The stability of imine-containing dynamic [2]rotaxanes to hydrolysis

π-Stacking Stopper-Macrocycle Stabilized Dynamically Interlocked [2]Rotaxanes

The synthesis of mechanically interlocked molecules is valuable due to their unique topologies. With π-stacking intercomponent interaction, e.g., phenanthroline and anthracene, novel [2]rotaxanes have been synthesized by dynamic imine clipping reaction. Their X-ray crystal structures indicate the π-stackings between the anthracene moiety (stopper) on the thread and the (hetero)aromatic rings at the macrocycle of the rotaxanes. Moreover, the length of glycol chains affects the extra π-stacking intercomponent interactions between the phenyl groups and the dimethoxy phenyl groups on the thread. Dynamic combinatorial library has shown at best 84% distribution of anthracene-threaded phenanthroline-based rotaxane, coinciding with the crystallography in that the additional π-stacking intercomponent interactions could increase the thermodynamic stability and selectivity of the rotaxanes.

Stimulus-cleavable chemistry in the field of controlled drug delivery

This review comprehensively summarises stimulus-cleavable linkers from various research areas and their cleavage mechanisms, thus provides an insightful guideline to extend their potential applications to controlled drug release from nanomaterials.

Regulating the Structures of Self-Assembled Mechanically Interlocked Moleculecular Constructs via Dianion Precursor Substituent Effects

Substituent effects play critical roles in both modulating reaction chemistry and supramolecular self-assembly processes. Using substituted terephthalate dianions (p-phthalic acid dianions; PTADAs), the effect of varying the type, number, and position of the substituents was explored in terms of their ability to regulate the inherent anion complexation features of a tetracationic macrocycle, cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene) (referred to as the Texas-sized molecular box; 1⁴⁺), in the form of its tetrakis-PF₆^- salt in DMSO. Several of the tested substituents, including 2-OH, 2,5-di(OH), 2,5-di(NH₂), 2,5-di(Me), 2,5-di(Cl), 2,5-di(Br), and 2,5-di(I), were found to promote pseudorotaxane formation in contrast to what was seen for the parent PTADA system. Other derivatives of PTADA, including those with 2,3-di(OH), 2,6-di(OH), 2,5-di(OMe), 2,3,5,6-tetra(Cl), and 2,3,5,6-tetra(F) substituents, led only to so-called outside binding, where the anion interacts with 1⁴⁺ on the outside of the macrocyclic cavity. The differing binding modes produced by the choice of PTADA derivative were found to regulate further supramolecular self-assembly when the reaction components included additional metal cations (M). Depending on the specific choice of PTADA derivatives and metal cations (M = Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Gd³⁺, Nd³⁺, Eu³⁺, Sm³⁺, Tb³⁺), constructs involving one-dimensional polyrotaxanes, outside-type rotaxanated supramolecular organic frameworks (RSOFs), or two-dimensional metal-organic rotaxane frameworks (MORFs) could be stabilized. The presence and nature of the substituent were found to dictate which specific higher order self-assembled structure was obtained using a given cation. In the specific case of the 2,5-di(OH), 2,5-di(Cl), and 2,5-di(Br) PTADA derivatives and Eu³⁺, so-called MORFs with distinct fluorescence emission properties could be produced. The present work serves to illustrate how small changes in guest substitution patterns may be used to control structure well beyond the first interaction sphere.

[2]Rotaxane End-Capping Synthesis by Click Michael-Type Addition to the Vinyl Sulfonyl Group

We report the application of the click Michael-type addition reaction to vinyl sulfone or vinyl sulfonate groups in the synthesis of rotaxanes through the threading-and-capping method. This methodology has proven to be efficient and versatile as it allowed the preparation of rotaxanes using template approaches based on different noncovalent interactions (i.e., donor-acceptor π-π interactions or hydrogen bonding) in yields of generally 60-80 % and up to 91 % aided by the mild conditions required (room temperature or 0 °C and a mild base such as Et₃ N or 4-(N,N-dimethylamino)pyridine (DMAP)). Furthermore, the use of vinyl sulfonate moieties, which are suitable motifs for coupling-and-decoupling (CAD) chemistry, implies another advantage because it allows the controlled chemical disassembly of the rotaxanes into their components through nucleophilic substitution of the sulfonates resulting from the capping step with a thiol under mild conditions (Cs₂ CO₃ and room temperature).

Probing the Dynamics of the Imine-Based Pentafoil Knot and Pentameric Circular Helicate Assembly

We investigate the self-assembly dynamics of an imine-based pentafoil knot and related pentameric circular helicates, each derived from a common bis(formylpyridine)bipyridyl building block, iron(II) chloride, and either monoamines or a diamine. The mixing of circular helicates derived from different amines led to the complete exchange of the N-alkyl residues on the periphery of the metallo-supramolecular scaffolds over 4 days in DMSO at 60 °C. Under similar conditions, deuterium-labeled and nonlabeled building blocks showed full dialdehyde building block exchange over 13 days for open circular helicates but was much slower for the analogous closed-loop pentafoil knot (>60 days). Although both knots and open circular helicates self-assemble under thermodynamic control given sufficiently long reaction times, this is significantly longer than the time taken to afford the maximum product yield (2 days). Highly effective error correction occurs during the synthesis of imine-based pentafoil molecular knots and pentameric circular helicates despite, in practice, the systems not operating under full thermodynamic control.

Synthesis of rotaxanes and catenanes using an imine clipping reaction

Supramolecular chemistry and self-assembly provide a valuable chance to understand the complicated topological structures on a molecular level. Two types of classical mechanically interlocked molecules, rotaxanes and catenanes, possess non-covalent mechanical bonds and have attracted more attention not only in supramolecular chemistry but also in the fields of materials science, nanotechnology and bioscience. In the past decades, the template-directed clipping reaction based on imine chemistry has become one of the most efficient methods for the construction of functionalized rotaxanes and catenanes. In this review, we outlined the main progress of rotaxanes and catenanes using the template-directed clipping approach of imine chemistry. The review contains the novel topological structures of rotaxanes and catenanes, functions and applications.

Formation of a hetero[3]rotaxane by a dynamic component-swapping strategy

Acid-catalysed scrambling of the mechanically interlocked components between two different homo[3]rotaxanes, constituted of dumbbells containing two secondary dialkylammonium ion recognition sites encircled by two [24]crown-8 rings, each containing a couple of imine bonds, affords a statistical mixture of a hetero[3]rotaxane along with the two homo[3]rotaxanes, indicating that neither selectivity nor cooperativity is operating during the assembly process.

Revisiting the formation and tunable dissociation of a [2]pseudorotaxane formed by slippage approach

A new [2]pseudorotaxane DB24C8⊃1-H·PF₆ with dibenzo[24]crown-8 (DB24C8) crown ether-dibenzylammonium (1-H·PF₆) binding which was formed by slippage approach at different solvents and temperature, had been isolated and characterized by NMR spectroscopy and mass spectrometry. The [2]pseudorotaxane DB24C8⊃1-H·PF₆ was stable at room temperature. The dissociation rate of [2]pseudorotaxane DB24C8⊃1-H·PF₆ could be tuned by using different stimuli such as triethylamine (TEA)/diisopropylethylamine (DIPEA) and dimethyl sulfoxide (DMSO). In particular, the dissociation of [2]pseudorotaxane DB24C8⊃1-H·PF₆ by an excess of TEA/DIPEA base mixture possessed a long and sustained, complete dissociation over 60 days. Other stimuli by DMSO possessed a relatively fast dissociation over 24 h.

Photo-responsive [2]catenanes: synthesis and properties

A series of novel dithienylethene-based macrocycles containing ammonium moieties has been synthesized.

Self-assembly, stability quantification, controlled molecular switching, and sensing properties of an anthracene-containing dynamic [2]rotaxane

The preparation of a novel anthracene-containing dynamic [2]rotaxane by a templating self-assembly process between a diamine and a dialdehyde to form a [24]crown-8 macrocyclic diimine, in the presence of a dumbbell containing a secondary dialkylammonium ion center as the template, which has been exploited for its sensing properties. By appealing to the ability of the anthracene ring system--one of the two stoppers associated with the dumbbell--to act as a fluorescent probe, the fluorescence and fluorescence-quenching nature of the dynamic rotaxane in an equilibrium mixture has been investigated and quantified in the presence of external stimuli such as water, acids, salts, and an amine. The stability, as expressed by the hydrolysis of the dynamic rotaxane has been monitored by following: (i) the anthracene fluorescence and (ii) the movements of the signals in the (1)H NMR spectra. The rate of hydrolysis (t(1/2) = 6.9 min) of the dynamic rotaxane in the presence of a small amount (1 equiv.) of acid was found to be very much faster than when the hydrolysis was carried out with a large amount (>100 equiv.) of water, when t(1/2) > 140 min. Furthermore, it has been established that the anthracene fluorescence of the dynamic rotaxane rises with an increasing amount of acid. Two acid sensors have been identified with different operating modes-namely, logarithmic and linear. The combination of different inputs involving water, acids, salts and an amine leads to different fluorescence outputs from the dynamic rotaxane, hence, producing a prototype for expressing molecular logic.