This International Collaboration in Chemistry between US Investigators and their Counterparts Abroad (ICC) project focuses on developing sophisticated supramolecular assemblies and measurements to advance the state of the art in this area of chemistry and nanoscience. Highly ordered cyclodextrin monolayers with short tethers are assembled on metal substrates. These assemblies are used for studies using high-resolution scanning tunneling microscopy (STM) to understand binding of hydrophobic guest molecules with unprecedented detail. Single (supra)molecular studies enable both electronic and chemical investigations of single-guest binding, as well as direct characterization of multivalent binding and active guest molecule patterning and coupling. The Weiss group at UCLA is supported by the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Chemistry Division, with contribution from the Office of International Science and Engineering. The Huskens group at the University of Twente is supported by the Netherlands Organization for Scientific Research (NWO), the partnering international funding agency.
The process of molecular interfacial recognition is central to many important technological and biological processes and phenomena. This work aims to gain a deeper understanding of molecular interfacial recognition which might be relevant for areas as diverse as solar energy conversion and electronics to sensors and biomedical applications. In addition, multivalency is known to be a critical component of activity in biological systems, in particular for cell membrane recognition. Cyclodextrin monolayers function as excellent model systems to address multivalency issues at such membranes. The strong interactive and diverse research environments of this project provides a setting for teaching, training and learning. The extended visits of students to partner laboratories for collaborative work and training provide students with highly valuable international experience.
We collaborated with the group of Prof. Dr. Jurriaan Huskens at the University of Twente to explore host-guest interactions on surfaces. We combined Huskens group expertise with cyclodextrins with Weiss group expertise on self-assembly of adamantanes and other cage molecules. We use scanning tunneling microscopy (STM) to measure structure, function, and spectra simultaneously of assemblies on surfaces with exquisite resolution. The thickness of the cyclodextrins precluded the use of STM, despite a number of attempts to change the linking groups that couple the molecules to the conducting substrate. Other measurement techniques did not have the resolution that we required for these studies. Ultimately, we found another system that enables the study of host-guest interactions. Open-cage carboranethiols and related molecules can be tethered to surfaces and made available for further coordination. They can also be made more conductive through further functionalization. These molecules are synthesized by Prof. Tomáš Baše of the Czech Academy of Science Institute of Inorganic Chemistry. Baše has received funding for synthesizing these molecules for the Weiss group. The Weiss group has applied for (NSF) funding to support this continuing work. We had student exchanges and extended visits from two graduate students from Twente. These visits and this project have catalyzed further interactions between MESA+ at the University of Twente and the California NanoSystems Institute (CNSI) at UCLA, two of the worldâ€™s leading nano centers. Both Huskens and Weiss visited each otherâ€™s laboratories and institutes, met elsewhere at conferences, and will continue to collaborate on the new chemical systems identified.