PET‐RAFT as a facile strategy for preparing functional lipid–polymer conjugates

Catalyzing PET-RAFT Polymerizations Using Inherently Photoactive Zinc Myoglobin

Protein photocatalysts provide a modular platform to access new reaction pathways and affect product outcomes, but their use in polymer synthesis is limited because co-catalysts and/or co-reductants are required to complete catalytic cycles. Herein, we report using zinc myoglobin (ZnMb), an inherently photoactive protein, to mediate photoinduced electron/energy transfer (PET) reversible addition-fragmentation chain transfer (RAFT) polymerizations. Using ZnMb as the sole reagent for catalysis, photomediated polymerizations of N,N-dimethylacrylamide in PBS were achieved with predictable molecular weights, dispersity values approaching 1.1, and high chain-end fidelity. We found that initial apparent rate constants of polymerization increased from 4.6×10-5 s-1 for zinc mesoporpyhrin IX (ZnMIX) to 6.5×10-5 s-1 when ZnMIX was incorporated into myoglobin to yield ZnMb, indicating that the protein binding site enhanced catalytic activity. Chain extension reactions comparing ZnMb-mediated RAFT polymerizations to thermally-initiated RAFT polymerizations showed minimal differences in block copolymer molecular weights and dispersities. This work enables studies to elucidate how protein modifications (e.g., secondary structure folding, site-directed mutagenesis, directed evolution) can be used to modulate polymerization outcomes (e.g., selective monomer additions towards sequence control, tacticity control, molar mass distributions).

Membrane-Active Thermoresponsive Block Copolymers Containing a Diacylglycerol-Based Segment: RAFT Synthesis, Doxorubicin Encapsulation, and Evaluation of Cytotoxicity against Breast Cancer Cells

Herein, we report the formation of drug delivery systems from original thermoresponsive block copolymers containing lipid-based segments. Two acrylate monomers derived from palmitic- or oleic-acid-based diacylglycerols (DAGs) were synthesized and polymerized by the reversible addition-fragmentation chain transfer (RAFT) method. Well-defined DAG-based polymers with targeted molar masses and narrow molar mass distributions were next used as macro-chain transfer agents (macro-CTAs) for the polymerization of N-isopropylacrylamide (NIPAAm) or N-vinylcaprolactam (NVCL). The obtained amphiphilic block copolymers were formed into polymeric nanoparticles (PNPs) with and without encapsulated doxorubicin and characterized. Their biological assessment indicated appropriate cytocompatibility with the representatives of normal cells. Furthermore, compared to the free drug, increased cytotoxicity and apoptosis or necrosis induction in breast cancer cells was documented, including a highly aggressive and invasive triple-negative MDA-MB-231 cell line.

Ca2+-Chelation-Induced Fabrication of Multistimuli-Responsive Charged Nanogels from Phospholipid-Polymer Conjugates and Use for Drug/Protein Loading

Thermoresponsive phospholipid-poly(N-isopropylacrylamide) (PL-PNIPAM) conjugates were synthesized via reversible addition fragmentation chain transfer polymerization mediated by a phospholipid-modified trithiocarbonate. Temperature triggered the micellization of the PL-PNIPAM conjugate to form phosphate group-decorated micelles in the aqueous solution. Driven by the chelation of phospholipids and Ca²⁺, the PL-PNIPAM conjugate and Ca²⁺ ions formed size-tunable nanoclusters at a temperature beyond the lower critical solution temperature. To fabricate cross-linked nanogels, NIPAM was copolymerized with N-succinimidyl acrylate (NSA) to obtain the PL-P(NIPAM-co-NSA) conjugate bearing pendent cross-linkable functionalities. Subsequently, the size-controllable nanogels containing disulfide linkages were generated at 37 °C by cross-linking the PL-P(NIPAM-co-NSA)/Ca²⁺ nanoclusters with cystamine through modulation of Ca²⁺ concentrations. These negatively charged nanogels demonstrate temperature/pH/reduction triple responsiveness. The nanogels can be efficiently loaded with doxorubicin (DOX) and proteins with various isoelectric points. The DOX-loaded nanogels exhibited a temperature/pH/reduction triple-responsive release profile. The immobilized RNase A, BSA, and GOx retained the protein bioactivity. The release of RNase A-loaded nanogels possesses a temperature-responsive profile. The immobilization of Lys and cytochrome C in nanogels inhibited protein bioactivity. However, the addition of NaCl triggered the recovery of bioactivity. These multistimuli-responsive nanogels can provide a versatile platform applicable in biotechnology and drug/protein delivery.

Direct routes to functional RAFT agents from substituted N-alkyl maleimides

Three different routes are presented for the synthesis of functional RAFT agents from N-substituted maleimides, which are then used to synthesise α,β,ω-functional RAFT polymers.

Polymer Coupling via Hetero-Disulfide Exchange and Its Applications to Rewritable Polymer Brushes

An iodide-terminated polymer (Polymer-I) is converted to a thiol-terminated polymer (Polymer-SH) using HSCH₂CH₂SH in a remarkably short time (10 min). Polymer-SH is further converted to a pyridyl disulfide-terminated polymer (Polymer-SS-Py). The hetero-coupling of Polymer-SH and Polymer-SS-Py is successfully achieved to quantitatively generate a polymer disulfide (Polymer-SS-Polymer). Exploiting this efficient hetero-coupling technique, Polymer-SH is attached (grafted) on a Py-SS-immobilized surface to generate a polymer brush via a disulfide (-SS-) linkage (writing process). The -SS- linkage is cleaved by the treatment with dithiothreitol (DTT) to detach the polymer from the surface (erasing process). Subsequently, another Polymer-SH is attached on the surface to generate another polymer brush (rewriting process). Thus, a writable, erasable, and rewritable polymer brush surface is achieved. Hydrophilic, hydrophobic, and super-hydrophobic polymers (Polymer-SH) are attached on the surface, tailoring the surface wettability in the writing-erasing-rewriting cycles. Polymer-SH is also attached on a chain-end Py-SS-functionalized polymer brush surface, generating a rewritable block copolymer brush surface. A patterned block copolymer brush surface is also obtained using photo-irradiation and a photo-mask in the erasing process. The metal-free synthetic procedure, accessibility to patterned brushes, and switchable surface properties via the writing-erasing-rewriting process are attractive features of the present approach.

PET-RAFT Polymerization: Mechanistic Perspectives for Future Materials

In the past decade, photochemistry has emerged as a growing area in organic and polymer chemistry. Use of light to drive polymerization has advantages by imparting spatial and temporal control over the reaction. Photoinduced electron/energy transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT) has emerged as an excellent technique for developing well-defined polymers from a variety of functional monomers. However, the mechanism, of electron versus energy transfer is debated in the literature, with conflicting reports on the underlying process. This perspective focuses on the mechanistic aspects of PET-RAFT, in particular, the electron versus energy transfer pathways. The different mechanisms are evaluated, including evidence for one versus the other mechanisms. The current literature has not reached a consensus across all PET-RAFT processes, but rather, each catalytic system has unique characteristics.

New Light in Polymer Science: Photoinduced Reversible Addition-Fragmentation Chain Transfer Polymerization (PET-RAFT) as Innovative Strategy for the Synthesis of Advanced Materials

Photochemistry has attracted great interest in the last decades in the field of polymer and material science for the synthesis of innovative materials. The merging of photochemistry and reversible-deactivation radical polymerizations (RDRP) provides good reaction control and can simplify elaborate reaction protocols. These advantages open the doors to multidisciplinary fields going from composite materials to bio-applications. Photoinduced Electron/Energy Transfer Reversible Addition-Fragmentation Chain-Transfer (PET-RAFT) polymerization, proposed for the first time in 2014, presents significant advantages compared to other photochemical techniques in terms of applicability, cost, and sustainability. This review has the aim of providing to the readers the basic knowledge of PET-RAFT polymerization and explores the new possibilities that this innovative technique offers in terms of industrial applications, new materials production, and green conditions.

Enlightening advances in polymer bioconjugate chemistry: light-based techniques for grafting to and from biomacromolecules

Photochemistry has revolutionized the field of polymer-biomacromolecule conjugation. Ligation reactions necessitate biologically benign conditions, and photons have a significant energy advantage over what is available thermally at ambient temperature, allowing for rapid and unique reactivity. Photochemical reactions also afford many degrees of control, specifically, spatio-temporal control, light source tunability, and increased oxygen tolerance. Light-initiated polymerizations, in particular photo-atom-transfer radical polymerization (photo-ATRP) and photoinduced electron/energy transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT), have been used for grafting from proteins, DNA, and cells. Additionally, the spatio-temporal control inherent to light-mediated chemistry has been utilized for grafting biomolecules to hydrogel networks for many applications, such as 3-D cell culture. While photopolymerization has clear advantages, there are factors that require careful consideration in order to obtain optimal control. These factors include the photocatalyst system, light intensity, and wavelength. This Perspective aims to discuss recent advances of photochemistry for polymer biomacromolecule conjugation and potential considerations while tailoring these systems.

SI-PET-RAFT: Surface-Initiated Photoinduced Electron Transfer-Reversible Addition-Fragmentation Chain Transfer Polymerization

In this communication, surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT) is introduced. SI-PET-RAFT affords functionalization of surfaces with spatiotemporal control and provides oxygen tolerance under ambient conditions. All hallmarks of controlled radical polymerization (CRP) are met, affording well-defined polymerization kinetics, and chain end retention to allow subsequent extension of active chain ends to form block copolymers. The modularity and versatility of SI-PET-RAFT is highlighted through significant flexibility with respect to the choice of monomer, light source and wavelength, and photoredox catalyst. The ability to obtain complex patterns in the presence of air is a significant contribution to help pave the way for CRP-based surface functionalization into commercial application.

What happens in the dark? Assessing the temporal control of photo-mediated controlled radical polymerizations

A signature of photo-mediated controlled polymerizations is the ability to modulate the rate of polymerization by turning the light source 'on' and 'off.' However, in many reported systems, growth can be reproducibly observed during dark periods. In this study, emerging photo-mediated controlled radical polymerizations are evaluated with in situ 1H NMR monitoring to assess their behavior in the dark. Interestingly, it is observed that Cu-mediated systems undergo long-lived, linear growth during dark periods in organic media.