Home    Staff    Contact us-



(c) Apycom      




 

Powered by Teklogin copyright 2004©
www.prlsamp.org

 

 

Chemistry

Acevedo Acevedo, Delgado
Aviles, Yadriel
Benítez, Jaime
Borrero, Solmarie
Burgos-Frontanes, Samuel
Campbell, Muriel
Cardona, Rocío del A.
Caro-Gautier, Humberto
Cartagena, Michelle
Castillo Rivera, Dorianne A
Cotto, Marlene
Crespo-Román, Gisela
Cruz, Nadya
Cruz Moreira, Solimar
Delgado, Dana
Díaz, Tanya
Domenech Garcia, Maribella
Echevarría Torres, David
Escalona, Yma              Flores, Rosangelly
García, Rafael

García Berríos, Edfardo
Gavalda, Salvador
Giménez, Lizabeth
Gonzalez, Cristian
Gonzalez Freire, Carol L. 
Gonzalez-Gonzalez, Ileana
Granell, Laura
Guillen, Nancy
Hernández, Emil
Hernández Lugo, Dionne M.
Justicia Leon, Shandra D.
López Pacheco, Lilibeth Lopez-Alvarez, Yania
Madero-Vergara, Mayraliz Maldonado, Omar D.
Marrero, Wilnelia
Martín, Mariana            Mattei, María de los A.
Morales, Eduardo M.
Morales, Victor M.
Nuñez, Daliangelis

 

Ortíz, Taymaliz
Quiñones, Alejandro
Quiñones, Luis
Restituyo, Jannelly
Rivera, Jessica
Rivera, Catherine
Rivera, Maria del Carmen
Rivera, Racquel
Rivera Gonzalez, Gustavo J.
Rodríguez, Kristy
Rodríguez, Marilyn
Rosario, Medardo
Ruiz, Mariangel
Sanchez-Baez, Eliany
Sanchez-Cortés, Juan-José
Suárez, Christian
Torres, Mayda
Torres Torres, Mirayda
Velez Ruiz, Gisselle A.
Velez-Camacho, Yahaira


Acevedo Acevedo, Delgado; Leon-Velasquez, Madeline; Cortes-Figueroa, Jose E.  Department of Chemistry, UPR-Mayagüez.

A biphasic displacement of 1,10-phenanthroline from fac-(dihapto-phenanthroline) (dihapto-[60]fullerene) tricarbonylmolybdenum(0) by triphenylphosphine

Triphenylphosphine displaces 1,10-phenanthroline from fac-(dihapto-phenanthroline)(dihapto-[60]fullerene)tricarbonylmolybdenum(0).  The reaction was studied under flooding conditions where the molar concentration of triphenylphosphine was at least 10,000 times the molar concentration of fac-(dihapto-phenanthroline)(dihapto-[60]fullerene)tricarbonylmolybdenum(0).  The reactions' progress were followed by measuring the absorbance at 440 nm.  Plots of absorbance - absorbance infinity vs. time showed a biphasic behavior.  This observation suggest that [60]fullerene is a cis labilizing ligand.  The mathematical description to resolve the biphasic plot into two consecutive first order reactions will presented in detail. Acknowledgments are made to the Petroleum Research Fund (PRF 36623-B3), Administered by the American Chemical Society, to National Science Foundation (CHEM-0102167) for support of this work. DAA received financial support from PR-LSAMP.

Back to Top


Aviles, Yadriel; Alejandro Blanco; Samuel P. Hernández-Rivera.  Center for Chemical Sensors Development for Explosives, Department of Chemistry. University of Puerto Rico. Mayagüez.

Investigación espectroscópica de 2,4-DNT y 2,6-DNT y sus interacciones con particulas de silica

A través de los años, como parte de conflictos bélicos, los dispositivos explosivos más se utilizados son minas terrestres.  Las mismas son cargas explosivas que se colocan bajo suelo y luego se detonan por contacto.  Existen miles de minas enterradas distribuidas atraves de 70 países en todo el mundo.  Hasta hace poco tiempo era factible utilizar detectores de metales para detectar este tipo de artefactos explosivos.  Hoy en día las minas se colocan en envases de plástico.  Otro problema es que la técnica es incapaz de detectar pequeñas cantidades de cristales de explosivos.  La Espectroscopia de Raman es una herramienta establecida para análisis de espectroscopia vibracional.  La interacción de explosivos con diferentes substratos puede ser estudiada de información del desplazamiento cuantitativo de señales vibracionales Raman asociada con dicha interacción.  Se hizo un estudio de espectroscopia vibracional para cristales de 2,4-DNT y 2,6-DNT.  Para esto se utilizó un microscopio de Raman equipado con una línea de excitación láser de 514 nm.  Las muestras se recristalizaron en diferentes solventes (agua, metanol y acetonitrilo) y luego se expusieron a la interacción con sílice.  La interacción con silica gel  dopadas con compuestos nitroaromáticos mostraron un desplazamiento significativo en las señales de los espectros.  Esta información se utilizó para detectar DNT en muestras de silica usando Microscopia de Raman. También se midió la variación del desplazamiento de la señal Raman a diferentes valores de pH (4, 7 y 9).  Estos resultados pueden servir de base para desarrollar nuevos sensores para detección de materiales explosivos.

 

 Back to Top


Benítez, Jaime; Marrero, Jeffrey; Rodríguez, Abimael D. Department of Chemistry, University of Puerto Rico, Río Piedras.

Isolation and structural elucidation of two highly oxygenated cembranoids diterpenoids from the Sea Plume Pseudopterogorgia kallos

The chemical study of the chloroform extract from the Colombian Sea Plume Pseudopterogorgia kallos resulted in the isolation of two new highly oxygenated cembranoids diterpenes, bipinnatin K (1) and L (2).  Their chemical structures were elucidated  using 1D- and 2D NMR experiments (HMQC, 1H-1H COSY, HMBC, and NOESY) in combination of UV, IR, and HR-MS analysis.  The biological activity of the forementioned compounds are currently under study.

 Back to Top


Borrero, Solmarie; Santiago, Mitk'El; Guadalupe, Ana R.; Colón, Jorge L.  Chemistry Department, University of Puerto Rico, Rio Piedras.

Synthesis, characterization and intercalation of [Co(tpy)2](PF6)2 into the 10.3 Å phase of layered zirconium phosphate

Zirconium phosphates (ZrP), which are acidic, inorganic, ion exchangers with layered structures, have been extensively investigated. We are investigating the use of these materials as hosts for inorganic complexes using a 10.3 Å phase of ZrP, which we have recently demonstrated directly exchanges large metal complexes. The inorganic complex chosen for our studies is [Co(tpy)2](PF6)2, an electron mediator suitable for biosensor applications.  The synthesis of the 10.3 Å ZrP phase, [Co(tpy)2](PF6)2, and were successful and all materials were characterized. The characterization was done using X-Ray Powder Diffraction, Infrared Spectroscopy, and UV-visible spectrophotometry.  Carbon paste electrodes were modified with [Co(tpy)2]2+-exchanged ZrP.   The electrochemical characterization of this material will also be presented. S.B.M. acknowledges the financial support of the PR-LSAMP program.  M.B.S. acknowledges the financial support of NIH-RISE/SUBE Graduate Fellowship.

Back to Top


Burgos-Frontanes, Samuel; Leonardo Pacheco Londoño; Oliva M. Primera Pedrozo; Samuel P. Hernandez Rivera. Centro de Desarrollo de Sensores Químicos para la Detección de Explosivos, Departamento de Quimica, University of Puerto Rico-Mayagüez.

Estudio de fases de RDX a diferentes concentraciones de cristalización en superficies

Existen cuatro confórmeros de RDX, en fase gaseosa.  En sólida solo se han descubierto dos de estos confórmeros, los cuales producen dos fases estables: RDX- y RDX-. Cuando se tiene RDX en solución y se deposita en una superficie este forma una de las dos fases.  La forma en la cual condense depende de la superficie, de la concentración, de la cantidad depositada y del solvente. En este trabajo se variaron estos cuatro parámetros, encontrando que la concentración y la cantidad depositada eran los factores más influyentes en la cristalización.  Para una superficie como acero inoxidable no-magnético tipo 316 se encontró que depositando 20 µL a una concentración mayor de 200 ppm de RDX en acetonitrilo se produce RDX- y a concentraciones RDX- es más estable y se produce en forma prominente, aunque no exclusivamente.  La verificación de las fases se hizo mediante Microscopia Raman, FT-IR y FT-IR acoplado a fibra óptica con sonda de Angulo de rozamiento.

Back to Top


Campbell, Muriel; Sanoguet Zuleika. Chemistry Department, UPR-Mayagüez  –  Hu, Haitao; Chazin, Walter. Center for Structural Biology, Vanderbilt University  –  Pastrana, Belinda. Chemistry Department, UPR-Mayagüez.

Characterization of phosphorylated Chlamydomonas centrin

Centrin, a 20 kD protein, is a member of the calmodulin superfamily of EF-hand calcium binding proteins. It plays an essential role is centrosome duplication by mediating chromosome segregation during mitosis. Centrin was originally cloned at the DNA level from the unicellular green algae Chlamydomonas reinhardtii. Since then, homologs of centrin have been identified in yeast, mice, and humans, among other species. Centrin has two structurally independent domains connected by a flexible linker. The C- terminal domain of centrin (CRC-C) has a PKA phosphorylation site at serine 167. In vitro phosphorylation was performed on both, full length centrin and CRC-C, in order to analyze the effects of phosphorylation on the protein’s conformation. Differential Scanning Microcalorimetry was performed on both samples. The results suggest that phosphorylated centrin adopts a slightly different conformation and is less stable than the unphosphorylated form of centrin.

Back to Top


Cardona, Rocío del A.; Muñoz, Lisa; Guadalupe, Ana R.  Department of Chemistry, University of Puerto Rico, Río Piedras Campus.

Development of a DNA sensor using peptide nucleic acid (PNA) as a probe attached to polystyrene films

The need for fast detection of harmful bacteria and other pathogens has lead the scientific community to study new sensor probes and devices. Peptide Nucleic Acid (PNA), a DNA synthetic analog, is a new tool in nucleic acid research. This molecule posses many of DNA properties but also present promising features because of its capacity to form more rigid structures, better hybridization and to detect bases mismatches. Due to its properties PNA has been used as a probe in the construction of DNA biosensors.   Thin films of polystyrene functionalized with succinimide were prepared over gold substrates.  PNA chains modified with amino groups were immobilized in the polymer surface.  The complementary DNA sequence for PNA was labeled with a ferrocene complex. The hybridization was monitored by the redox process of ferrocene using Osteryoung Square Wave Voltammetry (OSWV). Atomic Force Microscopy (AFM) and X-Ray Photoelectron Spectroscopy (XPS) were used to determine morphology changes after immobilization and hybridization. The electrochemical studies showed that the response time for double strand formation were around 60 min.  Using AFM and XPS the formation of the double strand was also confirmed after changes in surface morphology and elemental analysis, respectively. To complete the development of our DNA/PNA sensor a calibration curve will be construct to evaluate the usable concentration range and the sensor analytical parameters.

Back to Top


Caro-Gautier, Humberto. Institute for Tropical Ecosystem Studies, University of Puerto Rico Rio Piedras and Department of Chemistry, University of Puerto Rico Rio Piedras  -  J. Lugo Vega; R. Ríos Dávila. Graduate School of Public Health, Department of Environmental Health, Medical Sciences Campus, University of Puerto Rico, San Juan   -   Mayol-Bracero, O.L.  Institute for Tropical Ecosystem Studies, University of Puerto Rico Rio Piedras and Department of Chemistry, University of Puerto Rico Rio Piedras.

Deposition of carbonaceous aerosol particles on the historical building “Ruinas de Caparra” in Puerto Rico

Atmospheric aerosols are collections of small particles suspended in the air originating from natural and anthropogenic sources. Carbonaceous aerosol particles (CAs), mainly composed of elemental and organic carbon (EC and OC), damage monuments and historical building around the world. These particles have been found in the inner surface of stone and mortars of historical buildings (mostly in Europe), generating the degradation of these materials by means of such chemicals reactions as the sulphatation of calcium carbonate into gypsum.  The purpose of this study is to investigate the relationship between the soiling produced by carbonaceous aerosol particles and the formation of the black patina on the surface layers of “Ruinas de Caparra”. Samples of the patinas were collected at several points from the upper and side surfaces of the ruins. Analyses of these samples were performed according to the procedure developed by Ghedini et al., 2000. Scanning electron microscope (SEM) with energy dispersive spectrometry was used for the study of the morphology and elemental composition of the particles deposited on the surface of the collected samples. The determination of water-soluble ions (SO3-2, SO4-2, NO3-), was performed using ion chromatography. Parallel to these analyses, air sampling with a low-pressure impactor was also performed for the determination of the size resolved EC and OC concentrations to which the ruins are exposed on a daily basis.  Preliminary results of this study will be discussed in this presentation.

 

 Back to Top


 Cartagena, Michelle; Reyes, Elba D. Chemistry Department, University of Puerto Rico, Cayey Campus.

Creating methodology to determine chemical changes of infusions

In Puerto Rico, infusions of plants with therapeutic effects are very useful but sometimes dangerous for the health. For many plants used to treat different illnesses, no phytochemical information are reported, therefore, nobody knows of possible secondary effects or side reactions that will happen due to changes in pH or side reactions with other synthetic drugs. The main goal of this research is to study the chemical changes of the plant compounds that have therapeutic effects (metabolites), which are namely ingested by humans. In particular, we want to answer the following questions: 1) Do the compounds present in an active extract suffer chemical changes at different pHs and temperatures? 2) Are all the organic compounds present or extracted from one source present in the infusions prepared by the population? We expect to: a) probe qualitatively if the general organic composition at specific infusions suffers chemical changes with lower or neutral pH’s; b) compare the total chemical compositions of the whole crude MeOH extracts of Citrus aurantium L. and Annona reticulata leaves with the extracted chemical composition in the aqueous phase when the infusions are prepared, and c) characterize the crude extracts presenting chemical changes. Preliminary TLC results, analyzing infusion extracts from leaves of Citrus aurantium L. and Annona reticulata (after mimicking human digestion, specifically stomach and plasma pH and corporal temperature) reveals irreversible chemical changes when the pH rises to 7.4. These preliminary results demonstrate that chemical changes could be occurring during the bioassays implicating that biological activity could be due to the chemical changes promoted by the extracts instead of natural metabolites. Extracts presenting chemical changes are submitted to Probit analyses, using brine shrimp as live source to probe citotoxicity. ED50  values and partially characterization of organic compounds using chromatographic (TLC, CC, GC) and spectroscopic techniques (IR, MS) will be presented. 


Back to Top


Castillo Rivera, Dorianne A; Rodriguez Reyes, David; Prieto, Jose A.  Chemistry Department,  UPR-Rio Piedras.

Studies toward the synthesis of Rifamycin S ansa chain

Rifamycin S is a member of the ansamycin family of antibiotics.  Its structure consists of an aliphatic ansa chain with eight consecutives stereogenic centers and an aromatic portion.  In order to construct the polypropionate array, we are currently working in a reiterative approach that consists in the stereoselective synthesis of epoxides, followed by a regioselective cleavage process with an organometallic compounds.  Following the proposed work, we epoxidized Ethyl trans crotonate with 3-chloroperoxybenzoic acid (mCPBA) in moderate yield.  This epoxide was cleaved with diethylpropynylalane in high yield (80%) and the alkynyl ester was transformed into its corresponding alkynyl acid in quantitative yield using microwave technology.  Then, a trans reduction of the alkyne functionality was performed in very high yield under sodium/ammonia conditions (95-100%). Iodolactonization followed by methanolysis produced a second epoxy ester (56%). Since the cleavage of this epoxide showed to be problematic , we are working in the reduction of the ester functionality and protection of the resulting primary alcohol before exposing the epoxide to the cleavage process.  At this stage, we have synthesized six of the stereogenic centers of Rifamycin S. Currently, we are investigating the best reaction conditions to finally incorporate the remaining two stereogenic centers of the ansa chain.  Work supported by NIH RISE (R25-GM-061151) and NIH SCORE (S06GM-08102).

 Back to Top


Cotto, Marlene; Miranda, Carlos.; Carballeira, Néstor M.  Department of Chemistry, University of Puerto Rico, Rio Piedras.

The total synthesis of (+)-2- methyldecanoic acid, a potential antimycobacterial fatty acid

Biologically active compounds containing methyl branching are abundant in nature. The fatty acid (+)-2-methyldecanoic acid was synthesized in three steps starting from  commercially available decanoic acid. This synthesis provided sufficient quantities for biological evaluation against Mycobacterium tuberculosis H37Rv. The previously synthesized 2-methoxydecanoic acid has demonstrated activity (99% inhibition) at 6.25 µg/mL against this strain of M. tuberculosis and such studies are underway.                                             

 

 M.Cotto thanks the UPR-RP RISE program for an undergraduated  fellowship

Back to Top


Crespo-Román, Gisela; Ocasio-Delgado, Yessenia; Cortes-Figueroa, Jose E.  Department of Chemistry, UPR-Mayagüez.

Mechanisms of ligand exchange reactions on (dihapto-[C60]fullerene) transition-metal carbonyl complexes

The Lewis bases (L) piperidine, triphenylphosphie, and triciclohylphosphine displace bidentate ligands (bidentate ligands =  1,2-bis(diphenylphosphino)ethane (dppe) and 1, 10-phenanthroline (phen)) from fac- and mer-(dihapto-C60)(dihapto-bidentate ligand)M(CO)3 to produce  fac- and/or mer- (dihapto)(monohapto-L)2M(CO)3 and (monohapto-L)(dihapto-bidentate ligand)M(CO)3  (M = Cr, Mo, W). The reactions are first order with respect to the molar concentration of (dihapto-C60)(dihapto-bidentate ligand)M(CO)3.  The order with respect to L is complex.  The proposed mechanisms involve a competition between a L-assisted ring-opening of the chelate ring to produce the electronically-saturated intermediate (dihapto-C60)(monohapto-L)(monohapto-bidentate ligand)M(CO)3, solvent-assisted ring-opening of the chelate ring to produce the electronically-saturated intermediate (dihapto-C60)(solvent)(monohapto-bidentate ligand)M(CO)3 and a solvent-assisted dissociation of C60 producing the electronically-saturated species (monohapto-L)(dihapto-bidentate ligand)M(CO)3. These mechanisms differ from previously proposed mechanisms for the ligand exchange reactions of closely-related complexes such as fac-(monohapto-L)(dihapto-dppe)M(CO)3 (L = CO, piperidine, pyridine) and is contrary to the known cis labilizing property of dppe.  These results suggest that [C60]fullerene has a strong steric influence on the inorganic moiety of the complex and on its chemical behavior.  Acknowledgments are made to the Petroleum Research Fund (PRF 36623-B3), Administered by the American Chemical Society, and to National Science Foundation (CHEM-0102167) for support of this work.

 Back to Top


Cruz, Nadya; Nieves, Ileana; Oyola, Rolando; García, Carmelo; Piñero, Luis; Rivera, Jessica;  Department of Chemistry, UPR-Humacao.

Imipramines tricyclic drugs: An electrochemistry study in different solvents

The tricyclic anti-depressive drugs Imipramine (IPA), Desimipramine (DIPA) and Cloimipramine (CIPA) are of significant pharmaceutical importance because of  their neuroleptic, sedative and antihistamic effects.  Because these drugs are susceptible to changes in their molecular structures, the redox potentials of these drugs are relevant to understand their photoelectron transfer mechanism involving short-lived oxidation-reduction intermediates. The oxidation-reduction capability of a given derivative have been investigated in different solvents by Cyclic and Differential Pulse Voltammetry (CV and DPV, respectively) with a BAS CV-50 Voltammetric Analyzer controlled by the CV-50W version 2.3 software installed in a Pentium II computer.  Results have shown that DIPA and IPA are easily oxidized compared to CIPA in the solvents used.  As expected, the behavior of CIPA can be attributed to the chlorine induced electron withdrawing effect. In addition, CIPA shows the formation of two distinct oxidation intermediates when IPA/CIPA or DIPA/CIPA drug concentration ratio is changed in acetonitrile and methanol. Although the intermediates have not been characterized in these studies, the CV and DPV results may be correlated with the photochemical and photophysical response of these drugs related to the side effects. The gathered results are relevant for new drug development of efficient formulation with fewer side effects for the proper treatment of patients.  Sponsored by Advance, NSF (SBE-0123645), UPR-Humacao

 Back to Top


Cruz Moreira, Solimar; Ramos, Maiella, Department of Physics-Chemistry, University  of Puerto Rico in Arecibo  -  Arbelo, José; Pantoja, Carlos; Mercado, Benjamín.  Department of Biology, University  of Puerto Rico in Arecibo.

Bioremediation of contaminated water with lead using Tropical plants in hydroponics cultures

Phytoremediation is a process of using plants to remove contaminants from the environment. The water hyacinth (Eichhornia crassipes) may be used as a sensitive bioindicator for continuously monitoring trace quantities of toxic heavy metals in aquatic systems. In this work we addressed the uptake of lead (Pb) by the water hyacinth aquatic plant. Hyacinth plants were grown in hydroponic solutions containing different concentrations of lead ranging from 0 ppm Pb to 10 ppm Pb. Levels of lead were determined in plant samples by means of an atomic absorption flame spectrometer. It was demonstrated that E. crassipes has a strong capability to accumulate higher lead concentrations in its roots than in its other parts. It was found that the concentrations of lead in the water hyacinth were higher than in the water. This heavy metal accumulated in the root tissues of water hyacinth may serve as a chemical marker for the evaluation of the remediation capabilities of this aquatic plant.

 Back to Top  


Delgado, Dana; Nuñez, Daliangelis; Torres, Ivelisse; Rosario, Osvaldo. Chemistry Department, UPR-Rio Piedras.

Isolation and characterization of marine humic substances from seawater  

The purpose of this investigation is to develop and validate methodology to study Endocrine Disrupting Chemicals (EDCs) in seawater using Solid Phase Microextraction (SPME) and GC/MS.  EDCs have generated interest because of their possible effects on human health and environmental organisms.  During the method development, a significant decrease in extraction efficiency of the standards was observed when commercial humic substances of terrestrial origin were added to the model matrix.  More experiments with spiked seawater samples demonstrated influence of humic material in the extraction efficiency of SPME.  Natural humic material has been sampled from seawater at the coast of Cabo Rojo (El Faro) since this material is not commercially available and its properties are unique of the source of the material.  This area was chosen due to the minimal interference of terrestrial humic material from river effluents or other water bodies.  The isolation procedure with XAD-8 resins was taken from previous studies presented in the literature and from the International Humic Substances Society.  A three day isolation procedure was set up on the beach in order to isolate the dissolved humic material from 500 L of seawater.  After this, the extraction procedure was completed in the laboratory.  FT-IR, H1 NMR, and UV/VIS spectra were acquired for the isolated fulvic and humic material.  Also, an Elemental Analysis for some specific elements was performed.  The presence of other elements will be determined with X-Ray Fluorescence Analysis.  A blank of the resin is now being studied to determine possible interferences in the isolated material.  

 Back to Top


Díaz, Tanya; Malavé, María; Rivera, Mirna; Castillo, Jorge; Tremont, Rolando.  Department of Chemistry, UPR-Humacao.

Self-assembled C26H24O2Fc on gold surface in ethanol solution  

Gold surface have been modified by self-assembled techniques. Controlling the adsorption time of C26H24O2Fc at gold surface. This study was followed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) analysis. The method used for the surface modification was the control of exposure time of gold surface in the modifier/ethanol solution. By CV and EIS we demonstrated that the gold surface was modified with C26H24O2Fc compound, avoiding the electron transference in the interface. In the study by XPS we observed that the organometallic molecule indeed has been adsorbed on the gold surface. In addition, it was observed that the molecule-gold interaction is through electrons of cyclopentadienyl, where the oxygen atoms are near the air-molecule interface.

 Back to Top


Domenech Garcia, Maribella.  Biotecnologia Industrial, UPR-Mayagüez  -  McFallin, Jose Luis. Ingenieria Quimica, UPR-Mayagüez  -  Velez, Gisselle. Quimica, UPR-Mayagüez  -  Justicia, Shandra. Biotecnologia Industrial, UPR-Mayagüez  -  Rodriguez, Kristy; Rodriguez, Lolita. Quimica, UPR-Mayagüez.

Effects of aqueous extracts of baquiña in free calcium ion levels determined with a calcium selective electrode

La planta Lepianthes peltatum (Baquiña) ha sido usada en la medicina tradicional para tratar calculos renales (riñón tracto urinario y vejiga). Aparentemente, los compuestos activos se encuentran en la decocción extraída de la raíz y de la hoja respectivamente. Las decocciones de Baquiña  preparadas en el laboratorio demuestran que la planta es capaz de formar complejos robustos con sales de calcio solubles y disolver las sales insolubles de oxalato y fosfato de calcio (titulación con calcio de la decocción de hoja, electrodo selectivo de calcio).  Se cree que el componente activo es el 4-neronidilcatecol, un compuesto insoluble en agua que acompleja calcio. Esto indica que lo más probable es que el principio activo de esta planta sea una forma soluble del mismo, posiblemente el propio catecol unido a un azúcar que lo haga soluble en agua.

Para identificar este posible principo activo hemos procedido a analizar los constituyentes hidrosolubles presentes en las hojas de Baquiña. El proceso de análisis de la planta, una vez las muestras se han secado (liofilización) y molido (2 mm) ha consistido en realizar una extracción Soxhlet con agua (5-10 gramos de material seco en 150 mL de agua), fraccionación por filtración gel (Sephadex G-10 y G-25 fino y superfino) y estudio de las fracciones resultantes por cromatografia líquida (HPLC,  Alltima C18 5um, 27:73 acetonitrilo – agua). Resultados preliminares indican que hay varias fracciones puras, llamándonos la atención un pico con tiempo de retención de 4 minutos.

 

Back to Top


 

Echevarría Torres, David; Santos, Lizette.  Chemistry, PUCPR.

The effect of anticonvulsants on the microsomal cytochrome  P450 monooxygenase system

The liver is one of the most important organs involved in the metabolism of exogenous and endogenous compounds in the body. The microsomal cytochrome P450 monooxygenase system is present in the liver. This system play a mayor role in the biotransformation of many compounds. The objective of this study is to measure the effect of some anticonvulsants drugs on the cytochrome P450 system. The anticonvulsants drugs to be studied are: Tegretol (carbamazepine), Divalproex (depakote), Trilepal (oxcarbazepine) and Dilantin (phenytoin). The isoenzymes that will be studied are CYP2C8 and CYP2C9. Microsomes will be prepare from Cricetulus griseus cells (CHO) cells and treated with the anticonvulsants drugs. Enzyme activities will be measured using HPLC Technique. Expected results will include the determination of possible effects on the CYP2C8 and CYP2C9 isoenzymes.

Back to Top


Escalona, Yma; Miller, Andrés. Natural Sciences Department, Inter American University, Bayamón Campus.

Determinación  de concentración de plomo en árboles frutales silvestres, en la Isla de Vieques

Vieques, isla oceánica de aproximadamente 20 millas de largo por 4.5millas de ancho. Clima promedio anual  79º F,  y  9,300 habitantes en la parte central.   Los últimos 60 años la Marina de  Estados Unidos la utilizó como polígono de tiros  para  prácticas militares generando materiales tóxicos en el ambiente, afectando plantas y animales del ecosistema. Dicha contaminación aún representa  peligro  para la salud humana al consumir  alimentos provenientes del sector agrícola.  De las sustancias nocivas  presentes en el ambiente, de prolongada vida media y marcado efecto de acumulación, adquieren especial significado los metales plomo y cadmio. El estudio de la nutrición mineral de las plantas muestra la composición química y la naturaleza y proporción de esos metales en el tejido vegetal para así con un  análisis químico cualitativo y cuantitativo, conocer si hay  aumento considerable de ellos en algunas plantas. La investigación nuestra, reflejó datos significativos para recomendar continuidad de estudios biológicos y químicos por la alta contaminación.  Un primer análisis reflejó la existencia de partículas microscópicas  contaminadas esparcidas en el ambiente y el segundo, determinó la concentración de contaminantes en  árboles frutales dentro  del perímetro cercano a las viviendas de la  población, que luego lo comparamos a árboles frutales de las mismas especies de áreas no contaminadas para evaluar el nivel de sustancias nocivas  en las plantas. Las concentraciones de plomo y otros contaminantes  no deben ser menos importantes para determinar impactos significativos, incluyendo el impacto directo a la población  y a las  especies en peligro de extinción.     

Back to Top


Flores, Rosangelly; Brito, Rosa; Hernandez, Jessica; Cabrera, Carlos R.  Department of Chemistry, University of Puerto Rico-Rio Piedras.

DNA density measurements using electrochemical methods on modified platinum electrodes

Recent research in the field of analytical chemistry has been directed on approaching biomedical problems through electrochemical analysis.  Problems such as the characterization of different DNA densities are being investigated.  One of the main objectives is to develop DNA arrays with large DNA densities.  This research involves the entrapment of DNA on a platinum surface, which has been modified using different thiol at optimum concentration.  The platinum plates were cleaned, in 0.1M sulfuric acid (H2SO4), by cyclic voltammetry.  X-Ray Photon Spectroscopy (XPS) was used to test how well the platinum surface was modified.  Once this was done optimum concentration for thiols were selected.  The concentrations used were 1-pentanethiol 5mM, 1-decanethiol 5mM and 1-dodecanethiol 10mM.  After obtaining these concentrations, measures of potential desorption were taken.  Briefly, this technique involves a voltage sweep (0 to –2000 mV) to indicate potential at which each thiol is removed from the Pt surface.  The measures where obtained through cyclic voltammetry in one segment of the surface.  Future experiments include taking different desorption potentials and the immobilization of DNA on platinum.  The DNA will be hybridized and measures of their densities will be taken through selected desorption potentials.

Back to Top


García, Rafael; Samuel P. Hernández-Rivera.  Center for Chemical Sensors Development for Explosives, Department of Chemistry, University of Puerto Rico , Mayagüez.

Vibrational spectroscopy and theoretical studies of transparent explosives

Explosives are a special group of chemicals that have a high energy in their chemical bonds that are able to release it in a short time in the form of hot gases.  In today’s modern world, explosives are important and useful tools that play central roles in such as mining of mineral ores and construction.  In the political scene, explosives has been give a more sinister and morbid use in terrorism.  In the past the kind of explosives that were used for terrorist application where somewhat common and easily acquired in the international weapons underground market: black powder, T.N.T, RDX and other military explosives.  But these explosives have an Aquiles heal, they can be detected in very small quantities by the instruments (Ion Mobility Spectrometers) that the transportation security agencies use.  Being a very adaptable entity terrorist, are now using exotic home-made explosives like Triacetone Triperoxe (T.A.T.P) and Diacetone Diperoxe (D.A.T.P) that are virtually invisible to current the technology used in these detection machines.  Our research centers in the analysis of this kind of chemical explosives: Transparent Explosives and in the design of sensors for their detection. In the initial experiments we combined different methodologies for characterization and analysis.  We used Spontaneous Raman spectroscopy for vibrational characterization.  Then the research centered about to the use of silver colloids for applications of Surface Enhanced Raman Spectroscopy. For target compounds we used model compounds with similar characteristics with the transparent explosives.  These compounds are easier to use and have low toxicity.

Back to Top


García Berríos, Edgardo; Elba Reyes; Raúl J. Castro.  Department of Chemistry, University of Puerto Rico at Cayey.

In-situ Friedel-Craft acylation of benzenethiol/Au self-assembled monolayers

Self-assembled benzenethiol (BT) molecules were chemisorpted on Au substrates by substrate immersion in BT/ethanol solution. SAM/Au substrates were prepared to react with adipoyl chloride to develop an aromatic-acylation reaction by the Friedel-Craft acylation method, by using aluminum chloride as a catalyst. The modified SAM moieties were characterized by reflectance Fourier transform infrared spectroscopy (rFTIR) in order to determine the presence of carbonyl groups specifically. X-ray photoelectron spectroscopy (XPS) was also used to determine the different element/bonds/oxidation states present in the SAM-modified films. In order to compare the different bonds present in the modified SAMs, BT was characterized (rFTIR, XPS) and reacted by the same Friedel-Craft reaction but without performing the BT-Au assembly.

Back to Top


Gavalda, Salvador; Rodriguez, Jose; Smotkin, Eugene.  Chemistry, UPR-Río Piedras.

Preparation and characterization of Cu/Zn/Al2O3 catalyst libraries for design of experiments (DOE) development of water-gas-shift and/or methanol reforming catalysts

The ability to rapidly prepare large catalytic libraries will facilitate the search for catalysts that are more practical and of greater activity.  Alumina supported Cu and Zn catalysts can be made through wet impregnation of these metal ions onto alumina beads using a robotic system.  The resulting actual metal compostion of the beads can then be obtained through differential pulse anodic stripping voltammetry (DPASV.)  Actual activity as methanol-reforming catalysts can be obtained through the use of laser-activated membrane introduction mass spectrometry (LAMIMS), a high-throughput screening method that evaluates heterogeneous catalysts under realistic conditions with results comparable to those of industrial micro-reactors. LAMIMS will enable the rapid ranking of catalyst libraries and the development of response surfaces that will be used in a DOE methodology for catalyst discovery.

Back to Top


Giménez, Lizabeth; Sanabria, David; Cruz, Clarisa; Carballeira, Néstor.  Department of Chemistry, University of Puerto Rico Río Piedras .

The synthesis of new fatty acids and their potential as antifungal compounds

Candida albicans, a component of the normal human microflora, is the most common cause of fungal infections. Studies have further shown that C. albicans can become transiently resistant to azole drugs rapidly after exposure to the antifungal drug fluconazole. Acids 1 and 2, isolated from the roots of Pentagonia gigantifoila, showed a potent antifungal activity against C. albicans and series of fluconazole-resistant. C. albicans strains. We are interested in studying the effect that the triple bond position and the carbon chain length have in the bioactivity of these acids. For these reasons, we plan to synthesize some analogues of acids 1 and 2, such as 9-hexadecynoic acid (3) and 5-hexadecynoic acid (4). For the synthesis of acid 3, we began with the commercially available 8-bromo-1-octanol and the overall yield of this five-step synthesis was 15%. The current results of our synthesis will be discussed.

Back to Top


Gonzalez, Cristian. Chemical Engineering, UPR-Mayagüez  -  Rivera, Luis A.  Chemistry, UPR-Mayagüez.

Design, synthesis, and characterization of potential biosensors for protein by covalent immobilization of the amino acid threonine

The purpose of this experiment was to create and develop a functional sequence in order to create a new biosensor. The reaction sequence consist of activation of the Silica Gel surface, followed by the addition of (Glycidoxypropyl)trimethoxysilane (GOPS) reagent to perform the silylation of the activated hydroxyl groups in the Silica Gel. Then the addition of 1,1-Carbonyldiimidazole was carried out to form the corresponding aromatic imidazole amide. Finally the introduction of the dl pair or individual enantiomeric amino acid isomers was performed by nucleophilic addition of the nitrogen atom of the amino group to the carbonyl carbon with displacement of the imidazole anion to give the expected product. Analysis and characterization of the reaction products at each stage of the reaction sequence was performed by attenuated total refractance infrared spectroscopy (ATR FT-IR) and surface analysis by electron microscopy.

Back to Top


Gonzalez Freire, Carol L.  Quimica, Universidad de Puerto Rico Recinto de Rio Piedras  -  Quesada Gonzalez, Orestes.  Estudios Generales, Universidad de Puerto Rico Recinto de Rio Piedras  -  Morales Guardia, Reginald. Quimica, Universidad de Puerto Rico Recinto de Rio Piedras.

Possible site of interaction of sanguinarine  chloride  and ipratropium bromide on the human erythrocyte membrane

Normally, drugs reach their target organ via the blood.  Therefore, the drug molecule first have to enter the circulation, in which the molecule interact with the human erythrocyte membrane and then through barrier membrane in the gastrointestinal tract. The speed of absorption depends on both the properties of the membrane and physicochemical properties of the drug.  Until know, drug localization within the membrane was achieve using reagent with known binding sites in the bilayer and monitoring the effect released by the drug.  This work present a novel assay using phospholipases A2 (PLA2) from snake venom as a probe for drug-membrane interaction of in human erythrocyte.  Binding assays with A. halys PLA shown a very limited number of high affinity binding sites. Also A. halys PLA does not require calcium for binding, but does so for hydrolysis. In addition, A. halys PLA specificity is dependent on enzyme concentration, indicating that such specificity is not due to a specific interaction with a given substrate, but is due to binding at the high affinity site.    Sanguinarine chloride hydrate an anti-inflammtory drug and Ipratropium bromide a bronchodilator were found to induce minor shape changes in erythrocytes membrane (0-250 nmol added/mL cells) and no significant hemolysis. The amount of bound A. halys PLA2 was increased by Ipratropium bromide and inhibit by Saguinarine  in a concentration dependent manner. These result suggest a possible common site of interaction near a membrane protein.  (Supported by MARC Grant 5T34GM07821-24)

Back to Top


Gonzalez-Gonzalez, Ileana; Tryk, Donald A.; Cabrera, Carlos R. Chemistry Department, University of Puerto Rico, Rio Piedras Campus.

A comparison of sulfur-doped and boron-doped diamond films as electrocatalyst supports

Diamond films exhibit very high stability versus various chemical and electrochemical treatments.  Two different possible types of diamond catalyst supports (boron-doped and sulfur-doped) have been characterized by SEM/EDS, AFM, XPS and electrochemical techniques,  both in terms of their intrinsic behavior and in terms of their characteristics as catalyst support, for examples for platinum alloys.  The characteristics were also compared before and after electrochemical and chemical oxidation of the surface.  Scanning electron microscopy images and X-ray diffraction analysis demonstrated that the diamond films are organized structures that include both (111) and (100) facets.  The Raman spectrum of the boron-doped diamond film was characteristic of a high quality material.  The energy dispersive spectra showed that the diamond film contains mainly carbon and oxygen. The boron doped-diamond films have a potential window of approximately three volts, contrasting with gold, platinum, and glassy carbon.  Due to the lack of activity for oxygen reduction, the potential window is adequate for some purposes even without removing oxygen.  The characteristics of boron-doped diamond film, such as hardness, stability up to high positive potentials and the wide potential range over which discharge of water does not occur, make it an excellent candidate as an anode in the oxidation of organic compounds.  The excellent electrochemical stability, together with the possibility for strong bonding with various types of metals, makes it also an excellent candidate for a general electrocatalyst support, for example, for fuel cells.

Back to Top


Granell, Laura; Pietri, Ruth; Lewis, Ariel; López-Garriga, Juan.  Chemistry, U.P.R.-Mayagüez Campus.

Determination of the open and closed conformations of the hemoglobin II from Lucina pectinata by FT-IR

Lucina pectinata is a bivalve mollusk that lives in the mangroves of Lajas, Puerto Rico . This mollusk contains three types of hemoglobin. Hemoglobin I (HbI) is sulfide reactive, but the other two, hemoglobin II and III (HbII and HbIII) are oxygen reactive proteins. HbII shows a unique structural organization of the heme pocket involving residues Gln (E7) and Tyr (B10) as recently demonstrated by the full length cDNA sequence. Crystallographic data shows that HbI has the same reactive center as HbII with the exception of a Phe residue in the B10 position.  To further elucidate the structural and functional properties of HbII, FT-IR analysis and kinetic studies of the ferrous HbII-CO derivative were performed.  The same studies were conducted in the Phe (B10)-Tyr HbI mutant. The results suggest the existence of two conformations: open and closed, due to the interactions of the Tyr residue with the heme ligand complex. Similar results were observed for the HbI mutant. The HbII-CO infrared spectra confirm the presences of an open (~1965 cm-1) and close conformation (~1925 cm-1) due to the orientation of the Tyr (B10) with respect to the heme active center. The Phe (B10)-Tyr HbI mutant shows frequencies at 1925 cm-1 in which the closed conformation predominates. Kinetic studies for HbIIO2 and Phe (B10)-Tyr HbIO2 confirm the authenticity of the mutant and the arrangement of the Tyr in the position B10.  It is suggested here that in the open conformation the Tyr (B10) swings away from the iron, while in the closed conformation it is in a favorable distance to interact with the ligand through hydrogen bond.

Back to Top


Guillen, Nancy; Narvaez, Daniel; Camacho, Carlos; Pastrana, Belinda.  Industrial Biotechnology, Chemistry Department, UPR-Mayagüez.

FT-IR studies of EGFR ligands

Growth factors are small proteins found in serum in very low concentrations. These proteins directly stimulate cell division. Epidermal growth factor (EGF) is a single chain growth factor containing 53 amino acids (6 kD) and three disulfide bonds. Transforming growth factor-alpha (TGF-α) is a small 50 amino acid mitogenic protein, which shares about 30% sequence identity with EGF and competes as a ligand with EGF for the same receptor sites of epidermal growth factor receptor (EGFR). EGFR is a transmembrane glycoprotein found primarily on cells of epithelial origin. It is a member of a family of growth-factor receptors with tyrosine kinase activity. Binding of ligands to the growth-factor receptor triggers a number of cellular responses that eventually lead to cell proliferation and act in an atypical manner in tumor cells.  As part of this research, fast H/D exchange studies of the ligands EGF and TGF-α were performed using Attenuated Total Reflectance (ATR)-FTIR spectroscopy. These experiments provided information on the ligands accessibility to its aqueous environment, its conformation and its dynamic behavior upon H/D exchange. The spectra obtained were analyzed by a two-dimensional correlation to determine which regions of the protein go through the H/D exchange first and the subsequent order of events during the exchange process. Changes in intensity and band position characteristic of the H/D exchange process were observed in the spectral region of 1700 to 1400 cm-1. Further FT-IR thermal perturbation studies were performed to analyze transition temperature.

Back to Top


Hernandez, Emil; Castro, Miguel E.  Chemistry, UPR-Mayagüez.

Nanoparticle synthesis in a bubble: microreactors for selective nanoparticle synthesis

Silver nanoparticles have many chemical and physical properties that make them suitable for a great variety of applications, such as biomarkers, optical, electrical and mechanical devices. Hence many methods have been developed for the tailored synthesis of nanoparticles. In any typical silver reduction, nanoparticles, rods and wires are formed. Here we report on results on the use of soap bubbles for the selective synthesis of silver spheres. Micelles are formed in the liquid detergent that serves as microreactors for the reduction of silver and the formation of spheres. The nanoparticles are characterized with a battery of electron and optical microscopy and UV-VIS spectroscopy.

Back to Top


Hernández Lugo, Dionne M.; García, Carmelo; Piñero, Luis E.; Oyola, Rolando.   Departamento de Química, Universidad de Puerto Rico en Humacao.

Photophysical properties of protriptyline and dibenzocycloheptene

Protriptyline hydrochloride (PTL-HCl) is a tricyclic antidepressant and a skin photosensitizing agent in humans. The mechanism of this cutaneous photosensitivity is still unknown.  It has been proposed that the excited states and some of the short-lived intermediates of this drug are directly associated with its in vivo phototoxic effects.  Therefore we have measured the photophysical properties of the protonated (PTL-HCl) and unprotonated (PTL) forms of protriptyline and the parent molecule (dibenzocycloheptene, DBCH). The ground and excited singlet state properties (molar extinction coefficient, fluorescence quantum yield, fluorescence lifetime and fluorescence quenching constant) were measured in methanol and acetonitrile. The ground state properties are solvent and protonation independent.  The fluorescence quantum yield and lifetime, on the other hand, strongly depend on the solvent.  The quenching studies were done in acetonitrile using diethyl and triethyl amine as quencher.  The Stern-Volmer quenching constants are also solvent dependent.   This work has been supported by NIH-MBRS Grant S06GM08216.

Back to Top


Justicia Leon, Shandra D.  Departamento de Biotecnologia Industrial, UPR-Mayagüez -  Souto Bachiller, Fernando; Rodriguez Rodriguez, Lolita.  Departamento de Quimica, UPR-Mayagüez  -  Justicia Leon, Shandra D.  Departamento de Biotecnologia Industrial, UPR-Mayagüez  -  Velez Ruiz, Gisselle A.; Rodriguez Colon, Kristy I.  Departamento de Quimica, UPR-Mayagüez  -  Domenech Garcia, Maribella.  Departamento de Biotecnologia Industrial, UPR-Mayagüez. 

Fitoquimica de plantas medicinales diureticas: Rubia tinctorum

Rubia tinctorum (R. tinctorum) es una planta medicinal diurética utilizada tradicionalmente para tratar calcificaciones, tales como la piedra del riñón, tracto urinario y vejiga, compuestas fundamentalmente de oxalato y fosfato de calcio. Existen múltiples testimonios de que las decocciones de esta planta preparadas según el método tradicional (té), tienen la capacidad de pulverizar dichas calcificaciones. Extracciones realizadas en el laboratorio confirman que los extractos de R. tinctorum son capaces de acomplejar sales de calcio solubles  y disolver las sales insolubles de oxalato y fosfato de calcio.  El acomplejamiento de calcio que presenta R. tinctorum se le ha adjudicado preliminarmente a sus componentes mayoritarios, alizarina, un pigmento anaranjado rojizo y purpurina, amarillo. Un tercer componente lo es la lucidina, pigmento con alto grado de toxicidad. El problema se fundamenta en que ninguno de los pigmentos acomplejantes se encuentran en el extracto acuoso de la planta pues son virtualmente insolubles en agua, por lo que se infiere la existencia de otros componentes solubles. Candidatos posibles son los correspondientes glicósidos solubles en solución acuosa. Para corroborar estas hipótesis, actualmente se están realizando extracciones soxhlet con agua a partir de las raíces de R. tinctorum, fraccionación por ultracentrífuga o filtración gel de dichas extracciones y, finalmente, estudios cromatográficos (HPLC) y espectrofotométricos (UV-VIS) para determinar la composición y pureza de fracciones recolectadas.  La evidencia obtenida indica que hemos aislado los glicósidos de alizarina y purpurina puros y que dichos glicósidos muestran actividad antilítica determinada por el electrodo selectivo de calcio. Además, no se puede decir que existen grandes cantidades del componente tóxico, lucidina o sus glicósidos, en extractos de R. tinctorum.  

Back to Top


López Pacheco, Lilibeth; Santos, Lizette.  Chemistry, Pontifical Catholic University of Puerto Rico .

El efecto de un complejo multivitamínico en el sistema de citocromo P450

El sistema de citocromo P450 está presente principalmente en el hígado y ayuda en la biotransformación de muchos compuestos extraños que entran al organismo. Este sistema puede ser inducido o inhibido por diferentes tipos de compuestos. El objetivo de este estudio es medir el efecto que tiene un suplemento vitamínico (Centrum) en el sistema de citocromo P450. Células de “hamster” chino fueron tratadas con el suplemento vitamínico y etanol. Un frasco de células fue utilizado como control. Se prepararon microsomas de las células. Actualmente, las células están siendo analizadas para el contenido de citocromo P450, proteína total y las actividades enzimáticas de las siguientes isoenzimas CYP1A y CYP 2E. Los resultados esperados son que este suplemento altere, inhibiendo o induciendo, el sistema de citocromo P450.

Back to Top


López-Alvarez, Yania M.   Industrial Biotechnology Program, UPR- Mayagüez  -  López, Gustavo E.  Department of Chemistry, UPR-Mayagüez.

Computational studies of the liquid-liquid equilibrium in Lagmuir monolayers

The liquid-liquid equilibrium of surfactant molecules forming an interphase between water and air has been considered using Monte Carlo computer simulations.  Specifically, the expanded and compressed liquid phases were characterized using two simulation models.  The first one consists of the coupling of an isothermal-isobaric simulation that describes the surfactant with a canonical simulation that describes the water phase.  The method permits the construction of adsorption isotherms, where the area of the monolayer is computed as a function of applied lateral pressure.  The second model was based on the use of the Gibbs ensemble to construct the Caillette-Matties phase diagram and the identification of the critical state.  The results obtained from these simulations are in good agreement with experimental studies.

Back to Top


Madero-Vergara, Mayraliz; García Fraga, Oscar; Díaz-Vazquez, Liz; Rosario, Osvaldo.  Chemistry Department, UPR Río Piedras.

Effects of extraction conditions and modifiers on the supercritical fluid extraction of some persistent organic pollutants from sebum

Sebum has been used to monitor use of controlled drugs as well as exposure to dioxins.  Based on this, it is logical to extrapolate its use to also monitor exposure to other environmental pollutants. We have been working on the development of methodology for the sampling, extraction and analysis of persistent organic compounds in sebum.  The use of patches and cotton swabs for the direct sampling of sebum has been tested.  Supercritical fluid extraction (SFE) conditions for isolation of different persistent organic pollutants (POPs) from human sebum are being evaluated using a synthetic sebum spiked with 8 different organic pollutants. The SFE parameters considered are  CO2 density, CO2 flow rate, extraction temperature, static and dynamic extraction times and addition of  modifier. This is compared to ultrasonic extraction. Eventually we plan to also try microwave solvent extraction for the recovery of POPS.

Back to Top


Maldonado, Omar D.; Castro, Raul.   Quimica, U.P.R. Cayey.

Aplicaciones de QCM y EQCM para el estudio de SAM’s

Los tioles son compuestos que han sido estudiados debido a que son absorbidos espontáneamente a la superficie de los metales. Las monocapas (SAM's) han sido estudiadas en diferentes compuestos debido a las multiples aplicaciones como la inhibición de la corrosión, como biosensor, sensores químicos y otros usos. Este trabajo se basa en bencenotiol, un tiol aromático que es uno estable. El estudio con el equipo de EQCM, QCM es para verificar el mejor voltagrama (el pico anódico diferenciable y reproducible) que se puede obtener y el cambio en frecuencia através del tiempo en el electrodo de oro. Con estos cambios en frecuencia y por la ecuación de Nersts poder calcular el cambio en masa que ocurre en el electrodo ya este es proporcional a la cantidad de moléculas absorbidas para formar la monocapa en la superficie del electrodo de oro. En donde concluimos que el equipo de QCM muestra una respuesta estable en el tiempo tanto en aire como en solución. Se obtuvo evidencia por QCM de la adsorción espontánea de bencenotiol sobre la superficie del disco de Au. Se encontró que la adsorción de bencenotiol al añadirse a la solución de etanol anhidro creá un cambio en la frecuencia de aproximadamente 6 Hz. Con los experimentos de EQCM nos demuestran que fuimos efectivos en lograr el acoplamiento del sistema ya que pudimos obtener data de los mismos y pudimos estudiar sistemas altamente conocidos con muy buenos resultados. Por último pudimos relacionar cambio en frecuencia y cambio en corriente del sistema electroquímico con QCM.

 Back to Top


Marrero , Wilnelia; Morales, Reginald.  Chemistry Department, UPR-Río Piedras  -  Quesada, Orestes.  General Studies, Physical Science, UPR-Río Piedras.

Phospholipase A2 competition in human erythrocyte studies using confocal microscopy

The existence of different interactive sites in human erythrocyte was confirmed by a series of binding studies that characterized the binding isotherms of the basic phospholipase A2 (PLA2) from A. halys and one of the PLA2 from N. nigricollis snake venom. The interaction of N. nigricollis PLA2 is characterized by its Ca+2 requirement for binding and had no acyl specificity in other hand, A. halys PLA does not require calcium for binding, but does so for hydrolysis and its specificity is dependent on enzyme concentration.  These studies reveled that A. halys interacted in a very limited number (5.2 x 107 per cells) of high affinity sites. Competition studies demonstrated that at high levels (50 ug/mL cells) N. nigricollis PLA competed for the high affinity site of A. halys PLA.  Confocal Microscopy imaging of intact human erythrocyte using A. halys and N. nigricollis PLA labeled with Alexa Fluor 488 and Alexa Fluor 532 respectively confirm the binding studies and calcium dependance.  Flourescence profile of both PLA2 at concentration in wich N. nigricollis displaced A. halys from its high affinity site were obtained.  (Supported by MARC Grant 5T34GM07821-24)

Back to Top


Martín, Mariana; Rodríguez, David; Castillo, Dorianne; Prieto, José A.  Department of Chemistry, University of Puerto Rico , Río Piedras.

A new epoxide approach to polypropionate chains using trimethylalane

Alternating hydroxyl and methyl groups on an aliphatic chain with a distinct stereochemistry is known as a polypropionate unit.  Polypropionates are a common feature of many macrolides and ionophores possessing remarkable biological activities.  In our research laboratory, we have been developing a general, stereoselective synthesis strategy to polypropionates based on oxirane and propynyl alane chemistry.  This strategy uses iodocyclization reactions to attain the required stereoselective epoxidations and propynyl alane as the epoxide cleaving agent.  Herein we report a new approach towards the preparation of polypropionates based on peroxide epoxidation and trimethylalane cleavage.  The protected dieneol 1is being transformed into 2 via a sequential monoepoxidation and epoxide cleavage with an alane reagent followed by a second epoxidation and alane cleavage.  This approach is different from our standard epoxide approach to polypropionates and should produce similar compounds more efficiently.  The details of this study will be presented.  Work supported by the NIH SCORE 2S0GGM-08102-29, NIH RISE (1R2S-GM-G11S1-01AI) and MARC (5T34GM07821).

 

Back to Top


Mattei, María de los A; Santos, Lizette.  Chemistry Department, Pontifical Catholic University of Puerto Rico .

Metal content determination of the potable water at the Pontifical Catholic University of Puerto Rico

Water is essential for all living organisms. It helps in maintaining body temperature and the structure of our tissues. At Pontifical Catholic University of Puerto Rico, the water that is consumed comes from a well. The specific objective of this work is to analyze the potable water consumed at the University to establish the presence of certain metals. The metals that were analyzed included antimony, arsenic, beryllium, cadmium, chromium, nickel, lead, selenium, and thallium. Samples were taken from three buildings at the institution: Ferré, Research Center and Perea. From each building samples were taken immediately after letting the water run during five minutes. Samples were obtained for three consecutive days at the same time and conditions. Samples were prepared to be analyzed for metal content using an Induced Coupled Plasma Spectrophotometer (ICP). Preliminary results showed that the following metals concentrations expressed in ppm were above the maximum level of pollution allowed in potable water establish by EPA: Pb 4.89, Ni 1.29, Cd 0.17, Be 0.16, Sb 12.02. These preliminary results are only for the month of august. We will continue these studies during the next few months in order to establish a possible correlation between metal content and certain pollution levels.  

Back to Top


Morales, Eduardo M.; Ortiz, Margarita.   Chemistry Deparment, UPR-Humacao.

Synthesis of  alpha silylated and alkylated O-tert-butyldimethyl silyl aromatic ketoximes

New synthetic methods for the chemo and stereoselective synthesis of important biologically active molecules are in grat demand.  Reactions of metal enolates and azaenolates are well-known methods for construction of C-Si and C-C bonds.  O-TBS ketoximes are novel precursors for the synthesis of highly rective azaenolates, which can be alpha-C substituted.  We studied the alpha silylation and alkylation of O-TBS substituted aromatic cyclic and acyclic ketoximes with LDA under several reactions conditions.  Complete conversion and high yields were afforded for the silylation of O-TBS-4-metoxyacetophenone and indanone oximes with LDA at -78 oC, using trimethyl chlorosilane as electrophiles. O-TBS-alpha-tetralone and 6-methoxy substituted oximes derivate, were also prepared and their silylation gave different substituted silylated products with expected molecular weight.  The alkylation of alpha tetralone with benzyl bromide was obtain in good conversion, but the product is unstable.  

Back to Top


Morales, Victor M.; Morales, Angel L.   Chemistry Department, UPR-Rio Piedras  -  Van Keuls, Fred.  NASA Glenn Research Center   -  Cabrera, Carlos.  Chemistry Department, UPR-Rio Piedras.

Chemisorption and chemical characterization of monolayers at barium strontium titanate Ba0.5Sr0.5tio3 (BSTO) for phase shifter applications

Ferroelectric materials are an enticing prospect for incorporation into agile frequency microwave components including phase shifters, varactors, tunable filters, resonators and antennas. Thin films of the ferroelectric barium strontium titanate Ba0.5Sr0.5TiO3 (BSTO) has been used in coupled microstripline phase shifters (CMPSs) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability and good structural stability. In attempt to improve the figure of merit K of phase shifters (phase shift (degrees) /dB of loss) of phase shifters, modification of the ferroelectric/metal interface of these devices was done through surface modification of the ferroelectrics layer using a self-assembled monolayer approach.  A new approach consists of the build-up of several layers of charge polyelectrolyte. The approach consists in two parts: (a) the chemisorption of 11-mercaptoundecylamine to construct a self-assembled monolayer with the consequent protonation of the amine and (b) the deposition of sandwiches of opposite charge polyelectrolytes. The electrostatic attraction between opposite charges is the driving force for the multilayer build up. This new approach conduces to a longer layer in the Ba0.5Sr0.5TiO3 surface that increased the performance of phase shifters. Multilayer assembly was characterized by X-ray photoelectron spectroscopy (XPS), Fourier-Transform Infrared (FT-IR) and atomic force microscopy (AFM).  

Back to Top


Nuñez, Daliangelis; Delgado, Dana; Torres, Ivel