Trinity University Chemistry Department Research Interests

Dr. Steven M. Bachrach

My research interests are divided into two broad areas: computational organic chemistry and internet chemistry. Both areas involve extensive use of computers, but interested students need not be experts in programming. Projects can be designed for the computer novice to the expert; what is needed is a strong motivation to learn and explore.

Our use of computational chemistry is to solve the Schodinger equation using ab intio techniques, the most rigorous and complete computrational method. We use a number of packages to solve the physics, providing us with optimized geometries, electron distributions, molecular orbitals, and reaction energetics. The current research efforts in this area focus on anion chemistry, particularly nucleophilic substitution at heteroatoms and elimination reactions leading to phosphaalkenes and thiocarbonyl compounds. I am interested in determining the mechanisms of these reactions and comparing them with carbon-based chemistry. Our studies of nucleophilic substitution at sulfur suggests an addition-elimination reaction and not a standard Sn1 or Sn2. Nucleophilic substitution at sulfur is a critical step in the activity of many biochemical processes, such as control of protein folding and the action of extremely potent antitumor agents. Novel compounds such as phosphaalkenes and phosphaalkynes are often prepared by an elimination process, but no study of the mechanism of these reactions have been performed. Computational chemistry provides an excellent tool for attacking these problems by allowing us to closely examine the transition state, the effect of solvent and substituents, and obtain accurate energetics.

I have a long standing interest in the mechanism of pericyclic reactions involving heteroatoms and will continue to explore new applications. Recently, we have examined the Diels-Alder and ene reactions of selenocarbonyl compounds.

My internet projects center on creating new resources for research chemists. The primary project is the Internet Journal of Chemistry, a completely electronic peer-reviewed journal. The journal is available at http://www.ijc.com/ and you are encouraged to examine this site. I will begin a new project developing a database collecting computational chemistry results and a novel synthesis database. The internet projects involve programming with HTML, java and perl and make use of high-performance Unix workstations.

Dr. Michelle Bushey

Capillary Electrophoresis (CE) is a technique that separates analytes on the basis of electrophoretic mobility differences in an instrumental format. Mobility is determined by the mass to charge ratio of the analyte. Extremely high separation efficiencies in the hundreds of thousands and millions of theoretical plates can be obtained in generally less than 20 minutes with automated and semi-automated equipment. The technique requires only small amounts of reagents and samples. By manipulating the size or charge of the analyte, or by manipulating the separation media, separation systems can be devised for very specific purposes. Both of these approaches are used in this lab.

Micellar Electrokinetic Chromatography (MEKC) is a related technique in which the capillary electrophoresis media has been manipulated to allow for the separation of neutral compounds in an electric field. MEKC utilizes a micellar pseudo-stationary phase to obtain separation of analytes. Virtually any micelle forming compound can be added to the buffer system to obtain separations. Lauryl sulfate, or SDS which is the soap found in shampoos, is a commonly used micelle forming additive. Analytes partition between the mobile buffer phase (usually aqueous) and the pseudo-stationary micellar phase as they move through the capillary. The technique can be applied to the separation of both charged and neutral analytes. Work in this lab is typically directed towards the investigation of micelle systems employing bile salts.

One of our projects involves studying the interactions of bilirubin in bile salt micellar systems. This is a project in collaboration with Dr. Kurtin’s research. We are studying the behavior of bilirubin in a variety of bile salt solutions under different conditions such as changing pH, and the presence of other bile components such as calcium, lecithin, and cholesterol. We are also comparing the behavior of bilirubin to the behavior of related compounds such as biliverdin, bilirubin dimethylester, xanthobiirubic acid, and mesodimethylbilirubin. Mixed micelles systems are of increasing interest to the research in this lab and it is expected that work this summer will involve mixed micelle systems. It is hoped that these investigations will yield information as to how bilirubin interacts with bile salts, and eventually, what factors are most important in the precipitation of bilirubin which is an important factor in the formation of pigment gallstones and other physiological conditions which are manifested by jaundice. Our goal is to eventually model the behavior of different biles in the capillary electrophoresis format so that we can better understand the behavior of bilirubin and bile salts.

A new project in the lab involves making molecularly imprinted polymers and porous polymer monoliths for use in capillary electrochromatography (CEC). A target molecule is included in a solution which can be later polymerized. A capillary is filled with the solution and the polymerization process started. The polymer is formed around the target molecule. Once the target molecule is removed, a cavity is left. Capillaries with very specific selectivities can then be produced. The polymers can also be made without imprinting a specific analyte. Some analytes will interact with the polymers more than others. These interactions will alter the migration behavior of the analytes in the column. Analytes are moved through the column with the application of voltage. Thus, CEC is a combination of liquid chromatography and electrophoresis. We are currently exploring new methods of polymer construction and characterizing the physical properties and separation properties of these polymers.

Dr. Bert Chandler

Research in our group is in the field of environmental heterogeneous catalysis and is motivated by a variety of environmental concerns and "green chemistry". In organic synthesis, the oxidation of various functional groups is often very unfriendly to the environment. Strong stoichiometric oxidants () such as MnO4-, Cr2O7-, and CrO3, often hazardous in and of themselves, generate large amounts of chemical waste that is expensive and hazardous to dispose of. Selective and partial oxidations (e.g. the oxidation of primary alcohols but not secondary alcohols) can often be difficult to accomplish and may require extensive use of solvents and difficult separations after the reaction is complete. Research in our lab is currently focused on preparing new heterogeneous catalysts and testing them as selective and partial oxidation catalysts. (1) they do not require strong stoichiometric oxidants (2) they allow the oxidations to be performed using much weaker and cleaner sources of oxygen (e.g. O2), (3) separating the solid catalyst from solution phase organic material is cheap and easy and can eliminate complicated separation procedures. Along with the development of new catalysts, we are also developing the necessary chemistry required to utilize renewable (biologically derived) resources rather than depleting (petroleum) resources for some important pharmaceutical intermediate chemicals.

Within these general themes, we are investigating new methods for preparing catalytic materials and studying the chemistry occurring on the catalyst surface. These studies are inherently interdisciplinary and routinely involve aspects of heterogeneous catalysis, chemical kinetics, organic, inorganic, organometallic, and even bioorganic chemistry. Our catalyst development efforts are focused on the application of a special class of polymers called "dendrimers" to the preparation of supported bimetallic catalysts. Dendrimers are hyperbranched polymers that emanate from a core and ramify outward. Polyamidoamine (PAMAM) dendrimers, in particular, contain a defined number of interior amine groups that can be used to bind metal ions; their composition and architecture (open spaces within the interior) create an ideal environment for trapping guest species. We are using >these dendrimers as nanoreactors to prepare very small metal particles (12-100 atoms) with designated sizes, compositions, and morphologies (see figure above). We then deposit the dendrimer-encapsulated nanoparticles onto an oxide support (e.g. silica) and remove the organic dendrimer shell to yield supported metal nanoparticles catalysts (figure below). These catalysts are then used to study the effects of metal particle size, composition, and morphology on various oxidation reactions. A wide variety of projects are available to chemistry and engineering majors including exploring new catalyst particle preparation methods, developing new catalytic reactions, studying the chemistry that occurs on catalyst surfaces, and studying the properties of our new metal particles.

Dr. William E. Kurtin

Current research efforts are directed toward understanding the interaction of naturally-occurring poorly water-soluble molecules such as bilirubin (BR) and fatty acids with the lipid components of hepatic bile, especially bile salts like taurocholate (TC). Our overall goal is to understand the biophysical chemistry involved in diseases of the biliary tract, such as gallstone disease.

When molecules such as BR complex with BS molecules, spectroscopic properties of the guest often change significantly. We are attempting to use these observations to obtain information about the specific conformations and aggregation behavior of these molecules in solutions that resemble natural bile. We use UV-VIS absorption and emission spectroscopy, and NMR spectroscopy methods in our research. We also plan to use computer modeling studies and molecular dynamics calculations to make predictions about the molecular interactions.

Dr. Nancy Mills

One of the most important concepts in organic chemistry is that of aromaticity. Benzene, the quintessential aromatic molecule, has a unique set of "behaviors" that indicate that something special is going on in the molecule and that special character of benzene is called aromaticity. Unfortunately, it is difficult to determine which of the ways that benzene behaves, its structure, or stability, or magnetic properties, is the best way to measure and evaluate aromaticity, this key concept in organic chemistry.

The flip side of aromaticity is antiaromaticity and people have tended not to study aromaticity because they assumed that the necessary species would be very difficult to make and study. Through a stroke of luck, we have identified a suite of compounds, shown below, that appear to be antiaromatic, in terms of their magnetic properties, but are still stable enough to characterize. That means that we can begin to compare the behavior of our "antiaromatic" species to that of benzene to begin to sort out which properties are truly characteristic of aromaticity. This is pretty cool because we are looking at one of the big questions in organic chemistry and doing so with the efforts of undergraduate researchers!

We are doing two kinds of projects. Part of the group is looking at species like 1 below which we have characterized by magnetic properties and are characterizing them by other properties, such as stability or by examining their structure. Other students are expanding the investigation to new species that theory says should have increased antiaromaticity, to see if theory is correct and if so, to see if there are new, unexpected behaviors in these previously unknown compounds.

Students working in my group spend a lot of time making the molecules that are converted to 1and2. The vast majority of the molecules we need are ones that have never been made before. Since everyone in the group gets a molecule of his or her own, you also get the opportunity to be the first person in the world to see a particular compound, which is pretty neat. Much of the efforts of the group involve organic synthesis, purification via chromatography, and characterization by NMR and IR spectroscopy. Since we also predict behavior of these compounds before we make them or rationalize their behavior by calculations, students with a particular interest in computer science and chemistry can become involved in computational chemistry.>

Dr. Chris Pursell

Our rresearch is concerned with examining heterogeneous chemical reactions on surfaces that simulate atmospheric particles. It is well known that aerosols are found throughout the earth’s atmosphere and play an important part in the chemistry and physics of the atmosphere. Recently, heterogeneous chemistry on the surface of ice aerosols has attracted much attention because of its role in ozone destruction in the Antarctic stratosphere. In the laboratory Dr. Pursell’s students utilize infrared spectroscopy to examine these important heterogeneous chemical reactions. A recent example is the ionization of nitric acid on ice. This reaction is very fast in liquid water but is much slower on ice, allowing us to examine the details of this important reaction.

Dr. John Spence

Research in my group is centered around the synthesis and properties of macrocycles related to porphyrins and calixarenes, two families of organic molecules that have found a number of applications as a result of their unique physical properties. Porphyrins are highly colored aromatic compounds and their ability to absorb visible light has made them valuable sensitizers for a form of cancer treatment known as photodynamic therapy. Calixarenes, on the other hand, are flexible molecules that primarily exist in a cone or ‘beaker-like’ geometry (see below) making them ideal molecules for host-guest complexes. We are currently interested in ‘fine-tuning’ these properties by replacing the bridging carbon atoms of these systems with nitrogen atoms. This substitution can have a profound affect on the wavelength of light absorbed by porphyrins and the introduction of an N-H into a calixarene can produce a more rigid system by providing new avenues for hydrogen bonding. We are exploring new, more flexible synthetic routes to prepare these compounds that may become improved agents for applications such as photodynamic therapy and host-guest chemistry. In addition to developing synthetic methods to prepare these molecules students in the group will study the new physical properties of their compounds and address what benefits our systems offer towards these specific applications.

In a related project we are utilizing porphyrins to control the biological activation of a synthetic drug designed to model a family of natural products known as the enediyne antibiotics. While these compounds are some of the most potent antitumor agents ever discovered they suffer from delayed organ toxicity and low natural abundance. The combination of a porphyrin with an enediyne unit offers a number of advantages over the natural products including the recognition of porphyrin molecules by the body (hemoglobin is a metallated porphyrin) which should minimize any delayed side effects. We are currently developing methods to synthesize these hybrid molecules and will examine the features controlling their activation as they are prepared.