Search Results (9)

This study presents a detailed thermodynamic investigation on the protonation behavior of tartronic acid in aqueous solutions of various ionic media, including sodium chloride, potassium chloride, tetramethylammonium chloride, and tetraethylammonium iodide. Specifically, potentiometric measurements were performed at temperatures ranging from 288.15 to 310.15 K and ionic strengths between 0.1 and 1.0 mol dm⁻³ to determine stoichiometric protonation constants in different ionic media. The formation of weak complexes between tartronate and alkaline metal cations was obtained by means of the ΔpK method. Moreover, data were modeled using the Debye–Hückel equation and Specific Ion Interaction Theory (SIT), allowing for the calculation of standard thermodynamic parameters and the assessment of the dependence of protonation constants on ionic strength. Additionally, the protonation behavior of tartronic acid was compared with that of structurally related acids, such as malonic and mesoxalic acids, providing insights into the role of molecular structure in acid dissociation. The results emphasize the significant role of entropic contributions in the protonation process and provide a comprehensive model for the thermodynamic properties of tartronic acid across a wide range of experimental conditions. Full article

Tartronic acid is known for its potential to inhibit sugar-to-lipid conversion in the human body, leading to weight loss and fat reduction. This compound is predominantly found in cucumbers and other cucurbit crops. Therefore, cultivating cucumbers with high tartronic acid content holds significant health implications. In this study, we assessed the tartronic acid content in 52 cucumber germplasms with favorable overall traits and identified 8 cucumber germplasms with elevated tartronic acid levels. Our investigation into factors influencing cucumber tartronic acid revealed a decrease in content with fruit development from the day of flowering. Furthermore, tartronic acid content was higher in early-harvested fruits compared to late-harvested ones, with the rear part of the fruit exhibiting significantly higher content than other parts. Foliar spraying of microbial agents increased tartronic acid content by 84.4%. This study provides valuable resources for breeding high tartronic acid cucumbers and offers practical insights for optimizing cucumber production practices. Full article

Mathematical modeling and computer simulation are tools of great importance for the development of fuel cells. Thus, the objective of this work is to carry out the kinetic modeling of glycerol oxidation in a DGFC (direct glycerol fuel cell), considering two different approaches: (1) realistic phenomenological models for the partial oxidation of glycerol in Pt/C, considering its adsorbed intermediates; (2) models of artificial neural networks (ANN—artificial neural networks) for oxidation mainly of PtAg/C and PtAg/MnO_x/C. The models were fitted to experimental data already available for validation and determination of their parameters, both using Matlab software, v. R2018a (MathWorks, Natick, MA, USA). Results for the phenomenological models developed showed excellent fits for the polarization curve, with an RMSE (root mean squared error) value on the order of 0.352 to 0.404 mA/cm², in addition to coverage fractions consistent with the literature for the adsorbed species. The kinetic parameters with the greatest influence on the response of the models were those associated with the consumption of glyceric acid and the formation of tartronic acid and with the dissociative adsorption of water and the formation of Pt-O_ads active sites. Regarding the neural models, excellent prediction fits were obtained for all of them, with RMSE values on the order of 0.008 to 0.014 mA/cm², indicating the possibility of representing the functional interdependence between input variables and the density cell current for cases where it would be too complex to do so via mechanistic modeling (i.e., for PtAg/C and PtAg/MnO_x/C oxidation). Full article

In this work, we show that finding and controlling optimum pH environments with Pt-based alloy catalysts can create high catalytic performances for electrocatalytic glycerol oxidation reaction (EGOR). Compared to a Pt/C catalyst, the PtCu/C alloy catalyst has higher reaction rate and turnover frequency (TOF) values by increasing the pH. Specifically, the reaction rate and TOF of the PtCu/C catalyst at pH 13 were 2.93 and 6.65 times higher than those of Pt/C, respectively. The PtCu/C catalyst also showed lower onset potential value and higher mass and specific activities than the Pt/C by increasing the pH. This indicates that the Cu in the PtCu alloy improves the catalytic activity for the EGOR in an OH⁻ group-rich environment. In the case of the PtCu/C catalyst at a high pH condition, the selectivities of tartronic acid and oxalic acid tended to increase as the selectivity of lactic acid decreased. This result means that the PtCu alloy follows primary alcohol oxidation pathways, which are more favorable in an OH⁻ group-rich environment than with only Pt. This study proposes that it is critical to optimize and control the reaction conditions for developing efficient EGOR catalysts. Full article

The interest in polymers with high thermal conductivity increased much because of their inherent properties such as low density, low cost, flexibility, and good chemical resistance. However, it is challenging to engineer plastics with good heat transfer characteristics, processability, and required strength. Improving the degree of the chain alignment and forming a continuous thermal conduction network is expected to enhance thermal conductivity. This research aimed to develop polymers with a high thermal conductivity that can be interesting for several applications. Two polymers, namely poly(benzofuran-co-arylacetic acid) and poly(tartronic-co-glycolic acid), with high thermal conductivity containing microscopically ordered structures were prepared by performing enzyme-catalyzed (Novozyme-435) polymerization of the corresponding α-hydroxy acids 4-hydroxymandelic acid and tartronic acid, respectively. A comparison between the polymer’s structure and heat transfer obtained by mere thermal polymerization before and enzyme-catalyzed polymerization will now be discussed, revealing a dramatic increase in thermal conductivity in the latter case. The polymer structures were investigated by FTIR spectroscopy, nuclear magnetic resonance (NMR) spectroscopy in liquid- and solid-state (ss-NMR), and powder X-ray diffraction. The thermal conductivity and diffusivity were measured using the transient plane source technique. Full article

In a course of metabolic experiments, we determined that the addition of δ-aminolevulinic acid (5-ALA) to a panel of glioblastoma multiforme (GBM) cells caused a steep reduction in their glycolytic activity. This reduction was accompanied by a decrease in adenosine triphosphate (ATP) production from glycolysis. These results suggested that 5-ALA is an inhibitor of glycolysis; due to the structural similarity of 5-ALA to the established lactate dehydrogenase (LDH) inhibitors oxamate (OXM) and tartronate (TART), we initially investigated LDH inhibition by 5-ALA in silico. The modelling revealed that 5-ALA could indeed be a competitive inhibitor of LDH but not a substrate. These theoretical findings were corroborated by enzymatic and cell lysate assays in which 5-ALA was found to confer a potent LDH inhibition comparable to that of OXM and TART. We subsequently evaluated the effect of 5-ALA-induced glycolysis inhibition on the viability of GBM cells with diverse metabolic phenotypes. In the Warburg-type cell lines Ln18 and U87, incubation with 5-ALA elicited profound and irreversible cell death (90–98%) at 10 mM after merely 24 h. In T98G, however, which exhibited both high respiratory and glycolytic rates, LD95 was achieved after 72 h of incubation with 20 mM 5-ALA. We additionally examined the production of the 5-ALA photosensitive metadrug protoporphyrin IX (PpIX), with and without prior LDH inhibition by TART. These studies revealed that ~20% of the 5-ALA taken up by the cells was engaged in LDH inhibition. We subsequently performed 5-ALA photodynamic therapy (PDT) on Ln18 GBM cells, again with and without prior LDH inhibition with TART, and found a PDT outcome enhancement of ~15% upon LDH pre-inhibition. We expect our findings to have a profound impact on contemporary oncology, particularly for the treatment of otherwise incurable brain cancers such as GBM, where the specific accumulation of 5-ALA is very high compared to the surrounding normal tissue. Full article

Gold nanoparticles supported on various oxides (CeO₂, CeO₂/TiO₂, MgO, MgO/TiO₂, La₂O₃, La₂O₃/TiO₂) (with 4 wt.% Au loading) were investigated in the liquid (aqueous) phase oxidation of glycerol by molecular oxygen under mild conditions, in the presence of alkaline earth (CaO, SrO and MgO) or alkaline (NaOH) bases. Full conversion and selectivity between 38 and 68% to sodium glycerate were observed on different Au supported catalysts (Au/MgO/TiO₂, Au/La₂O₃/TiO₂, Au/CeO₂ and Au/CeO₂/TiO₂). The combined effect of Au particle size and basicity of the support was suggested as the determining factor of the activity. Agglomeration of gold nanoparticles, found after the reaction, led to the deactivation of the catalysts, which prevents the further oxidation of sodium glycerate into sodium tartronate. Promising results were obtained with the use of alkaline earth bases (CaO, SrO, MgO), leading to the formation of free carboxylic acids instead of salts, which are formed in the presence of the more usual base, NaOH. Full article

Unannealed CuNiMoP electrocatalyst was found active in electrochemical oxidation of glycerol, providing over 60% conversion without optimization. Prompted by this result, the same catalyst was investigated for the thermochemical oxidation of glycerol. For the thermochemical oxidation of glycerol using the as-deposited electroless CuNiMoP catalyst, a 2³ full factorial design of experiments (two level factorial experiment design with three factors) to assess the influence of temperature (A), reaction time (B) and pressure (C). The major reaction products detected by high performance liquid chromatography (HPLC) were glyceric, hydroxypyruvic, tartronic, oxalic and formic acids. The factors found to be most significant for the production of glyceric and tartronic acids were A, B, C, AB and BC. The highest percent conversion obtained for 30-min and 60-min catalysts was 10.6% and 9.4%, respectively. The presence of lactic acid was observed only for the 60-min as-deposited electroless CuNiMoP/Al₂O₃ catalyst. The results suggest the feasibility of an inexpensive catalyst based on non-noble metals for the thermochemical oxidation of glycerol through the electroless deposition technique. Some differences exist between the thermochemical and electrochemical product selectivity of the CuNiMoP catalyst, and reasons are suggested for the observed differences. Full article

The present work deals with the kinetic analysis and modelling of glycerol (GLY) oxidation in the liquid phase over a supported gold catalyst. A Langmuir-Hinshelwood model was proposed, after considering the effect of the reaction temperature, the NaOH/GLY ratio and the initial concentrations of GLY and GLY-Product mixtures. The proposed model effectively predicted the experimental results, and both the global model and the individual parameters were statistically significant. The results revealed that the C–C cleavage to form glycolic and formic acids was the most important reaction without a catalyst. On the other hand, the supported Au catalyst promoted the GLY oxidation to glyceric acid and its further conversion to tartronic and oxalic acids. Regarding the adsorption terms, glyceric acid showed the highest constant value at 60 °C, whereas those of GLY and OH⁻ were also significant. Indeed, this adsorption role of OH⁻ seems to be the reason why the higher NaOH/GLY ratio did not lead to higher GLY conversion in the Au-catalysed reaction. Full article