Having established that complexes between large organic cations and montmorillonite 
are readily formed raises the question: Does the formation of such complexes change 
the stability of the organic molecules themselves? Ensminger and Gieseking (3) noted 
that protein-montmorillonite complexes prepared for laboratory study showed only a 
slight tendency to putrefy. Subsequent studies (4) demonstrated that the absorption of 
albumen and hemoglobin by montmorillonitic clays interferedwiththe enzymatic hydroly- 
sis of these proteins. Further investigations were conducted by Pinck and coworkers (9) 
on the mechanism and extent of the decomposition of protein-montmorillonite complexes 
by microorganisms. Table I (9,p.117) shows the characteristics of the protein-mont- 
morillonite complexes used and their decomposition. The low-protein complexes, 10 
percent, had a 15 A c-spacing which suggests that the protein between the crystal lattices 
was a mono- layer. Only 20 percent of the protein in these systems was decomposed 
in 4 weeks and the interlayer spacing remained essentially unaffected indicating that the 
protein decomposed was limited to that absorbed on the external surfaces. On the other 
hand, the complexes having 50-percent protein had a 30 A c-spacing suggesting two or: 
more layers of protein betweenthe crystal lattices. These complexes decomposed readily. 
Apparently the proteolytic enzymes were not able to penetrate the layers having only a 
15 A c-spacing, but if the spacing is large enough the enzymes are able to enter and 
decomposition proceeds. 
The adsorption of biologically active substances by clays or soils raises the addi- 
tional question: Has the bioactivity of the molecule been impaired? Studies on anti- 
biotics in soils by Pinck and coworkers (10,11) are of interest in this respect. The 10 
antibiotics used may be conveniently divided into 3 groups based upon their chemical 
and physical properties, namely; strongly basic, amphoteric, and acidic or neutral. The 
strongly basic and amphoteric types formed antibiotic-montmorillonite complexes. The 
former expanded the crystal lattice to 4.4 A and the latter, 7.6 A corresponding to 
mono- and di- layers, respectively. The antimicrobial properties of these complexes 
were measured by bioassay. The complexes containing strongly basic antibiotics ex- 
hibited no antimicrobial properties, whereas complexed amphoteric antibiotics could be 
released from the clay minerals by means of a suitable buffer and thereby regain their 
bactericidal activity. 
The foregoing discussion has dealt with a single absorption reaction, its mechanism, 
and consequences. The unique feature being the expansion of crystal lattices which can 
be closely followed by x-ray defraction techniques. But, many soils contain no mont- 
morillite, and the adsorption of certain organic molecules also occurs. These adsorption 
reactions involve the external surfaces rather than the surfaces of the inner layers of 
crystals, and it has not been possible to define the mechanism or products exactly. 
Complex organic anions do not spread the crystal lattice of montmorillonite, but they 
are strongly adsorbed by the same crystals (12). The adsorption of sodium polymetha- 
crylate is an example, and in this instance an anion exchange reaction was presumed, 
The classifying of soils, in respect to the types of adsorption reactions that they will 
support with organic molecules, appears to be an important prerequisite to predicting 
the fate of pesticides in soils. 
TABLE 1.--Characteristics of protein-montmorillonite complexes and their 
decomposition in 4 weeks (9). 
Protein in ‘complex c-Spacing 
Protein-carbon 
; evolved as COs Before 
decomposition | decomposition 
Percent A. AR 
Gelatin 54.8 82.0 292 WAS 7/ 
Do 10.6 18.4 13560) 14.6 
Egg albumen BBhalss 86.4 30.0 aS 
Do 9.4 17.4 15.4 15.0 
68 
