Solid-state 29Si MAS NMR studies of diatoms: structural characterization of biosilica deposits

Four different diatom species (Chaetoceros debilis, Chaetoceros didymum, Cylindrotheca fusiformis, Nitzschia angularis) were studied by solid-state 29Si MAS NMR spectroscopy. To determine the Q2:Q3:Q4 ratios in the biosilica deposits of the diatoms, quantitative 29Si MAS NMR experiments were performed. This analysis did not reveal any differences regarding the molecular architecture of the silica (i.e. the degree of condensation of the SiOH units (2 ≡SiOH → ≡Si–O–Si≡ + H2O)) from the different diatom species. However, complete cells showed significantly smaller Q4:Q3 ratios (1.8–1.9) than extracted cell walls (2.5–2.8), indicating the existence of intracellular pools of less condensed silica.