Education

B.A., 1990, Wellesley College
Ph.D., 1997, Massachusetts Institute of Technology

Honors and Awards

2021 SC Governor’s Award for Scientific Awareness, Fulbright Scholar Award, 2017-2018 to Austria; Michael J. Mungo Undergraduate Teaching Award, 2016; SC ACS Volunteer of the Year, 2014;  ACS Women Chemists Committee Rising Star Award, 2013;  USC Breakthrough Rising Star, 2011.

Research

Research Summary: 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.

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.

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.

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:

Professor 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 Prof. Shimizu directly.

Selected Publications

1. Islam, Md. Faizul; Adame-Ramirez, Emely; Williams, Eric; Kittikhunnatham, Preecha, Smith, Mark, D.; Pellechia, Perry J.; Greytak, Andrew B.; Shimizu, Linda S.* Assembled triphenylamine bis-urea macrocycles employed as confined environments for polymerization of pyrrole or ethylenedioxythiophene, Macromolecules. 2022, 55, 11013-11022. https://doi.org/10.1021/acs.macromol.2c02042.
2. Helmers, Ingo; Hossain, Muhammad S.; Bäumer, Niles; Wesarg, Paul, Soberats, Bartolome; Shimizu, Linda S.*; Fernández, Gustavo* Anti-cooperative Self-Assembly with maintained Emissions Regulated by Conformational and Steric Effects. Angew.Chem. Int. Ed. 2022 61 (17), e202200390. https://doi.org/10.1002/anie.202200390
3. Hossain, Muhammad Saddam; Ahmed, Fiaz, Karakalos, Stavros G.; Smith, Mark, D.; Garashchuk, Sophya; Greytak, Andrew B.; Docampo, Pablo; Shimizu, Linda S.* Structure Property Investigations in Urea Tethered Iodinated Triphenylamines. Phys. Chem. Chem. Phys. 2022, 24, 18729-18737.  https://doi.org/10.1039/D2CP01856J
4. Goodlett, Dustin W.; Sindt, Ammon J.; Islam, Md Faizul.; Smith, Mark D.; Shimizu, Linda S.* Selective Loading of Xylene Constitutional Isomers in a Self-Assembled Triphenylamine bis-Urea Macrocycle Host.Cryst.Growth Des. 2022, 22, 1017-1023. https://doi.org/10.1021/acs.cgd.1c00846.
5. Islam, Md. Faizul; Sindt, Ammon J.; Hossain, Muhammad Saddam; Ayare, Pooja, J.; Smith, Mark D.; Vannucci, Aaron K.; Garashchuk, Sophya; Shimizu, Linda S.* Assembled triphenylamine bis-urea macrocycles: Exploring photodriven electron transfer from host to guests. Phys.Chem. Chem. Phys., 2021 23, 23952-23960. https://doi.org/10.1039/D1CP03000K