Co‐conformational Exchange Triggered by Molecular Recognition in a Di(acylamino)pyridine‐Based Molecular Shuttle Containing Two Pyridine Rings at the Macrocycle

Abstract

We describe the incorporation of endo-pyridine units into the tetralactam ring of di(acylamino)pyridine-based rotaxanes. This macrocycle strongly associates with the linear interlocked component as confirmed by X-ray diffraction studies of rotaxane 2 b. Dynamic NMR studies of 2 b in solution revealed a rotational energy barrier that was higher than that of the related rotaxane 2 a, which lacks of pyridine rings in the macrocycle. The macrocycle distribution of the molecular shuttle 4 b, containing two endo-pyridine rings, shows that the major co-conformer is that with the cyclic component sitting over the di(acylamino)pyridine station. DFT calculations also support the marked preference of the ring for occupying the heterocyclic binding site. The association of N-hexylthymine with the di(acylamino)pyridine binding site of 4 b led to the formation of a rare 'S'-shaped co-conformer in which the tetralactam ring interacts simultaneously with both stations of the thread.

Crystallization Mechanisms Applied to Understand the Crystal Formation of Rotaxanes

“…[53] Fourteen molecules that represented all the range of volumes ( Figure S2 and Table S2) were chosen. [33,36,46,47,49,50,[54][55][56][57][58][59] Consequently, rotaxanes containing different stations and threads (varying the functional groups) were selected, which furnished representative examples of [2]rotaxanes with different characteristics to be studied in a supramolecular perspective. In this sense, the crystalline structures selected are described in Figure 2.…”

“…The volumes were obtained by the Voronoi–Dirichlet polyhedral (VDP) using the software ToposPro . Fourteen molecules that represented all the range of volumes (Figure S2 and Table S2) were chosen , , , , , , . Consequently, rotaxanes containing different stations and threads (varying the functional groups) were selected, which furnished representative examples of [2]rotaxanes with different characteristics to be studied in a supramolecular perspective.…”

Remote Photoregulated Ring Gliding in a [2]Rotaxane via a Molecular Effector

“…Indeed, this ordering may be anticipated on the basis of the number of available hydrogen bonds formed between a barbital guest and 1 , 2 , and 1 c , namely 6 (with H-bonding pattern DADDAD:ADAADA) vs 3 (DAD:ADA) vs <3, respectively. Additionally, considering translational motion of the ring in 2 , some of us reported that guest binding at both rotaxane diamidopyridine sites had a direct influence on the amplitude of the ring shuttling. , Therefore, as represented in Scheme , in the initial state B would be anticipated to reside quasi-exclusively at receptor 1 , and an unimpeded, large amplitude translational motion of the macrocycle would occur in rotaxane 2 . Photoirradiation would provoke release of B , chemical transfer, and effective chemical communication with the rotaxane, thereby restricting the forward and backward ring motion through the formation of a ternary aggregate (2 B · 2) .…”

“…Thus, the state of the system and average instantaneous position of effector and ring components could be read out. Based on relative and absolute association constants for B with receptor 1 and rotaxane 2 , a mixture of 1 , B , and 2 ensuring preponderant complexation at 1 (89% B ⊂ 1 ; ≈ 2% 2 B · 2 ) was determined to be a molar ratio of 1:1:0.5, respectively, at 2 mM concentration of 1 . , Following irradiation, a dramatic population inversion was anticipated ( B ⊂ 1 C ≈ 2%; 2 B · 2 = 65%). Direct titration of barbiturate into mixtures of 1 and 2 or 1 C and 2 gave similar values, showing the rapid redistribution of B (Figures S1 and S2) compatible with reversible binding.…”

Effects on Rotational Dynamics of Azo and Hydrazodicarboxamide-Based Rotaxanes

“…The synthesis of hydrogen-bonded rotaxanes requires the presence of suitable binding sites able to template the formation of the corresponding tetralactam macrocycle. In this sense, the employment of 1,4-dicarboxamides [ 13 , 14 , 15 ], nitrones [ 16 , 17 ], squaraines [ 18 , 19 ] or di(acylamino)pyrididines [ 20 , 21 , 22 , 23 ], together with hydrogen-bonding templation with anions [ 24 , 25 ] can be highlighted. In this arena, some of us reported that azodicarboxamides are able to act as effective templates for driving the assembly of hydrogen-bond-assembled [2]rotaxanes [ 26 , 27 , 28 ].…”