“If we did only teaching and not research, we would still be teaching that the earth was flat. But we would be teaching it very, very well.” – Ivan Light
Our primary research interests are in – Materials Organic Chemistry – and the design and synthesis of new organic materials together with experimental and theoretical analysis of their formation and properties:
Research in our lab focuses on the design, synthesis, and analysis of new organic materials utilizing molecular recognition, self-assembly, dynamic covalent chemistry, and “click” chemistry. By themselves (and especially in combination) these four areas of chemical research have enabled molecules and supramolecules of incredible complexity to be constructed from relatively simple starting materials. The breadth and modularity of these synthetic approaches makes them amenable to address questions and solve problems across multiple chemical, environmental, biological, and materials disciplines. Our interests range from the properties of mechanically interlocked polymers, to the dynamic synthesis of covalent organic polygons and nanoparticles, to the highly efficient synthesis of dendrimers We rely on a variety of tools – NMR and UV-Vis spectroscopies, gel permeation chromatography, differential scanning calorimetry, Atomic Force Microscopy (AFM), light scattering, computational modeling, and others – to understand the formation, structure, and functional properties of the new materials developed in our lab.
Mechanically Interlocked Molecules
Molecules can be connected or associated with each other by a number of different means, with covalent bonds, noncovalent interactions, and metal-ligand coordination being the most common. Mechanical bonds, on the other hand, represent a more “exotic” manner of joining two or more molecules. Catenanes, for example, are molecules composed of two macrocyclic rings looped through each other so that they are mechanically bound and cannot be separated. Developing ways of controlling the positions of two mechanically interlocked molecules relative to each other has allowed interlocked molecules to be developed into a variety of “molecular machines” such as motors, muscles, and switches. Less explored, however, have been mechanically interlocked polymer system. It is expected that mechanically interlocked polymers will have properties that differ from purely covalent polymers. In particular, because monomer units can move relative to each other without breaking the polymer they will likely be more resistant to stress. It is also possible to prepare responsive interlocked polymers whose properties change with external stimuli. The synthesis of mechanically interlocked polymers is very modular, and small variations in their structure may generate many different polymers with widely varying properties. A variety of molecular recognition motifs and self-assembling systems are also being studied en route to the synthesis of mechanically interlocked polymers.
Covalent Organic Polygons and Nanoparticles
The condensation of boronic acids with organic diols provides an efficient and versatile route to boronate esters. This synthetic protocol has been applied to the dynamic assembly of covalent organic frameworks (COFs) and complex macrocycles and cage compounds. In our lab we prepare fairly simple boronic acids and organic diols, which we can then condense to form structures such as covalent organic polygons and synthetic nanoparticles. The judicious design of target molecules allows for a range of organic polygons and nanoparticles of well-defined shapes, sizes, and geometries to be synthesized. These structures are not only interesting themselves but they also have the potential to be self-assembled onto solid substrates. The conformations and stability of their surface monolayers can be investigated using scanning probe microscopy techniques such as AFM and STM. Covalent organic polygons may ultimately be used to pattern and systematically functionalize solid substrates for the purposes of developing hybrid solid-organic materials.
Dendrimers are highly branched, globular macromolecules that have shown considerable promise in biomedical applications ranging from carriers for drug and gene delivery, diagnostic tools for in vivo imaging, and as scaffolds for tissue repair. Several key characteristics of dendrimers – their core-shell architecture, surface multivalency, globular structure, well-defined molecular weight, monodispersity, and their ability to have their biocompatibility and pharmacokinetics tuned through synthetic design – make them superior to liposomes and polymers that are currently being used in drug delivery applications. Despite their considerable advantages, dendrimers suffer from time consuming, multi-step synthetic protocols often involving laborious purification methods and the generation of significant waste from unreacted starting material, side products, and imperfect conversion. Before dendrimers can be fully explored and put into practice addressing areas of human health and disease it is imperative that new, highly efficient methods for synthesizing biocompatible dendrimers be developed. We are currently developing such routes to biocompatible dendrimers in order to address the synthetic limitations that are currently impeding the full development of dendrimers in biomedical applications.