Structural and theoretical-experimental physicochemical study of trimethoprim/randomly methylated-β-cyclodextrin binary system.

Here we report the structural characterization, physicochemical study and molecular modeling of the inclusion complex of trimethoprim in randomly methylated beta-cyclodextrin. The phase-solubility diagram obtained at pH 7.0 exhibited a linear behavior for the RAMEB concentrations studied suggesting a 1:1 stoichiometry and absence of aggregation in solution. From stoichiometric determination by the continuous variation method we confirmed a 1:1 stoichiometry. To make a detailed characterization of the inclusion mode, spectroscopic measurements by infrared and 1D and 2D (1)H NMR spectroscopy provided evidence that the inclusion mode is characterized by inclusion of the trimethoxyphenyl ring in the cavity; interactions with methyl groups located in the border of the cavity were also detected. The structure proposed was also confirmed by semiempirical molecular modeling.