UM-St. Louis Department of Chemistry

Research Experience for Undergraduates Program

St. Louis is a major metropolitan area with a population of approximately 2 million, and is located near the confluence of the Missouri and Mississippi rivers. It is a major chemical industrial center, serving as the headquarters for such companies as Monsanto, Mallinckrodt and Sigma Aldrich. St. Louis is also a major center for the arts, particularly music and theater, as well as being home to major sports teams and the world famous Missouri Botanical Gardens.

The University of Missouri-St. Louis is the largest university in the St. Louis metropolitan area with a student body of approximately 15,000. It is one of the four campuses of the University of Missouri system. The campus, 20 minutes from downtown, is located on a scenic, forested 175 acre tract in northwest St. Louis County. The campus is easily accessed from highways I-70 and I-170, is close to the airport, and is well served by the bi-state transit system.

The Department of Chemistry has 16 regular faculty members and several adjunct professors. The department is committed to excellence in both teaching and research and has maintained a summer REU program for several years. Research is presently carried out in a modern, air conditioned laboratory space in the new science complex. Modern instrumentation includes a Varian Unity Plus 300 MHz NMR Spectrometer with both liquid and solid-state NMR capabilities, a Varian XL300 NMR spectrometer, a Bruker ARX 500 MHz NMR spectrometer, a Seimens R3 single crystal diffractometer, a HP 5988A GC-mass spectrometer, a Finnegan-MAT 311A double focusing mass spectrometer, and several state-of-the-art UV-visible and IR spectrometers.

The 1996 REU program, supported by the National Science Foundation and other grants, will run for 11 weeks (May 20 to August 2). Participants will receive an anticipated stipend of $3,000 with additional supplements available to offset the cost of accommodations and travel. The number of fellowships is limited and will be awarded on a competitive basis. Successful students will join ongoing projects in the areas of organic, inorganic, physical, biological and theoretical chemistry. In addition to conducting research the participants will visit industrial research labs, attend seminars given by guest speakers on diverse aspects of chemistry, attend a short course on the written and verbal communication of scientific results, have the opportunity to participate in a hands-on short course concerning modern NMR techniques, and present the results of their research in a seminar.

A list of faculty and their research interests are given below. More information about the available projects, or about the overall program may be obtained by calling or writing to:

Dr. Keith J. Stine

Department of Chemistry

University of Missouri-St. Louis

8001 Natural Bridge Road

St. Louis, MO 63l21

Tel: (314)-516-5346

UNDERGRADUATE RESEARCH MENTORS

Gordon K. Anderson, Professor: Organometallic and coordination chemistry of the late transition metals, homogeneous catalysis, and reaction mechanisms, NMR spectroscopy.

Lawrence Barton, Professor: Synthesis, structure, and chemistry of borane and metalloborane cage compounds, organometallic chemistry.

Lee Brammer, Assistant Professor: Structure and bonding in organometallic chemistry, transition metal-hydrogen interactions, hydrogen bonding, weak bonding interactions, X-ray and neutron diffraction.

Ian Brown, Research Professor and Fellow for the Center of Molecular Electronics: Improvements in the conductivity, processibility, and environmental stability of conducting polymers.

James S. Chickos, Professor: Synthesis and characterization of small ring ketones, oxocarbon chemistry, stereochemistry, NMR, keto-enol tautomerism, kinetics.

Joyce Y. Corey, Professor: Synthesis and characterization of organometallic compounds of Group IV, including analogs of pharmaceutically active derivatives, catenated compounds and novel heterocycles.

Valerian T. D'Souza, Associate Professor: Bio-organic chemistry, enzyme mechanisms, enzyme mimics, cyclodextrin chemistry.

David L. Garin, Associate Professor: Synthesis of organic compounds including steroids, carbene addition using phase transfer catalysts, electrochemical syntheses.

Harold H. Harris, Associate Professor: Dynamics of flames, especially cellular flames; self-organizing chemical systems, chemical education.

Wesley R. Harris, Associate Professor: Bioinorganic chemistry, coordination chemistry, UV-Vis spectroscopy, computer models for metal speciation in serum.

James J. O'Brien, Assistant Professor: Experimental physical chemistry; vapor phase spectroscopy; ultrasensitive detection by laser techniques (e.g., intracavity laser spectroscopy (ILS) and laser induced fluorescence); in situ diagnostics of CVD processes; studies of silicon CVD processes by ILS analysis of gas phase intermediates and ESCA analysis of deposited films.

Nigam P. Rath, Research Assistant Professor: Single crystal X-ray structure determination of novel organic and organometallic compounds, structural data base, systematic analysis of structural data.

Christopher D. Spilling, Assistant Professor: New methods for organic synthesis, total synthesis of natural products, synthetic applications of organophosphorus chemistry, NMR spectroscopy.

Keith J. Stine, Assistant Professor: Surface chemistry: Langmuir monolayers, Langmuir-Blodgett films, self-assembled monolayers; molecular recognition at interfaces; biosensors; biomembranes; colloid science.

William J. Welsh, Associate Professor: Structure-property relationships in high performance polymers useful for aerospace applications; theoretical and computer graphics studies of anticancer drugs and other biomolecules.

Janet Braddock-Wilking, Research Assistant Professor: Synthesis and characterization of silymetallic complexes including silicon nanoclusters and complexes containing low valent silicon species, NMR spectroscopy, photochemistry of silicon containing compounds.

Rudolph Ernst K. Winter, Associate Professor: The organic and bioorganic chemistry of naturally occurring substances, especially plant materials; isolation, structure determination, chemical interconversion and synthesis of terpenoids, alkaloids and other natural products; biogenetic relationships among natural substances; chemical ecology involving plant products.

Zhi Xu, Assistant Professor: Molecular engineering of picosecond optical switch using organic molecules; nonlinear optics and its application in solid-liquid interfacial chemistry; picosecond and nanosecond laser spectroscopy.

Dr. Gordon K. Anderson

Room B319 Benton Hall

Phone 516-5437

Our research involves synthetic and spectroscopic studies of organometallic compounds of the late transition metals, such as palladium and platinum, including studies aimed at understanding the mechanisms of their reactions.

Modern organometallic chemistry is only about 30 years old. New types of compounds are being made and new reaction pathways discovered all the time. Transition metal complexes are now used widely as catalysts in organic synthesis, and their role is increasing. One of our major interests is to develop greater understanding of how transition metal species facilitate the forming and breaking of chemical bonds, processes that are vital to catalysis of all kinds. We are also interested in developing new transition metal catalysts.

Owing to the expense of precious metals, such as palladium and platinum, we work with only small amounts of materials. Some of our compounds are air- or moisture-sensitive and must be handled under an inert atmosphere, either using standard vacuum line/Schlenk techniques or in a controlled atmosphere glove box. The instrumental techniques of which we make greatest use are NMR spectroscopy (1H, 13C, 31P, 195Pt) and X-ray diffraction.

Projects suitable for undergraduate student participation are available for one semester or longer periods. These might involve, for example, palladium-catalyzed coupling reactions, catalytic reactions using rhodium or palladium complexes, or NMR and/or X-ray diffraction studies of weak metal-ligand interactions. Further details are available from Dr. Anderson, Room B319 Benton Hall.

Dr. Lawrence Barton

Room B315b Benton Hall

Phone 516-5311

SYNTHESIS AND CHARACTERIZATION OF METALLABORANE CLUSTERS

Our research program involves the synthesis and characterization of organometallic clusters based on boron and metals. Clusters are either the regular polyhedral solid with triangular faces or fragments of them. We typically take boron hydrides and incorporate metal-containing groups into them such that the integrity of the boron cluster is not substantially altered. The borane templates upon which we built these metallaborane clusters are typically pentaborane(9), I, and hexaborane(10), II, shown below. A target we have set for ourselves is the development of heptaborane chemistry, based on the little studied cluster [B7H7]2-, III, shown below. We use high vacuum , glove box and inert atmosphere techniques , multinuclear NMR and IR spectroscopy, mass spectrometry and Xray crystallography to characterize the products.

We have developed research involving stannylboranes and more recently bridged penta-boranyl(9) cages. An example is ,'-SnPh2(B5H8)2, IV, shown below. An example of our transition metallaborane chemistry is a system we have studied involving a B6H10 cage coupled to a Fe(CO)4 group, B6H10Fe(CO)4, V.

V

We are also developing chemistry of the metallahexaboranes such as (PPh3)2(CO)OsB5H9 and (PPh3)2(CO)IrB5H8. Examples of systems we have prepared and studied are VI, a nido-bimetalla-pentaborane, VII a closo-bimetallahexaborane and VIII a pileo-bimetallaheptaborane, all containing the metals Os and Ir.

Dr. Lee Brammer

Room B316 Benton Hall

Phone 516-5345

Research Projects

Dr. Brammer's research is focused primarily on understanding aspects of transition metal organometallic chemistry based upon: (i) the structure of metal complexes determined by X-ray and neutron diffraction or by computational means, and (ii) bonding, i.e. intramolecular and intermolecular interactions, which can also be studied by experimental (diffraction) methods and theoretical (computational) approaches. Specific projects may also involve the synthesis and spectroscopic characterization of new compounds which exhibit unusual interactions. In particular, our recent efforts have been geared towards the study of weak chemical interactions. Such interactions are often poorly understood but its has recently been realized that such interactions have substantial importance in areas of chemistry as diverse as biochemistry and materials chemistry.

In conducting this work we make use of excellent facilities for X-ray diffraction, and computer-aided analysis of experimental results. Laboratory space for the preparation and handling of air-sensitive compounds is available, as are excellent facilities for spectroscopic characterization of new compounds by NMR and IR spectroscopy.

Current research projects include work in the following areas:

(i) Compounds with transition metal-hydrogen interactions. In addition to studies of important metal hydride interactions and so-called 'agostic' C-H-M interactions, we have recently identified a new type of interaction analogous to a hydrogen bond, but remarkable in that it involves a transition metal as the proton acceptor. Shown below is an example of a compound with an N-H…Co hydrogen bond, whose structure was determined by X-ray diffraction. We are currently involved in projects which range from preparing new compounds, to test the strengths of these interactions, to studying the details of these types of bonds from experimental determinations of the electron distribution in the bonds.

(ii) Transition metal cluster compounds. These compounds serve as useful models for the binding of organic molecules to metal surfaces

involved in heterogeneous catalysis. High resolution diffraction studies currently are being utilized to understand metal-metal and metal-ligand bonding as well as ligand mobility.

(iii) Gas hydrates. These remarkable examples of molecular recognition in which small hydrocarbons, halogens, halocarbons, and many other small gas molecules are encapsulated in cavities within a hydrogen bonded water framework have potential applications in areas as diverse as outer planetary science and medicine. High resolution diffraction studies are being utilized to understand the host-guest interactions.

Dr. Brammer is also interested in the utilization of chemical databases for understanding molecular structural trends and modeling pathways for chemical reactions.

Dr. Ian Brown

Room B315i Benton Hall

Phone 516-5340

Conducting Polymers:

This research is concerned with improvements in the conductivity, processibility and environmental stability of conducing polymers. The scientific objectives involve an understanding of the mechanisms that lead to electrical conductivity in polymers. In our approach we use thermal analysis, cw and pulsed Electron Spin Resonance techniques, as well as optical absorption, and Fourier Transform Infrared spectroscopies.

Two types of polymers are being studied: viz., metallized polymers and conjugated polymers. In the metallized polymer work we are using polymer films (5 to 200 microns thick), which have been cast (or spin cast) from solution, as substrates for a metal layer (3 to 4 microns thick). The polymers under investigation can complex with metal ions. In the conjugated polymer studies we are trying to develop conducting thermoset polymers where the -conjugation extends along the backbone and through the crosslink to form an extensively conjugated 3-dimensional network.

This research is directed toward the use of these conducting polymers as microwave-device materials, electromagnetic interference (EMI) shielding materials, and miniature circuit interconnects.

An undergraduate who has completed course work in organic, inorganic, analytical and/or physical chemistry could benefit from this research exposure. Undergraduate will gain experience in the processibility and synthesis of conducting polymers as well as learn to make measurements of the electrical, optical and magnetic (ESR) properties of polymers.

Dr. James S. Chickos

Room B435 Benton Hall

Phone 516-5377

All Scientific endeavors are dependent on the availability of reliable thermodynamic and physical property data. This data forms the foundations on which our current understanding of the physical world is based. The measurement and collection of such data is a fundamental scientific task, common to all who practice the discipline.

We have had an interest in developing simple algorithms to model some of these physical properties. The purpose for doing so is to provide data in the absence of experiment and to provide a basis for the selection of particular measurement in the presence of two or more discordant values. In addition, the process of distilling this physical data using these algorithms can sometimes produce parameters that can be useful in evaluating molecular properties that can not be measured directly.

Simple models have been developed to estimate condensed phase properties such as vaporization enthalpies, heat capacities, fusion entropies and enthalpies, vapor pressures and sublimation enthalpies of small molecules. Recently, the parameters generated by these algorithms have also been used in estimating fusion enthalpies of polymers and conformational entropy changes in globular proteins.

The development of models to mimic physical properties requires extensive database. This has resulted in a collaborative interaction with the National Institutes of Standards and Technology in Washington DC.

Coupled with our interest to develop models for such properties, is the need to obtain experimental data. A variety of physical properties are measured in our research laboratories that include measurements of vaporization, sublimation and fusion enthalpies. We are also examining new simpler methods of making these measurements. One such process developed recently, correlation gas chromatography, affords the vaporization enthalpy of a solid or liquids at 298 K by simply using retention time measurements of knowns and unknowns.

Research problems are available in developing new algorithms to mimic the properties mentioned above as well as new ones. Experimental problems are available in both physical measurements and in the development of new protocol for these measurements.

Dr. Joyce Y. Corey

Room B318 Benton Hall

Phone 516-5360

Dr. Corey is engaged in synthetic organosilicon chemistry with emphasis on transition metal-catalyzed reactions of hydrosilanes. Primary and secondary silanes, RSiH3 and RR'SiH2 condense to form polymers and oligomers respectively in the presence of selected transition metal complexes. Dr. Corey and her coworkers have developed an approach to effective catalysts that involves adding BuLi (or other RLi or RMgX reagents) to commercially available metallocene dihalides of Ti, Zr, and Hf. From this combination catalyst oligomers with 2 to 8 silicon atoms and polymers with average molecular weights up to 3500 have been obtained.

On aspect of the current work involves varying the catalyst structure in order to improve the molecular weight of the polysilanes produced. The new structural type include ansa-metallocenes, Cp'MCl3 and bimetallic complexes where the distance between the two metal centers can be varied. These investigations involve the synthesis of new ligands for the titanium triad metals.

With the ability to prepare silicon oligomers with functional groups in such a simple manner another area of investigation involves the development of the chemistry of small chains. As an example, the phenyl groups in H(PhMeSi)xH can be removed with 1 to x equivalents of triflic acid to give H(PhMeSi)y(MeSiOTf)zH(z+y=x). The triflate substituent (OTf) can be replaced in a variety of ways to give new oligomers. The initial study of trisilanes showed that rearrangement of groups on silicon took place possible through a siliconium-ion like intermediate (see scheme). The terminal SiH bond is also a functional group that can be developed. Reactions of the disilane, H(PhMeSi)2H, with CuF22H2O have generated F(PhMeSi)2F as well as products from silicon-silicon bond cleavage. The F(PhMeSi)2F which is produced initially as a 50:50 mixture of diastereomers, converts to a meso-enriched mixture on crystallization. Other reactions of the oligomers are under investigation.

Another area of research effort focuses on the synthesis and structural characterization of silicon heterocycles that are analogs of psychotropic drugs of the anti-pychotic and anti-depressant classes. Methods of synthesis have been developed for a variety of benzene-annellated derivatives that contain a silicon atom and in some cases additional oxygen, nitrogen or sulfur atoms in a 5-, 6-, 7- or 8-membered central ring. The most recent effort in this area involved the synthesis of rigid tricycles by incorporating suitable substituents on the benzene ring. Ongoing work involves systems that contain fluoro substituents in positions ortho to the ethano bridge in dibenzo[b,f]silepins as a complement to the published study in which the substituents were incorporated ortho to the silicon center. The crystal structure of one of the fluoro substituted compounds is shown below.

Dr. Valerian T. D'Souza

Room B221 Benton Hall

Phone 516-5324

The main goal of our research project is to build redox catalysts based on the chemistry of biological redox enzymes. The incredible power of the enzymes to bring about chemical transformations with large acceleration and high specificity has been attributed to mainly their ability to bind the substrate and catalyze specific reactions of the bound substrate. Thus, these redox catalysts are designed to have a binding site to bind particular molecules and a catalytic site to catalyze redox enzymes. We have synthesized the first generation of these artificial enzymes using cyclodextrins as a binding site and flavin derivatives as catalytic site as shown in the figure.

This artificial enzyme can accelerate oxidation of benzyl alcohols up to 650 fold over that catalyzed by riboflavin. We are in the process of designing and synthesizing the second generation of artificial redox enzyme which should have enhanced catalytic ability. These enzymes are designed using computational chemistry techniques.

In the process of developing the methodology to build these artificial enzyme, we have also produced a method to synthesize custom designed cyclodextrins. Cyclodextrins are cyclic oligosacharides which have gained prominence in the last two decades as complexing agents for various organic molecules in artificial enzymes, foods, flavors etc. However, the main shortcoming of this, otherwise remarkable, molecule is that the functionalities available for useful chemical processes are limited to simply hydroxyl groups. The new method developed by us given below, allows one to synthesize cyclodextrins with any desired functionalities.

We are presently investigating the binding and catalytic properties of these new cyclodextrins.

Dr. David L. Garin

Room B315f Benton Hall

Phone 516-5349

The major focus of my research group is synthetic organic chemistry. Current target molecules include compounds that should have interesting metal chelating properties, macrocyclic compounds, specifically labelled steroids, and strained cyclic molecules (propellanes). We have utilized phase transfer catalysts for many of our reactions. Undergraduate research students are usually given projects that correlate with the ongoing research of one of the graduate students

Dr. Harold H. Harris

Room B315e Benton Hall

Phone: 516-5344

Dr. Harris is interested in the ways in which some chemical systems spontaneously organize. In particular, his experimental and theoretical research focuses on the dynamics of certain types of flames that exhibit cellular structure. The cells result from instabilities due to the fact that the rates of species diffuse is not equal to the rate at which heat diffuses in such flames. When the limiting reagent is smaller in mass than the other reagent in the system, cellular structures result. For example, cells can be observed in "rich" propane-air combustion or in "lean" methane-air systems.

An especially intriguing phenomenon is that these cellular structures are very susceptible to perturbation by an electric field. Dr. Harris and his students have observed rotating cellular instabilities in a small part of the (large) parameter space of flames across which a potential of a few hundred volts is applied. Since the applied potential can affect the spatial distribution of only the charged species in the combustion, it is hoped that studies of electrically-perturbed flames may provide a more thorough understanding of the role of ions in flames.

The video image above is part of a series we recorded using a video camera interfaced to a "frame-grabber" board in a personal computer. In this propane/air flame, two cells in the center rotate at about 150 rpm. The twelve cells around the outside of the circular burner are stationary.

Dr. Wesley R. Harris

Room B320 Benton Hall

Phone 516-5321

Dr. Wesley Harris and his students are involved in bioinorganic chemistry. Bioinorganic chemistry involves studies of the interactions of metal ions with biological molecules and the functional role of these metal complexes in living systems. Dr. Harris' group is particularly interested in the iron protein serum transferrin. The insolubility and toxicity of free Fe3+ under physiological conditions requires that organisms carefully control this essential element at all stages of its metabolism. Transferrin is the protein that transports iron through the blood between sites of uptake, utilization, and storage.

Dr. Harris' work on transferrin can be divided into two broad areas. The first involves kinetic studies on the mechanism of the exchange of ferric ion between the protein and low molecular weight chelating agents. These studies are part of the search for a more effective drug for the treatment of iron overload, which is a fatal complication of diseases which require long-term administration of blood transfusions. This research has demonstrated that there are at least two different pathways for the removal of iron, and that the process appears to be strongly affected by charged, non-coordinating lysine and arginine side chains located near the iron binding sites. Future research will include kinetic studies on genetically engineered proteins, in which these charged residues have been selectively replaced with neutral amino acid side chains.

Calculated Speciation of Al3+ in normal serum

Transferrin is rather indiscriminate in its binding of metal ions and can act as the serum transport agent for other metal ions. These include pharmaceuticals (Ga3+, In3+) physiological metals (Mn2+, Zn2+) and toxic metals (Pu4+, Al3+). Dr. Harris has been conducting a systematic evaluation of the transferrin binding affinities of several of these metal ions. The focus is now shifting to the use of this growing data base of metal-transferrin binding constants to evaluate the molecular factors that control the binding selectivity of a protein towards various metal ions. This research is directed toward the development of simple empirical equations that will allow medical researchers to quickly estimate binding affinities for a wide range of possible metal-protein complexes.

There is currently a great deal of interest in the neurotoxicity of aluminum. The Al3+ ion is transported through serum primarily as the Al-transferrin complex. The Al-transferrin binding constants that have been measured in Dr. Harris' lab are being used to develop computer models for the distribution of Al among the various metal-binding components of normal serum. These computer models will be used to assist toxicologists in understanding the in vivo chemistry of new drugs that are currently being developed for the treatment of Al toxicity.

Dr. Nigam P. Rath

Room B436 Benton Hall

Phone 516-5333

Dr. Nigam Rath's primary research interests involve single crystal X-ray structure determination of novel organic and organometallic compounds. X-ray diffraction study is one of the unambiguous methods of solid state structure determination. With the advancement of diffraction instrumentation and faster computers this technique can now be used as a routine analytical tool for elucidation of three dimensional structure of newly synthesized compounds.

Very recently, we have acquired the most advanced diffraction system available for small molecule structure determination. This area detector system is equipped with a charge coupled device (CCD) camera detector and is capable of very fast data collection. Also, due to the extremely high sensitivity, crystals which could not be used before with normal diffractometers can now be investigated. This research project will involve development of improved data collection strategies for the CCD diffraction system. Even though, the instrument and basic software is commercially available due to the involvement of new technology a lot of research is required to develop proper data collection strategies for accurate data collection as well as for better performance. Also, the most important step after the data collection is the integration of the collected frames which affects the quality of the data and hence the quality of the structure. Several data sets will be collected on compounds for which data have been collected previously with point detector system and the analysis will involve parameter optimization for best possible data quality.

A second on-going project of interest is solid state structure determination of photo-products of fused ring systems. It is very difficult to derive the structure and absolute configuration of these compounds without x-ray diffraction studies. Several very interesting molecular structures have been observed during the course of investigation for the dibenzobarrelene derivatives. This project will involve crystallization and structure elucidation of dibenzobarrelene derivatives which are obtained from photochemical reactions.

Dr. James J. O'Brien

Room B414 Benton Hall

Phone 516-5717

Dr. O'Brien, an experimental physical chemist, applies laser spectroscopy techniques to investigate gas phase systems. The primary method employed is intracavity laser spectroscopy (ILS) which provides an ultrasensitive method for measuring absorption spectra. In ILS, the molecules, atoms, or radicals are contained in a special intracavity laser compartment, and effective absorption pathlengths greater than 100 km can be achieved using cavities less than 1 meter in length by operating the laser in a special fashion. The ultra-sensitivity and other desirable features, make the ILS method very suitable for quantitatively determining the absorption spectra of weakly absorbing molecules or for monitoring gas phase species present in low concentration in diagnostic applications.

Methane Spectra for Studies of the Atmospheres of the Outer Planets. The sunlight reflected from the outer planets provides information on the composition and structure of the atmospheres of those bodies. Spectroscopic observations made from ground- and spacecraft-based telescopes, indicate methane is present in the atmospheres of the outer planets (Jupiter ® Pluto). Though a minor component of the atmospheres, the methane features observed in the 400-1000 nm spectral region provide information concerning the pressure, temperature, and dynamics of the atmospheres. Interpreting the planetary spectral data has been hampered, however, by the lack of appropriate laboratory data obtained at conditions of very low temperature and pressure, comparable to the planetary environments. Methane features in the 400-1000 nm region are due to igh overtone, vibrational transitions. These are intrinsically weak and can be observed using traditional techniques only by employing high methane pressures and temperatures. They are observed in the planetary spectra because the sunlight travels through 10-100 km of the atmosphere prior to being scattered and reflected to the observing instrument. ILS does provide sufficient sensitivity to perform the laboratory measurements at the appropriate conditions; it is being used to determine quantitative absorption parameters for individual isolated lines and methane bands at temperatures from room to -321 oF using dye- and Ti:sapphire-laser systems.

Intermediates in the Formation of Diamondlike Films. In the second major application, ILS is used to probe the gas phase reaction intermediates involved in radiofrequency (RF) plasma- initiated, chemical vapor deposition (CVD) processes. Currently, the deposition of diamondlike films from various hydrocarbon plasmas is being investigated. Other systems slated for study include the deposition of diamondlike-silica composite materials, and amorphous SiC films from novel organometallic precursors compounds. Other techniques available in addition to ILS include: quadrupole mass spectrometry to monitor the gaseous products of the plasma discharge; microwave interferometry to determine electron number densities in the plasma; and optical emission spectroscopy to monitor plasma emission. The deposition of transparent films is monitored in situ using a reflectivity technique which yields the refractive index, the extinction coefficient and the deposition rate.

ILS absorption spectrum of water vapor at 296 K (Leff = 0.53 km, 3.5 torr). Solid line = initial spectrum, dotted line = deconvolved spectrum. Inset shows the instrument function.

Dr. Christopher D. Spilling

Room B425 Benton Hall

Phone 516-5314

Professor Spilling's interests are in the development of new synthetic methods with application in the total synthesis of biologically active compounds. His current research efforts involve the use of chiral phosphonates and phosphonamides in asymmetric bond forming reactions.

We recently reported the synthesis, properties and chemistry of chiral phosphorous acid diamides. These diamides react with haloalkanes to give phosphonamides, with trialkylsilyl triflates to give trialkylsilyl phosphorimidites, with aldehydes to give a-hydroxy phosphonamides, and with imines to give a-amino phosphonamides.

This project has evolved and expanded and the current emphasis is the synthesis of metal complexes as catalysts for the phosphonylation of aldehydes. We will attempt to develop catalysts that result in high yield, high stereoselectivity, generality for a range of aldehydes, and tolerance to other functionalities. During the course of this study we will acquire an understanding of metal phosphonate/phosphite bonding and structure, and the factors that promote the efficient transfer of phosphite from the metal to the aldehyde carbon. A wide variety of techniques will be employed for mechanistic analysis and determining active catalyst structures, including NMR, HPLC, kinetic measurements, and crystallographic analysis.

In addition, we are examining a series of synthetically useful stereoselective reactions of allylic hydroxyphosphonates. Acyclic stereocontrol is an efficient strategy for the generation of new stereocenters, and allylic alcohols are perhaps the best recognized substrates in this regard. Allylic hydroxyphosphonates are expected to display the chemistry associated with allylic alcohols, however the steric and electronic influence of the phosphorus moiety will help to control the stereochemical and regiochemical outcome of the reactions.

The reactions developed for the structural elaboration of allylic hydroxyphosphonates will be applied to the synthesis of some target molecules or molecule fragments. The target molecules may retain the phosphorus moiety in the form of biologically active phosphonic acids. Alternatively, the phosphonate group (or phosphine oxide) may be lost either in a P-C bond cleavage reaction. In particular, applications in the synthesis of enzyme inhibitors will be explored.

Other projects include:

The Total Synthesis of Some Marine Sponge Metabolites: Psammaplysin and Fistularin are two biologically active metabolites isolated from sponges. This family of brominated spirocyclic compounds are related biosynthetically as oxidation products of tyrosine. We are investigating a biomimetic synthesis of the spirocyclic compounds via a common arene oxide intermediate.

Chemistry of Glucal Halohydrins and Glucal Epoxides: We are exploring new ways to prepare glucal epoxides and methods for C-glycoside formation form glycals and the corresponding halohydrins.

New Chiral Aminophosphine ligands for Asymmetric Catalysis: We interested in the design and evaluation of some new phosphine ligands for platinum, palladium, nickel and rhodium centered catalysts

Dr. Keith J. Stine

Room B417 Benton Hall

Phone 516-5346

Organic Thin Films

The study of organic thin films is relevant and useful due to their capacity to serve as model systems for biomembrane behavior, their utility in surface modification for analytical and biotechnological applications, and their central role in the emerging research area of molecular electronics.

Our studies of organic thin films currently focus on:

Langmuir monolayers - These are single molecule thick films formed by spreading at the water-air interface. Films can be formed from a range of molecules from simple long-chain fatty acids and phospholipids to more complex molecules such as macrocyclic compounds, polypeptided, and polymers. Our methods of study include the measurement of surface pressure versus area per molecule isotherms to identify phase transitions in the monolayer, the measurement of surface potential, and imaging of the monolayer domain structure with Brewster angle or fluorescence microscopy. Current projects include: a) Study of the interaction of monolayers of macrocyclic compounds, in particular derivatives of cyclodextrin and calixarenes, with subphase species with which they can form host-guest complexes at the water-air interface. b) Study of the transfer of these films to substrates using the Langmuir-Blodgett technique.

Self-Assembled Monolayers - Self-assembled monolayers form by the absorption followed by chemisorption of molecules with groups capable of forming ionic or covalent bonds with a solid surface resulting in an organized monolayer structure. We are studying the formation of monolayers on gold and silver coated substrates from solutions of alkyl thiol derivatives. In collaboration with Professor D'Souza, we are examining the formation, structure, and electrochemical behavior of cyclodextrin derivatives. These films have potential application in analytical chemistry as modified surfaces for use in chemical sensors. The techniques employed include surface plasmon spectroscopy, quartz crystal microbalance measurements, external reflection infrared spectroscopy, and electrochemistry.

Future research areas being planned for development are: a) formation of Langmuir-Blodgett and self-assembled films of nanoparticles, b) the combination of Langmuir-Blogett and self-assembly methods, and c) the study of chemical reactions in organized surfactant media.

Numerous past undergraduates have contributed, especially in the area of Langmuir film studies, and became co-authors on publications.

Dr. William J. Welsh

Room B433 Benton Hall

Phone 516-5318

The focus of Dr. Welsh's research program is computational chemistry and the computer-aided molecular design of polymers and biological molecules. He currently has active research projects in the following areas: (1) discovery of chemotherapeutic drugs for the treatment of cancer, AIDS, and Alzheimer's Disease; (2) design and optimization of high-performance polymers capable of surviving extreme and hostile environments for aerospace applications; (3) applications of computer-based artificial neural networks and related pattern-searching paradigms for the "fingerprinting" of drug formulations to ensure the safety and efficacy of FDA-approved drugs; and (4) computer-based simulations of the chromatographic separation of chiral and isomeric pairs of drug compounds by liquid-crystalline stationary phases in order to understand and optimize the separation mechanism at the molecular level.

A High-Performance Polyimide Under Investigation for Aerospace Applications

Chemotherapeutic Drugs for Treating Memory Losses in Alzheimer's Patients

Dr. Janet Braddock-Wilking

Room B207 Benton Hall

Phone 516-6436

Research Projects:

Polyhedral silicon clusters, (RSi)n (where R is an organic substituent and n = 4-8) are unusual molecules that exhibit remarkable electronic properties. These clusters will inevitably lead to new solid state applications such as non-linear optical materials. Theoretical calculations on these types of molecules show that they have lower ring strain energies than their carbon analogs and that the substituents, R, can alter the strain energy. This project involves the synthesis, characterization and reactivity of silicon clusters where R = transition-metal fragment. To date, all reported syntheses on these polyhedral silicon clusters utilize organic substituents. It is expected that the silicon-silicon framework and the transition-metal moiety will contribute strongly to the electronic properties of the molecule. The proposed synthetic route for the preparation of polyhedral compounds of silicon containing transition-metal substituents involves the reductive coupling of a (trihalosilyl) metal complexe with an appropriate reducing agent such as sodium metal (eq. 1).

LnM-SiCl3 + Na [LnM-Si]x (1)

Transition-metal silylene complexes, LnM=SiR2 have been postulated in a number of metal mediated processes but their synthetic applications and reactivity are largely unexplored. Due to the electrophilic nature of the silylene fragment, SiR2, an electron rich metal (i.e. Pt) in a low oxidation state is required to stabilize the metal-silylene complex. Sterically demanding ligands at silicon should lend increased kinetic stability to the complex and prevent external attack or dimerization. The substituents on silicon that will be investigated are bulky aryl groups with varying electronic properties. Some of the precursors to the metal fragments that will be studied are (dppe)Pt(C2H4), (PPh3)4Pt, and (dppe)PtMe2 (dppe = 1,2-bis(diphenylphos-phino)ethane).

The reaction that is being investigated to produce a metal-silylene complex requires an oxidative-addition of a silicon-hydrogen bond to a metal center followed by a reductive-elimination of dihydrogen to produce the LnM=SiR2 species as shown in eq. 2.

The techniques used in these projects include simple reaction setups under an inert atmosphere, handling of air and moisture sensitive compounds, and chromatography or distillation for purification and separation. UV-Vis, IR, and NMR spectroscopy will be used to characterize the clusters and metal-silylene complexes.

Dr. Rudolph E. K. Winter

Room B315j Benton Hall

Phone 516-5337

The chemistry of naturally occurring substances has long been an important part of Organic Chemistry, but in recent years there has been a renewed interest in natural product research. This revival has been stimulated not only by new instrumental methods for identification and structure determination and development of innovative separation/isolation techniques, but is also the result of new perspectives for such research derived from better understandings of the associated Biology. Professor Winter's research involves organic and bioorganic chemistry of plant metabolites, particularly terpenes. Projects include isolation and identification of novel biologically significant compounds, synthesis and chemical transformation among structurally related classes and biosynthesis and chemical ecology of plant materials. Several currently active projects are described below.

Stereocontrolled Transformation of Farnesol Derivatives to Cyclic and Bicyclic Sesquiterpenes - Regio- and stereochemical control in the cyclization of acyclic terpenoids remains a major challenge for the synthetic chemist. Recently, we have effected cyclication of an allene-containing farnesol derivative, producing thereby a ten-membered carbocycle characteristic of germacrane type sesquiterpenes. Current efforts are directed at investigating stereochemical aspects of this reaction and effecting transannular reactions to produce guaiane- and eudesmane-types.

Biodirected Isolation of Novel Compounds from Gouania Iupuloides (Jamaican chawstick) - Extracts of this neotropical vine show antimicrobial activity against a number of oral microorganisms associated with periodontal diseases. This project is directed toward compounds of potential value in dental medicine, and of particular interest are several novel minor triterpenoids which are structurally related to ceanothic acid a long known triterpene tricarbocyclic acid. Our present efforts are aimed at a semi-syntheses of these materials exploiting Ceanothus americanus (common red root) as a source of ceanothic acid.

Oxidative Transformation of Guaiol - Oxidations of this readily available sesquiterpene alcohol are being reinvestigated with the aim of producing functionalities commonly found in more highly oxidized plant natural products. Present emphasis is on guaiol-derived epoxides and hydroperoxides and study of their intramolecular reactions as methods for controlling the positions of oxidation.

Dr. Zhi Xu

Room B434 Benton Hall

Phone: 516-5328

The undergraduate study in my research lab consists of the following two projects:

(1) Determination of molecular orientation at air-solid interfaces using UV-Vis absorption and fluorescence emission spectroscopy. The purpose of this project is to provide a fundamental understanding of the interactions of organic molecules with solid substrates, and to establish a reliable and independent method for the determination of the molecular orientation at air-solid interfaces. This research project has very close connection with our on going experimental study of solid-liquid interfacial chemistry using sum-frequency generation (SFG) spectroscopy.

(2) Detection of trace amount organic and inorganic chemicals using pulse laser and time gating technique. Time gating detection technique is the most sensitive detection technique available today, with which the detection of single molecule is possible. The goal of this is to explore the potential applications of this new technique in environmental chemistry and trace analysis.

This figure shows the comparison of the experimental result and the theoretical calculation. The tilting angle for this particular molecule, Rhodamine-6G, is about 62° from the surface normal.