Faculty Research Summaries | Chairman 's Introduction

• R. Stephen Berry, James Franck Distinguished Service Professor, Department of Chemistry, James Franck Institute, and the College; Irving B. Harris Graduate School of Public Policy Studies
• Brice Bosnich, Professor, Department of Chemistry and the College
• Laurie J. Butler, Professor, Department of Chemistry, James Franck Institute, and the College
• Robert N. Clayton, Enrico Fermi Distinguished Service Professor, Departments of Chemistry and Geophysical Sciences, Enrico Fermi Institute, and the College
• Philip E. Eaton, Professor, Department of Chemistry and the College
  
• Karl F. Freed, Professor, Department of Chemistry, James Franck Institute, and the College
• Josef Fried, Louis Block Professor Emeritus, Departments of Chemistry, Biochemistry & Molecular Biology, and Ben May Laboratory, and the College
• Robert Gomer, Carl William Eisendrath Distinguished Service Professor Emeritus, Department of Chemistry, James Franck Institute, and the College
• Philippe Guyot-Sionnest, Associate Professor, Departments of Chemistry and Physics, James Franck Institute, and the College
• Jack Halpern, Louis Block Distinguished Service Professor Emeritus, Department of Chemistry
• Robert Haselkorn, Fanny L. Pritzker Distinguished Service Professor, Departments of Molecular Genetics & Cell Biology, Biochemistry & Molecular Biology, Chemistry, and the College; Director, Center for Photochemistry & Photobiology
• Gregory L. Hillhouse, Professor, Department of Chemistry and the College
• Michael D. Hopkins, Professor, Department of Chemistry and the College
• Richard F. Jordan, Professor, Department of Chemistry and the College
• Clyde A. Hutchison Jr., Carl William Eisendrath Distinguished Service Professor Emeritus, Department of Chemistry, Enrico Fermi Institute, and the College
• Ole J. Kleppa, Professor Emeritus, Departments of Chemistry and Geophysical Sciences and James Franck Institute
• Sergey A. Kozmin, Assistant Professor, Department of Chemistry and the College
• Ka Yee C. Lee, Assistant Professor, Department of Chemistry and the College
• Donald H. Levy, Albert A. Michelson Distinguished Service Professor, Department of Chemistry, James Franck Institute, and the College
• John C. Light, Professor, Department of Chemistry, James Franck Institute, and the College
• David G. Lynn, Professor, Department of Chemistry and the College
• Milan Mrksich, Assistant Professor, Department of Chemistry and the College
• James R. Norris, Jr., Professor, Department of Chemistry and the College, Chairman, Department of Chemistry
• Takeshi Oka, Robert A. Millikan Distinguished Service Professor, Departments of Chemistry and Astronomy & Astrophysics, Enrico Fermi Institute, and the College
• David W. Oxtoby, Mellon Professor, Department of Chemistry, James Franck Institute, and the College; Dean, Division of the Physical Sciences
• Joseph A. Piccirilli, Assistant Professor, Departments of Chemistry and Biochemistry & Molecular Biology, and the College
• Viresh H. Rawal, Professor, Department of Chemistry and the College
• Stuart A. Rice, Frank P. Hixon Distinguished Service Professor, Department of Chemistry, James Franck Institute, and the College
• Clemens C. J. Roothaan, Louis Block Professor Emeritus, Departments of Chemistry and Physics
• Norbert F. Scherer, Professor, Department of Chemistry , James Franck Institute and the College
• Joan-Emma Shea, Assistant Professor, Department of Chemistry and the College
• Steven J. Sibener, Professor, Department of Chemistry, James Franck Institute, and the College; Director, Materials Research Laboratory
• John Willard Stout, Professor Emeritus, Department of Chemistry and James Franck Institute
• Anthony L. Turkevich, James Franck Distinguished Service Professor Emeritus, Department of Chemistry, Enrico Fermi Institute, and the College
• William D. Wulff, Professor, Department of Chemistry and the College
• Nien-Chu Yang, Gustavus and Ann M. Swift Distinguished Service Professor, Depart-ment of Chemistry, Center for East Asian Studies, and the College
• Luping Yu, Professor, Department of Chemistry, James Franck Institute, and the College

R. Stephen Berry

Dynamics of small and medium size systems. This subject has several facets. One is the exploration of the effects of correlation on the electronic structure of atoms and molecules, for example on whether the quantization is independent-particle-like or collective. Electron correlation plays a particularly important role in negative ions. We are carrying out experiments on two-photon detachment of electrons from negative atomic and molecular ions and also on detachment of electrons in collisions of negative ions with excited, neutral energy donors - "Penning detachment."

Another aspect of this general area concerns the behavior of atomic and molecular clusters. An important issue here is exploring the topography of the multi-dimensional potential surfaces and relating the topography to such manifestations as dynamic equilibrium among isomers, phase equilibria, surface melting, and glass formation. For example, many kinds of clusters can exhibit solid-like and liquid-like forms that coexist in equilibrium like chemical isomers within a band of temperatures and pressures. How this coexistence behaves as the number of particles in the cluster increases has generated new insights into the nature of the melting/freezing process and into super heating and super cooling.

The interpretation of topographies and dynamics on complex potential surfaces has led our group into a study of protein folding, dynamics and kinetics. This work has shown that the same general principles that determine how well a cluster finds a selective structure, such as a crystalline or polyhedral form, also determine how effectively a protein finds its active structure. This work has now led into investigations of self-assembly of proteins and of effects of mutations on structure and folding.

Clusters have also proven to be useful laboratories for studying chaos and ergodicity. Very small systems actually become more ordered and less chaotic when they "melt" but the pseudo ordering process associated with a very few degrees of freedom is masked in larger clusters composed of even as few as 5-7 particles. The research on clusters has consisted of computational and theoretical studies until now. We are beginning a program of experimental work to complement the theoretical studies, especially of phase equilibria.

Finite-time thermodynamics. The extension of thermodynamics to describe processes operating under constraints of finite time or nonzero rate is the goal of this work. finding natural bounds on performance of processes with time constraints is part of the objective of this work; finding the process paths that yield optimum performance is another part. Examples include finding the optimum performance of the idealized automobile engine and how existing engines could be made to operate more efficiently, and determination of the limits on performance of distillation and other heat-driven separation processes.

Brice Bosnich

Three projects are currently in progress. The respiratory protein hemerythrin found in marine worms transports molecular oxygen by employing two iron atoms in a chemically subtle way. The mechanism of this process is currently being studied using low molecular weight analogues of the protein. In a related project, bimetallic complexes which activate molecular oxygen are being studied with a view to developing catalysts which use atmospheric oxygen for the oxygenation of organic substrates, particularly hydrocarbons. A third area of study concerns the use of supramolecular chemistry for recognition and incorporation of inorganic salts and of charged organic molecules. The supramolecular structure are such that molecular switches may be developed with these incorporated guests.

Laurie J. Butler

Our research investigates the fundamental molecular dynamics and electronic energy transfer processes that determine the pathways of chemical reactions. Much of the current understanding of chemical reaction dynamics relies on the Born-Oppenheimer separation of nuclear and electronic motion; this approximation allows one to calculate, for instance, the energetic barrier to the chemical reaction from first principles quantum mechanics. Our experiments show that for wide classes of chemical reactions this approximation breaks down, reversing the expected branching between energetically allowed chemical product channels (e.g. a different bond will break than the one predicted to!). The experimental studies are designed to both provide critical comparisons with predictions of emerging quantum theories on nonadiabatic reaction dynamics in small systems where the usual approximations we make for chemical dynamics break down and to develop an intuitive framework for understanding chemical reactions in condensed phase and biological systems.

Our work uses two powerful and complementary experimental techniques, polarized emission spectroscopy to study the evolution of the dynamics during the subpicosecond reaction and measurement of photofragment velocity and angular distributions by crossed laser-molecular beam methods to determine the mechanism for forming specific reaction products over several energetically allowed ones. Recent work includes studies of the dynamics and product branching in reactions important in atmospheric processes and in combustion. The photodissociation channels of nitric acid, a molecule important in reactions involving OH radicals in the atmosphere, cannot be predicted within the usual chemical reaction rate theories. Our experiments show the orientation of the radical p electron on the forming OH radical as the N-OH bond breaks results in the NO2 reaction product only being formed in excited electronic states, never in the ground electronic state. In other work, we investigated the competition between two bond fission channels in amides, molecules which link together the peptides in proteins. We are interested in understanding unexplored features of reaction dynamics coming to the forefront with recent theory and experiment, including the effect of accessing different regions of the excited potential surfaces on the ensuing dynamics and branching between possible product channels.

Robert N. Clayton

Many chemical elements show variations in the abundances of their stable isotopes in extraterrestrial materials (e.g., meteorites and lunar samples) which are much greater than variations in terrestrial materials. In some instances, these variations can be traced back to processes of nucleosynthesis, both in stars and in interstellar space. In other cases, isotopic variability has been introduced by processes of evaporation and condensation in the solar nebula from which the sun and planets formed. For other elements, isotopic variability results from interactions with energetic particles from the sun (solar ?ares and solar wind) or from the galactic cosmic rays. We use a variety of mass spectrometric techniques to measure isotopic abundances of many elements: H, C, N, O, Mg, Si, K, Ca, Ti, Cr, Fe, Ni, Sr, Zr, Mo, and others. In collaboration with scientists at the Argonne National Laboratory, we use Resonance Ionization Mass Spectrometry (RIMS) for measurement of nucleosynthetic effects in minor elements present in individual interstellar grains preserved in primitive meteorites.

Isotope abundance variations are also powerful tools for investigation of terrestrial natural processes. For example, the geochemical cycling of carbon and nitrogen through the Earth's crust and mantle can be traced by means of their isotopic compositions. Similarly, the movements of aqueous ?uids in the Earth's interior are studied through the isotopic ratios of hydrogen and oxygen.

Philip E. Eaton

My group's research interests are focused on the synthesis and examination of new ring systems specifically designed as probes into the effects of molecular geometry on bonding, reactivity, strain, etc. In the course of our work we were first to synthesize cubane, pentaprismane, [2.2.2]propellane, the [n.2.2.2]paddlanes, and many other highly strained "unnatural" compounds. These systems have given us special opportunities to study the behavior of exceptionally strained molecules vis-à-vis their propensity for rearrangement and reaction.

Cubane is the most highly strained, kinetically stable ring system available in quantity. We have used it as the source of even more highly strained compounds including 1(9)-homocubene (the most highly twisted olefin), cubene, (the most highly pyramidalized olefin), and such intriguing species as 1,4-dehydrocubane, cubyl cation (the "least likely" cation), and the cubylcarbinyl radical (the fastest rearranging saturated radical). These have "record" properties and as such have proven to be of fundamental importance in developing an understanding of bonding in strained systems.

We have underway now synthetic efforts to synthesize hexaprismane (2 flat cyclohexanes fused by 6 cyclobutanes), the enormously high energy "flat" carbon system of [2.2.2.2]paddlane, and hetero analogs of such unnatural ring systems, for example, azacubane.

As the geometric requirements of such compounds are far from ordinary, tactical synthesis is an exceptional challenge. Much of our work, therefore, is on the development and application of new synthesis methods and techniques. Diels-Alder reactions, photochemical cyclizations, electrochemical couplings, and metal-induced transformations are of particular interest.

Cubanes and other unnatural products offer interesting practical applications as diverse as anti-viral agents, explosives, high-refractive index lenses, liquid crystals, specialty polymers, and fuel additives. We are particularly interested in the construction of new materials for use in nanoarchitecture projects. For example, we are now working on the synthesis and characterization of n-[cubylcubanes] and n-[diethynylcubanes]. These are stiff, rigid rods with dimensional stability. We plan to use their derivatives for the construction of 2-dimensionally crystalline Langmuir film gratings with controlled spacing at the molecular scale level

Karl F. Freed

Our research interests cover several areas of theoretical chemistry, including the electronic structure of molecules, the statistical mechanics of polymers in the liquid phase, and the long time dynamics of peptides and polymers in solution.

We have developed a highly correlated ab initio electronic structure method that is designed to tackle the difficult problem of describing molecular electronic excited states. The method is a multiconfigurational generalization of the widely used MPn single reference configuration methods, which are available in many commercial electronic structure packages but which are unsuitable for treating highly open shell systems such as those in excited states. These new ab initio methods have been applied to describe the excited states of a number of conjugated pi-electron systems, where our computed energies and oscillator strengths rival in accuracy the most advanced ab initio methods. Additional applications have been made to computing two-dimensional methyl mercaptan and three-dimensional hydrogen sulfide potential energy surfaces for the electronically excited states that are accessed in non-adiabatic photodissociation experiments carried out by Professor Butler's group. (In fact, the computations have been performed by a theory-experiment student working jointly with Prof. Butler and me.) More recent interests are associated with aiding Professor Moffat to understand the photodynamics of photoactive yellow protein, a protein in purple bacteria that signals the presence of blue light so the bacteria can swim away from the light.

Our electronic structure methods are unique in enabling us to derive from first principles the true valence shell effective Hamiltonian that is mimicked by the model Hamiltonians of purely semiempirical molecular orbital theories of molecular electronic structure. We have computed the first fully correlated "ab initio" pi-electron Hamiltonian that demonstrates why some assumptions of semiempirical pi-electron theories are correct, but our computations for small conjugated pi-electron systems indicate deficiencies of these older methods along with theoretically justified methods for their improvement.

We have been developing a theory of the statistical thermodynamics of polymers in the liquid state. Our theory is the first and only one to describe the influence of monomer molecular structure on the thermodynamic properties of polymer mixtures. Several applications explain small angle neutron scattering and thermodynamic experiments for mixtures of polymers in the liquid state. Our theoretical predictions of a strong pressure dependence to the small angle neutron scattering intensities has been verified. Likewise, we have predicted the possibility that certain block copolymers will form mesoscopically ordered self-assembled structures in the liquid phase upon heating, a bold prediction subsequently verified experimentally. Recent extensions of the theory consider random copolymers, the influence of short chain branching and chain semiflexibility on miscibilities of polymers in the liquid phase, as well as the phase behavior of liquid crystalline systems. Other work in this area is devoted to developing a theory of interfaces in polymer systems. Particular examples include the interfaces between phase separated polymers, surface segregation profiles of polymers near an impenetrable surface, and the interfaces in self-assembling block copolymer systems. A key motivation is to understand the molecular features governing the rich array of observed phenomena.

Flexible aqueous peptides and polymers in solution have important dynamical processes occurring on time scales far exceeding current capabilities for computer simulations of these systems. Thus, we are developing a theory of the long time protein and polymer dynamics which can use input information that is accessible to current computer capabilities. The theory is able successfully uses this information to provide a realistic description of the longer time dynamics. While the initial applications of the theory compare well with experiments made by Professor Fleming's group, current research has considered simpler alkanes, polypeptides, and small neurotransmitting peptides for testing and refining various components of the theory. This work focuses on the internal chain dynamics and on the nonequilibrium dynamics modeling protein unfolding, but future extensions are planned to consider the fundamentals of molecule-solvent interactions.

Robert Gomer

Experimental and theoretical studies of surface diffusion of adsorbates on single crystal metal surfaces.

Thermal desorption from single crystal surfaces.

Electron-stimulated desorption of chemisorbed and physisorbed atoms and molecules.

Ultraviolet and X-ray photoelectron spectroscopy of adsorbates on metals.

Chemisorption on metal overlayers on refractory substrates, e.g., CO or O on W(110)/Cu1 or W(110)/Pd1, W(110)/Hg.

Philippe Guyot-Sionnest

Surface nonlinear optics. The interaction of laser radiation and surfaces is studied. The polarization and spectroscopic response of surfaces prepared in Ultra-High Vacuum and in liquids is used to determine their structure and composition.

Surface dynamics. The very fast energy transfer and coupling mechanisms of small molecules with surfaces are followed with time-resolved laser spectroscopy. Relaxation of excited vibrational and electronic states will be investigated.

Nanoscale optics. The optical response of subwavelength structures such as semiconductor clusters or "quantum dots" will be studied and new approaches will be investigated to perform optical spectroscopy on a nanometer scale.

Jack Halpern

My research encompasses the fields of coordination and organometallic chemistry, kinetics and mechanisms of inorganic and organometallic reactions, catalytic phenomena, and bioinorganic chemistry.

Chemistry of vitamin B12 and related compounds. The chemical properties of certain low-spin cobalt complexes, containing liquids such as cyanide, dimethylglyoxime, and Schiff bases, exhibit striking parallels with those of vitamin B12 and its derivatives, including reactions with alkylating agents to form organometallic derivatives. I am examining the mechanisms of these reactions and their possible significance as vitamin B12 model systems. Current studies are focused on the determination of cobalt-alkyl bond energies, particularly in relation to the role of cobalt-carbon bond homolysis in coenzyme B12 dependent rearrangements.

Chemistry of oxygen complexes. Although the formation of dioxygen adducts of metal complexes is well known, such complexes have thus far exhibited disappointingly limited reactivity of the coordinated oxygen and little utility as intermediates in catalytic oxidation. Our studies are directed at the preparation of new oxygen adducts, their physical and chemical characterization, and the elucidation of the mechanisms of catalytic oxidation reactions involving such adducts.

Oxidative addition and reductive elimination reactions. Our studies on such reactions are concerned with the elucidation of their mechanisms and reactivity patterns and with synthetic and catalytic applications. Current research is focused particularly on intra- and intermolecular reductive elimination reactions involving C-H bond formation.

Free radical processes in organometallic chemistry. Current studies are focused on several types of reactions of metal complexes leading to the formation of free radicals, notably: LnM• + RX —> LnM - X + R•; LnM - H + >C = C< —> LnM• + >CH - C <•; LnM - R —> LnM• + R•. The mechanisms and catalytic roles of such reactions are being examined. Kinetic studies on the last class of reactions also are being applied to determine transition metal-alkyl bond dissociation energies.

Mechanisms of catalytic reactions of coordination and organometallic compounds. Transition metal complexes catalyze a variety of organic reactions such as oxidation, hydrogenation, carbonylation, and decarbonylation. While it is appreciated that such reactions proceed through stepwise mechanisms involving organo-metallic intermediates, the detailed mechanisms for the most part remain to be elucidated. My studies, directed at such elucidation are currently focusing with considerable success on the mechanisms of homogeneous catalytic hydrogenation of olefins, including asymmetric catalytic hydrogenation and hydrogenation via free radical mechanisms.

Robert Haselkorn

We study the molecular genetics of nitrogen fixation and photosynthesis in cyanobacteria and purple bacteria. Recently, we have begun to study genes encoding the enzyme acetyl-CoA carboxylase in plants.

The cyanobacterium Anabaena grows in filaments of 100 cells or more. When starved for nitrogen, specialized cells called heterocysts differentiate from the photosynthetic vegetative cells at regular intervals along each filament. Heterocysts are anaerobic factories for nitrogen fixation; in them, the nitrogenase enzyme complex is synthesized and the components of the oxygen-evolving photosystem II are turned off. More than 1000 genes are believed to be differentially expressed during the (irreversible) development of a heterocyst from a vegetative cell. We have cloned and sequenced genes for nitrogen fixation (nif) and others encoding RuBP carboxylase, glutamine synthetase, the D1, CP-47 and water-oxidizing proteins of photosystem II, all the components of phycobilisome rods, and the sigma and core sub-units of RNA polymerase. We also constructed cDNA libraries corresponding to the mRNA populations present uniquely at particular times of heterocyst development. More than 200 clones from these stage-specific libraries have been sequenced. Finally, mutants unable to fix nitrogen aerobically have been isolated. Among these are some that have altered heterocyst morphology or an altered pattern. Four of these have been studied in detail, using a complementation system to isolate the wild-type gene defective in the mutants. One mutant fails to deposit the necessary glycolipid layer that forms part of the heterocyst envelope. A second mutant fails to make any heterocysts at all. A third makes them only at the ends of filaments. A fourth makes them too late and too frequently! In these cases, the sequences of the complementing genes are highly informative, corresponding to proteins that participate in environment-sensing regulatory cascades. The relationships among these regulatory proteins are being worked out by using the Green Fluorescent Protein from the jellyfish as a cell-specific reporter of gene expression.

The purple bacterium Rhodobacter capsulatus carries out photosynthesis and nitrogen fixation at the same time. Its chromosome is a circle containing 3.7 Mb of DNA. We have constructed a fine-structure physical map of the chromosome based on a set of overlapping cosmids that cover it completely. All of the known genes of Rhodobacter have been located on the physical map. We have begun to determine the complete sequence of the chromosomal DNA, one cosmid at a time. To date, we have sequenced 3.7 Mb, nearly the entire chromosome. The few remaining gaps are being closed by walking steps on chromosomal DNA. One of the most remarkable discoveries in the sequence is the presence of nine different prophage chromosomes embedded in the bacterial chromosome.

Several unicellular cyanobacteria provide superb experimental systems for studies of the photosynthetic apparatus. We have cloned many of the genes encoding components of the light-harvesting systems and reaction centers and used those genes as insertional mutagens, inactivating one or more of the polypeptides of the photosystems. The mutant strains are being used in studies of energy transfer and electron transfer, monitored by time-resolved fluorescence decay measurements.

Fatty acid synthesis, in plants as well as in cyanobacteria, begins with the reaction catalyzed by acetyl-CoA carboxylase (ACC). ACC in bacteria, including cyanobacteria, is comprised of four subunits: biotin carboxyl carrier protein (BCCP), biotin carboxylase (BC), and two subunits of carboxyltransferase. In chicken, rat, yeast and plants all of these domains reside in a single polypeptide. We have cloned and sequenced genes encoding BC and BCCP from two cyanobacteria and used this information to design probes for the cloning of ACC cDNA from wheat. We have complete cDNAs for the wheat cytoplasmic and chloroplast forms of the enzyme and have expressed them in yeast. Yeast using the wheat enzyme are sensitive to herbicides that target the wheat enzyme, allowing a full study of structure/function relationships for this important enzyme. The wheat/yeast system will also be useful for production of crystallizable amounts of protein for structure determinations. We recently discovered that apicomplexan parasites (malaria, toxoplasma) have an ACCase that is similar to the wheat chloroplast form of the enzyme, that is, extremely sensitive to herbicides that target the wheat enzyme. The herbicides may be fruitfully used to treat the diseases caused by these parasites.

Gregory L. Hillhouse

Our research is focused on studies of the interactions of very reactive, energy-rich molecules with transition-metal complexes. In some cases, the goal is to trap unusual molecular fragments as ligands; in other cases, to use metals to prepare otherwise inaccessible, very unstable molecules so that the fundamental details of their reaction chemistry can be studied. Two projects that reflect current research interests are outlined below:

I. Oxygen Transfer Reactions of Nitrous Oxide: One of today's greatest chemical challenges is the selective oxidation of organic substrates. We have found a way of utilizing nitrous oxide (N2O) in clean O-atom transfer reactions, and have observed the first examples of O-atom addition to metal-carbon bonds using N2O as the oxidant. Moreover, we have defined the mechanistic pathway by which N2O delivers its oxygen. Using this methodology, we can carry out unique, selective oxidations of alkynes on metals.

Since the early metals are oxophilic, it is unlikely that useful catalytic chemistry will be uncovered here, so we are now expanding our research to include late-metal organometallics in which the M-O bonds, once formed, will not be so strong that they can't be easily broken.

II. Chemistry of Diazene, NH=NH, and Related Molecules: Reactive molecules are often stabilized by coordination to metals, thus isolation and characterization of these species as complexed ligands can provide unique opportunities for their study. Moreover, under the appropriate conditions displacement of the unstable ligands is possible. We have used this approach to prepare diazenes of the type NH=NR, and are now investigating the physical properties and solution reaction chemistries of these unstable molecules. Diazenes are recognized as ubiquitous, key intermediates in a number of very important chemical transformations, and the elucidation of their chemistry will shed light on a range of mechanistic problems such as nitrogen fixation and the mode of carcinogenesis of azo compounds. The synthetic methodology used to prepare diazenes is being extended to prepare other unusual, simple, reactive molecules like PH=PH and NH=O.

Michael D. Hopkins

The goal of our research is to design, synthesize, and study inorganic and organometallic complexes and polymers that possess interesting electronic, optical, nonlinear-optical, magnetic, and photochemical properties. Central to our research is the use of high-resolution and time-resolved spectroscopic methods. We use the information from these techniques to develop a detailed understanding of the structures, bonding, and dynamics of the ground states and electronic excited states of molecules.

This knowledge enables us to rationally design new materials with enhanced properties. One of our goals is to prepare and electronically characterize transition-metal analogues of conjugated organic compounds and polymers. Our interest in developing these materials is motivated by the expectation that incorporating optically tunable and redox-tunable metal centers into the backbones on unsaturated organic compounds will significantly enhance the technologically valuable physical properties of conjugated organic systems. We have prepared a broad array of conjugated transition-metal complexes and polymers from multiply metal-metal and metal-ligand bonded building blocks and have systematically explored the electronic and structural analogies among these species and their organic counterparts. We are presently investigating the properties of these new classes of materials, particularly with reference to their potential applications in molecular electronics.

A second major area of research centers on the photochemistry and photophysics of high-valent complexes that contain multiple metal-ligand bonds. A primary objective of this work is to develop powerful excited-state oxidants. To this end, we have discovered rare examples of d0 complexes that possess long-lived excited states in fluid solution at room temperature. We are also exploring the photochemistry alkene and alkyne metathesis catalysts, with the aims of kinetically and thermodynamically enhancing the ground-state reactivity of these species and of developing systems capable of activating inert substrates as N2.

Richard F. Jordan

The Jordan research group is interested in the design, synthesis, and study of reactive organotransition metal complexes and the application of these compounds in catalysis, olefin polymerization, and organic synthesis. Students develop an extensive knowledge of the structures, bonding, and reactivity of organic, inorganic, and organometallic systems and use state-of-the-art laboratory and spectroscopic methods for the manipulation and characterization of reactive materials. Our current efforts focus on olefin polymerization catalysts and organic and organometallic synthesis.

Cationic, d0 metallocene complexes Cp2M(R)+ (Cp=h -C5H5; M=Ti, Zr, Hf) have been implicated as active species in soluble Ziegler-Natta olefin polymerization catalyst systems (e.g., Cp2MX2/MAO). The group has discovered general methods for the synthesis and isolation of complexes of this type and is studying their chemistry. We have shown that cationic Cp2Zr(R)(L)+ complexes (L=labile ligand) polymerize ethylene under mild conditions in the absence of Al cocatalysts or oxide supports.

Detailed studies of Cp2Zr(R)(L)+ complexes have provided important information about insertion, b -H elimination, M-R bond hydrogenolysis, and other reactions which are important in catalytic olefin polymerization. Such studies are providing new insights about the generation, structures, and reactivity of the active species/sites of soluble and heterogeneous olefin polymerization catalysts.

The group also is exploring applications of Cp2Zr(R)+ species in organic synthesis. This effort has led to the discovery of a Zr-catalyzed process for coupling pyridines and olefins in which ortho C-H activation in a Cp2Zr(H) (pyridine)+ species is a key step. Current efforts are focused on the development of chiral catalysts for stereoselective C-H activation/C-C coupling reactions.

We have used the insights gained from our studies of cationic metallocene complexes to develop many new classes of reactive metal alkyls and olefin polymerization catalysts which contain a variety of ligand types. For example, by utilizing carboranyl ligands in place of Cp- ligands, we have constructed neutral complexes, i.e. (h -C2B9H11)(h -C 5R5) M(R), which have the same structures, electron count, and frontier orbital properties as Cp2Zr(R)+ cations.

The carboranyl systems are very active catalysts for olefin polymerization and selective alkyne dimerization. More recently we have prepared novel cationic main group alkyl species, e.g., {RC(NR')2}Al(R)+ MeB(C6F5)3- , which polymerize ethylene in the absence of transition metals. These novel compounds offer many avenues for future research.

Ole J. Kleppa

Thermodynamics, high temperature calorimetry. Recently our work on high temperature reaction calorimetry has stressed: 1) development of calorimetric facilities for precision calorimetry above 1100o; and 2) applications of these methods and techniques in thermodynamic studies of high temperature melts and refractory materials. Recent investigations have emphasized work on 1) mixtures of the noble metals with transition metals; 2) refractory borides, silicides, and related compounds; 3) intermetallic compounds formed between early and late transition metals.

Ka Yee C. Lee

With the application of various microscopy and scattering techniques, my research group examines specific interactions between lipids and proteins in systems of biomedical relevance. Monolayers, either at the air-water interface or transferred onto solid substrates, and supported bilayers are used as model membranes in these studies. Our research goals are to better understand the physical and physicochemical aspects of these ultra-thin films, and to elucidate the biophysical aspects of certain diseases.

Lung Surfactant System and Respiratory Distress Syndrome (RDS). A complex mixture of lipids and proteins, known as lung surfactant, forms monolayers at the alveolar air-water interface. A lack of surfactant, either due to immaturity in premature infants or disease or trauma in adults, can result in RDS. We will examine the phase behavior of various mixtures of lung surfactant components, as well as the interactions between lung surfactant specific proteins and the surrounding lipid matrix to identify factors responsible for the proper functioning of the lung. We will also study the effect of mutant surfactant proteins on monolayer collapse dynamics, and that of serum proteins on the normal functioning of the lung surfactant to pinpoint on some of the causes for RDS.

Amyloid beta (A beta) Peptides and Alzheimer's Disease. A beta, a self-assembling 39-43 residue peptide generated by the proteolytic processing of the amyloid precursor protein, comprises the major proteinaceous component of neuritic plaques and vascular deposits that appear in Alzheimer's disease, and is implicated as one of the causal factors in the pathology of the disease. My group is interested in understanding the aggregation of the A beta peptides, and in using two-dimensional thin films as "templates" to explore the possibility of surface-induced aggregation. We plan to study various isoforms of A beta and to examine their surface activities and their association with model membrane systems. A beta is also known to aggregate and form fibrils. Since the rate of this process can be adjusted by various experimental parameters, we plan to monitor the formation process, and characterize the structure of the fibrils formed.

Donald H. Levy

Van der Waals molecules. The structures of van der Waals molecules are extracted from the rotational fine structure in the electronic spectrum. The details of internal energy transfer and photodissociation are studied using emission spectroscopy. Mode selective van der Waals chemistry has been observed.

Amino acids and peptides in the gas phase. Amino acids and peptides are injected into a supersonic molecular beam by means of laser vaporization of the solid, and the electronic spectra of these species are studied. Information on conformations and on the excited electronic states of these species is obtained.

Intramolecular energy and electron transfer. Energy and electron transfer processes are studied in molecules consisting of two different chromophores spearated by various molecular spacers. The dependence of energy transfer rates on molecular conformation are observed.

Laser desorption. The properties of laser desorbed solids are measured to provide insight into the mechanism of the laser desorption process.

John C. Light

Development of mathematical and advanced computational methods to solve problems in chemical physics.

Quantum theory of gas-phase atomic and molecular scattering, both for inelastic (energy transfer) and reactive processes. State-to-state cross sections and rate constants are calculated.

Exact quantum reaction rate constants by flux-flux autocorrelation function methods.

Theory of molecule-surface collision processes including inelastic processes.

Exact quantum statics and dynamics of small polyatomic molecules including theoretical spectroscopy, intramolecular vibrational energy relaxation, pre-dissociation, and isomerization.

David G. Lynn

Our research group is currently considering three broad chemical questions that range from chemical information storage to molecular genomics. While chemical synthesis and physical organic methods underpin all of our studies, the powerful methods of molecular genetics and the theories of evolutionary biology are central both to our ability to make materials and to formulate questions. Our contributions have fallen into the general areas of molecular recognition, bioorganic chemistry and chemical biology and are represented by the questions below.

What is the minimal structure and the molecular limits on systems capable of replication? Biological information storage and transfer occurs exclusively by template-directed synthesis. By carefully studying the thermodynamic stability of structurally modified nucleic acid duplexes, we have developed a system capable of catalytic translation of the information encoded within DNA oligomers into new materials. This system, for the first time, avoids product inhibition in a template-directed oligomerization, but important conceptually as it provides a method to extend the genetic code into new materials. We know now that the transfer can be extended to larger polymers and even peptides and hope to construct fundamentally different genomes that survive in a defined environment.

Can a genome's autonomy be grown and expanded to survive in different environments? This question will be difficult to ask in our synthetic genomes until they become more complex, but can be asked in suitable biological counterparts. Agrobacterium tumefaciens harbors a parasitic genome, the Ti plasmid, which is capable of coordinating both the bacterium and a plant cell in a state known as Crown Gall Disease. An elaborate metabolic interface with the bacterium and the resulting genetically transformed plant cell defines the success of this genome. What is the molecular strategy and what are its limitations? We have defined essential elements in the bacterial background that limit its success and are asking how the plasmid can be reconstructed to broaden the bacterial host range. We hope to learn the general rules that will allow this model genome to be added to and expanded in order to explore the general concept of a minimal genome structure capable of replication.

How are genome sizes reduced or paired down? The rules of genome efficiency and reduction will also be difficult to ask in synthetic genomes, but may be understood in certain biological systems. Higher plants represent a most autonomous genome. Nevertheless, there are flowering plants, in fact 1% of all flowering plants, who succeed only when parasitically affixed to another's genome. Questions relating to what stage does viability become limiting? How is it controlled? How are the specific genes for host attachment turned on and what is their function? How did such a strategy evolve? A unique model and the entire pathway that controls the differentiation of specific cell types that form the host interface has emerged from our studies. A eukaryotic redox pathway, one that appears to function in cellular defense against microbial invasion, has been co-opted for the control of cell development. The entire strategy for the evolution of this parasitism has emerged and the molecular events responsible can be defined. This genome has lost machines that were once essential, what are they? Where did the genes for parasitism come from? Can the lessons learned from this system be applied to synthetic systems and vice versa?

Ultimately, we hope to define the limits on the simple models of replication and extend to the construction of novel molecules capable of sustained growth. Only in this way can we expand the limits of what is chemically possible and, by doing so, prove that we understand the essential features of the living organism. The growing information defining genome structures will provide a valuable perspective for what are the minimal requirements for an autonomous system

Milan Mrksich

My research group uses structurally well-defined organic monolayers to study a variety of problems ranging from cell biology to smart materials. Our work is characterized by the development of new synthetic strategies for tailoring the structure of interfaces and the use of these substrates to understand complicated processes at the molecular scale.

Cell Adhesion and Migration. We have found that monolayers that present short peptide ligands can support the adhesion and spreading of mammalian cells. Because these substrates can be easily tailored--with control over the structure, density and environment of attached ligands--they provide a new opportunity to understand the molecular mechanisms underlying cell adhesion and spreading. My group uses a related class of monolayers that present gradients of carbohydrate ligands with which to understand the directed migration of fibroblast cells.

Electroactive Interfaces. A separate effort in the group uses this same surface chemistry to create electroactive interfaces. We have demonstrated several functionalized monolayers that can release attached groups under electrical control. We are now using this methodology in creating substrates for studies in cell adhesion and migration. Separately, we are characterizing aspects of reactivity that differ when molecules are attached to the surface of an electrode, including mechanisms by which applied potentials can control the reactivity and conformation of attached molecules.

James R. Norris, Jr.

Several distinctly different studies in biophysical and physical chemistry are being pursued. One of our ultimate goals is to understand more fully the fundamentals of the primary acts of photosynthesis. Included in our investigations are questions concerned with light absorption as well as energy conversion and storage. Photosynthetic reaction center proteins and light harvesting complexes are examined by a variety of spectroscopic probes. A major component of this work will be the development of picosecond time domain x-ray diffraction studies of the photosynthetic electron transfer reactions using intense synchrotron radiation pulses. The final major goal is the development of a single molecule, in a single molecule cage, to serve ultimately as a single molecule probe.

Natural and artificial photochemistry is explored by a variety of spectroscopic techniques specifically designed to probe mechanisms involved in photochemistry. Special modifications or perturbations, such as static and time dependent electric and magnetic fields, alter the photochemistry and spectroscopy. Implementation of these methods requires application of advanced optical and magnetic resonance spectroscopy. Of particular value is our time-domain electron paramagnetic magnetic resonance spectrometer with a time resolution of less than ten nanoseconds.

Light harvesting complexes are the principle light gathering "antenna" for the bacterial photosynthetic reaction center. Two light harvesting complexes exist in Rhodobacter sphaeroides while only one antenna complex is found in Rhodopseudomonas viridis. These complexes are an example of sophisticated integral membrane proteins with highly optimized function. The three dimensional organization of the antenna proteins results in the assembly of an unusually symmetric array of chlorophyll molecules whose function is to transfer incident light energy into the reaction center where chemical potential energy is trapped.

Important questions remain regarding these light harvesting complexes with their large arrays of "antenna" bacteriochlorophyll molecules. The mechanism of energy transfer is the subject of considerable interest. What distinguishes energy transfer and storage in antenna complexes from reaction-center protein complexes? In addition, can either the in vivo or modified antenna protein complexes be coupled to other photochemical processes in order to perform useful photochemistry?

With the goal of answering these questions as well as developing a better understanding of energy transfer and storage, normal and isotopically altered integral membrane proteins are manipulated by site directed mutagenesis via the photosynthetic bacterium Rhodopseudomonas viridis. These manipulated proteins exhibit modified chemical kinetics that are interpreted using detailed electron transfer theory. Interestingly, the core light-harvesting complex of photosynthetic bacteria yields stable radicals upon chemical oxidation. An intriguing feature of these oxidized antenna complexes is rapid electron transfer that can be uniquely explored with electron paramagnetic resonance (EPR). This aspect is intriguing because in nature these antenna are not oxidized, nor do they perform electron transfer chemistry. Consequently, exploration of a completely new facet of integral membrane proteins is possible while at the same time contributing to the better understanding of the overall process of photosynthesis. Along these lines, we have performed variable temperature EPR measurements with the aim of elucidating the mechanism of this electron transfer chemistry. The results are indicative of electron transfer among the bacteriochlorophyll molecules comprising the chromophore network of the light harvesting complex.. The available x-ray structural information makes possible the simulation the EPR spectra. A description for the temperature dependence of the electron-transfer rate constants is obtained using non-adiabatic electron transfer theory.

Finally, special probe molecules are being designed and synthesized to explore and to exploit single molecules. The fundamental idea is to modify dramatically the chemical and physical properties of single molecules or ions by insertion into another single molecule, i.e., the development of single molecule containers for single molecules. Caged molecules will necessarily possess modified chemical and physical properties in comparison to the corresponding un-caged molecules. However, to what extent the properties of caged molecules can be tailored remains to be seen and is a question to be explored in the course of these studies. This work involves the chemical synthesis of caged molecules or ions using nano-structures such as nano-bubbles and nano-tubes. The synthesis of caged molecules is interesting quite apart from any potential application. Eventually, one of the goals is to employ these caged molecules as single molecule probes of other systems such as membranes, gels, living cells, etc.

Takeshi Oka

We combine the technique of high resolution high sensitivity laser infrared spectroscopy and plasma chemistry to observe laboratory spectra of fundamental molecular ions such as H3+, CH3+, CH2+, C2H2+, C2H3+, CH5+ , NH2+, NH3+, NH4+, H3O+ etc. We then use these spectra as fingerprints to search for the molecular ions in astronomical objects by infrared telescopes. Those molecular ions are assumed to play pivotal roles in interstellar chemistry and thus in star formation.

Our work has contributed to identify the intense and pure H3+ infrared emission lines that were observed in Jupiter. The V2 fundamental spectrum we observed in 1990 has become a powerful tool to study morphology and temporal variation of plasma activities in planetary ionospheres. In 1996 we detected the absorption spectrum of interstellar H3+ towards young stellar objects that are deeply embedded in molecular clouds. This has given a most direct support to the currently accepted mechanism of the ion-neutral reaction scheme in which H3+ is the cornerstone. Our observation in 1998 of a large amount of H3+ towards a visible star and the galactic center brought a surprise since it clearly demonstrates abundance of H3+ also in diffuse clouds, where density is predicted to be very low because of its recombination with abundant electrons. The enigma brought up by this observation will be studied intensively in the next several years.

David W. Oxtoby

Methods of statistical mechanics are being used to study the dynamics of phase transitions, in particular the rates of nucleation and growth for new phases. Applications include order-disorder transitions in solids, gas-to-liquid transitions (and the reverse), the freezing of liquids and melting of solids, and transitions to mesophases such as liquid crystals and plastic crystals.

A new theoretical approach has been developed to study the nucleation of liquids from the vapor and is being applied to pure substances and to gas mixtures, including the highly non-ideal mixtures of water and sulfuric acid that dominate in polar stratospheric cloud formation. The reverse process of bubble formation in superheated, stretched, or supersaturated liquids is also being studied. Cavitation and sonoluminescence are two areas in which mass transfer across a bubble interface plays a critical role, and where a microscopic picture of the structure and dynamics of the interface would help scientists to understand what is happening on a molecular level.

When a liquid is cooled, it can crystallize, form a glass, or pass through a mesophase such as a plastic crystal or liquid crystal. Information from theory and diffraction experiments on the structure of the liquid (packing of atoms and molecules, positional and orientational correlations) is being used to predict which outcome is seen in a given situation. Colloidal suspensions provide a useful test case in which crystallization dynamics can be monitored on a particle-by-particle basis, while alloy crystallization provides an important arena for application of the theory. Predictions of rates of growth of crystals from the melt are also being made through a dynamical extension of the equilibrium statistical theory of freezing.

Viresh H. Rawal

My research efforts are directed toward the design of new chemical reactions and strategies for the synthesis of compounds, both natural and unnatural, that possess a unique, challenging architecture. The research projects that we are currently pursuing chemical problems in several different areas of organic chemistry, including: (1) exploration of the high reactivity of strained-ring compounds and applying this chemistry to the synthesis of medically important compounds, such as cardiac steroids and triquinane natural products (2) development of new, highly efficient routes to indole alkaloids, such as those of the strychnos and aspidosperma families, (3) development of methods for asymmetric synthesis, and (4) exploration of aspects of biomimetic chemistry and design of effective catalysts for asymmetric synthesis. Our study of these problems has already resulted in the discovery and development of several new bond-forming strategies.

Stuart A. Rice

My research interests are currently in two broad areas: active control of quantum dynamical processes, the properties of interfaces, and other quasi-two-dimensional systems.

In the first category, the goal is to develop theoretical understanding of methods to achieve control of selectivity of product formation in a chemical reaction. At present the focus of the research effort is on developing a general formalism for the control of quantum dynamical systems, on understanding the limitations to the use of optimally shaped time dependent fields to control the evolution of a molecule, extending the theory of control to reactions in condensed media, and developing a version of the general theory that is useful when applied to large molecules.

In the second category, the aim is to understand the properties of inhomogeneous liquids (e.g. the structure of the liquid-vapor and liquid-solid interfaces) in terms of the molecular interactions in the system. Among the questions of interest are: How does the structure of the inhomogeneous interface of a metallic alloy depend on the electronic structure of the species? How does the structure of the interface depend on the structure of the contact medium? What determines the concentration profile of a component that segregates at a liquid-x interface? What kinds of phases can exist in such a system and what are the structures of such phases? What are the dynamical properties of two-dimensional liquids? Is the surface of a liquid effectively two-dimensional or not? Typical studies involve the development of theoretical models, the utilization of computer simulations of model systems, the use of grazing incidence X-ray diffraction to study the interface structure in the plane, and of X-ray reflection to study the density distribution of the inhomogeneous system along the normal, to the interface, the use of evanescent wave dynamical light scattering to study motion in the interface, and video microscope studies of phase transitions and diffusion in quasi-two- dimensional colloid suspensions.

Norbert F. Scherer

The focus of our research is the direct time-domain (femtosecond-picosecond) study of chemical reactions and photophysical processes in condensed media and at interfaces. Our interest is the elucidation of the microscopic dynamics of the reactant and the role of the solvent (or interface) through the development and application of new spectroscopic methods. A variety of chemical processes including photodissociation, predissociation, reactant-solvent bimolecular reaction, electron transfer and energy relaxation are under investigation. The research program may be classified into several catagories: (i) femtosecond nonlinear spectroscopy of chemical and biological reactions, (ii) coherent transient spectroscopy of complex systems, (iii) solvent and protein response to chemical reaction. We are also working on novel spatially localized microscopy methods in conjunction with (femtosecond) laser methods for (iv) femtosecond scanning probe microscopy and (v) nanometer-scale optical microscopy.

In terms of problems we are interested in how chemical reactions (i.e. dissociation and electron-transfer) exchange energy with the surrounding environment (liquid, solid, protein). We are examining the intra-protein charge transfer dynamics and protein fluctuations that affect these dynamics in blue-copper systems, photosynthetic systems and photoactive yellow protein. In the area of spatially localized spectroscopy we are measuring and beginning to understand the localized electron(ic) dynamics at interfaces and their connection to reactivity and importance for electrochemistry. Finally, we are embarking on new research to examine dynamics in 2-dimensional systems including the dynamics of biological membranes, the vibrational dynamics of membrane-bound proteins, and optically-induced charge-transfer reactions and processes at metal-liquid and semiconductor-liquid interfaces.

Scherer's research program is built upon three concepts that are fundamental to chemical processes occurring in solution, in biological systems (especially proteins) and at metal and semiconductor interfaces. The first is the determination of the time-dependent interaction of a chromophore or reactant with the solvent bath. The second theme is the elucidation of protein dynamics that facilitate unique chemical reactivity. The third direction involves simultaneous spatial and temporal study of dynamics at chemically and technologically important interfaces. Five state-of-the-art femtosecond time-resolved techniques relevant to addressing the issues mentioned above are currently in use or development within the group: (1) novel photon echo methods to probe optical coherence decay of chromophores and reactions, (2) pump-probe and polarization spectroscopy to probe the dynamics of reactions in solution and in protein environments, (3) teraherz (THz) spectroscopy and probing of optically-induced reactions in solution and at solid-liquid interfaces, (4) polarizability probing of optically-induced reactions in solution and protein environments, and (5) unique studies that allow temporal as well as spatially localized examination of chemical processes using pulsed laser techniques and scanning probe microscopy. Efforts into first principles computer simulations (mixed classical and quantum) of the material responses and reaction behavior observed using photon echo, pump-probe and terahertz spectroscopy are underway.

Steven J. Sibener

Our research interests currently center on using experimental and theoretical techniques to address fundamental questions in the fields of surface chemistry and catalysis, surface physics, and materials research. In particular, we are using a variety of molecular beam, laser spectroscopic, and scanning probe microscopy techniques, as well as computational tools such as molecular dynamics, to examine issues central to our understanding of surface chemical dynamics. Illustrative topics include: surface chemical kinetics and reaction dynamics, heterogeneous combustion and catalysis, surface photochemistry, metallic oxidation and corrosion, self-organization of atomically structured thin films, atomic-scale interfacial chemistry, supersonic molecular beam growth of electronic materials including diamond, and, most recently, thin film polymer dynamics. Our newest endeavor centers on examining how highly energetic reagents, such as atomic oxygen, interact with materials, a topic of fundamental importance to materials chemistry, including reactions in the low-earth-orbit space environment. These studies are being conducted under ultra-high vacuum conditions, with recent extension to electrochemical environments. They are motivated by a desire to understand and control surface chemical processes at the molecular level, and by the increasing need to understand the physical properties of low-dimensional interfacial systems. More details can be found at our extensive group web page: http://sibener-group.uchicago.edu.

Anthony Turkevich

In the area of planetary exploration, the instrument that Thanasis Economou and I have helped the Germans to design is on its way to Mars. The scheduled landing is July 4, 1997. The instrument will provide a chemical analyses of Martian rocks and soil. The original alpha weathering and proton production modes have been supplemented by an x-ray mode. This will provide a more detailed analysis for chemical elements heavier than silicon.

We have received samples of uranium from Vienna that have been stored since World War II. It is important to repeat the double beta decay experiment on U238.

William D. Wulff

Our research interests range from the total synthesis of natural products, the development of new methodology in organic synthesis and to asymmetric synthesis with chiral catalysts. Several new reactions of transition metal carbene complexes with potential applications in synthetic organic chemistry are being investigated. These include the benzannulation reaction with acetylenes, Diels-Alder reactions, Michael additions, Aldol reactions, C-H insertions, cyclopropanations, [3 + 2]-cycloadditions and [2 + 2] cycloadditions. Synthetic targets for which these reactions are being evaluated include anthracyclines, indole alkaloids, taxol, fostriecin, and methoxatin. Another area of interest involves the development of new chiral ligands for catalysts in asymmetric synthesis. A new family of chiral biaryls has been developed which can be used as chiral ligands for aluminum based Lewis acids that provide chiral Diels-Alder catalysts that give asymmetric induction and turnover numbers that are superior to existing catalysts. The evaluation of these ligands in the generation of chiral catalysts for asymmetric applications to other classes of organic reactions are currently being investigated.

Nien-chu Yang

Photochemistry. Our current interest in photochemistry concerns the inter-actions between excited state groups and other groups through sigma-bonds, C-C and Si-Si bonds. We have found both electron-transfer interactions and exciton interactions through these bonds, and they occur both in solution and in gas phase. The latter work, in collaboration with Professor Donald Levy, was performed in a supersonic jet. The kinetics of the interactions in solution will be carried out in collaboration with Professor Norbert Scherer. The interactions through Si-Si bonds were more distinctive than those through C-C bonds. Our interest in this area also extends into the possible applications of our compounds in material sciences.

Chemistry of Synthetic Proteins. Amphiphilic peptides self-associate to form well-defined oligomers. These peptides may exhibit polymorphism under different experimental conditions, including their associations with membrane-mimetics. Our peptides form well defined supramolecular complexes with organic ligands and metal ions. They were characterized by fluorescence, X-ray crystallography, multi-dimensional NMR spectrometry, and other physical techniques. We are exploring the relationships between primary structures of synthetic proteins and their foldings into different secondary structures. Some of our peptides exhibit anti-microbial activities higher than Magainins, a group of natural occuring antibiotics. Our aims are to design and synthesize oligo-peptides in order (1) to explore their foldings into different secondary structures, and (2) to study their structure: anti- microbial-activity relationship.

Luping Yu

My research has focused on the synthesis and characterization of multifunctional polymers and on the development of new polymerization methodology. New materials, including conjugated photorefractive polymers, second order/third order nonlinear optical (NLO) polymers and conjugated liquid crystalline polymers, have been designed, synthesized and characterized.

The photorefractive (PR) effect involves the change in the index of refraction via the linear electro-optic effect modulated by a photoinduced space charge field. This effect can be utilized in three-dimensional holographic light processing and in handling a large quantity of information in real time. Four functionalities are necessary to show photorefractive effects: a charge generator, a charge transporting species, a charge trapper (due to defects) and a second order nonlinear optical species. We have developed three new polymer systems: the first PR polymer system contains the NLO chromophore, the charge generator and the transporting compound covalently linked onto the polymer backbone. The second system contains a conjugated backbone and a second order NLO chromophore, synthesized from the Stille coupling reaction. Nonlinear optical measurements revealed a large dynamic refractive index change. The third system utilize the charge transfer properties in photosynthetic model compounds. They are functionalized polyimides which contain metalloporphyrin moiety and a second order nonlinear optical chromophore. An asymmetric optical energy exchange was detected in two beam coupling experiments, indicating the photorefractive nature of the polymer.

One of the crucial problems hindering the practical applications of current second order NLO polymers is the instability of the dipole orientation induced by an electrical field. To overcome this problem, we developed a series of cross-linkable polyamides and functionalized polyimides with high glass-transition temperature. These materials demonstrated large and stable second harmonic coefficients which remain stable even at 150°C. These results indicated that our second order nonlinear optical polymers are very promising in practical applications.

Conjugated polymers such as (poly(2,5-dialkoxy-p-phenylene-co-2,5-thiophene) were synthesized by utilizing the Stille reaction and found to possess a nematic liquid crystalline phase above the melting temperature. The major implication of this discovery is that the inherent molecular orientation of liquid crystalline conjugated polymers may significantly enhance their physical properties, such as electric conductivity. These effects are being actively investigated.

Recently, we initiated a project to synthesize conjugated diblock copolymers which can self-assemble into conductive microdomain on nanometer size. These materials offer the opportunity to address issues such as the quantum confinement effects, tunneling effects in carrier transport and phase transition phenomenon. A unique approach was developed to synthesize these materials so that the architecture of the conjugated block can be precisely controlled, such as molecular length and the constitutional regularity and their physical properties can be correlated with defined structural parameters.

Another unique approach I am taking in my research is to carry out extensive physical studies of our new polymers by ourselves. We have built up a laser spectroscopic lab that allows us to run all of the measurements, including second harmonic generation, electro-optic measurements, photoconductivity measurements, two beam coupling and four wave mixing experiments. The spectroscopic and synthetic labs also allow my students to get training both in organic synthesis and in physical chemistry. From these physical measurements, we gain not only the physical data, but also the insight into the structure/property relationship which gives us guidance in searching for new materials.