Macrocycle Breathing in [2]Rotaxanes with Tetralactam Macrocycles

Abstract

The structural dynamics of two pairs of [2]rotaxanes were compared using variable-temperature NMR. Each rotaxane had a surrounding tetralactam macrocycle with either 2,6-pyridine dicarboxamide or isophthalamide bridging units. Differences were observed in two types of rotational processes: spinning of the phenylene wall units in the surrounding macrocycle of squaraine rotaxanes and macrocycle pirouetting in xanthone rotaxanes. The rotaxanes with macrocycles containing 2,6-pyridine dicarboxamide bridges exhibited higher rotational barriers due to a cavity contraction effect, which disfavored macrocycle breathing.

Conformer Distribution in Rotaxanes Containing Nonsymmetric Threads: A Systematic Approach

“…Variable‐temperature (VT) 1 H NMR studies were performed to analyze the intramolecular interactions present in the rotaxanes and to calculate the rates of the macrocycle pirouetting around the thread . These experiments provide a good measure of the relative strengths of the intercomponent interactions through the energy barriers of rotational motion in deuterated solvents , , , . Increased temperatures make it possible to observe a “break” and/or the formation of intramolecular interactions, such as the macrocycle circling around the thread …”

“…[22] These experiments provide a good measure of the relative strengths of the intercomponent interactions through the energy barriers of rotational motion in deuterated solvents. [8,10,33,34] Increased temperatures make it possible to observe a "break" and/or the formation of intramolecular interactions, such as the macrocycle circling around the thread. [22] The main intermolecular interactions that can be observed in solution are the hydrogen bonds and CH···π interactions.…”

“…One of the key features of these systems is the control of movement of the macrocycle in relation to the thread. These movements are mainly affected by the interactions between the two subcomponents .…”

“…These movements are mainly affected by the interactions between the two subcomponents. [8][9][10] These unique characteristics have led to rapid advances in the synthesis of these systems. [10][11][12][13][14] In general, diamides are effective templates for obtaining rotaxanes in a five-component clipping reaction, because amide threads can be good hydrogen-bond acceptors.…”

Induction of Motion in a Synthetic Molecular Machine: Effect of Tuning the Driving Force

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Rotaxane-based molecular shuttles are a prototypical class of synthetic molecular machines. [19,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] They consist of (at least) two components mechanically linked together: a macrocyclic ring, which surrounds a linear unit (thread) with bulky groups (stoppers) at the ends that prevent the macrocycle from slipping off. The two parts can move relatively easily with respect to each other because there is no covalent bonding between them.…”