Water-Soluble Deep-Cavity Cavitands: Synthesis, Molecular Recognition, and Interactions with Phospholipid Membranes
Date of Award
Gibb, Bruce C.
Water-soluble deep-cavity cavitands provide a rare opportunity to study self-assembly driven by the hydrophobic effect. These molecular hosts dimerize in the presence of certain guest molecules to form water-soluble molecular capsules. These systems have given rise to numerous novel chemical phenomena and have potential use in drug delivery. The host octaacid (OA) has been particularly well-characterized, but studies are limited to basic pH because of limited host solubility.
Herein we report an improved synthesis of OA and the syntheses of three new water-soluble deep-cavity cavitands. The new hosts are soluble at neutral pH, increasing relevance for biological studies. The new syntheses are versatile enough to apply to the synthesis of additional water- soluble cavitands in the future. We also describe preliminary characterization of the molecular recognition properties of the new hosts. Binding of organic guest molecules to form 1:1 host:guest complexes and 2:1 host:guest capsules was qualitatively similar to that of OA. However, binding of anions spanning the Hofmeister series revealed interesting new behavior. The new hosts bound a wider range of anions inside the hydrophobic pocket with much higher association constants. Moreover, external binding of several anions to the cavitand pendant feet was observed.
Looking towards biological applications, we desired to learn how these molecules interact with phospholipid membranes. Six water-soluble cavitands were tested for their ability to permeabilize liposomal POPC membranes. One host showed very high potency in permeabilizing membranes, while three other hosts showed moderate activity. Host binding of POPC was found to be at least one factor in host-induced permeabilization. A requenching assay to determine leakage mechanism strongly supported all-or-none leakage, whereby some vesicles lose all contents while others lose none. These results suggest that these cavitands induce partial transient leakage of vesicles by the formation of transient membrane pores. These findings show potential for the use of these hosts as drug delivery carriers, antimicrobial compounds, and tools in membrane alteration studies.
Ioup, Sarah E., "Water-Soluble Deep-Cavity Cavitands: Synthesis, Molecular Recognition, and Interactions with Phospholipid Membranes" (2012). University of New Orleans Theses and Dissertations. 1572.
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