In this project we aim to use visible light to drive electrons across a membrane and to accumulate charges in such a way that NAD+ (nicotinamide adenosine dinucleotide) can be converted to NADH. The latter can then fuel enzymatic cascade reactions which ultimately lead to value-added products that are synthesized in the closed compartment of a molecular factory. The use of vesicles made from block copolymer membranes that make up the closed compartment offers the advantage that the enzymatic chemistry can be performed in a protected environment and that oxidation and reduction products resulting from photochemistry can be spatially separated from one another.
The photophysical and photochemical aspects of this project are addressed by the Wenger group while the enzyme chemistry is taken care of by the Ward group. Vesicles built from block copolymers will be made in collaboration with the groups of Meier and Palivan.
In the first phase of the project, strategies for photodriven electron accumulation are explored in suitable model compounds. For example, covalently linked Ru(bpy)32+ (bpy = 2,2’-bipyridine) – naphthalene diimide (NDI) systems are investigated with a view to reducing NDI to NDI- and finally NDI2- in the course of photoirradiation of the Ru(bpy)32+ photosensitizer in presence of sacrificial or non-sacrificial electron donors. Once the challenge of achieving efficient electron accumulation has been tackled, it will be possible to perform light-driven two-electron reduction of suitable small molecule catalysts which are able to reduce NAD+ to NADH.
In parallel, the Wenger group explores the possibility of obtaining other fuels by means of photochemistry, for example formate from CO2. Formate can act as an electron source for various enzymatic reactions hence this molecule can potentially be used to initiate enzyme cascades. Close interaction between the Wenger and Ward groups is key for this purpose.
Furthermore, strategies for the oriented incorporation of molecular wires into block copolymer membranes are explored jointly between the Palivan and Wenger groups. In order to obtain net electron transfer from the outside to the inside of the molecular factories made from vesicles, it will be essential to orient donor-bridge-acceptor systems properly in the membrane.
Possible long-term perspectives include the incorporation of proton pumps into the vesicles in order to transport protons across the membranes, in addition to electrons. This avenue will be explored jointly with the group of Fotiadis. An addition possible avenue is the use of artificial metalloenzymes in the enzyme cascades that rely on engineered anion-π catalysis, as implemented jointly be the groups of Matile and Ward.