Compartmentalization Accelerates Photosensitized NADH to NAD⁺ Conversion

Abstract

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.

Photocatalytic Regeneration of a Nicotinamide Adenine Nucleotide Mimic with Water-Soluble Iridium(III) Complexes

“…For the rhodium co-catalyzed reduction considered here, this could play an important role in the sense that electrostatic interactions between the negatively charged iridium­(III) photosensitizers and the positively charged rhodium co-catalyst could further facilitate the desired photoinduced electron transfer reaction. Such pre-aggregation effects that promote photochemical reactions beyond mere diffusion control could indeed play an underappreciated role in photocatalysis. − Furthermore, it seems that the development of water-soluble strong photoreductants lags considerably behind recent advances made in that regard for organic solvents. − We hope that the insights gained herein and our potent water-soluble iridium­(III) photoreductants will be useful for future developments in photobiocatalysis …”

Initial Quenching Efficiency Determines Light‐Driven H2 Evolution of [Mo3S13]2− in Lipid Bilayers

“…The amphiphilic photosensitizer RuC 9 is known to integrate at the bilayer-water interface of phospholipid membranes due to hydrophobic interactions between the alkyl tails and the hydrophobic core of the membrane, and electrostatic interactions of its [Ru(bpy) 3 ] 2 + -type headgroup and the lipid headgroups. [5,[13][14][15] Upon incorporation into the membrane, RuC 9 retains its photosensitizer activity, as exemplified for lightdriven CO 2 reduction. [5,14] Molecular molybdenum sulfides (thiomolybdates), and specifically [Mo 3 S 13 ] 2À , are known to be highly active HER catalysts when dissolved in organic solvent, [16][17][18][19] while their HER reactivity is affected in presence of water.…”

Alignment and photooxidation dynamics of a perylene diimide chromophore in lipid bilayers

“…In this case the lipid bilayer membrane builds up vesicles which can be varied in size and shape, 5 and can prospectively act as nano-photoreactors. 6 Successful light-driven CO 2 reduction, hydrogen evolution and water oxidation and NADH oxidation at biomimetic lipid bilayer vesicles (liposomes) have previously been reported using metal based photosensitizers based on ruthenium polypyridyl complexes. [5][6][7][8][9][10][11][12] Our motivation to investigate an organic chromophore is to enable light-driven chemical transformations with photosensitizers from more abundant resources.…”

“…6 Successful light-driven CO 2 reduction, hydrogen evolution and water oxidation and NADH oxidation at biomimetic lipid bilayer vesicles (liposomes) have previously been reported using metal based photosensitizers based on ruthenium polypyridyl complexes. [5][6][7][8][9][10][11][12] Our motivation to investigate an organic chromophore is to enable light-driven chemical transformations with photosensitizers from more abundant resources. By constructing a photoactive molecular system with lipid bilayers, the microenvironment of the individual chromophore is altered from typical solution environment which can change and oftentimes improves reaction dynamics or chromophore stability.…”

“…size and surface curvature on the reaction dynamics,6,29 unilamellar, monodisperse vesicles with an average hydrodynamic diameter of around 120 nm were prepared, providing a high surface area compared to giant multilamellar vesicles. The reaction progress was monitored using time resolved and steady state UV-vis absorption spectroscopy, emission spectroscopy and the radical generation was additionally characterized using electron paramagnetic resonance spectroscopy (EPR).…”