Fig. 3.

Hierarchical order of intricacy associated with the structural analysis of materials, in terms of polydispersity and molecular heterogeneity (see the main text). The structures (connectivities and stereochemistry) of monodisperse molecules are readily accessible (provided that sufficient amounts of the material are available) by organic structural spectroscopy [7–9]. Supramolecular structures [10–12] require an adequate definition of the covalently bonded molecules and of their noncovalent interactions [13–16]. The structural analysis of nonrepetitive complex unknowns, which feature substantial levels of both polydispersity and molecular heterogeneity [17, 18], is most demanding in terms of methodology and concepts [19–22]. Any highly resolved three-dimensional structure of a monodisperse biomolecule is based on a precise description of the unique chemical environment of any single atom [23, 24]. Currently, the molecular-level structural analysis of complex systems is primarily focused on covalent bond definition. Future high-quality structural analyses of these materials will have to assess both the (classes of) individual molecules and their interaction mechanisms [25]