Jesús Ágreda

Jesús Ágreda
National University of Colombia | UNAL · Quimica (Chemistry)

Dr. Sc.

About

30
Publications
4,182
Reads
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229
Citations
Additional affiliations
January 2005 - present
National University of Colombia
Position
  • Professor (Associate)
Description
  • Estudio de metales pesados en muestras de interés ambiental.
October 2003 - June 2004
University of Puerto Rico at Rio Piedras
Position
  • PostDoc Position
Description
  • Photophysics and Photochemistry of 1-Nitropyrene.

Publications

Publications (30)
Article
The generation of amino acid homochirality under prebiotic atmosphere conditions is a relevant issue in the study of the origin of life. This research is based on the production of amino acids via Strecker synthesis and how it is adjusted to the Kondepudi-Nelson autocatalytic model. The spontaneous mirror symmetry breaking (SMSB) of the new Kondepu...
Poster
The theoretical titration curve based on mass and charge balances was investigated as an alternative to the empirical equations used to obtain the endpoint time in the coulometric titration of potassium hydrogen phthalate. Two algorithms, available in R software, for the non-linear fitting of the theoretical titration curve to the experimental data...
Code
Simplex optimization algorithms as firstly proposed by Spendley et al. (1962) <doi:10.1080/00401706.1962.10490033> and later modified by Nelder and Mead (1965) <doi:10.1093/comjnl/7.4.308> for laboratory and manufacturing processes. The package also provides tools for graphical representation of the simplexes and some example response surfaces that...
Article
Full-text available
A method for quantification of arsenic, cadmium, mercury, and lead in pineapple using inductively coupled plasma-mass spectrometry (ICP-MS) was developed, validated, and used to test the homogeneity and stability of in-house reference materials. The method was tested at the regulation levels given by the Food and Agriculture Organization of the Uni...
Article
Full-text available
CHEMical KINetics SimuLATOR is a Graphical User Interface for the simulation of reaction mechanisms. The interface allows the user to see and change the parameters of a reaction network within a single window. Chemkinlator comes with built-in support for three types of kinetic simulations: Time Series, which computes the concentration of all specie...
Article
Full-text available
The goal of our research is the development of algorithmic tools for the analysis of chemical reaction networks proposed as models of biological homochirality. We focus on two algorithmic problems: detecting whether or not a chemical mechanism admits mirror symmetry-breaking; and, given one of those networks as input, sampling the set of racemic st...
Poster
We analyzed the autocatalytic models Frank, Kondepudi-Nelson, Calvin and Iwamoto proposed to explain the emergence of homochirality. Our own proposed model, called Ternary-chiral, was also analyzed. Two Computational tools were developed in order to make the analysis: Listanalchem for the linear stability analysis of chemical networks throught five...
Article
Full-text available
This paper presents a study that aimed to determine the mechanism of a process for Cr(VI) removal from aqueous solutions, using compost of carnation crop residues as the adsorbent. We assessed whether the microbiota present in the absorbent material affected the removal of Cr(VI) using respirometric measurements and evaluating the removal capacity...
Article
Full-text available
We look for structural properties of chemical networks giving place to homochiral phenomena. We found a necessary condition for homochirality that we call Frank inequality, and which is a linear inequality related to the entries of the jacobian matrices that occur at racemic steady states. We also investigate the existence of stronger conditions th...
Article
Full-text available
We study a particular set of chemical reaction networks related to the emergence of homochirality. Each element of this set is a chemical reaction mechanism intended to produce homochirality. Those mechanisms contains a pair of enan-tiomers, the central subject of this study, which are involved in a series of reactions that produce and consume them...
Article
We apply stoichiometric network analysis (SNA) to study enantioselective chemical reaction schemes, subject to various thermodynamic architectures, that may lead to spontaneous mirror symmetry breaking (SMSB). The stoichiometric matrices are used to calculate the extreme currents or fluxes: the vector basis for the convex polyhedral cone of all sta...
Article
Full-text available
A kinetic study of the uncatalyzed bromate oscillator (UBO) using phenol was carried out by chemometric analysis of the UV/Vis data. The reaction was studied with different starting concentrations of the reagents (sulfuric acid and potassium bromate) and by changing phenol for 2-bromophenol and 4-bromophenol. The number of chemical absorbing specie...
Article
The classical Oregonator model of the Belou- sov–Zhabotinsky reaction is used to examine the response of an oscillating reaction to a chemical perturbation in a batch calorimeter. To do this, a reaction step for the per- turbing chemical substance and the energy balance equa- tion are added to the model. Changes in the frequency and amplitude of th...
Article
Full-text available
The classic Belousov-Zhabotinsky reaction was modified by adding phenol as a second organic substrate that kinetically competes with the malonic acid in the reduction of Ce4+ to Ce3+and in the removal of molecular bromine of the reaction mixture. The oscillating reaction of two substrates exhibited burst firingand an oscillatory period of long dura...
Cover Page
Full-text available
Phenol added to the classical Belousov-Zhabotinsky reaction drives a bifurcation from regular oscillations to a transient bursting phenomena. It was explained as a complex process that involves a kinetic competition between an aromatic redox cycle of phenolic compounds and the Ce4+/Ce3+ catalytic cycle of the BZ classic oscillator. Details are pres...
Article
Full-text available
The signal produced by a pseudo-adiaba-tic calorimeter is simulated by numerical solution of the differential equations that model the chemical kinetics [1], the thermal properties of the calorimetric cell [2], and the response of the thermistor used as a thermometric sensor [3]. These equations show that the calorimetric signal is related with con...
Article
Full-text available
The removal of Cr(VI) from aqueous solutions was studied using a compost generated from carnation flowers waste. The highest percentage of removal achieved (ca. 99 %) was obtained at pH 2.0, using a 10 mg L -1 of Cr(VI) solution, a dose of 10 g L -1 of compost, and with an equilibrium time of 3 hours. Under these conditions, the kinetics and adsorp...
Article
Full-text available
This work presents the optimization process of mercury determination by Anodic Stripping Voltammetry (ASV), using a glassy carbon modified with a gold film as working electrode, in samples extracted by aqua regia. The samples may contain Cu, Fe or Pb in high concentrations. In these conditions the usual Hg determination by ASV is almost impossible....
Article
Full-text available
Chemical analysis has evolved towards automation to satisfy the current requirements: fast analysis and certainty in the results. Flow injection analysis (FIA) is a way to reach automation. This work presents the necessary steps to obtain an optimized FIA methodology for the determination of Pb(II) in water by classic methods. The result was a FIA...
Article
Full-text available
1-Nitropyrene (1NPy) is the most abundant nitropolycyclic aromatic contaminant encountered in diesel exhausts. Understanding its photochemistry is important because of its carcinogenic and mutagenic properties, and potential phototransformations into biologically active products. We have studied the photophysics and photochemistry of 1NPy in solven...
Article
The kinetics of the reaction HBrO(2) + HBrO(2) --> HOBr + BrO(3)(-) + H(+) is investigated in aqueous HClO(4) (0.04-0.9 M) and H(2)SO(4) (0.3-0.9 M) media and at temperatures in the range 15-38 degrees C. The reaction is found to be cleanly second order in [HBrO(2)], with the experimental rate constant having the form k(exp) = k + k'[H(+)]. The hal...
Article
The kinetics of the reaction HBrO2 + HBrO2 -> HOBr + BrO3- + H+ is investigated in aqueous HClO4 (0.04-0.9 M) and H2SO4 (0.3-0.9 M) media and at temperatures in the range 15- 38 degrees C. The reaction is found to be cleanly second order in [HBrO2], with the experimental rate constant having the form k(exp) = k + k'[H+]. The half- life of the react...
Article
Full-text available
No presente estudo apresentamos a dependência do tempo de indução da reação Belousov- Zhabotinsky (BZ) em função da concentração inicial do ácido malonico, bromato e cerium. Os resultados mostram que o tempo de indução aumenta com o aumento da concentração de bromato e tal comportamento não coincide com o mecanismo proposto para as reações BZ. Prop...
Article
The complexity of oscillating chemical reactions makes difficult a direct calorimetric study of them. It is more advantageous to carry out studies of the component steps and then try to put the parts together. Here, a mass-flow heat conduction calorimeter was used to study component reactions of two of the principal chemical oscillators. The studie...
Article
The kinetics of the Dushman reaction, 5I- + IO3- + 6H+ → 3I2 + 3H2O, is considerably more complex in aqueous, acidic media than is the behavior of the analogous reaction of Br- with BrO3-. The latter reaction is first order in both [Br-] and [BrO3-] and is believed to proceed via a series of simple oxygen-atom transfers, there being no evidence for...
Article
The simulations of some electric and chemical processes in a mass flow heat conduction calorimeter are shown. The simulation of the thermal processes related with the oxidation reaction of Ce3+ with BrO3− in 1M H2SO4 are based on the kinetics mechanism proposed by Turanyi, Gyorgy, Field and on estimated values for the heat of reaction of every step...
Article
When a methyl ketone is added to the Belousov−Zhabotinskii (BZ) reaction, an increase of the induction period and in the number of oscillations is observed. This behavior can be explained by the competition of malonic acid and the methyl ketone for molecular bromine. We studied the effect of four methyl ketones in the BZ reaction and found a direct...
Article
Contrary to what has been thought, systems classified as bromine-hydrolysis-controlled (BHC) show an induction period. In studies on the effect of a family of ketones upon this type of oscillators, it was found that an induction period appears in an interval of concentrations of the ketone, or in an interval of the value of the enolization constant...
Article
Full-text available
RESUMEN Se propone un método para la interpre-tación de mecanismos complejos de reac-ción, el cual es aplicado a la simulación del mecanismo de Gyórgyi-Field, (GF) desarrollado para la reacción química os-cilante de Belousov-Zhabotinsky (BZ). El método basado en la ley de acción de masas y en el principio de independencia y coexistencia de los paso...

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Projects

Projects (2)
Project
To optimize and validate the coulometric titration of potassium hydrogen phthalate for its certification as reference material.
Project
Select the most reasonable model to produce homochirality.