester concentrations sufficient to damage the intracellular amastigotes may be obtained within the p.v. after exposure of infected macrophages to the esters. Esters preferentially hydrolyzed by parasite enzymes may be expected to be leishmanicidal, but less damaging to the host.

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Liu, Shanshan, Mingyue Shen, Jianhua Xie, Bohan Liu y Chang Li. "Effects of Endogenous Antioxidants in Camellia Oil on the Formation of 2-Monochloropropane-1, 3-diol Esters and 3-Monochloropropane-1,2-diol Esters during Thermal Processing". Foods 13, n.º 2 (14 de enero de 2024): 261. http://dx.doi.org/10.3390/foods13020261.

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2-Monochloropropane-1, 3-diol (2-MCPD) esters and 3-monochloropropane-1,2-diol (3-MCPD) esters, a class of substances potentially harmful to human health, are usually formed during the refining of vegetable oils under high temperature. The effects of endogenous antioxidants in vegetable oils on the formation of 2- and 3-MCPD esters is still unknown. In this study, the effects of endogenous antioxidants (α-tocopherol, stigmasterol and squalene) on the formation of 2- and 3-MCPD esters in model thermal processing of camellia oil were investigated. The possible formation mechanism of 2- and 3-MCPD esters was also studied through the monitoring of acyloxonium ions, the intermediate ions of 2- and 3-MCPD esters formation, and free radicals by employing infrared spectra and electron paramagnetic resonance (EPR), respectively. The results indicated that the addition of α-tocopherol had either promoting or inhibiting effects on the formation of 2- and 3-MCPD esters, depending on the amount added. Stigmasterol inhibited the formation of 3-MCPD ester and 2-MCPD ester at low concentrations, while promoting their formation at high concentrations. Squalene exhibited a promotional effect on the formation of 3-MCPD ester and 2-MCPD ester, with an increased promotion effect as the amount of squalene added increased. The EPR results suggested that CCl3•, Lipid alkoxyl, N3• and SO3• formed during the processing of camellia oil, which may further mediate the formation of chlorpropanol esters. This study also inferred that squalene promotes the participation of the free radical in chlorpropanol ester formation.

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Kim, Y. B., C. H. Jung, S. J. Choi, W. J. Seo, S. H. Cha y D. E. Sok. "Potentiation effect of choline esters on choline-catalysed decarbamoylation of dimethylcarbamoyl-acetylcholinesterase". Biochemical Journal 284, n.º 1 (15 de mayo de 1992): 153–60. http://dx.doi.org/10.1042/bj2840153.

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The choline esters potentiated the choline-catalysed decarbamoylation of dimethylcarbamoyl-acetylcholinesterase in proportion to the length of acyl group, although esters containing an acyl chain longer than the hexanoyl group exhibited a corresponding decrease in the potentiation. In structural requirement analysis it was found that both the quaternary ammonium moiety and the ester bond were important for the effective acceleration of choline-catalysed decarbamoylation. In general, the respective thiocholine ester was found to be more effective than the corresponding choline ester. Whereas the binding affinity (Ka) of choline in the decarbamoylation was not significantly altered, the maximum decarbamoylation rate (kr(max.)) of choline was greatly enhanced in the presence of choline esters or thiocholine esters. Along with the above observation, the isotope solvent effect, the effect of ionic strength and the antagonism studies demonstrate that the choline esters or thiocholine esters may interact with one of peripheral anionic sites, and thereby make the choline-catalysed decarbamoylation more favourable.

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Rozga, Pawel, Abderrahmane Beroual, Piotr Przybylek, Maciej Jaroszewski y Konrad Strzelecki. "A Review on Synthetic Ester Liquids for Transformer Applications". Energies 13, n.º 23 (4 de diciembre de 2020): 6429. http://dx.doi.org/10.3390/en13236429.

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Synthetic esters have become more and more popular in last few decades, explaining the increasing number of units filled with this liquid year by year. They have been investigated under different aspects, both from the fundamental point of view and breakdown mechanisms, well as from the application point of view. However, their use in high voltage equipment is always a challenge and deeper knowledge of the various aspects that can be encountered in their exploitation is needed. The intent of this review paper is to present the recent research progress on synthetic ester liquid in relation to the selected issues, most important for ester development in the authors’ opinion. The described issues are the breakdown performance of synthetic esters, lightning impulse strength and pre-breakdown phenomena of synthetic esters, synthetic esters-based nanofluids, combined paper-synthetic ester based insulating systems, application of synthetic ester for retro-filling and drying of mineral oil-immersed transformers, DGA(dissolved gas analysis)-based diagnosis of synthetic esters filled transformers as well as static electrification of synthetic esters. The different sections are based both on the data available in the literature, but above all on the authors’ own experience from their research work on synthetic ester liquids for electrical application purposes.

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Li, Huaqiang, Linfeng Xia, Shengwei Cai, Zhiqiang Huang, Jiaqi Li y Lisheng Zhong. "Influence of Molecule Structure on Lightning Impulse Breakdown of Ester Liquids". Energies 14, n.º 4 (18 de febrero de 2021): 1061. http://dx.doi.org/10.3390/en14041061.

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Ester liquids are environmentally friendly insulating oils, and they can be used as an alternative to mineral oil in transformers, even though in most countries spills of ester oils must be treated like spills of mineral oil. Furthermore, the breakdown characteristics of ester liquids are worse than those of mineral oils in heterogeneous electric fields. In this paper, we present a comprehensive experimental research on both positive and negative lightning impulse breakdown properties in point-plane geometries with gaps varying from 1 mm to 50 mm. The breakdown voltages and streamer velocities of five kinds of ester liquids, including natural ester, synthetic ester, and three kinds of single component esters have been measured. The results show that the double bonds have no effect on the breakdown voltage of ester liquids. The average streamer velocities of mono-esters are faster than that of other esters under positive polarity, and the breakdown voltages of all esters are close.

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Chen, Ming y Shan Shan Li. "The catalysts for synthesis of citrate esters plasticizers and the application of citrate esters plasticizers". Cambridge Science Advance 2024, n.º 2 (4 de junio de 2024): 13–17. http://dx.doi.org/10.62852/csa/2024/10.

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The latest research progress in citrate esters plasticizers at home and abroad was introduced. The advance in the catalysts for the syn thesis of citrate esters plasticizers and the application of citrate esters plasticizers were reviewed in detail. The catalysts for the synthesis of citrate esters included sulfonic acid, solid super acid, heteropolyacids, ionic liquids and inorganic salts. The citric acid ester plasticizers were applied in the fields of food packaging, children's toys and medical instrument. The development prospects of citric acid ester plasticizers were outlined.

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9

Wang, Liyuan, Ying Ying, Zhengyan Hu, Tianjiao Wang, Xianghong Shen y Pinggu Wu. "Simultaneous Determination of 2- and 3-MCPD Esters in Infant Formula Milk Powder by Solid-Phase Extraction and GC-MS Analysis". Journal of AOAC INTERNATIONAL 99, n.º 3 (1 de mayo de 2016): 786–91. http://dx.doi.org/10.5740/jaoacint.15-0310.

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Abstract The objective of this study was to establish a method for detecting fatty acid esters of chloropropanols [including 2-monochloropropane-1,3-diol (2-MCPD) ester and 3-monochloropropane-1,2-diol (3-MCPD) ester] in infant milk powder using isotope dilution and GC-MS. The fat fraction in infant milk powder samples was extracted and treated with sodium methylate–methanol to cleave the ester bonds of the 2- and 3-MCPD esters. The resultant 2- and 3-MCPDs in the samples were purified with matrix solid-phase liquid–liquid extraction and derivatized with heptafluorobutyryl imidazole for GC-MS analysis. Standard samples of deuterium isotope–labeled 2- and 3-MCPD palmitic acid double esters and stearic acid double esters were used as the internal standards. We also detected 2- and 3-MCPD ester contents in 88 commercial samples of infant formula milk powder using this system. The detection system we established showed a good linearity of 2- and 3-MCPD ester contents in serially diluted standard solutions within the concentration range 25−1000 μg/L, with r2 > 0.9995 and an LOD of 30 μg/kg for both of the MCPD esters. The recoveries of the two MCPD esters spiked at 25, 50, 100, and 200 μg/kg in blank infant formula milk ranged from 98.2 to 110.5%, with RSDs <4.8%, suggesting good accuracy and reliability of this method. In the 88 commercial infant formula milk powder samples, the mean content of 2-MCPD ester was 41 μg/kg (0–52 μg/kg) and that of 3-MCPD was 185 μg/kg (0–316 μg/kg). Based on these results, we estimated the exposure levels of the two MCPD esters in infants fed on formula milk, and the results indicate potential health risks of consuming formula milk products contaminated by the two MCPD esters.

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Syarifah Ali, Gita, Rista Fitria, Mira Rivai, Erliza Hambali, Rini Purnawati y Ari Imam Sutanto. "Oleochemical Synthesis of Sucrose Esters from Methyl Esters of Palm Stearic and Oleic Fatty Acids". IOP Conference Series: Earth and Environmental Science 1354, n.º 1 (1 de junio de 2024): 012027. http://dx.doi.org/10.1088/1755-1315/1354/1/012027.

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Abstract Palm oil contains fatty acids such as stearic ranges from 3.40 – 5.47% and oleic ranges from 34.85 – 40.78% which can be used as materials for the synthesis of sucrose ester. This study aimed to increase and optimize the potential of palm oil raw materials through the oleochemical synthesis of sucrose ester. The process of sucrose ester synthesis consisted of two stages, i.e., the esterification process of fatty acids into methyl esters and the transesterification process of fatty acid methyl esters with sucrose to become sucrose esters. Esterification of stearic and oleic fatty acids was performed using H2SO4 catalyst and methanol as a solvent. Transesterification of sucrose with stearic and oleic methyl esters was performed using two types of catalysts K2CO3 6% and Na2CO3 6%, without solvents. The results showed that sucrose ester made from stearic acid methyl ester with K2CO3 catalyst tended to achieve better performance and physicochemical properties as follows: pH ranged from 10.29 – 10.45, foam stability ranged from 55.497 – 88.082%, emulsion stability ranged from 40.211 – 78.435%, surface tension ranged from 25.4 – 27.60 dyne/cm, and interfacial tension ranged from 9.69 – 10.91dynes/cm.

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Ghalia, Mohamed H., Mohamed Abd El-Hamid, Mohamed A. Zweil, Abd El-Galil E. Amr y Shimaa A. Moafi. "Synthesis and Reactions of New Chiral Linear and Macrocyclic Tetraand Penta-peptide Candidates". Zeitschrift für Naturforschung B 67, n.º 8 (1 de agosto de 2012): 806–18. http://dx.doi.org/10.5560/znb.2012-0116.

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9a A series of linear and macrocyclic pentapeptide derivatives have been prepared via the coupling of pyridine-2,6-dicarboxylic acid (1) or pyridine-2,6-dicarbonyl dichloride (2) with appropriate amino acid methyl esters. The coupling of 1or 2with aminoacid methyl esters gave the corresponding pyridine dipeptide methyl esters 3, which were hydrolyzed with sodium hydroxide to the corresponding acids 4. The latter compounds 4were coupled with other amino acid methyl esters to afford the corresponding tetrapeptide esters 5, which were hydrolyzed with sodium hydroxide to the corresponding acids 6. Cyclization of tetrapeptide acids with L-lysine methyl ester or with aliphatic diamide derivatives afforded the corresponding cyclic pentapeptide methyl ester derivatives 7and cyclic tetrapeptide diamines 8, respectively. Finally, hydrolysis with 1 N sodium hydroxide or hydrazinolysis with hydrazine hydrate of methyl esters 7afforded the corresponding acids - e and hydrazides 10a - e, respectively

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Ferenczi, Alejandra, Nobuko Sugimoto y Randolph M. Beaudry. "Emission Patterns of Esters and Their Precursors Throughout Ripening and Senescence in ‘Redchief Delicious’ Apple Fruit and Implications Regarding Biosynthesis and Aroma Perception". Journal of the American Society for Horticultural Science 146, n.º 5 (septiembre de 2021): 297–328. http://dx.doi.org/10.21273/jashs05064-21.

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The volatile profile of ‘Redchief Delicious’ apple (Malus ×domestica Borkh.) fruit was evaluated at 18 time points from 3 weeks before to 8 weeks after onset of autocatalytic ethylene production to capture the dynamics associated with development from mature green to senescent fruit. Minor amounts of ester production began several days before the onset of ethylene production. Ester production rose rapidly as internal ethylene levels increased beyond 22 nmol·L−1 (0.5 µL·L−1). Peak ester production roughly coincided with maximum ethylene synthesis, declining thereafter. Ester production was further evaluated according to the acid- (alkanoate) and alcohol- (alkyl) derived portions of the ester. The maximum rate of production for a given ester tended to occur later in development as the chain length of the alcohol-derived portion declined. The production rate for many esters paralleled the rate of emanation of their respective alcohol substrates, suggesting that availability of the alcohols limits ester production more than availability of the acid substrates. Combining production rates with sensory descriptors and human sensitivity to individual volatiles permitted approximations of aroma sensations likely engendered by the fruit throughout ripening. Overripe and alcoholic sensations are predicted to increase 2 weeks after the initiation of ripening in response to an increase in the production of ethyl esters. Acetate esters predominated, comprising 50% to 80% of esters throughout maturation and ripening, indicating that the substrate acetyl-CoA may be at saturating levels for alcohol acyl transferase (AAT) at the final step of ester formation. Acetate feeding did not enhance ester production, although label from 13C-acetate was extensively incorporated into esters. The data are consistent with the action of multiple AAT isozymes differing in activity and substrate preference. Incorporation of labeled 13C-acetate into precursors of esters, alcohols, and acids, reflected ester biosynthesis via 1- and 2-carbon chain elongation pathways in ripening ‘Redchief Delicious’ apple fruit.

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Mammadyarov, M. A., K. O. Israfilova, F. Kh Aliyeva y F. I. Akhmedov. "Research of electric conductivity of esters of (C4-C10) terminal dicarboxylic acids depending on their chemical structure". World of petroleum products 06 (2021): 29–32. http://dx.doi.org/10.32758/2782-3040-2021-0-6-29-32.

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Using a teraohmmeter, the resistance indices of synthesized symmetric, asymmetric and complex esters of terminal dicarboxylic acids (TDA) of various structures were determined. The specific resistance and electrical conductivity of the obtained samples were determined. The properties of electrical conductivity are investigated depending on the structure of diesters and complex esters of TDA. It was found that in complex esters of TDA containing 3 or 4 ester groups, with an increase in the length of the carbon chain in the acid molecule, the electrical conductivity decreases. It was revealed that symmetric, asymmetric and complex esters of succinic acid, complex ester of adipic acid (based on octanol-1, ethylene glycol and caproic acid) and dibenzyl ester of sebacic acid have relatively good electrical conductivity.

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Jargalsaikhan, U., S. Javzan, D. Selenge, D. Nedelcheva, S. Philipov y J. Nadmid. "Fatty acids and their esters from Cicuta virosa L." Mongolian Journal of Chemistry 14 (3 de octubre de 2014): 71–74. http://dx.doi.org/10.5564/mjc.v14i0.203.

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n-Hexane and chloroform fractions of aerial parts and roots of Cicuta virosa L. were investigated by GC-MS. As a result of the study 25 fatty acids and their esters have been identified. Two unsaturated esters such as linoleic acid ethyl ester (IX, 16.66%), and n- hexadecanoic acid ethyl ester (VII, 10.12%), the fatty acid n-hexadecanioc acid (VI, 8.10%) made up the bulk of the aerial parts. Four unsaturated esters such as linoleic acid ethyl ester (IX, 10.15%), dibutylphthalate (XII, 9.55%), n-hexadecanoic acid ethyl ester (VII, 8.19%) and 9, 12, 15 - octadecatrienoic acid ethyl ester (X, 5.9%), two fatty acids as n-hexadecanoic acid (VI, 8,15%) and 9,12-octadecadienoic acid (VIII, 4,5%) predominated in the roots of Cicuta virosa L. These known fatty acids and their esters were found for the first time in this plant species. DOI: http://dx.doi.org/10.5564/mjc.v14i0.203 Mongolian Journal of Chemistry 14 (40), 2013, p71-74

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Sumarni, Erwin Abdul Rahim, Ni Ketut Sumarni, Ruslan, Hardi Ys. y Moh Mirzan. "Sintesis Metil Ester Asam Lemak dari Biji Alpukat (Parsea americana Mill) Menggunakan Polimer Penyangga Katalis Berbahan Dasar Eugenol". KOVALEN: Jurnal Riset Kimia 6, n.º 3 (30 de diciembre de 2020): 206–11. http://dx.doi.org/10.22487/kovalen.2020.v6.i3.13053.

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Research on the manufacture of methyl esters from avocado seeds (Parsea americana Mill) with eugenol-based catalysts has been conducted. The aim is to determine the catalyst concentration used to produce methyl esters with the highest rendement and determine the composition of fatty acid methyl ester in avocado seeds. This study was used variations in concentrations of 0.25%, 1%, 1.75%, 2.25%, and 3%. The results of this study showed that the best concentration is 2.25% with the calculation of the results of 24.8% methyl esters in avocado seeds, namely lignoceric and octadecenoic acid methyl ester. Keywords: Avocado seeds, fatty acid methyl esters

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Mozhaitsev, Evgenii S., Alexandra L. Zakharenko, Evgeniy V. Suslov, Dina V. Korchagina, Olga D. Zakharova, Inna A. Vasil'eva, Arina A. Chepanova et al. "Novel Inhibitors of DNA Repair Enzyme TDP1 Combining Monoterpenoid and Adamantane Fragments". Anti-Cancer Agents in Medicinal Chemistry 19, n.º 4 (25 de junio de 2019): 463–72. http://dx.doi.org/10.2174/1871520619666181207094243.

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Background and Objective: The DNA repair enzyme tyrosyl-DNA-phosphodiesterase 1 (TDP1) is a current inhibition target to improve the efficacy of cancer chemotherapy. Previous studies showed that compounds combining adamantane and monoterpenoid fragments are active against TDP1 enzyme. This investigation is focused on the synthesis of monoterpenoid derived esters of 1-adamantane carboxylic acid as TDP1 inhibitors. Methods: New esters were synthesized by the interaction between 1-adamantane carboxylic acid chloride and monoterpenoid alcohols. The esters were tested against TDP1 and its binding to the enzyme was modeling. Results: 13 Novel ester-based TDP1 inhibitors were synthesized with yields of 21–94%; of these, nine esters had not been previously described. A number of the esters were found to inhibit TDP1, with IC50 values ranging from 0.86–4.08 µM. Molecular modelling against the TDP1 crystal structure showed a good fit of the active esters in the catalytic pocket, explaining their potency. A non-toxic dose of ester, containing a 3,7- dimethyloctanol fragment, was found to enhance the cytotoxic effect of topotecan, a clinically used anti-cancer drug, against the human lung adenocarcinoma cell line A549. Conclusion: The esters synthesized were found to be active against TDP1 in the lower micromolar concentration range, with these findings being corroborated by molecular modeling. Simultaneous action of the ester synthesized from 3,7-dimethyloctanol-1 and topotecan revealed a synergistic effect.

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Nesterkina, Mariia, Ulrich R. Bernier, Nurhayat Tabanca y Iryna Kravchenko. "Repellent activity of monoterpenoid esters with neurotransmitter amino acids against yellow fever mosquito, Aedes aegypti". Open Chemistry 16, n.º 1 (9 de marzo de 2018): 95–98. http://dx.doi.org/10.1515/chem-2018-0015.

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AbstractRepellent activity of monoterpenoid esters (1-6) with neurotransmitter amino acids (GABA and glycine) was investigated against Aedes aegypti by using a “cloth-patch” assay and compared to reference standard N,N-diethyl-3-methylbenzamide (DEET). Monoterpenoid esters showed repellent activity with minimum effective dosages (MED) in the range of 0.031-0.469 mg/cm2. The carvacrol ester of GABA (2, MED of 0.031 ± 0.008 mg/cm2) exhibited the highest repellency of six monoterpenoid esters tested in comparison to the standard repellent DEET (MED of 0.009 ± 0.002 mg/cm2); however, the repellent activity of carvacrol-glycine ester (5) decreased 4-fold compared to the carvacrol-GABA derivative (2). The repellent activities of menthol GABA (1, MED= 0.375 ± 0.000 mg/cm2) and glycine ester (4, MED=0.312 ± 0.063 mg/cm2) were similar The guaiacol-glycine ester (6) was 3.75-fold more efficacious than the guaiacol ester of GABA (3). In the present study, we report repellent efficacy of prolonged exposure to GABA and glycine esters of menthol, carvacrol, guaiacol (1-6) as compared to the repellent activities of their monoterpene moieties alone.

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Nottingham, Stephen F., Orestes T. Chortyk y Michael G. Stephenson. "Sugar Esters from Nicotiana Species as Potential Insecticides Against the Sweetpotato Whitefly (Homoptera: Aleyrodidae)". Journal of Entomological Science 31, n.º 3 (1 de julio de 1996): 331–39. http://dx.doi.org/10.18474/0749-8004-31.3.331.

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Eight Nicotiana species and three species accessions were grown and their sugar esters were isolated. Nicotiana trigonophylla, N. palmeri, and N. glutinosa gave the highest sugar ester yields. Sugar ester isolates were bioassayed at concentrations from 1.0 to 0.05 mg/ml against nymphs of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). The highest mortalities were observed with isolates from N. gossei and N. langsdorffii. As the sugar ester isolate from N. gossei contained both sucrose esters and glucose esters, these were bioassayed separately and both caused high mortality. The isolates of three N. glutinosa accessions varied in sucrose ester and labdane terpenoid content; labdane fractions were less toxic than sucrose ester fractions. Nicotiana glutinosa 24, N. langsdorffii, and N. trigonophylla, in addition to N. gossei, showed good potential as sources of biorational insecticide against whitefly.

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Bardi, Laura, Cristina Crivelli y Mario Marzona. "Esterase activity and release of ethyl esters of medium-chain fatty acids by Saccharomyces cerevisiae during anaerobic growth". Canadian Journal of Microbiology 44, n.º 12 (1 de diciembre de 1998): 1171–76. http://dx.doi.org/10.1139/w98-124.

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During anaerobic fermentation, Saccharomyces cerevisiae releases large amounts of medium-chain fatty acids (MCFAs) and related ethyl esters which are very important for aromatic quality of fermented beverages. The physiological function of ester synthesis is not yet understood. As MCFAs are toxic, their conversion to esters has been proposed to be a detoxification mechanism. Esterases possess ester synthesizing ability. Throughout an anaerobic fermentation of a lipid-free synthetic medium carried out with a S. cerevisiae strain selected for wine making, we have monitored MCFA and ethyl ester production and, at the same time, measured growth and esterasic activity of intact cells. Because no correlation was found between the concentration of each fatty acid and its ethyl ester, there is no evidence that ester synthesis reduces the toxicity of MCFAs. Esterasic activity did not show any correlation with ester synthesis, but it was related to the release of MCFAs. A model is proposed in which ester synthesis is a consequence of the arrest of lipid biosynthesis resulting from a lack of oxygen. Under these conditions, an excess of acyl coenzyme A is produced, and acyl esters are formed as secondary products of reactions aimed at recovering free coenzyme A.Key words: yeast, esterase, medium-chain fatty acids, toxicity, ethyl esters.

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Hennessy, Mary C., Hirenkumar Gandhi y Timothy P. O’Sullivan. "Organocatalytic Asymmetric Peroxidation of γ,δ-Unsaturated β-Keto Esters—A Novel Route to Chiral Cycloperoxides". Molecules 28, n.º 11 (24 de mayo de 2023): 4317. http://dx.doi.org/10.3390/molecules28114317.

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A methodology for the asymmetric peroxidation of γ,δ-unsaturated β-keto esters is presented. Using a cinchona-derived organocatalyst, the target δ-peroxy-β-keto esters were obtained in high enantiomeric ratios of up to 95:5. Additionally, these δ-peroxy esters can be readily reduced to chiral δ-hydroxy-β-keto esters without impacting the β-keto ester functionality. Importantly, this chemistry opens up a concise route to chiral 1,2-dioxolanes, a common motif in many bioactive natural products, via a novel P2O5-mediated cyclisation of the corresponding δ-peroxy-β-hydroxy esters.

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21

Santoso, Umam, M. Rizky, Sumari Sumari, Anugrah Ricky Wijaya, Rini Retnosari y Muhammad Roy Asrori. "Effect of various alcohols in Trans-Esterification of Palm Oil (CPO) with CaO-MgO Catalyst". Rekayasa Bahan Alam dan Energi Berkelanjutan 5, n.º 1 (28 de junio de 2021): 1–9. http://dx.doi.org/10.21776/ub.rbaet.2021.005.01.01.

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The purpose of this research is the synthesis of alkyl esters from CPO through transesterification reaction using catalyst CaO-MgO. This experimental laboratory research through stages: (1) CPO refinement, (2) determination of CPO free fatty acid numbers, (3) activation of CaO-MgO catalysts, (5) synthesis of alkyl esters from CPO with alcohol (methanol and ethanol), (6) identification of the components of synthesized alkyl ester using GC-MS,characterization of alkyl esters including density, viscosity, refractive index and acid number test. The results showed that (1) alkyl esters can be synthesized from CPO through the transesterification reaction with methanol and CaO-MgO catalysts with a yield of 85.72%, while the transformation of ethanol is difficult to form ethyl ether (2) the character of methyl ester: density 0.86 g/mL, viscosity 3.23 cSt, refractive index 1.44819, and acid number 0.747 mg KOH/g methyl ester, (3) the main component of the synthesized alkyl ester contains 1.20% methyl myristic compound, methyl palmitate 40.637% methyl linoleate 9.332%, methyl 7-octadecenoate 42.986%, and methyl stearate 4.427%.

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22

Dali, Seniwati, Firdaus Firdaus y Hendra J. Rusman. "Produksi DAG Dari Virgin Coconut Oil (VCO) Melalui Reaksi Trans-Esterifikasi Menggunakan Enzim Lipase Dedak Padi (Oryza Sativa L.) Spesifik C18-20 Terimobilisasi Karbon Aktif Sebagai Biokatalis". Indo. J. Chem. Res. 5, n.º 1 (31 de julio de 2017): 37–46. http://dx.doi.org/10.30598//ijcr.2017.5-sen.

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This research aims to produce DAG of the VCO through the substrate reaction of trans-esterification using lipase enzymes specifically C18-20 from rice bran (Oryza Sativa L.) immobiled of activated carbon as a catalyst. Phases of this research starts with the enzyme lipase do immobile using activated carbon; next enzymes of immobile used to produce DAG through the trans-esterification reaction using a VCO as a substrate and methanol as ko-substrate; DAG and methyl ester produced identified using FTIR instrument and GC-MS instruments. The results showed that there were three compounds DAG and three compound methyl ester produced trans-esterification reaction, namely (1) 1-laurin, 3-heksanoin esters of glycerol; (2) 2-laurin, 3-oktanoin esters of glycerol; (3) 1-laurin, 3-heksanoin esters of glycerol; (4) methyl ester oleic; (5) methyl ester stearic acids; and (6) methyl ester arachidat.

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23

de, Hong, Hong Liu y Zhao Wang. "Optimization of the fermentation conditions and substrate specifity of mycelium-bound ester hydrolases of Aspergillus oryzae Cs007". Journal of the Serbian Chemical Society 80, n.º 1 (2015): 1–8. http://dx.doi.org/10.2298/jsc140401071d.

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In order to improve mycelium-bound ester hydrolases activities of Aspergillus oryzae Cs007, the main production conditions were investigated. The ester hydrolases activities were simultaneously determined by titration assay and spectrophotometric assay methods, using olive oil and p-nitrophenyl esters as substrates, respectively. The optimum carbon source and nitrogen source were olive oil and peptone, with the concentrations of 1% and 2.2%, respectively. The effects of carbon source, nitrogen source and their concentrations on the production of enzymes were identical when the enzymes activities were assayed by the two methods. The mycelium-bound enzymes showed hydrolytic activity toward all the tested p-nitrophenyl esters, triglycerides and fatty acid ethyl esters. But it showed greater preference for long-chain triglycerides and short-chain p-nitrophenyl esters.

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24

Baum, James Clayton, Bradley Eugene Black, Laura Precedo, John Edward Goehl y Richard Francis Langler. "Sulfonyl esters 6. Elucidation of the first sequence in the Trithioorthoformate Reaction". Canadian Journal of Chemistry 73, n.º 3 (1 de marzo de 1995): 444–52. http://dx.doi.org/10.1139/v95-058.

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The one-pot conversion of a mercaptan and an aryl methanesulfonate into a trithioorthoformate is described. The intermediacy of a sulfide-sulfonate ester is firmly established. Experimental and computational results permit the formulation of a possible pathway for the formation of the intermediate sulfide-sulfonate ester. Keywords: single electron transfer, sulfonate esters, sulfide-sulfonate esters.

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25

Alfieri, Silvia C., V. Zilberfarb y M. Rabinovitch. "Destruction of Leishmania mexicana amazonensis amastigotes by leucine methyl ester: protection by other amino acid esters". Parasitology 95, n.º 1 (agosto de 1987): 31–41. http://dx.doi.org/10.1017/s0031182000057528.

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SUMMARYl-Amino acid esters, such as leucine methyl ester (Leu-OMe) can destroy intracellular as well as isolated amastigotes of Leishmania mexicana amazonensis by a mechanism which may involve ester hydrolysis by parasite enzymes. We show here that several other esters prevented the killing of the amastigotes by Leu-OMe. Destruction of Leishmania within macrophages in culture was assessed microscopically and viability of isolated parasites was monitored by reduction of the tetrazolium MTT. The main features of the protective effect were similar for intracellular and for isolated amastigotes. Thus, (i) effective prevention of parasite killing required that the protective ester be present in the medium prior to and during exposure of infected cells or parasites to Leu-OMe; (ii) the same esters protected intracellular and isolated Leishmania against damage by Leu-OMe. Ranks of protective activity, as determined on isolated amastigotes were: Gly-OBz > Tyr-OMe > Ile-OMe > Met-OMe > Val-OMe > Ala-OMe > Gly-OMe > D-Leu-OMe; (iii) several esters were inactive in both systems (Leu-OBz, Trp-OMe and Phe-OMe). Protective activity was associated with leishmanicidal (e.g. Gly-OBz, Tyr-OMe) as well as with non-leishmanicidal (e.g. Ile-OMe, Val-OMe) esters. The results are compatible with the hypothesis that protective esters inhibit the activity of parasite enzyme(s) which hydrolyse Leu-OMe.

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26

Schrøder, Malene, Christiane Fricke, Kirsten Pilegaard, Morten Poulsen, Ingmar Wester, Dieter Lütjohann y Alicja Mortensen. "Effect of rapeseed oil-derived plant sterol and stanol esters on atherosclerosis parameters in cholesterol-challenged heterozygous Watanabe Heritable Hyperlipidaemic rabbits". British Journal of Nutrition 102, n.º 12 (22 de septiembre de 2009): 1740–51. http://dx.doi.org/10.1017/s0007114509991206.

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Rapeseed oil (RSO) is a novel source of plant sterols, containing the unique brassicasterol in concentrations higher than allowed for plant sterol blends in food products in the European Union. Effects of RSO sterols and stanols on aortic atherosclerosis were studied in cholesterol-fed heterozygous Watanabe heritable hyperlipidaemic (Hh-WHHL) rabbits. Four groups (n 18 per group) received a cholesterol-added (2 g/kg) standard chow or this diet with added RSO stanol esters (17 g/kg), RSO stanol esters (34 g/kg) or RSO sterol esters (34 g/kg) for 18 weeks. Feeding RSO stanol esters increased plasma campestanol (P < 0·001) and sitostanol (P < 0·001) and aortic campestanol (P < 0·05) compared with controls. Feeding RSO sterol esters increased concentrations of plasma campesterol (P < 0·001), sitosterol (P < 0·001) and brassicasterol (P < 0·001) and aortic campesterol (P < 0·01). Significantly lower plasma cholesterol (P < 0·001) was recorded in the treated groups after 3 weeks and throughout the study. LDL-cholesterol was reduced 50 % in the high-dose RSO sterol ester (P < 0·01) and high-dose RSO stanol ester (P < 0·001) groups compared with controls. Atherosclerotic lesions were found in three rabbits in each of the RSO stanol ester groups and in one in the RSO sterol ester group. Aortic cholesterol was decreased in the treated groups (P < 0·001) in response to lowering of plasma cholesterol induced by RSO sterol and stanol esters. In conclusion, RSO stanol and sterol esters with a high concentration of brassicasterol were well tolerated. They were hypocholesterolaemic and inhibited experimental atherosclerosis in cholesterol-fed Hh-WHHL rabbits. A significant uptake of plant sterols into the blood and incorporation of campesterol and campestanol into aortic tissue was recorded.

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27

Huseynov, K. Z., P. A. Aliyev, M. A. Mirzoyeva, I. M. Eyvazova y N. A. Aliyev. "SYNTHESIS OF ALKOXYCARBONYLMETHYL ESTERS OF THIOACETIC AND THIOBENZOIC ACIDS AND THEIR INVESTIGATION AS ADDITIVES TO LUBRICATING OILS". Chemical Problems 21, n.º 3 (2023): 294–300. http://dx.doi.org/10.32737/2221-8688-2023-3-294-300.

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The method for obtaining alkoxycarbonylmethyl esters of thioacetic acid, based on the interaction of mercaptoacetic acid esters with acetic anhydride in an alkaline medium was proposed. It showed that an alternative way to obtain alkoxycarbonylmethyl esters of thioacetic acid is the reaction of mercaptoacetic acid esters with acetyl chloride in the presence of equimolar quantities of triethylamine. The interaction of mercaptoacetic acid esters with benzoyl chloride in the presence of equimolar amounts of triethylamine was used to synthesize appropriate alkoxycarbonylmethyl esters of thioacetic and thiobenzoic acids. Study into synthesized compounds as additives to lubricating oils revealed that addition of butoxycarbonyl methyl ester of thioacetic acid at a concentration of 1% in M-8 oil practically eliminated its corrodibility, while butoxycarbonyl methyl esters of thioacetic and thiobenzoic acids also had some lubricating and antimicrobial properties.

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28

Goffreda, J. C., J. C. Steffens y M. A. Mutschler. "Association of Epicuticular Sugars with Aphid Resistance in Hybrids with Wild Tomato". Journal of the American Society for Horticultural Science 115, n.º 1 (enero de 1990): 161–65. http://dx.doi.org/10.21273/jashs.115.1.161.

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Behavioral studies have shown that aphid resistance in Lycopersicon pennellii (Corr.) D'Arcy is due to the presence of sugar esters in glandular exudate of the type IV trichomes. In this study, various methods for the estimation of epicuticular sugar ester concentrations were examined. There was a significant negative relationship between the concentration of sugar esters on the leaf and the level of potato aphid infestation in a segregating L. esculentum × L. pannellii F2 population. Selection for sugar ester accumulation should be an efficient selection technique for the aphid resistance of L. pennellii and other species that synthesize epicuticular sugar esters.

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29

Srivastava, Akanksha. "CURING AND DEGRADATION BEHAVIOR OF VINYL ESTERS OF CYCLOALIPHATIC EPOXY RESINS". International Journal of Advanced Research 10, n.º 03 (31 de marzo de 2022): 944–49. http://dx.doi.org/10.21474/ijar01/14475.

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Curing and degradation behavior of two unsaturated esters based on cycloaliphatic epoxy resin containing glycidyl epoxy group (C1E) and epoxy cyclohexane group (C2E)were studied using DSC and TGA Techniques. DSC thermograms of ester C1E and C2E mixed with reactive styrene (40% w/w) and initiator benzoyl peroxide (2%) shows that the curing of ester C2E takes place at higher temperature range in comparison to C1E due to their dense rigid structure. The degradation behavior of cured esters are studied using thermal analyst 2000 equipped with 2950 thermal gravimetric analysis at heating rate 100C min-1. The TG and DTG thermogram of both esters show single step degradation. The temperature of 1-10% weight loss for both ester was studied from TGA. Thethermal stability of the ester C2E was found to be higher than that of C1E.

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30

Srivastava, Akanksha. "CURING AND DEGRADATION BEHAVIOR OF VINYL ESTERS OF CYCLOALIPHATIC EPOXY RESINS". International Journal of Advanced Research 10, n.º 03 (31 de marzo de 2022): 944–49. http://dx.doi.org/10.21474/ijar01/14475.

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Curing and degradation behavior of two unsaturated esters based on cycloaliphatic epoxy resin containing glycidyl epoxy group (C1E) and epoxy cyclohexane group (C2E)were studied using DSC and TGA Techniques. DSC thermograms of ester C1E and C2E mixed with reactive styrene (40% w/w) and initiator benzoyl peroxide (2%) shows that the curing of ester C2E takes place at higher temperature range in comparison to C1E due to their dense rigid structure. The degradation behavior of cured esters are studied using thermal analyst 2000 equipped with 2950 thermal gravimetric analysis at heating rate 100C min-1. The TG and DTG thermogram of both esters show single step degradation. The temperature of 1-10% weight loss for both ester was studied from TGA. Thethermal stability of the ester C2E was found to be higher than that of C1E.

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31

Langer, Dominik, Barbara Wicher, Wojciech Szczołko, Maria Gdaniec y Ewa Tykarska. "Self-assembly modes of glycyrrhetinic acid esters in view of the crystal packing of related triterpene molecules". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 72, n.º 4 (1 de agosto de 2016): 584–92. http://dx.doi.org/10.1107/s2052520616008180.

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The crystal structures of three ester derivatives of glycyrrhetinic acid (GE) are reported. X-ray crystallography revealed that despite differences in the size of the ester substituents (ethyl, isopropyl and 2-morpholinoethyl) the scheme of molecular self-assembly is similar in all three cases but differs significantly from that observed in other known GE esters. According to our analysis, the two basic patterns of self-assembly of GE esters observed in their unsolvated crystals correspond to two distinct orientations of the ester groups relative to the triterpene backbone. Moreover, comparison of the self-assembly modes of GE esters in their unsolvated forms with the supramolecular organization of GE and carbenoxolone in their solvated crystals revealed that ester substituents replace solvent molecules hydrogen bonded to the COOH group at the triterpene skeleton, resulting in similar packing arrangements of these compounds.

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32

Köffel, René, Rashi Tiwari, Laurent Falquet y Roger Schneiter. "The Saccharomyces cerevisiae YLL012/YEH1, YLR020/YEH2, and TGL1 Genes Encode a Novel Family of Membrane-Anchored Lipases That Are Required for Steryl Ester Hydrolysis". Molecular and Cellular Biology 25, n.º 5 (1 de marzo de 2005): 1655–68. http://dx.doi.org/10.1128/mcb.25.5.1655-1668.2005.

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ABSTRACT Sterol homeostasis in eukaryotic cells relies on the reciprocal interconversion of free sterols and steryl esters. The formation of steryl esters is well characterized, but the mechanisms that control steryl ester mobilization upon cellular demand are less well understood. We have identified a family of three lipases of Saccharomyces cerevisiae that are required for efficient steryl ester mobilization. These lipases, encoded by YLL012/YEH1, YLR020/YEH2, and TGL1, are paralogues of the mammalian acid lipase family, which is composed of the lysosomal acid lipase, the gastric lipase, and four novel as yet uncharacterized human open reading frames. Lipase triple-mutant yeast cells are completely blocked in steryl ester hydrolysis but do not affect the mobilization of triacylglycerols, indicating that the three lipases are required for steryl ester mobilization in vivo. Lipase single mutants mobilize steryl esters to various degrees, indicating partial functional redundancy of the three gene products. Lipase double-mutant cells in which the third lipase is expressed from the inducible GAL1 promoter have greatly reduced steady-state levels of steryl esters, indicating that overexpression of any of the three lipases is sufficient for steryl ester mobilization in vivo. The three yeast enzymes constitute a novel class of membrane-anchored lipases that differ in topology and subcellular localization.

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33

Schioppa, Laura, Fanta Fall, Sergio Ortiz, Jacques H. Poupaert y Joelle Quetin-Leclercq. "A Validated HPLC-PDA-HRMS Method to Investigate the Biological Stability and Metabolism of Antiparasitic Triterpenic Esters". Molecules 26, n.º 23 (26 de noviembre de 2021): 7154. http://dx.doi.org/10.3390/molecules26237154.

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Pentacyclic triterpenes (PTs) are commonly found in medicinal plants with well-known antiparasitic effects. Previous research on C-3 and C-27 triterpenic esters showed effective and selective in vitro antiparasitic activities and in vivo effectiveness by parenteral routes. The aim of this study was to determine triterpenic esters’ stability in different biological-like media and the main microsomal degradation products. An HPLC-PDA method was developed and validated to simultaneously analyze and quantify bioactive triterpenic esters in methanol (LOQ: 2.5 and 1.25–100 µg/mL) and plasma (LOQ: 5–125 µg/mL). Overall, both triterpenic esters showed a stable profile in aqueous and buffered solutions as well as in entire plasma, suggesting gaining access to the ester function is difficult for plasma enzymes. Conversely, after 1 h, 30% esters degradation in acidic media was observed with potential different hydrolysis mechanisms. C-3 (15 and 150 µM) and C-27 esters (150 µM) showed a relatively low hepatic microsomal metabolism (<23%) after 1 h, which was significantly higher in the lowest concentration of C-27 esters (15 µM) (>40% degradation). Metabolic HPLC-PDA-HRMS studies suggested hydrolysis, hydroxylation, dehydration, O-methylation, hydroxylation and/or the reduction of hydrolyzed derivatives, depending on the concentration and the position of the ester link. Further permeability and absorption studies are required to better define triterpenic esters pharmacokinetic and specific formulations designed to increase their oral bioavailability.

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34

Rodriguez, K. A. y A. T. Tsin. "Retinyl esters in the vertebrate neuroretina". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 256, n.º 1 (1 de enero de 1989): R255—R258. http://dx.doi.org/10.1152/ajpregu.1989.256.1.r255.

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High-performance liquid chromatography (HPLC) was employed to measure retinyl esters in the vertebrate retina. Both retina and retinal pigment epithelium (RPE) from frog, chicken, and bovine eyes were studied. In comparison to the RPE, the retina possessed a significant level of 11-cis and all trans retinyl palmitate. Using a sensitive radioassay, we also detected the presence of retinyl ester hydrolase (REH) activity in homogenates prepared from both retina and RPE. The rate of retinyl ester hydrolysis in these retinas was sufficiently high to supply retinal chromophores for the metabolic renewal and for the regeneration of visual pigments. In comparison to retinyl esters in the RPE, retinyl esters in the retina are located much closer to the sites of visual pigment synthesis and regeneration. Hence it is possible that these retinyl esters play a more important role in the visual cycle than those in the RPE.

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35

Fiume, Monice M., Wilma F. Bergfeld, Donald V. Belsito, Ronald A. Hill, Curtis D. Klaassen, Daniel C. Liebler, James G. Marks et al. "Safety Assessment of Sorbitan Esters as Used in Cosmetics". International Journal of Toxicology 38, n.º 2_suppl (septiembre de 2019): 60S—80S. http://dx.doi.org/10.1177/1091581819871877.

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The Cosmetic Ingredient Review Expert Panel (Panel) assessed the safety of 20 sorbitan esters; this report included sorbitan esters that were reviewed in 1985 and 2002, as well as 3 previously unreviewed sorbitan esters (sorbitan undecylenate, sorbitan sesquicaprylate, and sorbitan palmate). Most of the sorbitan esters are reported to function in cosmetics as surfactant-emulsifying agents. The Panel reviewed the data from previous sorbitan ester reports, as well as additional data included in this report, to determine the safety of these ingredients. The Panel concluded that the sorbitan esters included in this safety assessment are safe in cosmetics in the present practices of use and concentration.

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36

Todoroki, Toru, Kojiro Matsumoto, Kiyoaki Watanabe, Yukio Tashiro, Makoto Shimizu, Torayuki Okuyama y Kazuhiro Imai. "Accumulated lipids, aberrant fatty acid composition and defective cholesterol ester hydrolase activity in cholesterol ester storage disease". Annals of Clinical Biochemistry: International Journal of Laboratory Medicine 37, n.º 2 (1 de marzo de 2000): 187–93. http://dx.doi.org/10.1258/0004563001899195.

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We confirmed accumulation of glycogen and lipids, particularly cholesterol esters, in the liver of a patient with cholesterol ester storage disease (CESD). Hepatic cholesterol ester concentration was 100-200 times that found in normal livers. Analysis of the fatty acid composition indicated a higher proportion (41%) of cholesterol linoleate (C18-2), a slightly lower proportion (33%) of cholesterol oleate (C18-1) and normal proportions (14%) of cholesterol palmitate (C16-0) in the CESD patient compared with the control. This fatty acid composition of cholesterol esters and the fatty acid composition of other classes of lipids in the patient's liver resembled that of LDL. We also found that acid cholesterol ester hydrolase activity in the CESD liver was reduced to 5% of that in the control liver, while neutral cholesterol ester hydrolase activity remained at the control level. These results suggest that accumulated cholesterol esters were derived mainly from serum LDL and that the accumulation resulted from lack of acid cholesterol ester hydrolase.

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37

Uno, Takuya, Yusuke Kobayashi y Yoshiji Takemoto. "N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters". Beilstein Journal of Organic Chemistry 8 (10 de septiembre de 2012): 1499–504. http://dx.doi.org/10.3762/bjoc.8.169.

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An efficient catalytic synthesis of α-amino-β-keto esters has been newly developed. Cross-coupling of various aldehydes with α-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to α-amino-β-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the α-amino-β-keto esters are formed under thermodynamic control.

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38

Santoso, Aman, Muhammad Roy Asrori, Sumari Sumari y Andyka Medarda Pradana. "Karakterisasi Metil Ester Dari Minyak Biji Bunga Matahari dan Minyak Zaitun di Bawah Katalis KOH". Journal of Engineering Science and Technology 1, n.º 1 (18 de enero de 2023): 24–31. http://dx.doi.org/10.47134/jesty.v1i1.5.

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Fatty acid methyl esters can be obtained from the synthesis of vegetable oil with methanol using a base catalyst. Vegetable oil has potential as biodiesel feedstock, the methyl ester character of various vegetable oils is different, for example from sunflower seed oil and olive oil. The synthesis of methyl esters by conventional transesterification reactions generally takes 1-2 hours. The purpose of this study was to synthesize methyl esters from sunflower seed oil and olive oil with a KOH catalyst and to determine the yield and its characteristics. This research is a type of laboratory experimental research. The research was carried out in 3 stages which included (1) determination of the free fatty acid content (ALB) of the oil, (2) transesterification of the oil with methanol and potassium hydroxide as a catalyst, and (3) characterization of the synthesized methyl ester which included density, viscosity, and number. acid. The results showed that the yield of methyl esters synthesized by transesterification reaction of sunflower seed oil was 95.61% and the yield of methyl esters synthesized by transesterification reaction of olive oil was 95.09.%. The methyl ester characters synthesized from sunflower seed oil are, density of 0.906 g/mL, viscosity of 5.035 cSt, acid number of 1.21 g KOH/g. The methyl ester characters synthesized from olive oil by transesterification reaction are density of 0.909 g/mL, viscosity of 12.203 cSt, acid number of 0.629 g KOH/g.

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39

Baum, James Clayton, Kathleen Anne Durkin, Laura Precedo, Stacy Brian O'blenes, John Edward Goehl, Richard Francis Langler, Gerald Kendall MacCormack y Lana Louise Smith. "Sulfonyl esters 3. The formation of sulfone-sulfonates in the reactions of aryl methanesulfonates with sodium hydride". Canadian Journal of Chemistry 69, n.º 12 (1 de diciembre de 1991): 2127–35. http://dx.doi.org/10.1139/v91-307.

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Sodium hydride reductions of aryl methanesulfonates afford dimeric sulfone-sulfonate esters as well as products arising from SO bond rupture. SO bond rupture becomes more competitive as the LUMO energy of the sulfonate ester declines. Exploration of the chemistry of a sulfone-sulfonate ester revealed a complex novel reaction that resulted in the formation of, inter alia, a dichloromethanesulfonate ester and a trichloromethanesulfonate ester. The first successful approaches to the synthesis of the heretofore unknown trichloromethanesulfonates and dichloromethanesulfonates are reported. Key words: sodium hydride reductions, sulfenes, sulfone-sulfonate esters

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40

Charlton, James L., Gaiklean Chee y Heather McColeman. "Synthesis of acetylenedicarboxylic acid esters and asymmetric Diels–Alder reactions of the bis(methyl (S)-lactyl) ester". Canadian Journal of Chemistry 73, n.º 9 (1 de septiembre de 1995): 1454–62. http://dx.doi.org/10.1139/v95-180.

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A general method has been developed for the preparation of acetylenedicarboxylic acid esters and applied to the synthesis of both achiral and chiral esters. Diels–Alder reactions of one of the chiral esters, the bis(methyl (S)-lactyl) ester, with various types of dienes, such as phenylbutadiene, orthoquinodimethanes, and isobenzofuran, have been investigated. Moderate asymmetric induction was observed in reactions with dienes bearing an α-hydroxyl group. In one case, an unusual solvent-induced reversal of asymmetric induction was observed. Keywords: acetylenedicarboxylic acid esters, phenylbutadiene, orthoquinodimethanes, isobenzofurans, Diels–Alder, asymmetric.

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41

Boontawee, Hasleena, Charoen Nakason, Azizon Kaesaman, Anoma Thitithammawong y Sopa Chewchanwuttiwong. "Influence of Benzyl Ester Oil on Processability of Silica Filled NR Compound". Advanced Materials Research 844 (noviembre de 2013): 221–24. http://dx.doi.org/10.4028/www.scientific.net/amr.844.221.

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Modified benzyl esters from coconut, palm, and soybean oil were used as alternative rubber processing oil to replace distillate aromatic extract oil (DAE). The effect of benzyl esters on mixing, curing properties, polymerfiller interaction and Mooney viscosity was investigated in silica filled natural rubber compound. Benzyl ester oil was found to be effective processing oil with decreasing of mixing energy and Mooney viscosity. Furthermore, it was found that coconut and palm benzyl esters showed higher torque difference than the aromatic oil filled compound. Also, benzyl ester oil gave similar level of cure time and dynamic properties compared with the rubber compound with aromatic oils.

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42

Schellenberger, Volker, Ute Schellenberger y Hans-Dieter Jakubke. "Specific water-soluble substrates for chymotrypsin: Attempts for compensating diminished P1-S1 interactions". Collection of Czechoslovak Chemical Communications 53, n.º 11 (1988): 2884–89. http://dx.doi.org/10.1135/cccc19882884.

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N-Maleyl-L-amino acid and peptide esters were synthesized and employed as substrates for α-chymotrypsin. From the kcat/KM values can be suggested that benzyl esters are significantly better substrates than the appropriate methyl esters. Further improvement in the substrate properties results from the introduction of the p-nitrobenzyl ester moiety. The choline ester of benzyloxycarbonyl-L-phenylalanine with the highest kcat/KM value confirmed the P1' leaving group specificity for positively charged residues. From the kinetic data can be concluded that acyl donors with high kcat/KM values, which are useful in kinetically controlled enzymatic peptide synthesis, need not contain aromatic amino acid residues in the P1 position.

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43

Esteban-Torres, María, José María Landete, Inés Reverón, Laura Santamaría, Blanca de las Rivas y Rosario Muñoz. "A Lactobacillus plantarum Esterase Active on a Broad Range of Phenolic Esters". Applied and Environmental Microbiology 81, n.º 9 (6 de marzo de 2015): 3235–42. http://dx.doi.org/10.1128/aem.00323-15.

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ABSTRACTLactobacillus plantarumis the lactic acid bacterial species most frequently found in the fermentation of food products of plant origin on which phenolic compounds are abundant.L. plantarumstrains showed great flexibility in their ability to adapt to different environments and growth substrates. Of 28L. plantarumstrains analyzed, only cultures from 7 strains were able to hydrolyze hydroxycinnamic esters, such as methyl ferulate or methyl caffeate. As revealed by PCR, only these seven strains possessed theest_1092gene. When theest_1092gene was introduced intoL. plantarumWCFS1 orL. lactisMG1363, their cultures acquired the ability to degrade hydroxycinnamic esters. These results support the suggestion that Est_1092 is the enzyme responsible for the degradation of hydroxycinnamic esters on theL. plantarumstrains analyzed. The Est_1092 protein was recombinantly produced and biochemically characterized. Surprisingly, Est_1092 was able to hydrolyze not only hydroxycinnamic esters, since all the phenolic esters assayed were hydrolyzed. Quantitative PCR experiments revealed that the expression ofest_1092was induced in the presence of methyl ferulate, an hydroxycinnamic ester, but was inhibited on methyl gallate, an hydroxybenzoic ester. As Est_1092 is an enzyme active on a broad range of phenolic esters, simultaneously possessing feruloyl esterase and tannase activities, its presence on someL. plantarumstrains provides them with additional advantages to survive and grow on plant environments.

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44

Nordøy, Erling S. "Do minke whales (Balaenoptera acutorostrata) digest wax esters?" British Journal of Nutrition 74, n.º 5 (noviembre de 1995): 717–22. http://dx.doi.org/10.1079/bjn19950174.

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Mammals are known to utilize wax esters with an efficiency of less than 50%. The purpose of the present study was to examine whether or not minke whales (Balaenoptera acutorostrata), which at times may eat considerable amounts of wax-ester-rich krill, represent an exception to this general pattern. Samples of fresh undigested forestomach, as well as colon, contents were obtained from minke whales (n5) that had been feeding on krill (Thysanoessa inermis) for some time. The samples were analysed for dry mass, energy density, lipid content and the major lipid classes, including wax esters. The concentrations of wax esters were compared with previous estimates of dry-matter disappearance of the same type of prey using anin vitrotechnique, to calculate the dry-matter digestibility of wax esters (DMDwax). Wax esters contributed 21% of the energy and 47% of total lipids in the krill diet. The energy density of gut contents decreased by 50% after their passage from forestomach to the end of the colon. The DMDwaxwas 94·1 (SD 2·8)% (n5). This high DMDwaxand the occurrence of fatty alcohols, one of the products of wax-ester hydrolysis, in faeces show that minke whales are very efficient digesters of wax esters and absorb most of the energy-rich products of this process.

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45

Prakoso, Tirto, Indra B. Kurniawan y R. Heru Nugroho. "Esterifikasi asam lemak bebas dalam minyak sawit mentah untuk produksi metilester". Jurnal Teknik Kimia Indonesia 6, n.º 3 (2 de octubre de 2018): 705. http://dx.doi.org/10.5614/jtki.2007.6.3.7.

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Methyl esters are one of alkyl esters compound that used as alternative diesel fuel became popular. Methyl esters have similarities on physical and chemical properties with the diesel fuel produced from fossil oil; however it has less combustion and environmental emissions. As fossil oil become rare to be exploited, and the rapid environmental issues, the efforts to develop methyl esters as alternative diesel fuel become a prospective one. One method to produce methyl esters from free fatty acids of crude palm oil (CPO) is the two step esterification-transesterification reaction, each step produce the same final product, however differs in the side product. Esterification produce water and transesterfication produce glycerin. The reaction uses alcohol as main reactant beside the free fatty acids, it can be conducted in batch or continuous production. In this research, the investigation is only emphasized in the first step that is the esterification step to produce methyl esters from free fatty acids contained in crude palm oil. Methanol and sulfuric acid are used as reactant and catalyst respectively. Methyl esters produced by esterification is affected by reaction temperature, amounts of catalyst, and methanol volume. The increase in temperature improved esterification conversion from 19% in 50C to 98% in 60C. While the usage of the highest amount of catalyst, 5 ml/1-CPO, led to produced the highest conversion relative to the conversion from 1 and 3 ml/1-CPO catalyst. Furthermore, 10% amount of methanol per volume CPO produced higher yield than 8%.Keywords : Biodiesel, CPO Free Fatty Acid Esterification, Methyl Ester ConversionAbstrak Metil ester merupakan suatu senyawa alkil ester yang dapat digunakan sebagai bahan bakar alternatif. Metil ester memiliki sifat fisik dan kimia yang hampir sam a dengan minyak diesel yang dihasilkan dari minyak bumi tetapi emisi pembakaran dari penggunaan ester metal lebih rendah dari pada emisi hasil penggunaan minyak solar. Seiring dengan semakin langkanya sumber minyak bumi dan semakin gencarnya isu lingkungan hidup, pengembangan ester metil sebagai bahan bakar pengganti minyak solar semakin prospektif. Pembuatan ester metil dari asam lemak bebas minyak sawit mentah (crude palm oil) dapat dilakukan dengan beberapa cara antara lain dengan reaksi esterifikasi dan transesterifikasi menggunakan alkohol. Reaksi-reaksi ini dapat dilaksanakan secara batch maupun kontinu. Pada penelitian yang telah dilakukan, pembuatan ester metil dari asam lemak bebas minyak sawit mentah dilakukan dengan reaksi esterifikasi secara batch, dengan reaktan berupa minyak sawit mentah dan metanol. Katalis yang digunakan adalah H2SO4. Konversi ester metil yang dihasilkan dipengaruhi oleh temperatur reaksi, konsentrasi katalis dan konsentrasi metanol. Kenaikan temperatur reaksi akan meningkatkan konversi dari 19% pada 50oC menjadi 98% pada 60oC. Dengan menggunakan konsentrasi katalis tertinggi 5ml/l CPO memicu konversi tertinggi relatif dibandingkan nilai konversi dari 1 dan 3 ml/l CPO. 10% metanol menghasilkan perolehan tinggi dibanding 8%.Kata Kunci: Biodiesel, EsterifikasiAsam Lemak Bebas CPO, Konversi Ester Metil

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46

Nevill, S. M. y J. A. Pincock. "The design of radical clocks to probe the reactivity of the intermediates in arylmethyl ester photochemistry". Canadian Journal of Chemistry 75, n.º 2 (1 de febrero de 1997): 232–47. http://dx.doi.org/10.1139/v97-027.

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The photochemistry in methanol of the esters 1–6was examined. These reactions normally proceed through radical pairs that result from homolytic cleavage of the carbon–oxygen bond in the excited singlet state. Each of the esters was designed to probe the intervention and reactivity of the substituted arylmethyl radical by incorporating a potential radical clock at the carbon of the reactive bond. For esters 1–5, the products isolated indicated that the radical clock was not reactive enough to compete with the very rapid alternate processes of the radical pair, namely, electron transfer to form the corresponding ion pair and decarboxylation of the phenylacyloxy radical (k = 4.6 × 109 s−1). Ester 6, which incorporates the extremely rapid fluorenylcyclopropylcarbinyl clock, showed very unusual reactivity. On thermal solvolysis in methanol, 6 rearranged quantitatively to the ester 20. No methyl ethers were detected. In contrast, photolysis of 6 in benzene resulted in an alternate rearrangement to the cyclobutyl ester, 22, resulting from the aryl version of the cyclopropyl-π-methane photochemical rearrangement. No ester cleavage occurred on excitation. A rationale for the latter conversion was based on stereoelectronic arguments provided by a crystal structure of 6. Keywords: photochemistry of arylmethyl esters, radical clocks.

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47

Mammadyarov, M. A., G. N. Gurbanov y K. M. Yusifova. "Development and study of new lubricating compositions based on compound esters of cyclic polyatomic alcohols and industrial pentaerithritol ester". Azerbaijan Oil Industry, n.º 8 (15 de agosto de 2020): 53–57. http://dx.doi.org/10.37474/0365-8554/2020-8-53-57.

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The simple and anisometric esters of 2.2.5.5-tetra methylol cyclopenthanole were synthesized with hexanole and heptanoic acids adding these esters to those of pentaerithritol and the mixture of fatty acids of С5-С9 fractions, oil compositions were prepared and studied as well. It was defined that operation characteristics of these compositions are significantly better than those of pentaerithritol ester and B-3W oil based on pentaerithritol ester. According to this data, the compositions based on polyol ester are recommended as new lubricants meeting modern standards.

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48

Santoso, Aman, Abdurrohman, Anugrah Ricky Wijaya, Dedek Sukarianingsih, Sumari y Daratu Eviana Kusuma Putri. "Synthesis of Methyl Ester from Rice Bran Oil through the Esterification Reaction". Key Engineering Materials 851 (julio de 2020): 164–71. http://dx.doi.org/10.4028/www.scientific.net/kem.851.164.

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Vegetable oil is one of rice bran components. As triglycerides, vegetable oil can be converted to fatty acid and alkyl esters for further treatments. Synthesis of alkyl ester oil can be carried out by esterification or transesterification reaction, depending on the quality of the oil and the catalyst. The purposes of this study are 1) Rice bran oil isolation, 2) Oil esterification 3) Characterization and identification of the methyl ester that compose rice bran oil. The stages in this research are 1) Extraction of rice bran oil, 2) Synthesis of methyl ester from rice bran through esterification reaction, 3) Methyl ester characterization of rice bran oil and its potential test as biodiesel included determination of density, viscosity, refractive index, and acid number test, 4) The identification of synthesized methyl esters composition using GC-MS. The results showed that rice bran oil has a yield of 18.09%. Synthesis of methyl esters from rice bran oil through the esterification reaction with a catalyst acid yields 72.37%. The characters of the synthesized methyl ester are on the range of biodiesel quality standards, namely, the density is 0.850 g/mL, viscosity is 4.73 cSt, a refractive index is 1.45871, and an acid number is 0.76 g KOH/g methyl ester, therefore it is claimed that the synthesized methyl esters have the potential as biodiesel. The GC-MS result showed the presence of compounds methyl tetradecanoate (0.38%), methyl hexadecanoate (40.67%), methyl 9-octadecenoate (53.68%), methyl octadecanoate (5.02%), and methyl eicosanoate (0.14%).

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49

Zhu, Zijian, Kai Hu, Siyu Chen, Sirui Xiong y Yongsheng Tao. "Increase in Fruity Ester Production during Spine Grape Wine Fermentation by Goal-Directed Amino Acid Supplementation". Fermentation 7, n.º 4 (16 de octubre de 2021): 231. http://dx.doi.org/10.3390/fermentation7040231.

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The aim of this work was to enhance the levels of fruity esters in spine grape (Vitis davidii Foёx) wine by goal-directed amino acid supplementation during fermentation. HPLC and GC-MS monitored the amino acids and fruity esters, respectively, during alcoholic fermentation of spine grape and Cabernet Sauvignon grape. HPLC was also used to determine the extracellular metabolites and precursors involved in the synthesis of fruity esters. Alanine, phenylalanine, and isoleucine levels in spine grape were less than those in Cabernet Sauvignon. Pearson correlation between amino acid profile and fruity ester content in the two systems indicated that deficiencies in alanine, phenylalanine, and isoleucine levels might have limited fruity ester production in spine grape wine. Supplementation of these three amino acids based on their levels in Cabernet Sauvignon significantly increased fruity ester content in spine grape wine. Interestingly, goal-directed amino acid supplementation might have led to changes in the distribution of carbon fluxes, which contributed to the increase in fruity ester production.

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50

Li, Duan-le, Da-peng Zheng, Dong-min Wang, Ji-hui Zhao, Cheng Du y Cai-fu Ren. "Influence of Organic Esters on Portland Cement Hydration and Hardening". Advances in Materials Science and Engineering 2018 (2018): 1–10. http://dx.doi.org/10.1155/2018/3203952.

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This paper investigated the effect of organic compounds with ester groups on the hydration and hardening of cement. The effects of five kinds of organic compounds with ester groups (ethyl acetate, dimethyl oxalate, glyceryl triacetate, trimethyl phosphate, and triethanolamine borate) on hydration heat, hydration degree, setting time, mechanical properties, microstructure, and pore structure of hardened cement slurry were studied. The test results showed that esters can make the end time of cement hydration induction longer and delay the occurrence of the second exothermic peak. Also, the effect of five kinds of esters on the hydration and hardening of cement was basically followed by TG> TB> DMO> EAC> TMP. In terms of molecular structure, for organic compounds containing only ester groups, the higher the number of ester groups, the greater the effect on the hydration of cement. The introduction of other functional groups (such as phosphate or borate) will influence the effect of the esters.

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