Utility of Triethyloxonium Tetrafluoroborate for Chloride Removal during Sarcosine N-Carboxyanhydride Synthesis: Improving NCA Purity.

The clinical translation of polysarcosine (pSar) as polyethylene glycol (PEG) replacement in the development of novel nanomedicines creates a broad demand of polymeric material in high-quality making high-purity sarcosine N-carboxyanhydride (Sar-NCA) as monomer for its production inevitable. Within this report, we present the use of triethyloxonium tetrafluoroborate in Sar-NCA synthesis with focus on amino acid and chloride impurities to avoid the sublimation of Sar-NCAs. With a view towards upscaling into kilogram or ton scale, a new methodology of monomer purification is introduced by utilizing the Meerwein's Salt triethyloxonium tetrafluoroborate to remove chloride impurities by covalent binding and converting chloride ions into volatile products within a single step. The novel straightforward technique enables access to monomers with significantly reduced chloride content (<100 ppm) compared to Sar-NCA derived by synthesis or sublimation. The derived monomers enable the controlled-living polymerization in DMF and provide access to pSar polymers with Poisson-like molecular weight distribution within a high range of chain lengths (Xn 25-200). In conclusion, the reported method can be easily applied to Sar-NCA synthesis or purification of commercially available pSar-NCAs and eases access to well-defined hetero-telechelic pSar polymers.

Antimicrobial Nanostructured Assemblies with Extremely Low Toxicity and Potent Activity to Eradicate Staphylococcus Aureus Biofilms.

Self-assembled cationic polymeric nanostructures have been receiving increasing attention for efficient antibacterial agents. In this work, a new type of antibacterial agents is developed by preparing pH-dependent nanostructured assemblies from cationic copolypeptoid poly(N-allylglycine)-b-poly(N-octylglycine) (PNAG-b-PNOG) modified with cysteamine hydrochloride ((PNAG-g-NH2 )-b-PNOG) driven by crystallization and hydrophobicity of the PNOG blocks. Due to the presence of confined domains arising from crystalline PNOG, persistent spheres and fiber-like assemblies are obtained from the same polymer upon a heating-cooling cycle. This allows for direct comparison of antimicrobial efficiency of nanostructured assemblies with various morphologies that are otherwise similar. Both nanostructured assemblies exhibit extremely low toxicity to human red blood cells, irrespective of the presence of the hydrophobic block. Enhanced antimicrobial performance of the fiber-like micelles compared to the spheres, which result in high selectivity of the fibers, is shown. Notably, the fiber-like micelles show great efficacy in inhibition of the Staphylococcus aureus (S. aureus) biofilm formations and eradication of the mature biofilms, superior to vancomycin. The micelles also show potent in vivo antimicrobial efficacy in a S. aureus infection mouse skin model. With a systematic study, it is demonstrated that both micelles kill the bacteria through a membrane disruption mechanism. These results imply great potential of polypeptoid assemblies as promising excellent candidates for antibacterial treatment and open up new possibilities for the preparation of a new generation of nanostructured antimicrobials.

Research Progress in Polypeptoids Prepared by Controlled Ring-Opening Polymerizations.

Polypeptoids, structural mimics of polypeptides, have attracted considerable attention due to their biocompatibility, proteolytic stability, thermal processability, good solubility, synthetic accessibility, and structural diversity. Polypeptoids have emerged as an interesting material in both polymer science and biological field. This review primarily discusses the research progress of polypeptoids prepared by controlled ring-opening polymerizations in the past decade, including synthetic strategies of monomers, polymerizations by different initiators, postfunctionalization, fundamental properties, crystallization-driven self-assembly, and potential biological applications.

Antibacterial Copolypeptoids with Potent Activity against Drug Resistant Bacteria and Biofilms, Excellent Stability, and Recycling Property.

The preparation of a type of innovative cationic copolypeptoid antimicrobials containing various hydrophobic moieties that resemble both structure and membrane-lytic antibacterial mechanism of natural antimicrobial peptides (AMPs) is reported. By finely tuning the hydrophilic/hydrophobic balance, the polypeptoids exhibit a wide spectrum of antibacterial activity against both Gram-positive bacteria and Gram-negative bacteria with the lowest minimum inhibitory concentration (MIC) at only 2 µg mL-1 , whereas they also show low haemolytic properties. In particular, high selectivity (>128) is achieved from the polymers with butyl moieties. Moreover, the polypeptoids can readily inhibit the formation of biofilms and effectively eradicate the bacteria embedded in the mature biofilms, which is superior to many natural AMPs and vancomycin. Unlike conventional antibiotics, the polypeptoids possess potent activity against drug-resistant bacteria without visible resistance development after repeated usage. Notably, the polypeptoid antimicrobials not only have inherently fast bactericidal properties and excellent stability against incubation with human plasma, but also show excellent in vivo antibacterial effect. The prepared antimicrobials, coated onto magnetic nanospheres show recycling properties and enhanced antibacterial activity as combined with near-infrared (NIR)-induced photothermal antibacterial therapy.

A Guideline for the Synthesis of Amino-Acid-Functionalized Monomers and Their Polymerizations.

Amino acids have emerged as a sustainable source for the design of functional polymers. Besides their wide availability, especially their high degree of biocompatibility makes them appealing for a broad range of applications in the biomedical research field. In addition to these favorable characteristics, the versatility of reactive functional groups in amino acids (i.e., carboxylic acids, amines, thiols, and hydroxyl groups) makes them suitable starting materials for various polymerization approaches, which include step- and chain-growth reactions. This review aims to provide an overview of strategies to incorporate amino acids into polymers. To this end, it focuses on the preparation of polymerizable monomers from amino acids, which yield main chain or side chain-functionalized polymers. Furthermore, postpolymerization modification approaches for polymer side chain functionalization are discussed. Amino acids are presented as a versatile platform for the development of polymers with tailored properties.

Ugi Reaction of Amino Acids: From Facile Synthesis of Polypeptoids to Sequence-Defined Macromolecules.

Polypeptoids have been prepared and researched for more than 20 years. However, the efficient generation of polypeptoids and sequence-defined polypeptoids faces many challenges and difficulties. The Ugi reaction of amino acids has recently been introduced into polypeptoid chemistry as a new and powerful method to furnish polypeptoids. In the following mini review, the recent progress on the application of the Ugi reaction of amino acids in polypeptoid science, including polypeptoid from sustainable furfural, sequence-defined polypeptoids, and more is summarized. Moreover, the future development of the Ugi reaction of amino acids in polypeptoid science is discussed.

An Inspection into Multifarious Ways to Synthesize Poly(Amino Acid)s.

Poly(α-amino acid)s (PAAs) attract growing attention due to their essential role in the application as biomaterials. To synthesize PAAs with desired structures and properties, scientists have developed various synthetic techniques with respective advantages. Here, different approaches to preparing PAAs are inspected. Basic features and recent progresses of these methods are summarized, including polymerizations of amino acid N-carboxyanhydrides (NCAs), amino acid N-thiocarboxyanhydrides (NTAs), and N-phenoxycarbonyl amino acids (NPCs), as well as other synthetic routes. NCA is the most classical monomer to prepare PAAs with high molecular weights (MWs). NTA polymerizations are promising alternative pathways to produce PAAs, which can tolerate nucleophiles including alcohols, mercaptans, carboxyl acids, and water. By various techniques including choosing appropriate solvents or using organic acids as promoters, NTAs polymerize to produce polypeptoids and polypeptides with narrow dispersities and designed MWs up to 55.0 and 57.0 kg mol-1 , respectively. NPC polymerizations are phosgene-free ways to synthesize polypeptides and polypeptoids. For the future prospects, detail investigations into polymerization mechanisms of NTA and NPC are expected. The synthesis of PAAs with designed topologies and assembly structures is another intriguing topic. The advantages and unsettled problems in various synthetic ways are discussed for readers to choose appropriate approaches for PAAs.

Polypeptoids synthesis based on Ugi reaction: Advances and perspectives.

Polypeptoids are peptidomimetic polymers invented in the early 1990s. Although polypeptoid chemistry is developing rapidly, the simple synthesis of polypeptoids and sequence-controlled polypeptoids still remains a challenge. Fortunately, we have seen a drastic rising trend in the area of Ugi reaction for polypeptoid chemistry. In the following article, recent examples of the Ugi reaction for polypeptoids synthesis will be presented, as will their suitability for sequence-defined peptide-peptoid hybrids. The advantages and limitations of the Ugi reaction will be discussed, which is important for the simple and general synthesis of polypeptoids.

Linking two worlds in polymer chemistry: The influence of block uniformity and dispersity in amphiphilic block copolypeptoids on their self-assembly.

The self-assembly of block copolymers has captured the interest of scientists for many decades because it can induce ordered structures and help to imitate complex structures found in nature. In contrast to proteins, nature's most functional hierarchical structures, conventional polymers are disperse in their length distribution. Here, we synthesized hydrophilic and hydrophobic polypeptoids via solid-phase synthesis (uniform) and ring-opening polymerization (disperse). Differential scanning calorimetry measurements showed that the uniform hydrophobic peptoids converge to a maximum of the melting temperature at a much lower chain length than their disperse analogs, showing that not only the chain length but also the dispersity has a considerable impact on the thermal properties of those homopolymers. These homopolymers were then coupled to yield amphiphilic block copolypeptoids. SAXS and AFM measurements confirm that the dispersity plays a major role in microphase separation of these macromolecules, and it appears that uniform hydrophobic blocks form more ordered structures.

Synthesis of Polypeptoid-Polycaprolactone-Polytetrahydrofuran Heterograft Molecular Polymer Brushes via a Combination of Janus Polymerization and ROMP.

Janus polymerization is a novel and efficient way to synthesize diblock and multiblock copolymers in one step by using Lu(OTf)3 and propylene epoxide as a catalytic system. By modifying the epoxide initiator, which is located at the block junction with various functional groups, the possibility for future topological design is provided. Herein, 2-bicyclo[2.2.1]hept-5-en-2-yl oxirane (NB-EO) is used as an alternative for propylene epoxide to synthesize a poly(THF-co-CL)-b-PCL diblock copolymer featuring a norbornene group at this position. This also results in multiblock [poly(THF-co-CL)-b-PCL]m copolymers carrying multiple norbornene moieties through Janus polymerization. Subsequent ring-opening metathesis copolymerization (ROMP) of the resulting poly(THF-co-CL)-b-PCL macromonomers with norbornenyl-terminated polysarcosine (PSar-NB) allows the facile preparation of heterograft molecular polymer brushes (MPBs). The MPBs feature three heterografts of PCL, P(CL-co-THF) and PSar, potentially equipping these structures with biocompatibility, biodegradability, semi-crystallinity, and amphiphilicity. A phase separation is observed after annealing in both TEM and AFM analysis. Due to their amphiphilic nature, the MPBs also undergo self-assembly into micelles in aqueous solution. Such materials combining polypeptoids, polyesters, and polyethers segments are expected to attract wide attention in drug delivery applications.

Electrospinning of Crystallizable Polypeptoid Fibers.

A unique fabrication process of low molar mass, crystalline polypeptoid fibers is described. Thermoresponsive fiber mats are prepared by electrospinning a homogeneous blend of semicrystalline poly(N-(n-propyl) glycine) (PPGly; 4.1 kDa) with high molar mass poly(ethylene oxide) (PEO). Annealing of these fibers at ≈100 °C selectively removes the PEO and produces stable crystalline fiber mats of pure PPGly, which are insoluble in aqueous solution but can be redissolved in methanol or ethanol. The formation of water-stable polypeptoid fiber mats is an important step toward their utilization in biomedical applications such as tissue engineering or wound dressing.

Polypept(o)ides: Hybrid Systems Based on Polypeptides and Polypeptoids.

Polypept(o)ides combine the multifunctionality and intrinsic stimuli-responsiveness of synthetic polypeptides with the "stealth"-like properties of the polypeptoid polysarcosine (poly(N-methyl glycine)). This class of block copolymers can be synthesized by sequential ring opening polymerization of α-amino acid N-carboxy-anhydrides (NCAs) and correspondingly of the N-substituted glycine N-carboxyanhydride (NNCA). The resulting block copolymers are characterized by Poisson-like molecular weight distributions, full end group integrity, and dispersities below 1.2. While polysarcosine may be able to tackle the currently arising issues regarding the gold standard PEG, including storage diseases in vivo and immune responses, the polypeptidic block provides the functionalities for a specific task. Additionally, polypeptides are able to form secondary structure motives, e.g., α-helix or ß-sheets, which can be used to direct self-assembly in solution. In this feature article, we review the relatively new field of polypept(o)ides with respect to synthesis, characterization, and first data on the application of block copolypept(o)ides in nanomedicine. The summarized data already indicates the great potential of polypept(o)ides.

One-pot glovebox-free synthesis, characterization, and self-assembly of novel amphiphilic poly(sarcosine-b-caprolactone) diblock copolymers.

Novel amphiphilic polypeptoid-polyester diblock copolymers based on poly(sarcosine) (PSar) and poly(ε-caprolactone) (PCL) are synthesized by a one-pot glovebox-free approach. In this method, sarcosine N-carboxy anhydride (Sar-NCA) is firstly polymerized in the presence of benzylamine under N(2) flow, then the resulting poly(sarcosine) is used in situ as the macro-initiator for the ring-opening polymerization (ROP) of ε-caprolactone using tin(II) octanoate as a catalyst. The degree of poly-merization of each block is controlled by various feed ratios of monomer/initiator. The diblock copolymers with controlled molecular weight and narrow molecular weight distributions (D(M) < 1.2) are characterized by (1)H NMR, (13)C NMR, and size-exclusion chromatography. The self-assembly behavior of PSar-b-PCL in water is investigated by dynamic light scattering (DLS) and transmission electron microscopy. DLS results reveal that the diblock copolymers associate into nanoparticles with average hydrodynamic diameters (D(H)) around 100 nm in water, which may be used as drug delivery carriers.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications.

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

Recent Experimental Advances in Characterizing the Self-Assembly and Phase Behavior of Polypeptoids.

Polypeptoids are a family of synthetic peptidomimetic polymers featuring N-substituted polyglycine backbones with large chemical and structural diversity. Their synthetic accessibility, tunable property/functionality, and biological relevance make polypeptoids a promising platform for molecular biomimicry and various biotechnological applications. To gain insight into the relationship between the chemical structure, self-assembly behavior, and physicochemical properties of polypeptoids, many efforts have been made using thermal analysis, microscopy, scattering, and spectroscopic techniques. In this review, we summarize recent experimental investigations that have focused on the hierarchical self-assembly and phase behavior of polypeptoids in bulk, thin film, and solution states, highlighting the use of advanced characterization tools such as in situ microscopy and scattering techniques. These methods enable researchers to unravel multiscale structural features and assembly processes of polypeptoids over a wide range of length and time scales, thereby providing new insights into the structure-property relationship of these protein-mimetic materials.

Fe3+@PDOPA­b­PSar Nanoparticles for Magnetic Resonance Imaging and Cancer Chemotherapy.

Purpose: Chemotherapy treatments for cancer are always accompanied by a low concentration of drug delivered in the tumor area and severe side effects including systemic toxicity. Improving the concentration, biocompatibility, and biodegradability of regional chemotherapy drugs is a pressing challenge in the field of materials. Methods: N-Phenyloxycarbonyl-amino acids (NPCs) which exhibit significant tolerance to nucleophiles, such as water and hydroxyl-containing compounds, are promising monomers for the synthesis of polypeptides and polypeptoids. Cell line and mouse models were used to comprehensively explore how to enhance the tumor MRI signal and evaluate the therapeutic effect of Fe@POS-DOX nanoparticles. Results: In this study, poly(3,4-dihydroxy-L-phenylalanine)-b-polysarcosine (PDOPA-b-PSar, simplified as POS) was synthesized by the block copolymerization of DOPA-NPC with Sar-NPC. Fe@POS-DOX nanoparticles were prepared in order to utilize the strong chelation of catechol ligands to iron (III) cations and the hydrophobic interaction between DOX and DOPA block to deliver chemotherapeutics to tumor tissue. The Fe@POS-DOX nanoparticles exhibit high longitudinal relaxivity (r 1 = 7.06 mM-1·s-1) and act as T 1-weighted magnetic resonance (MR) imaging contrast agents. Further, the main focus was improving tumor site-specific bioavailability and achieving therapeutic effects through the biocompatibility and biodegradability of Fe@POS-DOX NPs. The Fe@POS-DOX treatment exhibited excellent antitumor effects. Conclusion: Upon intravenous injection, Fe@POS-DOX delivers DOX specifically to the tumor tissues, as revealed by MR, and leads to the inhibition of tumor growth without overt toxicity to normal tissues, thus displaying considerable potential for use in clinical applications.

A mini-review on bio-inspired polymer self-assembly: single-component and interactive polymer systems.

Biology demonstrates meticulous ways to control biomaterials self-assemble into ordered and disordered structures to carry out necessary bioprocesses. Empowering the synthetic polymers to self-assemble like biomaterials is a hallmark of polymer physics studies. Unlike protein engineering, polymer science demystifies self-assembly by purposely embedding particular functional groups into the backbone of the polymer while isolating others. The polymer field has now entered an era of advancing materials design by mimicking nature to a very large extend. For example, we can make sequence-specific polymers to study highly ordered mesostructures similar to studying proteins, and use charged polymers to study liquid-liquid phase separation as in membraneless organelles. This mini-review summarizes recent advances in studying self-assembly using bio-inspired strategies on single-component and multi-component systems. Sequence-defined techniques are used to make on-demand hybrid materials to isolate the effects of chirality and chemistry in synthetic block copolymer self-assembly. In the meantime, sequence patterning leads to more hierarchical assemblies comprised of only hydrophobic and hydrophilic comonomers. The second half of the review discusses complex coacervates formed as a result of the associative charge interactions of oppositely charged polyelectrolytes. The tunable phase behavior and viscoelasticity are unique in studying liquid macrophase separation because the slow polymer relaxation comes primarily from charge interactions. Studies of bio-inspired polymer self-assembly significantly impact how we optimize user-defined materials on a molecular level.

Effects of Amphiphilic Polypeptoid Side Chains on Polymer Surface Chemistry and Hydrophilicity.

Polymers are commonly used in applications that require long-term exposure to water and aqueous mixtures, serving as water purification membranes, marine antifouling coatings, and medical implants, among many other applications. Because polymer surfaces restructure in response to the surrounding environment, in situ characterization is crucial for providing an accurate understanding of the surface chemistry under conditions of use. To investigate the effects of surface-active side chains on polymer surface chemistry and resultant interactions with interfacial water (i.e., water sorption), we present synchrotron ambient pressure X-ray photoelectron spectroscopy (APXPS) studies performed on poly(ethylene oxide) (PEO)- and poly(dimethylsiloxane) (PDMS)-based polymer surfaces modified with amphiphilic polypeptoid side chains, previously demonstrated to be efficacious in marine fouling prevention and removal. The polymer backbone and environmental conditions were found to affect polypeptoid surface presentation: due to the surface segregation of its fluorinated polypeptoid monomers under vacuum, the PEO-peptoid copolymer showed significant polypeptoid content in both vacuum and hydrated conditions, while the modified PDMS-based copolymer showed increased polypeptoid content only in hydrated conditions due to the hydrophilicity of the ether monomers and polypeptoid backbone. Polypeptoids were found to bind approximately 2.8 water molecules per monomer unit in both copolymers, and the PEO-peptoid surface showed substantial water sorption that suggests a surface with a more diffuse water/polymer interface. This work implies that side chains are ideal for tuning water affinity without altering the base polymer composition, provided that surface-driving groups are present to ensure activity at the interface. These types of systematic modifications will generate novel polymers that maximize bound interfacial water and can deliver surface-active groups to the surface to improve the effectiveness of polymer materials.

High Antibacterial Activity and Selectivity of the Versatile Polysulfoniums that Combat Drug Resistance.

Sulfonium-ion-containing polymers exhibit significant potential benefits for various applications. An efficient strategy to synthesize a type of antibacterial sulfonium-ion-bearing polypeptoids via a combination of ring-opening polymerization and a post-polymerization functionalization with various functional epoxides is presented. A systematic investigation is further performed in order to explore the influence of the overall hydrophobic/hydrophilic balance on the antimicrobial activity and selectivity of the prepared polysulfoniums. Notably, those chlorepoxypropane-modified polysulfoniums with an optimized amphiphilic balance show higher selectivity toward both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, than to red blood cells. The polymers also show great efficiency in inhibiting S. aureus biofilm formations, as well as in further eradicating the mature biofilms. Remarkably, negligible antibacterial resistance and cross-resistance to commercial antibiotics is shown in these polymers. The polysulfoniums further show their potent in vivo antimicrobial efficacy in a multidrug-resistant S. aureus infection model that is developed on mouse skin. Similar to the antimicrobial peptides, the polysulfoniums are demonstrated to kill bacteria through membrane disruption. The obtained polypeptoid sulfoniums, with high selectivity and potent antibacterial property, are excellent candidates for antibacterial treatment and open up new possibilities for the preparation of a class of innovative antimicrobials.

Solution Self-Assembly of Coil-Crystalline Diblock Copolypeptoids Bearing Alkyl Side Chains.

Polypeptoids, a class of synthetic peptidomimetic polymers, have attracted increasing attention due to their potential for biotechnological applications, such as drug/gene delivery, sensing and molecular recognition. Recent investigations on the solution self-assembly of amphiphilic block copolypeptoids highlighted their capability to form a variety of nanostructures with tailorable morphologies and functionalities. Here, we review our recent findings on the solutions self-assembly of coil-crystalline diblock copolypeptoids bearing alkyl side chains. We highlight the solution self-assembly pathways of these polypeptoid block copolymers and show how molecular packing and crystallization of these building blocks affect the self-assembly behavior, resulting in one-dimensional (1D), two-dimensional (2D) and multidimensional hierarchical polymeric nanostructures in solution.