Contribution of multi-nuclear solid state NMR to the characterization of the Thalassiosira pseudonana diatom cell wall.

ABSTRACT

A major issue in the study of biosilicification processes is the harsh chemical conditions required for silica dissolution, which often lead to denaturation of the associated bio-organic matter. In order to demonstrate the potential of solid state NMR for investigating silicified materials of natural origin, this technique was applied to isotopically enriched Thalassiosira pseudonana diatom cells. (29)Si, (1)H,(31)P, (13)C and (15)N solid state NMR studies were performed on whole cells, SDS-extracted and H(2)O(2)-cleaned silica shells. Cross-polarization techniques were useful for identifying the presence of mobile and rigid molecules, allowing loosely bound and silica-entrapped species to be discriminated. Successive cleaning procedures efficiently eliminated weakly associated organic matter. The H(2)O(2)-cleaned silica shell still contained carbohydrates (mainly chitin) and proteins as well as lipids. This suggests that the role of lipids in diatom shell formation may have been underestimated so far, demonstrating the potential of solid state NMR for studying composite biomaterials.