Rational design and synthesis of self-assembling dendrons via the retrostructural analysis of their supramolecular dendrimers
ABSTRACT Nature consistently relies on large molecules such as proteins to perform many important chemical functions required for life. The functions of biomacromolecules are determined by their tertiary and quaternary structures. The creation of non-biological macromolecules with biological functions requires understanding of the principles involved in the design of synthetic macromolecules that are able to adopt well-defined tertiary and quaternary structures via the engineering of their primary and secondary structures. This dissertation describes the elaboration of synthetic methods and architectural concepts as well as the understanding of those fundamental principles that govern the formation of complex molecular, macromolecular and supramolecular non-biological systems with biological function. Our investigation employed dendritic building blocks able to self-assembly into cylindrical or spherical supramolecular dendrimers that subsequently self-organize hexagonal columnar or cubic thermotropic lattices. To date we have investigated a library of monodendrons containing second through fifth generation self assembling 3,4,5-trisubstituted, 3,4-disubstituted and 3,5-disubstituted benzyl ether moieties containing four different minidendritic architectural motifs on their periphery. Structural analysis of these monodendrons facilitated the identification of building blocks displaying the following shapes: tapered, half-disk, disklike, conical, half-sphere and spherical. These experiments have confirmed and quantified the prediction that the shape of a monodendron or dendrimer should change by increasing the generation number. In addition, we have demonstrated that the shape of the monodendrons and supramolecular dendrimers is mainly determined by the architecture of the minidendritic building blocks attached to their periphery and their internal units. Also, temperature and core functionality can be used to reversibly interconvert the shape of supramolecular dendrimers. Subsequent investigation involved the first library of monodendrons containing crown-ether moieties at their focal point. Retrostructural analysis of these lattices and of the lattices generated from the corresponding monodendrons containing various other core functionalities by X-ray diffraction provided the first correlation between the molecular structure and the shape of the monodendron, the shape of the supramolecular dendrimer and the symmetry of the lattice. It has been shown that complexation with NaOTf provides the following five different trends: (a) stabilizes the 3-D Pm 3¯ n cubic lattice self-organized from spherical dendrimers that are self-assembled from conical monodendrons; (b) stabilizes the 2-D S A phase generated from parallelepiped monodendrons; (c) has no effect on the stability of the 2-D SB phase generated from parallelepiped monodendrons; (d) stabilizes the 2-D p 6mm hexagonal columnar phase self-organized from cylindrical supramolecular dendrimers that are self-assembled from tapered monodendrons; and (e) destabilized the 2-D p 6mm hexagonal columnar phase self-organized from cylindrical supramolecular dendrimers self-assembled from half-disc monodendrons.