The Pyruvate Aldol Condensation Product: A Metabolite that Escaped Synthetic Preparation for Over a Century

<p>The homo-aldol condensation product of pyruvate, <a>2-methyl-4-oxopent-2-enedioic acid (OMPD) </a>has been recently implicated as a catabolic intermediate in the bacterial degradation of lignin and previously identified from other biological sources in reports ranging over sixty years. Yet, while a preparation of the pyruvate aldol-product precursor, 4-hydroxy-4-methyl-2-oxoglutaric acid (HMOG) was first reported in 1901, there has not been a complete published synthesis of OMPD. Analysis of reaction mixtures have helped identify that it is zymonic acid, the lactone of HMOG, that is the direct precursor to OMPD. The reaction appears to proceed through an acid or base mediated ring opening that does not involve formal lactone hydrolysis. In addition to a preparative protocol we provide a proposed mechanism for the formation of methylsuccinic acid that arises from the non-oxidative decarboxylation of OMPD. Lastly, we report on the relative stability of the possible isomers of the condensation product and find that at all pH values, Z-OMPD is the most abundant.</p>

The Pyruvate Aldol Condensation Product: A Metabolite that Escaped Synthetic Preparation for Over a Century

<p>The homo-aldol condensation product of pyruvate, <a>2-methyl-4-oxopent-2-enedioic acid (OMPD) </a>has been recently implicated as a catabolic intermediate in the bacterial degradation of lignin and previously identified from other biological sources in reports ranging over sixty years. Yet, while a preparation of the pyruvate aldol-product precursor, 4-hydroxy-4-methyl-2-oxoglutaric acid (HMOG) was first reported in 1901, there has not been a complete published synthesis of OMPD. Analysis of reaction mixtures have helped identify that it is zymonic acid, the lactone of HMOG, that is the direct precursor to OMPD. The reaction appears to proceed through an acid or base mediated ring opening that does not involve formal lactone hydrolysis. In addition to a preparative protocol we provide a proposed mechanism for the formation of methylsuccinic acid that arises from the non-oxidative decarboxylation of OMPD. Lastly, we report on the relative stability of the possible isomers of the condensation product and find that at all pH values, Z-OMPD is the most abundant.</p>

The Pyruvate Aldol Condensation Product: A Metabolite that Escaped Synthetic Preparation for Over a Century

<p>The homo-aldol condensation product of pyruvate, <a>2-methyl-4-oxopent-2-enedioic acid (OMPD) </a>has been recently implicated as a catabolic intermediate in the bacterial degradation of lignin and previously identified from other biological sources in reports ranging over sixty years. Yet, while a preparation of the pyruvate aldol-product precursor, 4-hydroxy-4-methyl-2-oxoglutaric acid (HMOG) was first reported in 1901, there has not been a complete published synthesis of OMPD. Analysis of reaction mixtures have helped identify that it is zymonic acid, the lactone of HMOG, that is the direct precursor to OMPD. The reaction appears to proceed through an acid or base mediated ring opening that does not involve formal lactone hydrolysis. In addition to a preparative protocol we provide a proposed mechanism for the formation of methylsuccinic acid that arises from the non-oxidative decarboxylation of OMPD. Lastly, we report on the relative stability of the possible isomers of the condensation product and find that at all pH values, Z-OMPD is the most abundant.</p>

Synthesis, Properties of Biodegradable Poly(Butylene Succinate-co-Butylene 2-Methylsuccinate) and Application for Sustainable Release

A novel biobased and biodegradable polyester, i.e., poly(butylene succinate-co-butylene 2-methylsuccinate) (P(BS-BMS)) was synthesized by succinic acid (SA), 2-methylsuccinic acid (MSA), and 1,4-butanediol (BDO) via a typically two-step esterification and polycondensation procedure. The chemical structure and macromolecular weight of obtained copolymers were characterized by 1H NMR, 13C NMR, and GPC. The melting temperature and degree of crystallinity were also studied by DSC, and it was found that the values were gradually decreased with increasing of MSA content, while the thermal stability remained almost unchanged which was tested by TGA. In addition, the biodegradation rate of the P(BS-BMS) copolymers could be controlled by adjusting the ratio of SA and MSA, and such biodegradability could make P(BS-BMS) copolymers avoid microplastic pollution which may be brought to the environment for applications in agricultural field. When we applied P(BS-BMS) copolymers as pesticide carriers which were prepared by premix membrane emulsification (PME) method for controlling Avermectin delivery, an improvement of dispersion and utilization of active ingredient was obviously witnessed. It showed a burst release process first followed by a sustained release of Avermectin for a long period, which had a great potential to be an effective and environmental friendly pesticide-release vehicle.

Compositional evolution of particle-phase reaction products and water in the heterogeneous OH oxidation of model aqueous organic aerosols

Organic compounds present at or near the surface of aqueous droplets can be efficiently oxidized by gas-phase OH radicals, which alter the molecular distribution of the reaction products within the droplet. A change in aerosol composition affects the hygroscopicity and leads to a concomitant response in the equilibrium amount of particle-phase water. The variation in the aerosol water content affects the aerosol size and physicochemical properties, which in turn governs the oxidation kinetics and chemistry. To attain better knowledge of the compositional evolution of aqueous organic droplets during oxidation, this work investigates the heterogeneous OH-radical-initiated oxidation of aqueous methylsuccinic acid (C5H8O4) droplets, a model compound for small branched dicarboxylic acids found in atmospheric aerosols, at a high relative humidity of 85 % through experimental and modeling approaches. Aerosol mass spectra measured by a soft atmospheric pressure ionization source (Direct Analysis in Real Time, DART) coupled with a high-resolution mass spectrometer reveal two major products: a five carbon atom (C5) hydroxyl functionalization product (C5H8O5) and a C4 fragmentation product (C4H6O3). These two products likely originate from the formation and subsequent reactions (intermolecular hydrogen abstraction and carbon–carbon bond scission) of tertiary alkoxy radicals resulting from the OH abstraction occurring at the methyl-substituted carbon site. Based on the identification of the reaction products, a kinetic model of oxidation (a two-product model) coupled with the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model is built to simulate the size and compositional changes of aqueous methylsuccinic acid droplets during oxidation. Model results show that at the maximum OH exposure, the droplets become slightly more hygroscopic after oxidation, as the mass fraction of water is predicted to increase from 0.362 to 0.424; however, the diameter of the droplets decreases by 6.1 %. This can be attributed to the formation of volatile fragmentation products that partition to the gas phase, leading to a net loss of organic species and associated particle-phase water, and thus a smaller droplet size. Overall, fragmentation and volatilization processes play a larger role than the functionalization process in determining the evolution of aerosol water content and droplet size at high-oxidation stages.

Protoenzymes: the case of hyperbranched polyesters

Enzymes are biopolymeric complexes that catalyse biochemical reactions and shape metabolic pathways. Enzymes usually work with small molecule cofactors that actively participate in reaction mechanisms and complex, usually globular, polymeric structures capable of specific substrate binding, encapsulation and orientation. Moreover, the globular structures of enzymes possess cavities with modulated microenvironments, facilitating the progression of reaction(s). The globular structure is ensured by long folded protein or RNA strands. Synthesis of such elaborate complexes has proven difficult under prebiotically plausible conditions. We explore here that catalysis may have been performed by alternative polymeric structures, namely hyperbranched polymers. Hyperbranched polymers are relatively complex structures that can be synthesized under prebiotically plausible conditions; their globular structure is ensured by virtue of their architecture rather than folding. In this study, we probe the ability of tertiary amine-bearing hyperbranched polyesters to form hydrophobic pockets as a reaction-promoting medium for the Kemp elimination reaction. Our results show that polyesters formed upon reaction between glycerol, triethanolamine and organic acid containing hydrophobic groups, i.e. adipic and methylsuccinic acid, are capable of increasing the rate of Kemp elimination by a factor of up to 3 over monomeric triethanolamine. This article is part of the themed issue ‘Reconceptualizing the origins of life’.

Compositional Evolution of Particle Phase Reaction Products and Water in the Heterogeneous OH Oxidation of Aqueous Organic Droplets

Organic compounds present at/near the surface of aqueous droplets can be efficiently oxidized by gas-phase OH radicals, which alter the molecular distribution of the reaction products within the droplet. A change in aerosol composition affects the hygroscopicity and leads to a concomitant response in the equilibrium amount of particle phase water. The variation in the aerosol water content affects the aerosol size and physicochemical properties, which in turn governs the oxidation kinetics and chemistry. To attain better knowledge of the compositional evolution of aqueous organic droplets during oxidation, this work investigates the heterogeneous OH radical initiated oxidation of aqueous methylsuccinic acid (C5H8O4) droplets, a model compound for small branched dicarboxylic acids found in atmospheric aerosols, at a high relative humidity of 85 % through experimental and modelling approaches. Aerosol mass spectra measured by a soft atmospheric pressure ionization source (Direct Analysis in Real Time, DART) coupled with a high-resolution mass spectrometer reveal two major products: a five carbon atom (C5) hydroxyl functionalization product (C5H8O5) and a C4 fragmentation product (C4H6O3). These two products likely originate from the formation and subsequent reactions (intermolecular hydrogen abstraction and carbon–carbon bond scission) of tertiary alkoxy radicals resulting from the OH-abstraction occurring at the methyl-substituted carbon site. Based on the identification of the reaction products, a kinetic model of oxidation (a two-product model) coupled with the Aerosol Inorganic Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model is built to simulate the size and compositional changes of aqueous methylsuccinic acid droplets during oxidation. Model results show that at the maximum OH exposure, the droplets become slightly more hygroscopic after oxidation, as the mass fraction of water predicted to increase from 0.362 to 0.424; however, the diameter of the droplets decreases by 6.1 %. This can be attributed to the formation of volatile fragmentation products that partition to the gas phase, leading to a net loss of organic species and associated particle phase water, and thus a smaller droplet size. Overall, fragmentation and volatilization processes play a larger role than the functionalization process in determining the evolution of aerosol water content and droplet size at high oxidation stages.

Electrocatalytic upgrading of itaconic acid to methylsuccinic acid using fermentation broth as a substrate solution

An electrocatalytic transformation of biomass based platform chemicals is feasible even using crude fermentation broth.