From globules to crystals: a spectral study of poly(2-isopropyl-2-oxazoline) crystallization in hot water

One easy strategy to comprehend the complex folding/crystallization behaviors of proteins is to study the self-assembly process of their synthetic polymeric analogues with similar properties owing to their simple structures and easy access to molecular design. Poly(2-isopropyl-2-oxazoline) (PIPOZ) is often regarded as an ideal pseudopeptide with similar two-step crystallization behavior to proteins, whose aqueous solution experiences successive lower critical solution temperature (LCST)-type liquid-liquid phase separation upon heating and irreversible crystallization when annealed above LCST for several hours. In this paper, by microscopic observations, IR and Raman spectroscopy in combination with 2D correlation analysis, we show that the second step of PIPOZ crystallization in hot water can be further divided into two apparent stages, i.e., nucleation and crystal growth, and perfect crystalline PIPOZ chains are found to only develop in the second stage. While all the groups exhibit changes in initial nucleation, only methylene groups on the backbone participate in the crystal growth stage. During nucleation, a group motion transfer is found from the side chain to the backbone, and nucleation is assumed to be mainly driven by the cleavage of bridging C=O···D-O-D···O=C hydrogen bonds followed by chain arrangement due to amide dipolar orientation. Nevertheless, during crystal growth, a further chain ordering process occurs resulting in the final formation of crystalline PIPOZ chains with partial trans conformation of backbones and alternative side chains on the two sides. The underlying crystallization mechanism of PIPOZ in hot water we present here may provide very useful information for understanding the crystallization of biomacromolecules in biological systems.

Multireactive Poly(2-oxazoline) Nanofibers through Electrospinning with Crosslinking on the Fly

Crosslinked hydrophilic poly(2-oxazoline)-based nanofibers amenable to facile multifunctionalization are fabricated using alkene-containing poly(2-alkyl-2-oxazoline)s (PAOx) via in situ photoinitiated radical thiol-ene crosslinking during electrospinning. The resulting crosslinked nanofibers are demonstrated to be multifunctionalizable using different chemistries as they contain two functional handles, being the alkene moieties from the parent copolymer and the residual thiol groups from the tetra-thiol-based crosslinker. While the thiol groups in these nanofibers could be passivated or conjugated to install functional molecules through thiol-maleimide conjugation, the alkene groups could sequentially be modified with thiol-containing molecules using photoinitiated radical thiol-ene reactions. Utilization of the photochemically induced conjugation of thiol-bearing molecules to the alkene groups on the nanofibers is used to obtain functionalization in a spatially controlled manner.

A novel approach to controlled self-assembly of pH-responsive thermosensitive homopolymer polyelectrolytes into stable nanoparticles

This review addresses the recent research progress in introducing and elaborating a novel approach to controlled polymer self-assembly into stable nanoparticles using pH-responsive thermosensitive homopolymer polyelectrolytes. Interesting aspect of this approach is that stable polymeric nanoparticles are formed from homopolymers of one type only and without any assembly-triggering additives. The process of their formation can be monitored online e.g. by light scattering and particle size can be finely custom tuned. Obtained nanoparticles have interesting properties and are very stable over long periods of time and over a broad range of salt concentrations including physiological conditions. Much effort was devoted not only to finding optimum experimental protocols and to characterizing resulting nanoparticles in detail, but also to understanding physical processes behind these successful protocols.

Conformational changes in the heat-induced crystallization of poly(2-isopropyl-2-oxazoline) in the solid state

Poly(2-isopropyl-2-oxazoline) (PIPOZ) with an isomeric structure of poly(N-isopropylacrylamide) (PNIPAM) represents an important class of stimuli-responsive synthetic polymers. Unlike PNIPAM, PIPOZ exhibits an unusual heat-induced crystallization behaviour at around 120 °C in the solid state, whose dynamic mechanism involving all group motions and conformational changes is still poorly understood. In this paper, IR spectroscopy in combination with two-dimensional analysis methods - the perturbation correlation moving window (PCMW) and two-dimensional correlation spectroscopy (2DCOS) - was used to monitor and study the conformational changes in the crystallization of PIPOZ in the solid state. The incorporated water molecules are found to be not necessary to assist the solid-state crystallization of the PIPOZ film. PCMW and 2DCOS analyses reveal that following the breaking of minor CH3O[double bond, length as m-dash]C hydrogen bonds, all the group moieties exhibit highly synergetic motions during crystallization, and methylene groups on the backbone do not show significant changes throughout the crystallization process. Raman spectroscopic and molecular dynamics simulation results further support this conclusion. The chain alignment of PIPOZ chains is shown to be mainly achieved by the lateral distortion of coplanar side chains or the ordered chain arrangement of amide dipoles together with the torsion of the backbone through C-N linkages. Upon heating, gauche conformations of methylene groups on the backbone are always dominating, resulting in an ordered PIPOZ chain with alternate side chains and a slightly distorted backbone.

Hyperbranched poly(N-(2-hydroxypropyl) methacrylamide) via RAFT self-condensing vinyl polymerization

We report the first synthesis of hyperbranched poly(N-(2-hydroxypropyl) methacrylamide) (HB-PHPMA) using reversible addition–fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP).

Enhanced cytocompatibility and functional group content of poly(l-lysine) dendrimers by grafting with poly(oxazolines)

We report the use of polyoxazolines as materials for modifying the surface of a generation 5 l-lysine dendrimer resulting in a significant improvement in the biocompatibility properties compared to the unmodified dendrimer. The polyoxazoline coatings represent interesting alternatives to polyethylene glycol and can also offer an opportunity for increasing drug loading.

Synthesis of novel boronic acid-decorated poly(2-oxazoline)s showing triple-stimuli responsive behavior

The synthesis of novel boronic-acid decorated poly(2-oxazoline)s showing a glucose- and pH dependent thermal transition is reported.

Protein cages and synthetic polymers: a fruitful symbiosis for drug delivery applications, bionanotechnology and materials science

Protein cages have become essential tools in bionanotechnology due to their well-defined, monodisperse, capsule-like structure. Combining them with synthetic polymers greatly expands their application, giving rise to novel nanomaterials fore.g.drug-delivery, sensing, electronic devices and for uses as nanoreactors.

Degradable polyurethane with poly(2-ethyl-2-oxazoline) brushes for protein resistance

The effects of chain length and graft density of poly(2-ethyl-2-oxazoline) on the protein resistance of degradable polyurethane-graft-poly(2-ethyl-2-oxazoline) with PCL as the soft segment have been investigated.

Facile one-pot/one-step synthesis of heterotelechelic N-acylated poly(aminoester) macromonomers for carboxylic acid decorated comb polymers

Optimal monomer ratios in the spontaneous zwitterionic copolymerisation yield defined telechelic macromonomers with near quantitative ω-carboxylic acid end groups.

Fluorescent amphiphilic heterografted comb polymers comprising biocompatible PLA and PEtOx side chains

The comb polymers are synthesized in three independent steps by ROP, CROP, and RAFT.

Sustainable Life Cycles of Natural-Precursor-Derived Nanocarbons

Sustainable societal and economic development relies on novel nanotechnologies that offer maximum efficiency at minimal environmental cost. Yet, it is very challenging to apply green chemistry approaches across the entire life cycle of nanotech products, from design and nanomaterial synthesis to utilization and disposal. Recently, novel, efficient methods based on nonequilibrium reactive plasma chemistries that minimize the process steps and dramatically reduce the use of expensive and hazardous reagents have been applied to low-cost natural and waste sources to produce value-added nanomaterials with a wide range of applications. This review discusses the distinctive effects of nonequilibrium reactive chemistries and how these effects can aid and advance the integration of sustainable chemistry into each stage of nanotech product life. Examples of the use of enabling plasma-based technologies in sustainable production and degradation of nanotech products are discussed-from selection of precursors derived from natural resources and their conversion into functional building units, to methods for green synthesis of useful naturally degradable carbon-based nanomaterials, to device operation and eventual disintegration into naturally degradable yet potentially reusable byproducts.

Polyplex Micelles with Double-Protective Compartments of Hydrophilic Shell and Thermoswitchable Palisade of Poly(oxazoline)-Based Block Copolymers for Promoted Gene Transfection

Improving the stability of polyplex micelles under physiological conditions is a critical issue for promoting gene transfection efficiencies. To this end, hydrophobic palisade was installed between the inner core of packaged plasmid DNA (pDNA) and the hydrophilic shell of polyplex micelles using a triblock copolymer consisting of hydrophilic poly(2-ethyl-2-oxazoline), thermoswitchable amphiphilic poly(2-n-propyl-2-oxazoline) (PnPrOx) and cationic poly(L-lysine). The two-step preparation procedure, mixing the triblock copolymer with pDNA below the lower critical solution temperature (LCST) of PnPrOx, followed by incubation above the LCST to form a hydrophobic palisade of the collapsed PnPrOx segment, induced the formation of spatially aligned hydrophilic-hydrophobic double-protected polyplex micelles. The prepared polyplex micelles exhibited significant tolerance against attacks from nuclease and polyanions compared to those without hydrophobic palisades, thereby promoting gene transfection. These results corroborated the utility of amphiphilic poly(oxazoline) as a molecular thermal switch to improve the stability of polyplex gene carriers relevant for physiological applications.

Smart Polymeric Nanoparticles as Emerging Tools for Imaging--The Parallel Evolution of Materials

The field of imaging has developed considerably over the past decade and recent advances in the area of nanotechnology, in particular nanomaterials, have opened new opportunities. Polymeric nanoparticles are particularly interesting and a number of novel materials, characterized by stimuli-responsive characteristics and fluorescent tagging, have allowed visualization, intracellular labeling and real-time tracking. In some of the latest applications the nanoparticles have been used for imagining of tumor cells, both in vivo and ex vivo.

Microwave-assisted cationic ring-opening polymerization of 2-oxazolines

Unlike any other polymer class, the (co-)poly(2-oxazoline)s have tremendously benefited from the introduction of microwave reactors into chemical laboratories. This review focuses on the research activities in the area of (co-)poly(2-oxazoline)s prepared by microwave-assisted syntheses and, correspondingly, summarizes the current-state-of the-art of the microwave-assisted synthesis of 2-oxazoline monomers and the microwave-assisted ring-opening (co-)polymerization of 2-oxazolines as well as prominent examples of post-polymerization modification of (co-)poly(2-oxazoline)s. Special attention is attributed to the kinetic analysis of the microwave-assisted polymerization of 2-oxazolines and the discussion of non-thermal microwave effects.

Multifunctional Thrombin-Activatable Polymer Capsules for Specific Targeting to Activated Platelets

Smart poly(2-oxazoline) (POx)-based multifunctional polymer capsules that specifically target glycoprotein (GP) IIb/IIIa on the surface of activated platelets are degraded by the serine protease thrombin and release the urokinase plasminogen activator loaded into the polymer capsules, only in the area of acute thrombosis.

Sulfolane as Common Rate Accelerating Solvent for the Cationic Ring-Opening Polymerization of 2-Oxazolines

The search for alternative solvents for the cationic ring-opening polymerization (CROP) of 2-methyl-2-oxazoline (MeOx) is driven by the poor solubility of P(MeOx) in polymerization solvents such as acetonitrile (CH₃CN) and chlorobenzene as well as in MeOx itself. In this study, solvent screening has revealed that especially sulfolane is a good solvent for PMeOx. Unexpectedly, an increased propagation rate constant (k_p) was found for the CROP of MeOx in sulfolane. Further extended kinetic studies at different temperatures (60-180 °C), revealed that the acceleration is due to an increase in frequency factor, while the activation energy (E_a) of the reaction is hardly affected. In order to explore the versatility of sulfolane as polymerization solvent for the CROP of 2-oxazolines in general, also the polymerization kinetics of other 2-oxazoline monomers, such as 2-ethyl-2-oxazoline (EtOx) and 2-phenyl-2-oxazoline (PhOx), have been studied, revealing a common acceleration of the CROP of 2-oxazoline monomers in sulfolane. This also enabled more controlled synthesis of PMeOx-block-PPhOx block copolymers that otherwise suffers from solvent incompatibility.

Properties and reactivity of polyoxazoline plasma polymer films

Polyoxazolines arise as a promising new class of polymers for biomedical applications, but creating oxzoline-based coatings via conventional methods is challenging. Herein, nanoscale polyoxazoline coatings were generated via a single step plasma deposition process. The effects of plasma deposition conditions on the film stability, structure and chemical group density were investigated. Detailed examination of the physical and chemical properties of plasma deposited polyoxazoline via XPS, FTIR, contact angle and ellipsometry unravels the complex functionality of the films. Partial retention of the oxazoline ring facilitates a covalent reaction with the carboxylic acid groups present on nanoparticles and biomolecules. Surface bound proteins effectively retain their bioactivity, therefore a vast range of potential applications unlocks for plasma deposited polyoxazoline coatings in the field of biosensing, medical arrays and diagnosis.

A Low Protein Binding Cationic Poly(2-oxazoline) as Non-Viral Vector

Developing safe and efficient non-viral gene delivery systems remains a major challenge. We present a new cationic poly(2-oxazoline) (CPOx) block copolymer for gene therapy that was synthesized by sequential polymerization of non-ionic 2-methyl-2-oxazoline and a new 2-oxazoline monomer, 2-(N-methyl, N-Boc-amino)-methyl-2-oxazoline, followed by deprotection of the pendant secondary amine groups. Upon mixing with plasmid DNA (pDNA), CPOx forms small (diameter ≈80 nm) and narrowly dispersed polyplexes (PDI <0.2), which are stable upon dilution in saline and against thermal challenge. These polyplexes exhibited low plasma protein binding and very low cytotoxicity in vitro compared to the polyplexes of pDNA and poly(ethylene glycol)-b-poly(L-lysine) (PEG-b-PLL). CPOx/pDNA polyplexes at N/P = 5 bound considerably less plasma protein compared to polyplexes of PEG-b-PLL at the same N/P ratio. This is a unique aspect of the developed polyplexes emphasizing their potential for systemic delivery in vivo. The transfection efficiency of the polyplexes in B16 murine melanoma cells was low after 4 h, but increased significantly for 10 h exposure time, indicative of slow internalization of polyplexes. Addition of Pluronic P85 boosted the transfection using CPOx/pDNA polyplexes considerably. The low protein binding of CPOx/pDNA polyplexes is particularly interesting for the future development of targeted gene delivery.

Poly(2-oxazoline) based micelles with high capacity for 3rd generation taxoids: preparation, in vitro and in vivo evaluation

The clinically and commercially successful taxanes, paclitaxel and docetaxel suffer from two major drawbacks, namely their very low aqueous solubility and the risk of developing resistance. Here, we present a method that overcomes both drawbacks in a very simple manner. We formulated 3rd generation taxoids, able to avoid common drug resistance mechanisms with doubly amphiphilic poly(2-oxazoline)s (POx), a safe and highly efficient polymer for the formulation of extremely hydrophobic drugs. We found excellent solubilization of different 3rd generation taxoids irrespective of the drug's chemical structures with essentially quantitative drug loading and final drug to polymer ratios around unity. The small, highly loaded micelles with a hydrodynamic diameter of less than 100nm are excellently suited for parenteral administration. Moreover, a selected formulation with the taxoid SB-T-1214 is about one to two orders of magnitude more active in vitro than paclitaxel in the multidrug resistant breast cancer cell line LCC6-MDR. In contrast, in wild-type LCC6, no difference was observed. Using a q4d×4 dosing regimen, we also found that POx/SB-T-1214 significantly inhibits the growth of LCC6-MDR orthotropic tumors, outperforming commercial paclitaxel drug Taxol and Cremophor EL formulated SB-T-1214.

Biocompatibility of poly(2-alkyl-2-oxazoline) brush surfaces for adherent lung cell lines

Development of synthetic surfaces that are highly reproducible and biocompatible for in vitro cell culture offers potential for development of improved models for studies of cellular physiology and pathology. They may also be useful in tissue engineering by removal of the need for biologically-derived components such as extracellular matrix proteins. We synthesised four types of 2-alkyl-2-oxazoline polymers ranging from the hydrophilic poly(2-methyl-2-oxazoline) to the hydrophobic poly(2-n-butyl-2-oxazoline). The polymers were terminated using amine-functionalised glass coverslips, enabling the synthetic procedure to be reproducible and scaleable. The polymer-coated glass slides were tested for biocompatibility using human epithelial (16HBE14o-) and fibroblastic (MRC5) cell lines. Differences in adhesion and motility of the two cell types was observed, with the poly(2-isopropyl-2-oxazoline) polymer equally supporting the growth of both cell types, whereas poly(2-n-butyl-2-oxazoline) showed selectivity for fibroblast growth. In summary, 2-alkyl-2-oxazoline polymers may be a useful tool for building in vitro model cell culture models with preferential adhesion of specific cell types.

Side-chain cysteine-functionalized poly(2-oxazoline)s for multiple peptide conjugation by native chemical ligation

We prepared statistical copolymers composed of 2-methyl-2-oxazoline (MeOx) in combination with 2-butenyl-2-oxazoline (BuOx) or 2-decenyl-2-oxazoline (DecOx) as a basis for polymer analogous introduction of 1,2-aminothiol moieties at the side chain. MeOx provides hydrophilicity as well as cyto- and hemocompatibility, whereas the alkene groups of BuOx and DecOx serve for functionalization with a thiofunctional thiazolidine by UV-mediated thiol-ene reaction. After deprotection the cysteine content in functionalized poly(2-oxazoline) (POx) is quantified by NMR and a modified trinitrobenzenesulfonic acid assay. The luminescent cell viability assay shows no negative influence of cysteine-functionalized POx (cys-POx) concerning cell viability and cell number. cys-POx was used for multiple chemically orthogonal couplings with thioester-terminated peptides through native chemical ligation (NCL), which was performed and confirmed by NMR and MALDI-ToF measurements.

Blending of reactive prepolymers to control the morphology and polarity of polyglycidol based microgels

The compartmentalization of microgels is a challenging task for synthetic polymer chemistry. Although the complexation with low molecular weight compounds or the use of microfluidic techniques offer attractive possibilities for other length scales, it is difficult to implement compartments in the mesoscale range of 10-100 nm. Herein we show how simple blending of reactive prepolymers is suitable to design new microgel morphologies with tailored compartments. We use poly(EEGE)-block-poly(AGE) as crosslinkable, pro-hydrophilic prepolymer in blends with varying amounts of crosslinkable, yet hydrophobic poly(THF-stat-AllylEHO) or inert and hydrophobic polystyrene, and crosslink the allyl functional prepolymer(s) in a thiol-ene click-type reaction after miniemulsification. Our strategy shows how arrested versus free nanophase separation can be used to control easily the morphology and polarity of microgel particles.

Design and evaluation of pH-sensitive liposomes constructed by poly(2-ethyl-2-oxazoline)-cholesterol hemisuccinate for doxorubicin delivery

In this study, a novel material, poly(2-ethyl-2-oxazoline)-cholesterol hemisuccinate (PEtOz-CHEMS), was synthesized to construct pH-sensitive liposomes. The structure of PEtOz-CHEMS was confirmed by thin-layer chromatography, Fourier transform infrared spectroscopy, and (1)H NMR. Anticancer fluorescent drug doxorubicin (DOX) was encapsulated into the liposomes. Compared with conventional liposomes (CL), CHEMS modified liposomes (CH-L) and PEGylated liposomes (PEG-L), the PEtOzylated liposomes (PEtOz-L) showed an acidic pH-induced increase in particle size. At pH 6.4, the heme release of PEtOz-L group was close to that of the positive control group, whereas that of CL, CH-L and PEG-L was close to that of the negative control group. In vitro drug release studies demonstrated that DOX was released from PEtOz-L in a pH-dependent manner, and the release of DOX from conventional DOX liposomes (CL-DOX), DOX loaded CH-L (CH-DOX-L) and PEGylated DOX liposomes (PEG-DOX-L) had no pronounced differences under each pH medium. In vitro cellular uptake assays showed that PEtOz-DOX-L indicated a significant fluorescence intensity at pH 6.4 compared with at pH 7.4. CL-DOX, CH-DOX-L and PEG-DOX-L did not achieve any obvious diversity at different pH conditions. Confocal laser scanning microscopy images showed that PEtOz-DOX-L can fuse with the endosomal membrane under acidic conditions of endosome, release DOX into the cytoplasm, then gather into the nucleus. Therefore, PEtOz can help liposomes achieve "endosomal escape". The in vitro cytotoxicity experiment results on A375 cells showed that PEtOz-DOX-L resulted in lower cell viability than CL-DOX, CH-DOX-L and PEG-DOX-L under low pH conditions. These results confirm that the pH-responsive PEtOz was a promising material for intracellular targeted delivery system and might be used for overcoming the "PEG dilemma".

Poly(l-lysine)-graft-folic acid-coupled poly(2-methyl-2-oxazoline) (PLL-g-PMOXA-c-FA): a bioactive copolymer for specific targeting to folate receptor-positive cancer cells

In this study, we present the preparation, characterization and application of a novel bioactive copolymer poly(l-lysine)-graft-folic acid-coupled poly(2-methyl-2-oxazoline) (PLL-g-PMOXA-c-FA), which has a specific interaction with folate receptor (FR)-positive cancer cells. Glass surface immobilized with PLL-g-PMOXA-c-FA was demonstrated to be adhesive to FR-positive cancer cells (HeLa, JEG-3) while nonadhesive to FR-negative ones (MCF-7, HepG2) in 3 h. The specific interaction between conjugated FA on the substrate and FRs on the cells could hardly be inhibited unless a high concentration (5 mM) of free FA was used due to the multivalent nature of it. The FA functionality ratio of the copolymer on the substrate had a significant influence on the adhesion of HeLa cells, and our experiments revealed that the affinity of the substrate to the cells declined dramatically with the decrease of functionality ratio. This was believed to be caused by the polydispersity of PMOXA tethers, as supported by GPC and ToF-SIMS data. As a proof of concept in the application of our material, we demonstrated successful recovery of HeLa cells from mixture with MCF-7 (1:100) on the copolymer-coated glass, and our results showed that both high sensitivity (95.6 ± 13.3%) and specificity (24.3 ± 8.6%) were achieved.

Supramolecular self-assembly of novel thermo-responsive double-hydrophilic and hydrophobic Y-shaped [MPEO-b-PEtOx-b-(PCL)2] terpolymers

Nonlinear amphiphilic block copolymer architectures with precisely controlled structures bring new challenges to biomedical materials research.

Solvent-free mechanochemical synthesis of a bicyclononyne tosylate: a fast route towards bioorthogonal clickable poly(2-oxazoline)s

The mechanochemical synthesis of a bicyclononyne tosylate (BCN-OTs) and its subsequent use for the CROP of 2-ethyl-2-oxazoline yielding bioorthogonal clickable poly(2-ethyl-2-oxazoline) is presented.

Antibiofouling polymer interfaces: poly(ethylene glycol) and other promising candidates

This review highlights antibiofouling polymer interfaces with emphasis on the latest developments using poly(ethylene glycol) and the design new polymeric structures.

Mild Brønsted acid initiated controlled polymerizations of 2-oxazoline towards one-pot synthesis of novel double-hydrophilic poly(2-ethyl-2-oxazoline)-block-poly(sarcosine)

Mild Brønsted acid initiator in polymerizations of 2-oxazoline was firstly reported as a workable protocol in the ROPs and BCPs.

Core cross-linked nanogels based on the self-assembly of double hydrophilic poly(2-oxazoline) block copolymers

The synthesis of poly(2-oxazoline)-based block copolymers consisting of a cationic and a hydrophilic segment is described.