Synthesis of amphiphilic polyethylene-b-poly(l-glutamate) block copolymers with vastly different solubilities and their stimuli-responsive polymeric micelles in aqueous solution

Synthesis and Thermoreversible Gelation of Coil-Rod Copolymers with a Dendritic Polyethylene Core and Multiple Helical Poly(γ-benzyl-L-glutamate) Arms

Coil-rod copolymers with a dendritic polyethylene (DPE) core and multiple helical poly(γ-benzyl-L-glutamate) (PBLG) arms (DPE-(PBLG)n) were prepared by palladium-catalyzed copolymerization in tandem with ring-opening polymerization (ROP). Macroinitiator (DPE-(NH2)11) was firstly prepared by the group transformation of DPE-(OH)11 generated from palladium-catalyzed copolymerization of ethylene and acrylate comonomer. Coil-helical DPE-(PBLG)11 copolymers were prepared by ROP of γ-benzyl-L-glutamate-N-carboxyanhydride (BLG-NCA). These DPE-(PBLG)11 copolymers could form thermoreversible gels in toluene solvent, and the dendritic topology of the DPE core increased the critical gelation concentrations. The self-assembled nanostructure of gels was fully characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD), and the morphology of the fibrous structure was a twisted flat ribbon through a self-assembled nanoribbon mechanism. The self-assembled fibers formed by DPE-(PBLG45)11 are more heterogeneous and ramified than previously observed fibers formed by PBLG homopolymer and block copolymers.

Amphiphilic Polyethylene-b-poly(L-lysine) Block Copolymer: Synthesis, Self-Assembly, and Responsivity

Polyethylene-b-polypeptide copolymers are biologically interesting, but studies of their synthesis and properties are very few. This paper reports synthesis and characterization of well-defined amphiphilic polyethylene-block-poly(L-lysine) (PE-b-PLL) block copolymers by combining nickel-catalyzed living ethylene polymerization with controlled ring-opening polymerization (ROP) of ε-benzyloxycarbonyl-L-lysine-N-carboxyanhydride (Z-Lys-NCA) and sequential post-functionalization. Amphiphilic PE-b-PLL block copolymers self-assembled into spherical micelles with a hydrophobic PE core in aqueous solution. The pH and ionic responsivities of PE-b-PLL polymeric micelles were investigated by means of fluorescence spectroscopy, dynamic light scattering, UV-circular dichroism, and transmission electron microscopy. The variation of pH values led to the conformational alteration of PLL from α-helix to coil, thereby changing the micelle dimensions.

Late Transition Metal Catalysts with Chelating Amines for Olefin Polymerization

Polyolefins are the most consumed polymeric materials extensively used in our daily life and are usually generated by coordination polymerization in the polyolefin industry. Olefin polymerization catalysts containing transition metal–organic compound combinations are undoubtedly crucial for the development of the polyolefin industry. The nitrogen donor atom has attracted considerable interest and is widely used in combination with the transition metal for the fine-tuning of the chemical environment around the metal center. In addition to widely reported olefin polymerization catalysts with imine and amide donors (sp2 hybrid N), late transition metal catalysts with chelating amine donors (sp3 hybrid N) for olefin polymerization have never been reviewed. In this review paper, we focus on late transition metal (Ni, Pd, Fe, and Co) catalysts with chelating amines for olefin polymerization. A variety of late transition metal catalysts bearing different neutral amine donors are surveyed for olefin polymerization, including amine–imine, amine–pyridine, α-diamine, and [N, N, N] tridentate ligands with amine donors. The relationship between catalyst structure and catalytic performance is also encompassed. This review aims to promote the design of late transition metal catalysts with unique chelating amine donors for the development of high-performance polyolefin materials.

Ovalbumin/carboxymethylcellulose colloids: Particle compactness and interfacial stability

A protein/polysaccharide colloidal particle was prepared via combined complex coacervation and heat-induction. When the ratio of ovalbumin (OVA) to carboxymethylcellulose (CMC) was at 1:2, loose flexible particles (low D_f) with low surface hydrophobicity were obtained. Conversely, dense and compact particles (high D_f) were easily formed at a higher OVA/CMC ratio. Only in the appropriate OVA/CMC ratio, pH will have a greater impact on the colloidal particles. At the pH value of 4.4, the OVA/CMC ratio had a greater impact on the colloidal particles compared to pH. The emulsion stabilized by loose particles had a mean particle size of 3888 nm and was easily flocculated and creamed. On the other hand, compact particles formed a stable emulsion, which had a higher exponent of Δr² (0.867) and could resist flocculation during the 7 days storage. As such, the results showed that stable emulsion could be realized by utilizing compact particles as emulsifiers.

Hydrophilic hindering and hydrophobic growing: a vesicle glycometabolism multi-drug combination therapeutic against Alzheimer's disease

Advanced drug vehicle exploitation and the sophisticated synergy mechanism revelation are two great difficulties in combination therapy. Compared with most readily available polymer micelles, some undiscovered complex chemical design principles limit the expanding research of polymer vesicles. Here, polycaprolactone (PCL)-g-Dextran vesicle that dextran brush steric hindrance guide PCL lamellae-aligned growth was synthesized. The effect of the glycometabolism multi-drug vesicle combination treatment and synergism mechanism were investigated on senescence-accelerated mouse prone 8 (SAMP8) mice. The main insulin sensitizer drug could improve the memory ability of mice to a small extent, and the main insulin secretion promoter drug had little beneficial effect. Moreover, the triple anti-insulin resistant drugs of insulin (INS), repaglinide (REP) and metformin hydrochloride (MET) activated the glycometabolism-related bio-signals, and the energy cycle was normalized successfully. The insulin intracellular uptake and utilization efficiency could be the reason for the gap. The upregulation of the brain-derived neurotrophic factor (BDNF) protein confirmed that the crosstalk between the mitochondria and synapse contributes to the nerve repair. This study provided an excellent drug combination vesicle to treat Alzheimer's disease (AD). The discovery of the combination mechanism leads to an improvement in the AD clinical treatment.

Surface sulfonamide modification of poly(N-isopropylacrylamide)-based block copolymer micelles to alter pH and temperature responsive properties for controlled intracellular uptake

Two different surface sulfonamide-functionalized poly(N-isopropylacrylamide)-based polymeric micelles were designed as pH-/temperature-responsive vehicles. Both sulfadimethoxine- and sulfamethazine-surface functionalized micelles were characterized to determine physicochemical properties, hydrodynamic diameters, zeta potentials, temperature-dependent size changes, and lower critical solution temperatures (LCST) in both pH 7.4 and 6.8 solutions (simulating both physiological and mild low pH conditions), and tested in the incorporation of a proof-of-concept hydrophobic antiproliferative drug, paclitaxel. Cellular uptake studies were conducted using bovine carotid endothelial cells and fluorescently labeled micelles to evaluate if there was enhanced cellular uptake of the micelles in a low pH environment. Both variations of micelles showed enhanced intracellular uptake under mildly acidic (pH 6.8) conditions at temperatures slightly above their LCST and minimal uptake at physiological (pH 7.4) conditions. Due to the less negative zeta potential of the sulfamethazine-surface micelles compared to sulfadimethoxine-surface micelles, and the proximity of their LCST to physiological temperature (37°C), the sulfamethazine variation was deemed more amenable for clinically relevant temperature and pH-stimulated applications. Nevertheless, we believe both polymeric micelle variations have the capacity to be implemented as an intracellular drug or gene delivery system in response to mildly acidic conditions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1552-1560, 2018.

Self-assembled polypeptide nanoparticles for intracellular irinotecan delivery

In this research poly(l-lysine)-b-poly(l-leucine) (PLys-b-PLeu) polymersomes were developed. It was shown that the size of nanoparticles depended on pH of self-assembly process and varied from 180 to 650nm. The biodegradation of PLys-b-PLeu nanoparticles was evaluated using in vitro polypeptide hydrolysis in two model enzymatic systems, as well as in human blood plasma. The experiments on the visualization of cellular uptake of rhodamine 6g-loaded and fluorescein-labeled nanoparticles were carried out and the possibility of their penetration into the cells was approved. The cytotoxicity of polymersomes obtained was tested using three cell lines, namely, HEK, NIH-3T3 and A549. It was shown that tested nanoparticles did not demonstrate any cytotoxicity in the concentrations up to 2mg/mL. The encapsulation of specific to colorectal cancer anti-tumor drug irinotecan into developed nanocontainers was performed by means of pH gradient method. The dispersion of drug-loaded polymersomes in PBS was stable at 4°C for a long time (at least 1month) without considerable drug leakage. The kinetics of drug release was thoroughly studied using two model enzymatic systems, human blood serum and PBS solution. The approximation of irinotecan release profiles with different mathematical drug release models was carried out and allowed identification of the release mechanism, as well as the morphological peculiarities of developed particles. The dependence of encapsulation efficiency, as well as maximal loading capacity, on initial drug concentration was studied. The maximal drug loading was found as 320±55μg/mg of polymersomes. In vitro anti-tumoral activity of irinotecan-loaded polymersomes on a colon cancer cell line (Caco-2) was measured and compared to that for free drug.

Simultaneous Polymerization and Polypeptide Particle Production via Reactive Spray-Drying

A method for producing polypeptide particles via in situ polymerization of N-carboxyanhydrides during spray-drying has been developed. This method was enabled by the development of a fast and robust synthetic pathway to polypeptides using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an initiator for the ring-opening polymerization of N-carboxyanhydrides. The polymerizations finished within 5 s and proved to be very tolerant toward impurities such as amino acid salts and water. The formed particles were prepared by mixing the monomer, N-carboxyanhydride of l-glutamic acid benzyl ester (NCAGlu) and the initiator (DBU) during the atomization process in the spray-dryer and were spherical with a size of ∼1 μm. This method combines two steps; making it a straightforward process that facilitates the production of polypeptide particles. Hence, it furthers the use of spray-drying and polypeptide particles in the pharmaceutical industry.

Amine–imine palladium catalysts for living polymerization of ethylene and copolymerization of ethylene with methyl acrylate: incorporation of acrylate units into the main chain and branch end

A bulky amine–imine palladium catalyst can polymerize ethylene in a living fashion. Copolymerizations of ethylene and methyl acrylate afford branched copolymers with terminal and main chain acrylate units.

Synthesis, characterization and micellization of amphiphilic polyethylene-b-polyphosphoester block copolymers

Amphiphilic polyethylene-block-polyphosphoester (PE-b-PPE) copolymers can self-assemble into spherical micelles in aqueous solution and efficiently carry paclitaxel (PTX) drug.