Insight into the Reduction of Pyruvic Acid to Lactic Acid over Cu{110}: The Crucial Role of Intramolecular Tunneling in Direct Hydrogenation
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This work presents results from density functional theory calculations which are used to elucidate the reduction of pyruvic acid to lactic acid by direct hydrogenation over Cu{110} in vacuo. We propose a plausible pathway from reactants to products that crucially relies upon an intramolecular tunneling step to circumvent energetically unfavorable hydrogen exchange with the surface. The conclusions are further augmented by analyzing the electron density and frontier orbitals of key reaction intermediates. This reveals the origin of the predicted activity to be intimately linked to the electronic structure, which in turn is dependent upon the asorption geometry of pyruvic acid. Through the use of equilibrium thermodynamics, we are able to show the influence of temperature and pressure on the reaction profile. Importantly showing, that as the temperature is raised at low pressure (1 × 10−10 mbar), so the rate-determining step switches from being the carbonyl reduction to the reprotonation of the carboxylate group (leading to the desorption of lactic acid). At ambient pressure of 1 bar, the influence of temperature on the relative barrier heights is much less significant. This is an important step in attempting to bridge the so-called "pressure gap" and opens up the possibility of understanding the reactivity of small biologically relevant molecules at metal surfaces.Keywords:
Pyruvic acid
Moiety
Atoms in molecules
Fluorine
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Abstract Solute descriptors characterizing major interactions in solution are accessible based on quantitative structure-property relationships (QSPR). Parameters of such relationships should be additive for functional groups. Because added parameters of monools describing molecular interaction do not meet the experimentally found intermolecular interaction parameters of diols and triols, it is assumed that intramolecular hydrogen bonding is responsible for these deviations. In this paper the intramolecular interactions in several diols are illuminated by IR measurements. Particularly, the influence of intramolecular hydrogen bonding on the absorbances of the OH groups is subject of investigation. Two conclusions can be drawn from the results: The terminal OH groups, which underlie an OH–OH interaction, also change their absorbance intensity in comparison to the free OH band. Secondly, the intermolecular interaction potential is strongly affected by intramolecular hydrogen bonding. The first observation is tentatively quantified as well as the position of the equilibrium between intramolecularly bonded and free diols.
Absorbance
Intermolecular interaction
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This paper discusses all the possible conformations and intramolecular hydrogen bonds of a series of amino-alcohols.The intramolecular hydrogen bonds have a substantial effect on the conformational stability of them.The most stable conformers is characterized by an OH…N intramolecular HB,and the next stable conformers by NH…O HB,while the less stable ones are those without HB.The strong intramolecular HB OH…N leading to the significantly lowered energy levels of the occupied lone-pair molecular orbitals were founded.And the temperature dependence of photoelectron spectra(PES) is interpreted
Conformational isomerism
Lone pair
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For the first time, the data on the problem of intramolecular coordination in organic derivatives of the elements have been compiled and a systematic and critical account has been given. A definition of intramolecular coordination in its various forms is proposed. It has been shown that intramolecular coordination may constitute the driving force of a number of reactions of such organic derivatives (α-, β-, and γ-elimination). The bibliography comprises 210 references
Coordination complex
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Owning to its biobased organic acid, low cost and multiple reactive functionalities as it contains both one carboxylic acid group and hydroxyl group, lactic acid has been described as a commodity chemical sleeping giant. In this review, the conversion of lactic acid to other important commodity chemicals, such as, poly L‐lactic acid, acrylic acid, 2, 3‐pentanedione, pyruvic acid, propanoic acid, 1, 2‐propanediol, acetaldehyde, ethyl lactate, using chemical or biological catalysts, and the economy analysis of conversions are depicted. The conversion would provide a new way for the solution of the present oil crisis.
Propanoic acid
Commodity chemicals
Pyruvic acid
Acrylic acid
Ethyl lactate
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Intramolecular isotope effects in the bond forming reactions following collisions of both CO22+ and CF32+ with HD have been investigated experimentally. For the CO22++HD system the bond-forming pathway forming XCO+ (X=H, D) exhibits a strong intramolecular isotope effect favoring the formation of DCO+ at low collision energies. For the CF32++HD system the bond-forming pathway forming XCF2+ also exhibits a strong intramolecular isotope effect favoring the formation of DCF2+ at low collision energies. However, in the CF32++HD system a weak, and previously unobserved, channel, forming XF+ exhibits no intramolecular isotope effect over the collision energy regime (0.2–0.5 eV) investigated. The absence of an intramolecular isotope effect in the formation of XF+ casts doubt on the previous explanation of such isotope effects as resulting from orientation effects in the approach of the dication to the HD molecule. Using a recently proposed mechanism for the reaction of CO22+ with H2, an analysis of the statistical and zero-point factors affecting the competition between the bond-forming channels is presented. This analysis shows that such factors can readily explain the intramolecular isotope effects observed in these reactive systems.
Kinetic isotope effect
Dication
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Fermentations were performed to investigate the effect of pyruvic acid addition, in the form of Na-pyruvate, on production of L-lactic acid from glucose by Lactobacillus casei. Results showed that 30g·L -1 of Na-pyruvate could increase the L-lactic acid production significantly, and the L-lactic acid production was 74g·L -1. During the 72h fermentation, pyruvic acid could increase the L-lactic acid production greatly when added at 24h and 42h.
Pyruvic acid
Lactobacillus casei
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Streptococcus (S.) oligofermentans is a newly identified bacteria with a yet to be defined mechanism of sucrose metabolism that results in acid production. This study aimed to investigate the biochemical mechanisms of S. oligoferm-entans glucose metaolism.The S. oligofermentans LMG21532, Lactobacillus (L.) fermentum 38 and the S. mutans UA140 were used to characterize sucrose metabolism by measuring lactate dehydrogenase (LDH) activity and lactic acid production. Continuous dynamics and high performance capillary electrophoresis were used to determine LDH activity and lactic acid production, respectively, from bacteria collected at 0, 10 and 30 minutes after cultured in 10% sucrose.These analyses demonstrated that LDH activity of the three bacterial strains examined remained stable but significantly different throughout the sucrose fermentation process. The S. oligofermentans LDH activity ((0.61 ± 0.05) U/mg) was significantly lower than that of L. fermentum ((52.91 ± 8.97) U/mg). In addition, the S. oligofermentans total lactate production ((0.048 ± 0.021) mmol/L) was also significantly lower than that of L. fermentum ((0.958 ± 0.201) mmol/L). Although the S. oligofermentans LDH production was almost double of that produced by S. mutans ((0.32 ± 0.07) U/mg), lactic acid production was approximately one sixth that of S. mutans ((0.296 ± 0.058) mmol/L). Additional tests examining pyruvic acid production (the LDH substrate) demonstrated that lactic acid concentrations correlated with pyruvic acid production. That is, pyruvic acid production by S. oligofermentans was undetectable following sucrose incubation, however, (0.074 ± 0.024) and (0.175 ± 0.098) mmol/L pyruvic acid were produced by S. mutans and L. fermentum, respectively.S. oligofermentans is incapable of fermenting carbohydrates to produce enough pyruvic acid, which results in reduced lactic acid production.
Pyruvic acid
Lactobacillus fermentum
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These experiments were performed to determine the factor(s) that regulate lactic acid production and utilization by rat tumors in vivo. Arteriovenous differences for glucose and lactic, pyruvic, 3-OH-butyric, and acetoacetic acids were measured across tissue-isolated Walker 256 sarcocarcinomas and Morris 5123C hepatomas in fasted rats anesthetized with sodium pentobarbital. Twenty-six per cent of the sarcocarcinomas (n = 53) and 48% of the hepatomas (n = 29) utilized blood lactic acid. The remainder released lactic acid into the venous blood. The steady-state rate of glucose consumption was similar in both lactate-producing and lactate-utilizing tumors. The range of lactate concentrations in the blood leaving the tumors was narrower than the range of lactate concentrations in the blood entering the tumors. This difference was caused by tumor lactic acid production at low arterial lactate concentrations and tumor lactic acid utilization at high arterial lactate concentrations. Individual tumors changed from lactic acid production to lactic acid utilization in a matter of minutes in response to an increase in the arterial lactic acid concentration. Mean lactic plus pyruvic acid concentrations and lactic/pyruvic acid ratios in the tumor venous blood were 2.15 +/- 0.22 and 23.4 +/- 3.7 mM, respectively, for Walker sarcocarcinoma 256 (n = 18) and 1.28 +/- 0.13 and 48.1 +/- 5.1 mM, respectively, for hepatoma 5123C (n = 11). The results suggest: that a steady-state lactic plus pyruvic acid concentration and lactic/pyruvic acid ratio are maintained in the tumor cell cytoplasm by the active glycolytic pathway and by lactic acid dehydrogenase; that the tumor intracellular concentrations equilibrate with the arterial blood and that the tumor steady state is expressed in the tumor venous blood; and that tumor lactic acid production or utilization results from the equilibration between the variable arterial lactic acid concentration and the more constant tumor intracellular steady-state lactic acid concentration. Since the arterial lactate concentration may be less than, greater than, or equal to the intracellular steady-state concentration, an individual tumor may produce, utilize or neither produce nor utilize lactic acid.
Pyruvic acid
Lactic acidosis
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