Article - Open access - Published: 10 June 2024

Harnessing Maxwell’s demon to establish a macroscale concentration gradient

Jiratheep Pruchyathamkorn, Bao-Nguyen T. Nguyen, Angela B. Grommet, Miroslava Novoveska, Tanya K. Ronson, John D. Thoburn & Jonathan R. Nitschke
Nature Chemistry (2024) Cite this article

Abstract

Maxwell’s demon describes a thought experiment in which a ‘demon’ regulates the flow of particles between two adjoining spaces, establishing a potential gradient without appearing to do work. This seeming paradox led to the understanding that sorting entails thermodynamic work, a foundational concept of information theory. In the past centuries, many systems analogous to Maxwell’s demon have been introduced in the form of molecular information, molecular pumps and ratchets. Here we report a functional example of a Maxwell’s demon that pumps material over centimetres, whereas previous examples operated on a molecular scale. In our system, this demon drives directional transport of o-fluoroazobenzene between the arms of a U-tube apparatus upon light irradiation, transiting through an aqueous membrane containing a coordination cage. The concentration gradient thus obtained is further harnessed to drive naphthalene transport in the opposite direction.

Main

In 1867, James Clerk Maxwell described a thought experiment that probed the limits of the second law of thermodynamics: a ‘demon’ gates the passage of particles between two neighbouring compartments, creating a potential gradient without appearing to do work. In the original thought experiment, two isolated compartments contain gas molecules at equal temperatures (or pressure) and are connected by a molecule-sized gate1,2,3,4,5. An active agent—the demon—selectively opens and closes the gate to partition hot and cold (or high velocity and low velocity) gas molecules into separate compartments. The demon thereby decreases the overall entropy of the system, creating a gradient that represents a source of potential energy. If the gate is frictionless, the demon appears to perform no work during this process—therein lies the paradox. A century later, Szilard developed a variation of Maxwell’s demon whereby a single gas molecule is hypothetically confined within a box and information about the molecule’s location is harnessed to produce work6. This formulation created a connection between Maxwell’s demon and information theory, allowing information to be considered as a physical property. The physicality of storage media thus implies that information must also obey the laws of thermodynamics as it is stored, transmitted and processed7,8,9. A demon must pay a thermodynamic cost to obtain information about individual molecules, thereby offsetting the reduction in entropy when creating a temperature gradient across the system. Furthermore, a physical demon’s capacity for remembering information about individual molecules must necessarily be finite; in forgetting this information to sort a new collection of molecules, heat must be dissipated.

Experimental analogues of Maxwell’s demon and molecular pumps have been developed10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33. A rotaxane-based molecular information ratchet, realized by David Leigh’s team, was arguably the first physical manifestation of a Maxwell’s demon. In Leigh’s system, a photoresponsive gate is positioned asymmetrically on the axle of a rotaxane, creating two neighbouring ‘compartments’ on either end29. Upon light irradiation, information regarding the proximity of the macrocycle to the gate drives unidirectional movement of the macrocycle across the axle. Whereas Leigh’s demon operates on a molecular scale, Raizen et al. demonstrated a similar principle within a system composed of many atoms, which reside in a potential well created by a magnet34, where a one-way gate composed of two optical beams plays the role of the demon, driving unidirectional movement of particles over an optical barrier and into a higher-energy compartment.

In this Article, we report a sorting system that drives the formation of an o-fluoroazobenzene (FAB) concentration gradient on the macroscale, across centimetres. As in Maxwell’s thought experiment, our system is composed of two neighbouring compartments, consisting of two layers of dodecane solvent in two arms of a U-tube apparatus (Fig. 1). Coordination cage 1 (Fig. 1a) functions as a molecule-sized, demon-attended gate. We also explore the addition of the competing guest naphthalene to push the system further out of equilibrium (Fig. 1b) and the use of our demon as a pump to create a naphthalene concentration gradient (Fig. 1c), as discussed below.