Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors

Abstract

Nitrous oxide (N 2 O) is a potent greenhouse and ozone-reactive gas for which emissions are growing rapidly due to increasingly intensive agriculture. Synthetic catalysts for N 2 O decomposition typically contain precious metals and/or operate at elevated temperatures driving a desire for more sustainable alternatives. Here we demonstrate self-assembly of liposomal microreactors enabling catalytic reduction of N 2 O to the climate neutral product N 2 . Photoexcitation of graphitic Ndoped carbon dots delivers electrons to encapsulated N 2 O Reductase enzymes via a lipid-soluble biomolecular wire provided by the MtrCAB protein complex. Within the microreactor, electron transfer from MtrCAB to N 2 O Reductase is facilitated by the general redox mediator methyl viologen. The liposomal microreactors use only earth-abundant elements to catalyze N 2 O removal in ambient, aqueous conditions.

Bioinspired photocatalytic systems towards compartmentalized artificial photosynthesis

“… a Liposome embedding a synthetic molecular CPQ triad, quinone and a F 0 -F 1 -ATP synthase for electron and proton transfer across the membrane with concomitant pH gradient generation coupled to the synthesis of ATP reported by A. Moore et al, 96 ( b ) proteoliposome embedding MtrCAB from S. oneidensis MR-1 and encapsulated N 2 O reductase for electron transfer across membrane with N 2 O-to-N 2 reduction reported by J. N. Butt et al, 58 ( c ) polymersome embedding donor and acceptor molecules at each domain of the membrane for transmembrane energy transfer reported by Y. Zheng, Y. Zhou et al, 119 ( d ) polymersome with embedded bacteriorhodopsin a F 0 -F 1 -ATP synthase for transmembrane proton transfer coupled to ATP synthesis reported by T. Vidaković-Koch et al, 99 ( e ) liposome containing a Ru-PS and a Ru-WOC for light-driven WO reported by L. Sun, B. König et al, 127 ( f ) liposome with a Ru-PS and a Co-HEC for light-driven HER reported by B. König et al, 132 ( g ) liposome with a Ru-PS and a Co-HEC for light-driven HER reported by S. Bonnet et al, 130 ( h ) liposome with a Ru-PS and a CoPc-CO 2 RC for light-driven CO 2 reduction to CO reported by L. Hammarström, E. Reisner et al, 93 ( i ) liposome with a HER-MOF embedded in the hydrophobic membrane and an encapsulated WO-MOF for overall light-driven WS reported by W. Lin, C. Wang et al 140 . …”

“…Moreover, in the recent years artificial vesicles have gained increasing interest to study the encapsulation of different biologic or synthetic catalysts and separate reactivity, with the potential to create very complex catalytic systems with synchronised reactivity towards chemical production but also in the field of energy 7 – 17 . Indeed, those artificial systems can be used as simplified model systems to study different processes in the membrane and at interfaces, such as vectorial electron transport, utilization of proton gradients as source of energy and transport of electrons, energy vectors and small molecules across membranes, relevant processes for AP 9 , 10 , 16 , 17 , 42 , 46 , 49 , 58 – 62 .…”

“…The use of simplified bioinspired artificial vesicles as model systems can shine a light on the intricate interplay of charge separation dynamics across membranes. Examples of bioinspired vesicular systems to study energy transfer, electron transfer, proton transfer, and transfer of other energy vectors across membranes have been reported in the last years 58 – 62 , 94 – 103 . A vast majority of those examples rely on liposomes, since their use gained increasing interest with the pioneer examples from the groups of JM.…”

“…The authors reported the integration of an icosa-haem transmembrane electron transfer protein (MtrCAB) 111 , 112 isolated from Shewanella oneidensis MR-1 into a liposome membrane. And demonstrated electron transport across the membrane towards the inner compartment of the liposomes where either a redox-active dye, reactive red 120 (RR120) 62 , or a N 2 O reductase enzyme 58 were encapsulated. In the first case, photoreduction of the embedded MtrCAB by an external synthetic light-harvester in the presence of an electron donor (EDTA) allowed for electron transport towards the inner space with concomitant bleaching of the RR120 band at 539 nm 62 .…”

“…Likewise, the photoreduction of MtrCAB in proteoliposomes containing the N 2 O reductase (N 2 OR) enzyme allowed the reduction of the greenhouse gas N 2 O to N 2 by the encapsulated enzyme upon electron transfer (Fig. 3b ) 58 . More recently, the groups of M. Ohba 113 , A. Ikeda 114 and S. Bonnet 115 – 118 demonstrated efficient energy transfer across lipid membranes.…”