Mark P. Heitz, Ph.D
Office: Smith Hall 223
- 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 - Analytical 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)
- CHM414/416 - Instrumental Analysis
- CHM 417 - Computational Chemistry
Our group is interested in molecular solvation processes and how the underlying interactions may influence solution chemistry. The development of a molecular-level understanding of the equilibrium and non-equilibrium aspects of solvation are the focus of our attention. Most recently, we have been interested in the solvation behavior of a model chromophore, coumarin 153, in room-temperature ionic liquids (ILs), deep eutectic solvents (DESs) and binary cosolvent mixtures with each. We use electronic spectroscopic techniques as the primary means of studying solvation, which includes static and dynamic (ps) fluorescence spectroscopies. In addition, through collaborative efforts our spectroscopic information is augmented by computational chemistry and simulation methods and ultrafast transient absorption spectroscopy. Beyond fundamental solute-solvent interactions, our research efforts have also included the study of liquid state dynamics of hydrophiles entrapped within nano- and microheterogeneous media (e.g., reverse micelles, ionic liquids, deep eutectic solvents), conformational biomolecule changes that in novel solvents (ionic liquids), enzymatic response to ionic liquid denaturation, and the application of supercritical fluid technology toward “green” solvent development.
Current Research Projects
Molecular Solvation Dynamics in Various Media
Alternative Solvents… Ionic Liquids (ILs) have been touted as environmentally friendly solvent alternatives to traditional organic solvents. ILs have shown great potential due to their thermal and chemical stability, intrinsic conductivity, ability to dissolve both polar and non-polar solutes, and large electrochemical window. Over several decades they have been a central point of research interests for a broad range of chemical applications (e.g., separations, synthetic chemistry, batteries, fuel cell technology, carbon capture chemistries). Attractive features include negligible vapor pressure, low flammability, and highly tunable physicochemical properties by selection of the ion pair. While initially thought to be good candidates for use as “green solvents”, many ILs are non-biodegradable and are toxic. ILs are generally expensive solvents thereby reducing their marketability in industrial scale processing. More recently, deep eutectic solvents (DESs) have generated a tremendous amount of interest and excitement because DESs are far cheaper, easier to manufacture, and derived from biologically and environmentally benign components, and are commonly formed from quaternary ammonium salts (e.g., choline chloride, ChCl) and a suitable hydrogen bond donors (HBD) such as urea, ethylene glycol (EG), glycerol, or carboxylic acids, but many more combinations are possible. DESs show promise for use as a renewable, recyclable, and sustainable solvent medium with extensive applications including gas capture, drug delivery systems, lubricants, extraction and separation media, electrochemistry, electrodeposition, organic synthesis, biocatalysis, and (nano)materials synthesis and processing to name just a few. The solventless, eco-friendly preparation from inexpensive natural compounds and vast numbers of donor/acceptor molecules allows for specifically tailored properties, giving DESs a “designer” nature.
Biomolecules... 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 have been interested in the interactions between biomolecules and ionic liquids. It is assured that with the dramatic increase in the application of ionic liquids, there will be ramifications downstream of processes. What are their effects on biomolecules? How are biomolecule conformational states affected by these interactions? In our research, we have used the model protein bovine serum albumin (BSA) to begin to examine these questions. Fluorescence is probed by covalently attaching an extrinsic fluorophore to the BSA disulfide bridge, which 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. Given the myriad of ionic liquids and proteins available, this is a rather protracted problem that provides a nearly unlimited number of systems to study. More recently, we have extended this interest to self-complimentary, double-stranded DNA oligomers. Our lab initiated an internal collaboration with Prof. Josh Blose to determine the intercalation effects of ILs on minor groove binding.
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) to be tuned by simply changing the system pressure. Supercritical fluids (SCFs) have gained attention as potential green solvent options for organic solvent replacement. SCFs 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 1-5 mol% of an organic cosolvent to mitigate the low polarity of the medium. But the addition of an 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 an amenity to the SCF medium.
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.