Ring-opening Polymerization Of N-carboxyanhydrides Research Articles

Self-assembling of biocompatible BAB amphiphilic triblock copolymers PLL(Z)–PEG–PLL(Z) in aqueous medium

A novel biocompatible BAB amphiphilic triblock copolymers which consist of poly(ethylene glycol) (PEG) and poly( ε-benzyloxycarbonyl l-Lysine) (PLL(Z)) were synthesized by anion ring opening polymerization of N-carboxyanhydride of ε-benzyloxycarbonyl- l-Lysine ( l-Lys(z)-NCA) using α-amino- ω-amino-poly(ethylene glycol) as initiator in DMF. The block copolymers were characterized by IR, 1H-NMR, GPC, DSC. The results showed that the block copolymers were of narrow molecular distribution and well defined structure. The self-assembled behaviors of block copolymers in aqueous medium were investigated. The effects of various factors, such as cosolvents, initial concentration, temperature, annealing time and times of frozen-thaw cycle etc., on the aggregate morphologies were investigated by transmission electron microscopy (TEM). Different morphological aggregates such as sphere, rod and vesicle etc. could be obtained at controlled conditions, at the same time, a novel helical aggregate was observed. These regular nanometer structures have potential applications in biomedicine due to the biocompatibility of two blocks.

Adsorption immobilization of Candida rugosa lipases on polypropylene hollow fiber microfiltration membranes modified by hydrophobic polypeptides

Poly(γ-ethyl- l-glutamate) (PELG) and poly(γ-stearyl- l-glutamate) (PSLG), two polypeptides with short and long hydrophobic side chains, respectively, were tethered on the polypropylene hollow fiber microfiltration membrane (PPHFMM) surface through the ring opening polymerization of N-carboxyanhydride of γ-ethyl- l-glutamate (γ-stearyl- l-glutamate) initiated by amino groups. Lipases from Candida rugosa were immobilized on these membranes by adsorption. Results on the basis of the enzyme adsorption capacity, activity and thermal stability were compared with those of the nascent PPHFMM. It was found that, as for the modified PPHFMM, the adsorption capacities of lipase are lower than that of the nascent ones, but the activity retention of the immobilized enzymes increases from 57% to 72% and to 62%, respectively for the PSLG-modified and PELG-modified PPHFMM. In addition, the experimental results of thermal stability show that the residual activity of the immobilized lipases at 50 °C for 2 h is respectively 64% for the PELG-modified PPHFMM and 58% for the PSLG-modified PPHFMM, which are higher than that of the nascent ones.

A comparative study on lipase immobilized polypropylene microfiltration membranes modified by sugar-containing polymer and polypeptide

Two protocols were used to modify polypropylene microfiltration membrane (PPMM): (a) a sugar-containing polymer was grafted onto the membrane surface by the plasma-induced polymerization of α-allyl glucoside (AG) and (b) poly(γ-stearyl l-glutamate) (PSLG) was tethered onto the membrane surface through the ring opening polymerization of N-carboxyanhydride (NCA) derived from γ-stearyl l-glutamate. Lipases from Candida rugosa were immobilized on these membranes by adsorption. Results on the basis of the enzyme adsorption capacity, activity and thermal stability were compared with those of the nascent PPMM. It was found that, as for the PAG-modified PPMM, the adsorption capacity and the activity retention of lipases were lower than those of the nascent ones, but the thermal stability was improved to some degree. On the other hand, tethering PSLG on the membrane surface increased the activity retention of lipases immobilized on the membrane from 57 to 72%, and the thermal stability was also improved.

Surface modification of microporous polypropylene membranes by the grafting of poly(γ-stearyl- l-glutamate)

A polypeptide, poly(γ-stearyl- l-glutamate) (PSLG), was grafted on the surface of hydrophobic polypropylene hollow fiber membranes through the ring opening polymerization of N-carboxyanhydride (NCA) of γ-stearyl- l-glutamate initiated by amino groups which was generated by ammonia plasma. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), together with water contact angle and bovium serum albumin adsorption measurements were used to characterize the modified membrane surface. The XPS and FT-IR spectra demonstrated that polypeptide was actually grafted on the membrane surface despite of the low degree of graft polymerization due to the hydroxyl groups on the membrane surface. To subject the ammonia plasma-treated membrane with γ-(aminopropyl)triethanoxysilane (γ-APS) which can react with hydroxyl groups and leave amino groups, the degree of graft polymerization could be improved. The bovium serum albumin adsorption measurement was conducted to further examine the surface properties of modified and original membranes. Potential applications of the PSLG grafted membranes are expected for enantiomer separation and/or enzyme immobilization.

Poly( l-histidine)–PEG block copolymer micelles and pH-induced destabilization

Poly( l-histidine)–poly(ethylene glycol) diblock copolymers (polyHis– b–PEG) were prepared and used for the construction of polymeric micelles responding to local pH changes in the body. PolyHis was synthesized by ring opening polymerization of l-histidine N-carboxyanhydride, the imidazole amine group of which was protected by the dinitrophenyl group. The resulting polymer ( M n: 5,000 g/mole) was coupled to poly(ethylene glycol) ( M n: 2,000 g/mole) via an amide linkage using the dicyclohexyl carbodiimide and N-hydroxysuccinimide-mediated reaction. The block copolymer in dimethyl sulfoxide formed polymeric micelles on diafiltration against a borate buffer at pH 8. Dynamic light scattering and atomic force microscopy showed the micelles were spherical, diameter ∼114 nm, with a unimodal distribution. The critical micelle concentration (CMC) at pH 8.0 was 2.3 mg/l. The CMC increased markedly on decreasing the pH of the diafiltration medium below 7.2. Micelles prepared at pH 8.0 were gradually destabilized below pH 7.4, as evidenced by a slight increase in light transmittance, an alteration in size distribution, and a decrease in the pyrene fluorescence intensity. It was concluded that the ionization of the polyHis block forming the micelle core determined the pH-dependent CMC and stability. After further optimization of the pH-sensitivity, pH-sensitive micelles are expected to have application for solid tumor treatment, exploiting the fact that most solid tumors have an acidic extracellular pH.

Surface Grafting of Poly(l-glutamates). 1. Synthesis and Characterization

The ring-opening polymerization of N-carboxyanhydrides (NCA) of γ-benzyl l-glutamate and γ-methyl l-glutamate from (γ-aminopropyl)triethoxysilane (APS) pretreated substrates such as silicon wafers and quartz slides was investigated. FT-IR transmission spectroscopy, circular dichroism measurements, and UV/vis spectroscopy confirmed the pure α-helix conformation of the grafted polypeptide layers. FT-IR spectroscopy also showed that the most important part of the polymer growth took place in the first 5 h of the polymerization. The average orientation of the rather rigid α-helical polypeptides, grown during a short period of time, was more perpendicular with respect to the substrate than the orientation of the polymers grown over a longer reaction time. For concentrations up to 2.0 M, the polymer growth from both NCA monomers showed a pronounced dependence on the monomer concentration. Moreover, it appeared that the higher the monomer concentration, the more perpendicular the average orientation of the helices with respect to the substrate. The thickness of the grafted polypeptide layers up to 400 Å was determined with ellipsometry and small-angle X-ray reflection measurements. The absence of chemical chain termination was demonstrated by additional polymer growth in a renewed polymerization.

Grafting of Polypeptide from Carbon Black by the Ring-Opening Polymerization of γ-Methyl l-Glutamate N-Carboxyanhydride Initiated by Amino Groups on Carbon Black Surface

Grafting of Polypeptide from Carbon Black by the Ring-Opening Polymerization of γ-Methyl l-Glutamate N -Carboxyanhydride Initiated by Amino Groups on Carbon Black Surface