Compartmentalization Accelerates Photosensitized NADH to NAD+ Conversion

Confinement of reaction spaces was achieved in a biomimetic manner by using liposome vesicles that are based on phospholipid bilayer membranes, similar to cellular compartments. Encapsulation of photosensitizer (PS) and substrate within the inner aqueous compartment of liposomes accelerated the photosensitized model reaction of nicotinamide adenine dinucleotide (NADH) conversion to its oxidized form (NAD+) by one order of magnitude compared to classical homogeneous reaction conditions. Furthermore, it was found that the reaction proceeds around 40 % faster when the photosensitizer is dissolved in the inner aqueous compartment instead of being embedded within the phospholipid bilayer which is attributed to the diffusion behavior of singlet oxygen which acts as oxidant in this reaction. These experimental findings will allow for reaction and molecular systems design for photochemical and catalytic conversions and will be relevant in the context of creating artificial cellular compartments such as fully artificial chloroplasts. Top speed: Acceleration of reaction rates by one order of magnitude was achieved through compartmentalization of the photosensitizer and the substrate nicotinamide adenine dinucleotide (NADH) in liposomes. Differences in reaction dynamics were found for two types of photosensitizer incorporation, probably due to local concentrations and the diffusion behavior of singlet oxygen. These findings might be relevant in the context of reaction engineering and artificial cellular compartments.