Dynamic negative allosteric effect: regulation of catalysis via multicomponent rotor speed

Nanorotor R1 (420 kHz) was assembled from five components utilizing three orthogonal interactions. Post-modification at the distal position generated the advanced six component rotor R2 (45 kHz). The decrease in R2 speed leads to the inhibition of a three-component reaction by reducing catalyst release.

Stepwise Dissipative Control of Multimodal Motion in a Silver(I) Catenate

Stepwise dissipative control of two distinct motions, i.e., shuttling and sliding, is demonstrated in a single multicomponent device. When [2]rotaxane 1, which acts as a biped, and deck 2 were treated with AgBF4/PhCH2Br+NEt3 as chemical fuel, the transient catenate [Ag(1)]+ ⋅ [Ag3(2)]3+ was instantly generated showing multimodal motion and autonomous return to 1 and 2. In the dissipative process, catenate [Ag(1)]+ ⋅ [Ag3(2)]3+ cleanly transformed into the follow-up transient device (1) ⋅ [Ag3(2)]3+ exhibiting only sliding motion. Two interference-free dissipative cycles proved the resilience and robustness of the process.

Interconversion between multicomponent slider-on-deck and palladium capsule: regulation of catalysis and encapsulation

When the slider-on-deck [Cu3(1)(2)]3+ and guest G were treated with palladium(II) ions, the biped 2 was released from [Cu3(1)(2)]3+ generating the nanocage [Pd2(2)4(G)]4+ with guest G being encapsulated (NetState-II). This transformation that was reversed by the addition of DMAP enabled modulation of both the overall fluorescence and the activity of copper(I) catalyzing an aza Hopf cyclization.

Proton transfer network with luminescence display controls OFF/ON catalysis that generates a high-speed slider-on-deck

A three-component network for OFF/ON catalysis was built from a protonated nanoswitch and a luminophore. Its activation by addition of silver(i) triggered the proton-catalyzed formation of a biped and the assembly of a fast slider-on-deck (k 298 = 540 kHz).

Synchronizing Two Distinct Nano-Circular Sliding Motions in Six-Component Machinery for Double Catalysis

The heteroleptic multi-component double slider-on-deck system DS3 exhibits tight coupling of motional speed of two distinct nano-circular sliders (k₂₉₈ =77 and 41 kHz) despite a 2.2 nm separation. In comparison, the single sliders in DS1 and DS2 move at vastly different speed (k₂₉₈ =1.1 vs. 350 kHz). Synchronization of the motions in DS3 remains even when one slows the movement of the faster slider using small molecular brake pads. In contrast to the individual DS1 and DS2 systems, DS3 is a powerful catalyst for a two-step reaction by using the motion of both sliders to drive two catalytic processes.

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

Supramolecular catalysis is reviewed with an eye on heteroleptic aggregates/complexation. Since most of the current metallosupramolecular catalytic systems are homoleptic in nature, the idea of breaking/reducing symmetry has ignited a vivid search for heteroleptic aggregates that are made up by different components. Their higher degree of functional diversity and structural heterogeneity allows, as demonstrated by Nature by the multicomponent ATP synthase motor, a more detailed and refined configuration of purposeful machinery. Furthermore, (metallo)supramolecular catalysis is shown to extend beyond the single "supramolecular unit" and to reach far into the field and concepts of systems chemistry and information science.

Catalytic machinery in motion: Controlling catalysis via speed

Three 3-component copper(I)-based slider-on-deck systems served as catalysts for a click reaction showing a higher catalytic activity with increasing sliding speed. Upon addition of brake stones, the motion of the...

Dynamics of the alkyne → copper(i) interaction and its use in a heteroleptic four-component catalytic rotor

The dynamics of alkyne → copper(i) interactions has been determined and used to self-assemble a fast nanorotor, which underwent a self-catalyzed click transformation to a triazole rotor, an interesting process for the production of biohybrid devices.

Self-Assembly of Octanuclear PtII/PdII Coordination Barrels and Uncommon Structural Isomerization of a Photochromic Guest in Molecular Space

Two tetragonal molecular barrels TB1 and TB2 were successfully synthesized by coordination-driven self-assembly of a tetrapyridyl donor (L) of the thiazolo[5,4-d]thiazole backbone with cis-blocked 90° Pd(II) and Pt(II) acceptors, respectively. The single-crystal structure analysis of TB1 revealed the formation of a two-face opened tetragonal Pd8 molecular barrel architecture. In contrast, the isostructural Pt(II) barrel (TB2) is water-soluble. The large confined hydrophobic molecular cavity including wide open windows and good water solubility of the barrel TB2 made it a potential molecular container for the encapsulation of guests with different sizes and properties. This has been exploited to encapsulate and stabilize the open form of a photochromic molecule (G2) in water, while the same photochromic molecule exists exclusively in a cyclic zwitterionic form in aqueous medium in the absence of the barrel TB2. This cyclic form is very stable in water and does not go back to its parent open form under common external stimuli. Surprisingly, reverse switching of the cyclic form to a colored hydrophobic open form was also possible instantly in water upon addition of the solid barrel TB2 into an aqueous solution of G2. Such a fast reverse isomerization of an irreversible process in aqueous medium by utilizing host-guest interaction of the barrel TB2 and the guest G2 is interesting. The barrel TB2 was also capable of encapsulating the water-insoluble radical initiator G1 in aqueous medium.

Fuel Acid Drives Base Catalysis and Supramolecular Cage-to-Device Transformation under Dissipative Conditions

In State-I, a mixture comprising a DABCO-bridged tris(zinc-porphyrin) double decker and a free biped (=slider), catalysis was OFF. Acid addition (TFA or Di-Stefano fuel acid) to State-I liberated DABCO-H⁺ while generating a highly dynamic slider-on-deck device (State-II). The released DABCO-H⁺ acted as a base organocatalyst for a Knoevenagel reaction (catalysis ON). The system was reversed to State-I (catalysis OFF) by reducing the acidity in the system (by adding DBU or via the fuel-derived base).

Evolution of catalytic machinery: three-component nanorotor catalyzes formation of four-component catalytic machinery

The three-component nanorotor [Cu2(S)(R)]2+ (k298 = 46.0 kHz) that is a catalyst for a CuAAC reaction binds the click product at each of its copper centers thereby creating a new platform and a dynamic slider-on-deck system. Due to this sliding motion (k298 = 65.0 kHz) the zinc-porphyrin bound N-methylpyrrolidine is efficiently released into solution and catalyzes a follow-up Michael addition.

New horizons for catalysis disclosed by supramolecular chemistry

The adoption of a supramolecular approach in catalysis promises to address a number of unmet challenges, ranging from activity (unlocking of novel reaction pathways) to selectivity (alteration of the innate selectivity of a reaction, e.g. selective functionalization of C-H bonds) and regulation (switch ON/OFF, sequential catalysis, etc.). Supramolecular tools such as reversible association and recognition, pre-organization of reactants and stabilization of transition states upon binding offer a unique chance to achieve the above goals disclosing new horizons whose potential is being increasingly recognized and used, sometimes reaching the degree of ripeness for practical use. This review summarizes the main developments that have opened such new frontiers, with the aim of providing a guide to researchers approaching the field. We focus on artificial supramolecular catalysts of defined stoichiometry which, under homogeneous conditions, unlock outcomes that are highly difficult if not impossible to attain otherwise, namely unnatural reactivity or selectivity and catalysis regulation. The different strategies recently explored in supramolecular catalysis are concisely presented, and, for each one, a single or very few examples is/are described (mainly last 10 years, with only milestone older works discussed). The subject is divided into four sections in light of the key design principle: (i) nanoconfinement of reactants, (ii) recognition-driven catalysis, (iii) catalysis regulation by molecular machines and (iv) processive catalysis.

A Self-Assembled Palladium(II) Barrel for Binding of Fullerenes and Photosensitization Ability of the Fullerene-Encapsulated Barrel

Fullerene extracts obtained from fullerene soot lack their real application due to their poor solubility in common solvents and difficulty in purification. Encapsulation of these extracts in a suitable host is an important approach to address these issues. We present a new Pd₆ barrel (1), which is composed of three 1,4-dihydropyrrolo[3,2-b]pyrrole panels, clipped through six cis-Pd^II acceptors. Large open windows and cavity make it an efficient host for a large guest. Favorable interactions between the ligand and fullerene (C₆₀ and C₇₀ ) allows the barrel to encapsulate fullerene efficiently. Thorough investigation reveals that barrel 1 has a stronger binding affinity towards C₇₀ over C₆₀ , resulting in the predominant extraction of C₇₀ from a mixture of the two. Finally, the fullerene encapsulated barrels C₆₀ ⊂1 and C₇₀ ⊂1 were found to be efficient for visible-light-induced singlet oxygen generation. Such preferential binding of C₇₀ and photosensitizing ability of C₆₀ ⊂1 and C₇₀ ⊂1 are noteworthy.

Multitasking with Chemical Fuel: Dissipative Formation of a Pseudorotaxane Rotor from Five Distinct Components

A 3-fold completive self-sorted library of dynamic motifs was integrated into the design of the pseudorotaxane-based rotor [Zn(2·H⁺)(3)(4)]²⁺ operating at k₂₉₈ = 15.4 kHz. The rotational motion in the five-component device is based on association/dissociation of the pyridyl head of the pseudorotaxane rotator arm between two zinc(II) porphyrin stations. Addition of TFA or 2-cyano-2-phenylpropanoic acid as a chemical fuel to a zinc release system and the loose rotor components 2-4 enabled the liberated zinc(II) ions and protons to act in unison, setting up the rotor through the formation of a heteroleptic zinc complex and a pseudorotaxane linkage. With chemical fuel, the dissipative system was reproducibly pulsed three times without a problem. Due to the double role of the fuel acid, two kinetically distinct processes played a role in both the out-of-equilibrium assembly and disassembly of the rotor, highlighting the complex issues in multitasking of chemical fuels.

Toward Molecular Cybernetics - the Art of Communicating Chemical Systems

The emerging field of molecular cybernetics has the potential to widely broaden our perception of chemistry. Chemistry will develop beyond its current focus that is mainly concerned with single transformations, pure compounds, and/or defined mixtures. On this way, chemistry will become autonomous, networked and smart through communicating molecules each of which serves a control engineering purpose, like the set of wheels in the machinery of life. The present personal account describes our latest developments in this field.

Using multiple self-sorting for switching functions in discrete multicomponent systems

Over years self-sorting has developed into a powerful tool in supramolecular chemistry, for instance, to promote the error-free formation of intricate multicomponent assemblies. However, in order to use the enormous potential of self-sorting for sophisticated information processing more recent developments have focused on the reversible reconfiguration of multicomponent systems driven by multiple self-sorting protocols. The present mini review will provide an overview over the latest advancements in this field with a focus on reversibly switchable functions in discrete supramolecular systems.

Multicomponent Metallo-Supramolecular Nanocapsules Assembled from Calix[4]resorcinarene-Based Terpyridine Ligands

Tetrafunctionalized calix[4]resorcinarene cavitands commonly serve as supramolecular scaffolds for construction of coordination-driven self-assembled capsules. However, due to the calix-like shape, the structural diversity of assemblies is mostly restricted to dimeric and hexameric capsules. Previously, we reported a spontaneous heteroleptic complexation strategy based on a pair of self-recognizable terpyridine-based ligands and Cd^II ions. Building on this complementary ligand pairing system, herein three types of nanocapsules, including a dimeric capsule, a Sierpiński triangular prism, and a cubic star, could be readily obtained through dynamic complexation reactions between a tetratopic cavitand-based ligand and various multitopic counterparts in the presence of Cd^II ions. The dimeric capsular assemblies display the spacer-length-dependent self-sorting behavior in a four-component system. Moreover, the precise multicomponent self-assembly of a Sierpiński triangular prism and a cubic star possessing three and six cavitand-based motifs, respectively, demonstrates that such self-assembly methodology is able to efficiently enhance architectural complexity for calix[4]resorcinarene-containing metallo-supramolecules.

Inhibition of Ligand Binding Ability of Three Porphyrins by an Organic Effector

A stimulus-responsive receptor 1 was designed and prepared to control the ligand-binding ability of three active sites, two zinc tetraphenylporphyrin units (P1) and one zinc diethynyldiphenylporphyrin unit (P2), with one effector molecule 2. Bulky hexarylbenzene units were incorporated as shielding panels in the middle of the flexible side arms of 1. Spectroscopic titrations indicated that a stable supramolecular complex 1⋅2 (K_1⋅2 =6.7×10⁶  m^-1 ) was produced by the cooperative formation of multiple hydrogen and coordination bonds. As a result, the binding of a ligand to P1 was inhibited by 2 in a competitive manner. Additionally, the formation of 1⋅2 brought about conformational restriction of the side arms to cover both faces of P2 with the shielding panels. The binding constant of 4-phenylpyridine with P2 in 1⋅2 decreased to 8.9 % of that in 1. Namely, the ligand-binding ability of P2 was inhibited according to an allosteric mechanism.

Coordination-Assisted Reversible Photoswitching of Spiropyran-Based Platinum Macrocycles

Control over the stimuli-responsive behavior of smart molecular systems can influence their capability to execute complex functionalities. Herein, we report the development of a suite of spiropyran-based multi-stimuli-responsive self-assembled platinum(II) macrocycles (5-7), rendering coordination-assisted enhanced photochromism relative to the corresponding ligands. 5 showed shrinking and swelling during photoreversal, while 6 and 7 are fast and fatigue-free supramolecular photoswitches. 6 turns out to be a better fatigue-resistant photoswitch and can retain an intact photoswitching ability of up to 20 reversible cycles. The switching behavior of the macrocycles can also be precisely controlled by tuning the pH of the medium. Our present strategy for the construction of rapid stimuli-responsive supramolecular architectures via coordination-driven self-assembly represents an efficient route for the development of smart molecular switches.

Allosteric regulation of rotational, optical and catalytic properties within multicomponent machinery

Allosteric regulation of various functions within multicomponent machinery was triggered by the reversible transformation of nanorotors (k₂₉₈ = 44–61 kHz) to “dimeric” supramolecular structures (k₂₉₈ = 0.60 kHz) upon adding a stoichiometric chemical stimulus.

Reversible switching from a three- to a nine-fold degenerate dynamic slider-on-deck through catenation

Two dynamic slider-on-deck assemblies, i.e. a two-component threefold degenerate (k₂₉₈ = 34.9 kHz) and a catenated three-component ninefold degenerate (k₂₉₈ = 27.9 kHz) system with allosteric effects on the sliding rates, were quantitatively interconverted.

Selective and reversible interconversion of nanosliders commanded by remote control via metal-ion signaling

A multi-device network mainly consisting of two two-component nanosliders was formed by self-sorting of six components. Addition/removal of zinc(ii) ions reversibly reorganized the network by chemical signaling involving the translocation of copper(i) from a relay station followed by the selective disassembly/assembly of one of both multi-component devices. The thus liberated machine parts served to erect a three-component nanoslider alongside the other unchanged two-component nanoslider.

Reversible Interconversion of a Static Metallosupramolecular Cage Assembly into a High-Speed Rotor: Stepless Adjustment of Rotational Exchange by Nucleophile Addition

The self-assembled cage ROT-1 was prepared from the pyridine-terminated rotator 1, the phenanthroline-appended stator 2, DABCO, and copper(I) ions in a ratio of 1:1:1:4. This four-component assembly is held together by two pyridine→[Cu(phenAr₂)]⁺ as well as two DABCO→zinc porphyrin interactions (phenAr₂ = 2,9-diarylphenanthroline) and does not show any motion on the NMR time scale ( k < 0.1 s^-1, 298 K). However, it is converted to the fast nanorotor ROT-1 _x^CD₃CN by addition of CD₃CN [ x = (v/v)% of acetonitrile in dichloromethane] due to acceleration of both pyridine→copper(I) dissociation steps. Now the rotator is able to visit all four copper(I)-loaded phenanthroline stations of the stator. Depending on the amount of CD₃CN, the exchange frequency of the nanorotor varies from 0.7 s^-1 (CD₃CN:CD₂Cl₂ = 1:29) to 8000 s^-1 (CD₃CN:CD₂Cl₂ = 1:5) at 25 °C. When iodide (I^-) is added to the static assembly ROT-1, the rotational speed increases even more drastically ( k = 20 000 s^-1), again due to accelerating the rate-determining pyridine→copper(I) dissociation step. In both cases, a sigmoidal relationship is established between exchange frequency and the concentration of added nucleophile (CD₃CN or iodide) that suggests the presence of a cooperative effect. Reversible switching between the static assembly and fast rotor was performed several times without any decomposition of the system. In contrast, addition of the common nucleophile PPh₃ to ROT-1 does not increase the rotational speed, a finding that is explained on thermodynamic grounds.

Machine Metathesis: Thermal and Catalyzed Exchange of Piston Rods in Multicomponent Nanorotor/Nanoslider Ensemble

Three-component nanorotor R1 ( k₂₉₈ = 80 kHz) and two-component slider-on-deck DS2 ( k₂₉₈ = 440 kHz) were prepared from rotator S1 and stator [Cu₃(1)]³⁺ and from S2 and deck D, respectively. Mixing of R1 with DS2 leads to clean metathesis, furnishing the slower nanodevices R2 ( k₂₉₈ = 29.6 kHz) and DS1 ( k₂₉₈ = 32.2 kHz). Exchange of the piston rods S1 and S2 is completed within 22 min (uncatalyzed) or 3 min (catalyzed) at 298 K.