Synthesis of novel water-soluble host-guest systems
Description
In an effort to construct and study aqueous supramolecular assemblies that mimick those of nature (proteins and viral capsids), a novel, water-soluble deep-cavity cavitand has been synthesized – tetra-exo-methyl octa-acid (TEXMOA). In addition, water-soluble cavitand tetra-exo-carboxy tetra-acid (TECTA) was synthesized as an anti-dimerization host to further explore the binding properties of a monomeric host-guest system. The synthetic processes are investigated and discussed in this dissertation. Driven by hydrophobic effect, long-chain alkane guests bind strongly to the pocket of TEMOA in aqueous media. Initial NMR studies suggest that the steric hindrance induced from the exo-methyl groups of TEXMOA is responsible for a non-monotonic assembly profile toward the guests (from monomeric to dimeric and mixture of both in some cases). The synthesis of TECTA required direct ortho metalation and careful purification steps. However, the host still displayed the binding properties as intended, since the carboxylate groups of TECTA in the exo position prevented capsule formation with various aliphatic guests in water. Based on previous findings, modified 1-adamantanoic acids were expected to be potential strong-binding guests for these hosts. Therefore, chloro-, bromo, and iodo-substituted adamantanoic acids were synthesized in order to expand the library of guest molecules. The Z-isomer of these halogenated adamantanoic acids were synthesized from the Z-2-hydroxy-5-adamantanoic acids with the corresponding mineral acids, and these reactions were found to be stereoselective. The amine-footed meta-basket was also synthesized as a potential detection ligand in biosensors via SPR (surface plasmon resonance). The synthesis of the host utilized a modified Staudinger reaction from the azido- precursor.