Figure 17. Characterization of diatom cell wall and frustule using ssNMR.

(A) SEM images of the diatom showing valve biosilica that have organic threads (white arrows)⁵⁰⁵. Panel A is adapted with permission from references^505,506. Copyright 2018 Frontiers Media S.A and copyright 2011 Springer Nature. (B) DNP-assisted ¹⁵N-edited ¹³C-¹³C PDSD correlation (top) and N(CA)CX experiments (bottom) detecting amino acid signals as mostly in β-sheet conformation in S. turris²²⁰. The structural model contains a 3 nm layer of carbohydrates and proteins covering the 40–80 nm silica domain with LCPAs enclosed. Organic matter and silicon can be detected within (C) whole cell and (D) extracted diatom shells (frustule) as adapted from Tesson et al.⁵⁰⁷. (C) ³¹P NMR detects lipids, glycerol 1,2-cyclic phosphate and polyphosphates, while ²⁹Si data reports Q2, Q3, and Q4 silicon environments. (D) ¹³C ssNMR reporting organic molecules including proteins and carbohydrates. Extracted shells with SDS conserve their overall native structure as seen by SEM⁵⁰⁸. The valve costa (green line), cross-connections (orange lines), areola pore (red circle) and fultoportula (yellow/blue circles, tube-like structures) can be observed. Panel B is adapted with permission from reference²²⁰.Copyright 2015 John Wiley and Sons. Panel C is adapted with permission from reference⁵⁰⁷. Copyright 2008 Springer Nature. Panel D is adapted with permission from reference^507,508. Copyright 2008 Springer Nature and copyright 2019 Springer Nature.