Alkyl Esters Research Articles

Transformation behaviour of salts composed of calcium ions and phosphate esters with different linear alkyl chain structures in a simulated body fluid modified with alkaline phosphatase

ABSTRACT Ceramic biomaterials have been used for the treatment of bone defects and have stimulated intense research on such materials. We have previously reported that a salt composed of calcium ions and a phosphate ester (SCPE) transformed into hydroxyapatite (HAp) in a simulated body fluid (SBF) modified with alkaline phosphatase (ALP), and proposed SCPEs as a new category of ceramic biomaterials, namely bioresponsive ceramics. However, the factors that affect the transformation of SCPEs to HAp in the SBF remained unclear. Therefore, in this study, we investigated the behaviour of calcium salts of methyl phosphate (CaMeP), ethyl phosphate (CaEtP), butyl phosphate (CaBuP), and dodecyl phosphate (CaDoP) in SBF with and without ALP modification. For the standard SBF, an X-ray diffraction (XRD) analysis indicated that these SCPEs did not readily transform into calcium phosphate. However, CaMeP, CaEtP, and CaBuP were transformed into HAp and octacalcium phosphate in the SBF modified with ALP; therefore, these SCPEs can be categorised as bioresponsive ceramics. Although CaDoP did not exhibit a sufficient response to ALP to be detected by XRD, it is likely to be a bioresponsive ceramic based on the results of morphological observations. The transformation rate for the SCPEs decreased with increasing size of the linear alkyl group of the phosphate esters. The rate-determining steps for the transformation reaction of the SCPEs were changed from the dissolution of the SCPEs to the hydrolysis of the phosphate esters with increasing size of the phosphate ester alkyl groups. These findings contribute to designing novel bioresponsive ceramic biomaterials.

Síntesis benigna y sencilla de dímeros de tipo lignano usando peroxidasa cruda de rábano rojo (Raphanus sativus var sativus)

Alkyl esters of hydroxycinnamic acids and vanillin derivatives were used as model compounds in the oxidative coupling reactions catalyzed by a crude enzymatic extract of Raphanus sativus var sativus (red radish). Six products were isolated and characterized: three alkyl esters of hydroxycinnamic acids dimers and three vanilloids dimers. Herein, we report the enzymatic extract of Raphanus sativus var. sativus showed peroxidase activity catalyzing the oxidative coupling of phenols. Vanilloid dimers were coupled in an ortho-ortho way as expected, while alkyl ester dimers were formed through 5-8 and 8-8 bonds via a radical mechanism prior to cyclization

Biodiesel production over sodium carbonate and bicarbonate catalysts

Biodiesel, a mixture of alkyl esters (FAME), is viewed as a feasible renewable fuel to substitute fossil diesel. The first-generation biodiesel raises several sustainability issues and new production processes using low-grade fats and heterogeneous catalysts are envisaged. Biodiesel from alimentary grade oil and waste frying oil was produced by methanolysis (oil/methanol = 12 M ratio), at 67 °C, using anhydrous sodium carbonate and bicarbonate, commercial materials as catalysts (5% by oil weight) in a batch reactor at atmospheric pressure. Sodium carbonate had a higher catalytic activity for the methanolysis of the fresh oil (97% of FAME after 90 min) than for the frying oil (12% of FAME after 90 min), which can be attributed to the greater acidity of the fried oil, which promotes the partial neutralization of the catalyst. Sodium bicarbonate, less active than sodium carbonate, showed similar catalytic activities for both fats (84–85% of FAME after 180 min), appearing to be less sensitive to the acidity of the raw material, which may derive from its lower basicity. Both catalysts suffer crystallographic changes during reaction being both converted into similar mixtures of hydrated carbonate/bicarbonate slats, like trona. The methanol solubility of sodium carbonate seems to have a null homogeneous contribution to the catalytic process since the co-produced glycerin presented a pale-yellow color which is characteristic of heterogeneous catalyzed methanolysis processes. Such result was corroborated by thermogravimetric analysis of glycerin which showed small residual masses due to minor solubilization of catalyst. FTIR spectra of glycerin showed low contamination with MONG (Matter Organic Non-Glycerin), thus the contribution of homogeneous catalysis was not meaningful.

Production of biodiesel from marine green seaweed using a renewable low-cost heterogeneous catalyst

In this study, the biodiesel produced from Ulva lactuca, a marine green seaweed by solid oxide catalyst derived from low-cost waste eggshells is evaluated. Waste eggshells were calcined at 500 °C, 600 °C and 700 °C to increase catalytic activity which was characterized by X-ray diffraction pattern. The peaks of CaO were obtained by calcinations carried out at 700 °C for varied time periods. Comparison of images of scanning electron microscope of calcined eggshells with natural eggshells showed the formation of porous structure with an average pore diameter of 39.17 nm. Biodiesel was prepared by transesterification of algal oil by uncalcined eggshells, calcined eggshells and commercial calcium oxide with methanol. The yield of biodiesel was higher for calcined eggshells (78 %) than uncalcined eggshells (53 %). The produced biodiesel was sampled and analyzed for Gas chromatography – mass spectrometry, which confirmed the presence of predominant alkyl esters like hexadecenoic acid methyl ester, docosanoic methyl ester, palmitic acid methyl ester and oleic acid methyl ester. The heterogeneous catalyst can be reused upto seven times without any prescribed loss of catalyst activity. The Introduction of this eco-friendly catalyst in the transesterification reaction of biodiesel from Ulva lactuca will be cost-reduction for the production of an alternative green fuel.

The effect of alkyl chain length of (R)-3-Hydroxybutyric alkyl ester on antibacterial activity and its antibacterial mechanism.

This work describes the relationship between the antibacterial activity and the ester chain length (C1-C8) of (R)-3-Hydroxybutyric ((R)-3-HB) alkyl esters that synthesized from (R)-3-HB acid ((R)-3-HBA) by esterification reaction. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) decrease as the length of the (R)-3-HB alkyl ester chain increases from 1 to 6, but (R)-3-HB-C7 and (R)-3-HB-C8 have their own rules for different microorganisms. Among them, the (R)-3HB-C6 has the relatively best antibacterial and antifungal properties, which MIC were 1.95mg mL-1 against E. coli and S. aureus; 0.98mg mL-1 against C. albicans and B. subtilis; 0.49mg mL-1 against A. niger. Finally, the antimicrobial mechanisms of the (R)-3HB-C6 are revealed, and these include disruption of biofilm and the bacterial wall/membrane, leakage of the intracellular content, and change in the transmembrane potential. These results imply the potential application of (R)-3-HB alkyl ester as new antimicrobial agents; future research can use this as an antibacterial element to synthesize new polymer materials or agents with high-efficiency antibacterial activity.

A Pd−H/Isothiourea Cooperative Catalysis Approach to anti‐Aldol Motifs: Enantioselective α‐Alkylation of Esters with Oxyallenes**

AbstractThe biological and therapeutic significance of natural products is a powerful impetus for the development of efficient methods to facilitate their construction. Accordingly, and reflecting the prevalence of β‐oxy‐carbonyl motifs, a sophisticated arsenal of aldol‐based strategies has evolved that is contingent on the generation of single enolate isomers. Since this has the potential to compromise efficiency in reagent‐based paradigms, direct catalysis‐based solutions would be enabling. To complement the array of substrate‐based strategies, and regulate enolate geometry at the catalyst level, a direct catalytic alkylation of esters with oxyallenes has been developed. Synergizing metal hydride reactivity with Lewis base catalysis has resulted in a broad reaction scope with useful levels of stereocontrol (up to >99 % ee). Facile derivatization of these ambiphilic linchpins is demonstrated, providing access to high‐value vicinal stereocenter‐containing motifs, including 1,2‐amino alcohols.

A Pd-H/Isothiourea Cooperative Catalysis Approach to anti-Aldol Motifs: Enantioselective α-Alkylation of Esters with Oxyallenes.

The biological and therapeutic significance of natural products is a powerful impetus for the development of efficient methods to facilitate their construction. Accordingly, and reflecting the prevalence of β-oxy-carbonyl motifs, a sophisticated arsenal of aldol-based strategies has evolved that is contingent on the generation of single enolate isomers. Since this has the potential to compromise efficiency in reagent-based paradigms, direct catalysis-based solutions would be enabling. To complement the array of substrate-based strategies, and regulate enolate geometry at the catalyst level, a direct catalytic alkylation of esters with oxyallenes has been developed. Synergizing metal hydride reactivity with Lewis base catalysis has resulted in a broad reaction scope with useful levels of stereocontrol (up to >99 % ee). Facile derivatization of these ambiphilic linchpins is demonstrated, providing access to high-value vicinal stereocenter-containing motifs, including 1,2-amino alcohols.

Facilitating Rh-Catalyzed C-H Alkylation of (Hetero)arenes and 6-Arylpurine Nucleosides (Nucleotides) with Electrochemistry.

An electrochemical approach to promote the ortho-C-H alkylation of (hetero)arenes via rhodium catalysis under mild conditions is described. This approach features mild conditions with high levels of regio- and monoselectivity that tolerate a variety of aromatic and heteroaromatic groups and offers a widely applicable method for late-stage diversification of complex molecular architectures including tryptophan, estrone, diazepam, nucleosides, and nucleotides. Alkyl boronic acids and esters and alkyl trifluoroborates are demonstrated as suitable coupling partners. The isolation of key rhodium intermediates and mechanistic studies provided strong support for a rhodium(III/IV or V) regime.

Sulfur-promoted, one-pot, and metal-free conversion of aromatic aldehydes to nitriles using an inorganic ammonium salt as the nitrogen source

A simple protocol for the sulfur-promoted conversion of aromatic aldehydes to aromatic nitriles has been developed. This strategy enables the one-pot conversion of inexpensive and readily available aromatic aldehydes into highly valuable aromatic nitriles using a cheap inorganic ammonium salt as the nitrogen source in the absence of metals. Significantly, a broad scope of substrates was explored using this strategy, and various groups, including alkyl, alkoxyl, alkylthiol, hydroxyl, amino, aryl, alkenyl, cyano, carboxyl, and borate ester groups were tolerated, and good to excellent yields were achieved in most cases. Additionally, polycyclic aromatic aldehydes and heteroaromatic aldehydes also could be converted to the corre-sponding nitriles with satisfactory yields. This method can be utilized as a powerful tool for the cyanation of complex molecules.

Cetane index prediction based on biodiesel distillation curve

Cetane number (CN) is one of the most important parameters affecting diesel fuel behavior. It is related to the time that elapses between fuel injection and beginning of combustion. To determine it, a combustion standardized test, under ASTM D613 regulation, needs to be carried out. As this process is limiting, since it requires a specific engine, CN can be approximated from the distillation temperatures of diesel fuels, providing another dimensionless parameter, named calculated cetane index (CCI). It also provides an approach to the explosion delay. ASTM D4737 standard is the regulation that allows its calculation. It is based on a four-term equation that may be applied to oil-derived products. Chemical composition of diesel fuel is composed exclusively of hydrocarbons of different nature. However, biodiesel is mainly composed of alkyl esters and, to a lesser extent, glycerides and glycerol impurities. This difference makes convenient to adapt the equation to biodiesel distillation curve. The aim of this work is to provide an alternative to CN calculation for biodiesel, based on CCI prediction. This manuscript presents distillation curves and density values of 14 different biodiesel types, from both animal and vegetable origin. This data, together with data from literature, have been used with non-linear equation modeling techniques. As a result, a modification of ASTM D4737 regulation with experimental data from biodiesel sources has been proposed. The proposed equation exhibits an error with respect to experimental data below 3.5% for most evaluated cases. Subsequently, it may be concluded that the proposed methodology may be applied to accurately calculate biodiesel CCI, as a substitute of CN.

Production and characterization of biodiesel from canola oil through enzymatic transesterification

Abstract Biodiesel, a promising type of biofuel, can be produced from various types of renewable feedstocks, ranging from animal fats to plant oil. It is mainly made up of fatty acid alkyl ester compounds due to the transesterification reaction. This work aims to synthesize and characterize biodiesel, known as fatty acid methyl esters, from canola oil using an enzymatic reaction involving immobilized Novozym 435 and Rhizomucor miehei (RM IM) lipase enzymes.4 g of canola oil was added to the reaction mixture consisting of 0.2 g immobilized lipase and 3:1 methanol to oil ratio. First, the enzymatic methanolysis reaction was conducted at the temperature of 35°C and at agitation rate of 216 rpm for 24 hours. Next, the synthesized biodiesel was characterized using the Gas Chromatography-Mass Spectroscopy (GC/MS) analysis. Based on the analysis results, the main fatty acid methyl esters present in both products were hexadecanoic acid, 9-octadecenoic acid (z)-, 9,12,15-octadecatrienoic acid, (z, z, z)-, and 11,14-eicosadienoic acid. The transesterification of canola oil using both enzymes consistently revealed methyl oleate as the methyl ester with the highest composition, ranging from 67 to 71 %. In conclusion, canola oil was successfully converted into fatty acid methyl ester via the enzymatic transesterification process in this study.

Experimental assessment of renewable diesel fuels (HVO/Farnesane) and bioethanol on dual-fuel mode

Currently, alkyl esters dominate the renewable share of the CI engine fuels market, but it can potentially be replaced by more modern diesel-like fuels such as HVO and farnesane. Aiming to integrate even more renewable alternatives, these second-generation fuels can be used alongside lower reactivity fuels such as ethanol, taking advantage of the so-called dual-fuel operation. In this study, the use of green diesel fuels operating with and without bioethanol in dual-fuel mode is assessed and compared to Brazilian commercial diesel for small scale power generation application. Experiments were carried out in a single-cylinder compression ignition engine with an electronic port-fuel injection system, and five different dual-fuel bioethanol energy fractions (EF) with both HVO and farnesane. The results show that using renewable diesel presented delayed start of injection, shorter ignition delay, lower heat release peak rate at premixed combustion phase, inferior combustion duration, reduced in-cylinder peak pressures (6.2% and 6.1% reduction for farnesane and HVO, respectively) and lower average in-cylinder temperatures when compared to diesel, decreasing NOx, CO, CO2, HC and particulate matter (PM) for nearly all tested conditions. Dual-fuel operation with bioethanol presented acceptable combustion stability up to 40% bioethanol energy fraction (COVIMEP < 5%), while decreasing NOx, PM and CO2. Considering EF = 40%, HVO-bioethanol dual-fuel operation reduced NOx up to 43% and PM up to 82% compared to diesel single-fuel condition. The addition of bioethanol reduced in-cylinder temperature, soot emissions and presented lower diffusive and total combustion durations. However, CO and HC emissions increased in dual-fuel mode, particularly for higher energy substitution rates (EF > 27%). Considering single-fuel condition, neat diesel presented the lowest brake thermal engine efficiency (23.59 %), followed by farnesane (24.37 %) and HVO (24.66%). Renewable diesel with bioethanol in dual-fuel mode showed an interesting option for a sustainable energy supply with reduced carbon footprint.

The effect of chemical substances on endocrine disorder and related with morbidity and mortality of sperms in albino rats

Parabens are a group of alkyl esters of p-hydroxybenzoic acid that is commonly added to personal care products, cosmetics, pharmaceuticals, beverages, and food processing as an antimicrobial preservative. Butylparaben has been reported to cause sperm poisoning. To identify a previous marker of the toxicity of environmental substances or food additives, this study determined whether Butylparaben had an effect on the external appearance of sperm. Where several concentrations of 400mg/kg, 300mg/kg, and 200mg/kg were used daily for 20 days and dissolved in corn oil. It was found that it had an effect, as treatment with this substance led to a reduction in the weight of the testes and epididymis in the adult male rats used understudy. The results also showed a decrease in the number of sperms and their vitality compared to the control group, and the higher concentration used in the study had the greatest effect as compared to the other study groups and control, where the abnormalities in the sperm were represented by the twisting and breaking off the tail with the separation of the head in some sperms and the deformation of the head and the tail agglutination.

CaM kinase phosphatase (CaMKP/PPM1F/POPX2) is specifically inactivated through gallate-mediated protein carbonylation

CaMK phosphatase (CaMKP/PPM1F/POPX2) is a Mn2+-dependent, calyculin A/okadaic acid-insensitive Ser/Thr protein phosphatase that belongs to the PPM family. CaMKP is thought to be involved in regulation of not only various protein kinases, such as CaM kinases and p21-activated protein kinase, but also of cellular proteins regulated by phosphorylation. A large-scale screening of a chemical library identified gallic acid and some of its alkyl esters as novel CaMKP inhibitors highly specific to CaMKP. Surprisingly, they caused specific carbonylation of CaMKP, leading to its inactivation. Under the same conditions, no carbonylation nor inactivation was observed when PPM1A, which is affiliated with the same family as CaMKP, and λ-phosphatase were used. The carbonylation reaction was inhibited by SH compounds such as cysteamine in a dose-dependent manner with a concomitant decrease in CaMKP inhibition by ethyl gallate. The pyrogallol structure of gallate was necessary for the gallate-mediated carbonylation of CaMKP. Point mutations of CaMKP leading to impairment of phosphatase activity did not significantly affect the gallate-mediated carbonylation. Ethyl gallate resulted in almost complete inhibition of CaMKP under the conditions where the carbonylation level was nearly identical to that of CaMKP carbonylation via metal-catalyzed oxidation with ascorbic acid/FeSO4, which resulted in only a partial inhibition of CaMKP. The gallate-mediated carbonylation of CaMKP absolutely required divalent cations such as Mn2+, Cu2+, Co2+ and Fe2+, and was markedly enhanced by a phosphopeptide substrate. When MDA-MB-231 cells transiently expressing CaM kinase I, a CaMKP substrate, were treated by ethyl gallate, significant enhancement of phosphorylation of CaM kinase I was observed, suggesting that ethyl gallate can penetrate into cells to inactivate cellular CaMKP. All the presented data strongly support the hypothesis that CaMKP undergoes carbonylation of its specific amino acid residues by incubation with alkyl gallates and the divalent metal cations, leading to inactivation specific to CaMKP.

Combination of Biocatalysis and Sonochemistry in the Ethyl Oleate Production

Objectives:Fatty acid alkyl esters (FAAEs) are a family of natural neutral lipids and can be produced cleanly and sustainably by esterification of free fatty acids (FFAs) with short chain alcohol using enzymatic catalysts. In this study, the use of lipases was evaluated in enzymatic esterification of oleic acid with ethanol using the combination of biocatalysis and sonochemistry (ultrasound) in the absence of co-solvents.Methods:Reaction parameters, such as type of lipase, amount of enzyme, reaction time, alcohol hydration level and enzyme turnover were evaluated for the enzymatic synthesis of ethyl oleate.Results:C. antarctica lipase provided yields above 95% in less than 10 h with 10% (w/w) of lipase. The use of hydrous ethanol (5% of water) showed a slight drop in yield but remained above 90% of ethyl oleate production. C. antarctica lipase showed no loss efficiency even after 10 reaction cycles.Conclusion:The combination of biocatalysis and ultrasound radiation provided a high yield, showing that the combination of these tools may be a good choice for the enzymatic synthesis of ethyl oleate.

Heterogeneous Catalyzed Synthesis of Biodiesel from Crude Sunflower Oil

Biodiesel is the fatty acid alkyl esters that are used as the substitute for petro-diesel. The aim of the present work is to optimize biodiesel production from plant based non-edible crude oils with methanol using heterogeneous catalyst by transesterification for its commercialization. The factors affecting the biodiesel production from plant oils are volume of feedstock (oil), volume of alcohol (excess reactant), quantity of calcium hydroxide (catalyst), reaction time, temperature, and agitation speed. Transesterification is the reaction between acid and alcohol to produce ester in the presence of alkali catalyst. In this work, transesterification was carried out between crude sunflower oil and methanol in the presence of calcium hydroxide as catalyst. Finally, the maximum conversion of 85.6% was achieved at the optimum process parameters of 2 L of crude sunflower oil, 0.3 L methanol, 23 g of calcium hydroxide, reaction time of 24 h, temperature of 65 °C, and agitation speed of 100 rpm. The results showed that crude sunflower oil could serve as potential renewable substrate for biodiesel commercialization.Biodiesel is the fatty acid alkyl esters that are used as the substitute for petro-diesel. The aim of the present work is to optimize biodiesel production from plant based non-edible crude oils with methanol using heterogeneous catalyst by transesterification for its commercialization. The factors affecting the biodiesel production from plant oils are volume of feedstock (oil), volume of alcohol (excess reactant), quantity of calcium hydroxide (catalyst), reaction time, temperature, and agitation speed. Transesterification is the reaction between acid and alcohol to produce ester in the presence of alkali catalyst. In this work, transesterification was carried out between crude sunflower oil and methanol in the presence of calcium hydroxide as catalyst. Finally, the maximum conversion of 85.6% was achieved at the optimum process parameters of 2 L of crude sunflower oil, 0.3 L methanol, 23 g of calcium hydroxide, reaction time of 24 h, temperature of 65 ?C, and agitation speed of 100 rpm. The results showed that crude sunflower oil could serve as potential renewable substrate for biodiesel commercialization.

Synthesis and biological evaluation of orally active prodrugs and analogs of para-aminosalicylic acid (PAS)

Tuberculosis (TB) is one of the world's most deadly infectious diseases resulting in nearly 1.3 million deaths annually and infecting nearly one-quarter of the population. para-Aminosalicylic acid (PAS), an important second-line agent for treating drug-resistant Mycobacterium tuberculosis, has moderate bioavailability and rapid clearance that necessitate high daily doses of up to 12 g per day, which in turn causes severe gastrointestinal disturbances presumably by disruption of gut microbiota and host epithelial cells. We first synthesized a series of alkyl, acyloxy and alkyloxycarbonyloxyalkyl ester prodrugs to increase the oral bioavailability and thereby prevent intestinal accumulation as well as undesirable bioactivation by the gut microbiome to non-natural folate species that exhibit cytotoxicity. The pivoxyl prodrug of PAS was superior to all of the prodrugs examined and showed nearly quantitative absorption. While the conceptually simple prodrug approach improved the oral bioavailability of PAS, it did not address the intrinsic rapid clearance of PAS mediated by N-acetyltransferase-1 (NAT-1). Thus, we next modified the PAS scaffold to reduce NAT-1 catalyzed inactivation by introduction of groups to sterically block N-acetylation and fluorination of the aryl ring of PAS to attenuate N-acetylation by electronically deactivating the para-amino group. Among the mono-fluorinated analogs prepared, 5-fluoro-PAS, exhibited the best activity and an 11-fold decreased rate of inactivation by NAT-1 that translated to a 5-fold improved exposure as measured by area-under-the-curve (AUC) following oral dosing to CD-1 mice. The pivoxyl prodrug and fluorination at the 5-position of PAS address the primary limitations of PAS and have the potential to revitalize this second-line TB drug.

P2O5-Promoted Cyclization of Di[aryl(hetaryl)methyl] Malonic Acids as a Pathway to Fused Spiro[4.4]nonane-1,6-Diones.

Conventional spiro-linked conjugated materials are attractive for organic optoelectronic applications due to the unique combination of their optical and electronic properties. However, spiro-linked conjugated materials with conjugation extension directed along the main axis of the molecule are still only rare examples among the vast number of spiro-linked conjugated materials. Herein, the synthesis, leading to π-extended spiro-linked conjugated materials─spiro[4.4]nonane-1,6-diones and spiro[5.5]undecane-1,7-diones─has been developed and optimized. The proposed design concept starts from readily available malonic esters and contains several steps: double alkylation of malonic ester with bromomethylaryl(hetaryl)s; conversion of a malonic ester into the corresponding malonic acid; electrophilic spirocyclization of the latter into the annulated spiro[4.4]nonane-1,6-dione or spiro[5.5]undecane-1,7-dione in the presence of phosphorus pentoxide. On the basis of these insights, the developed method yielded spiro-linked conjugated cores fused with benzene, thiophene, and naphthalene, decorated with active halogen atoms. The structures of the synthesized spirocycles were determined by single-crystal X-ray diffraction analysis. Benzene fused spiro[4.4]nonane-1,6-dione decorated with bromine atoms was transformed into V-shape phenylene-thiophene co-oligomer type spirodimers via Stille coupling. The spiro-bis(4-n-dodecylphenyl)-2,2'-bithiophene derivative possessed high photoluminescence properties in both solution and solid state with a photoluminescence quantum yield (PL QY) of 38%.

Investigation of the antioxidation capacity of gallic acid and its alkyl esters with different chain lengths for dried oyster during ambient storage

SummaryThe antioxidant capacity of gallic acid (GA) and its fatty alkyl esters such as butyl gallate, octyl gallate (OG), lauryl gallate and hexadecyl gallate in freeze‐dried oyster was investigated. During ambient storage, the significant increase of peroxide value and thiobarbituric acid value together with the decline for docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents indicated the occurrence of lipid autoxidation in freeze‐dried oysters. Meanwhile, the oxidative degradation of glycerol phosphocholine (GPC), glycerol phosphoethanolamine (GPE) and triacylglycerols (TAG) molecular species carrying DHA or EPA in oyster ranked as: TAG &gt; GPE &gt; GPC. GA and its alkyl esters could effectively be prevented dried oyster lipid from oxidation. Among them, OG stood out as the most effective individual. This work implied that the chain lengths of GA alkyl esters affect their antioxidant ability for dried oysters, which provides the information for selecting eligible antioxidants to enhance the oxidative stability of freeze‐dried seafood.

Alkyl esters of umbelliferone-4-acetic acid as protonophores in bilayer lipid membranes and ALDH2-dependent soft uncouplers in rat liver mitochondria

A great variety of coumarin-related compounds, both natural and synthetic, being often brightly fluorescent, have shown themselves beneficial in medicine for both therapeutic and imaging purposes. Here, in search for effective uncouplers of oxidative phosphorylation, we synthesized a series of 7-hydroxycoumarin (umbelliferone, UB) derivatives combining rather high membrane affinity with the presence of a hydroxyl group deprotonable at physiological pH - alkyl esters of umbelliferone-4-acetic acid (UB-4 esters) differing in alkyl chain length. Addition of UB-4 esters to isolated rat liver mitochondria (RLM) resulted in their rapid depolarization, unexpectedly followed by membrane potential recovery on a minute time scale. According to TLC and HPLC data, incubation of RLM with UB-4 esters caused their hydrolysis, which led to disappearance of the uncoupling activity (recoupling). Both mitochondrial recoupling and hydrolysis of UB-4 esters were suppressed by inhibitors of mitochondrial aldehyde dehydrogenase (ALDH2), disulfiram and daidzin, thus pointing to the involvement of this enzyme in the recoupling of RLM incubated with UB-4 esters. The protonophoric mechanism of mitochondrial uncoupling by UB-4 esters was proved in experiments with artificial bilayer lipid membranes (BLM): these compounds induced proton-selective electrical current across planar BLM and caused dissipation of pH gradient on liposomes. UB-4 esters showed antibacterial activity against Bacillus subtilis, Staphylococcus aureus and Mycobacterium smegmatis.