DNP-supported solid-state NMR studies of 13C,15N,29Si-enriched biosilica of Cyclotella cryptica and Thalassiosira pseudonana

Solid-state NMR spectroscopy represents a powerful method for the investigation of diatom biosilica but detailed studies regarding its chemical composition and structural organization can be prohibited by insufficient spectroscopic sensitivity. Here, we used two-dimensional (2D) Dynamic Nuclear Polarization (DNP)-supported solid-state NMR experiments to obtain information about the molecular composition and supramolecular organization of proteins and carbohydrates in 13C,15N,29Si-labeled biosilica of C. cryptica. As a reference, we conducted DNP experiments on isotope-labeled biosilica of T. pseudonana. DNP-enhancement factors for different NMR signals, and thus, for different organic compounds, provide information about the supramolecular architecture of the biosilica. In addition, DNP-supported heteronuclear nitrogen-carbon correlation experiments allowed us to prove the presence of different structural elements of long chain polyamines (LCPAs) and revealed the occurrence of amine-nitrogen moieties exhibiting a correlation with carbonyl carbons that may indicate cross-linking of LCPAs to proteins as previously seen in studies on proteins extracted from other diatoms.