Noncovalent Synthesis of Self-Assembled Nanotubes through Decoupled Hierarchical Cooperative Processes

Abstract

Due to their wide number of biological functions and potential applications, self-assembled nanotubes constitute highly relevant targets in noncovalent synthesis. Herein, we introduce a novel approach to produce supramolecular nanotubes with defined inner and outer diameters from rigid rod-like monomers programmed with complementary nucleobases through two distinct, decoupled cooperative process of different hierarchy and acting in orthogonal directions: chelate cooperativity, responsible for the formation of robust Watson-Crick H-bonded cyclic tetramers, and nucleation-growth cooperative polymerization.

Nanostructured Micelle Nanotubes Self‐Assembled from Dinucleobase Monomers in Water

“…In all cases, the presence of longitudinal objects was observed. Width dimensions obtained by TEM (Figure c–e; Supporting Information, Figure S2F–I), between 3 and 5 nm, matched rather well the outer diameter expected in our nanotube models (Figure f; Supporting Information, Figure S2N) and the dimensions of related lipophilic systems . AFM profiles (Supporting Information, Figure S2E) showed nonetheless smaller height values, between 2 and 4 nm, which could be the result of the compression of side‐ chains by the force applied by the AFM probe, and by the affinity of the assemblies for the surface.…”

“…However, at intermediate V THF , aggregated species can be detected in slow NMR exchange with the monomer that show typical 1 H signals for G:C pairing, with H‐bonded G‐amide and C‐amine protons at around 13.0 and 9.5 ppm. Although this result resembles what we observed along the cyclotetramerization process of related molecules in organic solvents, we cannot really assign the new set of NMR signals to discrete c (GC2) 4 cyclic tetramers, since they are too broad and principally because fluorescence quenching, mainly attributable to stacked species, is quite pronounced within this intermediate V THF =0.3–0.1 range (see Figure h). Instead, this picture is consistent with the formation of small aggregates by G:C H‐bonding and stacking interactions that then grow as the water content is increased.…”

“…Such association process can be monitored by: 1) the recovery of the original CD signal, displaying a negative Cotton effect (Figures a,d); 2) the growth of a red‐shifted absorption band at 418 nm (Figures b,e); and 3) a notable red‐shift (from 434 to 488 nm) and decrease in emission intensity (Figures c,f). It should be remarked that these spectral changes are very similar to the ones recorded along the cyclization and polymerization processes of related lipophilic dinucleobase monomers in organic solvents, which preliminarily suggests that the GC2 assemblies are constituted by the corresponding c (GC2) 4 cyclic units.…”

“…On the other hand, the tubular nature of the GC2 assemblies was confirmed in stained samples measured by TEM (Figure c,d; Supporting Information, Figure S2F), in which nanotube walls presented darker contrast. In all cases, and in analogy with their lipophilic version, the nanotubes displayed a large tendency to organize in aligned bundles, independently of sample preparation and experimental conditions.…”

1D to 2D Self Assembly of Cyclic Peptides

“…Since the early years of supramolecular chemistry, artificial molecular designs have been extensively studied to mimic the hierarchical assembly of proteins with controlled topology. [2][3][4][5][6][7][8][9][10] Recent advances to control the topology and function of synthetic supramolecular systems include the application of chirality, 11 mechanical stress 12 and oscillating assembly mechanisms. 13 The unique chemical reactivity and physical properties of two-dimensional (2D) molecular allotropes has opened new and exciting opportunities in chemistry, nanotechnology and materials science.…”