Heavy Metal Removal from Wastewater Using Poly(Gamma-Glutamic Acid)-Based Hydrogel.

The removal of toxic heavy metal ions from wastewater is of great significance in the protection of the environment and human health. Poly(gamma-glutamic acid) (PGA) is a non-toxic, biodegradable, and highly water-soluble polymer possessing carboxyl and imino functional groups. Herein, water-insoluble PGA-based hydrogels were prepared, characterized, and investigated as heavy metal adsorbents. The prepared hydrogels were recyclable and exhibited good adsorption effects on heavy metal ions including Cu2+, Cr6+, and Zn2+. The effects of adsorption parameters including temperature, solution pH, initial concentration of metal ions, and contact time on the adsorption capacity of the hydrogel for Cu2+ were investigated. The adsorption was a spontaneous and exothermic process. The process followed the pseudo-first-order kinetic model and Langmuir isotherm model, implying a physical and monolayer adsorption. The adsorption mechanisms investigation exhibited that Cu2+ adsorbed on the hydrogel via electrostatic interactions with anionic carboxylate groups of PGA in addition to the coordination interactions with the -NH groups. Importantly, the PGA hydrogel exhibited good reusability and the adsorption capability for Cu2+ remained high after five consecutive cycles. The properties of PGA hydrogel make it a potential candidate material for heavy metal ion removal in wastewater treatment.

Preparation, characterization and biological activity of phosphorylated surface deacetylated chitin nanofibers.

Phosphorylation is a key route to achieve varieties of biological activities for polysaccharides. Here, we report the phosphorylated surface deacetylated chitin nanofibers (PS-ChNFs) using the sodium tripolyphosphate/sodium trimetaphosphate (STPP/STMP) method. Response surface methodology (RSM) was employed to optimize in this study. Under optimal conditions, a maximum degree of substitution (DS) of 0.13 was obtained. In addition, the structures of PS-ChNFs were investigated by Fourier transform infrared spectroscopy (FT-IR), Nuclear Magnetic Resonance spectra (NMR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM) and (Energy Dispersive Spectroscopy-mapping) EDS-mapping. The findings revealed that the FT-IR spectroscopy and XPS analysis confirmed the appearance of phosphate groups in PS-ChNFs. The 31P NMR results indicate that the PS-ChNFs structure has characteristic peaks of P elements. SEM images showed that PS-ChNFs had a rough surface with many cavities, but the P elements on the surface of the EDS-mapping are uniformly distributed throughout the sample without any enrichment. Antioxidant and antibacterial test showed that PS-ChNFs had significant scavenging effect on free radicals and antibacterial effect. The above results indicate that the chemical modification of PS-ChNFs was successful.

Phenylboronic-acid-modified amphiphilic polyether as a neutral gene vector.

A phenylboronic-acid-modified amphiphilic block polyether is prepared via reaction of polyglycidol-block-poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)-block-polyglycidol (Pluronic-PG) with 2-(N,N-dimethylaminomethyl)-5-aminomethyl phenylboronic acid using phosgene as a coupling reagent. The boronic-acid-modified non-cationic polymer binds plasmid pGL3 effectively, forms sub-µm polymer/DNA complex particles, and greatly facilitates the cell uptake of the plasmid. The efficiency of the polymer as a gene vector is evaluated in vitro by transfection of pGL3 to HeLa, COS-7 and HepG2 cells. Pluronic-PG-BA enhances the transfection efficiency by 100 to 1000 times compared with Pluronic-PG. The presence of serum does not significantly affect the transfection efficiency.

Self-assembled micellar aggregates based monomethoxyl poly(ethylene glycol)-b-poly(ε-caprolactone)-b-poly(aminoethyl methacrylate) triblock copolymers as efficient gene delivery vectors.

Amphiphilic triblock copolymers monomethoxyl poly(ethylene glycol) (mPEG)-b-poly(ε-caprolactone) (PCL)-b-poly(aminoethyl methacrylate)s (PAMAs) (mPECAs) were synthesized as gene delivery vectors. They exhibited lower cytotoxicity and higher transfection efficiency in COS-7 cells in presence of serum compared to 25 kDa bPEI. The influence of mPEG and PCL segments in mPECAs was evaluated by comparing with corresponding diblock copolymers. The studies showed the incorporation of the hydrophobic PCL segment in triblock copolymers affected the binding capability to pDNA and surface charges of complexes due to the formation of micelles increasing the local charges. The presence of mPEG segment in gene vector decreased the surface charges of the complexes and increased the stability of the complexes in serum because of the steric hindrance effect. It was also found that the combination of PEG and PCL segments into one macromolecule might lead to synergistic effect for better transfection efficiency in serum.

Enhanced gene transfection capability of polyethylenimine by incorporating boronic acid groups.

Phenylboronic acid-modified PEI was prepared by the reaction of 1800 Da PEI with 4-(bromomethyl)phenylboronic acid. It is much more effective than unmodified PEI for gene delivery. The covalently incorporated boronic acid groups achieve the greatly enhanced gene delivery efficiency partially through improving condensation ability to DNA, and partially through facilitating cell uptake due to interaction with ligands in cells.

Low molecular weight polyethylenimine conjugated gold nanoparticles as efficient gene vectors.

Gold nanoparticles (GNPs) conjugated with low molecular weight polyethylenimine (PEI 800 Da) were synthesized, and their characteristics as gene transfection vectors were investigated. The polyethylenimine conjugated GNPs (GNP-PEI800s) can retard plasmid DNA completely at N/P ratios above 4 in electrophoresis on agarose gel, and they also render effective protection of DNA from attack by DNase. TEM imaging revealed that GNP-PEI800s with higher PEI grafting density resulted in more compact and smaller complexes with plasmid DNA, compared to those obtained with lower grafting density ones. These complexes showed high efficiency in gene delivery in monkey kidney cells in vitro. In the absence of serum, GNP-PEI800s can transfect pGL-3 to COS-7 cells 3 to 4 orders more efficient than unmodified PEI800, reaching almost the same magnitude of PEI 25 kDa. More importantly, in contrast to the dramatically lowered efficiency of high molecular weight PEIs such as PEI 25 kDa in the presence of serum, the efficiency of GNP-PEI800s can be retained or even enhanced in serum-containing media. GNP-PEI800 1.3 exhibited transfection efficiency exceeding 60-fold that of PEI 25 kDa in 10% serum medium. All GNP-PEI800s exhibit mild cytotoxicity in comparison with that of PEI 25 kDa.

Amphiphilic Block-Graft Copolymers with a Degradable Backbone and Polyethylene Glycol Pendant Chains Prepared via Ring-Opening Polymerization of a Macromonomer.

Well-defined amphiphilic block-graft copolymers PCL-b-[DTC-co-(MTC-mPEG)] with polyethylene glycol methyl ether pendant chains were designed and synthesized. First, monohydroxyl-terminated macroinitiators PCL-OH were prepared. Then, ring-opening copolymerization of 2,2-dimethyltrimethylene carbonate (DTC) and cyclic carbonate-terminated PEG (MTC-mPEG) macromonomer was carried out in the presence of the macroinitiator in bulk to give the target copolymers. All the polymers were characterized by (1) H NMR and gel permeation chromatography (GPC). The polymers have unimodal molecular weight distributions and moderate polydispersity indexes. The amphiphilic block-graft copolymers self-assemble in water forming stable micelle solutions with a narrow size distribution.

Poly(ethylene glycol)-block-poly(glycidyl methacrylate) with oligoamine side chains as efficient gene vectors.

Well-defined diblock copolymers, poly(ethylene glycol)-block-poly(glycidyl methacrylate)s (PEG-b-PGMAs), with different poly(glycidyl methacrylate) (PGMA) chains, were prepared via atom transfer radical polymerization (ATRP) from the same macromolecular initiator 2-bromoisobutyryl-terminated poly(ethylene glycol) (PEG). Ethyldiamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), and polyethyleneimine (PEI) with an M(W) of 400 (PEI(400)) were used to decorate PEG-b-PGMAs to get the cationic polymers PEG-b-PGMA- oligoamines. These cationic polymers possessed high buffer capability and could condense plasmid DNA (pDNA) into nanoscaled complexes of 125-530 nm. These complexes showed the positive zeta potential of 20-35 mV at N/P ratios of 10-50. Most of them exhibited very low cytotoxicity and good transfection efficiency in 293T cells. The presence of the serum medium did not decrease the transfection efficiency due to the steric stabilization of the PEG chains.