Biomedical subjects
Publications and source records attributed to Matthew T Stone.
Trends obtained from systematic studies based on chain-length variation have provided valuable insight and understanding into the behavior of m-phenylene ethynylene foldamers. The generalization of this experimental approach, the chain-length dependence test, is useful for studying solution conformation, packing in the solid state, specific intrachain interactions, and the contributions of end groups to a particular property.
Crystallographic analysis revealed that pyridine-palladium complexation is a good geometric match to the m-phenylene ethynylene (mPE) repeat unit and thus could serve as a reversible linking group to join oligomer segments together. A series of pyridine-terminated mPE oligomers were then synthesized and found to coordinate with palladium dichloride to give complexes effectively twice the length of the free oligomers. A quantitative analysis of these coordination equilibria by isothermal calorimetry found the ability of the pyridine end-group to form a coordination complex corresponded with their ability to fold. Oligomers that were able to form complexes of sufficient length to fold showed positive cooperativity based on experimental determination of their association constants with a palladium ion. We suggest that the additional free energy of complexation for the folded oligomers is analogous to chelation by multidentate ligands, but here the "multidentate ligand" is held together by supramolecular rather than covalent bonds.
[structure: see text] A m-phenylene ethynylene oligomer containing a helicene unit was synthesized to bias the twist sense of the folded helical conformation. The CD spectra of the helicene oligomer exhibited large Cotton effects that varied greatly with the solvent composition, including three separate conformational transitions.
[reaction: see text] A water-soluble m-phenylene ethynylene (mPE) foldamer was realized by appending hexaethylene glycol side chains to the backbone repeat unit. UV spectra of the oligomer in aqueous solutions were consistent with a helical conformation. The association constant of the oligomer with (-)-alpha-pinene increased dramatically with increasing water composition, peaking at 90% water by volume in acetonitrile. The rate of the host/guest system's approach to equilibrium was found to decrease considerably with increasing water content.
To investigate the helical conformation of oligo(m-phenylene ethynylene)s, a pair of TEMPO spin labels were appended to the backbone. The two TEMPO radicals were separated by the four, five, and six repeating units. ESR spectra of the labeled oligomers were measured in chloroform and in ethyl acetate solvents in which the oligomers are disordered and folded, respectively. The measurement and analysis of ESR spectra revealed that six repeating units make one helical turn.