Spectroscopic studies on the interaction of bilirubin with symmetrical alkyl diamines.

ABSTRACT

The interactions of symmetrical alkyldiamines with bilirubin-IX α have been examined in dichloromethane and dioxane solutions, by visible region difference spectroscopy and florescence methods. In dioxane solutions a clear difference is observed between the complexes of the shorter chain diamines (number of spacer methylene groups (n ≤ 4)) and the longer chain diamines (n ≥ 6). The variations in spectral features with diamine chain length are less pronounced in dichloromethane. The spectroscopic results are consistent with the occurrence of distinct bilirubin conformations depending upon the solvent and the geometry of the interacting receptor. Based on molecular modelling two conformations are proposed. A ‘ridge-tile’ model similar to that observed in crystals is favoured for binding to the longer diamines, while a ‘quasi-cyclic’ structure is preferred for interaction with the short chain diamines.