X‐Ray Diffraction, Electron Microscopy, Electrophoretic Mobility, and pH of some Stable Smectite‐Protein Complexes

X‐ray diffractometry, electron microscopy, electrophoretic mobility, and pH measurements have been used in an attempt to understand the mechanisms involved in the formation of stable clay‐protein complexes. Pepsin was apparently adsorbed to positive edge sites on the smectite, and all other proteins were adsorbed on planar surfaces. Casein, chymotrypsin, lysozyme, and ovomucoid intercalated the H and Na‐smectites, and catalase may have intercalated the H‐smectite. All proteins, except catalase, appeared to intercalate the clays when the weight ratio of protein‐to‐clay exceeded about 1:5. Catalase did not appear to intercalate the Ca, Al, La, or Th‐smectites, even though the ratio of adsorbed protein‐to‐clay exceeded 1:5. The electrophoretic mobility of the H, Na, and Th‐smectites became less negative upon adsorption of proteins, indicating a physical or chemical covering of the negative clay surface charge and a flocculation of the complex. When protein was adsorbed by Ca, Al, and La‐smectites they either showed little change or increased in electrophoretic mobility, indicating a tendency for clay tactoids to be broken. The pH of all protein‐clay complexes tended to approach neutrality. In the acid clays (H, Al, and Th‐smectite), especially, this indicated a cation exchange reaction, since the exchanged inorganic ions would be subsequently removed from the clay.