Partial Esters Research Articles

Advantages of hydroxyl radical water treatment for the fruits and vegetables preservation

In this study, the effects of hydroxyl radical water (HRW) treatment on the functional components, volatile compounds, and preservation properties of cherry tomatoes, grapes, coriander, and celery were investigated. The results demonstrated that HRW treatment could be significantly effective in delaying the color change and decay of fruits and vegetables. The loss of total sugars in the HRW-treated samples was relatively low, ranging from 0.02% to 0.84%. However, other functional components will be more severely affected. Specifically, celery exhibited a 17.95% decrease in total phenols and a 13.01% decrease in ascorbic acid, which may be caused by excessive surface area, indicating that the applicability of HRW to celery remains to be studied. The loss of functional components of both fruits could be controlled under 4%. Throughout the treatment, the phenolic profiles and volatile compounds remained stable. Notably, an increase in partial ester compounds, such as ethyl caproate, was observed in HRW-treated cherry tomatoes, which might improve the sensory function. Moreover, the reduction of some compounds obtained from the decomposition of fatty acid hydroperoxides may enhance the fresh odor of fruits and vegetables. Consequently, HRW treatment emerges as a safe and environmentally friendly technology for postharvest processing of fruits and vegetables.

Filament-based 3D-printing of placebo dosage forms using brittle lipid-based excipients

In order to expand the limited portfolio of available polymer-based excipients for fabricating three-dimensional (3D) printed pharmaceutical products, Lipid-based excipients (LBEs) have yet to be thoroughly investigated. The technical obstacle of LBEs application is, however their crystalline nature that renders them very brittle and challenging for processing via 3D-printing. In this work, we evaluated the functionality of LBEs for filament-based 3D-printing of oral dosage forms. Polyglycerol partial ester of palmitic acid and polyethylene glycols monostearate were selected as LBEs, based on their chemical structure, possessing polar groups for providing hydrogen-bonding sites. A fundamental understanding of structure–function relationship was built to screen the critical material attributes relevant for both extrusion and 3D-printing processes. The thermal behavior of lipids, including the degree of their supercooling, was the critical attribute for their processing. The extrudability of materials was improved through different feeding approaches, including the common powder feeding and a devised liquid feeding setup. Liquid feeding was found to be more efficient, allowing the production of filaments with high flexibility and improved printability. Filaments with superior performance were produced using polyglycerol ester of palmitic acid. In-house designed modifications of the utilized 3D-printer were essential for a flawless processing of the filaments.

Theoretical and Kinetic Analysis of the Esterification of Undecylenic Acid with Glycerol.

The synthesis of undecylenic acid partial esters can be performed at mild temperature with a classical esterification reaction catalyzed by dodecylbenzene sulfonic acid (DBSA). A semi-empirical molecular modeling on the different reaction intermediates indicates that DBSA can strongly decrease their heats of formation through hydrogen bonding. Diester formation seems to be thermodynamically favored with a selectivity for alpha, alpha, or alpha, beta forms that depend on the geometry of the catalyst-intermediate configuration. Triesters are not favored but a high selectivity for monoesters requires a kinetic control. Experimental approach, considering different DBSA concentrations and temperature partially confirms the theoretical predictions but surfactant properties of DBSA and monoesters may induce nonpredicted geometries. Global apparent activation energies are calculated, corresponding to the formation and hydrolysis of mono and diesters. If water trapping allows the decrease of hydrolysis reaction constants, the presence of water and subsequent phase separation may explain differences between theoretical and experimental results and could help increasing monoester selectivity.

Assessment of bacterial contributions to the biochemical changes of chill-stored blunt snout bream (Megalobrama amblycephala) fillets: Protein degradation and volatile organic compounds accumulation

In this study, we evaluated the contributions of three bacteria (Pseudomonas versuta, Shewanella putrefaciens, and Aeromonas sobria) to the proteolysis, biogenic amines formation, volatile organic compounds accumulation, lipid oxidation, nucleotide catabolism, discoloration, and water migration of bream flesh during chilled storage. The results showed that P. versuta exhibited hydrolyzing activity against sarcoplasmic proteins, and all three strains could degrade myofibrillar proteins, specifically actin. The highest producer of putrescine was S. putrefaciens, which reached a maximum level 5.05 mg/kg after 14 days. Compared with the A. sobria group, hypoxanthine riboside degraded faster in samples inoculated with P. versuta or S. putrefaciens, A. sobria, P. versuta, and S. putrefaciens were responsible for the production of alcohol and aldehydes, whereas only S. putrefaciens produced thiophene and partial esters. Fish flesh inoculated with P. versuta, S. putrefaciens, and A. sobria presented slight green, yellow, and pink discoloration, respectively.

IDENTIFICATION AND QUANTITATIVE DETERMINATION OF ESTERS OF CITRIC ACID

The necessity and possibility of creating a domestic technology for the production of citric acid esters - trialkyl citrates - effective and environmentally friendly plasticizing compositions based on renewable raw materials are substantiated. Trialkylcitrates a purity of 98-99% are obtained by azeotropic esterification of citric acid with aliphatic alcohols C4-C5 under conditions of homogeneous acid catalysis. Using the synthesis of triamyl citrate as an example, the esterification of a polybasic hydroxy acid has been considered. It was established that during the synthesis a complex mixture is formed consisting of unreacted citric acid, incomplete mono-, diesters and triamyl citrate. The influence of synthesis conditions (temperature, reagent ratio, catalyst amount and reaction time) on the composition of the reaction mass is shown. A method of gas chromatographic analysis of citric acid esters has been developed. Taking into account the structural features of citric acid and its partial esters containing polar carboxyl groups, the reaction mass was pre-methylated with synthesized diazomethane. The resulting mixture consists of six esters of citric acid: trimethylcitrate; 2-hydroxy-1,3-dicarboxymethyl-2-carboxyamylpropane; 2-hydroxy-1,2-dicarboxymethyl-3-carboxyamil propane; 2-hydroxy-1-carboxymethyl-2,3-dicarboxysamyl propane; 2-hydroxy-2-carboxymethyl-1,3-dicarboxyamyl propane; triamylcitrate. The analysis was performed on a chromatographic complex "Crystal-2000M" on a capillary column with a grafted non-polar phase OV-101, length 100 m. The analysis time ranged from 22 to 49.5 min. Empirical equations were obtained using the internal standard method (the standard is dicyclohexyl adipate) to determine the calibration coefficients of the starting (trimethyl citrate т citric acid) and final (triamyl citrate) products in a wide concentration range. The results of identification of structures of six esters of citric acid for which there is no information in existing databases are presented. The study was carried out by method of chromato-mass spectrometry on the instrument SHIMADZU GCMS – QP2010 with ionization by electron impact at ionization energy of 130 eV. The analysis of the obtained spectra made it possible to determine the most probable ways of fragmentation of organic molecules and the intensity of the peaks of the ions formed.

Fast microwave-assisted hydrolysis of unsaturated polyester resin into column packing for rapid purifying of dye wastewater

Microwave-assisted selective degradation successfully converts thermosetting unsaturated polyester resins into a low-swelling (below 10 g g−1) gel material (GM) with a high yield (58–65%) in water at 100°C for only 1 h. The obtained GM possesses rough and porous structure while the content of carboxylate group obtained by cleavage of partial ester groups is more than 10%, varying with the concentration of the catalyst. It is suitable for use as packing of adsorption column to rapidly purify sewage. Super high filtering rates of 18582–27002 L h−1 m−3 without external pressure and high removal efficiency of more than 99.8% were achieved, promoting practical application for rapid removal of organic pollutants.

Synthesis of Fe3O4@SiO2-PHEMA via redox of H2O2 and Fe2+ for efficient removal of Cu2+ from aqueous solution

A facile and energy-efficient synthesis of Fe3O4@SiO2-PHEMA complex and its application as adsorbent for removal of Cu2+ from aqueous solution were investigated. Fe3O4@SiO2-PHEMA was synthesized by mixing Fe3O4@SiO2 and HEMA monomer and then initiating the polymerization of HEMA monomer by H2O2 under Fe2+ catalyzing at room temperature. As adsorbent, the maximum sorption capacity of Fe3O4@SiO2-PHEMA for Cu2+ was calculated to be 20.7 mg/g at pH 6.0. And the efficient enrichment of Cu2+ on Fe3O4@SiO2-PHEMA depended on its multiple carbonyl groups and the electrostatic interaction between carboxyl groups and Cu2+. The carboxyl groups were from slow hydrolysis of partial ester bonds of PHEMA under acidic conditions. The possible hydrolysis process of ester bonds was facilitated to avoid sorption capacity of Cu2+ decreasing caused by other ions sorption (like Fe2+) during the synthesis of the adsorbent. The adsorption of Cu2+ on Fe3O4@SiO2-PHEMA coincided with Langmuir model. The Fe3O4@SiO2-PHEMA had good dispersity in water and it could be easily collected from wastewaters by a magnet. The results showed that Fe3O4@SiO2-PHEMA was a promising adsorbent in wastewater treatment.

Formation of Bicyclic Cyclopentenone Derivatives by Robinson-Type Annulation of Cyclic β-Oxoesters Containing a 1,4-Diketone Moiety

Robinson-type cyclopentannulations of cyclic β-oxoesters possessing a 1,4-diketone moiety are accomplished under four different Brønsted basic reaction conditions. Using pyrrolidine/acetic acid in DMSO, an oxohexahydrocyclopenta[a]indene (42%) and an N-Boc-protected oxohexahydrocyclopenta[c]pyridine derivative (62%) are obtained with retention of the ester moieties. The latter compound defines an interesting new scaffold for medicinal chemistry with three positions allowing further derivatizations. The use of KOtBu in DMSO or NaH in toluene leads to cyclopentene derivatives with either partial ester saponification and decarboxylation or displacement of the ester moiety within the carbon skeleton. With aqueous KOH, the cyclopentannulations are successful in almost all cases, but with the ester moieties cleaved off. The respective bicyclic and tricyclic products are obtained in good to excellent yields. The 1,4-diketone starting materials are prepared by cerium-catalyzed oxidative coupling of β-oxoesters with isopropenyl acetate. Alternatively, a two-step sequence consisting of α-propargylation followed by palladium-catalyzed alkyne hydration is used.

Safety and efficacy of polyoxyethylene (20) sorbitan monooleate as a feed additive for all animal species

The additive is a mixture of the partial esters of sorbitol and its mono- and dianhydrides with edible commercial oleic acid and condensed with approximately 20 moles of ethylene oxide per mole of sorbitol and its anhydrides. It contains a minimum of 65% of oxyethylene groups, equivalent to not less than 96.5% of polyoxyethylene (20) sorbitan monooleate on the anhydrous basis and less than 3% water. The following concentrations of polyoxyethylene (20) sorbitan monooleate per kg complete feedingstuffs are considered safe: 1,260 mg for salmonids, 1,100 mg for cattle for fattening, 830 mg for pigs for fattening and sows, 750 mg for turkeys for fattening, 720 mg for dairy cows, 500 mg for piglets, 420 mg for chickens for fattening and laying hens, 1,320 mg for dogs and 1,100 mg for cats; and 5,000 mg/kg milk replacer are considered safe for calves. The use of polyoxyethylene (20) sorbitan monooleate as feed additive for all animal species at the maximum concentration proposed of 5,000 mg/kg complete feedingstuffs would not raise concerns for the consumer. Polyoxyethylene (20) sorbitan monooleate is non-irritant to skin and eyes, and is not a skin sensitiser. There is evidence that dermal or oral exposure to the additive can exacerbate the symptoms in individuals who are already sensitised. Users are unlikely to be exposed to the additive by inhalation. The lack of data and the inherent uncertainties do not allow concluding on the safety for the environment. Polyoxyethylene (20) sorbitan monooleate is a recognised emulsifier used in food and it is expected to have the same effect when applied to feed. From the practical examples provided, polyoxyethylene (20) sorbitan monooleate appears to be effective in aiding and maintaining the homogeneous distribution of feed materials and/or additives in feedingstuffs.

Structural requirements for bisphosphonate binding on hydroxyapatite: NMR study of bisphosphonate partial esters.

Eighteen different bisphosphonates, including four clinically used bisphosphonate acids and their phosphoesters, were studied to evaluate how the bisphosphonate structure affects binding to bone. Bisphosphonates with weak bone affinity, such as clodronate, could not bind to hydroxyapatite after the addition of one ester group. Medronate retained its ability to bind after the addition of one ester group, and hydroxy-bisphosphonates could bind even after the addition of two ester groups. Thus, several bisphosphonate esters are clearly bone binding compounds. The following conclusions about bisphosphonate binding emerge: (1) a hydroxyl group in the geminal carbon takes part in the binding process and increases the bisphosphonate's ability to bind to bone; (2) the bisphosphonate's ability to bind decreases when the amount of ester groups increases; and (3) the location of the ester groups affects the bisphosphonate's binding ability.

Synthesis and Structure of an Intramolecularly Coordinated Diaryltelluronic Acid and Its Dimethyl Ester

The oxidation of the telluroxane cluster (8-Me2NC10H6Te)6O8(OH)2 (4) or the diaryl ditelluride (8-Me2NC10H6Te)2 (7) using H2O2 provided the diarylditelluronic acid [8-Me2NC10H6Te(O)(OH)2]2(O) (6), which is the second member of this compound class and the first one to contain an intramolecularly coordinated substituent. Attempts at recrystallizing 6 from Methanol provided the partial ester [8-Me2NC10H6Te(O)(OH)(OMe)]2(O) (8). In addition structural motifs of known diaryltelluronic acids were compared using DFT calculations.

Polymer hollow particles: Encapsulation of phosphoric acid partial esters and morphology manipulation

The present work demonstrates the possible use of emulsion polymerization for fabricating structured-polymer particles which can store active materials. The hollow polymer particles were synthesized by multi-stage emulsion polymerization consisting of four main stages, (1) the preparation of alkali-swellable core latexes containing active materials, (2) first core-shell polymerization of a monomer mixture of methyl methacrylate (MMA), butyl acrylate (BA) and methacrylic acid (MAA), (3) second core-shell polymerization of styrene and (4) a neutralization stage. The morphology of synthesized capsules was observed by transmission electron microscopy (TEM). The size of the capsule prepared by standard recipe was around 300 nm and the polydispersity index was 0.024 representing that size distribution was highly monodisperse. The specific target material of encapsulation was the phosphoric acid partial ester. The amount of phosphoric acid partial ester encapsulated was determined by thermogravimetric analysis (TGA). From studies of encapsulation behaviors, it was found that the encapsulation efficiency and location of phosphoric acid partial ester in the interior of the particles were mainly dependant on its partition coefficient. In addition, the morphology of polymer capsule was manipulated by varying process parameters. The morphology changes, such as those of pore size and roughness of polymer shell, were characterized by scanning electron microscopy (SEM) and analysis of nitrogen adsorption and desorption isotherm. When neutralized with N,N′-dimethylethanolamine simultaneously during the styrene polymerization, the surface area of polymer capsule was increased drastically by about 5 times due to the formation of mesopores and the roughening of the surface on the hollow polymer shell.

A structural study of metal complexes of bisphosphonate partial ester derivatives

A structural study of metal complexes of bisphosphonate partial ester derivatives

Esters of Pyromellitic Acid. Part I. Esters of Achiral Alcohols: Regioselective Synthesis of Partial and Mixed Pyromellitate Esters, Mechanism of Transesterification in the Quantitative Esterification of the Pyromellitate System Using Orthoformate Esters, and a Facile Synthesis of the Ortho Pyromellitate Diester Substitution Pattern

Mild conditions and reversible anhydride formation allow a relative differentiation to be made of the four equivalent carbonyl groups of pyromellitic dianhydride (PMDA, benzene-1,2,4,5-tetracarboxylic dianhydride) in esterification, leading to regioselective methods to generate a wide range of partially or totally esterified products or products bearing differing esterifying groups at the different positions. Pyromellitate monoester anhydrides form efficiently in dichloromethane/triethylamine from 1 equiv of the alcohol. Under the same conditions, two different alcohols can be made to react sequentially. With 2 equiv of an alcohol, the usual mixture of meta and para diesters is obtained, separated by crystallization from HOAc. Meta and para dibenzyl pyromellitates served as regiospecific sources of other diesters, by further esterification followed by hydrogenolysis. Refluxing orthoformate triesters were found to effect quantitative esterification of the pyromellitate system under autocatalytic conditions; minor ester exchange with pre-existing esters (0-5% of total product) was ascribed to reversible anhydride formation. For general esterification with alcohols, partial ester acid chlorides were obtained using oxalyl chloride. Pyromellitate triesters afforded the ortho diester anhydrides upon distillation, thereby providing facile entry into the mostly novel ortho substitution pattern in this system. The requisite triesters were prepared by selective saponification or by the prior incorporation of one benzyl ester substituent, which could be removed by catalytic hydrogenolysis. The various benzyl esters of pyromellitates hydrogenolyzed smoothly to release the carboxylic acid groups without disturbance of pyromellitate aromaticity.

Preparation of regioprotected morins by lipase-catalysed transesterification

Different morin acetates have been prepared by alcoholysis of peracetate ( 6) in tetrahydrofuran with butanol, using Candida antarctica B or Rhizomucor miehei lipase as catalysts. The first enzyme recognised preferentially the acetate group located at position C-4′ on B ring, giving 3,5,7,2′-tetraacetylmorin ( 7). The second one, less selective, hydrolysed with comparable rates ester groups at position C-7 on A ring and C-4′ on B ring, furnishing 7 and 3,5,2′,4′-tetraacetylmorin ( 8) respectively. Prolonging alcoholysis time, both lipases gave a morin ester having free OH groups at C-7 and C-4′, 3,5,2′-triacetylmorin ( 9). In any case lipases did not affect ester groups located at position C-3, C-5 and C-2′. Morin derivative having free function OH in C-5, 3,2′-diacetylmorin ( 11) was prepared in high yield using as substrate for alcoholysis the partial ester 3,7,2′,4′-tetraacetylmorin ( 10) easily prepared by chemical conventional method.

Study on Effect of Hydroxyl Group on Lubrication Properties of Palm Based Trimethylolpropane Esters: Development of Synthesis Method

Some concerns have been raised regarding the oxidative stability of vegetable oil-base fluids. Thus, wide ranges of palm-based trimethylolpropane esters, which contain different percentages of partial esters, were synthesized. The palm-based TMP were esterified from Palm Oil Methyl Esters (POME) with trimethylolpropane [2-ethyl-2-(hydroxymethyl)-1,3-propanediol;TMP] and sodium methoxide (CH3ONa) as catalyst. Quantification of methyl esters, mono, di- and tri-TMP esters were performed using a gas chromatography (GC), with a high temperature capillary column (SGE HT5), operated at a temperature gradient of 6°C min-1 starting from 80 to 340°C. The influence of operating variables (temperature, pressure, molar ratio of palm methyl esters to TMP and catalyst amount) on diesters formation was studied and analyzed. Palm oil TMP ester containing 10-30% partial esters (monoesters and diesters) was successfully synthesized.

A Comparison of Tissue-Engineered Hyaluronic Acid Dermal Matrices in a Human Wound Model

The derivatives of hyaluronic acid (hyaluronan) have been extensively studied in the field of tissue engineering. Several forms of the material are available (benzyl esters of hyaluronic acid, HYAFF), with differing degradation profiles. This study compared 2 such products used for dermal regeneration (HYAFF p80 and HYAFF p100, the partial and total benzyl ester of hyaluronan, respectively), in a human model. In a prospective, randomized, controlled trial, 20 tattoos were tangentially excised and 1 of 2 hyaluronic acid-derived dermal matrices were applied to the wound bed. The partial ester was changed after 1 week and the total ester was kept for 2 weeks. After 2 weeks, cultured epidermal autograft was applied using the Laserskin method. Wounds were subsequently assessed by several modalities and by such features as rate of epithelialization, wound contraction, and histologic and immunohistologic appearances. Subtle differences were seen between the 2 groups, indicating that the total ester, which showed better clinical performance, could be used, especially in burns. This has the advantage of a single application for a 2-week period, rather than the comparison material, a partial ester, which requires weekly changing and degrades faster. Further, the method of epidermal grafting with a dermal substitute shows excellent results and adds to the armory for the treatment of both chronic and acute wounds.

Complete UV emission of ZnO nanoparticles in a PMMA matrix

Preparation and photoluminescence (PL) properties of zinc oxide (ZnO) nanoparticles embedded in a lipophilic polymethyl methacrylate (PMMA) matrix are reported in detail with an unbalanced sol–gel route. A high-resolution transmission electron microscope (HRTEM) indicates that ZnO particles are highly crystallized, with a size of 5–6 nm and hexagonal wurtzite structure. During the sol–gel reaction, partial ester groups of R-COOCH3 in PMMA are hydrolyzed to form carboxylic ion groups, which chemisorb on the surface of ZnO nanoparticles to eliminate the defects; thus ZnO nanoparticles in the PMMA matrix exhibit complete ultraviolet (UV) emissions, while emissions in the visible region are fully quenched.

Investigation of Acid-Base Equilibria for Symmetrically Substituted P,P′-Dialkyl Partial Esters of Bisphosphonic Acids

Bisphosphonic acids are powerful metal chelating reagents with a wide spectrum of applications. A series of partial ester derivatives of bisphosphonic acids was synthesized in order to investigate the physico-chemical changes induced by partial protection of the acid groups. The acid dissociation constants K1 and K2 for a homologous series of short-chain aqueous-soluble dibasic bisphosphonic acids, i.e., the P,P′-diethyl methylene-, ethylene- and propylene-bisphosphonic acid partial esters, H2DEt[MBP], H2DEt[EBP] and H2DEt[PrBP], respectively, were determined by potentiometric titration and 31P NMR spectrometry. All three diethyl esters are rather acidic with pK1 < 1.2 and pK2 < 2.2. The influence of the separation between the phosphonate groups on ligand acidity and successive pKa values is rationalized in terms of solvation, inductive and electrostatic effects.

Bisphosphonate prodrugs: synthesis of new aromatic and aliphatic 1-hydroxy-1,1-bisphosphonate partial esters

Methods for the preparation of various 1-hydroxy-1,1-bisphosphonate partial esters were developed. They were obtained from (alkyl or phenyl) bis(trimethylsilyl) phosphite and aromatic or aliphatic acid chlorides, followed by methanolysis.