The interaction of silicic acid with protein monolayers: Effect of pH and ionic strength of substrate

Abstract The existence of a silicic-protein interaction is proved by comparing the compression and decompression isotherms of gelatin and collagen monolayers spread on silicic substrates with those obtained on silica-free substrates. This interaction took place in a pH range 2–8. with a maximum at pH 6.8 in the case of gelatin and 5.0 for collagen. The fact that poly-DL-alanine also interacts with polysilicic acid seems to confirm that the interaction is due to the formation of hydrogen bonds between the silanol (SiOH) groups of polymerized silicic acid and the carboxyl, amino and ketoimino groups of the protein. Polysilicic acid also interacts with human serum albumin monolayers and the intensity of this interaction increases as the ionic strength (μ) of the substrate is increased. Also in the case of poly- dl -alanine, the greater the ionic strength of the substrate the more intense the interaction, but here the ionic strength plays an even more fundamental role, since μ must be 0.5 or greater for the interaction to take place at all.