A “nano-windmill” driven by a flux of water vapour: a comparison to the rotating ATPase

Patrycja Nitoń,Andrzej Żywociński,Robert Hołyst,Marcin Fiałkowski

doi:10.1039/c3nr03496h

Patrycja Nitoń, Andrzej Żywociński + Show 2 more

Open Access

https://doi.org/10.1039/c3nr03496h

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Abstract

We measure the frequency of collective molecular precession as a function of temperature in the ferroelectric liquid crystalline monolayer at the water-air interface. This movement is driven by the unidirectional flux of evaporating water molecules. The collective rotation in the monolayer with angular velocities ω ~ 1 s(-1) (at T = 312 K) to 10(-2) s(-1) (at T = 285.8 K) is 9 to 14 orders of magnitude slower than rotation of a single molecule (typically ω ~ 10(9) to 10(12) s(-1)). The angular velocity reaches 0 upon approach to the two dimensional liquid-to-solid transition in the monolayer at T = 285.8 K. We estimate the rotational viscosity, γ1, in the monolayer and the torque, Γ, driving this rotation. The torque per molecule equals Γ = 5.7 × 10(-8) pN nm at 310 K (γ1 = 0.081 Pa s, ω = 0.87 s(-1)). The energy generated during one turn of the molecule at the same temperature is W = 3.5 × 10(-28) J. Surprisingly, although this energy is 7 orders of magnitude smaller than the thermal energy, kBT (310 K) = 4.3 × 10(-21) J, the rotation is very stable. The potential of the studied effect lies in the collective motion of many (>10(12)) "nano-windmills" acting "in concerto" at the scale of millimetres. Therefore, such systems are candidates for construction of artificial molecular engines, despite the small energy density per molecular volume (5 orders of magnitude smaller than for a single ATPase).

Highlights

The human endeavour to create arti cial molecular machines (AMMs) has become more realistic since the mechanism of biological conversion of chemical energy to mechanical work at the level of a single molecule was understood.[1,2] It resulted in the design of many molecules or assemblies of molecules with the ability to perform work.[3,4,5] Very recently a critical assessment on expectations and promise in relation to arti cial molecular motors was published by Coskun et al.[6]
None of the papers dealing with AMMs considered the Lehmann effect,[12] which describes the collective rotation of chiral molecules of a liquid crystal (LC) driven by a temperature gradient, as a possible mechanism driving the AMMs
Another possible mechanism for powering AMMs was discovered by Tabe and Yokoyama;[13] here collective molecular precession occurs in Langmuir monolayers of chiral LC

Summary

Introduction

The human endeavour to create arti cial molecular machines (AMMs) has become more realistic since the mechanism of biological conversion of chemical energy to mechanical work at the level of a single molecule was understood.[1,2] It resulted in the design of many molecules or assemblies of molecules with the ability to perform work.[3,4,5] Very recently a critical assessment on expectations and promise in relation to arti cial molecular motors was published by Coskun et al.[6]. None of the papers dealing with AMMs considered the Lehmann effect,[12] which describes the collective rotation of chiral molecules of a liquid crystal (LC) driven by a temperature gradient, as a possible mechanism driving the AMMs. Another possible mechanism for powering AMMs was discovered by Tabe and Yokoyama;[13] here collective molecular precession occurs in Langmuir monolayers of chiral LC.

Results

Conclusion