Heat Engine Drives Transport of an Fe^II₄L₄ Cage and Cargo

Abstract

The directed motion of species against a chemical potential gradient is a fundamental feature of living systems, underpinning processes that range from transport through cell membranes to neurotransmission. The development of artificial active cargo transport could enable new modes of chemical purification and pumping. Here, a heat engine is described that drives chemical cargo between liquid phases to generate a concentration gradient. The heat engine, composed of a functionalized FeII4L4 coordination cage, is grafted with oligoethylene glycol imidazolium chains. These chains undergo a conformational change upon heating, causing the cage and its cargo to reversibly transfer between aqueous and organic phases. Furthermore, sectional heating and cooling allow for the cage to traverse multiple phase boundaries, allowing for longer‐distance transport than would be possible using a single pair of phases.

Metal‐Organic Frameworks and Metal‐Organic Cages – A Perspective

“…[121] MOCs can be designed to preferentially partition into one phase and have unique host-guest chemistry in that phase. Even more excitingly, movement of MOCs between phases in response to chemical stimuli [71a] or heat, [122] allows selective transport of their cargoes, and can be engineered to achieve useful outcomes such as anion extraction from water into a less polar solvent. [123] MOCs can also embed in membranes, where transient guestbinding ability allows them to gate the passage of guests such as the alkali metal cations [124] and the chloride anion [125] across boundaries.…”

Functional Material Systems Based on Soft Cages

“…A series of FeII 4 L 4 metal‐organic cages were employed to realize such stimuli‐responsive cargo transportation. A thermoswitchable molecular phase transition was realized using a PEG 1000 (mim) + functionalized cage, cage 24 [41] . The PEG 1000 (mim) + chain is thermal responsive, which expands and exposes hydrophobic ethylene group and thus is less soluble in water at 70 °C.…”

Guest Encapsulation within Surface‐Adsorbed Self‐Assembled Cages

“…The assembly of discrete supramolecular hosts and their solution-phase behavior have been well studied. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Such species adopt a variety of geometries and have found uses in the encapsulation and separation of valuable and hazardous materials, [18][19][20][21] moving cargoes between immiscible phases, [22,23] and catalysis. [24][25][26][27][28][29][30][31] The translation of solution-state chemistry on to solid supports has revolutionized the preparation of peptides and nucleotides, resulting in increased synthetic simplicity, speed, and efficiency.…”

“…The assembly of discrete supramolecular hosts and their solution‐phase behavior have been well studied. [ 1–17 ] Such species adopt a variety of geometries and have found uses in the encapsulation and separation of valuable and hazardous materials, [ 18–21 ] moving cargoes between immiscible phases, [ 22,23 ] and catalysis. [ 24–31 ]…”