Solubilities of Water-Insoluble Dyes in Internal Water of Swollen Sephadex Gels

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Abstract
It was found that internal water of swollen Sephadex gels could dissolve appreciable amounts of water-insoluble dyes, azobenzene (AB) and dimethylaminoazobenzene (DMAB). The solubilities of AB and DMAB increased exponentially with the concentration of dextran chain in swollen Sephadex gels, i.e., plots of solubility (CG) vs. dextran-chain concentration (Cf) were well described by a family of quartic regression curves (CG=kcf4+C0, k and C0 being constants). The thermodynamic parameters pertaining to the transfer of the dyes from external water to internal water indicate that in water extensively hydrated by gel matrices, “iceberg” formation is markedly hindered and hence the hydrophobic free energy is correspondingly reduced, thereby increasing the solubilities of hydrophobic dyes. Since the solubilities of the dyes are proportional to the fourth power of the dextran-chain concentration in swollen Sephadex gels, it can be assumed that the dyes are accommodated in cooperatively hydrated water contained in unit cells made up of four dextran chains.

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