Chemically Fueled Logic AND Gate with Double Encoding in the Time Domain.

To increase information density and security in communication, Nature at times encodes signals in the time domain, for instance, Ca2+ ion signals. Double encoding in the time domain operates beyond this level of security because the data are encoded in two time-dependent output signals showing distinct periods, frequencies, and full duration half-maxima. To illustrate such a protocol, a three-component ensemble consisting of a double ion-selective luminophore with two distinct receptor sites, hexacyclen, and diaza-18-crown-6 ether is demonstrated to act as a logic AND gate with Ag+ and Ca2+ ions as inputs. The gate shows an unprecedented 2-fold time-encoded fluorescence output at 590 and 488 nm based on metal ion pulses with distinct periods when trichloroacetic acid is applied as chemical fuel.

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.

Orthogonal Initiation of Molecular Motion Devices by Two Chemical Fuels.

Herein, we demonstrate the selective dissipative and orthogonal actuation of two distinct molecular devices controlled by alternate fuel use. When the multicomponent ensemble of [2]rotaxane 1 and turnstile [Cu(2)(3)]+ was charged with AgBF4 as chemical fuel (Fuel 1) together with NEt3/PhCH2Br (cofuels), the transiently formed [Ag(1)]+ showed a stochastic shuttling of the silver macrocycle between two degenerate triazole stations on the thread (k298 = 1.2 × 105 s-1), whereas [Cu(2)(3)]+ was unperturbed. Instead, treatment of the mixture with PPh3 as an alternative fuel (Fuel 2) in the presence of oxidant 4 (cofuel) generated the complex [Cu(3)(PPh3)2]+ and transient thermal motion in rotor 2 (k298 = 4.9 × 104 s-1), whereas rotaxane 1 stayed dormant. Thus, two distinct chemical fuels selectively and orthogonally activated two distinct transient motion devices from a multicomponent mixture. In total, four interference-free dissipative cycles were demonstrated by using alternating fuel additions.

Multicomponent Pseudorotaxane Quadrilateral as Dual-Way Logic AND Gate with Two Catalytic Outputs.

A multicomponent pseudorotaxane quadrilateral was reversibly toggled between three distinct switching states. Switching in the forward conversion was achieved by addition of H+ and K+ ions, and switching in the reverse direction was performed by addition of 18-crown-6 and 1-aza-18-crown-6. In both the forward and backward ways, the inputs operated an AND gate with distinct catalytic outputs. While in the forward direction the logic AND operation starting from a heteroleptic five-component assembly turned "ON" an imine hydrolysis as output (AND-1), in the inverse direction a Michael addition was ignited as the output starting from a seven-component aggregate following the AND gate logic (AND-2).

Potential-Dependent Adhesion Forces between dsDNA and Electroactive Surfaces.

A promising approach to regulating the interactions between polyelectrolytes and materials is the use of electroactive surfaces that can change their charge state. However, common electroactive groups are too unstable to be practical for this purpose. Here we have performed a single molecule force spectroscopy study of the interactions between dsDNA and an 1,1'-biferrocenylene (BFD = bis(fulvalene)diiron)-terminated self-assembled monolayer surface that allows us to reversibly change the charge state. We found that the interaction force between DNA and the surface is correlated to the oxidation state of the BFD groups, which is conveniently controlled by the electrochemical potentials. We discovered that the electroactive SAM produces much stronger interaction forces than its nonelectroactive counterpart. A model based on the Grahame equation was able to quantitatively reproduce the experimentally observed relation between the applied potentials and adhesion forces. Our electroactive surface provides a model system for quantitative studies of the interactions between polyelectrolyte and charged surfaces in liquid. These insights may enable new opportunities for actively manipulating the binding, orientations, and conformations of polyelectrolytes for biosensing, nanomotors, and other applications.

Three-Input Logic AND Gate Drives Sequential Three-Step Catalysis by Parallel Activation of H+ and Ag+ as a Catalyst Duo.

Boolean operations with multiple catalysts as output are yet unknown using molecular logic. The issue is solved using a two-component ensemble, composed of a receptor and rotaxane, which acts as a three-input AND gate with a dual catalytic output. Actuation of the ensemble gate by the stoichiometric addition of metal ions (Ag+ and Cd2+) and 2,2,2-trifluoroacetic acid generated in the (1,1,1) truth table state a catalyst duo that synergistically enabled a three-step reaction, furnishing a dihydroisoquinoline as the output of a three-input logic AND gate operation.

(Nano)mechanical Motion Triggered by Metal Coordination: from Functional Devices to Networked Multicomponent Catalytic Machinery.

A look at the elegance and efficiency of biological machines readily reveals that Nature masters the full gamut of chemical interactions to compose masterpieces of the living world. The present analysis singles out metal coordination for the actuation of nanomechanical motion. According to our analysis, metal coordination has a manifold of rewards, putting it primo loco in opportunities for putting nanomechanical systems into action: (i) its strength and dynamics can be properly modulated and fine-tuned by the choice of metal, redox state, and ligand(s), (ii) the high directionality of the interaction allows reliable design, and (iii) the emergence of novel self-sorting algorithms allows multiple of these interactions to be working in parallel. On top of all these advantages, intermolecular metal-ion translocation is a well-known factor in biological signaling. These benefits have recently proven their usefulness in the operation of networked devices and in overcoming the limitations of traditional stand-alone molecular systems.

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.

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.

Off-Equilibrium Speed Control of a Multistage Molecular Rotor: 2-Fold Chemical Fueling by Acid or Silver(I).

Driving conformational motion in defined off-equilibrium oscillations can be achieved using chemical fuels. When the ultrafast turnstile 1 (k298> 1012 Hz) was fueled with 2-cyano-2-phenylpropanoic acid (Fuel 1), the diprotonated rotor [H2(1)]2+ (k298 = 84.0 kHz) formed as a transient regaining the dynamics of the initial turnstile after consumption of the fuel (135 min). Upon addition of silver(I) (Fuel 2) to turnstile 1, the metastable rotor [Ag2(1)]2+ (k298 = 1.57 Hz) was initially furnished, but due to a consequentially triggered SN2 reaction, the Ag+ ions were consumed as insoluble AgBr along with regeneration of 1 (within 3 h). The off-equilibrium fast ⇆ slow rotor conversions fueled by acid and silver(I) were directly monitored by fluorescence and 1H NMR. In addition, metal ion exchange was fueled enabling off-equilibrium oscillations between rotors [Li2(1)]2+ ⇆ [Ag2(1)]2+. In the end, both sustainability and efficiency of the process were increased in unison by using the interfering proton waste in the formation of a [2]pseudorotaxane.

A Switchable Catalyst Duo for Acyl Transfer Proximity Catalysis and Regulation of Substrate Selectivity.

Enzymes are encoded with a gamut of information to catalyze a highly selective transformation by selecting the proper reactants from an intricate mixture of constituents. Mimicking biological machinery, two switchable catalysts with differently sized cavities and allosteric control are conceived that allow complementary size-selective acyl transfer in an on/off manner by modulating the effective local concentration of the substrates. Selective activation of one of two catalysts in a mixture of reactants of similar reactivity enabled upregulation of the desired product.

Cooperative Effects in Switchable Catalysis: Enhancing Double-Click Reaction Yield of Symmetrical Rotaxanes.

Reversible switching between the closed cyclic dimeric assembly [Cu2 (1)2 ]2+ (OFF state) and the extended dimeric homoleptic complex [FeCu2 (1)2 ]4+ (ON State) by addition/removal of Fe2+ triggered catalysis of a double-click reaction and high yield preparation of [2]rotaxanes. Mechanistic and computational studies provide valuable general insight for double-click strategies by revealing cooperative effects in the second cycloaddition step due to a distance-tolerant preorganization of the first-click product by the two copper(I)-loaded phenanthroline subunits of [FeCu2 (1)2 ]4+ .

Reversible Multicomponent AND Gate Triggered by Stoichiometric Chemical Pulses Commands the Self-Assembly and Actuation of Catalytic Machinery.

The present work demonstrates the operation of a reversible supramolecular gate, i.e., an ensemble of various components linked by chemical communication, which is triggered by stoichiometric chemical inputs and by obeying the AND truth table delivers a stoichiometric chemical signal. The output triggers a series of events that finally set up a catalytic process. In detail, a three-component AND gate, composed of two distinct nanoswitches, a copper-loaded and an unloaded one {= state (0,0)}, was actuated with stoichiometric amounts of two inputs (IN-1 = Zn2+, IN-2 = Hg2+) generating copper(I) ions as output in state (1,1). The utility of this information processing was highlighted by using the copper(I) output for triggering the self-assembly of the four-component rotor ROT-2 through metal translocation. In the presence of suitable reactants, ROT-2 acted as a catalytic machinery catalyzing a click reaction (= signal amplification). Verification of the functioning of the AND gate in a mixture of 12 components was thus accomplished by monitoring formation of the click product. Due to the stoichiometric design, the gate was reset to state (0,0) by adding hexacyclen and reactivated by adding inputs IN-1 and IN-2 alike in the first cycle.

Dynamics of Hydrogen Bonding in Three-Component Nanorotors.

The dynamics of hydrogen bonding do not only play an important role in many biochemical processes but also in Nature's multicomponent machines. Here, a three-component nanorotor is presented where both the self-assembly and rotational dynamics are guided by hydrogen bonding. In the rate-limiting step of the rotational exchange, two phenolic O-H-N,N(phenanthroline) hydrogen bonds are cleaved, a process that was followed by variable-temperature 1 H NMR spectroscopy. Activation data (ΔG≠ 298 =46.7 kJ mol-1 at 298 K, ΔH≠ =55.3 kJ mol-1 , and ΔS≠ =28.8 J mol-1 K-1 ) were determined, furnishing a rotational exchange frequency of k298 =40.0 kHz. Fully reversible disassembly/assembly of the nanorotor was achieved by addition of 5.0 equivalents of trifluoroacetic acid (TFA)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) over three cycles.

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.

Double Rotors with Fluxional Axles: Domino Rotation and Azide-Alkyne Huisgen Cycloaddition Catalysis.

The simple preparation of the multicomponent devices [Cu4 (A)2 ]4+ and [Cu2 (A)(B)]2+ , both rotors with fluxional axles undergoing domino rotation, highlights the potential of self-sorting. The concept of domino rotation requires the interconversion of axle and rotator, allowing the spatiotemporal decoupling of two degenerate exchange processes in [Cu4 (A)2 ]4+ occurring at 142 kHz. Addition of two equiv of B to rotor [Cu4 (A)2 ]4+ afforded the heteromeric two-axle rotor [Cu2 (A)(B)]2+ with two distinct exchange processes (64.0 kHz and 0.55 Hz). The motion requiring a pyridine→zinc porphyrin bond cleavage is 1.2×105 times faster than that operating via a terpyridine→[Cu(phenAr2 )]+ rupture. Finally, both rotors are catalysts due to their copper(I) content. The fast domino rotor (142 kHz) was shown to suppress product inhibition in the catalysis of the azide-alkyne Huisgen cycloaddition.

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.

Time-Dependent Pulses of Lithium Ions in Cascaded Signaling and Out-of-Equilibrium (Supra)molecular Logic.

The present paper adds the time domain to chemical ion translocation and (supra)molecular logic. When the self-sorted system of [Zn(1)]2+ + [Li(2)]+ + 3 (composed of hexacyclen 1, nanoswitch 2, luminophore 3) was treated with 2-cyano-2-phenylpropanoic acid (4) as a chemical fuel, protonation of 1 entailed a cascade translocation of first Zn2+, then Li+, resulting in the system [H(1)]+ + [Zn(2)]2+ + [Li(3)]+ that slowly reversed back to the initial state. The kinetic evolution of the lithium pulses was followed by changes in color and luminescence using the lithium-sensitive probe 3. The utility of fueling in combination with lithium pulses was exemplified among others by generating time-encoded SOS morse signals and implementing the time domain in two distinct AND gates.

Switching Dual Catalysis without Molecular Switch: Using A Multicomponent Information System for Reversible Reconfiguration of Catalytic Machinery.

Different from the current paradigms of chemistry, a switchable catalytic system is presented that does not rely on a molecular switch in different toggling states but on a smart seven-component mixture that manages the reversible ON/OFF regulation of two catalytic processes. Hereunto, the workflow of two multicomponent rotary catalytic machineries was interlinked by the simultaneous shuffling of two components (metal and ligand) requiring perfect signaling in a 13-component system (see Movie 1). This network underwent reversible switching over three cycles as demonstrated by 1H NMR, UV-vis, and fluorescence spectroscopies and electrospray ionization mass spectrometry. Addition and removal of zinc(II) ions trigger three distinct events in parallel: the (i) mutually dependent self-assembly of three-component nanorotors and two-component reservoirs by resorting components, (ii) toggling between vastly different rotational exchange rates in the self-assembled rotors that directly affect catalysis, and (iii) toggling between two diverse catalytic reactions in a fully reproducible manner. Because of this information system, the concentrations of free aza-crown ether 7 and its complex with copper(I), that is, [Cu(7)]+, which represent the effective catalysts, are up- and downregulated in a manner to alternately switch ON/OFF a catalytic conjugate addition and a click reaction.