Crosslinking of poly(γ-dec-1-enyl-L-glutamate) and poly(γ-dec-1-enyl-co-γ-alkyl-L-glutamate) through interchain olefin metathesis

Summary Poly(γ-dec-1-enyl-L-glutamate) and poly(γ-dec-1-enyl-co-γ-alkyl-L-glutamate), helical polypeptides with pendent, terminal C-C double bonds in the side chains, were crosslinked through an intermolecular olefin metathesis reaction using Grubbs' ruthenium catalyst. Polymer samples were crosslinked at a variety of concentrations and with varying content of pendent C-C double bonds. Base promoted hydrolysis of the resulting gels was carried out to determine the nature of the chemical crosslink in the gel. Received: 25 May 1999/Accepted: 17 June 1999     

Effect of immobilization of poly(γ-glutamic acid) on the biocompatibility of electrospun poly (L-lactide) mats

In this study, poly(L-lactide) (PLLA) non-woven mats were prepared by electrospinning technique, followed by treating with oxygen plasma and grafting with 3-aminopropyl triethoxysilane (APTES), then immersed in poly(γ-glutamic acid) (γ-PGA) solution to form a layer of γ-PGA on the surface. In so doing, hydrophobic PLLA would become highly hydrophilic. Through characterization of hydrophilicity and biocompatibility, the feasibility of these modified mats for wound dressing was evaluated. The results show that after the grafting of γ-PGA, the swelling ratio increased greatly from 7% for pristine PLLA mat to 321% for γ-PGA-grafted PLLA mat, and the contact angle decreased from 112° to 25°. In vitro cytocompatibility tests against L929 fibroblast show that γ-PGA-grafted PLLA was non-cytotoxic. In addition, the proliferation of fibroblasts was higher on γ-PGA-grafted PLLA than on pristine PLLA.     

Biosynthesis and chemical modification of poly(γ-glutamic acid)

Summary The water soluble poly(-glutamic acid) (-PGA) was synthetized by bacteria. A series of new, less water soluble -esters were prepared by repeated esterification.The characterization of the resulted polymers was performed by 200 MHz ¹H and 75.4 MHz ¹³C NMR spectroscopy.     

Effects of ionic group incorporation into model polypeptide,poly(γ-benzyl-L-glutamate) (PBLG)

Effects of incorporation of ionic groups and ionic interactions to a model polypeptide, poly(γ-benzyl-L-glutamate) (PBLG), are studied. Partial conversion of γ-benzyl-L-glutamate residues to glutamic acid residues does not change molecular conformation (α-helix) and shows little change in properties. By contrast, partial conversion to sodium glutamates (ionic groups) leads to conversion from a rigid rod to a semi-flexible rod at low ion contents and causes significant changes in thermal stability and birefringence. In solution, lyotropic liquid crystalline behavior of PBLG is lost at ion content as low as 3.2 mol %. In solid, birefringence is still observed at this ion content, suggesting thermotropic liquid crystallinity of this ionic PBLG. Molecular composites made of ionic PBLG as a reinforcer and poly(4-vinylpyridine) (PVP) as a matrix polymer show significant enhancement in strength and toughness as a result of ion-dipole interactions between the component polymers.     

Effect of Processing Variables on the Solution Characteristics of γ-Glycidoxypropyltrimethoxysilane (γ-GPS)

The effects of the hydrolysis and condensation processes on the molecular structure of γ-glycidoxypropyltrimethoxysilane (γ-GPS) in aqueous solutions were investigated using Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy and FT-Raman spectroscopy. Hydrolysis was characterized by monitoring the production of methanol and the decrease in concentration of SiOCH₃ groups in 1% solutions of deuterium oxide using proton NMR. The production of methanol and loss of methoxy groups in 25% solutions of γ-GPS in water was characterized using Raman spectroscopy. Hydrolysis was found to be a very rapid process, whose rate could be increased or decreased by altering the pH of the solution. NMR spectroscopy showed that hydrolysis was complete in a 1% γ-GPS solution in deuterium oxide after 34 minutes. Raman spectroscopy also showed hydrolysis to be rapid and complete in a 25% solution of γ-GPS in water after 1 hour. Condensation, on the other hand, took a relatively long time to occur. In the NMR spectra, condensation was observed by the broadening of peaks due to the protons on the carbon atom adjacent to the silicon atom. In the Raman spectra, condensation was characterized by the disappearance of the SiOH band near 725 cm^?1 and the development of an SiOSi band near 600 cm^?1. In addition to the proton NMR, Si-29 NMR was used to characterize the silane in 10% solutions of γ-GPS in water. The Si-29 NMR showed oligomer growth with respect to time. The oligomer growth was correlated with mechanical test results.     

选择性PPARγ调节剂(SPPARγMs)研究新进展

2型糖尿病是全球性的重大公共卫生问题,过氧化物酶体增殖物激活受体γ(PPARγ)是发展抗2型糖尿病药物最受关注的靶点之一。由于已上市的PPARγ完全激动剂存在安全性问题,以PPARγ为作用靶点的抗2型糖尿病药物研究重心已经转移到开发安全性更好的选择性PPARγ调控剂(SPPARγMs),并且已有多个候选化合物进入到临床开发阶段。     

Preparation of highly flexible chitin nanofiber-graft-poly(γ-l-glutamic acid) network film

In the previous study, we successfully prepared a chitin nanofiber film by regeneration from a chitin ion gel with an ionic liquid using methanol. In this study, we performed surface-initiated graft polymerization of γ-benzyl l-glutamate N-carboxyanhydride (BLG-NCA) from amino groups on a partially deacetylated chitin nanofiber (PDA-CNF) film. First, the chitin nanofiber film was immersed in 40 % NaOH aq. at 80 °C for 7 h for partial deacetylation. Then, the PDA-CNF film was immersed in a solution of BLG-NCA in ethyl acetate at 0 °C for 24 h for graft polymerization from amino groups on nanofibers to give a chitin nanofiber-graft-poly(γ-benzyl l-glutamate) (CNF-g-PBLG) film. The analytical results of the film indicated that graft polymerization of BLG-NCA occur on surface of nanofibers. Furthermore, the film was treated with 1.0 mol/L NaOH aq. to convert PBLG on nanofibers into poly(γ-l-glutamic acid sodium salt) (PLGA). Then, condensation of the resulting carboxylates with amino groups at the terminal ends of PLGAs or the remaining amino groups on nanofibers was performed using the condensing agent to produce a CNF-g-PLGA network film. The resulting film showed the good mechanical properties with high flexibility, which has potentials as promising materials for practical applications.     

Synthesis of novel ABA triblock and (ABA)n multiblock copolymers comprised of polyisobutylene and poly(γ-benzyl-l-glutamate) segments

The synthesis of ABA triblock copolymers comprised of polyisobutylene (PIB) and poly(γ-benzyl-l-glutamate) (PBLG) segments has been demonstrated for the first time by the polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA) initiated with well-defined α,ω-primary amino-functional PIBs. The ammonium-mediated polymerization of BLG-NCA provided better control of molecular weights and lower polydispersity indices (PDIs) compared to the conventional polymerization. The compositional homogeneity of the block copolymers has been confirmed by GPC-MALLS and ¹H NMR spectroscopy. Since the resulting ABA triblock copolymer possessed primary amino groups at α,ω-ends, further extension reaction with 4,4′-methylene-bis(phenyldiisocyanate) was possible to afford a novel (ABA)_n multiblock copolymer.     

Morphology and Properties of Poly(γ-benzyl L-glutamate)-block-poly(ethylene glycol)/Poly(L-lactic acid) Blend Membrane

A series of poly(γ-benzyl L-glutamate)-block-poly(ethylene glycol) (PBLG-block-PEG)/poly(L-lactic acid) (PLLA) blend membranes were prepared by casting the polymer blend solution in chloroform. Surface morphologies of the PBLG-block-PEG/PLLA blend membranes were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Thermal, mechanical, and chemical properties of PBLG-block-PEG/PLLA blend membranes were studied by thermogravimetric analysis (TGA), tensile tests, and contact angle testing. It was found that the introduction of PLLA could exert outstanding effects on the morphology and the properties of polypeptide copolymer membrane.     

Structure and Performance of Poly(vinyl alcohol)/Poly(γ-benzyl L-glutamate) Blend Membranes

Poly(vinyl alcohol) (PVA)/poly(γ-benzyl L-glutamate) (PBLG) blend membranes with different PBLG wt contents were prepared by pervaporation. Structure and surface morphologies of PVA/PBLG blend membranes were investigated by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Thermal, mechanical, and chemical properties of PVA/PBLG blend membrane were studied by differential scanning calorimeter (DSC), tensile strength tests, and other physical methods. It was revealed that the introduction of PBLG homopolymer into PVA could exert an outstanding effect on the properties of PVA membrane.     

Surface Morphology and Properties of Rigid Poly(γ-benzyl L-glutamate) Membrane Modified by Flexible Poly(Vinyl Chloride)

Rigid poly(γ-benzyl L-glutamate)/flexible poly(vinyl chloride) (PBLG/PVC) blend membranes were prepared by casting the polymer blend solution in dichloroethane. Structure and morphologies of the PBLG/PVC blend membranes were investigated by Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Thermal, mechanical, and chemical properties of PBLG/PVC blend membranes were studied by differential scanning calorimetry (DSC), tensile tests, and other physical methods. It was found that the introduction of PVC could exert marked effects on the morphology and the properties of PBLG membrane.     

γ-FeOOH脱水产品γ-Fe_2O_3性能初探(二)

<正> 本文在先前对γ-FeOOH脱水产品γ-Fe_2O_3(以下称样品I)的XDA和TG—DTA分析研究的基础上,进一步对此产品进行电镜形貌分析和穆斯堡尔谱分析,并与由γ-FeOOH经还原氧化的产品γ-Fe_2O_3(以下简称样品Ⅱ)比较,进一步从结构和形貌上找出样品I磁性能低的原因,并进而探讨了γ-FeOOH在脱水的热处理过程中晶粒生长的情况,结合磁性测量,得出仅由对γ-FeOOH作长时间     

γ-irradiation hardness investigations of (PANI)1−x(Bi2Te3)x composites for thermistor applications

The (PANI)_1−x(Bi₂Te₃)_x composites were successfully synthesized. These composites have a simple physical combination of intrinsic conducting polymer and nanocrystal topological insulator materials which are promising new materials for unusual applications. The influence of γ-irradiation (100 kGy doses) on the performance of the (PANI)_1−x(Bi₂Te₃)_x composites was described by atypical techniques to assess the radiation hardness of the samples. X-ray diffraction and Raman spectroscopy measurements show the semi-crystalline phases, the other structural parameters, and the phonon modes. The compositional analysis and the morphological properties were investigated by energy-dispersive X-ray, while transmission electron microscopy imaging confirmed the morphology of the dopants of Bi₂Te₃ nanoparticles into the polyaniline (PANI) matrix, which shows the accumulation of the particles. Thermogravimetric analysis figured out the degradation behavior of the compositions. The representative electron spin resonance (ESR) signal exhibits a narrow single-line ESR spectrum for PANI/Bi₂Te₃ nanoparticle concentrations. (PANI)_1−x(Bi₂Te₃)_x illustrates unexpected ferromagnetic behavior that confirms the magnetic performance of the samples without introducing any magnetic dopants. The obtained materials showed promising performance for using such hybrid materials as a positive temperature coefficient thermistor.     

Synthesis and self-assembly of comb-like amphiphilic Doxifluridine-poly(?-caprolactone)-graft-poly(γ-glutamic acid) copolymer

Advances in amphiphilic copolymers can potentially be exploited in drug or gene delivery. This study develops novel comb-like amphiphilic copolymers that comprise poly(γ-glutamic acid) (γ-PGA) as a hydrophilic backbone and Doxifluridine-poly-(?-caprolactone) (5′-deoxy-5-fluorouridine-poly(?-caprolactone), 5′DFUR-PCL) as a hydrophobic side chain. A novel 5′DFUR-PCL polymer was synthesized with antitumor agent Doxifluridine (5′DFUR) as the initiator via the ring-opening polymerization of ?-caprolactone (?-CL) using tin(II) 2-ethylhexanoate (Sn(Oct)₂) as the catalyst. The 5′DFUR-PCL polymer was then grafted on γ-PGA to yield a 5′DFUR-PCL-γ-PGA comb-like copolymer with the help of 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide (EDC). The characteristics of these copolymers were examined by ¹H NMR, FT-IR, GPC, contact angle measurement and thermal properties. Grafting 5′DFUR-PCL would significantly increase the contact angle and decrease the melting temperature (T_m) of the copolymers. The micelles self-assembled from these amphiphilic copolymers were formed in an aqueous phase and were examined via fluorescence approaches, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The average sizes of the micelles were in the range from 130 to 230 nm and their zeta potentials were negative and less than −16.7 mV. The critical micelle concentration (CMC) was from 1.49 mg/L to 4.63 mg/L at 25 °C. TEM images demonstrated that the micelles were spherical and clearly had a core-shell structure.     

Chain stiffness and chain conformation of poly(α-methylene-γ-butyrolactone) in dilute solutions

The chain stiffness and local chain conformation of atactic poly(α-methylene-γ-butyrolactone) (PMBL), which is a side chain cyclic structural analog of poly(methyl methacrylate) (PMMA), with a weight-average molecular weight (M_w) ranging from 2.8 × 10³ to 2.6 × 10⁶ in N,N-dimethylformamide (DMF) and γ-butyrolactone (GBL) were characterized by size exclusion chromatography with a multi-angle light-scattering detector (SEC-MALS) and synchrotron radiation small-angle X-ray scattering (SAXS). Based on the Kratky-Porod worm-like chain model, the scattering functions and the M_w dependence of z-average root-mean-square radius of gyration <S²>_z^1/2 yielded the Kuhn segment lengths λ⁻¹, the diameter of the PMBL chains d, and the excluded-volume strengths in DMF and GBL. The local conformation of atactic PMBL in DMF and GBL were slightly larger than those of atactic PMMA, due to the presence of the conformationally rigid lactone ring structure.     

Surface Morphology and Properties of Poly(γ-benzyl L-glutamate)/Poly(butyl acrylate-co-methyl Methacrylate) Blend Film

Poly(γ-benzyl L-glutamate)/poly(butyl acrylate-co-methyl methacrylate) (PBLG/Poly(BA-co-MMA)) blend films were prepared by casting the polymer blend solution in dichloroethane. Surface morphology of the polymer blend film was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Thermal and mechanical properties of the polymer blend film were studied using differential scanning calorimeter (DSC) and tensile tests. It was revealed that the introduction of Poly(BA-co-MMA) into PBLG could exert marked effects on the surface morphology and the properties of the PBLG film.