Autonomous fuelled directional rotation about a covalent single bond

Abstract

Biology operates through autonomous chemically fuelled molecular machinery, 1 including rotary motors such as ATP synthase 2 and the bacterial flagellar motor. 3 Chemists have long sought to create analogous molecular structures with chemically powered, directionally rotating, components. 4-17 However, synthetic motor-molecules capable of autonomous 360 directional rotation about a single bond have proved elusive, previous designs lacking either autonomous fuelling 7,10,12 or directionality. 6 Here we show that 1-phenylpyrrole 2,2′-dicarboxylic acid 18,19 (1a) is a catalysis-driven 20,21 motor that can continuously transduce energy from a chemical fuel 9,20-27 to induce repetitive 360 directional rotation of the two aromatic rings around the covalent N-C bond that connects them. Upon treatment of 1a with a carbodiimide, 21,25-27 intramolecular anhydride formation between the rings, and the anhydride's hydrolysis, both occur incessantly. Both reactions are kinetically gated 28-30 causing directional bias. Accordingly, catalysis of carbodiimide hydration by the motor-molecule continuously drives net directional rotation around the N-C bond. The directionality is determined by the handedness of both an additive 31 that accelerates anhydride hydrolysis and that of the fuel, and is easily reversed. >97% of fuel molecules are consumed through the chemical engine cycle 24 with a directional bias of up to 71:29 with a chiralitymatched fuel and additive. In other words, the motor makes a 'mistake' in direction every 3-4 turns. The 26-atom motor-molecule's simplicity augurs well for its structural optimisation and the development of derivatives that can be interfaced with other components for the performance of work and tasks. 32-36In 1999, Feringa reported 13 the first synthetic molecular rotary motor, based on light-driven isomerisation around a double bond. 14 Contemporaneously, 5 Kelly explored a chemically fuelled triptycene derivative, 15 conceptually related to Feynman's ratchet, 16,17 that directionally rotated 120 about a single bond. Our group have described catenanes that undergo pulsed 11 or autonomous 9 chemically fuelled rotation of one macrocycle around another and have recently used 21 carbodiimide chemical fuels to drive a rotaxane-based information 37-41 ratchet. A feature of the latter system's fuelling cycle (Supplementary Information, Section S2.5) is the formation of a transient activated ester. 23 Similar activated ester and anhydride intermediates have been exploited in dissipative assembly [25][26][27] and Hartley has shown that tethering diphenic acids as anhydrides produces a dynamic change in the angle between the biphenyl rings. 42,43 As both carbodiimide-fuelled formation of an anhydride and its subsequent hydrolysis can occur under the same set of conditions, 25,26,42,43 we reasoned that asymmetric catalysis of the formation and/or hydrolysis of the anhydride could potentially directionally bias the rotation of rings joined by

Information thermodynamics for deterministic chemical reaction networks

“…To fix ideas, the Pac-Man shaped molecule can be thought of as an enzyme binding (state x) the monomeric form of a substrate and phosphorylated (state y) by adenosine triphosphate (F) to adenosine diphosphate (W) hydrolysis. A concrete example with a simpler yet similar bipartite structure is found in a recently reported single-molecule molecular motor, where the two states are the axial chirality (which can be in the R state or S state) and the chemical state (which can be in the diacid state or anhydride state) of the motor 73. The latter results in a linear bipartite network to which the treatment in Ref.…”

“…A concrete example with a simpler yet similar bipartite structure is found in a recently reported single-molecule molecular motor, where the two states are the axial chirality (which can be in the R state or S state) and the chemical state (which can be in the diacid state or anhydride state) of the motor. 73 The latter results in a linear bipartite network to which the treatment in Ref. 40 straightforwardly applies.…”

Chemically Driven Rotatory Molecular Machines

“… The first autonomous engine to cause 360° rotation around a single bond by catalysis.1‐Phenylpyrrole‐2,2′‐dicarboxylic acid 24 can continuously convert energy from a chemical fuel to cause repeated 360° rotation of the two aromatic rings through the continuous intramolecular anhydride formation between the rings and hydrolysis of the anhydride. The chiral fuel 25 and the hydrolysis catalyst 26 are used to create a directional bias leading to a net rotation around the N−C bond [101] …”

Control on dissipative kinetics reveals the entropically-dominated essence of interlocked molecular machines

“…Indeed, from the point of view of the underlying physics, cyclic chemical reaction networks that are traveled unidirectionally represent a clear demarcation point between chemical reaction networks that can or cannot absorb work from the environment repeatedly, operating as molecular ratchets. [12][13][14][15][16][17][18][19][20][21] Thus, cyclic reaction sequences are a prerequisite to perform more elaborated tasks, such as directional motion and progressive driving chemical reactions away from equilibrium. [7,22] As a general example of cyclic chemical reaction network, we consider a square reaction scheme for pseudorotaxane assembly that can be traveled unidirectionally upon alternating acid-base stimuli, leading to energetically-demanding transport (Figure 1).…”