238 



MACROMOLECULAR COMPLEXES 



y 



."-7^'- 





/ ; 

 ' I / / / 



/ / / / •' 



.^^^ 



7^^ 



-y^ 



7^ 



/ 



/ 



^-^ 



-7^ 



7^ 



7^ 



7^^^ 



J-> 



7^ 



■7^ 





;^ 



/ / 



/ / / 





Fig. 6. Diagrammatic representation of a cellulose microfibril in transverse 

 section. Oblique solid lines, projection of polyglucose chains; oblique broken 

 lines, projection of chains containing sugars other than glucose. The central 

 lattice represents the crystalline core, and the longer edges of the core are 

 parallel to the planes of 6.1 -A spacing. 



When celluloses are immersed in solutions of salts of heavy 

 metals, the cation is rapidly adsorbed according to a Langmuir 

 isotherm (Belford and Preston, 1959; Belford et ah, 1958; Belford 

 et al., 1957, 1959). Parallel bundles of the microfibrils then yield 

 one of two electron-diffraction diagrams, of which one is illustrated 

 in Fig. 7. This is quite different from the diagram yielded by cellu- 

 lose alone (Fig. 5) and has been interpreted as arising from a two- 

 dimensional array of heavy metal ions (Fig. 8). The diagram, and 

 therefore the lattice producing it, is the same whatever metal is 

 used and whatever the source of the cellulose. Two txpes of array 

 have been calculated, defined by the parameters: 



Type I p = 6.15 A, q = 7.05 A, = 90° 



Type II p = 7.32 A, q = 5.68 A, <f> = 87°-90° (variable) 



which explain quantitatively the positions of all the arcs in the 

 diagrams. These parameters do not correspond to those in crystals 

 of the metals, in any metal salt, or in cellulose ( see spacings quoted 

 on p. 235). Since the only surfaces available for adsorption are those 

 of the microfibrils, this two-dimensional array must lie on these sur- 

 faces, and the mutual arrangement of the ions must be governed 

 by the surface. The only possible inference seems to be that the 

 molecular chains lying on the surface of the microfibrils are folded 

 in one of two wavs, bringing points of attraction into a lattice de- 



