Mark P. Heitz, Ph.D
Professor and Interim Chair
Office: Smith Hall 228
- PhD, SUNY Buffalo; Research Advisor: Frank V. Bright
- Postdoctoral Research, Penn State; Research Advisor: Mark Maroncelli
Areas of Specialty
- Physical/Analytical Chemistry
- CHM 205 - General Chemistry I and Lab
- CHM 303 - Analyitical Chemistry I (Quantitative Analysis)
- CHM 400 - Seminar I
- CHM 401 - Seminar II
- CHM 405/408 - Physical Chemistry I (Quantum Mechanics)
- CHM 406/409 - Physical Chemistry II (Thermodynamics & Kinetics)
- CHM 417 - Computational Chemistry
Our group is interested in the process of molecular solvation and how this process affects solution chemistry. The development of a molecular-level understanding of the equilibrium and non-equilibrium aspects of solvation are the focus of our attention. Research efforts have included determining liquid state dynamics in chemical systems including the 1) response of hydrophiles to entrapment within microheterogeneous media (e.g., reverse micelles); 2) conformational changes that occur in proteins, both in bulk solution and at liquid/micelle interfaces; and 3) application of supercritical fluid technology (supercritical carbon dioxide) toward green solvent development. Most recently, we have been interested in the solvation behavior of a model chromophore, coumarin 153, in room-temperature ionic liquids and mixed ionic liquid/cosolvent systems. We use electronic spectroscopic techniques as the primary means of studying solvation, which includes static and dynamic (ps, TCSPC) fluorescence spectroscopies. In addition, emission spectroscopic information is augmented by computational chemistry methods, and ultrafast transient absorption spectroscopy.
Current Research Projects
DYNAMICS OF SOLVATION IN VARIOUS MEDIA
Ionic Liquids… or, implicitly “room-temperature” ionic liquids (ILs) since they are liquid salts with melting points <100°C. ILs are composed of usually bulky organic cations (e.g., imidazolium, phosphonium, ammonium, pyrrolidinium) and either organic (e.g., acetate, alkylimidazole) or inorganic anions (e.g., Cl-, PF6-, dicyanamide). Attractive features include negligible vapor pressure, low flammability, and highly tunable physicochemical properties by selection of the ion pair. The number of potential ILs exceeds 106 ion combinations. Our group is interested in measuring the solvation dynamics in ILs and IL/cosolvent (binary and ternary) systems. Recent work has focused mostly on phosphonium ionic liquid-based mixed solvent systems. The cosolvent includes not only traditional organic solvents but supercritical fluids, specifically carbon dioxide. We are also interested in using ILs to studying protein denaturation and the impact of ILs on protein functionality.
Proteins... function is driven by structure, which is in turn governed by the medium surrounding the protein. As an extension of our work on ionic liquid solvation, we are also interested in the interactions between biomolecules and ionic liquids. It is assured that with the dramatic increase in application of ionic liquids that they will interact with biomolecules. What is the downstream effect of these interactions? Is a protein’s conformational state unaffected by these interactions? In our research efforts we are using the model protein BSA to examine these questions. Given the myriad of ionic liquids available, this is a rather protracted problem. We using a two-pronged approach to this system. Tryptophan (trp) residues serve as an intrinsic fluorescence source to probe changes in protein conformation. However, since most protein contain multiple trp residues the signal generated by trp can report on multiple effects simultaneously making it exceedingly difficult to deconvolute the information. As a second approach, we covalently attach an extrinsic fluorophore through disulfide bridge chemistry. With BSA, this affords us the ability to look at signal from a single microdomain within the protein. Thus, we can assess the impact ionic liquids have, at least within this well-defined region of the protein.
Supercritical Fluids… another general interest of our group lies in the area of supercritical fluid technology. One advantage of these fluids is that they allow for density and related physicochemical properties (e.g., viscosity) Supercritical fluids (particularly CO2) have gained attention as green solvent option for organic solvent replacement. The show interesting features, among which the most commonly cited is density fluctuations near the critical point. These fluctuations have been observed to cause a “local density enhancement” of the supercritical fluid that surrounds a solute molecule, which makes solvation in this medium unique. One of the shortcomings of supercritical fluids, and CO2 in particular, is the limited ability to solvate polar solutes. One means to circumvent this problem has been to add organic cosolvents to mitigate the low polarity of the medium. But the addition of traditional organic cosolvent partially defeats the purpose of using a supercritical fluid. So what are the options? As a general class of solvent, ionic liquids are also considered to be “greener” options for finding replacements for organic solvents. Toward that end, we are putting efforts into studying the use of ionic liquids as a fluid amenity.
Microheterogeneous Media…a wide variety of polar molecules, such as proteins, enzymes, chromophore dyes, etc., can be hosted in the water pool of reverse micelles. Further, it is well known that a molecule’s local microenvironment has a significant impact on its physicochemical properties. The interest in studying reverse micelle systems stems from the ability to control the hydration environment by varying the amount of water added to the reverse micelle. Thus, the microenvironment sensed by the entrapped species is readily controlled. This can greatly impact chemistry such as proton and electron transfer and allows the study of hydration effects on protein conformations.