The reaction between silicic acid and proteins has been studied qualitatively by a number of workers 1 -5. It is now fairly well established that the reaction product is not merely a precipitate obtained through mutual coagulation but is formed as a result of the combination of the silicic acid with the protein. The recent work of Clark and co-workers 6'7 on the reaction of silicic acid with insulin, albumin and nylon monolayers using surface pressure measurements, has provided evidence for the formation of hydrogen bonds between keto-imino groups of the proteins and the -OH groups of the silicic acid. Bergman and Nelson 8 have investigated the binding power of a silica sol for both fibrillar and globular proteins over a wide pH range and have reported data on the stoichiometry of the reaction. More recently, Shvaiger 9 has used the reaction of gelatin with silicic acid for the gravimetric estimation of the latter.
The aim of the present communication is to show that the pH-metric method is of more general application than the methods so far used in investigating the silicic acid-protein reactions. This method not only provides a means of determining the extent of binding but also throws light on the mechanism: of the reaction. For this purpose two proteins, viz. hemoglobin, a protein of physiological importance, and soybean, a protein of high food value, were allowed to react with silicic acid sols at-pH 2.0, 2.5 and 3.0.