Química

URI permanente para esta colección

https://hdl.handle.net/10669/281

Examinar

Mostrando 1 - 20 de 367

1,1-Diphenyl-4-(thiophen-2-yl)but-3-yn-1-ol
(2018-11) Umaña, Christian A.; Pineda Cedeño, Leslie William; Cabezas Pizarro, Jorge A.
The asymmetric unit of the title homopropargyl alcohol, C20H16OS, contains two independent molecules comprising a hydroxy group, a 3-(2-thiophenyl)- propargylic moiety and two aromatic rings linked to a central carbon atom. The two unique molecules are linked into a dimer by an O—HO hydrogen bond. In one molecule, the thiophene ring is disordered over two orientations rotated by 180 with a refined occupancy ratio of 0.575 (4):0.425 (4). The crystal structure is stabilized by O—H and C—H hydrogen-bond interactions. The crystal studied was a two-component non-merohedral twin, the refined ratio of the twin components being 0.575 (4):0.425 (4).
1,3-Bis{[(2,6-dimethylphenyl)sulfanyl]methyl}benzene
(2019) Garita Salazar, Bruno; Pineda Cedeño, Leslie William
The structure of the title compound, C24H26S2, an example of a pincer ligand with an SCS-chelation motif, illustrates the steric effects of the methyl groups in the thiophenyl rings at the 2- and 6-positions, forcing a dissimilar spatial orientation of the thiophenyl rings relative to the central aryl group [dihedral angles = 33.58 (7) and 40.49 (7)°]. In the crystal, weak S⋯S contacts [3.4009 (7) Å] link the molecules into inversion dimers.
1-Nitro-4-(1-propyn-1-yl)benzene
(2019) Campos Fernández, Cristian Saúl; Pineda Cedeño, Leslie William; Cabezas Pizarro, Jorge A.
The title compound, C9H7NO2, was prepared by alkynylation of 4-iodonitrobenzene with 1,3-dilithiopropyne in the presence of 1 equivalent of CuI and catalytic amounts of Pd(PPh3)2Cl2. The complete molecule is generated by crystallographic twofold symmetry with the C—N and C—C[triple bond]C—C units lying on the rotation axis. No directional interactions beyond normal van der Waals contacts could be identified in the packing.
(1S,3R)-N-{(3S,10S,12S,13R,17R)-12-Hydroxy-17- [(R)-5-hydroxypentan-2-yl]-10,13-dimethylhexa- decahydro-1H-cyclopenta[a]phenanthren-3-yl}- adamantane-1-carboxamide 0.25-hydrate
(2022-10-12) Campos Fernández, Cristian Saúl; Procúpez Schtirbu, Rolando; Soto Tellini, Victor Hugo; Salazar Camacho, Juan Carlos; Jancik, Vojtech
The title compound, C 35H 57 NO 3 0.25H 2O, was synthesized from deoxycholic acid followed by a protection, a Mitsonobu substitution, a Staudinger reduction, formation of an amide and final reduction in the lateral chain. The compound crystallizes in the P1 space group with four steroid molecules and one water molecule in the triclinic cell unit. The crystal structure features O—H O hydrogen bonding. The crystal studied was refined as a non-merohedral twin
5,5-Diphenyl-cis-penta-2,4-dienoic acid
(2019) Pineda Cedeño, Leslie William; Amey, Adam R.; Cabezas Pizarro, Jorge A.
In the title compound, C17H14O2, the dihedral angle between the phenyl rings is 76.52 (7)°. In the crystal, pairwise O—H⋯O hydrogen bonds link the molecules into carboxylic acid inversion dimers.
A Chronoamperometric Screen Printed Carbon Biosensor Based on Alkaline Phosphatase Inhibition for W(VI) Determination in Water, Using 2-Phospho-l-Ascorbic Acid Trisodium Salt as a Substrate
(2015) Alvarado Gámez, Ana Lorena; Alonso Lomillo, María Asunción; Domínguez Renedo, Olga; Arcos Martínez, María Julia
This paper presents a chronoamperometric method to determine tungsten in water using screen-printed carbon electrodes modified with gold nanoparticles and cross linked alkaline phosphatase immobilized in the working electrode. Enzymatic activity over 2-phospho-l-ascorbic acid trisodium salt, used as substrate, was affected by tungsten ions, which resulted in a decrease of chronoamperometric current, when a potential of 200 mV was applied on 10 mM of substrate in a Tris HCl buffer pH 8.00 and 0.36 M of KCl. Calibration curves for the electrochemical method validation, give a reproducibility of 5.2% (n = 3), a repeatability of 9.4% (n = 3) and a detection limit of 0.29 ± 0.01 μM. Enriched tap water, purified laboratory water and bottled drinking water, with a certified tungsten reference solution traceable to NIST, gave a recovery of 97.1%, 99.1% and 99.1% respectively (n = 4 in each case) and a dynamic range from 0.6 to 30 μM. This study was performed by means of a Lineweaver–Burk plot, showing a mixed kinetic inhibition.
A facile method for the preparation of bishomopropargylic alcohols from acyl chlorides
(2014) Vásquez Céspedes, Suhelen; Cabezas Pizarro, Jorge A.
Controlled dilithiation of propargyl bromide with two equivalents of n-butyllithium, in the presence of TMEDA, produces the operational equivalent of the dianion 1,3-dilithiopropyne. The latter reacts efficiently with acid chlorides to produce bishomopropargylic alcohols in a single step route and with high regioselectivity and moderate yields.
A Facile Method for the Titration of Organolithium Reagents using Naphtylamine or Naphtylmethylamine as Indicators
(2019) Cabezas Pizarro, Jorge A.
A simple method for the titration of alkyllithiums with sec-butanol, using naphtylamine or naphtylmethylamine as color indicator, is reported. Both amines gave sharp-end points, easily determined by color changes from brown to yellow (naphtylamine) and from green to colorless (naphtylmethylamine). The accuracy of the determination was in accordance with the values obtained by a standard method.
A Metabolic Widget Adjusts the Phosphoenolpyruvate-Dependent Fructose Influx in Pseudomonas putida
(2016) Chavarría Vargas, Max; Goñi Moreno, Ángel; de Lorenzo, Víctor; Nikel Mayer, Pablo Iván
Fructose uptake in the soil bacterium Pseudomonas putida occurs through a canonical phosphoenolpyruvate (PEP)-dependent sugar transport system (PTSFru). The logic of the genetic circuit that rules its functioning is puzzling: the transcription of the fruBKA operon, encoding all the components of PTSFru, can escape the repression exerted by the catabolite repressor/activator protein Cra solely in the presence of intracellular fructose-1-P, an agonist formed only when fructose has been already transported. To study this apparently incongruous regulatory architecture, the changes in the transcriptome brought about by a seamless Δcra deletion in P. putida strain KT2440 were inspected under different culture conditions. The few genes found to be upregulated in the cra mutant unexpectedly included PP_3443, encoding a bona fide glyceraldehyde-3-P dehydrogenase. An in silico model was developed to explore emergent properties that could result from such connections between sugar uptake with Cra and PEP. Simulation of fructose transport revealed that sugar uptake called for an extra supply of PEP (obtained through the activity of PP_3443) that was kept (i.e., memorized) even when the carbohydrate disappeared from the medium. This feature was traced to the action of two sequential inverters that connect the availability of exogenous fructose to intracellular PEP levels via Cra/PP_3443. The loss of such memory caused a much longer lag phase in cells shifted from one growth condition to another. The term “metabolic widget” is proposed to describe a merged biochemical and regulatory patch that tailors a given node of the cell molecular network to suit species-specific physiological needs.
A new and efficient synthesis of (3E,8Z,11Z)-tetradeca-3,8,11-trienyl acetate, the major sex pheromone component of the tomato leafminer Tuta absoluta
(2018) Cabezas Pizarro, Jorge A.
An efficient synthesis of (3E,8Z,11Z)-tetradeca-3,8,11-trienyl acetate, the major sex pheromone component of the tomato leafminer moth, Tuta absoluta, was accomplished. The synthesis started with but-3-yn-1-ol and gave an overall yield of 41%.
A new method for the preparation of 1,3-dilithiopropyne: an efficient synthesis of homopropargyl alcohols
(2001) Cabezas Pizarro, Jorge A.; Pereira, Albán R. ; Amey, Adam R.
Controlled dilithiation of propargyl bromide with two equivalents of n-butyllithium, in the presence of TMEDA, produces the operational equivalent of the dianion 1,3-dilithiopropyne. The latter reacts efficiently with aldehydes and ketones to produce homopropargyl alcohols in a single step route and in high yields. Controlled dilithiation of propargyl bromide with n-BuLi, in the presence of TMEDA, produces the operational equivalent of the dianion 1,3-dilithiopropyne. The latter reacts efficiently with aldehydes and ketones to produce homopropargyl alcohols in a single step route in high yields.
A New Method for the Preparation of 1,5-Diynes. Synthesis of (4E,6Z,10Z)-4,6,10-Hexadecatrien-1-ol, the Pheromone Component of the Cocoa Pod Borer Moth Conopomorpha cramerella
(2004) Pereira, Albán R.; Cabezas Pizarro, Jorge A.
A new method for the synthesis of 1,5-diynes, from the reaction of 1,3-dilithiopropyne and propargyl chlorides, was developed. This new methodology was used to prepare (4E,6Z,10Z)-4,6,10-hexadecatrien-1-ol, one of the pheromone components of the cocoa pod borer moth Conopomorpha cramerella, in 51% overall yield.
A New Method for the Preparation of 1-Ethynyl Ethers
(1994) Cabezas Pizarro, Jorge A.; Oehlschlager, Allan Cameron
During our study of the stannylcupration of acetylenic ethers we required [2-13C]-1 for mechanistic studies. Existing methods for the synthesis of acetylenic ethers involve dehydrohalogenation of 2-halo, 1,2-dihalo vinyl ether, or haloacetals using KOH, NaNH2, or n-BuLi. These procedures are incompatible with labile functional groups and, if applied to the preparation of 13C-labeled compounds, would require regiospecific preparation of 1- or 2-13C-labeled halo vinyl ethers, which is cumbersome. We report a new, general and efficient method for the preparation of acetylenic ethers which we have applied to the preparation of 13C-labeled and functionalized acetylenic ethers
A new methodology for the synthesis of δ-substituted α,β-unsaturated δ-lactones
(2020) Cabezas Pizarro, Jorge A.; Amey, Adam R.
A new protocol for the synthesis of δ-substituted-α,β-unsaturated δ-lactones was developed. Selective reaction of 1,3-dilithiopropyne with ketones, followed by addition of ethyl chloroformate formed ethyl 5-[(ethoxycarbonyl)oxy]-5-substituted-2-ynoates, used as the basic framework for the synthesis of δ-substituted α,β-unsaturated-δ-lactones
Aceptación de un jugo de mora endulzado con estevia en contraste con otros edulcorantes
(2017) González Torrivilla, César; Hernández Peñaranda, Alicia María; Cubero Castillo, Elba María
El objetivo de la presente investigación fue desarrollar un jugo de mora (Rubus adenotrichus), endulzado con esteviolglucósidos (glucósidos obtenidos a partir de las hojas de Stevia rebaudina Bertoni) como una bebida alternativa para regímenes especiales de alimentación. Para garantizar su aceptación, se tomaron criterios sensoriales en cada una de las fases requeridas para su elaboración: definición del porcentaje de dilución del zumo de la fruta, proporción de hojas deshidratadas de estevia-jugo, valoración del medio de extracción de los esteviolglucósidos (agua o zumo de mora), así como las principales propiedades organolépticas del productomicrofiltrado (acidez, dulzor y sabor residual) antes y después de ser sometido a pasteurización formulados con estevia y sacarosa y su comparación con otros endulzantes comerciales. Las puntuaciones señaladas por los panelistas, permitieron definir la proporción de hojas deshidratadas de estevia en polvo a emplear (2,5 g/L) para alcanzar el dulzor requerido y corroboraron que el medio de extracción (agua o zumo) no tiene influencia sobre los tres atributos juzgados por los panelistas. Del mismo modo, se determinó que no existen diferencias estadísticamente significativas entre la muestra endulzada con estevia y las endulzadas con sacarosa o el edulcorante comercial valorado. Por último, la comparación sensorial de los jugos pasteurizados o no, endulzados con sacarosa y estevia, permitieron afirmar que el tratamiento térmico aplicado (90ºC por 30 segundos), no influye significativamente en su gusto, asegurando la misma calidad sensorial de una bebida endulzada con sacarosa obtenida a través de tratamientos térmicos convencionales aplicados regularmente en la industria de alimentos.
Actividades experimentales para la educación secundaria en química: Estudio de factibilidad de negocio
(2023) Casto Cabezas, Aaron Josué; Romero Chacón, Rosaura
En pruebas internacionales del Programa para la Evaluación Internacional de Alumnos (PISA, por sus siglas en inglés) aplicadas en el año 2015 a estudiantes costarricenses dieron como resultado, mayoritariamente, los niveles más bajos de la escala evaluativa en la competencia científica, según la escala propuesta por la Organización para la Cooperación y el Desarrollo Económicos (OECD, por sus siglas en inglés). El uso de actividades experimentales en las lecciones de química puede ayudar a fortalecer los conceptos teóricos estudiados en clase, así como mejorar la capacidad de las personas estudiantes para desarrollar el pensamiento crítico y resolver problemas complejos, necesarios en el nuevo perfil deseado del estudiantado. Actualmente, el Ministerios de Educación Pública de Costa Rica propone una metodología de indagación para impartir las lecciones de química. Sin embargo, las personas docentes no cuentan con la preparación, ni los recursos necesarios para este fin. Por esta razón, se suele caer en metodologías tradicionales como la clase magistral. Al realizar una encuesta sobre el interés para hacer uso de un servicio de aplicación y asesoría en actividades experimentales educativas, se evidencia la existencia de una necesidad no satisfecha y por lo tanto una ventana de acceso al mercado. En este proyecto, se muestra la factibilidad económica en la comercialización de un servicio de asesoría y aplicación de actividades experimentales en las clases de química en instituciones educativas de Costa Rica a nivel de educación secundaria. Este servicio (i) facilitará el fortalecimiento de conceptos básicos estudiados en las clases de teoría, (ii) aumentará el interés de la población estudiantil por la química, y (iii) permitirá identificar habilidades vocacionales en las personas a temprana edad.
Adipostatins E-J, new potent antimicrobials identified as inhibitors of coenzyme-A biosynthesis
(2020-01) Gómez Rodríguez, Lyanne; Schultz, Pamela J.; Tamayo Castillo, Giselle; Dotson, Garry D.; Sherman, David H.; Tripathi, Ashootosh
Phosphopantetheine is a key structural element in biological acyl transfer reactions found embedded within coenzyme A (CoA). Phosphopantothenoylcysteine synthetase (PPCS) is responsible for installing a cysteamine group within phosphopantetheine. Therefore, it holds considerable potential as a drug target for developing new antimicrobials. In this study, we adapted a biochemical assay specific for bacterial PPCS to screen for inhibitors of CoA biosynthesis against a library of marine microbial derived natural product extracts (NPEs). Analysis of the NPE derived from Streptomyces blancoensis led to the isolation of novel antibiotics (10-12, and 14) from the adipostatin class of molecules. The most potent molecule (10) displayed in vitro activity with IC50 = 0.93 µM, against S. pneumoniae PPCS. The whole cell antimicrobial assay against isolated molecules demonstrated their ability to penetrate bacterial cells and inhibit clinically relevant pathogenic strains. This establishes the validity of PPCS as a pertinent drug target, and the value of NPEs to provide new antibiotics.
Aggregation Pheromone of Coconut Rhinoceros Beetle, Oryctes rhinoceros (L.) (Coleoptera: Scarabaeidae)
(1995-10) Hallett, Rebecca H.; Pérez Sánchez, Alice Lorena; Gries, Gerhard; Gries, Regine; Pierce Jr., Harold D.; Yue, Junming; Oehlschlager, Allan Cameron; González, Lilliana M.; Borden, John H.
Male coconut rhinoceros beetles,Oryctes rhinoceros (L.), produce three sex-specific compounds, ethyl 4-methyloctanoate, ethyl 4-methylheptanoate, and 4-methyloctanoic acid, the first of which is an aggregation pheromone. Synthesis of these compounds involving conjugate addition of organocuprates to ethyl acrylate is reported. In field trapping experiments, (4S)-ethyl 4-methyloctanoate and the racemic mixture were equally attractive and 10 times more effective in attracting beetles than ethyl chrysanthemumate, a previously recommended attractant. Ethyl 4-methylheptanoate was as attractive as ethyl chrysanthemumate and more attractive than 4-methyloctanoic acid, but further studies are required before it can be classed as an aggregation pheromone. Compared to ethyl 4-methyloctanoate alone, combinations of the three male-produced compounds did not increase attraction, whereas addition of freshly rotting oil palm fruit bunches to pheromone-baited traps significantly enhanced attraction. With increasing dose, captures of O. rhinoceros increased, but doses of 6, 9, and 18 mg/day were competitive with 30 mg/day lures. Newly designed vane traps were more effective in capturing beetles than were barrier or pitfall traps. Results of this study indicate that there is potential for using ethyl 4-methyloctanoate in operational programs to control O. rhinoceros in oil palm plantations.
Aggregation Pheromone of Palm Weevil, Dynamis borassi
(1997) Peña, Jorge E.; Giblin Davis, Robin M.; Gries, Regine; Gries, Gerhard; Peña Rojas, E.; Pinzón, I.; Pérez Sánchez, Alice Lorena; Pierce Jr., Harold D.; Oehlschlager, Allan Cameron
4-Methyl-5-nonanol (1) is the male-produced aggregation pheromone of the palm weevil, Dynamis borassi (F.) from Colombia. The pheromone was identified by coupled gas chromatographic–electroantennographic detection (GC-EAD) analysis of male- and female-produced volatiles, and comparative GC–mass spectrometry (MS) of weevil-produced 1. In field experiments in Colombia, traps baited with a stereoisomeric mixture of synthetic 1 (3 mg/day) plus sugarcane captured more weevils than traps baited with 1 or sugarcane alone, suggesting that pheromone and plant volatiles are synergistically attractive. Use of a chiral, stereoisomer-separating Cyclodex-B column in GC-EAD and GC-MS analyses revealed that D. borassi males produce, and antennae of males and females respond to (4S,5S)-1. Previously identified palm weevil (Rhynchophorus spp.) aggregation pheromones 5-methyl-4-octanol (cruentol) and 6-methyl-2-hepten-4-ol (rhynchophorol) also elicited antennal responses by D. borassi. In field experiments, D. borassi females were captured equally well in traps baited with sugarcane plus either 1, cruentol or rhynchophorol. In contrast, D. borassi males were captured most often in traps baited with sugarcane plus 1. Because D. borassi is a potential vector of the red ring nematode that causes the lethal red ring disease of palms, pheromone-based trapping of D. borassi could aid in monitoring or management of red ring disease in commercial palm plantations.
Aggregation pheromone of palmetto weevil, Rhynchophorus cruentatus (F.) (Coleoptera: Curculionidae)
(1994) Weissling, Thomas J.; Giblin Davis, Robin M.; Gries, Gerhard; Gries, Regine; Pérez Sánchez, Alice Lorena; Pierce Jr., Harold D.; Oehlschlager, Allan Cameron
5-Methyl-4-octanol is the major aggregation pheromone of the palmetto weevil,Rhynchophorus cruentatus (F.). The pheromone (cruentol) was identified by coupled gas chromatographic-electroantennographic (GC-EAD) analysis of male-produced volatiles, coupled GC-mass spectrometry (MS) in electron impact and chemical ionization mode, and coupled GC-high resolution MS. In laboratory and field assays, a diastereomeric mixture of synthetic cruentol greatly enhanced attraction of weevils to cabbage palmetto,Sabal palmetto (Walter), stem tissue, indicating that cruentol and host volatiles are synergistically attractive. An attractive lure in combination with efficient traps should facilitate development of semiochemical-based management forR. cruentatus.

Examinar

Examinando Química por Título

Resultados por página

Opciones de ordenación