| AVS 60th International Symposium and Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+AS+NS+SP-WeA |
| Session: | Single Molecules at Surfaces: Structure and Dynamics |
| Presenter: | J. Olson, Florida Institute of Technology |
| Authors: | J. Olson, Florida Institute of Technology J.C. Baum, Florida Institute of Technology M. Novak, Florida Institute of Technology K. Sriraman, Florida Institute of Technology |
| Correspondent: | Click to Email |
Tryptanthrins represent a class of compounds of interest for their anti-parasitic properties. Particularly, they have shown in-vitro efficacy versus organisms that cause malaria, leishmania, trypanosomiasis, tuberculosis, and fungal infections. However, little is known of their mode(s) of action at the molecular level. To investigate their geometric and electronic behavior, STM has been used to observe molecular monolayers of these compounds. Sub-molecular resolution has allowed the direct observation of individual lobes of the HOMO and LUMO states. The parent compound forms rows that alternate in contrast (light/dark), which is attributed to adsorption-induced stereoisomerization, with each row comprised of one enantiomer. Also excellent lobe-to-lobe resolution is observed for the LUMO of the parent compound as well as the HOMO of 8-fluorotryptanthrin (which similarly displays adsorption-induced stereoisomerization). Additionally, the authors have undertaken measurements of the tunneling barriers of these molecules, with a quantitative structure-activity relationship (QSAR) correlation as the goal. Sub-molecular quantitative measurements of the tunneling barriers have been accomplished for the parent compound, and show an interesting correlation to its known chemistry. Also, preliminary correlations of biological efficacy and molecular barrier heights have been observed over several analogs. Generally speaking, increased anti-parasitic efficacy corresponds to lower measured barrier heights, which is consistent with a possible tunneling mechanism.