The impact of tether hydrophobicity on stoichiometry of immobilized indicator-analyte complexes

The effect of adding side chains of increasing hydrophobicity to a molecular tether that binds an analytical indicator to a silica gel substrate is described. The hydrophobicity of the side chain is shown to have an impact on the analytical characteristics of the indicator. For the model system studied, increasing the hydrophobicity of the side chain increased the sensitivity of the indicator. The impact of the side chain is interpreted as that of an anchor that inhibits short range movement increasing the proportion of the indicator-analyte complex that is the spectroscopically active mono form as opposed to the bis form of the complex. The hydrophobic side chain inhibits the short range movement normally allowed by a covalent immobilization tether further restricting the area that is readily accessed by the indicator. This attribute appears, in the short term, to inhibit the simultaneous interaction of several indicator molecules with the same analyte species.