Alginate circular dichroism

Fig. 26.—Circular Dichroism of Alginate from the Stipes of Alaria esculenta Gathered at...

Conformational changes are easily followed by optical rotation (Hui and Neukom, 1964). Circular dichroism spectroscopy (CD) of polysaccharides (Morris, 1994) exploits optical anisotropy. In a CD instrumental design, the clockwise and counterclockwise rotation of two polarized beams of equal intensity, traversing a 180° path through a chiroptical medium, display a molar ellipticity maximum and minimum. CD is the differential measurement as a function of X. By CD spectroscopy, mixed interchain association rather than nonspecific incompatibility or exclusion was identified as the molecular basis of alginate-polyguluronate interaction (Thom et al., 1982). 

For polysaccharides with an accessible u.v. chromophore, circular dichroism (c.d.) provides a sensitive index of structure, conformation, and interactions. This is illustrated by the very different c.d. spectra shown (28,29) by the three block types present in alginate, and, as shown below, by the large spectral changes on chelation of calcium ions on specific binding sites around the carboxy chromophore (l4,15) ... 

Another question to be addressed is the status of the protein structure after release from the microspheres. Secondary structure cmi provide a qualitative estimate of function and reflects to some extent biological activity. Protein inactivation by unfolding is one of the major obstacles in drug delivery. For this purpose, analysis of BSA structure by circular dichroism before and after the release from the microspheres was assessed. After release from the emulsan-alginate microspheres, BSA showed some loss in helix content based on the decrease of negative elipcticity at 222 run typical of a-helix (Figure 10). 

Figure 10. Circular dichroism spectra ofBSA after adsorption (continuous line), and before release (dashed line) from emulsan-alginate microspheres.

A short presentation of the electrostatic interactions of acidic polysaccharides with d- and L-enantiomers of polylysine is given. As polysaccharide components pectate and alginates rich in l-guluronate and D-mannuronate, respectively were used. The results of the study by means of circular dichroism showed that the complex formation is governed by the stoichiometric ratio of the charges of both interacting components. The conformation of polysaccharide used for complexation was proved to be the decisive factor influencing the interaction efficiency. 

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