个人简介

B.A., 1990, Wellesley College Ph.D., 1997, Massachusetts Institute of Technology NIH Postdoctoral Fellow, 1997–1998, Massachusetts Institute of Technology Research Assistant Professor, 1999-2005, University of South Carolina, Assistant Professor, 2005-2011, University of South Carolina. SC ACS Volunteer of the Year 2014 ACS Women Chemists Committee Rising Star Award 2013 USC Breakthrough Rising Star 2011

研究领域

Organic

Research Areas: Organic, Supramolecular Chemistry, Nanomaterials, Bioorganic, Organic Photochemistry, and Crystal Engineering. Research Summary: Organic chemists use C-C bond forming strategies to elaborate molecules generating a myriad of compounds. Nature uses non-covalent interactions to organize huge arrays of nanomaterials. We are interested in developing predictable supramolecular chemistry using non-covalent urea-urea interactions to build an array of structures and materials with a diverse array of applications. Self-assembled bis-urea macrocycles: The study of enzymes has demonstrated that reactions carried out in confined environments proceed with extraordinary efficiency and selectivity. However, the development of synthetic reaction environments has been very challenging. We have identified bis-urea macrocyclic building blocks that predictably assemble to form porous crystalline materials (Figure 1). It is constructed from molecular units (bis-urea macrocycles) that are readily synthesized from rigid spacers and protected ureas. These macrocycles self-assembly one on top of each other by the urea hydrogen bonding motif and by aryl stacking to give functional materials that depend on the size of the macrocycle. For example, macrocycles that contain no cavity (Figure 1a) assemble to give strong pillars. Macrocycles with sizeable cavities (5-10 Å) assemble to give columns with accessible channels (Figure 1b). These columns subsequently pack together to form porous crystals with aligned one-dimensional channels. The dimensions of the homogeneous channels are controlled by the size of the macrocyclic units, which allows for precise and rational control over cavity dimensions, shape, and functionality. Strong pillars with external functional groups such as basic lone pairs (Figure 1c) afford materials that can expand like clays to accept guests in the flexible binding site in between the pillars. This simple approach is remarkably powerful and can precisely and rationally control the synthesis of functional tubular structures. The goal of our research is to understand and apply this supramolecular assembly strategy to generate homogeneous microporous materials for use as confined environments for a wide range of chemical reactions. Figure 1. The bis-urea macrocycle assembly motif. (a) Macrocycles that lack pores assemble into robust one-dimensional pillars. (b) Macrocycles that contain sizeable cavities give homogeneous channels that can bind guests, can facilitate selective reactions, and can be used to study molecular transport. (c) Macrocycles with exterior groups (red) may expand to absorb guests that contain complementary functional groups. Columns of 3 contain exterior hydrogen bond acceptors that drive the absorption of alcohol guests. (from Acc. Chem. Res. 2014, in press.) We are investigating the utility of functional porous to absorb, transport, and organize guests and to facilitate their subsequent photoreactions. Each hosts is crystallized from a suitable solvent (DMSO, DMF, hot AcOH) and self-assembles into columnar structures. If the host contains a sizeable interior cavity than the interior columns contain the solvent of crystallization (Figure 2a). Heating removes this solvent and the empty hosts can be readily loaded with new guests simply by vapor loading or by soaking directly in the liquid guest or in a solution of the liquid guest (Figure 2b). Hosts 2 , 4 , and 5 show strong preferences for binding polar guests that are matched to the size and shape of their channels. Figure 2. Absorption of guests by porous bis-urea hosts. a) Schematic depiction of the desorption of solvent followed by exposure to a new guest to form a second host:guest complex. b) Loading can be accomplished by soaking the empty host crystals in the neat liquid guest or in a solution that contains the guest or by exposing the host crystals to the guest vapor. The table shows examples of hosts:guest complexes formed by host 2, 4, and 5 . (from Acc. Chem. Res. 2014, in press.) Reactions in confined environments. We are investigating the use of these porous hosts as ‘stoichiometric’ containers in the solid-state to facilitate photoreactions and oxidations as well as examining them as catalysts in solution. This two-fold approach has several advantages. Characterization of the solid-state complexes allows us to probe how confinement in the channel influences the mechanism, product distribution, yield and selectivity for a specific reaction. Photoreactions and oxidations provide controlled model systems to test how effectively we can probe the effects of confinement on reactions. Ultimately, a better understanding of a reaction mechanism aids in the optimization of conditions and in the development of catalysts. Currently, we are examining the effects of binding on the outcome of bimolecular reactions ([2+2]-cycloadditions and singlet oxygen ene reactions). For example, phenylether host 4 has a zig-zag shaped channel (Figure 3a and b) that facilitates the [2+2]-cycloaddition of enone guests such as 3-methyl-2-cyclopentenone and 2-cyclohexenone in high yield and with high selectivity for the exo head-to-tail dimer (Figure 3c). We study the scope and application of these hosts as catalysts, and investigate the use of micro/nanocrystalline host suspensions in solutions for mediating oxidations of alkenes by singlet oxygen. Our goal is to expand to base-catalyzed reactions and polymerizations. Figure 3. Host 4 facilitates [2+2] cycloaddition of enones. a) Schematic of the zig-zag channel of the host. b) Spartan models of 3-methyl-2-cyclopentene loaded in host 4 illustrate the guests bound head to tail. c) UV-irradiation of the host 4•3-methyl-2-cyclopentene complex affords the exo-HT dimer in high conversion and selectivity. d) UV-irradiation of the host 4•2-cyclohexene complex selectively affords the exo -HT dimer. (from Acc. Chem. Res. 2014 , in press.) Effects of molecular confinement on physical properties: The three dimensional structure and orientation of molecules is known to influence their physical properties including their conductivity and optical properties. We are currently investigating the feasibility of loading or synthesizing conjugated polymers within our columnar nanotubes. We will study the effect of this encapsulation on their stability and on their absorptive and emissive properties. 

 Chemistry Outreach Program to K-12 schools

 Dr. Shimizu also runs a program that brings chemists to K-12 classrooms to showcase chemistry and the scientific method. Initiated in 2000, the program connects faculty, post-docs, graduate students and undergraduates with K-12 students and teachers. We visit schools to present experiments that encourage participation and highlight the curriculum standards of 2nd (states of matter, magnets), 5th (mixtures and solutions), 7th (introductory chemistry) and high school chemistry. Each spring, we visit ~ 10 schools giving nearly forty presentations for a thousand students. If you are interested in participating in the program please email Dr. Shimizu directly.

近期论文

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Dawn, S.; Salpage, S. R.; Koscher, B. A.; Bick, A.; Wibowo, A. C.; Pellechia, P. J.; Shimizu, L. S. Applications of a Bis-Urea Phenylethynylene Self-Assembled Nanoreactor for [2+2] Photodimerizations. J. Phys. Chem. A 2014, 118, 10563-10574. DOWNLOAD Shimizu, L. S.; Salpage, S. R.; Korous, A. A. ""Functional Materials from Self-Assembled Bis-urea Macrocycles."" Acc. Chem. Res. 2014, 47, 2116-2127. DOWNLOAD Xu, W. L.; Smith M. D.; Krause, J. A.; Greytak, A. B.; Ma, S.; Read, C. M.; Shimizu, L. S. ""Single Crystal to Single Crystal Polymerization of a Self-Assembled Diacetylene Macrocycle Affords Columnar Polydiacetylenes."" Cryst. Growth Des. 2014, 14, 993-1002. DOWNLOAD Xu, Y.; Xu, W. L.; Smith, M. D.; Shimizu, L. S. “Self-assembly and Ring Opening Metathesis Polymerization of a Bifunctional Carbonate-Stilbene Macrocycle.” RSC Advances 2014, 4, 1675-1682. DOWNLOAD Geer, M. F.; Walla, M. D.; Solntsev, K. M.; Strassert, C. A.; Shimizu, L. S. ""Self-assembled benzophenone bis-urea macrocycles facilitate selective oxidations by singlet oxygen."" J. Org. Chem. 2013, 78, 5568-5578. DOWNLOAD Caricato, M.; Leza, N. J.; Roy, K.; Dondi, D.; Gattuso, G.; Shimizu, L. S.; Van der Griend, D. A.; Pasini, D. ""A chiroptical probe for sensing metal ions in water."" Eur. J. Org. Chem. 2013, 6078-6083. DOWNLOAD Geer, M. F.; Mazzuca, J.; Smith, M. D.; Shimizu, L. S. ""Short strong halogen bonding in co-crystals of pyridyl bis-urea macrocycles and iodo perfluorocarbons."" Cryst. Eng. Comm. 2013, 15, 9923-9929. DOWNLOAD Roy, K.; Wibowo, A. C.; Pellechia, P. J.; Ma, S.; Geer, M. F.; Shimizu, L. S. ""Absorption of hydrogen bond donors by pyridyl bis-urea crystals."" Chem. Mater. 2012, 24, 4773-4781. DOWNLOAD Dawn, S.; Salpage, S. R.; Smith, M. D.; Sharma, S. K.; Shimizu, L. S. ""A trinuclear silver coordination polymer from a bipyridine bis-urea macrocyclic ligand and silver triflate."" Inorg. Chem. Commun. 2012, 15, 88-92 DOWNLOAD Xu, Y.; Shimizu, L. S. (2012). Urea Capsules in The Encyclopedia of Supramolecular Chemistry; Atwood, J. L.; Steed, J. W.; Wallace, K. J, Ed.; Taylor and Francis, CRC Press. 10.1081/E-ESMC-120048280, pp 1-9. DOWNLOAD Geer, M. F.; Shimizu, L. S. “Self-Assembly and Self-Organization” Chapter in Volume 1: Concepts in the series Supramolecular Chemistry From Molecules to Nanomaterials Series Editors: Philip A. Gale, Jonathan, W. Steed, John Wiley & Sons, Ltd. United Kingdom, 2012, 1, 167-180. DOWNLOAD Dawn, S.; Dewal, M. B.; Sobransingh, D.; Paderes, M. C.; Wibowo, A. C.; Smith, M. D.; Krause, J. A.; Pellechia, P. J.; Shimizu, L. S. ""Porous crystals from self-assembled phenylethynylene bis-urea macrocycles facilitate the selective photodimerization of coumarin."" J. Am. Chem. Soc. 2011, 133, 7025-7032. DOWNLOAD Roy, K.; Wang, C.; Smith, M. D.; Dewal, M. B.; Wibowo, A. C.; Brown, J. C.; Ma, S.; Shimizu, L. S. ""Guest induced transformations of assembled pyridyl bis-urea macrocycles."" Chem. Commun. 2011, 47, 277-279. DOWNLOAD Geer, M. F.; Smith, M. D.; Shimizu, L. S. ""A bis-urea naphthalene macrocycle displaying two crystal structures with parallel ureas."" Cryst. Eng. Comm. 2011, 13, 3665-3669. DOWNLOAD Roy, K.; Smith, M. D.; Shimizu, L. S. ""1D Coordination network formed by a cadmium based pyridyl urea helical monomer."" Inorg. Chim. Acta. 2011, 376, 598-604. DOWNLOAD Xu, Y.; Smith, M. D.; Geer, M.; Pellechia, P. J.; Brown, J.; Wibowo, A.; Shimizu, L. S. ""Thermal reaction of a columnar assembled diacetylene macrocycle."" J. Am. Chem. Soc. 2010, 132, 5334-5335. Highlighted by Synfacts 2010, 7, 0775. DOWNLOAD Tian, L.; Wang, C.; Dawn, S.; Smith, M. D.; Krause, J. A.; Shimizu, L. S. “Macrocycles with switchable exo/endo metal binding sites.” J. Am. Chem. Soc. 2009, 131, 17620-17629. DOWNLOAD