Adamantan-1-ylamine and adamantan-1-ylamine hydrochloride complexes with cycloamyloses

Abstract

Using both pH potentiometry and spectrophotometry, aqueous complex formation constants have been measured over a range of temperatures for both cyclohexa-amylose (α-cyclodextrin) and cycloheptaamylose (β-cyclodextrin) with substrates amantadine (adamantan-1-ylamine) and amantadine hydrochloride. Both forms of cycloamylose complex with either amantadine or the hydrochloride with 1:1 stoicheiometry and cyclohexa-amylose complexes with amantadine with 2:1 stoicheiometry also. The formation constants for the cyclohepta-amylose adducts are unusually strong, ca. 1 × 10⁵ and 1 × 10⁴ for amantadine and the hydrochloride, respectively. Enthalpies and entropies of formation are estimated for each complex from the temperature dependence of the equilibrium constants. These ΔH° and ΔS° values together with measurements of ¹³C n.m.r. chemical shift displacements of carbons on both host and substrate species lead to speculation about the structures and binding mechanisms of the complexes. The spectrophotometric experiments also yielded complex formation constants of both cycloamyloses with acidic and basic forms of the indicator Methyl Orange. ΔH° and ΔS° values of these complexes are also calculated.