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Synthetic Confined Environments as Tools for Manipulating Chemical Reactivities and Preparing New Nanostructures

Final Report Summary - CONFINEDCHEM (Synthetic Confined Environments as Tools for Manipulating Chemical Reactivities and Preparing New Nanostructures)

Nature has long inspired chemists with its abilities to stabilize ephemeral chemical species, to perform chemical reactions with impressive rates and selectivities, and to synthesize complex molecules and inorganic nanostructures. What natural systems consistently exploit, and what is yet to be routinely by synthetic chemists, is the aspect of nanoscale confinement. Inspired by Nature, and building on our research group’s studies on light-responsive materials (azobenzene-decorated nanoparticles), we considered the use of nanopores between dynamically self-assembling nanoparticle aggregates as environments for carrying our chemical reactions. We demonstrated that as ultraviolet-light-responsive nanoparticles self-assemble, they could readily trap various molecules from the surrounding solution. Once trapped, these molecules can undergo chemical reactions with increased rates and with stereoselectivities different from those in bulk solution. Visible light could be used to disassemble the nanoparticle aggregates, and additional assembly-disassembly cycles could be performed (Nature Nanotechnology 2016). To achieve further control over the assembly process, we synthesized nanoparticles decorated with a modified azobenzene, which induced self-assembly upon exposure to blue light. This advancement allowed us to selectively control the assembly of two differently sized nanoparticles using different colors of light (Angewandte Chemie 2015). At the same time, we are interested in novel approaches to light-controlled self-assembly of nanomaterials. Here, we showed that it is possible to direct - using light! - the assembly of nanoparticles that are not photoresponsive. This goal was achieved by placing the nanoparticles in photoresponsive media - that is, solutions of small light-responsive molecules. This new approach to nanoparticle self-assembly could also be utilized for trapping various molecules from solution (Nature Chemistry 2015). We are also interested in studying the behavior of chemical species in other types of confined spaces. For example, we have demonstrated efficient trapping of a synthetic photoswitchable molecule within the cavities of several proteins and supramolecular cages (Nature Communications 2018). We were also actively engaged in developing new families featuring the aspect of confinement, such as the recently developed non-close-packed nanoparticle arrays (Science 2017).