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Polysarcosine (M-n = 3650-20 000 g mol(-1), D similar to 1.1) was synthesized from the air and moisture stable N-phenoxycarbonyl-N-methylglycine. Polymerization was achieved by in situ transformation of the urethane precursor into the corresponding N-methylglycine-N-carboxyanhydride, when in the presence of a non-nucleophilic tertiary amine base and a primary amine initiator.
Polysarcosine (Mn = 3650–20 000 g mol−1, Đ ∼ 1.1) was synthesized from the air and moisture stable N-phenoxycarbonyl-N-methylglycine. Polymerization was achieved by in situ transformation of the urethane precursor into the corresponding N-methylglycine-N-carboxyanhydride, when in the presence of a non-nucleophilic tertiary amine base and a primary amine initiator.
Polypeptides having secondary structures often undergo self-assembly which can extend over multiple length scales. Poly(γ-benzyl-L-glutamate) (PBLG), for example, folds into α-helices and forms physical organogels, whereas poly(L-glutamic acid) (PLGA at acidic pH) or poly(L-glutamate) (PLG at neutral/basic pH) do not form hydrogels. We explored the gelation of modified PBLG and investigated the deprotection of the carboxylic acid moieties in such gels to yield unique hydrogels. This was accomplished through photo-crosslinking gelation of poly(γ-benzyl-L-glutamate-co-allylglycine) statistical copolymers in toluene, tetrahydrofuran, and 1,4-dioxane. Unlike most polymer-based chemical gels, our gels were prepared from dilute solutions (<20 g L−1, i.e., <2% w/v) of low molar mass polymers. Despite such low concentrations and molar masses, our dioxane gels showed high mechanical stability and little shrinkage; remarkably, they also exhibited a porous fibrillar network. Deprotection of the carboxylic acid moieties in dioxane gels yielded pH responsive and highly absorbent PLGA/PLG-based hydrogels (swelling ratio of up to 87), while preserving the network structure, which is an unprecedented feature in the context of crosslinked PLGA gels. These outstanding properties are highly attractive for biomedical materials.
Due to their unique morphology-related properties, yolk@shell materials are promising materials for catalysis, drug delivery, energy conversion, and storage. Despite their proven potential, large-scale applications are however limited due to demanding synthesis protocols. Overcoming these limitations, a simple soft-templated approach for the one-pot synthesis of yolk@shell nanocomposites and in particular of multicore metal nanoparticle@metal oxide nanostructures (M-NP@MOx) is introduced. The approach here, as demonstrated for Au-NP@ITOTR (ITOTR standing for tin-rich ITO), relies on polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) inverse micelles as two compartment nanoreactor templates. While the hydrophilic P4VP core incorporates the hydrophilic metal precursor, the hydrophobic PS corona takes up the hydrophobic metal oxide precursor. As a result, interfacial reactions between the precursors can take place, leading to the formation of yolk@shell structures in solution. Once calcined these micelles yield Au-NP@ITOTR nanostructures, composed of multiple 6 nm sized Au NPs strongly anchored onto the inner surface of porous 35 nm sized ITOTR hollow spheres. Although of multicore nature, only limited sintering of the metal nanoparticles is observed at high temperatures (700 degrees C). In addition, the as-synthesized yolk@shell structures exhibit high and stable activity toward CO electrooxidation, thus demonstrating the applicability of our approach for the design of functional yolk@shell nanocatalysts.
As polypeptoids become increasingly popular, they present a more soluble and processable alternative to natural and synthetic polypeptides; the breadth of their potential functionality slowly comes into focus. This report analyzes the ability of an alkyne-functionalized polypeptoid, poly(N-propargyl glycine), to crosslink upon heating. The crosslinking process is analyzed by thermal analysis (differential scanning calorimetry and thermogravimetric analysis), Fourier-transform infrared, electron paramagnetic resonance, and solid-state NMR spectroscopy. While a precise mechanism cannot be confidently assigned, it is clear that the reaction proceeds by a radical mechanism that exclusively involves the alkyne functionality, which, upon crosslinking, yields alkene and aromatic products.
The protein corona, which forms on the nanoparticle's surface in most biological media, determines the nanoparticle's physicochemical characteristics. The formation of the protein corona has a significant impact on the biodistribution and clearance of nanoparticles in vivo. Therefore, the ability to influence the formation of the protein corona is essential to most biomedical applications, including drug delivery and imaging. In this study, we investigate the protein adsorption on nanoparticles with a hydrodynamic radius of 30 nm and a coating of thermoresponsive poly(2-isopropyl-2-oxazoline) in serum. Using multiangle dynamic light scattering (DLS) we demonstrate that heating of the nanoparticles above their phase separation temperature induces the formation of agglomerates, with a hydrodynamic radius of 1 mu m. In serum, noticeably stronger agglomeration occurs at lower temperatures compared to serum-free conditions. Cryogenic transmission electron microscopy (cryo-TEM) revealed a high packing density of agglomerates when serum was not present. In contrast, in the presence of serum, agglomerated nanoparticles were loosely packed, indicating that proteins are intercalated between them. Moreover, an increase in protein content is observed upon heating, confirming that protein adsorption is induced by the alteration of the surface during phase separation. After cooling and switching the surface back, most of the agglomerates were dissolved and the main fraction returned to the original size of approximately 30 nm as shown by asymmetrical flow-field flow fractionation (AF-FFF) and DLS. Furthermore, the amounts of adsorbed proteins are similar before and after heating the nanoparticles to above their phase-separation temperature. Overall, our results demonstrate that the thermoresponsivity of the polymer coating enables turning the corona formation on nanoparticles on and off in situ. As the local heating of body areas can be easily done in vivo, the thermoresponsive coating could potentially be used to induce the agglomeration of nanopartides and proteins and the accumulation of nanoparticles in a targeted body region.
Polypeptoids have been of great interest in the polymer science community since the early half of the last century; however, they had been basically forgotten materials until the last decades in which they have enjoyed an exciting revival. In this mini-review, we focus on the recent developments in polypeptoid chemistry, with particular focus on polymers synthesized by the ring-opening polymerization (ROP) of amino acid N-carboxyanhydrides (NCAs). Specifically, we will review traditional monomer synthesis (such as Leuchs, Katchalski, and Kricheldorf) and recent advances in polymerization methods to yield both linear, cyclic, and functional polymers, solution and bulk thermal properties, and preliminary results on the use of polypeptoids as biomaterials (i.e immunogenicity, biodistribution, degradability, and drug delivery).
Self-assembly of macromolecules is fundamental to life itself, and historically, these systems have been primitively mimicked by the development of amphiphilic systems, driven by the hydrophobic effect. Herein, we demonstrate that self-assembly of purely hydrophilic systems can be readily achieved with similar ease and success. We have synthesized double hydrophilic block copolymers from polysaccharides and poly(ethylene oxide) or poly(sarcosine) to yield high molar mass diblock copolymers through oxime chemistry. These hydrophilic materials can easily assemble into nanosized (<500nm) and microsized (>5m) polymeric vesicles depending on concentration and diblock composition. Because of the solely hydrophilic nature of these materials, we expect them to be extraordinarily water permeable systems that would be well suited for use as cellular mimics.
This article presents a simple and facile method to fabricate thermoresponsive polymer-grafted silica particles by direct surface-initiated photopolymerization of N-isopropylacrylamide (NIPAM). This method is based on silica particles bearing thiol functionalities, which are transformed into thiyl radicals by irradiation with UV light to initiate the polymerization of NIPAM in aqueous media at room temperature. The photopolymerization of NIPAM could be applied to smaller thiol-functionalized particles (approximate to 48 nm) as well as to larger particles (approximate to 692 nm). Hollow poly(NIPAM) capsules could be formed after etching away the silica cores from the composite particles. It is possible to produce tailor-made composite particles or capsules for particular applications by extending this approach to other vinyl monomers. (c) 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015, 53, 1260-1267
Formation of DNA-Copolymer Fibrils Through an Amyloid-Like Nucleation Polymerization Mechanism
(2015)
Conjugation of a hydrophobic poly(2-oxazoline) bearing tertiary amide groups along its backbone with a short single stranded nucleotide sequence results in an amphiphilic comb/graft copolymer, which organizes in fibrils upon direct dissolution in water. Supported by circular dichroism, atomic force microscopy, transmission electron microscopy, and scattering data, fibrils are formed through inter- and intramolecular hydrogen bonding between hydrogen accepting amide groups along the polymer backbone and hydrogen donating nucleic acid grafts leading to the formation of hollow tubes.
Polypeptides having secondary structures often undergo self-assembly which can extend over multiple length scales. Poly(gamma-benzyl-L-glutamate) (PBLG), for example, folds into a-helices and forms physical organogels, whereas poly(L-glutamic acid) (PLGA at acidic pH) or poly(L-glutamate) (PLG at neutral/basic pH) do not form hydrogels. We explored the gelation of modified PBLG and investigated the deprotection of the carboxylic acid moieties in such gels to yield unique hydrogels. This was accomplished through photo-crosslinking gelation of poly(gamma-benzyl-L-glutamate-co-allylglycine) statistical copolymers in toluene, tetrahydrofuran, and 1,4-dioxane. Unlike most polymer-based chemical gels, our gels were prepared from dilute solutions (<20 g L-1, i.e., <2% w/v) of low molar mass polymers. Despite such low concentrations and molar masses, our dioxane gels showed high mechanical stability and little shrinkage; remarkably, they also exhibited a porous fibrillar network. Deprotection of the carboxylic acid moieties in dioxane gels yielded pH responsive and highly absorbent PLGA/PLG-based hydrogels (swelling ratio of up to 87), while preserving the network structure, which is an unprecedented feature in the context of crosslinked PLGA gels. These outstanding properties are highly attractive for biomedical materials.
Bio-inspired V2O5-polymer hybrid films were prepared following a one-step self-organization procedure based on liquid crystal formation of organic and inorganic components. These materials were previously reported to exhibit advantageous mechanical properties, comparable to biomaterials, such as human bone and dentin. Here, we show that these hybrid films prepared via a fast and simple synthesis procedure have an additional function as an electrochromic material, exhibiting a long-term cycle stability under alternating potentials. The structures were found to remain intact without visible changes after more than hundred switching cycles and storing the devices for several weeks. Consequently, this multifunctional V2O5-polymer hybrid system shows great promise for various technical applications.
Poly(N-propargyl glycine) (PNPG) can be readily prepared by ring-opening polymerization of N-propargyl glycine N-carboxyanhydride (NCA) and modified using various addition reactions such as copper catalyzed [3+2] cycloaddition of azide, radical (photo-)addition of thiol, nucleophilic addition of ethylene oxide, and thermal induced cross-linking. It is demonstrated that PNPG can serve as a modular platform to produce a bibliography of novel functional polypeptoid or pseudopeptide materials, including polypeptoid ionic liquids and graft copolymers.
Langmuir polymers films (LPFs) frequently form non-equilibrium states which are manifested in a decay of the surface pressure with time when the system is allowed to relax. Monitoring and manipulating the temporal evolution of these relaxations experimentally helps to shed light on the associated molecular reorganization processes. We present a systematic study based on different compression protocols and show how these reorganization processes impact the morphology of LPFs of poly(gamma-benzyl-L-glutamate) (PBLG); visualized by means of atomic force microscopy. Upon continuous compression, a fibrillar morphology was formed with a surface decorated by squeezed-out islands. By contrast, stepwise compression promoted the formation of a fibrillar network with a bimodal distribution of fibril diameters, caused by merging of fibrils. Finally, isobaric compression induced in-plane compaction of the monolayer. We correlate these morphological observations with the kinetics of the corresponding relaxations, described best by a sum of two exponential functions with different time scales representing two molecular processes. We discuss the observed kinetics and the resulting morphologies in the context of nucleation and growth, characteristic for first-order phase transitions. Our results demonstrate that the preparation conditions of LPFs have tremendous impact on ordering of the molecules and hence various macroscopic properties of such films.
We report herein on the polymer-crystallization-assisted thiol-ene photosynthesis of an amphiphilic comb/graft DNA copolymer, or molecular brush, composed of a hydrophobic poly(2-oxazoline) backbone and hydrophilic short single-stranded nucleic acid grafts. Coupling efficiencies are above 60% and thus higher as compared with the straight solid-phase-supported synthesis of amphiphilic DNA block copolymers. The DNA molecular brushes self-assemble into sub-micron-sized spherical structures in water as evidenced by light scattering as well as atomic force and electron microscopy imaging. The nucleotide sequences remain functional, as assessed by UV and fluorescence spectroscopy subsequent to isoindol synthesis at the surface of the structures. The determination of a vesicular morphology is supported by encapsulation and subsequent spectroscopy monitoring of the release of a water-soluble dye and spectroscopic quantification of the hybridization efficiency (30% in average) of the functional nucleic acid strands engaged in structure formation: about one-half of the nucleotide sequences are available for hybridization, whereas the other half are hindered within the self-assembled structure. Because speciation between complementary and non complementary sequences in the medium could be ascertained by confocal laser scanning microscopy, the stable self-assembled molecular brushes demonstrate the potential for sensing applications.
High fractions of gold nanorods were locally aligned by means of a polymeric liquid crystalline phase. The gold nanorods constituting >80 wt % of the thin organic-inorganic composite films form a network with side-by-side and end-to-end combinations. Organization into these network structures was induced by shearing gold nanorod-LC polymer dispersions via spin-coating. The LC polymer is a polyoxazoline functionalized with pendent cholesteryl and carboxyl side groups enabling the polymer to bind to the CTAB stabilizer layer of the gold nanorods via electrostatic interactions, thus forming the glue between organic and inorganic components, and to form a chiral nematic lyotropic phase. The self-assembled locally oriented gold nanorod structuring enables control over collective optical properties due to plasmon resonance coupling, reminiscent of enhanced optical properties of natural biomaterials.
1,4-Di(homo)allyl-2,5-diketopiperazines are synthesized and polymerized via ADMET using the Hoveyda-Grubbs 2nd generation catalyst. The but-3-enylated diketopiperazine can be converted into unsaturated tertiary polyamide with molar mass of <3000 g mol(-1), whereas the allylated diketopiperazine cannot. Double-bond isomerization occurs regardless of whether or not benzoquinone is present. A polyesteramide with a higher molar mass of ca. 4800 g mol(-1) is obtained by the alternating copolymerization (ALTMET) of 1,4-di(but-3-enyl)-2,5-di ketopiperazine and ethylene glycol diacrylate. A post-polymerization modification of the poly(ester)amides via radical thiol-ene chemistry, however, fails.
Thiol-X chemistry has proven to be a valuable toolbox for modification of peptides, proteins, monomers, and polymers. Recently, this has become especially true for the modification of polypeptides (monomers or polymers), which has resulted in a plethora of novel polymers and materials. With this in mind, this highlight focuses on the recent literature concerning the modification of polypeptides by the use of thiol-X chemistry, in particular to synthetic polypeptides either at the monomer or polymer stage modified by thiol-ene, -Michael addition, and -yne chemistries. (C) 2014 Published by Elsevier Ltd.
The surface modification of mesoporous silica monoliths through thiol-ene chemistry is reported. First, mesoporous silica monoliths with vinyl, allyl, and thiol groups were synthesized through a sol-gel hydrolysis-poly-condensation reaction from tetramethyl orthosilicate (TMOS) and vinyltriethoxysilane, allyltriethoxysilane, and (3-mercaptopropyl) trimethoxysilane, respectively. By variation of the molar ratio of the comonomers TMOS and functional silane, mesoporous silica objects containing different amounts of vinyl, allyl, and thiol groups were obtained. These intermediates can subsequently be derivatized through radical photoaddition reactions either with a thiol or an olefin, depending on the initial pore wall functionality, to yield silica monoliths with different pore-wall chemistries. Nitrogen sorption, small-angle X-ray scattering, solid-state NMR spectroscopy, elemental analysis, thermogravimetric analysis, and redox titration demonstrate that the synthetic pathway influences the morphology and pore characteristics of the resulting monoliths and also plays a significant role in the efficiency of functionalization. Moreover, the different reactivity of the vinyl and allyl groups on the pore wall affects the addition reaction, and hence, the degree of the pore-wall functionalization. This report demonstrates that thiol-ene photoaddition reactions are a versatile platform for the generation of a large variety of organically modified silica monoliths with different pore surfaces.
The self-assembly of double-hydrophilic poly(ethylene oxide)-poly(2-methyl-2-oxazoline) diblock copolymers in water has been studied. Isothermal titration calorimetry, small-angle X-ray scattering, and analytical ultracentrifugation suggest that only single polymer chains are present in solution. In contrast, light scattering and transmission electron microscopy detect aggregates with radii of ca. 100 nm. Pulsed field gradient NMR spectroscopy confirms the presence of aggregates, although only 2% of the polymer chains undergo aggregation. Water uptake experiments indicate differences in the hydrophilicity of the two blocks, which is believed to be the origin of the unexpected aggregation behavior (in accordance with an earlier study by Ke et al. [Macromolecules 2009, 42, 5339-5344]). The data therefore suggest that even in double-hydrophilic block copolymers, differences in hydrophilicity are sufficient to drive polymer aggregation, a phenomenon that has largely been overlooked or ignored so far.
Commercially available 1,2-PB was transformed into a well-defined reactive intermediate by quantitative bromination. The brominated polymer was used as a polyfunctional macroinitiator for the cationic ring-opening polymerization of 2-ethyl-2-oxazoline to yield a water-soluble brush polymer. Nucleophilic substitution of bromide by 1-methyl imidazole resulted in the formation of polyelectrolyte copolymers consisting of mixed units of imidazolium, bromo, and double bond. These copolymers, which were soluble in water without forming aggregates, were used as stabilizers in the heterophase polymerization of styrene and were also studied for their ionic conducting properties.
Polymer brushes on thiol-modified gold surfaces were synthesized by using terminal thiol groups for the surface initiated free radical polymerization of methacrylic acid and dimethylaminotheyl methacrylate, respectively. Atomic force microscopy shows that the resulting poly(methacrylic acid (PMAA) and poly(dimethylaminothyl methacrylate) (PDM- AEMA) brushes are homogeneous. Contact angle measurements show that the brushes are pH responsive and can reversibly be protonated and deprotonated. Mineralization of the brushes with calcium phosphate at different pH yields homogeneously mineralized surfaces, and preosteoblastic cells proliferate-on be number of living cells on the mineralized hybrid surface is ca. 3 times (P corresponding nonmineralized brushes.
The kinetics of the crystallization of thermoresponsive poly(2-isopropyl-2-oxazoline) in water and the time- dependent evolution of the morphology were examined using wide-angle X-ray scattering and conventional and cryogenic scanning electron microscopy. Results indicate that a temperature-induced phase separation produces a bicontinuous polymer network-like structure, which with the onset of crystallization collapses into individual particles (1-2 mu m in diameter) composed of a porous fiber mesh. Nanofibers then preferentially form at the particle surface, thus wrapping the microspheres like a ball of wool. The particle morphology is severely affected by changes in temperature and less by the initial polymer concentration.
Intermolecular hydrogen bonding, not hydrophobic interaction, is the driving force for the spontaneous self- assembly of glycosylated polyoxazoline chains into nanotubes in dilute aqueous solution. The structural information is encoded in the relatively simple molecular structure of chains consisting of a tertiary polyamide backbone (hydrogen- accepting) and glucose side chains (hydrogen-donating). The formation of the nanotubes should occur through bending and closing of a 2D hydrogen-bonded layer of interdigitated polymer chains.
Calcium phosphate mineralization from aqueous solution in the presence of organic growth modifiers has been intensely studied in the recent past. This is mostly due to potential applications of the resulting composites in the biomaterials field. Polymers in particular are efficient growth modifiers. As a result, there has been a large amount of work on polymeric growth modifiers. Interestingly, however, relatively little work has been done on polycationic additives. The current paper shows that poly(ethylene oxide)b-poly(L-lysine) block copolymers lead to an interesting morphology of calcium phosphate precipitated at room temperature and subjected to a mild heat treatment at 85 degrees C. Electron microscopy, synchrotron X-ray diffraction, and porosity analysis show that a (somewhat) porous material with channel-like features forms. Closer inspection using transmission electron microscopy shows that the channels are probably not real channels. Much rather the morphology is the result of the aggregation of ca. 100-nm-sized rodlike primary particles, which changes upon drying to exhibit the observed channel-like features. Comparison experiments conducted in the absence of polymer and with poly(ethylene oxide)-b-poly(L-glutamate) show that these features only form in the presence of the polycationic poly(L-lysine) block, suggesting a distinct interaction of the polycation with either the crystal or the phosphate ions prior to mineralization.
In this work, the basic principles of self-organization of diblock copolymers having the in¬herent property of selective or specific non-covalent binding were examined. By the introduction of electrostatic, dipole–dipole, or hydrogen bonding interactions, it was hoped to add complexity to the self-assembled mesostructures and to extend the level of ordering from the nanometer to a larger length scale. This work may be seen in the framework of biomimetics, as it combines features of synthetic polymer and colloid chemistry with basic concepts of structure formation applying in supramolecular and biological systems. The copolymer systems under study were (i) block ionomers, (ii) block copolymers with acetoacetoxy chelating units, and (iii) polypeptide block copolymers.