Naphthyridine-Based Helical Foldamers and Macrocycles:  Synthesis, Cation Binding, and Supramolecular Assemblies

Abstract

Unraveling the factors that control the conformation of molecular chains is of great interest both for understanding the shape of biological molecular strands and for designing artificial ones that adopt desired forms. Thus, a variety of artificial folding codons have been identified that enforce the formation, among others, of helices, strands, and loops, the major emphasis being on the shape of the foldamer. We report herein the synthesis and study of a family of foldamers and macrocycles based on the 1,8-naphthyridine and pyrimidine units, whose internal cavity is large enough to accommodate ionic substrates, and focus on the impact of guest binding within a cylindrical environment. Interestingly, the binding event within these large oligomers is translated to the outside of the receptors and affects the interaction of the overall complexes with the outside world. For instance, alkali cations bind to the one-turn helices and macrocycles to promote fibril formation and aggregation. Also, polyammonium substrates are able to tune the length of the overall helix assemblies and the rigidity of long oligomers. The reported data on one-turn, two-turn helices and macrocycles not only allows one to devise a model for the ion-controlled supramolecular assembly of such systems but also provides evidence that such controlled scaffolds bear promise in the design of complex systems.

Molecular Recognition with Linear Molecules as Receptors

“…CD data of two-turn helicate 46b in the presence of the chiral guests were also investigated (Fig. 25), which also confirmed this rationale [82]. The monoamine 48a led to a slight chiral induction with a very weak signal, probably because this substrate was too short to force a strong organization of the whole strand of 46b.…”

“…(26). Models for the pseudorotanxane-styled supramolecular oligomers between 46 and 47 and chiral 48 (the curved arrow indicates chirality transfer) [81,82]. bonds and therefore should have many different conformers.…”

Hierarchical Formation of Fibrillar and Lamellar Self‐Assemblies from Guanosine‐Based Motifs

“…Structural observation of self-assembled system can easily be achieved by TEM approaches, as widely used and described in the literature [65, 66]. …”

Metal-containing nanofibers via coordination chemistry

“…Lehn and co-workers obtained nanofibers from macrocycle 7 (Fig. 8) through K + ioninduced assembly [43]. The central cavity of macrocycle 7, which has three 1,8-naphthyridine groups with the lone pairs on the nitrogen atoms directed inwards, resembles that of an aza-crown and thus was expected to bind K + ions in solution (Fig.…”

“…Kimizuka and co-workers have also prepared a family of one-dimensional halogen-bridged, mixed valence Pt complexes from [Pt(en) 2 ][PtCl 2 (en) 2 ](ClO 4 ) 4 with lipid counteranions (36)(37)(38)(39)(40)(41)(42)(43)Fig. 38) The lipid counteranions and solvents not only influence the color of the Pt complexes, but also the morphology of the superstructures of the coordination polymers.…”