Our next webinar will take place via the internet on Tuesday November 2nd at 11 AM EDT/ 3 PM GMT (please note the daylight savings time change). Sign up on our mailing list to receive the Zoom link!
We hope to see/hear from you all at one of our sessions or as one of the next speakers. If you are an early career scientist and would like to present your research, don't hesitate to submit an abstract today! For now, please learn more about our current speakers and their research below. We also thank the generous support from Cell Reports Physical Science, Merck, and the Royal Society of Chemistry.
Our featured speakers this week are Ho Fung (Edmund) Cheng (graduate student, Northwestern University, USA), and Tyler Collins (graduate student, Purdue University, USA).
LEARN MORE ABOUT THE SPEAKERS AND THEIR TALKS BELOW
HO FUNG (EDMUND) CHENG (on Twitter @edmundhfc)
Biography: Ho Fung (Edmund) is a sixth-year Ph.D. candidate in chemistry at Northwestern University. Born in Hong Kong, Edmund received his master’s degree in chemistry from the University of Oxford in 2016. Edmund is interested in macromolecular and supramolecular architectures that can endow materials with unconventional structures, properties, or functions. In his graduate research in the Mirkin group, Edmund develops dynamic and switchable nanoparticle assemblies and metal complexes with molecular precision. Outside of research, Edmund is learning to be a dad to his two-month-old, his cat, and his plants.
Title of Talk: Nanoparticle Superlattices Through Template-Encoded DNA Dendrimers
Abstract: The chemical interactions used to create hierarchical structures are often complex and difficult to program. Developing nanoscale building blocks capable of dynamic and sequence-defined interactions enables nanoparticle assemblies with novel structure types and provides important insights as to how hierarchical architectures arise in natural and synthetic systems. In this talk, I will discuss the synthesis of a series of nanoparticle superlattices based upon structurally reconfigurable DNA dendrimers, each of which presents a well-defined number of single-stranded oligonucleotides (i.e., sticky ends) on their surface. These DNA dendrimers assemble with complementary DNA-functionalized gold nanoparticles (AuNPs) to yield five distinct crystal structures dependent upon dendrimer architecture. We discovered that these DNA dendrimers can associate to form micelle-dendrimers, whereby the extent of association can be modulated through changing surfactant concentration and dendrimer length. This template-encoded method enables the formation of a low-symmetry superlattice with a Ti5Ga4-type structure, which has yet to be reported in the field of colloidal crystal engineering. Taken together, colloidal crystals that feature three different types of particle bonding interactions – template-dendron, dendrimer-dendrimer, and DNA-modified AuNP-dendrimer – are reported, illustrating how sequence-defined recognition and dynamic association can be combined to yield complex hierarchical materials.
TYLER COLLINS (on Twitter @TCollins_26)
Biography: I am a fifth year PhD Candidate at Purdue University where I work with Dr. Suzanne C. Bart. I am working on the synthesis of uranyl imido and high-valent uranium multiple imido complexes. I received my undergraduate degree in chemistry from Michigan State University, while there I worked with Dr. James K. McCusker on the synthesis of iron(II) bipyridyl complexes.
Title of Talk: Origin of Bond Elongation in a Uranium(IV) cis-bis(imido)
Abstract: Efficient chemical processing of spent nuclear fuels represents a major hurdle in the nuclear fuel cycle, as strong actinide-element multiple bonds prevent conversion to useful materials. These bonds can be weakened in systems that are electron- rich or sterically saturated. Herein, activation of uranium-nitrogen multiple bonds in an imido analogue of the uranyl ion is accomplished with these strategies. Treating the uranium(VI) trans-bis(imido), UI2(NDIPP)2(THF)3 (DIPP=2,6-diisopropylphenyl), with tert-butyl(dimethylsilyl)amide (NTSA) results in reduction and rearrangement to form the uranium(IV) cis-bis(imido), [U(NDIPP)2(NTSA)2]K2. This compound features long U-N bonds, pointing towards substantial activation of the N=U=N unit, as determined by X-ray crystallography, 1H NMR, infrared, and electronic absorption spectroscopies. Computational analyses show that the U(IV)-imido bonds are significantly weakened multiple bonds due to polarization towards antibonding and non-bonding orbitals.