Susnata Pramanik

Reversible ON/OFF nanoswitch for organocatalysis: mimicking the locking and unlocking operation of CaMKII.

Flip a switch: a nanoswitch uses chemical inputs to turn an organocatalytic Knoevenagel reaction on and off (see scheme: R=reactant, P=product). To stop catalysis the chemical input (pink and green) wraps around the inhibitory segment of the nanoswitch to effect release or unlocking of the switch. The process can run reversibly over three cycles without loss of activity.

A Toggle Nanoswitch Alternately Controlling Two Catalytic Reactions

Reversible switching between two states of the triangular nanoswitch [Cu(1)](+) was accomplished by alternate addition of 2-ferrocenyl-1,10-phenanthroline (2) and copper(I) ions. The two switching states regulate the binding and release of two distinct catalysts, piperidine and [Cu(2)](+), in a fully interference-free manner and allow alternating on/off switching of two orthogonal catalytic processes. In switching state I, piperidine is released from the nanoswitch and catalyzes a Knoevenagel addition between 4-nitrobenzaldehyde and diethyl malonate (ON-1 and OFF-2), while in state II the released [Cu(2)](+) catalyzes a click reaction between 4-nitrophenylacetylene and benzylazide (OFF-1 and ON-2). Upon addition of one equivalent of 2 to the (OFF-1 and ON-2)-state, both catalytically active processes are shut down (OFF-1 and OFF-2).

Bidirectional Chemical Communication between Nanomechanical Switches

The interplay of biological machines depends critically on the bidirectionality of chemical information exchange. The implementation of such a communication procedure for abiological systems is achieved using two nanoswitches that both operate as transmitters and receivers by transfering copper ions in oxidation states +I and +II. Even at micromolar concentrations, communication in both directions is remarkably fast, occurring at t1/2 =2-3 min. Metal ion translocation triggers a 20 Å relocation of the toggle at both nanoswitches, entailing major geometric and electronic changes.

Networking Nanoswitches for ON/OFF Control of Catalysis

The nanoswitches 1 and 2 are interdependently linked in so-called network states (NetStates). In NetState I, defined by presence of [Cu(1)]+ and 2, the organocatalyst N-methylpyrrolidine catalyzes a conjugate addition. Addition of iron(II) ions as an external chemical trigger to NetState I discharges Cu+ from [Cu(1)]+. The liberated copper(I) ion acts as a second messenger and changes the toggling state at nanoswitch 2. The resulting nanoswitch [Cu(2)]+ captures the catalytically active species from solution and the conjugate addition is turned OFF. Removal of the original trigger reverses the sequence and turns catalysis ON. The ON/OFF catalytic cycle was run three times in situ.

Photochromic Hydrazone Switches with Extremely Long Thermal Half-Lives

A family of easily accessible light-activated hydrazone switches has been developed having thermal half-lives of up to 2700 years! Structure-property analysis shows that replacing the rotor pyridyl group of our typical hydrazone switch with a phenyl one leads to the long-lived negative photochromic compounds. The switching properties of the hydrazones in both toluene and DMSO were assessed offering insights into the kinetics and thermodynamics of the switching process.

Catalytically active nanorotor reversibly self-assembled by chemical signaling within an eight-component network

A catalytically active three-component nanorotor is reversibly self-assembled and disassembled by remote control. When zinc(ii) ions (2 equiv.) are added as an external chemical trigger to the mixture of transmitter [Cu(1)]+ and pre-rotor assembly [(S)·(R)], two equiv. of copper(i) ions translocate from [Cu(1)]+ to the two phenanthroline sites of [(S)·(R)]. As a result, [Zn(1)]2+ forms along with the three-component assembly [Cu2(S)(R)]2+, which is both a nanorotor (k298 = 46 kHz, ΔH‡ = 49.1 ± 0.4 kJ mol-1, ΔS‡ = 9.5 ± 1.7 J mol-1 K-1) and a catalyst for click reactions (catalysis ON: A + B→AB). Removal of zinc from the mixture reverts the translocation sequence and thus commands disassembly of the catalytically active rotor (catalysis OFF). The ON/OFF catalytic cycle was run twice in situ in the full network.