Oxalate Esters Research Articles

Inhibitory Effects of Powdered Liquid Smoke from Mangrove (Avicennia marina) Twigs on Spoilage Bacteria

This study investigated the inhibitory effects of powdered liquid smoke derived from Avicennia marina (mangrove) twigs on spoilage bacteria. The research method used was experimental. Branches of mangrove (A. marina) were burned and distilled to produce liquid smoke. The powdered liquid smoke was subsequently tested for its antibacterial capabilities against foodborne pathogen bacteria. The damage to the bacterial formation was further illustrated using a Scanning electron micrograph. The components of liquid smoke were analysed using GC-MS. GC-MS test results on liquid smoke from mangrove twigs revealed several components including groups of acids such as butanoic acid, 1H-pyrrole-3-propanoic acid, 2-(4-methoxy-3-methylphenyl)-thiazolidine-4-carboxylic acid, hexanedioic acid, 2-bromo propionic acid, carbamic acid, oxalic acid, ritalinic acid and 7-dimethyl-6-octenyl acetate (acetic acid), as well as oxalic acid decyl propyl ester and 1,2-benzene dicarboxylic acid. The phenol group includes cyclohexanol, 2-cyclohexen-1-ol, 2-methyl-5-(1-methylethenyl)-, cis, 1,4-dihydroxy-p-menth-2-ene, phenol, 3-methyl, phenol, 2-methoxy-4-(1-propenyl)-, acetate, 1,2-diphenyl-2-ethanediol and 1,2-ethanediol. The ketone group includes beta-piperidino propiophenone, pyrrolidine-2-one, 5-[2-benzoylethyl]-,benzoyl amino-1-(4-methylphenyl)-3-piperidinyl propane, 3-nonen-5-one, 1-(1-butoxypropan-2-yloxy) propan-2-yl 2-methylbut-2-enoate, 6-octen-1-ol, 3,7-dimethyl, 4-(2,2,6-trimethyl cyclohexyl)-2-butanone and the carbonyl group includes N2-[(phenylmethoxy) carbonyl].

PISOX Copolyesters-Bio- and CO2-Based Marine-Degradable High-Performance Polyesters.

Oxalate esters and isosorbide serve as intriguing polymer building blocks, as they can be sourced from renewable resources, such as CO2 and glucose, and the resulting polyesters offer outstanding material properties. However, the low reactivity of the secondary hydroxyl groups makes it difficult to generate high-molecular-weight polymers from isosorbide. Combining diaryl oxalates with isosorbide appears to be a promising approach to produce high-molecular-weight isosorbide-based polyoxalates (PISOX). This strategy seems to be scalable, has a short polymerization time (<5 h), and uniquely, there is no need for a catalyst. PISOX demonstrates outstanding thermal, mechanical, and barrier properties; its barrier to oxygen is 35 times better than PLA, it possesses mechanical properties comparable to high-performance thermoplastics, and the glass transition temperature of 167 °C can be modified by comonomer incorporation. What makes this high-performance material truly exceptional is that it decomposes into CO2 and biomass in just a few months in soil under home-composting conditions and it hydrolyzes without enzymes present in less than a year in 20 °C water. This unique combination of properties has the potential to be utilized in a range of applications, such as biomedical uses, water-resistant coatings, compostable plastic bags for gardening and agriculture, and packaging plastics with diminished environmental impact.

Creating Pores in Chitosan-Derived Humins via in Situ CO2 Formation

Converting chitosan-derived humins into nitrogen-doped porous carbon (NPC) is a promising approach to the valorization of humins owing to their inherent nitrogen-containing advantage. Herein, we report the first example of NPC made from chitosan-derived humins, whereby a novel method to fabricate porous humins from chitosan by in situ CO2 strategy was demonstrated. By means of GPC, FT-IR, XPS, and TEM, the formation mechanism of chitosan-derived humins by catalysis of weak acids was proposed via oligomer mechanism. By catalysis of oxalic acid (OA), oxalic ester oligomers were generated to form soluble nanoparticles as precursors for humins formation. Then through intramolecular and intermolecular deamination/dehydration, the ester oligomers precipitate as humins solid due to reduced solubility, which further decompose to release CO2 from the interior of humins and transform into porous material. Otherwise, without the in situ release of CO2, humins remain almost nonporous by catalysis of HOAc.

Selective reduction of oxalic acid to glycolic acid at low temperature in a continuous flow process

Oxalic acid from CO2 is a new platform chemical for a future fossil-free chemical industry. Oxalic acid can now be efficiently converted to glycolic acid via direct hydrogenation in flow reactors without requiring oxalic acid esters as intermediates.

Activated Carbon Modified by Ester Hydrolysis of Ethyl Acetate for Water Vapor Adsorption Enhancement

To improve water vapor adsorption, this study employed oxalic acid–ethyl acetate acidic hydrolysis to modify honeycomb activated carbon and introduce hydrophilic functional groups. Scanning electron microscopy (SEM), Boehm titration, Fourier transform infrared spectroscopy (FT-IR), and an automatic surface area analyzer (BET) were used to characterize the microscopic morphology, surface functional groups, specific surface area, and pore size changes. The results showed that, when the concentration of oxalic acid is 0.0006 mol/cm3, the specific surface area is 179.06 m2/g. After hydrolysis with ethyl acetate, the original functional groups became more abundant, while the number of total acidic functional groups on the surface grew from 0.497 mmol/g to 1.437 mmol/g. The static water vapor adsorption experiments were conducted on modified activated carbon under constant temperature and humidity conditions. Compared with unmodified activated carbon, the activated carbon modified with 0.0006 mol/cm3 oxalic acid increased the adsorption capacity of water vapor by 15.7%. The adsorption capacity of activated carbon after being combined with 0.0006 mol/cm3 oxalic acid and ester hydrolysis modification increased by 37.1%. At the same temperature, the adsorption capacity increased with a higher relative humidity. At the same relative humidity, the adsorption capacity decreased as the temperature rose. Therefore, this modification method may provide clues for the application of enhancing the hygroscopic ability of activated carbon.

Selectively Fluorinated Citronellol Analogues Support a Hydrogen Bonding Donor Interaction with the Human OR1A1 Olfactory Receptor.

C-2 fluorinated and methylated stereoisomers of the fragrance citronellol 1 and its oxalate esters were prepared from (R)-pulegone 11 and explored as agonists of the human olfactory receptor OR1A1 and assayed also against site-specific mutants. There were clear isomer preferences and C-2 difluorination as in 18 led to the most active compound suggesting an important hydrogen bond donor role for citronellol 1. C-2 methylation and the corresponding oxalate ester analogues were less active.

Cyclic Peroxidic Carbon Dioxide Dimer Fuels Peroxyoxalate Chemiluminescence.

Peroxyoxalate chemiluminescence is used in self-contained light sources, such as glow sticks, where oxidation of aromatic oxalate esters produces a high-energy intermediate (HEI) that excites fluorescence dyes via electron transfer chemistry, mimicking bioluminescence for efficient chemical energy-to-light conversion. The identity of the HEI and reasons for the efficiency of the peroxyoxalate reaction remain elusive. We present here unequivocal proof that the HEI of the peroxyoxalate system is a cyclic peroxidic carbon dioxide dimer, namely, 1,2-dioxetanedione. Oxalic peracids bearing a substituted phenyl group were unable to directly excite fluorescent dyes; hence, they could be ruled out as the HEI. However, base-catalyzed cyclization of these species results in bright chemiluminescence, with decay rates and chemiexcitation quantum yields that are influenced by the electronic phenylic substituent properties. Hammett (ρ = +2.2 ± 0.1) and Brønsted (β = -1.1 ± 0.1) constants for the cyclization step preceding chemiexcitation imply that the loss of the phenolate-leaving group and intramolecular nucleophilic attack of the percarboxylate anion occur in a concerted manner, generating 1,2-dioxetanedione as the unique outcome. The presence of better leaving groups influences the reaction mechanism, favoring the chemiluminescent reaction pathway over the nonemissive formation of aryl-1,2-dioxetanones.

Water Effect on Peroxyoxalate Kinetics and Mechanism for Oxalic Esters with Distinct Reactivities.

The peroxyoxalate reaction is being widely used for various analytical and bioanalytical applications, and however, few mechanistic studies are performed in aqueous media, important mainly for bioanalytical applications, where low chemiluminescence emission quantum yields are obtained. In this sense, we report here kinetic studies on the peroxyoxalate reaction, using two commercially available and widely utilized esters, bis(2,4-dinitrophenyl) oxalate (DNPO) and bis(2,4,6-trichlorophenyl) oxalate (TCPO), in 1,2-dimethoxyethane:water mixtures. The reaction of the much more reactive DNPO, in anhydrous and aqueous media, occurs by a direct nucleophilic attack of H2 O2 to the oxalic ester, not involving nucleophilic catalysis by imidazole. Contrary, in the reaction of the less reactive TCPO with H2 O2 , imidazole acts mainly as nucleophilic catalyst. For both esters, experimental conditions are established where precise kinetic data and emission quantum yields can be obtained. Interestingly, the quantum yields in 1,2-dimethoxyethane water mixtures increase up to a water concentration of 0.7molL-1 and decrease significantly with higher concentrations.

Antioxidant, Preliminary Phytochemicals, and GC-MS Analysis Reveald Bioactive Potential of Mucuna Pruriens (L.) DC. Leaves and Seeds

The bioactive potential of Mucuna pruriens leaves and seed extracted in five different solvents was evaluated by preliminary phytochemicals, antioxidant and GCMS analysis. The maximum antioxidant activity was found to be 76.96% in seeds extracted with ethanol and 72.50% in leaves extracted with petroleum ether. The preliminary photochemical analysis revealed presence of alkaloids, flavonoids, phenols, tannins, saponins, glycosides, steroids and terpenoids in plant but this detection was solvent dependent. The GCMS profiling reported 24 and 30 bioactive compounds in various solvents leaves and seeds extracts respectively. Among these compounds 20 compounds from leaves and 16 compounds from seeds reported bioactivity. The solvent dependent variations in compounds extraction were also observed. The major relative percentage of compounds in leaves extract includes Benzamide,N-[2-[4-[5-[3,3-dimethyloxiranyl]-4-hydroxy-3-methyl-2-pentenyl]oxy] phenyl]ethyl (15.83%) in petroleum ether, 2-Pentanone,4-hydroxy-4-methyl (35.52%) in acetone, 2-2-Dimethyl butanedioic acid (35.52%) in ethanol and 2-Pentanone.4-methoxy-4-methyl (47.12%) in methanol. While in seed extract Oxalic acid cyclohexyl pentyl ester (13.37%), n-Hexadecanoic acid (11.28%), 9,12-octadecadienoic acid[zz] (39.08%) in petroleum ether, 1-octadecyne (19.08%) in chloroform and 2-Pentanone.4-methoxy-4-methyl (47.64%) in methanol. Most of the compounds has antioxidant, antifungal, hypocholesterolemic, antimicrobial, anti-malarial, anti-diabetic and anti-cancerous properties. Therefore these bioactive compounds validate the use of the plant to cure various ailments by traditional practitioners and bioactive profiling will helpful for researchers to explore its applicability.

Use of coumarin derivatives as activators in the peroxyoxalate system in organic and aqueous media

The peroxyoxalate system – base catalyzed reaction of oxalic ester derivatives with hydrogen peroxide in the presence of a fluorescent activator – is one of the most efficient chemiluminescence transformations known and widely utilized in analytical and bioanalytical applications. Coumarin derivatives have found widespread application as fluorescent labels for the determination of enzymatic activity in biological fluids and in fluorescence immunoassays, among others. In this work, we show that coumarin derivatives can be utilized as activators in the peroxyoxalate reaction (with two oxalic esters, including a new, environmentally compatible derivative) in anhydrous and aqueous systems, leading to reproducible kinetic results and singlet quantum yields similar to that obtained with commonly utilized activators. Quantum yields are lower in aqueous than in anhydrous medium, however still considerably high to allow the application in analytical and bioanalytical assays. The chemiluminescence parameters (singlet quantum yields at infinite activator concentration and relative electron transfer rate constants) determined in the systems indicate the occurrence of electron or charge transfer steps according to the Chemically Initiated Electron Exchange Luminescence (CIEEL) mechanism.

Mechanistic Study of the Peroxyoxalate System in Completely Aqueous Carbonate Buffer.

The peroxyoxalate reaction is one of the most efficient chemiluminescence transformations, with emission quantum yields of up to 50%; additionally, it is widely utilized in analytical and bioanalytical assays. Although the real reason for its extremely high efficiency is still not yet understood, the mechanism of this transformation has been well elucidated in anhydrous medium. Contrarily, only few mechanistic studies have been performed in aqueous media, which would be of great importance for its application in biological systems. We report here our experimental results of the peroxyoxalate reaction in completely aqueous carbonate buffer, using fluorescein as chemiluminescence activator. The kinetics are very fast in the used basic conditions (pH>9); despite this, reproducible kinetic results were obtained. The reaction proceeds by specific base catalysis, with rate-limiting attack of hydrogen peroxide anion to the oxalic ester, in competition with ester hydrolysis by hydroxide ion. Emission quantum yields increase with the hydrogen peroxide concentration up to an optimal concentration of 10mmol L-1 . The infinite singlet quantum yield of (5.8±0.2)×10-7 is much lower than in anhydrous medium; however, it is similar to quantum yields measured before in partially aqueous media.

Predicting the Logarithmic Distribution Factors for Coprecipitation into an Organic Salt: Selection of Rare Earths into a Mixed Oxalate

Thermodynamic modelling of a leaching system that involves concurrent precipitation depends on an understanding of how the metals distribute into the precipitate before an assessment of solubility can be made. It has been suggested in the past that a pair of rare earths (A and B) in solution will separate from each other by oxalate precipitation according to a logarithmic distribution coefficient (λ), determined by the kinetics of the precipitation. By contrast, the present study hypothesises that λ may be approximated from thermodynamic terms, including the solubility product (KSp) of each rare earth oxalate and the stability constant (β1) for the mono-oxalato complex of each rare earth. The proposed model was used to calculate λ between pairs of rare earths. An experimental study was conducted to determine λ between selected pairs using homogenous precipitation through the hydrolysis of an oxalic acid ester, with fairly close agreement to the values under the proposed model. Though this model requires more thorough testing, as well as application to other organic salts, it may provide insight into distribution factors of a precipitate formed by a sequence of organic complexes.

Better late than never! Transition state character involved in the neutral solvolysis of an oxalic ester determined by the ionizing power of ethanol/water and methanol/water mixtures

Solvation effects and solvolysis extent are major aspects of the decomposition of esters, particularly in polar protic media. Among the many different ester derivatives, oxalic esters are substances that have two ester groups in the same molecular framework, but with potentially different reactivities. Aryl oxalic esters are commonly used in efficient organic chemiluminescent reactions, leading to important analytical and biological applications. We studied the decomposition of bis(2,4,6-trichlorophenyl) oxalate (TCPO) in 100, 98, 95, 90, 80, 70, 60, and 50% ethanol/water (EtOH/W) and 100, 90, 80, and 70% methanol/water (MeOH/W) mixtures (% in v/v). In these media, one phenolic residue is generated in a fast addition–elimination (step 1), followed by a second slower addition–elimination (step 2), thus, two rate constants are observed. Using a Grunwald–Winstein (G–W) relationship between these rate constants and the solvent ionizing power (Υ), we determined the sensibility (m) to solvation effects and charge development associated with the transition state (TS) of the rate-determining step (rds). We also determined the Gibbs free energy of activation (∆‡G, at 25 °C) associated with each step, and used it to rationalize the TS character of the rds, considering that in both steps a zwitterionic intermediate is generated and that the addition step is rate limiting. In EtOH/W binary mixtures a non-linear G–W plot was observed, and for 100–95% EtOH/W mixtures the sensibility was m = 1.0 (step 1, ∆‡G = 21.6 to 20.6 kcal mol−1) and 1.1 (step 2, ∆‡G = 23.9 to 23.0 kcal mol−1), indicating full ionization in the TS of the addition step. Smaller Y values in 90–50% EtOH/W reflect a more symmetrical TS, with not as many charges being generated (step 1, m = 0.196, ∆‡G = 20.3 to 19.4 kcal mol−1; step 2, m = 0.30, ∆‡G = 22.6 to 21.7 kcal mol−1). In 100%–70% MeOH/W binary mixtures, with Y values similar to those for 90–50% EtOH/W, m = 0.52 (step 1, ∆‡G = 20.3 to 18.8 kcal mol−1) and 0.27 (step 2, ∆‡G = 21.5 to 20.9 kcal mol−1) were observed. Particularly for step 1 in MeOH/W, the observation of a solvent kinetic isotope effect that varies from inverse (0.63 ± 0.09 in pure MeOH) to normal (1.9 ± 0.3 in 70% MeOH/W) is consistent with the significant participation of the solvent in TS stabilization, resembling general acid catalysis.

Nutrient and Sensory Metabolites Profiling of Averrhoa Carambola L. (Starfruit) in the Context of Its Origin and Ripening Stage by GC/MS and Chemometric Analysis.

Averrhoa carambola L. is a tropical tree with edible fruit that grows at different climatic conditions. Despite its nutritive value and reported health benefits, it is a controversial fruit owing to its rich oxalate content. The present study aimed at investigating aroma and nutrient primary metabolites distribution in A. carambola fruits grown in Indonesia, Malaysia (its endemic origin) versus Egypt, and at different ripening stages. Two techniques were employed to assess volatile and non-volatile metabolites including headspace solid-phase micro-extraction (HS-SPME) joined with gas chromatography coupled with mass-spectrometry (GC-MS) and GC-MS post silylation, respectively. Twenty-four volatiles were detected, with esters amounting for the major class of volatiles in Egyptian fruit at ca. 66%, with methyl caproate as the major component, distinguishing it from other origins. In contrast, aldehydes predominated tropically grown fruits with the ether myristicin found exclusively in these. Primary metabolites profiling led to the identification of 117 metabolites viz. sugars, polyols and organic acids. Fructose (38–48%) and glucose (21–25%) predominated sugar compositions in ripe fruits, whereas sorbitol was the major sugar alcohol (2.4–10.5%) in ripe fruits as well. Oxalic acid, an anti-nutrient with potential health risks, was the major organic acid detected in all the studied fruits (1.7–2.7%), except the Malaysian one (0.07%). It increases upon fruit ripening, including considerable amounts of volatile oxalate esters detected via SPME, and which must not be omitted in total oxalate determinations for safety assessments.

Kinetic studies on 2,6-lutidine catalyzed peroxyoxalate chemiluminescence in organic and aqueous medium: Evidence for general base catalysis

The peroxyoxalate reaction, base catalyzed perhydrolysis of activated aromatic oxalate esters in the presence of chemiluminescence activators, has widespread analytical and bioanalytical applications and is one of the most efficient chemiluminescence transformations known. We report here a kinetic study on this reaction using 2,6-lutidine as catalyst in organic (1,2-dimethoxyethane) and aqueous medium. In both media, experimental conditions can be designed which lead to reproducible results important for analytical applications. Observed rate constants (determined by observing the light emission intensity as well as absorbance variation due to phenol releases) show dependence on both the 2,6-lutidine and the hydrogen peroxide concentration, indicating their participation in the rate-limiting step of the transformation. The rate constants obtained from these kinetic studies proved to be at least one order of magnitude higher in water than in 1,2-dimethoxyethane as solvent. Kinetic experiments designed to distinguish between three different types of catalysis (nucleophilic, specific base and general base catalysis) clearly indicate that the role of 2,6-lutidine in this reaction is as general base catalyst in water as well as most likely in organic medium.

Free Radical Scavenging Activities of Extracts and Bioactive Constituents from the Roots of Plumbago zeylanica (Linn.)

Bioactive constituents from the methanolic extract (ME) and ethylacetate extract (EA) of Plumbago zeylanica were characterized by gas chromatography‐mass spectrometry. The free radical scavenging activities of ME and EA was determined using 1,1‐diphenyl‐2‐picryl‐hydrazyl (DPPH). Major bioactive compounds found in the ME includes oxalic acid allyltridecyl ester, decane, 2‐piperidinone‐N‐[4‐bromo‐n‐butyl] and tetradecane, compounds obtained from EA were 1‐(ethenyloxyl) octadecane and cis‐13‐octadecenoic acid. Cis‐13‐octadecenoic acid, though known, was isolated for the first time from the root of P. zeylanica. The highest percentage antioxidant activities of ME and EA were 98.5% and 45.5% respectively at 350 μg/ml concentration of extracts. Results obtained from this study justify the use of P. zeylanica in traditional medicine for treatment of different ailments and it could be a potential source for novel drug compounds.Support or Funding InformationContributions from authorsThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Interception of Radicals by Molecular Oxygen and Diazo Compounds: Direct Synthesis of Oxalate Esters Using Visible-Light Catalysis.

The synthesis of oxalate esters through a radical process, rather than the traditional ionic reaction, has been well developed in which the radicals induced by visible light are trapped by molecular oxygen and diazo compounds under room temperature. This reaction is operationally simple, mild, and shows broad substrate scopes in α-bromo ketones and diazo compounds.

Hypervalent Iodine(III)-Mediated Decarboxylative Ritter-Type Amination Leading to the Production of α-Tertiary Amine Derivatives.

α-Tertiary amines (ATAs) are attractive structural motifs that are frequently found in biologically active molecules. Therefore, the development of an efficient method for the synthesis of ATAs represents an important research topic in the field of medicinal chemistry as well as organic chemistry. Although the Ritter reaction is a reliable approach for preparing α-tertiary amine derivatives via intermolecular amination reactions, the typical methods suffer from disadvantages such as harsh reaction conditions and the use of strong acids. Because of this, it has been of limited use in the synthesis of ATAs. We report here on the decarboxylative Ritter-type amination of carboxylic acids bearing an α-quaternary carbon center using a combination of PhI(OAc)2 and molecular iodine (I2) to produce the corresponding α-tertiary amine derivatives. This reaction proceeded at ambient temperature on the benchtop with a fluorescent light. Mechanistic investigations suggest that the reaction proceeds via the formation of an alkyl iodide and a higher oxidation state iodine(III) species as key intermediates. Similarly, a stepwise protocol for the Ritter-type amination of alcohols via the formation of oxalic acid monoalkyl esters was also achieved. The present methods represent a useful tool for the synthesis of ATAs that are difficult to prepare by conventional methods.

Transition-Metal-Free Decarboxylative Photoredox Coupling of Carboxylic Acids and Alcohols with Aromatic Nitriles

A transition-metal-free protocol for the redox-neutral light-induced decarboxylative coupling of carboxylic acids with (hetero)aromatic nitriles at ambient temperature is presented. A broad scope of acids and nitriles is accepted, and alcohols can be coupled in a similar fashion through their oxalate half esters. Various inexpensive sources of UV light and even sunlight can be used to achieve this C-C bond formation proceeding through a free radical mechanism.

General Acid and Base Catalysis by Phosphate in Peroxyoxalate Chemiluminescence

AbstractThe peroxyoxalate reaction, one of the most efficient chemiluminescent transformations, is widely utilized in analytical and bioanalytical assays. Although the mechanism of this transformation has been extensively studied, it is still not yet fully clarified. Furthermore, no detailed mechanistic studies have been performed in aqueous media, highly important for analytical applications. The light emission kinetic behaviour of the peroxyoxalate reaction is studied here in phosphate buffered binary 1,2‐dimethoxyethane/water mixtures at different pH values using three oxalic ester derivatives. The results indicate that conditions can be found where the chemiluminescent perhydrolysis is predominant over dark ester hydrolysis; the reactions are subject to general acid and base catalysis by phosphate ions; are reasonably reproducible, although, generally fast. However, chemiluminescence emission quantum yields are much lower than in organic solvents.