B.S., Universidad del Tolima, Ibague, Colombia, 1989
M.S., Universidad del Valle, Cali, Colombia, 1996
Ph.D., University of Miami, Coral Gables, FL., 2000
Postdoctoral Research, Texas A&M University, College Station, TX, 2000-2004
Honors and Awards
National Science Foundation Career Award 2007
Excellence in Scholarship Award, College of Humanities and Sciences, VCU, 2007
Outstanding Graduate Student Award, University of Miami, 2000
We are interested in using platforms containing micro and nanoscopic domains (i.e. microchannels, nanoparticles, etc.) to tackle problems in the areas of bioanalytical, biophysical and electroanalytical chemistry. The specific projects that are currently under way in our laboratory are:
Using Surface Charge as a Tool for Studying Chemical and Biochemical Processes
The surface charge of a microchannel can be easily determined by monitoring the voltage developed at two electrodes located at the outlets of the microchannel when a liquid is passed through using pressure driven flow. The spontaneous generation of this electrical potential is proportional to the liquid pressure and the surface charge of the microchannel. In our group this principle is being applied to study chemical and biochemical reactions occurring on plastic microchannel surfaces.
For instance, the adsorption of a positively charged protein (lysozyme) on the surface of a negatively charged microchannel can be monitored in real time by measuring the potential generated by the liquid stream. As the adsorption of lysozyme takes place, the normalized negative charge of the microchannel decreases reaching a saturation point that is reversed when the lysozyme starts to desorb due to the injection of protein-free solution. The original surface charge is not fully reestablished due to residual non-specific adsorption of lysozyme even after 800 seconds. The most important aspect of this approach is that the analytical signal is originated without labeling the molecular probes under study. Additionally, this technique has been developed with very simple and low cost instrumentation, and unlike other techniques the signal is uniquely related to the surface charge.
It is envisioned that this approach could be useful to study the kinetics of surface chemical reactions induced by light, pH or temperature. Similarly, interactions and functions of more complex bioprobes such as viruses, cells and bacteria could also be investigated. Current efforts in our lab are focused in this direction.
Catalysis of Redox Reactions Involving Proton-Coupled Electron Transfer
The goal of this research is to facilitate kinetically and thermodynamically redox reactions that involve the transfer of protons and electrons. These reactions which can occur in solution or across electrochemical interfaces usually take place in coupled fashion, that is, the pH affects the redox potential of the species and its pKa is determined by its oxidation state. Several processes technologically and biologically relevant are based on reactions involving proton-coupled electron transfer (PCET), for instance, the electrochemical oxidation of methanol in fuel cells, the reduction of water in the photogeneration of hydrogen and, respiration and photosynthesis in living beings.
To facilitate these PCET reactions, we propose to use acid-base catalysis, hydrogen bonding and local control of the dielectric environment, which are strategies employed by some enzymes that catalyze reactions coupled to proton transfer (PT). Acid-base catalysis is a well known type of catalysis in which acids or bases are used to neutralize highly charged intermediates by either donating or accepting a proton. The PT is usually preceded by a hydrogen bonded intermediate which is promoted by the lower dielectric environment in the active site of the enzyme and presumably allows the reaction to occur in one concerted step. These strategies allow PT-coupled reactions to be accelerated in conditions of virtual absence of protons! (pH = 7.0) as found in biological solutions.
For example, the electrochemical oxidation of 1,4-hydroquinone (1,4-H2Q) in acetonitrile is a typical PCET that was studied in the presence of Brønsted bases in acetonitrile. Bases make the oxidation of 1,4-H2Q easier because they can accept the protons produced during the two-electron oxidation of 1,4-H2Q. Of the two types of bases studied, the negatively charged carboxylates, trifluoroacetate (TFAC-), showed hydrogen bonding with 1,4-H2Q, whereas the neutral amine, pyridine (PY), did not. This difference allowed a unique investigation of the effect of proton transfer on PCET with and without the influence of hydrogen bonding using two bases (TFAC- and PY) with approximately the same pKa (~12). The study revealed that hydrogen bonding of 1,4-H2Q with the base TFAC- made the half wave redox potential of 1,4-H2Q more negative (easier to oxidize) by 0.186 V with respect to the oxidation in the presence of the same concentration of added PY, which does not hydrogen bond with 1,4-H2Q. Both types of bases studied, showed a combination of kinetic and thermodynamic effects in the oxidation voltammerty of 1,4-H2Q; however, no evidence of concerted pathways was found at the conditions studied as indicated by H/D kinetic isotope experiments. The mechanism from fitted digital simulations for the bases supports a stepwise PCET, even in the presence of hydrogen bonding, implying that the latter does not prevail in the transition state nor is rate determining.
Alligrant, T. M., Alvarez, J. C., “The Role of Intermolecular Hydrogen Bonding and Proton Transfer in Proton-Coupled Electron Transfer”, J. Phys. Chem. C, 2011, 115, 10197-10805.
Luna-Vera, F., Ferguson, J. D., Alvarez, J.C., “Real Time Detection of Lysozyme by Pulsed Streaming Potentials Using Polyclonal Antibodies Immobilized on a Renewable Nonfouling Surface Inside Plastic Microfluidic Channels”, Anal. Chem., 2011, 83, 2012-2019.
Alligrant, T.M.; Hackett, J.; Alvarez, J. C., “Acid/Base and Hydrogen Bonding Effects on the Coupled Proton-Electron Transfer of Quinones and Hydroquinones in Acetonitrile: Mechanistic Investigation by Voltammetry,1H-NMR, Electronic Spectra and Computation”, Electrochimica Acta,2010, 55, 6507-6516.
Gupta, M. L., Brunson, K., Chakravorty, A., Kurt, P., Alvarez, J. C., Luna-Vera, F., Wynne, K. J.,“Quantifying Surface-Accessible Quaternary Charge for Surface Modified Coatings via Streaming Potential Measurements”, Langmuir, 2010, 23, 9032-9039
Luna-Vera, F., Alvarez, J.C, “Adsorption Kinetics of Proteins in Plastic Microfluidic Channels: Real-time Monitoring of Lysozyme Adsorption by Pulsed Streaming Potentials”, Biosens. Bioelectron., 2009, 25, 1539-1543.
Khalid, M., I., Alvarez, J. C., “Removal of Electroanalytical Interferences Using Thermodymanic and Kinetic Effects Induced by In-Situ Electrogeneration of Protons”, J. Electroanal. Chem., 2009, 631, 76-79.
Pu, Q., Elazazy, M., Alvarez, J. C., “Label- Free Detection of Heparin, Streptavidin, and Other Probes By Pulsed Streaming Potentials in Plastic Microfluidic Channels”. Anal. Chem., 2008, 80, 6532-6536.
Pu, Q., Oyesanya, O., Thompson, B., Alvarez, J. C.; “On-Chip Micropatterning of Plastic (Cylic Olefin Copolymer, COC) Microfluidic Channels for the Fabrication of Biomolecule Microarrays Using Photografting Methods”, Langmuir, 2007, 23, 1577-1583. (Highlighted in: Biophotonics International, “Producing Sensors with Light and Plastic”, page 40, Feb./2007.)
Khalid, I. M, Pu, Q., Alvarez, J. C.; “Thermodynamic and Kinetic Enhancement of Electrochemical Sensitivity by Chemical Coupling in Microfluidic Systems”; Angew. Chem. Int. Ed., 2006, 45, 5829-5832.