Modelling Photosynthesis with Zn(II)‐Protoporphyrin all‐DNA G‐Quadruplex/Aptamer Scaffolds

All-DNA scaffolds act as templates for the organization of photosystem I (PS I) model systems. A series of DNA templates composed of Zn(II)-protoporphyrin IX (Zn(II)PPIX)-functionalized G-quadruplex conjugated to the 3 ' - or 5 ' -end of the tyrosinamide (TA) aptamer and Zn(II)PPIX/G-quadruplex linked to the 3 ' - and 5 ' -ends of the tyrosinamide aptamer through a four-thymidine (4xT) bridge, structures I to IV. Effective photoinduced electron transfer (ET) from Zn(II)PPIX/G-quadruplex to bipyridinium functionalized tyrosinamide, TA-MV 2+ , bound to the TA aptamer units is demonstrated. The order of photosensitized ET quenching in the photosystems is III > IV > I > II and follows the binding affinities of TA-MV 2+ to the aptamer units. The effectiveness of the primary ET quenching of Zn(II)PPIX/G-quadruplex by TA-MV 2+ controls the efficiency of the generation of TA-MV +* , under steady-state illumination, in the presence of 2-mercaptoethanol as sacrificial electron donor. The photosystem-controlled formation of TA-MV +* by the different photosystems dictates the secondary activation of the ET cascade corresponding to the ferredoxin-NADP + reductase, FNR, catalysed reduction of NADP + to NADPH by TA-MV +* , and the sequestered alcohol dehydrogenase catalysed reduction of acetophenone to 1-phenylethanol by NADPH. The photosensitizer-aptamer conjugates reveal switchable "ON"/"OFF" photoactivities. Also, a photosystem consisting of Zn(II)PPIX/G-quadruplex linked to the 3 ' - and 5 ' -ends of two TA aptamer units, structure V, revealing the improved photoinduced ET quenching and subsequent biocatalytic cascades, is presented. Scaling of the all-DNA photosensitizer-aptamer/electron acceptor is achieved by the rolling-circle-amplified (RCA) synthesis of micrometre-long chains consisting of Zn(II)PPIX/G-quadruplex linked to two TA aptamer repeat units.