X-Ray Diffraction, Electron Microscopy, Electrophoretic Mobility, and pH of some Stable Smectite-Protein Complexes1
- Robert D. Harter and
- G. Stotzky2
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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