A Water‐Soluble Organic Photocatalyst Discovered for Highly Efficient Additive‐Free Visible‐Light‐Driven Grafting of Polymers from Proteins at Ambient and Aqueous Environments

Abstract

Since the pioneering discovery of a protein bound to poly(ethylene glycol), the utility of protein–polymer conjugates (PPCs) is rapidly expanding to currently emerging applications. Photoinduced energy/electron‐transfer reversible addition–fragmentation chain‐transfer (PET‐RAFT) polymerization is a very promising method to prepare structurally well‐defined PPCs, as it eliminates high‐cost and time‐consuming deoxygenation processes due to its oxygen tolerance. However, the oxygen‐tolerance behavior of PET‐RAFT polymerization is not well‐investigated in aqueous environments, and thereby the preparation of PPCs using PET‐RAFT polymerization needs a substantial amount of sacrificial reducing agents or inert‐gas purging processes. Herein a novel water‐soluble and biocompatible organic photocatalyst (PC) is reported, which enables visible‐light‐driven additive‐free “grafting‐from” polymerizations of a protein in ambient and aqueous environments. Interestingly, the developed PC shows unconventional “oxygen‐acceleration” behavior for a variety of acrylic and acrylamide monomers in aqueous conditions without any additives, which are apparently distinct from previously reported systems. With such a PC, “grafting‐from” polymerizations are successfully performed from protein in ambient buffer conditions under green light‐emitting diode (LED) irradiation, which result in various PPCs that have neutral, anionic, cationic, and zwitterionic polyacrylates, and polyacrylamides. It is believed that this PC will be widely employed for a variety of photocatalysis processes in aqueous environments, including the living cell system.

Silver Sulfide Nanocrystals as a Biocompatible and Full-Spectrum Photocatalyst for Efficient Light-Driven Polymerization under Aqueous and Ambient Conditions

“…In contrast to the normal oxygen tolerance behavior, Boyer et al reported an oxygen-mediated reductive quenching process during PET-RAFT polymerization, where the polymerization rate was considerably enhanced in the presence of both oxygen and sacrificial reducing agents (e.g., tertiary amines) under red-NIR illumination . Kwon et al reported the “oxygen-acceleration” phenomenon during the PET-RAFT polymerization of different acrylic and acrylamide monomers in the absence of sacrificial reducing agents and the presence of the newly designed PC . Both studies indicated that oxygen acts as a catalyst to facilitate the electron transfer between the PC in the excited state and the RAFT agent (Figure f).…”

“…This “oxygen-acceleration” behavior was also observed for other types of methacrylic monomers; however, oligo­(ethylene glycol) methyl ether methacrylate (OEGMA) exhibited it most notably, as depicted in Figure e. It is worth noting that “oxygen-acceleration” behavior was recently reported by Boyer et al and Kwon et al , Without degassing and with excellent conversion and polymerization control (α = 97%, M n = 28 600, Đ = 1.08), block copolymer synthesis (PMMA- b -PBzMA) was accomplished, confirming the high vitality of the reaction under those conditions (Figure f).…”

Photoinduced oxygen-catalyzed RAFT polymerization using heterogeneous bionic enzymes

“…40 Furthermore, the removal of the requirement for harsh buffer solvents and the use of non-toxic, environmentally friendly water as solvent, coupled with the recyclability of the heterogeneous phase, promises to expand its use in biomedical applications such as protein-polymer conjugates. 41,42 Mechanistic validation of the OH • -RAFT protocol catalyzed by heterogeneous COF-based bionic enzymes…”

Recognition of “Oxygen-/Water-Fueled” PET-RAFT Protocol Matched to Covalent Organic Frameworks

“…Subsequently, the PET-RAFT protocol of the oxygen-mediated reductive quenching pathway (O-RQP) was defined and its thermodynamic constraints were clarified by density functional theory (DFT) calculations, providing an attractive avenue for the development of oxygen-catalyzed processes . Kwon et al exploited a water-soluble and biocompatible organic small-molecule catalyst to propose a PET-RAFT protocol with molecular oxygen as the electron shuttle, without additional electron sacrificial amine addition …”