Adsorption of salivary proteins onto Ca apatites

The adsorption of small molecules such as amino‐acids, and even large molecules such as the acidic proline‐rich salivary proteins onto calcium apatites, is well described‐ by the Langmuir isotherm when only one adsorbate is present in solution. Apparent anomalies in the adsorption parameters are not consistent with a simple electrostatic model for adsorption of polar molecules onto apatites. The thermodynamics of adsorption indicates that the process is endothermic; consequently, the driving force for adsorption is entropic. The increase in entropy probably arises from changes in the secondary structure of the proteins and displacement of water molecules from the adsorbent and the adsórbate upon adsorption. Marked changes (in the amide I region) were observed between the FTIR spectra of the PRP in solution and in the adsorbed state consistent with significant changes in their beta‐sheet and beta‐turn contents upon adsorption. The extension of the Langmuirian model to binary and ternary mixtures was inadequate to describe experimental adsorption results from these systems. A model based on the equilibrium conditions in polycomponent systems describes very well the adsorption behaviour of binary mixtures. This thermodynamic model was successfully extended to ternary mixtures of salivary proteins.

Key words:

• Adsorption
• apatites
• proteins

Notes

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