Using Acetate Anions To Induce Translational Isomerization in a Neutral Urea-Based Molecular Switch

Dynamic Metalloporphyrin-Based [2]Rotaxane Molecular Shuttles Stimulated by Neutral Lewis Base and Anion Coordination

A series of dynamic metalloporphyrin [2]rotaxane molecular shuttles comprising of bis-functionalised Zn(II) porphyrin axle and pyridyl functionalised macrocycle components are prepared in high yield via active metal template synthetic methodology. Extensive variable temperature 1 H NMR and quantitative UV-Vis spectroscopic titration studies demonstrate dynamic macrocycle translocation is governed by an inter-component co-ordination interaction between the macrocycle pyridyl and axle Zn(II) metalloporphyrin, which serves to bias a 'resting state' co-conformation. The dynamic shuttling behaviour of the interlocked structures is dramatically inhibited by the addition of a neutral Lewis base such as pyridine, but can also be tuned via post-synthetic rotaxane demetallation of the porphyrin axle core to give free-base, or upon subsequent metallation, Ni(II) [2]rotaxane analogues. Importantly, the Lewis acidic Zn(II) porphyrin axle component is also capable of coordinating anions which induces mechanical bond shuttling behaviour resulting in a novel optical sensing response.

Unveiling anion-induced folding in tripodal imidazolium receptors by ion-mobility mass spectrometry

The anion-induced folding of tripodal imidazolium receptors has been investigated by NMR spectroscopy, electrospray ionization ion mobility mass spectrometry and DFT calculations. Such folding can be switched by anion release upon collision induced dissociation.

Artificial Light-Harvesting Systems Based on AIEgen-branched Rotaxane Dendrimers for Efficient Photocatalysis

Aiming at the construction of novel platform for efficient light harvesting, the precise synthesis of a new family of AIEgen-branched rotaxane dendrimers was successful realized from an AIEgen-functionalized [2]rotaxane through a controllable divergent approach. In the resultant AIE macromolecules, up to twenty-one AIEgens located at the tails of each branches, thus making them the first successful example of AIEgen-branched dendrimers. Attributed to the solvent-induced switching feature of the rotaxane branches, the integrated rotaxane dendrimers displayed interesting dynamic feature upon the aggregation-induced emission (AIE) process. Moreover, novel artificial light-harvesting systems were further constructed based on these AIEgen-branched rotaxane dendrimers, which revealed impressive generation-dependent photocatalytic performances for both photooxidation reaction and aerobic cross-dehydrogenative coupling (CDC) reaction.

Fast Track to Acetate-Based Ionic Liquids: Preparation, Properties and Application in Energy and Petrochemical Fields

Acetate-based ionic liquids (AcILs), as a kind of typical carboxylate-based ILs, display excellent structure tunability, non-volatility, good solubility to biomass, and favorable adsorption capacity, etc. These unique characteristics of AcILs make them important candidates for a range of applications in the field of energy and in the petrochemical industry. This paper intends to provide a comprehensive overview of recent advances in AcILs, including pure AcILs, AcIL-based multi-solvents, and AcIL-based composites, etc. Preparation methods, with one- and two-step synthesis, are reviewed. The relationship between properties and temperature is discussed, and some physical and thermodynamic properties of different AcILs are summarized and further calculated. The applications of AcILs in the fields of biomass processing, organic synthesis, separation, electrochemistry, and other fields are reviewed based on their prominent properties. Thereinto, the dual functions of AcILs as solvents and activators for biomass dissolution are discussed, and the roles of AcILs as catalysts and reaction mediums in clean organic synthesis are highlighted. Meanwhile, the reaction mechanisms of AcILs with acid gases are posed by means of molecular simulation and experimental characterization. Moreover, AcILs as electrolytes for zinc batteries, supercapacitors, and electrodeposition are particularly introduced. Finally, the future research challenges and prospects of AcILs are presented.

Orientation of the α-CD component of [2]rotaxanes affects their specific molecular recognition behaviour

An α-CD component enhanced the anion recognition ability of the urea moiety and the deprotonation of the phenol moiety in the axle component in orientationally isomeric [2]rotaxanes with the OH groups on the wide rim of the α-CD, respectively.

Luminescent Anion Sensing by Transition-Metal Dipyridylbenzene Complexes Incorporated into Acyclic, Macrocyclic and Interlocked Hosts

A series of novel acyclic, macrocyclic and mechanically interlocked luminescent anion sensors have been prepared by incorporation of the isophthalamide motif into dipyridylbenzene to obtain cyclometallated complexes of platinum(II) and ruthenium(II). Both the acyclic and macrocyclic derivatives 7⋅Pt, 7⋅Ru⋅PF6 , 10⋅Pt and 10⋅Ru⋅PF6 are effective sensors for a range of halides and oxoanions. The near-infra red emitting ruthenium congeners exhibited an increased binding strength compared to platinum due to the cationic charge and thus additional electrostatic interactions. Intramolecular hydrogen-bonding between the dipyridylbenzene ligand and the amide carbonyls increases the preorganisation of both acyclic and macrocyclic metal derivatives resulting in no discernible macrocyclic effect. Interlocked analogues were also prepared, and preliminary luminescent chloride anion spectrometric titrations with 12⋅Ru⋅(PF6 )2 demonstrate a marked increase in halide binding affinity due to the complementary chloride binding pocket of the [2]rotaxane. 1 H NMR binding titrations indicate the interlocked dicationic receptor is capable of chloride recognition even in competitive 30 % aqueous mixtures.

Weak functional group interactions revealed through metal-free active template rotaxane synthesis

Modest functional group interactions can play important roles in molecular recognition, catalysis and self-assembly. However, weakly associated binding motifs are often difficult to characterize. Here, we report on the metal-free active template synthesis of [2]rotaxanes in one step, up to 95% yield and >100:1 rotaxane:axle selectivity, from primary amines, crown ethers and a range of C=O, C=S, S(=O)2 and P=O electrophiles. In addition to being a simple and effective route to a broad range of rotaxanes, the strategy enables 1:1 interactions of crown ethers with various functional groups to be characterized in solution and the solid state, several of which are too weak - or are disfavored compared to other binding modes - to be observed in typical host-guest complexes. The approach may be broadly applicable to the kinetic stabilization and characterization of other weak functional group interactions.

Light-controlled switchable complexation by a non-photoresponsive hydrogen-bonded amide macrocycle

A light controlled switchable host–guest system based on a non-photoresponsive H-bonded macrocycle and pyridinium salts was developed using a photoacid.

Step-by-step reaction-powered mechanical motion triggered by a chemical fuel pulse

Natural molecular machines perform important tasks in organisms under a reasonable energy supply strategy: a series of step-by-step biochemical reactions after the intake of a fuel such as glucose. As analogues of biomolecular machines, most artificial molecular machines and shuttles are still powered by two opposite stimuli, such as acid and base or oxidation and reduction. This inconvenient stimulus method for artificial molecular machines and shuttles creates great obstacles for realizing more functions of artificial molecular machines and shuttles owing to low energy utilization efficiency and troublesome operation. In this work, we report a new step-by-step reaction system combining two known reactions: (1) the formation of [bis(trifluoroacetoxy)iodo]benzene from the reaction of iodosylbenzene and trifluoroacetic acid; and (2) the catalytic oxidation of alcohols by [bis(trifluoroacetoxy)iodo]benzene in the presence of TEMPO. Owing to the acid absorption features of the first reaction and the acid releasing characteristics of the second reaction, the new step-by-step reaction obtains a pH oscillation feature. Taking advantage of the pH oscillation feature, the new reaction cycle triggered by iodosylbenzene was coupled with an acid-base switchable helicarene-based molecular shuttle. Benefitting from the reaction rate difference of the two known reactions (the reaction rate of the first reaction is faster than that of the second reaction), the movement of the helicarene on the axle could be controlled automatically by the reaction system through adding iodosylbenzene to a solution of alcohol, TEMPO and protonated rotaxane, and the manual addition of another opposite stimulus could be avoided.

Acid/base-controllable fluorescent molecular switches based on cryptands and basic N-heteroaromatics

Two kinds of fluorescent BMP32C10-based cryptands 1 and 2 have been developed. Cryptand 1 contains a binaphthol group, while cryptand 2 bears a coumarin group in their third arms. Based on this design, novel self-assemblies constructed from cryptand 1 or 2 and basic N-heteroaromatic guests 3-6 were successfully obtained. Moreover, the threading/dethreading processes of the host-guest complexes could be well switched by the alternate addition of acid/base, and accompanied by concurrent changes in fluorescence.

Complexation Between (O-Methyl)6 -2,6-Helic[6]arene and Tertiary Ammonium Salts: Acid/Base- or Chloride-Ion-Responsive Host-Guest Systems and Synthesis of [2]Rotaxane

Complexation between (O-methyl)₆ -2,6-helic[6]arene and a series of tertiary ammonium salts was described. It was found that the macrocycle could form stable complexes with the tested aromatic and aliphatic tertiary ammonium salts, which were evidenced by ¹ H NMR spectra, ESI mass spectra, and DFT calculations. In particular, the binding and release process of the guests in the complexes could be efficiently controlled by acid/base or chloride ions, which represents the first acid/base- and chloride-ion-responsive host-guest systems based on macrocyclic arenes and protonated tertiary ammonium salts. Moreover, the first 2,6-helic[6]arene-based [2]rotaxane was also synthesized from the condensation between the host-guest complex and isocyanate.

Rapidly accessible “click” rotaxanes utilizing a single amide hydrogen bond templating motif

The rapid synthesis (in yields of up to 47%) and co-conformational study of hydrogen bond templated rotaxanes are presented.

Metal-induced dynamic conformational and fluorescence switch of quinone-appended Zn-porphyrin

In this report, we have designed and synthesized a novel switching molecule whose fluorescence can be switched via dynamic conformational change between expanded and shrunk states induced by metal complexation and decomplexation. The switching molecule is composed of three kinds of components, namely, a Zn 2+-porphyrin fluorophore, two quinone quenchers, and their linkers containing a 4,4′-bipyridine moiety. UV-vis and fluorescence titration studies revealed that metal complexation of the bipyridine units with Zn 2+ ions induced the dynamic structural change of the molecular shape and simultaneous enhancement of fluorescence of the Zn 2+-porphyrin fluorophore.

Sterically controlled functionalization of carbon surfaces with -C6H4CH2X (X = OSO2Me or N3) groups for surface attachment of redox-active molecules

Glassy carbon electrodes were modified by electrochemical reduction of a diazonium molecule ((i)Pr3SiOCH2C6H4N2(+)BF4(-)) featuring a triisopropylsilyl-protected benzylic hydroxyl group. This electrochemical process introduced a monolayer of (i)Pr3SiOCH2C6H4- groups onto the surface of the electrode. The bulky -Si(i)Pr3 protecting group not only prevents the uncontrolled growth of structurally ill-defined and electronically blocking polyphenylene multilayers, but also separates the phenyl groups in the monolayer. Thus, the void spaces between these aryl units should allow a better accommodation of sizable molecules. Removal of the -Si(i)Pr3 protecting groups by (n)Bu4NF exposed the reactive benzylic hydroxyl functionalities that can undergo further transformations to anchor functional molecules. As an example, redox-active ferrocene molecules were grafted onto the modified electrode via a sequence of mesylation, azidation, and copper-catalyzed [3 + 2] cycloaddition reactions. The presence of ferrocenyl groups on the surface was confirmed by X-ray photoelectron spectroscopic and electrochemical studies. The resulting ferrocene-modified glassy carbon electrode exhibits cyclic voltammograms typical of surface-bound redox active species and remarkable electrochemical stability in an acidic aqueous environment.

Selecting reactions and reactants using a switchable rotaxane organocatalyst with two different active sites

The activation mode of a rotaxane-based organocatalyst with both secondary amine and squaramide catalytic units can be switched with acid or base. The macrocycle blocks whichever of the catalytic sites it is positioned over. The switchable rotaxane catalyst generates different products from a mixture of three building blocks according to the location of the macrocyclic ring in the rotaxane.

Advances in anion supramolecular chemistry: from recognition to chemical applications

Since the start of this millennium, remarkable progress in the binding and sensing of anions has been taking place, driven in part by discoveries in the use of hydrogen bonding, as well as the previously under-exploited anion-π interactions and halogen bonding. However, anion supramolecular chemistry has developed substantially beyond anion recognition, and now encompasses a diverse range of disciplines. Dramatic advance has been made in the anion-templated synthesis of macrocycles and interlocked molecular architectures, while the study of transmembrane anion transporters has flourished from almost nothing into a rapidly maturing field of research. The supramolecular chemistry of anions has also found real practical use in a variety of applications such as catalysis, ion extraction, and the use of anions as stimuli for responsive chemical systems.

Competitive binding for triggering a fluorescence response in a hydrazodicarboxamide-based [2]rotaxane

The design and synthesis of an interlocked receptor based on a hydrogen bonded [2]rotaxane containing a hydrazodicarboxamide binding site are reported. An anion recognition process with tetrabutylammonium benzoate triggers the submolecular translational movement of its benzylic amide macrocycle developing a progressive increase of the fluorescence intensity, effectively quenched at the original state. The binding of the anion competes with the hydrogen-bond-connected cyclic component for the bis(urea)-based station pushing it towards a stoppered alkyl chain. Moreover, this interlocked system is able to work as a molecular switch restoring its initial state in two ways, either by an ion exchange reaction or by a high yielding oxidation/reduction sequence.