Synthesis of Hyperbranched Polypeptide and PEO Block Copolymer by Consecutive Thiol-Yne Chemistry

Hyperbranched poly­(ε-benzyloxycarbonyl-l-lysine) (HPlys) with multiple alkyne peripheries was synthesized through the click polycondensation of an AB₂ type Plys macromonomer with α-thiol and ω-alkyne terminal groups (thiol is the A unit, and each π bond in alkyne is the B unit), and the resulting HPlys was further conjugated with thiol-termined poly­(ethylene oxide) (PEO) to generate HPlys-b-PEO block copolymer by consecutive thiol-yne chemistry. Their molecular structures and physical properties were characterized in detail by FT-IR, ¹H NMR, gel permeation chromatography, differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. HPlys and HPlys-b-PEO mainly assumed an α-helix conformation similar to the linear precursors, while the liquid crystalline phase transition of Plys segment disappeared within HPlys and HPlys-b-PEO. HPlys-b-PEO self-assembled into nearly spherical micelles in aqueous solution, while it gave a 5-fold lower critical aggregation concentration (8.9 × 10^–3 mg/mL) than a linear counterpart (4.5 × 10^–2 mg/mL), demonstrating a dendritic topology effect. Compared with a linear counterpart, HPlys-b-PEO gave a higher drug-loading capacity and efficiency for the anticancer drug doxorubicin (DOX) and a slower drug-release rate with an improved burst-release profile, enabling them useful for drug delivery systems. Importantly, this work provides a versatile strategy for the synthesis of hyperbranched polypeptides and related block copolymers by utilizing thiol-yne chemistry

Preparation, Characterization, and Self-Assembled Properties of Biodegradable Chitosan−Poly(l-lactide) Hybrid Amphiphiles

Biodegradable chitosan-graft-poly(l-lactide) (CS-g-PLLA) hybrid amphiphiles were prepared through direct grafting of a PLLA precursor to the backbone of CS. The average number of PLLA grafts per CS could be adjusted by the feed ratio of PLLA to CS, and it varied from 1.3 to 16.8. Moreover, both the crystallization rate and degree of crystallization of PLLA grafts with these graft copolymers could be adjusted by the chain length of PLLA and the number of PLLA grafts per CS, respectively. Meanwhile, CS-g-PLLA exhibited good solubility in some nonpolar and polar organic solvents compared with the original CS. Furthermore, self-assembled nanoparticles could be generated by direct injection of these graft copolymer solutions into distilled water, and their critical aggregation concentration decreased with increasing number of PLLA grafts per CS. The average size of the nanoparticles (25−103 nm) could be adjusted through the graft copolymer composition and the graft copolymer concentration, which was very different from the observations in ordinary PLLA-b-poly(ethylene oxide) amphiphiles. Significantly, this will provide a convenient method not only to combine the bioactive functions of CS with the good mechanical properties of biodegradable polymers, but also to generate nanoparticles with adjustable sizes for targeted drug release

Versatile Strategy for the Synthesis of Hyperbranched Poly(ε-caprolactone)s and Polypseudorotaxanes Thereof

A novel class of hyperbranched poly(ε-caprolactone)s (HPCLs) and polypseudorotaxanes (HPPRs) thereof was synthesized through the polycondensation of AB2 type poly(ε-caprolactone) or polypseudorotaxanes macromonomers with α-thiol and ω-alkyne terminal groups (thiol is A unit, and each π bond in alkyne is B unit) by using thiol−yne chemistry. Their molecular structures and physical properties were characterized in detail by FT-IR, NMR, time-of-flight mass spectrometry, gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. The molecular weights of HPCLs gradually increased over the irradiation time, while weight-average molecular weight grew faster than number-average molecular weight, resulting in broadening their polydispersities. The cross-linking side reaction occurred in the polycondensation of poly(ε-caprolactone) with α-thiol and ω-alkyne terminal groups (PA-PCL-SH); however, this side reaction was prohibited if PA-PCL-SH was completely threaded by α-cyclodextrin to form the rigid polypseudorotaxanes. Both the maximal melting point and the crystallization point of HPCLs gradually decrease with increasing their molecular weights, and they are in the order of PA-PCL-SH > HPCL-3 > HPCL-6 > HPCL-10 > HPCL-15 > HPCL-30 (the number within sample denotes the irradiation time used). Furthermore, the degree of crystallization of HPCLs decreases from 51.4% to 30.4% with increasing the molecular weights

Photoresponsive Poly(<i>S</i>-(<i>o</i>-nitrobenzyl)-l-cysteine)-<i>b</i>-PEO from a l-Cysteine <i>N</i>-Carboxyanhydride Monomer: Synthesis, Self-Assembly, and Phototriggered Drug Release

A photoresponsive <i>S</i>-(<i>o</i>-nitrobenzyl)-l-cysteine <i>N</i>-carboxyanhydride (NBC-NCA) monomer was for the first time designed, and the related poly­(<i>S</i>-(<i>o</i>-nitrobenzyl)-l-cysteine)-<i>b</i>-poly­(ethylene glycol) (PNBC-<i>b</i>-PEO) block copolymers were synthesized from the ring-opening polymerization (ROP) of NBC-NCA in DMF solution at 25 °C. Their molecular structures, physical properties, photoresponsive self-assembly, and drug release of PNBC-<i>b</i>-PEO were thoroughly investigated. The β-sheet conformational PNBC block within copolymers presented a thermotropic liquid crystal phase behavior, and the crystallinity of PEO block was progressively suppressed over the PNBC composition. The characteristic absorption peaks of these copolymers at about 310 and 350 nm increased over UV irradiation time and then leveled off, indicating that the <i>o</i>-nitrobenzyl groups were gradually photocleaved from copolymers until the completion of photocleavage. The PNBC-<i>b</i>-PEO copolymers self-assembled into spherical nanoparticles in aqueous solution, presenting a photoresponsive self-assembly behavior, together with a size reduction of nanoparticles after irradiation. The anticancer drug doxorubicin can be released in a controlled manner by changing the light irradiation time, which was induced by gradually photocleaving the PNBC core of nanoparticles. This work provides a facile strategy not only for the synthesis of photoresponsive polypeptide-based block copolymers but also for the fabrication of photoresponsive nanomedicine potential for anticancer therapy

pH-Sensitive Supramolecular Polypeptide-Based Micelles and Reverse Micelles Mediated by Hydrogen-Bonding Interactions or Host−Guest Chemistry: Characterization and In Vitro Controlled Drug Release

A versatile strategy is provided for the fabrication of pH-sensitive polypeptide-based normal micelles and reverse micelles from the same polypeptide-based copolymers via hydrogen-bonding interactions or host−guest chemistry. The pH-sensitive self-assembly of both linear and dendron-like/linear poly(l-glutamic acid)-b-poly(ethylene oxide) (Dm-PLG-b-PEO) block copolymers was investigated in detail by means of UV−vis, dynamic light scattering, NMR, fluorescence spectroscopy, and transmission electron microscopy. It was demonstrated that both the copolymer topology and the composition controlled the morphology of the polypeptide-cored normal micelles. Importantly, a novel class of polypeptide-shelled reverse micelles was for the first time generated by host−guest-chemistry-mediated self-assembly of these copolymers and α-cyclodextrin (α-CD) in alkaline solution. The supramolecular inclusion complexation between PEO and α-CD was confirmed by wide-angle X-ray diffraction, differential scanning calorimetry, and NMR. Moreover, the ζ potential of the reverse micelles ranged from −20.2 to −24.2 mV, convincingly demonstrating that the reverse micelles had an anionic PLG shell. Furthermore, the anticancer doxorubicin (DOX)-loaded micelles fabricated from the dendron-like/linear copolymer showed a higher DOX loading efficiency (38%) and capacity (24%) and sustained a longer drug-release period (∼70 days) than the linear counterpart. Consequently, this will provide a platform for the fabrication of supramolecular polypeptide-cored and polypeptide-shelled micelles for the anticancer drug delivery systems

Phototriggered Ring-Opening Polymerization of a Photocaged l‑Lysine <i>N</i>‑Carboxyanhydride to Synthesize Hyperbranched and Linear Polypeptides

Increasing efforts are being made on controlled photopolymerization methodologies; however, the previous polymerization systems need additional photoactive initiators or catalysts. The controlled synthesis of the hyperbranched polypeptide is still challenging, and developing a photopolymerization method to prepare a hyperbranched polypeptide is urgent for constructing biodegradable polymers and biomaterials. Without addition of any initiator/catalyst, we combine the inimer (initiator + monomer) ring-opening polymerization (ROP) and photocaged chemistry to prepare hyperbranched and linear polypeptides. The photocaged Nε-(<i>o</i>-nitrobenzyloxycarbonyl)-l-lysine-<i>N</i>-carboxyanhydride possesses intrinsic photosensitivity and will be transformed into an activated AB* inimer-type α-amino acid <i>N</i>-carboxyanhydride (NCA) containing a primary ε-amine, which further triggers ROP to produce linear and/or hyperbranched polypeptides in one pot and at room temperature. The microstructure and topology of the resulting polypeptide were clarified by means of mass spectroscopy and various NMR techniques including ¹H NMR, ¹H, ¹H–COSY, and quantitative ¹³C NMR. By tuning the UV irradiation time or intensity, this methodology can produce a linear polypeptide with a high <i>M</i>_w,GPC of 109 kDa and/or (hyper)­branched counterparts with tunable <i>M</i>_w,GPC’s of 1.4–73.5 kDa and degree of branching of 0.09–0.60

Synthesis and Characterization of Linear-Dendron-like Poly(ε-caprolactone)-<i>b</i>-poly(ethylene oxide) Copolymers via the Combination of Ring-Opening Polymerization and Click Chemistry

A new class of linear-dendron-like poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) copolymers with unsymmetrical topology was synthesized via controlled ring-opening polymerization (ROP) of ε-caprolactone (CL) followed by a click conjugation with azide-terminated PEO (PEO-N3). The dendron-like PCL terminated with a clickable alkyne group (Dm-PCL, m = 0, 1, 2, and 3) was for the first time synthesized from the ROP of CL monomer using a propargyl focal point dendrons Dm with primary amine groups as the initiators and stannous octoate as catalyst in bulk at 130 °C. Then, the linear-dendron-like Dm-PCL-b-PEO copolymers were obtained by the click conjugation of Dm-PCL with PEO-N3 using PMDETA/CuBr as catalyst in DMF solution at 35 °C. Their molecular structures and physical properties were in detail characterized by FT-IR, NMR, MALLS-GPC, DSC, and WAXD. Both DLS and TEM analyses demonstrated that the biodegradable micelles and vesicles with different sizes (less than 100 nm) self-assembled from these Dm-PCL-b-PEO copolymers in aqueous solution, and both the PEO composition and the linear-dendron-like architecture of copolymers controlled the morphology and the average size of nanoparticles. To the best of our knowledge, this is the first report that describes the synthesis of linear-dendron-like PCL-b-PEO block copolymers via the combination of ROP and click chemistry. Consequently, this provides a versatile strategy not only for the synthesis of biodegradable and amphiphilic block copolymers with linear-dendron-like architecture but also for fabricating biocompatible nanoparticles with suitable size for controlled drug release

Versatile Strategy for the Synthesis of Dendronlike Polypeptide/Linear Poly(ε-caprolactone) Block Copolymers via Click Chemistry

A new class of dendron-like polypeptide/linear poly(ε-caprolactone) block copolymers with asymmetrical topology (i.e., dendron-like poly(γ-benzyl-l-glutamate)/linear PCL copolymers having 2m PBLG branches, m = 0, 1, 2, and 3; denoted as PCL-Dm-PBLG) was for the first time synthesized via the combination of controlled ring-opening polymerization (ROP) of ε-caprolactone, click chemistry, and the ROP of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA). The linear hydroxyl-terminated PCL (PCL-OH) was synthesized by controlled ROP of ε-caprolactone and then transformed into clickable azide-terminated PCL (PCL-N3). The PCL-N3 precursor was further click conjugated with propargyl focal point PAMAM-typed dendrons (i.e., Dm having 2m primary amine groups) to generate PCL-dendrons (PCL-Dm) using CuBr/PMDETA as catalyst in dimethylformamide solution at 35 °C. Finally, PCL-Dm was used as macroinitiator for the ROP of BLG-NCA monomer to produce the targeted PCL-Dm-PBLG block copolymers. Their molecular structures and physical properties were characterized in detail by FT-IR, NMR, matrix assisted laser desorption ionization time-of-flight mass spectrometry, gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. To the best of our knowledge, this is the first report that describes the synthesis of dendron-like polypeptide/linear PCL block copolymers with asymmetrical topology via the combination of ROP and click chemistry. Consequently, this provides a versatile strategy for the synthesis of biodegradable and biomimetic dendron-like polypeptide-based biohybrids

Synthesis, Self-Assembly, and In Vitro Doxorubicin Release Behavior of Dendron-like/Linear/Dendron-like Poly(ε-caprolactone)-<i>b</i>-Poly(ethylene glycol)-<i>b</i>-Poly(ε-caprolactone) Triblock Copolymers

Dendron-like/linear/dendron-like poly(ε-caprolactone)-b-poly(ethylene glycol)-b-poly(ε-caprolactone) triblock copolymers with controlled molecular weights (Mn = 9550−30 460) and low polydispersities were synthesized by a click conjugation between dendron-like poly(ε-caprolactone) and bifunctional azide-terminated poly(ethylene glycol) (copolymer yield = 56−89%). Their molecular structures and physicochemical and self-assembly properties were thoroughly characterized by means of FT-IR, 1H NMR, multiangle laser light scattering coupled with gel permeation chromatography, differential scanning calorimetry, wide-angle X-ray diffraction, dynamic light scattering, and transmission electron microscopy. Using a nanoprecipitation method, these triblock copolymers self-assembled into spherical flower-like micelles with an average diameter of less than 50 nm in aqueous solution, and both the copolymer composition and the dendritic topology of the hydrophobic core had no apparent influence on the morphology of nanoparticles. The critical aggregation concentrations of these copolymers ranged from 0.034 to 0.048 mg/mL. However, the anticancer doxorubicin-loaded nanoparticles showed worm-like micelles similar to blank nanoparticles fabricated by a dialysis method, and the loaded doxorubicin drug hardly affected the final morphology of nanoparticles. Moreover, the doxorubicin-loaded nanoparticles fabricated from the dumbbell copolymer showed a higher drug loading efficiency of 18% and a longer drug-release time of 45 days than the linear counterpart. Consequently, this provides a versatile strategy not only for the synthesis of biodegradable and biocompatible dendron-like/linear/dendron-like triblock copolymers with dumbbell topology by using click chemistry but also for fabricating worm-like doxorubicin-loaded nanoparticles for anticancer drug release

Supramolecular and Biomimetic Polypseudorotaxane/Glycopolymer Biohybrids: Synthesis, Glucose-Surfaced Nanoparticles, and Recognition with Lectin

A new class of supramolecular and biomimetic glycopolymer/poly(ε-caprolactone)-based polypseudorotaxane/glycopolymer triblock copolymers (poly(d-gluconamidoethyl methacrylate)−PPR−poly(d-gluconamidoethyl methacrylate), PGAMA−PPR−PGAMA), exhibiting controlled molecular weights and low polydispersities, was synthesized by the combination of ring-opening polymerization of ε-caprolactone, supramolecular inclusion reaction, and direct atom transfer radical polymerization (ATRP) of unprotected d-gluconamidoethyl methacrylate (GAMA) glycomonomer. The PPR macroinitiator for ATRP was prepared by the inclusion complexation of biodegradable poly(ε-caprolactone) (PCL) with α-cyclodextrin (α-CD), in which the crystalline PCL segments were included into the hydrophobic α-CD cavities and their crystallization was completely suppressed. Moreover, the self-assembled aggregates from these triblock copolymers have a hydrophilic glycopolymer shell and an oligosaccharide threaded polypseudorotaxane core, which changed from spherical micelles to vesicles with the decreasing weight fraction of glycopolymer segments. Furthermore, it was demonstrated that these triblock copolymers had specific biomolecular recognition with concanavalin A (Con A) in comparison with bovine serum albumin (BSA). To the best of our knowledge, this is the first report that describes the synthesis of supramolecular and biomimetic polypseudorotaxane/glycopolymer biohybrids and the fabrication of glucose-shelled and oligosaccharide-threaded polypseudorotaxane-cored aggregates. This hopefully provides a platform for targeted drug delivery and for studying the biomolecular recognition between sugar and lectin