Introduction

Below is a summary of my research projects, which can be broadly categorized as the investigation of reactivity and selectivity in organic chemistry. Students at the Pitzer, Scripps, or Claremont McKenna College (or perspective students) are free to e-mail me or stop by my office to discuss research opportunities in my group. Alternatively, a booklet of faculty research projects available in the Joint Science Dept. is kept in the front office of the W.M. Keck Science Center. A more detailed list of projects available in the Poon research group can be found in this booklet.

Zeolites are microporous crystalline solids that possess a primary structure composed of MO_n polyhedra, where M is usually silicon or aluminum. The most frequently encountered polyhedra in zeolites are tetrahedra (n=4) and they are arranged such that each oxygen atom on one tetrahedron is attached to the central atom of another. The tetrahedra combine in an ordered fashion to form polygonal or polyhedral units, which in turn combine to form the framework structure of zeolites. The progression from a single tetrahedron all the way to the framework structure of the faujasite class of zeolites is shown below...

Imagine taking a bottle so small that only one or two molecules will fit inside of it! The rightmost structure in the figure above is known as a supercage, and it is just large enough (diameter = 1.3 nm) to fit one or two small to medium-sized organic molecules. It turns out that molecules can often undergo completely different reactions inside these zeolites than they do in solution (the traditional way of running reactions). This is a good thing because we can get molecules to react in ways that were never believed possible. For example, a molecule (e.g. a potential drug) that may take 6-8 steps to make using traditional methods might take only 1-3 steps to make when zeolites are employed. Another way that we use zeolites is to cause reactions to proceed by what is normally the least favorable pathway in solution. We are also interested in investigating how molecules behave inside zeolites. Finding new reactions that take place inside zeolites and the study of zeolite properties is currently a hot topic in chemistry and there are many projects within my research group through which you can contribute.

Papers in this area (student coauthors underlined)

J. Sivaguru, H. Saito, M. R. Solomon, L. S. Kaanumalle, S. Lakshmi, T. Poon, S. Jockusch, W. Adam, V. Ramamurthy, Y. Inoue, and N. J. Turro “Control of Chirality by Cations in Confined Spaces: Photooxidation of Enecarbamates Inside Zeolite Supercages” Photochemistry and Photobiology, 2006, vol 82, pp 123-131.

J. Sivaguru, T. Poon, R. Franz, S. Jockusch, W. Adam, and N. J. Turro “Stereocontrol Inside Confined Spaces: Enantioselective Photooxidation of Enecarbamates Inside Zeolite Supercages” Journal of the American Chemical Society, 2004, vol 126, pp 10816-10817.

T. Poon, N. J. Turro, J. Chapman, P. Lakshminarasimhan, X. Lei, W. Adam, and S. Bosio “A Supramolecular ‘Ship in Bottle’ Strategy for Enantiomeric Selectivity in Geminate Radical Pair Recombination” Organic Letters , 2003, vol 5, pp 2025-2028.

Molecular oxygen (O₂) is everpresent in our everyday lives. It is in the air we breath and in our bodies and that of other living organisms. Oxygen exerts both beneficial as well as detrimental effects on nearly everything that it encounters. For example, it is responsible for the spoilage of food on the one hand, but on the other hand, the lack of oxygen is responsible for the pain we feel in our muscles upon excessive physical exertion. Because oxygen and its chemistry are so prevalent, it is important that we understand as much as possible about its reactivity.

Singlet oxygen is a form of oxygen that occurs when oxygen has been excited to a higher energy level. It has been implicated in biological damage in several studies and has also been used as a reagent for a variety of organic reactions. The electronic configuration of singlet oxygen and ground state oxygen (molecular oxygen that we breath everyday) is shown in the figure above. Also shown above are examples of reactions that singlet oxygen undergoes. In this group, we are interested in understanding the factors that affect the reactivity of singlet oxygen. Such factors include solvent, temperature, the structure of the compound that ¹O₂ is reacting with, pressure, etc. The goal of these projects is to study the reactions of ¹O₂ in model systems, especially those pertinent to biology or biochemistry, and to discover how the factors mentioned above contribute to their overall reactivity.

Papers in this area (student coauthors underlined)

J. Sivaguru, M.R. Solomon, T. Poon, S. Jockusch, S.G. Bosio, W. Adam, and N. J. Turro. “The Reaction of Singlet Oxygen with Enecarbamates: A Mechanistic Playground for Investigating Chemoselectivity, Stereoselectivity and Vibratioselectivity of Photooxidations” Accounts of Chemical Research (in press).

J. Sivaguru, T. Poon, C. Hooper, H. Saito, M. Solomon, S. Jockusch, W. Adam, Y. Inoue, and N. J. Turro. “A Comparative Mechanistic Analysis of the Stereoselectivity Trends Observed in the Oxidation of Chiral Oxazolidinone-Functionalized Enecarbamates by Singlet Oxygen, Ozone and Triazolinedione” Tetrahedron (Symposia-in-Print; invited review article), 2006, vol 62, pp 10647-10659.

J. Sivaguru, M. R. Solomon, H. Saito, T. Poon, S. Jockusch, W. Adam, Y. Inoue, and N. J. Turro “Conformationally controlled (entropy effects), stereoselective vibrational quenching of singlet oxygen in the oxidative cleavage of oxazolidinone-functionalized enecarbamates through solvent and temperature variations” Tetrahedron (Symposia-in-Print; invited review article), 2006, vol 62, pp 6707-6717.

J. Sivaguru, H. Saito, T. Poon, T. Omonuwa, R. Franz, S. Jockusch, C. Hooper, Y. Inoue, W. Adam, and N. J. Turro “Stereoselective Photooxidation of Enecarbamates: Reactivity of Ozone vs Singlet Oxygen” Organic Letters, 2005, vol 7, pp 2089-2092.

T. Poon, J. Sivaguru, R. Franz, S. Jockusch, C. Martinez, I. Washington, W. Adam, Y. Inoue, and N. J. Turro "Multidimensional Control of Stereoselectivity in the Reactions of Singlet Oxygen with Oxazolidinone-substituted Enecarbamates" Journal of the American Chemical Society, 2004, vol 126, pp 10498-10499.

T. Poon, N. J. Turro, J. Chapman, P. Lakshminarasimhan, X. Lei, S. Jockusch, R. Franz, W. Adam, and S. Bosio “Stereochemical Features of the Physical and Chemical Interactions of Singlet Oxygen with Enecarbamates” Organic Letters, 2003, vol 5 , pp 4951-4953.

Liquidambar styraciflua, commonly known as the sweetgum tree, is characterized by its mace-like fruit which falls from the tree after the fruit has released its seeds. The tree is one of the few that possesses leaves that change color in warm weather climates. Its ornamental nature is the reason that sweetgum has been planted in many municipalities throughout the United States. Our research group was the first to discover that an important chemical, shikimic acid, can be obtained in relatively large quantities from its seeds. Shikimic acid is the key ingredient in the industrial synthesis of oseltamivir, the only drug capable of treating the H5N1 form of the avian flu.

Claremont, CA is known as the "City of Trees and PhD's" because of its abundance of flora and residents with graduate degrees per capita. We are currently exploring new ways to utilize the natural products found within the vast variety of plant organisms found in the city.

Papers in this area (student coauthors underlined)

L. B. Enrich, M. L. Scheuermann, A. Mohadjer, K. R. Matthias, C. F. Eller, M. S. Newman, M. Fujinaka, and T. Poon, "Liquidambar styraciflua: a renewable source of shikimic acid" Tetrahedron Letters 2008, 49, 2503-2505.

Listen to Dr. Poon's National Public Radio (NPR) interview on this discovery.