Browsing by Subject "Kinetics"
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- PublicationOpen AccessA simplified kinetic model to describe the solvent-free enzymatic synthesis of wax esters(2021-04-17) Serrano-Arnaldos, M.; Murcia, M.D.; Ortega Requena, Salvadora; Montiel, M.C.; Máximo, F.; Gómez, E.; Bastida, J.; Ingeniería QuímicaBACKGROUND: The use of biotechnological processes at industrial scale is a promising tool to replace conventional synthesis as an efficient and eco-friendly technology. For that purpose, the kinetic modelling of an in-lab optimized enzymatic process prior to scaling-up is of great utility. RESULTS: In this work, a kinetic model for the solvent-free synthesis of cetyl laurate, myristate, palmitate and stearate using different commercial immobilized lipases has been developed. In order to describe the esterification process of the cetyl esters separately and as a mixture similar to natural spermaceti, a pseudo-first-order kinetic has been proposed and tested. A relation between the inverse values of the kinetic constant and the amount of biocatalyst has been observed. The effect of temperature on the reaction rate can be accurately described by the Arrhenius equation except for immobilized Thermomyces lanuginosus, which appears to be less resistant to temperatures above 70 °C. CONCLUSION: Low deviations between experimental and predicted values (R2 ≥ 0.99) indicate that this pseudo-first-order kinetic model can be considered valid for the data range studied. In addition, the reaction rate of spermaceti can be successfully predicted through a weighted average of the kinetic constants obtained during the synthesis of each cetyl ester. This simple but accurate kinetic model for describing the solvent-free enzymatic biosynthesis of wax esters from spermaceti may contribute to extending the application of lipases as industrial catalysts.
- PublicationOpen AccessAdvances on kinetics and thermodynamics of non-catalytic supercritical methanol transesterification of some vegetable oils to biodiesel(Elsevier, 2018-07-29) Andreo Martínez, Pedro; García Martínez, Nuria; Durán del Amor, María del Mar; Quesada Medina, Joaquín; Ingeniería QuímicaKinetic and thermodynamic parameters of the non-catalytic supercritical methanol transesterification reaction of castor, jatropha, pongamia, tobacco, soybean and jojoba oils to biodiesel production were evaluated in the present study. The experiments were conducted in an 83 ml closed batch reactor at different temperatures (250–350 °C) and reaction times (15–90 min), and at optimal methanol-to-oil molar ratios (15:1 in the case of jojoba wax-oil and 43:1 for the rest of the oils). The pressure reached in the reactor ranged from 10 to 43 MPa. Integral method was used to determine appropriated reaction orders by an adjustment of experimental data to pseudo-zero, pseudo-first and pseudo-second order kinetic equations using Levenberg-Marquardt algorithm. Pseudo-first-order kinetic equation was found to be the most appropriate to describe the supercritical transesterification reaction of the vegetable oils studied. Rate constants and Arrhenius parameters were calculated, the activation energy followed the sequence: castor oil < jatropha oil < tobacco oil < pongamia oil < soybean oil < jojoba wax-oil. It is difficult to explain the behavior of jojoba and castor oils in relation to that of the rest of vegetable oils because they have a very different structure and fatty acid composition, respectively. However, the aforementioned sequence observed for the rest of vegetable oils (jatropha, tobacco, pongamia and soybean oils), which have a similar structure and fatty acid composition, can be attributed to the content of linolenic acid in the oil: the higher the content of linolenic acid, the higher the activation energy and the lower the reaction rate. Finally, thermodynamic study showed that the non-catalytic supercritical methanol transesterification reaction is non-spontaneous (endergonic) and endothermic in nature.
- PublicationOpen AccessAre we ready to measure running power? Repeatability and concurrent validity of five commercial technologies(Wiley, 2021-03) Cerezuela Espejo, Víctor; Hernández Belmonte, Alejandro; Courel Ibáñez, Javier; Conesa Ros, Elena; Mora Rodríguez, Ricardo; García Pallarés, Jesús; Actividad Física y DeporteTraining prescription in running activities have benefited from power output (PW) data obtained by new technologies. Nevertheless, to date, the suitability of PW data provided by these tools is still uncertain. The present study aimed to: (i) analyze the repeatability of five commercially available technologies for running PW estimation, and (ii) examine the concurrent validity through the relationship between each technology PW and oxygen uptake (VO2). On two occasions (test-retest), twelve endurance-trained male athletes performed on a treadmill (indoor) and an athletic track (outdoor) three submaximal running protocols with manipulations in speed, body weight and slope. PW was simultaneously registered by the commercial technologies StrydApp, StrydWatch, RunScribe, GarminRP and PolarV, while VO2 was monitored by a metabolic cart. Test-retest data from the environments (indoor and outdoor) and conditions (speed, body weight and slope) were used for repeatability analysis, which included the standard error of measurement (SEM), coefficient of variation (CV) and intraclass correlation coefficient (ICC). A linear regression analysis and the standard error of estimate (SEE) were used to examine the relationship between PW and VO2. Stryd device was found as the most repeatable technology for all environments and conditions (SEM ≤ 12.5 W, CV ≤ 4.3%, ICC ≥ 0.980), besides the best concurrent validity to the VO2 (r ≥ 0.911, SEE ≤ 7.3%). On the contrary, although the PolarV, GarminRP and RunScribe technologies maintain a certain relationship with VO2, their low repeatability questions their suitability. The Stryd can be considered as the most recommended tool, among the analyzed, for PW measurement.
- PublicationOpen AccessDisease-causing mutations in the serpin antithrombin reveal a keydomaincritical for inhibiting protease activities(Elsevier, American Society for Biochemistry and Molecular Biology , 2017-10-06) Águila Martínez, Sonia; Izaguirre, G.; Vicente García, Vicente; Martínez-Martínez, I.; Olson, S. T.; Corral de la Calle, Javier; Medicina InternaAntithrombin mainly inhibits factor Xa and thrombin. The reactive center loop (RCL) is crucial for its interactions with its protease targets and is fully inserted into the A-sheet after its cleavage, causing translocation of the covalently linked protease to the opposite end of the A-sheet. Antithrombin variants with altered RCL hinge residues behave as substrates rather than inhibitors, resulting in stoichiometries of inhibition greater than one. Other antithrombin residues have been suggested to interfere with RCL insertion or the stability of the antithrombin–protease complex, but available crystal structures or mutagenesis studies have failed to identify such residues. Here, we characterized two mutations, S365L and I207T, present in individuals with type II antithrombin deficiency and identified a new antithrombin functional domain. S365L did not form stable complexes with thrombin or factor Xa, and the I207T/I207A variants inhibited both proteases with elevated stoichiometries of inhibition. Close proximity of Ile-207 and Ser-365 to the inserted RCL suggested that the preferred reaction of these mutants as protease substrates reflects an effect on the rate of the RCL insertion and protease translocation. However, both residues lie within the final docking site for the protease in the antithrombin–protease complex, supporting the idea that the enhanced substrate reactions may result from an increased dissociation of the final complexes. Our findings demonstrate that the distal end of the antithrombin A-sheet is crucial for the last steps of protease inhibition either by affecting the rate of RCL insertion or through critical interactions with proteases at the end of the A-sheet.
- PublicationOpen AccessInvestigating comproportionation in multielectron transfers via UV–visible spectroelectrochemistry: the electroreduction of anthraquinone-2-sulfonate in aqueous media(ACS Publications, 2022-08-22) Romay García, Luis; González Sánchez, Joaquín; Molina Gómez, Ángela; Laborda Ochando, Eduardo; Química Física; Facultad de QuímicaUV–vis spectroelectrochemistry is assessed as a tool for the diagnosis and quantitative in situ investigation of the incidence of comproportionation in multielectron transfer processes. Thus, the sensitivity of the limiting current chronoabsorptometric signals related to the different redox states to the comproportionation kinetics is studied theoretically for different working modes (normal and parallel light beam arrangements) and mass transport regimes (from semi-infinite to thin layer diffusion). The theoretical results are applied to the spectroelectrochemical study of the two-electron reduction of the anthraquinone-2-sulfonate in alkaline aqueous solution, tuning the thermodynamic favorability of the comproportionation reaction through the electrolyte cation. The quantitative analysis of the experimental results reveals the occurrence of comproportionation in the three media examined, showing different kinetics depending on the cationic species in solution.
- PublicationOpen AccessKinetics of gelation and thermal sensitivity of N-Isobutyryl Chitosan hydrogels(American Chemical Society, 2005-06-25) Félix, Leticia; Hernández, Javier; Argüelles Monal, Waldo M.; Goycoolea Valencia, Francisco Martín; Biología Celular e HistologíaN-Acylation of chitosan with carboxylic anhydrides in dilute acetic acid/methanol has been a well documented strategy to selectively modify chitosan. Although this reaction is known to lead to irreversible gel formation, the kinetics and mechanism of this process have not so far been addressed. To this purpose, gel formation during the N-isobutyrylation of chitosan was investigated as a function of the reaction stoichiometry (R), chitosan concentration, and temperature by small deformation oscillatory rheology. Gel formation follows closely the chemical reaction and it proceeds predominantly under second-order kinetics as established from the dependence of critical gel time, tgel, on R and concentration. The activation energy value derived from tgel vs 1/T data (Ea ) 68.29 ( 1.80 kJ/mol) was almost identical to values reported for the chitosan N-acetylation reaction in previous studies. An excess isobutyric anhydride is suggested to be necessary for nucleation and hydrophobic association. The potential application of N-isobutyrylchitosan (NIBC) hydrogels in the design of thermally sensitive materials is also demonstrated.
- PublicationOpen AccessMechanical bonding activation in rotaxane-based organocatalysts(Royal Society of Chemistry, 2021) Pérez Martínez, Jesús de Maria; Puigcerver, Julio; Orlando, Tainara; Martins, Marcos A. P.; Alajarín, Mateo; Martinez-Cuezva, Alberto; Berná Cánovas, José; Pastor, Aurelia; Química OrgánicaWe report here the enhanced efficiency as organocatalysts of a series of succinamide-based hydrogen-bonded [2]rotaxanes functionalized with an acyclic secondary amine as the catalytic active site. We also evaluated their catalytic activity, comparing with that of their non-interlocked threads, in an iminium-type process between crotonaldehyde and acetylacetone. The presence of an interlocked polyamide macrocycle notably increased the catalytic activity of the entwined organocatalysts. The mechanized catalysts rapidly form the reactive iminium intermediate with the aldehyde, increasing its population. The hydrogen-bonding interaction established between the macrocycle and the electrophile has been proposed as one of the reasons for the rapid formation and stabilization of this key intermediate.