Light-Driven Biocatalysis in Liposomes and Polymersomes: Where Are We Now?

Abstract

The utilization of light energy to power organic-chemical transformations is a fundamental strategy of the terrestrial energy cycle. Inspired by the elegance of natural photosynthesis, much interdisciplinary research effort has been devoted to the construction of simplified cell mimics based on artificial vesicles to provide a novel tool for biocatalytic cascade reactions with energy-demanding steps. By inserting natural or even artificial photosynthetic systems into liposomes or polymersomes, the light-driven proton translocation and the resulting formation of electrochemical gradients have become possible. This is the basis for the conversion of photonic into chemical energy in form of energy-rich molecules such as adenosine triphosphate (ATP), which can be further utilized by energy-dependent biocatalytic reactions, e.g. carbon fixation. This review compares liposomes and polymersomes as artificial compartments and summarizes the types of light-driven proton pumps that have been employed in artificial photosynthesis so far. We give an overview over the methods affecting the orientation of the photosystems within the membranes to ensure a unidirectional transport of molecules and highlight recent examples of light-driven biocatalysis in artificial vesicles. Finally, we summarize the current achievements and discuss the next steps needed for the transition of this technology from the proof-of-concept status to preparative applications.

Polymeric Micro/Nanocarriers and Motors for Cargo Transport and Phototriggered Delivery

“…PAMs can link the hydrophobic and hydrophilic segments of the polymer (Figure 3B) or the hydrophobic segments of the polymersome (Figure 6C). UV-NIR irradiation photoactivates the PAMs, destabilizing the hydrophobic/hydrophilic balance via photoisomerization and photocleavage mechanisms for spatiotemporal control of cargo delivery [231]. For example, Molla et al developed a new light-induced interfacial layer from an oil-azobenzene-water nanopolymersome of 100 nm in diameter, encapsulating rhodamine 6G dye (hydrophilic molecule) and Dil dye (hydrophobic molecule).…”

Toward Artificial Cells: Novel Advances in Energy Conversion and Cellular Motility

“…Although GUVs are becoming a promising approach to tackling the problem of sophisticated interchanges in living cells, groups developing artificial cells around the world are still struggling to mimic the complex biochemical reactions in GUVs . Nonetheless, this continuous endeavor has not produced tangible results because the reaction cascades in the GUVs are still challenging despite the huge efforts to achieve reaction cascades in vesicles .…”

“…An appropriate interface can be achieved from different building blocks, such as natural and synthetic lipids, three‐block copolymers, or hybrid materials 50c,105a,121. Phospholipids are the most favorable building blocks because they are versatile and more biocompatible than copolymers .…”

Light‐Driven Proton Transfer for Cyclic and Temporal Switching of Enzymatic Nanoreactors

“…Light‐driven proton transfer is widely employed by living cells and bacteria to initiate signal transduction of biological pathways. [ 11,42–45 ] Recently, light‐induced proton‐pumps (LIPPs) have been unidirectionally incorporated within polymeric and liposomal vesicles to pump protons into the lumen [ 46,47 ] or outside of the vesicles [ 48 ] and to fabricate larger complex cellular compartments with LIPPs inducing artificial photosynthetic processes. [ 49,50 ] Inspired by these results, light‐driven proton transfer triggered by the switching of MEH/SP [ 51,52 ] (Scheme 1) and its derivatives [ 51,53,54 ] has been successfully applied for the temporal control of pH switches, [ 51,52 ] proton‐catalyzed reactions, [ 51 ] proton/ion transfer through bilipid vesicles, [ 38 ] self‐assembly of nanoparticles, [ 55 ] and proton‐driven molecular machines.…”