Synthesis, characterization and biological activity of Schiff bases based on chitosan and arylpyrazole moiety

 
4.1.2. X-Ray diffraction 
Fig. 2 Shows the X-Ray diffraction patterns of chitosan and ChBs. The chitosan sample shows two 
strong peaks at 2θ = 10.1 and 20.4 ° corresponding to the (020) and (110) planes of the crystalline 
lattice with inter-plane distances of 8.8 and 4.6 Å, respectively. This suggests the formation of inter- 
and intra-molecular hydrogen bonds in the presence of free amino groups in chitosan. For ChBs, the 

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peak in the vicinity of 10.1° seems to be disappeared, and the one at 2θ of 20.4◦ became broader 
and less intense, which reflects a more amorphous nature. This is probably due to the deformation 
of the strong hydrogen bond in the chitosan backbone with the substitution of arylpyrazole aldehyde 
on the N-atom of chitosan [48].
For comparison, the crystallinity index (CI) was estimated from the following equation [49]:
Crystallinity index % 


 
 



X 100 (2) 
where I
110
 is the maximum intensity at 2θ = 20.4° and  I
am
 is the intensity of amorphous diffraction 
at 2θ ~ 16° [50]. The calculated CI values were found to be 73.6, 52.8, 31.7, 41.7, 34.3 and 42.2 % 
for Ch, Ch-H, Ch-CH
3
, Ch-OCH
3
, Ch-Cl and Ch-NO
2
, respectively. The change of crystallinity is 
mainly dependent on the degree of formation of Schiff base and to some extent on other factors, 
such as special hindrance, hydrophobic force and π-π stacking [51]. The loss of macromolecular 
organization of ChBs compared with that of chitosan is probably due to the 
disturbing
effect of the 
introduction of bulky arylpyrazole groups and the loss of NH
2
groups and their hydrogen-bond 
aptitude.
Fig. 2.