How Large Can We Build a Cyclic Assembly? Impact of Ring Size on Chelate Cooperativity in Noncovalent Macrocyclizations

Abstract

Self‐assembled systems rely on intramolecular cooperative effects to control their growth and regulate their shape, thus yielding discrete, well‐defined structures. However, as the size of the system increases, cooperative effects tend to dissipate. We analyze here this situation by studying a set of oligomers of different lengths capped with guanosine and cytidine nucleosides, which associate in cyclic tetramers by complementary Watson–Crick H‐bonding interactions. As the monomer length increases, and thus the number of C(sp)–C(sp2) σ‐bonds in the π‐conjugated skeleton, the macrocycle stability decreases due to a notable reduction in effective molarity (EM), which has a clear entropic origin. We determined the relationship between EM or ΔS and the number of σ‐bonds, which allowed us to predict the maximum monomer lengths at which cyclic species would still assemble quantitatively, or whether the cyclic species would not able to compete at all with linear oligomers over the whole concentration range.

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

“…Upon cooling, GC cyclotetramerization is promoted and a single, rigid conformation, that maintains the two Watson-Crick edges pointing in the same direction, is fixed. [32][33][34][35] This is typically monitored by: 1) a red-shift in absorbance with a characteristic new maximum at 420 nm; 2) a decrease in emission intensity and a marked red-shift from 439 nm (GC) to 525 nm (cGC4); and 3) a CD Cotton effect, positive for cS-GC4 and negative for cR-GC4, with zero-crossing at 434 nm. Figures S1D-E contain additional temperature-and concentration-dependent spectra in THF.…”

“…Figures S1D-E contain additional temperature-and concentration-dependent spectra in THF. [32][33][34][35] Such spectroscopy changes can be used to determine the molar fraction of GC molecules associated as cGC4 (T) as a function of temperature (Figure 2f) or concentration (Figure 2g). The cyclization trends obtained from NMR and CD measurements at the same concentrations show an excellent agreement.…”

“…First, chelate cooperativity is responsible for the formation of unstrained cyclic tetramers through G:C Watson-Crick H-bonding interactions, 31 as demonstrated previously with related molecules bearing bulky riboses. [32][33][34][35][36][37][38] After these planar macrocycles are generated quantitatively, a polymerization process, that occurs through a nucleationgrowth mechanism and is guided by  and H-bonding interactions along the stacking axis, can be triggered by a change in experimental conditions. Hence, both cooperative processes are independent and self-assembly can be controlled either at the cycle stage or at the polymer stage.…”

Columnar Liquid-Crystalline Macrocycles Synthesized via Metal Ion-Assisted Self-Assembly

“…Such thermodynamically stable, intramolecular cyclization is favored over intermolecular polymerization, which would require an entropic loss. 26 The cyclization of a 1:1 mixture of copper acetate and L4 having tris(ethylene glycol)decyl groups was carried out by heating the solution for 27 h followed by purification by recycling gel-permeation chromatography (GPC), and the 3:3 metallomacrocycle was obtained in 46% yield, which showed a single chromatographic peak in the GPC chart with a shorter retention time than that of precursor ligand L4 (Figure 3a). Electrospray ionization−time-of-flight mass spectroscopy (ESI−TOF MS) also supported the formation of target Cu 3 L4 3 based on the signal with m/z 1834 for [M + 4Na + ] 4+ (Figure 3b).…”

Exploring the tubular self-assembly landscape of dinucleobase amphiphiles in water

“…The general structure of our amphiphile monomers, as shown in Figure 1a, consists of a rigid π-conjugated central block disubstituted with complementary guanine (G) and cytosine (C) nucleobases in a linear fashion. [21][22][23][24][25][26] The central unit is made amphiphilic by installing a chiral lipophilic chain at one side and a hydrophilic tail at the other, which can be neutral or ionic. At the same time, the nucleobases are equipped at the N-1 or N-9 positions with a lateral chain comprising a hexamethylene apolar section followed by a tetraethyleneglycol residue.…”