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

Artificial Zymogen Based on Protein-Polymer Hybrids

This study explores the synthesis and application of artificial zymogens using protein-polymer hybrids to mimic the controlled enzyme activation observed in natural zymogens. Pro-trypsin (pro-TR) and pro-chymotrypsin (pro-CT) hybrids were engineered by modifying the surfaces of trypsin (TR) and chymotrypsin (CT) with cleavable peptide inhibitors utilizing surface-initiated atom transfer radical polymerization. These hybrids exhibited 70 and 90% reductions in catalytic efficiency for pro-TR and pro-CT, respectively, due to the inhibitory effect of the grafted peptide inhibitors. The activation of pro-TR by CT and pro-CT by TR resulted in 1.5- and 2.5-fold increases in enzymatic activity, respectively. Furthermore, the activated hybrids triggered an enzyme activation cascade, enabling amplification of activity through a dual pro-protease hybrid system. This study highlights the potential of artificial zymogens for therapeutic interventions and biodetection platforms by harnessing enzyme activation cascades for precise control of catalytic activity.

Pickering Emulsions Biocatalysis: Recent Developments and Emerging Trends

Biocatalysis within biphasic systems is gaining significant attention in the field of synthetic chemistry, primarily for its ability to solve the problem of incompatible solubilities between biocatalysts and organic compounds. By forming an emulsion from these two-phase systems, a larger surface area is created, which greatly improves the mass transfer of substrates to the biocatalysts. Among the various types of emulsions, Pickering emulsions stand out due to their excellent stability, compatibility with biological substances, and the ease with which they can be formed and separated. This makes them ideal for reusing both the emulsifiers and the biocatalysts. This review explores the latest developments in biocatalysis using Pickering emulsions. It covers the structural features, methods of creation, innovations in flow biocatalysis, and the role of interfaces in these processes. Additionally, the challenges and future directions are discussed in combining chemical and biological catalysts within Pickering emulsion frameworks to advance synthetic methodologies.

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

Aqueous photo-RAFT polymerization under ambient conditions: synthesis of protein-polymer hybrids in open air

A photoinduced reversible addition-fragmentation chain-transfer (photo-RAFT) polymerization technique in the presence of sodium pyruvate (SP) and pyruvic acid derivatives was developed. Depending on the wavelength of light used, SP acted as a biocompatible photoinitiator or promoter for polymerization, allowing rapid open-to-air polymerization in aqueous media. Under UV irradiation (370 nm), SP decomposes to generate CO2 and radicals, initiating polymerization. Under blue (450 nm) or green (525 nm) irradiation, SP enhances the polymerization rate via interaction with the excited state RAFT agent. This method enabled the polymerization of a range of hydrophilic monomers in reaction volumes up to 250 mL, eliminating the need to remove radical inhibitors from the monomers. In addition, photo-RAFT polymerization using SP allowed for the facile synthesis of protein-polymer hybrids in short reaction times (<1 h), low organic content (≤16%), and without rigorous deoxygenation and the use of transition metal photocatalysts. Enzymatic studies of a model protein (chymotrypsin) showed that despite a significant loss of protein activity after conjugation with RAFT chain transfer agents, the grafting polymers from proteins resulted in a 3-4-fold recovery of protein activity.

Near-Infrared Light and Acid/Base Dual-Regulated Polymerization Utilizing Imidazole-Anion-Fused Perylene Diimides as Photocatalysts

This work presents the first example of acid/base-responsive and near-infrared (NIR)-absorbing photocatalysts based on imidazole-anion-fused perylene diimide chromophores. The photocatalysts were in situ generated by deprotonation of imidazole-fused perylene diimide under an alkaline environment. NIR (λ = 730 nm, 128 mW/cm2) photoinduced atom transfer radical polymerization (ATRP) was implemented, exhibiting high efficiency and excellent livingness under ppm level of photocatalysts (15 ppm relative to monomer) and Cu(II) complex (10 ppm relative to monomer) concentrations. The method showed capabilities to polymerize behind opaque barriers (i.e., paper and pig skin) and under aerobic condition. Notably, this work demonstrated a dual temporal control of polymerization by adding weak base/acid and switching NIR light on/off. The polymerization can even be halted by bubbling CO2 and was then fully recovered by adding triethylamine. The NIR photoATRP of acrylamide monomers in aqueous solution was also performed, which can be regulated by the change of pH.

Thermoresponsive Coiled-Coil Peptide-Polymer Grafts

Alkyl halide side groups are selectively incorporated into monodispersed, computationally designed coiled-coil-forming peptide nanoparticles. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) is polymerized from the coiled-coil periphery using photoinitiated atom transfer radical polymerization (photoATRP) to synthesize well-defined, thermoresponsive star copolymer architectures. This facile synthetic route is readily extended to other monomers for a range of new complex star-polymer macromolecules.

Red-Light-Driven Atom Transfer Radical Polymerization for High-Throughput Polymer Synthesis in Open Air

Photoinduced reversible-deactivation radical polymerization (photo-RDRP) techniques offer exceptional control over polymerization, providing access to well-defined polymers and hybrid materials with complex architectures. However, most photo-RDRP methods rely on UV/visible light or photoredox catalysts (PCs), which require complex multistep synthesis. Herein, we present the first example of fully oxygen-tolerant red/NIR-light-mediated photoinduced atom transfer radical polymerization (photo-ATRP) in a high-throughput manner under biologically relevant conditions. The method uses commercially available methylene blue (MB+) as the PC and [X-CuII/TPMA]+ (TPMA = tris(2-pyridylmethyl)amine) complex as the deactivator. The mechanistic study revealed that MB+ undergoes a reductive quenching cycle in the presence of the TPMA ligand used in excess. The formed semireduced MB (MB•) sustains polymerization by regenerating the [CuI/TPMA]+ activator and together with [X-CuII/TPMA]+ provides control over the polymerization. This dual catalytic system exhibited excellent oxygen tolerance, enabling polymerizations with high monomer conversions (>90%) in less than 60 min at low volumes (50-250 μL) and high-throughput synthesis of a library of well-defined polymers and DNA-polymer bioconjugates with narrow molecular weight distributions (Đ < 1.30) in an open-air 96-well plate. In addition, the broad absorption spectrum of MB+ allowed ATRP to be triggered under UV to NIR irradiation (395-730 nm). This opens avenues for the integration of orthogonal photoinduced reactions. Finally, the MB+/Cu catalysis showed good biocompatibility during polymerization in the presence of cells, which expands the potential applications of this method.

Design of an Oxygen-Tolerant Photo-RAFT System for Protein-Polymer Conjugation Achieving High Bioactivity

Protein-polymer conjugates have significant potential in pharmaceutical and biomedical applications. To enable their widespread use, robust conjugation techniques are crucial. This study introduces a photo-initiated reversible addition-fragmentation chain-transfer (Photo-RAFT) polymerization system that exhibits excellent oxygen tolerance. This system allows for the synthesis of protein-polymer conjugates with high bioactivity under mild and aerobic conditions. Three photocatalytic systems utilizing Eosin Y (EY) as the photocatalyst with two different cocatalysts (ascorbic acid and triethanolamine) were investigated, each generating distinct reactive oxygen species (ROS) such as singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radicals. The impact of these ROS on three model proteins (lysozyme, albumin, and myoglobin) was evaluated, demonstrating varying bioactivities based on the ROS produced. The EY/TEOA system was identified as the optimal photo-RAFT initiating system, enabling the preparation of protein-polymer conjugates under aerobic conditions while maintaining high protein enzymatic activity. To showcase the potential of this approach, lysozyme-poly(dimethylaminoethyl acrylate) conjugates were successfully prepared and exhibited enhanced antimicrobial property against Gram-positive and Gram-negative bacteria.

Synthesis of Multifunctional Protein-Polymer Conjugates via Oxygen-tolerant, Aqueous Copper-Mediated Polymerization, and Bioorthogonal Click Chemistry

Oxygen-tolerant, aqueous copper-mediated polymerization approaches are combined with click chemistry in either a sequential or a simultaneous manner, to enable the synthesis of multifunctional protein-polymer conjugates. Propargyl acrylate (PgA) and propargyl methacrylate (PgMA) grafting from a bovine serum albumin (BSA) macroinitiator is thoroughly optimized to synthesize chemically addressable BSA-poly(propargyl acrylate) and BSA-poly(propargyl methacrylate) respectively. The produced multifunctional bioconjugates bear pendant terminal 1-alkynes which can be readily post-functionalized via both [3+2] Huisgen cycloaddition and thiol-yne click chemistry under mild reaction conditions. Simultaneous oxygen-tolerant, aqueous copper-catalyzed polymerization, and click chemistry mediate the in situ multiple chemical tailoring of biomacromolecules in excellent yields.

Visible Light-ATRP Driven by Tris(2-Pyridylmethyl)Amine (TPMA) Impurities in the Open Air

Atom transfer radical polymerization (ATRP) of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA500 ) in water is enabled using CuBr2 with tris(2-pyridylmethyl)amine (TPMA) as a ligand under blue or green-light irradiation without requiring any additional reagent, such as a photo-reductant, or the need for prior deoxygenation. Polymers with low dispersity (Đ = 1.18-1.25) are synthesized at high conversion (>95%) using TPMA from three different suppliers, while no polymerization occurred with TPMA is synthesized and purified in the laboratory. Based on spectroscopic studies, it is proposed that TPMA impurities (i.e., imine and nitrone dipyridine), which absorb blue and green light, can act as photosensitive co-catalyst(s) in a light region where neither pure TPMA nor [(TPMA)CuBr]+ absorbs light.

Conserved Protein-Polymer Interactions across Structurally Diverse Polymers Underlie Alterations to Protein Thermal Unfolding

Protein-polymer conjugates are widely used in many clinical and industrial applications, but lack of experimental data relating protein-polymer interactions to improved protein stability prevents their rational design. Advances in synthetic chemistry have expanded the palette of polymer designs, including development of nonlinear architectures, novel monomer chemical scaffolds, and control of hydrophobicity, but more experimental data are needed to transform advances in chemistry into next generation conjugates. Using an integrative biophysical approach, we investigated the molecular basis for polymer-based thermal stabilization of a human galectin protein, Gal3C, conjugated with polymers of linear and nonlinear architectures, different degrees of polymerization, and varying hydrophobicities. Independently varying the degree of polymerization and polymer architecture enabled delineation of specific polymer properties contributing to improved protein stability. Insights from NMR spectroscopy of the polymer-conjugated Gal3C backbone revealed patterns of protein-polymer interactions shared between linear and nonlinear polymer architectures for thermally stabilized conjugates. Despite large differences in polymer chemical scaffolds, protein-polymer interactions resulting in thermal stabilization appear conserved. We observed a clear relation between polymer length and protein-polymer thermal stability shared among chemically different polymers. Our data indicate a wide range of polymers may be useful for engineering conjugate properties and provide conjugate design criteria.

Fully Oxygen-Tolerant Visible-Light-Induced ATRP of Acrylates in Water: Toward Synthesis of Protein-Polymer Hybrids

Over the last decade, photoinduced ATRP techniques have been developed to harness the energy of light to generate radicals. Most of these methods require the use of UV light to initiate polymerization. However, UV light has several disadvantages: it can degrade proteins, damage DNA, cause undesirable side reactions, and has low penetration depth in reaction media. Recently, we demonstrated green-light-induced ATRP with dual catalysis, where eosin Y (EYH2) was used as an organic photoredox catalyst in conjunction with a copper complex. This dual catalysis proved to be highly efficient, allowing rapid and well-controlled aqueous polymerization of oligo(ethylene oxide) methyl ether methacrylate without the need for deoxygenation. Herein, we expanded this system to synthesize polyacrylates under biologically relevant conditions using CuII/Me6TREN (Me6TREN = tris[2-(dimethylamino)ethyl]amine) and EYH2 at ppm levels. Water-soluble oligo(ethylene oxide) methyl ether acrylate (average M n = 480, OEOA480) was polymerized in open reaction vessels under green light irradiation (520 nm). Despite continuous oxygen diffusion, high monomer conversions were achieved within 40 min, yielding polymers with narrow molecular weight distributions (1.17 ≤ D̵ ≤ 1.23) for a wide targeted DP range (50-800). In situ chain extension and block copolymerization confirmed the preserved chain end functionality. In addition, polymerization was triggered/halted by turning on/off a green light, showing temporal control. The optimized conditions also enabled controlled polymerization of various hydrophilic acrylate monomers, such as 2-hydroxyethyl acrylate, 2-(methylsulfinyl)ethyl acrylate), and zwitterionic carboxy betaine acrylate. Notably, the method allowed the synthesis of well-defined acrylate-based protein-polymer hybrids using a straightforward reaction setup without rigorous deoxygenation.

Antibody–Biopolymer Conjugates in Oncology: A Review

Cancer is one of the most prevalent diseases and affects a large proportion of the population worldwide. Conventional treatments in the management include chemotherapy, radiotherapy, and surgery. Although being well-accepted, they have many lacunas in the form of severe side effect resulting from lack of targeted delivery. Antibody biopolymer conjugates are a novel method which is an add-on to older methods of immunization. It is used in various diseases and disorders. It ensures the targeted delivery of molecules to increase its efficacy and reduce unwanted effects of the molecule/drug to normal cells. It shows miraculous results in the treatment and management of several cancers even in advanced stages. Herein, we present the chemistry between biopolymer and antibody, their effects on cancer as well as the basic differences between antibody–drug conjugates and antibody–biopolymer conjugates.

Photocrosslinkable natural polymers in tissue engineering

Natural polymers have been widely used in scaffolds for tissue engineering due to their superior biocompatibility, biodegradability, and low cytotoxicity compared to synthetic polymers. Despite these advantages, there remain drawbacks such as unsatisfying mechanical properties or low processability, which hinder natural tissue substitution. Several non-covalent or covalent crosslinking methods induced by chemicals, temperatures, pH, or light sources have been suggested to overcome these limitations. Among them, light-assisted crosslinking has been considered as a promising strategy for fabricating microstructures of scaffolds. This is due to the merits of non-invasiveness, relatively high crosslinking efficiency via light penetration, and easily controllable parameters, including light intensity or exposure time. This review focuses on photo-reactive moieties and their reaction mechanisms, which are widely exploited along with natural polymer and its tissue engineering applications.

Visible-Light-Mediated Controlled Radical Branching Polymerization in Water

Hyperbranched polymethacrylates were synthesized by green-light-induced atom transfer radical polymerization (ATRP) under biologically relevant conditions in the open air. Sodium 2-bromoacrylate (SBA) was prepared in situ from commercially available 2-bromoacrylic acid and used as a water-soluble inibramer to induce branching during the copolymerization of methacrylate monomers. As a result, well-defined branched polymethacrylates were obtained in less than 30 min with predetermined molecular weights (36 000<M_n <170 000), tunable degree of branching, and low dispersity values (1.14≤Đ≤1.33). Moreover, the use of SBA inibramer enabled the synthesis of bioconjugates with a well-controlled branched architecture.

Excitation Dependence in Photoiniferter Polymerization

We report on a fundamental feature of photoiniferter polymerizations mediated with trithiocarbonates and xanthates. The polymerizations were found to be highly dependent on the activated electronic excitation of the iniferter. Enhanced rates of polymerization and greater control over molecular weights were observed for trithiocarbonate- and xanthate-mediated photoiniferter polymerizations when the n → π* transition of the iniferter was targeted compared to the polymerizations activating the π → π* transition. The disparities in rates of polymerization were attributed to the increased rate of C-S photolysis which was confirmed using model trapping studies. This study provides valuable insight into the role of electronic excitations in photoiniferter polymerization and provides guidance when selecting irradiation conditions for applications where light sensitivity is important.

Chemical Approaches to Synthetic Drug Delivery Systems for Systemic Applications

Poor water solubility and low bioavailability of active pharmaceutical ingredients (APIs) are major causes of friction in the pharmaceutical industry and represent a formidable hurdle for pharmaceutical drug development. Drug delivery remains the major challenge for the application of new small-molecule drugs as well as biopharmaceuticals. The three challenges for synthetic delivery systems are: (i) controlling drug distribution and clearance in the blood; (ii) solubilizing poorly water-soluble agents, and (iii) selectively targeting specific tissues. Although several polymer-based systems have addressed the first two demands and have been translated into clinical practice, no targeted synthetic drug delivery system has reached the market. This Review is designed to provide a background on the challenges and requirements for the design and translation of new polymer-based delivery systems. This report will focus on chemical approaches to drug delivery for systemic applications.

Polynorbornene-based bioconjugates by aqueous grafting-from ring-opening metathesis polymerization reduce protein immunogenicity

Protein-polymer conjugates (PPCs) improve therapeutic efficacy of proteins and have been widely used for the treatment of various diseases such as cancer, diabetes, and hepatitis. PEGylation is considered as the "gold standard" in bioconjugation, although in practice its clinical applications are becoming limited because of extensive evidence of immunogenicity induced by pre-existing anti-PEG antibodies in patients. Here, optimized reaction conditions for living aqueous grafting-from ring-opening metathesis polymerization (ROMP) are utilized to synthesize water-soluble polynorbornene (PNB)-based PPCs of lysozyme (Lyz-PPCs) and bacteriophage Qβ (Qβ-PPCs) as PEG alternatives. Lyz-PPCs retain nearly 100% bioactivity and Qβ-PPCs exhibit up to 35% decrease in protein immunogenicity. Qβ-PPCs derived from NB-PEG show no reduction in recognition by anti-PEG antibodies while Qβ-PPCs derived from NB-Zwit show >95% reduction as compared with Qβ-PEG. This work demonstrates a new method for PPC synthesis and the utility of grafting from PPCs to evade immune recognition.

Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X-CuII/L). The role of PC was to trigger and drive the polymerization, while X-CuII/L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X-CuII/L, generating CuI/L activator and PC˙+. The ATRP ligand (L) used in excess then reduced the PC˙+, closing the photocatalytic cycle. The continuous reduction of X-CuII/L back to CuI/L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X-CuII/L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions.

Rapid Oxygen-Tolerant Synthesis of Protein-Polymer Bioconjugates via Aqueous Copper-Mediated Polymerization

The synthesis of protein-polymer conjugates usually requires extensive and costly deoxygenation procedures, thus limiting their availability and potential applications. In this work, we report the ultrafast synthesis of polymer-protein bioconjugates in the absence of any external deoxygenation via an aqueous copper-mediated methodology. Within 10 min and in the absence of any external stimulus such as light (which may limit the monomer scope and/or disrupt the secondary structure of the protein), a range of hydrophobic and hydrophilic monomers could be successfully grafted from a BSA macroinitiator, yielding well-defined polymer-protein bioconjugates at quantitative yields. Our approach is compatible with a wide range of monomer classes such as (meth) acrylates, styrene, and acrylamides as well as multiple macroinitiators including BSA, BSA nanoparticles, and beta-galactosidase from Aspergillus oryzae. Notably, the synthesis of challenging protein-polymer-polymer triblock copolymers was also demonstrated, thus significantly expanding the scope of our strategy. Importantly, both lower and higher scale polymerizations (from 0.2 to 35 mL) were possible without compromising the overall efficiency and the final yields. This simple methodology paves the way for a plethora of applications in aqueous solutions without the need of external stimuli or tedious deoxygenation.

Sulfoxide-Containing Polyacrylamides Prepared by PICAR ATRP for Biohybrid Materials

Water-soluble and biocompatible polymers are of interest in biomedicine as the search for alternatives to PEG-based materials becomes more important. In this work, the synthesis of a new sulfoxide-containing monomer, 2-(methylsulfinyl)ethyl acrylamide (MSEAM), is reported. Well-defined polymers were prepared by photoinduced initiators for continuous activator regeneration atom transfer radical polymerization (PICAR ATRP). The polymerizations were performed in water under biologically relevant conditions in a small volume without degassing the reaction mixture. DNA-PMSEAM and protein-PMSEAM hybrids were also synthesized. The lower critical solution temperature (LCST) of PMSEAM was estimated to be approximately 170 °C by extrapolating the LCST for a series of copolymers with variable content of N-isopropylacrylamide. The cytotoxicity studies showed excellent biocompatibility of PMSEAM, even at concentrations up to 2.5 mg/mL. Furthermore, the MSEAM monomer exhibited relatively lower toxicity than similar (meth)acrylate-based monomers at comparable concentrations.

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

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.

Expanding the functionality of proteins with genetically encoded dibenzo[b,f][1,4,5]thiadiazepine: a photo-transducer for photo-click decoration

Genetic incorporation of novel noncanonical amino acids (ncAAs) that are specialized for the photo-click reaction allows the precisely orthogonal and site-specific functionalization of proteins in living cells under photo-control. However, the development of a r̲ing-strain i̲n situ l̲oadable d̲ipolarophile (RILD) as a genetically encodable reporter for photo-click bioconjugation with spatiotemporal controllability is quite rare. Herein, we report the design and synthesis of a photo-switchable d̲ib̲enzo[b,f][1,4,5]t̲hiad̲iazepine-based a̲lanine (DBTDA) ncAA, together with the directed evolution of a pyrrolysyl-tRNA synthetase/tRNACUA pair (PylRS/tRNACUA), to encode the DBTDA into recombinant proteins as a RILD in living E. coli cells. The fast-responsive photo-isomerization of the DBTDA residue can be utilized as a converter of photon energy into ring-strain energy to oscillate the conformational changes of the parent proteins. Due to the photo-activation of RILD, the photo-switching of the DBTDA residue on sfGFP and OmpC is capable of promoting the photo-click ligation with diarylsydnone (DASyd) derived probes with high efficiency and selectivity. We demonstrate that the genetic code expansion (GCE) with DBTDA benefits the studies on the distribution of decorated OmpC-DBTD on specific E. coli cells under a spatiotemporal resolved photo-stimulation. The GCE for encoding DBTDA enables further functional diversity of artificial proteins in living systems.

Molecular Self-Assembly and Supramolecular Chemistry of Cyclic Peptides

This Review focuses on the establishment and development of self-assemblies governed by the supramolecular interactions between cyclic peptides. The Review first describes the type of cyclic peptides able to assemble into tubular structures to form supramolecular cyclic peptide nanotubes. A range of cyclic peptides have been identified to have such properties, including α-peptides, β-peptides, α,γ-peptides, and peptides based on δ- and ε-amino acids. The Review covers the design and functionalization of these cyclic peptides and expands to a recent advance in the design and application of these materials through their conjugation to polymer chains to generate cyclic peptide-polymer conjugates nanostructures. The Review, then, concentrates on the challenges in characterizing these systems and presents an overview of the various analytical and characterization techniques used to date. This overview concludes with a critical survey of the various applications of the nanomaterials obtained from supramolecular cyclic peptide nanotubes, with a focus on biological and medical applications, ranging from ion channels and membrane insertion to antibacterial materials, anticancer drug delivery, gene delivery, and antiviral applications.

Aqueous Protein-Polymer Bioconjugation via Photoinduced RAFT Polymerization Using High Loading Heterogeneous Catalyst

Light-driven polymerization, such as photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, enables biological benign conditions and versatile functional polymer structure design, which is readily used in protein-polymer bioconjugates. However, conventional metalloporphyrinic homogeneous catalysts for PET-RAFT polymerization suffer from limited aqueous solubility and tedious purification. Here we demonstrate the design of PET-RAFT photocatalyst from the reticular assembled Zr-porphyrinic metal-organic frameworks (MOFs), along with a biomacromolecule-based chain transfer agent, as efficient bioconjugation tools in water. Our methodology offers manufacturing advantages on bioconjugates under mild conditions such that MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) and cytotoxicity assays have shown the preservation of the protein integrity, bioactivity, and high cell viability after PET-RAFT polymerization. We find that the fast kinetics are benefiting from the ultrahigh loading of metalloporphyrins in MOF-525-Zn. This heterogeneous catalyst also allows us to maintain living characteristics to incorporate myriads of monomers into block copolymers. Other advantages like easy postreaction purification, reusability, and high oxygen tolerance even in an open system are demonstrated. This study provides a tool of highly efficient heterogeneous photocatalysts for polymer-protein bioconjugation in aqueous media and paves the road for biological applications.

Protein-, (Poly)peptide-, and Amino Acid-Based Nanostructures Prepared via Polymerization-Induced Self-Assembly

Proteins and peptides, built from precisely defined amino acid sequences, are an important class of biomolecules that play a vital role in most biological functions. Preparation of nanostructures through functionalization of natural, hydrophilic proteins/peptides with synthetic polymers or upon self-assembly of all-synthetic amphiphilic copolypept(o)ides and amino acid-containing polymers enables access to novel protein-mimicking biomaterials with superior physicochemical properties and immense biorelevant scope. In recent years, polymerization-induced self-assembly (PISA) has been established as an efficient and versatile alternative method to existing self-assembly procedures for the reproducible development of block copolymer nano-objects in situ at high concentrations and, thus, provides an ideal platform for engineering protein-inspired nanomaterials. In this review article, the different strategies employed for direct construction of protein-, (poly)peptide-, and amino acid-based nanostructures via PISA are described with particular focus on the characteristics of the developed block copolymer assemblies, as well as their utilization in various pharmaceutical and biomedical applications.

Light-Triggered Click Chemistry

The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels-Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Making ATRP More Practical: Oxygen Tolerance

Atom-transfer radical polymerization (ATRP) is a well-known technique for the controlled polymerization of vinyl monomers under mild conditions. However, as with any other radical polymerization, ATRP typically requires rigorous oxygen exclusion, making it time-consuming and challenging to use by nonexperts. In this Account, we discuss various approaches to achieving oxygen tolerance in ATRP, presenting the overall progress in the field.Copper-mediated ATRP, which we first discovered in the late 1990s, uses a Cu^I/L activator that reversibly reacts with the dormant C(sp³)-X polymer chain end, forming a X-Cu^II/L deactivator and a propagating radical. Oxygen interferes with activation and chain propagation by quenching the radicals and oxidizing the activator. At ATRP equilibrium, the activator is present at a much higher concentration than the propagating radicals. Thus, oxidation of the activator is the dominant inhibition pathway. In conventional ATRP, this reaction is irreversible, so oxygen must be strictly excluded to achieve good results.Over the last two decades, our group has developed several ATRP techniques based on the concept of regenerating the activator. When the oxidized activator is continuously converted back to its active reduced form, then the catalytic system itself can act as an oxygen scavenger. Regeneration can be accomplished by reducing agents and photo-, electro-, and mechanochemical stimuli. This family of methods offers a degree of oxygen tolerance, but most of them can tolerate only a limited amount of oxygen and do not allow polymerization in an open vessel.More recently, we discovered that enzymes can be used in auxiliary catalytic systems that directly deoxygenate the reaction medium and protect the polymerization process. We developed a method that uses glucose oxidase (GOx), glucose, and sodium pyruvate to very effectively scavenge oxygen and enable open-vessel ATRP. By adding a second enzyme, horseradish peroxidase (HPR), we managed to extend the role of the auxiliary enzymatic system to generating carbon-based radicals and changed ATRP from an oxygen-sensitive to an oxygen-fueled reaction.While performing control experiments for the enzymatic methods, we noticed that using sodium pyruvate under UV irradiation triggers polymerization without the presence of GOx. This serendipitous discovery allowed us to develop the first oxygen-proof, small-molecule-based, photoinduced ATRP system. It has oxygen tolerance similar to that of the enzymatic methods, exhibits superior compatibility with both aqueous media and organic solvents, and avoids problems associated with purifying polymers from enzymes. The system was able to rapidly polymerize N-isopropylacrylamide, a challenging monomer, with a high degree of control.These contributions have substantially simplified the use of ATRP, making it more practical and accessible to everyone.

Dealing with the complexity of conjugated and self-assembled polymer-nanostructures using field-flow fractionation

Broad diversity and heterogeneity are inherently showcased by both natural and synthetic macromolecular structures. The high application potential for such structures and their combinations calls for novel analytical approaches that allow for comprehensive characterization and a full understanding of their complex composition. This review gives an overview of recent advances in designing and fabricating bioconjugated and self-assembled polymer structures, and introduces adequate characterization protocols for sufficient elucidation of their specific molecular properties. Possible pitfalls in their analysis are demonstrated, and potential alternatives are discussed. The primary focus is on addressing the highlights, and future prospects of applying field-flow fractionation coupled and/or hyphenated to different detection methods as a powerful separation and analytical technique for bioconjugate and self-assembled nanostructures.

Interrogating biological systems using visible-light-powered catalysis

Light-powered catalysis has found broad utility as a chemical transformation strategy, with widespread impact on energy, environment, drug discovery and human health. A noteworthy application impacting human health is light-induced sensitization of cofactors for photodynamic therapy in cancer treatment. The clinical adoption of this photosensitization approach has inspired the search for other photochemical methods, such as photoredox catalysis, to influence biological discovery. Over the past decade, light-mediated catalysis has enabled the discovery of valuable synthetic transformations, propelling it to become a highly utilized chemical synthesis strategy. The reaction components required to achieve a photoredox reaction are identical to photosensitization (catalyst, light source and substrate), making it ideally suited for probing biological environments. In this Review, we discuss the therapeutic application of photosensitization and advancements made in developing next-generation catalysts. We then highlight emerging uses of photoredox catalytic methods for protein bioconjugation and probing complex cellular environments in living cells.

Pyridine-2,6-dicarboxaldehyde-Enabled N-Terminal In Situ Growth of Polymer-Interferon α Conjugates with Significantly Improved Pharmacokinetics and In Vivo Bioactivity

Polymer-protein conjugates are a class of biohybrids with unique properties that are highly useful in biomedicine ranging from protein therapeutics to biomedical imaging; however, it remains a considerable challenge to conjugate polymers to proteins in a site-specific, mild, and efficient way to form polymer-protein conjugates with uniform structures and properties and optimal functions. Herein we report pyridine-2,6-dicarboxaldehyde (PDA)-enabled N-terminal modification of proteins with polymerization initiators for in situ growth of poly(oligo(ethylene glycol)methyl ether methacrylate) (POEGMA) conjugates uniquely at the N-termini of a range of natural and recombinant proteins in a mild and efficient fashion. The formed POEGMA-protein conjugates showed highly retained in vitro bioactivity as compared with free proteins. Notably, the in vitro bioactivity of a POEGMA-interferon α (IFN) conjugate synthesized by this new chemistry is 8.1-fold higher than that of PEGASYS that is a commercially available and Food and Drug Administration (FDA) approved PEGylated IFN. The circulation half-life of the conjugate is similar to that of PEGASYS but is 46.2 times longer than that of free IFN. Consequently, the conjugate exhibits considerably improved antiviral bioactivity over free IFN and even PEGASYS in a mouse model. These results indicate that the PDA-enabled N-terminal grafting-from method is applicable to a number of proteins whose active sites are far away from the N-terminus for the synthesis of N-terminal polymer-protein conjugates with high yield, well-retained activity, and considerably improved pharmacology for biomedical applications.

Visible light-responsive micelles enable co-delivery of nitric oxide and antibiotics for synergistic antibiofilm applications

Tetraphenylethylene (TPE) moieties have been employed as a light-absorbing antenna for the activation of photoresponsive N-nitrosamine derivatives, enabling visible light-triggered NO release and efficient biofilm dispersal.

Photo-liberated amines for N-carboxyanhydride (PLANCA) ring-opening polymerization

Photo-liberated amines for N-carboxyanhydride (PLANCA) ring-opening polymerization affords narrow molecular weights, chain-end retention, and the formation of block copolypeptides.

Nanoengineering with RAFT polymers: from nanocomposite design to applications

Reversible addition–fragmentation chain-transfer (RAFT) polymerization is a powerful tool for the precise formation of macromolecular building blocks that can be used for the construction of well-defined nanocomposites.

Redox responsive activity regulation in exceptionally stable supramolecular assembly and co-assembly of a protein

Supramolecular assembly of biomolecules/macromolecules stems from the desire to mimic complex biological structures and functions of living organisms. While DNA nanotechnology is already in an advanced stage, protein assembly is still in its infancy as it is a significantly difficult task due to their large molecular weight, conformational complexity and structural instability towards variation in temperature, pH or ionic strength. This article reports highly stable redox-responsive supramolecular assembly of a protein Bovine serum albumin (BSA) which is functionalized with a supramolecular structure directing unit (SSDU). The SSDU consists of a benzamide functionalized naphthalene-diimide (NDI) chromophore which is attached with the protein by a bio-reducible disulfide linker. The SSDU attached protein (NDI-BSA) exhibits spontaneous supramolecular assembly in water by off-set π-stacking among the NDI chromophores, leading to the formation of spherical nanoparticles (diameter: 150-200 nm). The same SSDU when connected with a small hydrophilic wedge (NDI-1) instead of the large globular protein, exhibits a different π-stacking mode with relatively less longitudinal displacement which results in a fibrillar network and hydrogelation. Supramolecular co-assembly of NDI-BSA and NDI-1 (3 : 7) produces similar π-stacking and an entangled 1D morphology. Both the spherical assembly of NDI-BSA or the fibrillar co-assembly of NDI-BSA + NDI-1 (3 : 7) provide sufficient thermal stability to the protein as its thermal denaturation could be completely surpassed while the secondary structure remained intact. However, the esterase like activity of the protein reduced significantly as a result of such supramolecular assembly indicating limited access by the substrate to the active site of the enzyme located in the confined environment. In the presence of glutathione (GSH), a biologically important tri-peptide, due to the cleavage of the disulfide bond, the protein became free and was released, resulting in fully regaining its enzymatic activity. Such supramolecular assembly provided excellent protection to the protein against enzymatic hydrolysis as the relative hydrolysis was estimated to be <30% for the co-assembled protein with respect to the free protein under identical conditions. Similar to bioactivity, the enzymatic hydrolysis also became prominent after GSH-treatment, confirming that the lack of hydrolysis in the supramolecularly assembled state is indeed related to the confinement of the protein in the nanostructure assembly.

Deposition of Copper on Polyester Knitwear Fibers by a Magnetron Sputtering System. Physical Properties and Evaluation of Antimicrobial Response of New Multi-Functional Composite Materials

In this study, copper films were deposited by magnetron sputtering on poly(ethylene terephthalate) knitted textile to fabricate multi-functional, antimicrobial composite material. The modified knitted textile composites were subjected to microbial activity tests against colonies of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and antifungal tests against Chaetomium globosum fungal molds species. The prepared samples were characterized by UV/VIS transmittance, scanning electron microscopy (SEM), tensile and filtration parameters and the ability to block UV radiation. The performed works proved the possibility of manufacturing a new generation of antimicrobial textile composites with barrier properties against UV radiation, produced by a simple, zero-waste method. The specific advantages of using new poly(ethylene terephthalate)-copper composites are in biomedical applications areas.

Fully oxygen-tolerant atom transfer radical polymerization triggered by sodium pyruvate

ATRP (atom transfer radical polymerization) is one of the most robust reversible deactivation radical polymerization (RDRP) systems. However, the limited oxygen tolerance of conventional ATRP impedes its practical use in an ambient atmosphere. In this work, we developed a fully oxygen-tolerant PICAR (photoinduced initiators for continuous activator regeneration) ATRP process occurring in both water and organic solvents in an open reaction vessel. Continuous regeneration of the oxidized form of the copper catalyst with sodium pyruvate through UV excitation allowed the chemical removal of oxygen from the reaction mixture while maintaining a well-controlled polymerization of N-isopropylacrylamide (NIPAM) or methyl acrylate (MA) monomers. The polymerizations of NIPAM were conducted with 250 ppm (with respect to the monomer) or lower concentrations of CuBr2 and a tris[2-(dimethylamino)ethyl]amine ligand. The polymers were synthesized to nearly quantitative monomer conversions (>99%), high molecular weights (M n > 270 000), and low dispersities (1.16 < Đ < 1.44) in less than 30 min under biologically relevant conditions. The reported method provided a well-controlled ATRP (Đ = 1.16) of MA in dimethyl sulfoxide despite oxygen diffusion from the atmosphere into the reaction system.