Study of the forces responsible for binding of polar substrates in the cyclohexaamylose cavity by positron annihilation techniques

The complex formation constants for a series of inclusion complexes of p-, m-, and o-nitrophenol and p-, m-, and o-nitrobenzyl alcohol with cyclohexaamylose were determined by positron annihilation techniques. The formation constants, K/sub c/, were found to be 341, 54, 8, 28, 25, and 9 M-1, respectively. The results seem to suggest that hydrogen bonding and/or London dispersion forces are mainly responsible for the binding of these guest molecules in the cyclohexaamylose cavity, while hydrophobic interactions play only a minor role in these systems. In the ortho isomers, complex stability is greatly reduced due to steric hindrance. 1 table