Methylsuccinic Acid Research Articles

Stereocomplementary Bioreduction of α,β-Unsaturated Dicarboxylic Acids and Dimethyl Esters using Enoate Reductases: Enzyme- and Substrate-Based Stereocontrol

Asymmetric bioreduction of alpha,beta-unsaturated dicarboxylic acids, such as 2-methylmaleic/fumaric and 2-methylenesuccinic acid, as well as the corresponding dimethyl esters, using three cloned enoate reductases furnished 2-methylsuccinic acid or dimethyl 2-methylsuccinate, respectively. Opposite stereoisomeric products were obtained in up to >99% ee either by choice of the enzyme or by using E/Z-configurated substrates. Cofactor-recycling systems (NADH/FDH/formate, NADH/GDH/glucose or NADPH/G6PDH/glucose-6-phosphate) only worked in presence of a divalent metal ion, such as Ca2+, Mg2+, or Zn2+.

A phase equilibrium model for atmospheric aerosols containing inorganic electrolytes and organic compounds (UHAERO), with application to dicarboxylic acids

Computation of phase and chemical equilibria of water‐organic‐inorganic mixtures is of significant interest in atmospheric aerosol modeling. A new version of the phase partitioning model, named UHAERO, is presented here, which allows one to compute the phase behavior for atmospheric aerosols containing inorganic electrolytes and organic compounds. The computational implementation of the model is based on standard minimization of the Gibbs free energy using a primal‐dual method, coupled to a Newton iteration. Water uptake and deliquescence properties of mixtures of aqueous solutions of salts and dicarboxylic acids, including oxalic, malonic, succinic, glutaric, maleic, malic, or methyl succinic acids, are based on a hybrid thermodynamic approach for the modeling of activity coefficients (Clegg and Seinfeld, 2006a, 2006b). UHAERO currently considers ammonium salts and the neutralization of dicarboxylic acids and sulfuric acid. Phase diagrams for sulfate/ammonium/water/dicarboxylic acid systems are presented as a function of relative humidity at 298.15 K over the complete space of compositions.

Equine biochemical multiple acyl-CoA dehydrogenase deficiency (MADD) as a cause of rhabdomyolysis

Two horses (a 7-year-old Groninger warmblood gelding and a six-month-old Trakehner mare) with pathologically confirmed rhabdomyolysis were diagnosed as suffering from multiple acyl-CoA dehydrogenase deficiency (MADD). This disorder has not been recognised in animals before. Clinical signs of both horses were a stiff, insecure gait, myoglobinuria, and finally recumbency. Urine, plasma, and muscle tissues were investigated. Analysis of plasma showed hyperglycemia, lactic acidemia, increased activity of muscle enzymes (ASAT, LDH, CK), and impaired kidney function (increased urea and creatinine). The most remarkable findings of organic acids in urine of both horses were increased lactic acid, ethylmalonic acid (EMA), 2-methylsuccinic acid, butyrylglycine (iso)valerylglycine, and hexanoylglycine. EMA was also increased in plasma of both animals. Furthermore, the profile of acylcarnitines in plasma from both animals showed a substantial elevation of C4-, C5-, C6-, C8-, and C5-DC-carnitine. Concentrations of acylcarnitines in urine of both animals revealed increased excretions of C2-, C3-, C4-, C5-, C6-, C5-OH-, C8-, C10:1-, C10-, and C5-DC-carnitine. In addition, concentrations of free carnitine were also increased. Quantitative biochemical measurement of enzyme activities in muscle tissue showed deficiencies of short-chain acyl-CoA dehydrogenase (SCAD), medium-chain acyl-CoA dehydrogenase (MCAD), and isovaleryl-CoA dehydrogenase (IVD) also indicating MADD. Histology revealed extensive rhabdomyolysis with microvesicular lipidosis predominantly in type 1 muscle fibers and mitochondrial damage. However, the ETF and ETF-QO activities were within normal limits indicating the metabolic disorder to be acquired rather than inherited. To our knowledge, these are the first cases of biochemical MADD reported in equine medicine.

Anaerobic Cometabolic Transformation of Polycyclic and Heterocyclic Aromatic Hydrocarbons: Evidence from Laboratory and Field Studies

The sulfate-reducing enrichment culture N47 can grow on naphthalene or 2-methylnaphthalene as the sole carbon and energy source. Here we show that the culture can furthermore cometabolicallytransform a variety of polycyclic and heteroaromatic compounds with naphthalene or methylnaphthalene as the auxiliary substrate. Most of the cosubstrates were converted to the corresponding carboxylic acids, frequently to several isomers. The mass spectra of specific metabolites that were extracted from supernatants of cultures containing the cosubstrates benzothiophene, benzofuran, and 1-methylnaphthalene resembled known intermediates of the anaerobic naphthalene and 2-methylnaphthalene degradation pathways (i.e., naphthyl-2-methylsuccinic acid and naphthyl-2-methylenesuccinic acid). This indicates that some of the tested compounds were first methylated and then transformed to the corresponding methylsuccinic acids by a fumarate addition to the methyl group. For some of the cosubstrates, a partial or total inhibition of growth on the auxiliary substrate was observed. This was not caused by the toxicity of the individual cosubstrate itself, but by a specific combination of auxiliary substrate and cosubstrate. None of the cosubstrates tested could be utilized as the sole carbon source and electron donor by the enrichment culture N47. Field investigations at the tar-oil-contaminated aquifer, where strain N47 originated, revealed the presence of a number of metabolites similar to the ones identified in batch culture supernatants. Our findings suggest that aromatic hydrocarbons and heterocyclic compounds can be converted by aquifer organisms and produce a variety of polar compounds that become mobile in groundwater.

Thermodynamic Models of Aqueous Solutions Containing Inorganic Electrolytes and Dicarboxylic Acids at 298.15 K. 1. The Acids as Nondissociating Components

Atmospheric aerosols contain a significant fraction of water-soluble organic compounds, including dicarboxylic acids. Water activities at approximately 298.15 K (including data for highly supersaturated solutions) of oxalic, malonic, succinic, glutaric, maleic, malic, and methyl succinic acids are first correlated as a function of concentration, treating the acids as nondissociating components. Methods proposed by Clegg et al. (J. Aerosol. Sci. 2001, 32, 713-738), and by Clegg and Seinfeld (J. Phys. Chem. A 2004, 108, 1008-1017) for estimating water activities and solute activity coefficients in aqueous mixtures containing both electrolytes and uncharged solutes are then evaluated from comparisons with literature data. These data include water activities, solubilities, and determinations of the eutonic points of solutions containing up to five acids, and solutions containing one or more acids and the salts (NH(4))(2)SO(4), NH(4)NO(3), or NaCl. The extended Zdanovskii-Stokes-Robinson approach of Clegg and Seinfeld yields the more accurate predictions for aqueous mixtures containing dicarboxylic acids only, and for aqueous mixtures of the acids and salts (though by a lesser margin). A number of hybrid modeling approaches, which contain elements of both methods, are outlined.

Phase Changes during Hygroscopic Cycles of Mixed Organic/Inorganic Model Systems of Tropospheric Aerosols

A correct description of the aerosol's phases is required to determine its gas/particle partitioning, its reactivity and its water uptake and release. In this study, we investigate organic/electrolyte interactions of ammonium sulfate, nitrate and sodium chloride with substances containing carboxylic acids (COOH) and hydroxyl (OH) functional groups. As organic model compounds, we chose polyols with different OH/CHn (n = 0-3) ratios-namely, glycerol, 1,4-butanediol, and 1,2-hexanediol-as well as PEG 400 and a mixture of dicarboxylic acids consisting of malic, malonic, maleic, glutaric, and methylsuccinic acid. Bulk solubility and water activity measurements of these model systems together with a survey of literature data showed that NaCl is a salting-out agent for alcohols and organic acids whereas ammonium nitrate and sulfate exhibited salting-in and salting-out tendencies depending on the nature and number of functional groups as well as on the concentration of the solution. All investigated salts induce a liquid-liquid phase separation in the 1,2-hexanediol/water system. Considering the composition of the tropospheric aerosol, such phase separations might indeed occur frequently when particles in the atmosphere are exposed to varying relative humidity. To complement the bulk experiments, we investigated single particles consisting of ammonium sulfate and dicarboxylic acids as well as of ammonium sulfate and PEG 400 in an electrodynamic balance. Whereas the relative humidities of total deliquescence as well as the water uptake and release of the fully deliquesced particles are in good agreement with the bulk results and represent thermodynamic equilibrium, the water uptake before full deliquescence shows significant deviations. These deviations may be caused by morphological effects.

Room-Temperature Polycondensation of Dicarboxylic Acids and Diols Catalyzed by Water-Stable Lewis Acids

Room-temperature polycondensations of methylsuccinic acid (MSA) (at 35 °C), bromosuccinic acid (BSA), 2-bromoadipic acid (BAA) (at 40 °C), and citraconic acid (CA) (at 60 °C) with diols containing 1,3-propanediol (1,3-PD) and 1,4-butanediol (1,4-BD) were performed under reduced pressure (0.3–30 mmHg) using scandium trifluoromethanesulfonate [Sc(OTf)3], scandium trifluoromethanesulfonimide [Sc(NTf2)3], and polymer-supported scandium trifluoromethanesulfonate (PS–Sc) to give poly(alkylene alkanoate)s with Mn = 0.67 × 104−1.41 × 104 (Mw/Mn = 1.4–2.1) with quantitative yields. The catalysts are recovered quantitatively and reused. Room-temperature polycondensation made it possible to use thermally unstable monomers containing carbon-carbon double bond and bromo functionality. The atom-transfer radical polymerization (ATRP) of methyl methacrylate (MMA) ([M]0/[I]0=10) using poly(butylene succinate-co-butylene bromoadipate) [poly(BS-co-BBA)] (Mn = 0.75 × 104, Mw/Mn = 2.0) as the macroinitiator and complex of CuBr and 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as the catalyst was carried out in anisole at 80 °C for 10 h under nitrogen atmosphere to give polyester having PMMA side chains [Mn = 2.01 × 104 and Mw/Mn = 1.9, 65% yield].

Neonatal Screening by Tandem Mass Spectrometry

After completing this article, readers should be able to: 1. List the major categories of diseases detectable by expanded newborn screening. 2. Give examples of the benefits and limitations of screening by tandem mass spectrometry. 3. Describe the appropriate follow-up for an abnormal screening result. The screening of newborns for inherited metabolic disorders is a well-established public health activity, first implemented in the early 1960s for the presymptomatic identification of patients who have phenylketonuria (PKU). Since then, significant technological advances, most importantly the development of tandem mass spectrometry (MS/MS), have enabled the detection of an increasing number of metabolic disorders in newborn blood. This article reviews the basic technology of MS/MS and its application to newborn screening, with the aim of highlighting the benefits and pointing out some limitations of this powerful technology. Early screening for PKU used the bacterial inhibition assay of Guthrie, in which inhibition of bacterial growth on an agar medium, introduced by the addition of a phenylalanine analog, was overcome by the presence of dried blood discs containing high levels of phenylalanine (such as from a PKU patient). This approach later was adapted for the detection of leucine in patients who have maple syrup urine disease (MSUD), methionine in patients who have classic homocystinuria, and tyrosine in patients who have tyrosinemia. Over the years, other techniques have been implemented to screen for additional disorders, including congenital hypothyroidism, biotinidase deficiency, galactosemia, hemoglobinopathies, and congenital adrenal hyperplasia. The classic criteria used to determine whether a disorder is suitable for screening include: 1) the disorder is clinically and biochemically well defined, 2) it is associated with significant morbidity or mortality, 3) an effective treatment is available, and 4) there is a simple and safe screening test. (1) By the early 1990s, all states offered screening for at least PKU and congenital hypothyroidism, …

Identification of 19 New Metabolites Induced by Abnormal Amino Acid Conjugation in Isovaleric Acidemia

Isovaleric acidemia (IVA) is an autosomal recessive genetic disorder of the enzyme isovaleryl-CoA dehydrogenase, which is involved in leucine metabolism (1). Clinical symptoms include poor feeding, tachypnea, vomiting (2), listlessness, lethargy, coma (2)(3), and dehydration (4). Individuals homozygous for this defect are characterized primarily by the excretion of isovalerylglycine (2). The metabolic profile may be further complicated by intermediate metabolites such as 3- and 4-hydroxyisovaleric acid (5), methylsuccinic acid (6), methylfumaric acid (7), isovalerylglucuronide (8), isovalerylglutamic acid (9), N -isovalerylalanine and N -isovalerylsarcosine (10), isovalerylcarnitine (11), 3-hydroxyisoheptanioc acid (12), and alloisoleucine (4). Diagnosis of IVA is based on clinical symptoms and the presence of isovalerylglycine and 3-hydroxyisovaleric acid (13), with some of the above-mentioned metabolites also occurring to a greater or lesser extent (4). Despite the large number of already identified excreted metabolites, their occurrence still does not entirely explain all of the clinical symptoms experienced by these patients. The statement made in 1982 by Duran et al. (14) that “[t]he continuing search for ‘new’ metabolites may eventually lead to a better understanding of the relationship between the clinical conditions and their biochemical abnormalities” is the motivation for our search for previously unidentified metabolites in IVA. In this study, we analyzed the urine of IVA patients for the presence of induced amino acid metabolites not previously identified in IVA. Most of the amino acid conjugates occurring in the …

Development of an HPLC-fluorescence determination method for carboxylic acids related to the tricarboxylic acid cycle as a metabolome tool

We report the simultaneous determination of the carboxylic acids related to the tricarboxylic acid (TCA) cycle, which plays an important role in producing adenosine triphosphate (ATP) and generating energy in mitochondria. Seven carboxylic acids from the TCA cycle, and pyruvic acid and 2-methylsuccinic acid, as an internal standard, were derivatized with a fluorescent reagent for carboxyl groups, 4-N,N-dimethylaminosulfonyl-7-piperazino-2,1,3-benzoxadiazole (DBD-PZ), in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and 4-N,N-dimethyaminopyridine as the coupling reagents, at 60 degrees C for 120 min. Subsequently, the excess DBD-PZ was removed efficiently using a cation-exchange cartridge, SDB-RPS (Empore). These fluorescent derivatives were separated well from each other on an octadecyl silica column (TSKgel ODS-80Ts, 250 x 4.6 mm, i.d.) with an eluent of acetonitrile-water containing 1% formic acid at a flow rate of 0.8 mL/min, and were detected fluorometrically at 560 nm, with excitation at 450 nm. The validation data were satisfactory in the range of 2.5-100 microm citric acid, isocitric acid, 2-oxoglutaric acid, succinic acid and fumaric acid. The detection limit (S/N = 3) for citric acid was 2 fmol on the column. The structures of these derivatives were confirmed by high-performance liquid chromatography-mass spectrometry, which proved that their carboxylic groups were completely labeled with DBD-PZ, except for oxaloacetic acid. This HPLC method was successfully applied to the analysis of TCA cycle metabolites in rat urine. The method will also be useful for metabolome research, such as for target analyses of metabolites with carboxyl groups, not only in urine but also in cells and organs.

D-Serine-induced nephrotoxicity: a HPLC–TOF/MS-based metabonomics approach

HPLC-MS-based metabonomic analysis was used to investigate urinary metabolic perturbations associated with D-serine-induced nephrotoxicity. D-Serine causes selective necrosis of the proximal straight tubules in the rat kidney accompanied by aminoaciduria, proteinuria and glucosuria. Alderely Park (Wistar-derived) rats were dosed with either D-serine (250 mg/kg ip) or vehicle (deionised water) and urine was collected at 0-12, 12-24, 24-36 and 36-48 h post-dosing. Samples were analysed using a Waters Alliance HT 2795 HPLC system coupled to a Waters Micromass Q-ToF-micro equipped with an electrospray source operating in either positive or negative ion mode. Changes to the urinary profile were detected at all time points compared to control. In negative ion mode, increases were observed in serine (m/z=103.0077), m/z=104.0376 (proposed to be hydroxypyruvate) and glycerate (m/z=105.0215), the latter being metabolites of D-serine. Furthermore, an increase in tryptophan, phenylalanine and lactate and decreases in methylsuccinic acid and sebacic acid were observed. Positive ion analysis revealed a decrease in xanthurenic acid, which has previously been assigned and reported using HPLC-MS following exposure to mercuric chloride and cyclosporine A. A general aminoaciduria, including proline, methionine, leucine, tyrosine and valine was also observed as well as an increase in acetyl carnitine. Investigation of additional metabolites altered as a result of exposure to D-serine is on-going. Thus, HPLC-MS-based metabonomic analysis has provided information concerning the mechanism of D-serine-induced renal injury.

Mixing of the Organic Aerosol Fractions: Liquids as the Thermodynamically Stable Phases

An increasing number of single-particle measurements show that organic and inorganic constituents of the atmospheric aerosol are internally mixed within the particles. Therefore, the phases of the aerosol will be influenced by both mixing of the organic substances with each other and mixing between organic and inorganic constituents. In this work, the mixing properties of the organic aerosol fractions have been investigated theoretically and experimentally with respect to melting and deliquescence. We show that a liquid (or an amorphous solid) is the thermodynamically stable phaseeven in the absence of water as a solventprovided that a sufficiently high number of miscible components are present. Furthermore, we show experimentally that the deliquescence relative humidity of aqueous solutions of dicarboxylic acids decreases with an increasing number of components present in the solution. A five-component mixture consisting of malic, malonic, maleic, glutaric, and methylsuccinic acids deliquesces at a relative humidity (RH) as low as 45.4% RH, while the pure dicarboxylic acids exhibit deliquescence points between 72 and 96% RH. A further reduction of the deliquescence relative humidity is observed when an inorganic salt is added to the dicarboxylic acid five-component mixture. For NaCl, deliquescence of the eutonic composition occurred at 41.3%, for ammonium sulfate at 36.4%, and for ammonium nitrate even at 27.1% RH. Interactions between the solutes lead to either higher or lower solubilities in the multicomponent mixture as compared to the respective single-component aqueous solutions. In the mixed dicarboxylic acids/inorganic salt solutions, the solubilities of ammonium nitrate and sulfate are increased by ∼40%, the one of sodium chloride is decreased by a similar amount. In summary, these mixing properties suggest that small fractions of organic species prevent tropospheric aerosols from becoming fully solid, and the organic fraction may even stay fully liquid irrespective of tropospheric humidity.

Влияние L-карнитина на метаболические нарушения при экспериментальной недостаточности ацил-КоА дегидрогеназ

Effect of L-carnitine (LC)on the metabolism of organic acids and carnitine homeostasis was studied in rats with riboflavin deficiency producing unusual dicarboxylic acidurea and modeling multiple acyl-CoA dehydrogenase deficiency in humans. Riboflavin deficient (RFD) rats exhibited increased excretion of glutaric, ethylmalonic, and methylsuccinic acids, as well as isovaleryl-, butyryl-, isobutyryl-, 2-methyl-butyryl-, and hexanoylglycine, short-chain and medium-chain saturated, and unsaturated dicarboxylic organic acids (C 6 -C 10 ). RFD rats also showed a decrease in the concentration of free LC in the blood plasma and in tissues, an increase in the level of isobutyryl- and isovalerylcarnitine in muscle tissue, and reduction in the level of acetyl- and propionylcarnitine in the blood plasma, kidney, and liver (all changes detected relative to animals in the control group). The introduction of LC to RFD rats normalized the LC homeostasis by increasing free LC concentration in the blood plasma and tissues, enhanced the acyl-LC excretion with urine and the level in tissues, and reduced the manifestations of organic acidurea.

Aqueous organometallic catalysis. Isotope exchange reactions in H2–D2O and D2–H2O systems catalyzed by water-soluble Rh- and Ru-phosphine complexes

The water-soluble complexes [{RuCl2(mTPPMS)2}2], [RuCl2(PTA)4], [RhCl(mTPPMS)3], [RhCl(mTPPTS)3], and [RhCl(PTA)3] (mTPPMS = sodium salt of meta-sulfonatophenyl-diphenylphosphine, mTPPTS = sodium salt oftris(meta-sulfonatophenyl)phosphine, and PTA = 1,3,5-triaza-7-phosphaadamantane) showed high catalytic activity (up to 1252 h−1) in the H–D isotope exchange reactions between H2 and D2O or D2 and H2O. The reactions took place at 20–70 °C, 0.1–2 MPa H2, and were strongly influenced by the pH. In the hydrogenation (with H2) of unsaturated acids in D2O, the relative rates of H–D exchange, hydrogenation and deuteration were determined by the individual substrates and catalysts: in the reaction of maleic acid catalyzed by [RhCl(mTPPMS)3] only hydrogenation took place with no deuteration and H–D exchange, whereas a similar reaction of itaconic acid was accompanied by a fast H–D exchange and the product methylsuccinic acid was highly deuterated.

Synthesis of Phosphorus-Substituted Derivatives of Methylsuccinic Acid

Synthesis of Phosphorus-Substituted Derivatives of Methylsuccinic Acid

‘Diopium’, a chiral phosphoniophosphine derived from Kagan's diop. Rhodium complexes and reducing catalytic properties

Cationic chiral monophosphines are devised as a novel type of ligands for catalytic transformations of polar substrates with polar reagents. A phosphonio-phosphine derived from ( R, R)-diop (‘methyldiopium’) proved to act as a chiral version of Baird's ω-phosphonio-phosphine ligands (‘phophos’) in Rh(I) complexes in both 1:1 and 2:1 P:Rh stoichiometry. Their versatile structure in CDCl 3 solution has been studied by NMR spectroscopy in the presence of various anions (Cl −, I −, BF 4 −, PF 6 −). The in situ 2.5:1 methyldiopium–Rh catalytic system slowly hydrogenated ( Z)-α-acetamidocinnamic acid in 63% conversion and 5% ee. This system was, however, specifically active in a novel hydrogen transfer procedure by a 1:1 HCOOH:NEt 3 mixture under mild conditions (40 °C, in the absence of DMSO), for which the corresponding diop–Rh system was not active. Itaconic acid was thus quantitatively reduced to racemic methylsuccinic acid. ( Z)-α-acetamidocinnamic acid was reduced in up to 85% conversion to N-acetylphenylalanine in various solvents. Though still moderate, the ee's depend on the solvent: 10% in ( R) product in THF, 14% in ( S) product in acetonitrile.

Catalytic behavior of silica‐supported methylcellulose–oxalic acid–Pt complex in asymmetric hydrogenation of 2‐butanone and itaconic acid

AbstractA new silica‐supported biopolymer–oxalic acid–Pt complex was prepared by a simple method. Methylcellulose (mc) reacted with oxalic acid in the presence of silica to give a complex SiO2–MC–(COOH)2 on the surface of silica, then reacted with H2PtCl6·6H2O to form a Pt complex [SiO2–MC–(COOH)2–Pt]. This complex was found to be able to catalyze the asymmetric hydrogenation of 2‐butanone to (S)‐(+)‐2‐butanol and itaconic acid to (S)‐(−)‐methylsuccinic acid, respectively, at room temperature and under 1 atm H2. The experimental results showed that the product and optical yields were remarkably affected by the Pt content in the complex and the catalyst could be reused without any remarkable change in optical catalytic activity. Copyright © 2002 John Wiley & Sons, Ltd.

Inhibition of creatine kinase activity in vitro by ethylmalonic acid in cerebral cortex of young rats.

Short-chain acyl-CoA dehydrogenase deficiency is an inherited metabolic disorder biochemically characterized by tissue accumulation of ethylmalonic (EMA) and methylsuccinic (MSA) acids and clinically by severe neurological symptoms. In the present study we investigated the in vitro effects of EMA and MSA on the activity of creatine kinase (CK) in homogenates from cerebral cortex, skeletal and cardiac muscle of rats. EMA significantly inhibited CK activity from cerebral cortex, but did not affect this activity in skeletal and cardiac muscle. Furthermore, MSA had no effect on this enzyme in all tested tissues. Glutathione (GSH), ascorbic acid and alpha-tocopherol, and the nitric oxide synthase inhibitor L-NAME, did not affect the enzyme activity per se, but GSH fully prevented the inhibitory effect of EMA when co-incubated with EMA. In contrast, alpha-tocopherol, ascorbic acid and L-NAME did not influence the inhibitory effect of the acid. The data suggest that inhibition of brain CK activity by EMA is possibly mediated by oxidation of essential groups of the enzyme, which are protected by the potent intracellular, endogenous, naturally occurring antioxidant GSH.

Geochemical roots of autotrophic carbon fixation: hydrothermal experiments in the system citric acid, H2O-(±FeS)−(±NiS)

Recent theories have proposed that life arose from primitive hydrothermal environments employing chemical reactions analogous to the reductive citrate cycle (RCC) as the primary pathway for carbon fixation. This chemistry is presumed to have developed as a natural consequence of the intrinsic geochemistry of the young, prebiotic, Earth. There has been no experimental evidence, however, demonstrating that there exists a natural pathway into such a cycle. Toward this end, the results of hydrothermal experiments involving citric acid are used as a method of deducing such a pathway. Homocatalytic reactions observed in the citric acid-H2O experiments encompass many of the reactions found in modern metabolic systems, i.e., hydration-dehydration, retro-Aldol, decarboxylation, hydrogenation, and isomerization reactions. Three principal decomposition pathways operate to degrade citric acid under thermal and aquathermal conditions. It is concluded that the acid catalyzed βγ decarboxylation pathway, leading ultimately to propene and CO2, may provide the most promise for reaction network reversal under natural hydrothermal conditions. Increased pressure is shown to accelerate the principal decarboxylation reactions under strictly hydrothermal conditions. The effect of forcing the pH via the addition of NaOH reveals that the βγ decarboxylation pathway operates even up to intermediate pH levels. The potential for network reversal (the conversion of propene and CO2 up to a tricarboxylic acid) is demonstrated via the Koch (hydrocarboxylation) reaction promoted heterocatalytically with NiS in the presence of a source of CO. Specifically, an olefin (1-nonene) is converted to a monocarboxylic acid; methacrylic acid is converted to the dicarboxylic acid, methylsuccinic acid; and the dicarboxylic acid, itaconic acid, is converted into the tricarboxylic acid, hydroaconitic acid. A number of interesting sulfur-containing products are also formed that may provide for additional reaction. The intrinsic catalytic qualities of FeS and NiS are also explored in the absence of CO. It was shown that the addition of NiS has a minimal effect in the product distribution, whereas the addition of FeS leads to the formation of hydrogenated and sulfur-containing products (thioethers). These results point to a simple hydrothermal redox pathway for citric acid synthesis that may have provided a geochemical ignition point for the reductive citrate cycle.

Thermodynamic study on the sublimation of succinic acid and of methyl- and dimethyl-substituted succinic and glutaric acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline dicarboxylic acids: succinic acid, between T= 360.11 K and T= 375.14 K; methylsuccinic acid, between T= 343.12 K and T= 360.11 K; 2,2-dimethylsuccinic acid, between T= 350.11 K, and T= 365.11 K; 2-methylglutaric acid, between T= 338.38 K and T= 347.63 K; and 2,2-dimethylglutaric acid between T= 342.18 K and T= 352.66 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds, the standard, po= 105Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T= 298.15 K, were derived: