Block copolymer micelles as colloidal catalysts for photocatalytic NAD+ reduction

Abstract

We herein report the preparation, characterization and (photo)catalytic investigation of block copolymer micelles based on amphiphilic, pH-responsive block copolymers featuring pendant bipyridyl rhodium complexes as NAD⁺ reduction catalyst and ruthenium polypyridyl complexes as photosensitizers. A well-defined polystyrene-block-poly((acrylic acid)-co-(2-(4-(4′-methyl-2,2′-bipyridyl))ethylacrylate)) (PS-b-P(AA-co-bpyEA)) block copolymer was synthesized via nitroxide-mediated polymerization (NMP). In post-polymerization functionalization reactions utilizing the pendant bpy moieties rhodium and ruthenium centers were covalently incorporated into the pH-responsive segment of the block copolymer. Proof of successful metal attachment was provided by nuclear magnetic resonance spectroscopy (NMR) and X-ray photoelectron spectroscopy (XPS) as well as size-exclusion chromatography (SEC). Morphological and structural investigations of the obtained block copolymer micelles in aqueous solutions using dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning transmission electron microscopy in combination with energy dispersive X-ray spectroscopy (STEM-EDX) were performed. The respective model complexes and the metal-functionalized block copolymer micelles were finally tested as soft matter-based photocatalytic systems for NADH formation.