Poly(2-oxazoline)-protein conjugates

Facile Generation of Heterotelechelic Poly(2-Oxazoline)s Towards Accelerated Exploration of Poly(2-Oxazoline)-Based Nanomedicine

Controlling the end-groups of biocompatible polymers is crucial for enabling polymer-based therapeutics and nanomedicine. Typically, end-group diversification is a challenging and time-consuming endeavor, especially for polymers prepared via ionic polymerization mechanisms with limited functional group tolerance. In this study, we present a facile end-group diversification approach for poly(2-oxazoline)s (POx), enabling quick and reliable production of heterotelechelic polymers to facilitate POxylation. The approach relies on the careful tuning of reaction parameters to establish differential reactivity of a pentafluorobenzyl initiator fragment and the living oxazolinium chain-end, allowing the selective introduction of N-, S-, O-nucleophiles via the termination of the polymerization, and a consecutive nucleophilic para-fluoro substitution. The value of this approach for the accelerated development of nanomedicine is demonstrated through the synthesis of well-defined lipid-polymer conjugates and POx-polypeptide block-copolymers, which are well-suited for drug and gene delivery. Furthermore, we investigated the application of a lipid-POx conjugate for the formulation and delivery of mRNA-loaded lipid nanoparticles for immunization against the SARS-COV-2 virus, underscoring the value of POx as a biocompatible polymer platform.

Glycopolymer Inhibitors of Galectin-3 Suppress the Markers of Tissue Remodeling in Pulmonary Hypertension

Pulmonary hypertension is a cardiovascular disease with a low survival rate. The protein galectin-3 (Gal-3) binding β-galactosides of cellular glycoproteins plays an important role in the onset and development of this disease. Carbohydrate-based drugs that target Gal-3 represent a new therapeutic strategy in the treatment of pulmonary hypertension. Here, we present the synthesis of novel hydrophilic glycopolymer inhibitors of Gal-3 based on a polyoxazoline chain decorated with carbohydrate ligands. Biolayer interferometry revealed a high binding affinity of these glycopolymers to Gal-3 in the subnanomolar range. In the cell cultures of cardiac fibroblasts and pulmonary artery smooth muscle cells, the most potent glycopolymer 18 (Lac-high) caused a decrease in the expression of markers of tissue remodeling in pulmonary hypertension. The glycopolymers were shown to penetrate into the cells. In a biodistribution and pharmacokinetics study in rats, the glycopolymers accumulated in heart and lung tissues, which are most affected by pulmonary hypertension.

Study of uricase-polynorbornene conjugates derived from grafting-from ring-opening metathesis polymerization

PEGylation has been the 'gold standard' in bioconjugation due to its ability to improve the pharmacokinetics and pharmacodynamics of native proteins. However, growing clinical evidence of hypersensitivity reactions to PEG due to pre-existing anti-PEG antibodies in healthy humans have raised concerns. Advancements in controlled polymerization techniques and conjugation chemistries have paved the way for the development of protein-polymer conjugates that can circumvent these adverse reactions while retaining the benefits of such modifications. Herein, we show the development of polynorbornene based bioconjugates of therapeutically relevant urate oxidase (UO) enzymes used in the treatment of gout synthesized by grafting-from ring-opening metathesis polymerization (ROMP). Notably, these conjugates exhibit comparable levels of bioactivity to PEGylated UO and demonstrate increased stability across varying temperatures and pH conditions. Immune recognition of conjugates by anti-UO antibodies reveal low protein immunogenicity following the conjugation process. Additionally, UO conjugates employing zwitterionic polynorbornene successfully avoid recognition by anti-PEG antibodies, further highlighting a potential replacement for PEG.

Schiff-Base Cross-Linked Poly(2-oxazoline) Micelle Drug Conjugates Possess Antiferroptosis Activity in Numerous In Vitro Cell Models

A great deal of nanocarriers have been applied to induce ferroptosis in cancer research, yet there are limited examples of nanocarrier formulations to rescue ferroptosis, which can be applied to neurodegeneration, inflammation, liver damage, kidney disease, and more. Here, we present the synthesis, characterization, and in vitro evaluation of pH-responsive, core-cross-linked micelle (CCM) ferrostatin-1 (Fer-1) conjugates with amine, valproic acid, and biotin surface chemistries. Fer-1 release from stable and defined CCM Fer-1 conjugates was quantified, highlighting the sustained release for 24 h. CCM Fer-1 conjugates demonstrated excellent ferroptosis rescue by their antilipid peroxidation activity in a diverse set of cell lines in vitro. Additionally, CCMs showed tunable cell association in SH-SY5Y and translocation across an in vitro blood-brain barrier (BBB) model, highlighting potential brain disease applications. Overall, here, we present a polymeric Fer-1 delivery system to enhance Fer-1 action, which could help in improving Fer-1 action in the treatment of ferroptosis-related diseases.

Multifunctional Poly(2-ethyl-2-oxazoline) Copolymers Containing Dithiolane and Pentafluorophenyl Esters as Effective Reactive Linkers for Gold Surface Coatings

Surface functionalization with biological macromolecules is an important task for the development of sensor materials, whereby the interaction with other biological materials should be suppressed. In this work, we developed a novel multifunctional poly(2-ethyl-2-oxazoline)-dithiolane conjugate as a versatile linker for gold surface immobilization of amine-containing biomolecules, containing poly(2-ethyl-2-oxazoline) as antifouling polymer, dithiolane for surface immobilization, and activated esters for protein conjugation. First, a well-defined carboxylic acid containing copoly(2-ethyl-2-oxazoline) was synthesized by cationic ring-opening copolymerization of 2-ethyl-2-oxazoline with a methyl ester-containing 2-oxazoline monomer, followed by postpolymerization modifications. The side-chain carboxylic groups were then converted to amine-reactive pentafluorophenyl (PFP) ester groups. Part of the PFP groups was used for the attachment of the dithiolane moiety, which can efficiently bind to gold surfaces. The final copolymer contained 1.4 mol% of dithiolane groups and 4.5 mol% of PFP groups. The copolymer structure was confirmed by several analytical techniques, including NMR spectroscopy and size-exclusion chromatography. The kinetics of the PFP ester aminolysis and hydrolysis demonstrated significantly faster amidation compared to hydrolysis, which is essential for subsequent protein conjugation. Successful coating of gold surfaces with the polymer was confirmed by spectroscopic ellipsometry, showing a polymer brush thickness of 4.77 nm. Subsequent modification of the coated surfaces was achieved using bovine serum albumin as a model protein. This study introduces a novel reactive polymer linker for gold surface functionalization and offers a versatile polymer platform for various applications including biosensing and surface functionalization.

Polyoxazoline-Based Nanovaccine Synergizes with Tumor-Associated Macrophage Targeting and Anti-PD-1 Immunotherapy against Solid Tumors

Immune checkpoint blockade reaches remarkable clinical responses. However, even in the most favorable cases, half of these patients do not benefit from these therapies in the long term. It is hypothesized that the activation of host immunity by co-delivering peptide antigens, adjuvants, and regulators of the transforming growth factor (TGF)-β expression using a polyoxazoline (POx)-poly(lactic-co-glycolic) acid (PLGA) nanovaccine, while modulating the tumor-associated macrophages (TAM) function within the tumor microenvironment (TME) and blocking the anti-programmed cell death protein 1 (PD-1) can constitute an alternative approach for cancer immunotherapy. POx-Mannose (Man) nanovaccines generate antigen-specific T-cell responses that control tumor growth to a higher extent than poly(ethylene glycol) (PEG)-Man nanovaccines. This anti-tumor effect induced by the POx-Man nanovaccines is mediated by a CD8+ -T cell-dependent mechanism, in contrast to the PEG-Man nanovaccines. POx-Man nanovaccine combines with pexidartinib, a modulator of the TAM function, restricts the MC38 tumor growth, and synergizes with PD-1 blockade, controlling MC38 and CT26 tumor growth and survival. This data is further validated in the highly aggressive and poorly immunogenic B16F10 melanoma mouse model. Therefore, the synergistic anti-tumor effect induced by the combination of nanovaccines with the inhibition of both TAM- and PD-1-inducing immunosuppression, holds great potential for improving immunotherapy outcomes in solid cancer patients.

Performance of a Flow-Through Enzyme Reactor Prepared from a Silica Monolith and an α-Poly(D-Lysine)-Enzyme Conjugate

Horseradish peroxidase (HRP) is covalently bound in aqueous solution to polycationic α-poly(D-lysine) chains of ≈1000 repeating units length, PDL, via a bis-aryl hydrazone bond (BAH). Under the experimental conditions used, about 15 HRP molecules are bound along the PDL chain. The purified PDL-BAH-HRP conjugate is very stable when stored at micromolar HRP concentration in a pH 7.2 phosphate buffer solution at 4 °C. When a defined volume of such a conjugate solution of desired HRP concentration (i.e., HRP activity) is added to a macro- and mesoporous silica monolith with pore sizes of 20-30 µm as well as below 30 nm, quantitative and stable noncovalent conjugate immobilization is achieved. The HRP-containing monolith can be used as flow-through enzyme reactor for bioanalytical applications at neutral or slightly alkaline pH, as demonstrated for the determination of hydrogen peroxide in diluted honey. The conjugate can be detached from the monolith by simple enzyme reactor washing with an aqueous solution of pH 5.0, enabling reloading with fresh conjugate solution at pH 7.2. Compared to previously investigated polycationic dendronized polymer-enzyme conjugates with approximately the same average polymer chain length, the PDL-BAH-HRP conjugate appears to be equally suitable for HRP immobilization on silica surfaces.

Smart Poly(lactide)-b-poly(triethylene glycol methyl ether methacrylate) (PLA-b-PTEGMA) Block Copolymers: One-Pot Synthesis, Temperature Behavior, and Controlled Release of Paclitaxel

This paper introduces a new class of amphiphilic block copolymers created by combining two polymers: polylactic acid (PLA), a biocompatible and biodegradable hydrophobic polyester used for cargo encapsulation, and a hydrophilic polymer composed of oligo ethylene glycol chains (triethylene glycol methyl ether methacrylate, TEGMA), which provides stability and repellent properties with added thermo-responsiveness. The PLA-b-PTEGMA block copolymers were synthesized using ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerization (ROP-RAFT), resulting in varying ratios between the hydrophobic and hydrophilic blocks. Standard techniques, such as size exclusion chromatography (SEC) and ¹H NMR spectroscopy, were used to characterize the block copolymers, while ¹H NMR spectroscopy, 2D nuclear Overhauser effect spectroscopy (NOESY), and dynamic light scattering (DLS) were used to analyze the effect of the hydrophobic PLA block on the LCST of the PTEGMA block in aqueous solutions. The results show that the LCST values for the block copolymers decreased with increasing PLA content in the copolymer. The selected block copolymer presented LCST transitions at physiologically relevant temperatures, making it suitable for manufacturing nanoparticles (NPs) and drug encapsulation-release of the chemotherapeutic paclitaxel (PTX) via temperature-triggered drug release mechanism. The drug release profile was found to be temperature-dependent, with PTX release being sustained at all tested conditions, but substantially accelerated at 37 and 40 °C compared to 25 °C. The NPs were stable under simulated physiological conditions. These findings demonstrate that the addition of hydrophobic monomers, such as PLA, can tune the LCST temperatures of thermo-responsive polymers, and that PLA-b-PTEGMA copolymers have great potential for use in drug and gene delivery systems via temperature-triggered drug release mechanisms in biomedicine applications.

Simple preparation of POxylated nanomaterials for cancer chemo-PDT/PTT

Near infrared (NIR) light-responsive nanomaterials hold potential to mediate combinatorial therapies targeting several cancer hallmarks. When irradiated, these nanomaterials produce reactive oxygen species (photodynamic therapy) and/or a temperature increase (photothermal therapy). These events can damage cancer cells and trigger the release of drugs from the nanomaterials' core. However, engineering nanomaterials for cancer chemo-photodynamic/photothermal therapy is a complex process. First, nanomaterials with photothermal capacity are synthesized, being then loaded with photosensitizers plus chemotherapeutics, and, finally functionalized with polymers for achieving suitable biological properties. To overcome this limitation, in this work, a novel straightforward approach to attain NIR light-responsive nanosystems for cancer chemo-photodynamic/photothermal therapy was established. Such was accomplished by synthesizing poly(2-ethyl-2-oxazoline)-IR780 amphiphilic conjugates, which can be assembled into nanoparticles with photodynamic/photothermal capabilities that simultaneously encapsulate Doxorubicin (DOX/PEtOx-IR NPs). The DOX/PEtOx-IR NPs presented a suitable size and surface charge for cancer-related applications. When irradiated with NIR light, the DOX/PEtOx-IR NPs produced singlet oxygen as well as a smaller thermic effect that boosted the release of DOX by 1.7-times. In the in vitro studies, the combination of DOX/PEtOx-IR NPs and NIR light could completely ablate breast cancer cells (viability ≈ 4 %), demonstrating the enhanced outcome arising from the nanomaterials' chemo-photodynamic/photothermal therapy.

Conformational Parameters and Hydrodynamic Behavior of Poly(2-Methyl-2-Oxazoline) in a Broad Molar Mass Range

In this work, we report our results on the hydrodynamic behavior of poly(2-methyl-2-oxazoline) (PMeOx). PMeOx is gaining significant attention for use as hydrophilic polymer in pharmaceutical carriers as an alternative for the commonly used poly(ethylene glycol) (PEG), for which antibodies are found in a significant fraction of the human population. The main focus of the current study is to determine the hydrodynamic characteristics of PMeOx under physiological conditions, which serves as basis for better understanding of the use of PMeOx in pharmaceutical applications. This goal was achieved by studying PMeOx solutions in phosphate-buffered saline (PBS) as a solvent at 37 °C. This study was performed based on two series of PMeOx samples; one series is synthesized by conventional living cationic ring-opening polymerization, which is limited by the maximum chain length that can be achieved, and a second series is obtained by an alternative synthesis strategy based on acetylation of well-defined linear poly(ethylene imine) (PEI) prepared by controlled side-chain hydrolysis of a defined high molar mass of poly(2-ethyl-2-oxazoline). The combination of these two series of PMeOx allowed the determination of the Kuhn-Mark-Houwink-Sakurada equations in a broad molar mass range. For intrinsic viscosity, sedimentation and diffusion coefficients, the following expressions were obtained: η=0.015M0.77, s0=0.019M0.42 and D0=2600M-0.58, respectively. As a result, it can be concluded that the phosphate-buffered saline buffer at 37 °C represents a thermodynamically good solvent for PMeOx, based on the scaling indices of the equations. The conformational parameters for PMeOx chains were also determined, revealing an equilibrium rigidity or Kuhn segment length, (A) of 1.7 nm and a polymer chain diameter (d) of 0.4 nm. The obtained value for the equilibrium rigidity is very similar to the reported values for other hydrophilic polymers, such as PEG, poly(vinylpyrrolidone) and poly(2-ethyl-2-oxazoline), making PMeOx a relevant alternative to PEG.

Preparation of Temperature-Responsive Antibody–Nanoparticles by RAFT-Mediated Grafting from Polymerization

Herein, we report the preparation of temperature-responsive antibody–nanoparticles by the direct polymerization of N-isopropylacrylamide (NIPAAm) from immunoglobulin G (IgG). To this end, a chain transfer agent (CTA) was introduced into IgG, followed by the precipitation polymerization of NIPAAm in an aqueous medium via reversible addition–fragmentation chain transfer polymerization above the lower critical solution temperature (LCST). Consequently, antibody–polymer particles with diameters of approximately 100–200 nm were formed. Owing to the entanglement of the grafted polymers via partial chemical crosslinking, the antibody–nanoparticles maintained their stability even at temperatures below the LCST. Further, the dispersed nanoparticles could be collected by thermal precipitation above the LCST. Additionally, the antibody–nanoparticles formulation could maintain its binding constant and exhibited a good resistance against enzymatic treatment. Thus, the proposed antibody–nanoparticles can be useful for maximizing the therapeutic potential of antibody–drug conjugates or efficacies of immunoassays and antibody recovery and recycling.

Safety and Biodistribution Profile of Poly(styrenyl acetal trehalose) and Its Granulocyte Colony Stimulating Factor Conjugate

Poly(styrenyl acetal trehalose) (pSAT), composed of trehalose side chains linked to a polystyrene backbone via acetals, stabilizes a variety of proteins and enzymes against fluctuations in temperature. A promising application of pSAT is conjugation of the polymer to therapeutic proteins to reduce renal clearance. To explore this possibility, the safety of the polymer was first studied. Investigation of acute toxicity of pSAT in mice showed that there were no adverse effects of the polymer at a high (10 mg/kg) concentration. The immune response (antipolymer antibody and cytokine production) in mice was also studied. No significant antipolymer IgG was detected for pSAT, and only a transient and low level of IgM was elicited. pSAT was also safe in terms of cytokine response. The polymer was then conjugated to a granulocyte colony stimulating factor (GCSF), a therapeutic protein that is approved by the Federal Drug Administration, in order to study the biodistribution of a pSAT conjugate. A site-selective, two-step synthesis approach was developed for efficient conjugate preparation for the biodistribution study resulting in 90% conjugation efficiency. The organ distribution of GCSF-pSAT was measured by positron emission tomography and compared to controls GCSF and GCSF-poly(ethylene glycol), which confirmed that the trehalose polymer conjugate improved the in vivo half-life of the protein by reducing renal clearance. These findings suggest that trehalose styrenyl polymers are promising for use in therapeutic protein-polymer conjugates for reduced renal clearance of the biomolecule.

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

Chemo-Enzymatic PEGylation/POxylation of Murine Interleukin-4

Interleukin-4 (IL-4) is a potentially interesting anti-inflammatory therapeutic, which is rapidly excreted. Therefore, serum half-life extension by polymer conjugation is desirable, which may be done by PEGylation. Here, we use PEtOx as an alternative to PEG for bioconjugate engineering. We genetically extended murine IL-4 (mIL-4) with the d-domain of insulin-like growth factor I (IGF-I), a previously identified substrate of transglutaminase (TG) Factor XIIIa (FXIIIa). Thereby, engineered mIL-4 (mIL-4-TG) became an educt for TG catalyzed C-terminal, site-directed conjugation. This was deployed to enzymatically couple an azide group containing peptide sequence to mIL-4, allowing C-terminal bioconjugation of polyethylene glycol or poly(2-ethyl-2-oxazoline). Both bioconjugates had wild-type potency and alternatively polarized macrophages.

Molecular Insights into Site-Specific Interferon-α2a Bioconjugates Originated from PEG, LPG, and PEtOx

Conjugation of biologics with polymers modulates their pharmacokinetics, with polyethylene glycol (PEG) as the gold standard. We compared alternative polymers and two types of cyclooctyne linkers (BCN/DBCO) for bioconjugation of interferon-α2a (IFN-α2a) using 10 kDa polymers including linear mPEG, poly(2-ethyl-2-oxazoline) (PEtOx), and linear polyglycerol (LPG). IFN-α2a was azide functionalized via amber codon expansion and bioorthogonally conjugated to all cyclooctyne linked polymers. Polymer conjugation did not impact IFN-α2a's secondary structure and only marginally reduced IFN-α2a's bioactivity. In comparison to PEtOx, the LPG polymer attached via the less rigid cyclooctyne linker BCN was found to stabilize IFN-α2a against thermal stress. These findings were further detailed by molecular modeling studies which showed a modulation of protein flexibility upon PEtOx conjugation and a reduced amount of protein native contacts as compared to PEG and LPG originated bioconjugates. Polymer interactions with IFN-α2a were further assessed via a limited proteolysis (LIP) assay, which resulted in comparable proteolytic cleavage patterns suggesting weak interactions with the protein's surface. In conclusion, both PEtOx and LPG bioconjugates resulted in a similar biological outcome and may become promising PEG alternatives for bioconjugation.

Poly(HPMA-co-NIPAM) copolymer as an alternative to polyethylene glycol-based pharmacokinetic modulation of therapeutic proteins

PEGylation is the standard approach for prolonging the plasma exposure of protein therapeutics but has limitations. We explored whether polymers prepared by Reversible Addition-Fragmentation chain-Transfer (RAFT) may provide better alternatives to polyethylene glycol (PEG). Four RAFT polymers were synthesised with varying compositions, molar mass (M_n), and structures, including a homopolymer of N-(2-hydroxypropyl)methacrylamide, (pHPMA) and statistical copolymers of HPMA with poly(ethylene glycol methyl ether acrylate) p(HPMA-co-PEGA); HPMA and N-acryloylmorpholine, p(HPMA-co-NAM); and HPMA and N-isopropylacrylamide, p(HPMA-co-NIPAM). The intravenous pharmacokinetics of the polymers were then evaluated in rats. The in vitro activity and in vivo pharmacokinetics of p(HPMA-co-NIPAM)-conjugated trastuzumab Fab' and full length mAb were then evaluated. p(HPMA-co-NIPAM) prolonged plasma exposure more avidly compared to the other p(HPMA) polymers or PEG, irrespective of molecular weight. When conjugated to trastuzumab-Fab', p(HPMA-co-NIPAM) prolonged plasma exposure of the Fab' similar to PEG-Fab'. The generation of anti-PEG IgM in rats 7 days after intravenous and subcutaneous dosing of p(HPMA-co-NIPAM) conjugated trastuzumab mAb was also examined and was shown to exhibit lower immunogenicity than the PEGylated construct. These data suggest that p(HPMA-co-NIPAM) has potential as a promising copolymer for use as an alternative conjugation strategy to PEG, to prolong the plasma exposure of therapeutic proteins.

On the identification and quantification of proton-initiated species in the synthesis of poly(2-alkyl-2-oxazoline)s by high resolution liquid chromatography

Hydrophilic poly(2-oxazoline)s represent a promising alternative to replace poly(ethylene glycol) in the biomedical field. For that purpose, reliable analytical protocols to confirm identity and quantity of impurities are required. In particular, side products deriving from chain transfer reactions occurring during the cationic ring-opening polymerization and incomplete end-capping processes may be present. The analytical approach must hence be capable of separating polymers according to minor changes regarding their end group. We demonstrate that liquid chromatography, relying on a monolithic C18-modified silica column and isocratic as well as gradient elution using water / acetonitrile mixtures and varying detectors, can accomplish such demanding high resolution separations. Poly(2-ethyl-2-oxazoline)s (PEtOx) with acetyl, hydroxyl, and phthalimide ω-end groups were investigated. Identification of side products was achieved through coupling with electrospray ionization mass spectrometry. UV / Vis detection was applied to quantify chain transfer products in PEtOx comprising biphenyl moieties. In addition, gradient elution enabled the separation of PEtOx into macromolecules according to their specific degrees of polymerization in molar mass ranges around 2,000 g mol^-1.

Effect of Polymer Hydrophilicity and Molar Mass on the Properties of the Protein in Protein-Polymer Conjugates: The Case of PPEylated Myoglobin

Polyphosphoesters (PPEs), a versatile class of biodegradable and biocompatible polymers, have been proposed as alternatives to poly(ethylene glycol) (PEG), which is suspected to be responsible for anaphylactic reactions in some patients after the administration of PEGylated compounds, e.g., in the current Covid-19 vaccines. We present the synthesis and characterization of a novel set of protein-polymer conjugates using the model protein myoglobin and a set of PPEs with different hydrophilicity and molar mass. We report an extensive evaluation of the (bio)physical properties of the protein within the conjugates, studying its conformation, residual activity, and thermal stability by complementary techniques (UV-vis spectroscopy, nano-differential scanning calorimetry, and fluorometry). The data underline the systematic influence of polymer hydrophilicity on protein properties. The more hydrophobic polymers destabilize the protein, the more hydrophilic PPEs protect against thermally induced aggregation and proteolytic degradation. This basic study aims at guiding the design of future PPEylated drugs and protein conjugates.

Poly(2-ethyl-2-oxazoline) Featuring a Central Amino Moiety

The incorporation of an amino group into a bifunctional initiator for the cationic ring-opening polymerization (CROP) is achieved in a two-step reaction. Detailed kinetic studies using 2-ethyl-2-oxazoline demonstrate the initiators' eligibility for the CROP yielding well-defined polymers featuring molar masses of about 2000 g mol^-1 . Deprotection of the phthalimide moiety subsequent to polymerization enables the introduction of a cyclooctyne group in central position of the polymer which is further exploited in a strain-promoted alkyne-azide click reaction (SpAAC) with a Fmoc-protected azido lysine representing a commonly used binding motif for site specific polymer-protein/peptide conjugation. In-depth characterization via electrospray ionization mass spectrometry (ESI) confirms the success of all post polymerization modification steps.

The role of poly(2-alkyl-2-oxazoline)s in hydrogels and biofabrication

Poly(2-alkyl-2-oxazoline)s (PAOXAs) have been rapidly emerging as starting materials in the design of tissue engineering supports and for the generation of platforms for cell cultures, especially in the form of hydrogels. Thanks to their biocompatibility, chemical versatility and robustness, PAOXAs now represent a valid alternative to poly(ethylene glycol)s (PEGs) and their derivatives in these applications, and in the formulation of bioinks for three-dimensional (3D) bioprinting. In this review, we summarize the recent literature where PAOXAs have been used as main components for hydrogels and biofabrication mixtures, especially highlighting how their easily tunable composition could be exploited to fabricate multifunctional biomaterials with an extremely broad spectrum of properties.

Ferrocene containing redox-responsive poly(2-oxazoline)s

A new monomer, 2-ferrocene-ethyl-2-oxazoline, was copolymerized with 2-alkyl-2-oxazolines. The cationic ring opening polymerization (CROP) of 2-oxazolines allows the synthesis of well-defined copolymers with adjustable molar masses as well as end-group control, which was also evident from kinetic studies. The utilization of this new comonomer led to redox-active polymers as proven by UV-VIS-measurements and cyclic-voltammetry.

Full Thermal Switching of Enzymes by Thermoresponsive Poly(2-oxazoline)-Based Enzyme Inhibitors

Controlling the activity of enzymes is an important feature for many processes in medicine, bioanalytics, and biotechnology. So far, it has not been possible to fully switch biocatalysts on and off by thermoresponsive enzyme inhibitors. Herein, we present poly(2-oxazoline)s with iminodiacetic acid end groups (POx-IDA) that are lower critical solution temperature (LCST) polymers and thus thermosensitive. They are capable of reversibly inhibiting the activity of horse radish peroxidase and laccase by more than 99 %. Increasing the temperature makes the POx-IDA precipitate, which leads to 100 % recovery of the enzyme activity. This switching cycle is fully reversible. The LCST of the POx-IDA can be tuned by varying the polymer composition to generate a wide range of switching windows.

Temperature Behavior of Aqueous Solutions of Poly(2-oxazoline) Homopolymer and Block Copolymers Investigated by NMR Spectroscopy and Dynamic Light Scattering

1H NMR methods in combination with dynamic light scattering were applied to study temperature behavior of poly(2-isopropyl-2-oxazoline) (PIPOx) homopolymer as well as PIPOx-b-poly(2-methyl-2-oxazoline) (PMeOx) and poly(2-ethyl-2-oxazoline) (PEtOx)-b-PMeOx diblock copolymers in aqueous solutions. 1H NMR spectra showed a different way of phase transition for the main and side chains in PIPOx-based solutions. Additionally, the phase transition is irreversible for PIPOx homopolymer and partially reversible for PIPOx-b-PMeOx copolymer. As revealed by NMR, the phase transition in PEtOx-based copolymers solutions exists despite the absence of solution turbidity. It is very broad, virtually independent of the copolymer composition and reversible with some hysteresis. Two types of water molecules were detected in solutions of the diblock copolymers above the phase transition-"free" with long and "bound" with short spin-spin relaxation times T2. NOESY spectra revealed information about conformational changes observed already in the pre-transition region of PIPOx-b-PMeOx copolymer solution.

Poly(2-oxazoline)s with a 2,2'-Iminodiacetate End Group Inhibit and Stabilize Laccase

Poly(2-oxazoline)s (POxs) with 2,2'-iminodiacetate (IDA) end groups were investigated as inhibitors for laccase. The polymers with the IDA end groups are reversible, competitive inhibitors for this enzyme. The IC50 values were found to be in a range of 1-3 mm. Compared with IDA alone, the activity was increased by a factor of more than 30; thus indicating that attaching a polymer chain to an inhibitor can already improve the activity of the former. The enzyme activity drops to practically zero upon increasing the concentration of the most active telechelic inhibitor, IDA-PEtOx30 -IDA (PEtOx: poly(2-ethyl-2-oxazoline)), from 5 to 8 mm. This unusual behavior was investigated by means of dynamic light scattering, which showed specific aggregation above 5 mm. Furthermore, the laccase could be stabilized in the presence of POx-IDA, upon addition at a concentration of 20 mm and higher. Whereas laccase becomes completely inactive at room temperature after one week, the stabilized laccase is fully active for at least a month in aqueous solution.