Biominerals are hybrid materials consisting of organic and inorganic constituents. Understanding the molecular structure of the interface between organic and inorganic constituents of biominerals is a main goal in biomineralization research. The interactions between organic and inorganic components are assumed to be of key importance for the formation of the remarkable structures of biominerals as well as their outstanding materials properties. Solid-state NMR spectroscopy is very well suited to investigate the organic-inorganic interface in biominerals as it allows for the detection of local interactions such as the magnetic dipole-dipole interaction which are strongly distance-dependent. This project aims to study of the structure and formation of the organic-inorganic interface as well as the characterization of the intermolecular interactions at this interface. The investigations will be performed following two routes: (i) Spectroscopic investigations of the intact, extracted diatom cell walls (isotope-labeled with 13C, 15N and 29Si) to identify the biomolecules that are located at the interface, and determine their types of interaction (Covalent bonding or not?). (ii) In vitro studies of organic matrices, their interactions with long-chain polyamines (LCPA) and their mineralization activities using 29Si-labeled silicic acid under physiologically relevant conditions. These studies are expected to answer a variety of key questions in silica biomineralization research including a molecular understanding of the interaction between insoluble organic matrices and soluble biomolecules, and the molecular mechanism through which they influence the silica polycondensation process. Analysis of such reconstituted in vitro systems is indispensable for elucidating the interactions and mechanism that are in operation during silica biomineralization in the living diatom cell.