US-Africa Collaboration in Guided Inquiry Synthesis and Characterization of the “Frustrated” Amino Acid-Based Calixarene Molecules

The Department of Chemistry at Missouri State University-West Plains (MSU-WP) is internationalizing the existing research activities by initiating a collaborative Kenya-U.S. Chiral Science (chiroscience) project. The overarching goalof the project is three-fold: 1) reinvigorate undergraduate research; 2) augment MSU-WP’s new Green Nanoscience Research and Mentoring Program; and 3) establish synergistic relationships between different research groups and academic institutions in Kenya and MSU-WP. To stimulate students’ interests in the collaborative chiroscience project, we have chosen projects that are not only aligned with NSF’s high priority areas but are also relevant to today’s society (e.g., cancer, tuberculosis, heart disease, HIV, and host-guest chemistry). For several years, our research groups have been working on two important supramolecular hosts, calixarenes and cyclodextrins (CDs). Calixarenes are macrocyclic structures with defined cavities, having host-guest complexation properties similar to CDs. One of the advantages that calixarenes have over naturally occurring host molecules, such as CDs, is that the size of the internal cavity of the macrocycle is more flexible, i.e., the number of constituent rings range from four to eight. This paper illustrates our ongoing efforts in the area of synthesis and complexation properties of calixarenes. Herein, we report the synthesis of new amino acid-based acylcalixarenes and characterization by means of 1H- and 13C-NMR spectroscopy. The calix[4]arenes possess L-alanine, L-valine, L-leucine, and L-isoleucine moeties at the lower rim. 1D and 2D NMR showed that the new calixarenes adopt the standard “cone” conformations in solution.