Chelation of vanadium(IV) by a natural and edible biopolymer poly(gamma-glutamic acid) in aqueous solution: structure and binding constant of complex

The naturally occurring edible biopolymer poly(gamma-glutamic acid) (gamma-PGA) is shown to be an efficient chelating agent of vanadium(IV). The structure of poly(gamma-glutamic acid)oxovanadium(IV) (VO-gamma-PGA) complex in solution has been analyzed by electron spin resonance and UV-visible absorption spectra. The equatorial coordination sphere of vanadium(IV) is proposed to be [2 x carboxylate (2O)-VO-(OH2)2]. The binding isotherm is determined for suspensions of gamma-PGA in vanadium(IV) oxide sulfate (VS) solutions of different concentrations, and the data have been adjusted to fit the modified Langmuir equation. The maximum amount of vanadium bound per gram of gamma-PGA is estimated to be 141 mmol . g(-1) with a binding constant of 22 L . g(-1) at pH 3.     

Ionic complexes of biosynthetic poly(malic acid) and poly(glutamic acid) as prospective drug-delivery systems

The hydrolytic degradability and erythromycin release from stoichiometric ionic complexes of biotechnological poly(beta,L-malic acid)s and poly(gamma,D-glutamic acid)s with alkyltrimethylammonium surfactants were investigated. The influence of pH, temperature and antibiotic load on hydrolysis rate was examined. It was found that poly(malic acid) complexes degraded by a surface erosion mechanism at a higher rate than poly(glutamic acid) complexes, which eroded in bulk. Erythromycin was lodged in the paraffinic subphase of the complexes and upon aging it was delivered according to a sigmoidal profile that appeared to be independent on the antibiotic load.     

Ionic Complexes of Biotechnological Polyacids with Cationic Surfactants

Summary: Stoichiometric complexes of biotechnological poly(γ-glutamic) acid and poly(β,L -malic) acid with alkyltrimethylammonium surfactants of long alkyl chains could be readily prepared in aqueous medium. They adopt a biphasic layered structures in which the main chain and the side chain alternate with nanometric periodicity. Alkyl side chains show reversible melting that involves generation of mesophases. Complexes degraded by water by different mechanisms depending on the constitution of the main chain; the polymalic complexes underwent surface erosion whereas the polyglutamic ones degraded in bulk. Erythromycin could be homogenously loaded into the paraffinic subphase of the complexes and delivered upon incubation under physiological conditions in parallel to the hydrolysis of the polymer.     

Investigation of a Cu(II)-poly(gamma-glutamic acid) complex in aqueous solution and its insulin-mimetic activity

The complexation between cupric ions (Cu(II)) and poly(gamma-glutamic acid) (gamma-PGA) in aqueous solutions (pH 3-11) has been studied by UV-visible absorption and electron spin resonance (ESR) techniques. Formation of the Cu(II)-gamma-PGA complex is confirmed by the observation of the blue shift of the absorption band in the visible region, anisotropic line shapes in the ESR spectrum at room temperature, and a computer simulation of the visible absorption spectrum of the complex. The structure of the Cu(II)-gamma-PGA complex, depending on the pH, has been determined. The in vitro insulin-mimetic activity of the Cu(II)-gamma-PGA complex is examined by determining both inhibition of free fatty acid release and glucose uptake in isolated rat adipocytes treated with epinephrine, in which the concentration of the Cu(II)-gamma-PGA complex for 50% inhibition of free fatty acid release is very similar to that of CuSO4. However, it is significantly lower than that of a previously reported insulin-mimetic bis(3-hydroxypicolinato)copper(II), [Cu(3hpic)2], complex.     

Ionic Complexes of Polyacids and Cationic Surfactants

Comb-like ionic complexes were prepared from polyuronic acids (pectinic and alginic acids) and alkyltrimethylammonium surfactants bearing linear alkyl chains with 18, 20 and 22 carbon atoms. In the condensed state, these complexes were able to self-assemble in ordered structures which were thermally stable up to ∼200 °C. The complexes were analysed by DSC and WAXS/SAXS and compared to their analogous made from poly(γ-glutamic acid). They all adopt a biphasic layered structure in which the main chain and the alkyl side chain alternate with a nanometric periodicity. Alkyl side chains were partially crystallized in these complexes and they show reversible melting at temperatures within the 60-80 °C range depending on the length of the polymethylene segment.     

Novel temperature‐ and pH‐responsive graft copolymers composed of poly(L‐glutamic acid) and poly(N‐isopropylacrylamide)

A series of novel temperature‐ and pH‐responsive graft copolymers, poly(L ‐glutamic acid)‐g‐poly(N‐isopropylacrylamide), were synthesized by coupling amino‐semitelechelic poly(N‐isopropylacrylamide) with N‐hydroxysuccinimide‐activated poly(L ‐glutamic acid). The graft copolymers and their precursors were characterized, by ESI‐FTICR Mass Spectrum, intrinsic viscosity measurements and proton nuclear magnetic resonance (¹H NMR). The phase‐transition and aggregation behaviors of the graft copolymers in aqueous solutions were investigated by the turbidity measurements and dynamic laser scattering. The solution behavior of the copolymers showed dependence on both temperature and pH. The cloud point (CP) of the copolymer solution at pH 5.0–7.4 was slightly higher than that of the solution of the PNIPAM homopolymer because of the hydrophilic nature of the poly(glutamic acid) (PGA) backbone. The CP markedly decreased when the pH was lowered from 5 to 4.2, caused by the decrease in hydrophilicity of the PGA backbone. At a temperature above the lower critical solution temperature of the PNIPAM chain, the copolymers formed amphiphilic core‐shell aggregates at pH 4.5–7.4 and the particle size was reduced with decreasing pH. In contrast, larger hydrophobic aggregates were formed at pH 4.2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4140–4150, 2008     

Microspheres made of poly(epsilon-caprolactone)-based amphiphilic copolymers: potential in sustained delivery of proteins

Microspheres of amphiphilic multi-block poly(ester-ether)s (PEE)s and poly(ester-ether-amide)s (PEEA)s based on poly(epsilon-caprolactone) (PCL) were investigated as delivery systems for proteins. The interest was mainly focused on the effect of their molecular structure and composition on the overall properties of the microspheres, encapsulating bovine serum albumin (BSA) as a model protein. PEEs and PEEAs were prepared using a alpha,omega-dihydroxy-terminated PCL macromer (Mn= 2.0 kDa) as a hydrophobic component. Hydrophilic oxyethylene sequences were generated using poly(ethylene oxide)s (PEO)s of different molecular mass (Mn= 300-600 Da) in the case of PEEs, or 4,7,10-trioxa-1,13-tridecanediamine (Trioxy) and PEO150 (Mn= 150 Da) in the case of PEEAs. The copolymers showed a decrease of Tm and crystallinity values as compared with PCL. Within each class of copolymers, the bulk hydrophilicity increased with increasing the number of oxyethylene groups in the chain repeat unit. PEEAs were more hydrophilic than PEEs with a similar number of oxyethylene groups. Discrete spherical particles were prepared by both PEEs and PEEAs and their BSA encapsulation efficiency related to copolymer properties. Interestingly, the insertion of short hydrophilic segments is enough to significantly affect protein distribution inside microspheres and its release profiles, as compared to PCL microspheres. Different degradation rates and mechanisms were observed for copolymer microspheres, mainly depending on the distribution of oxyethylene units along the chain. The results highlight that a fine control over the structural parameters of amphiphilic PCL-based multi-block copolymers is a key factor for their application in the field of protein delivery.     

N-烷基化聚对苯二甲酰对苯二胺梳状高分子中烷基侧链对刚性主链堆积行为的影响

基于聚对苯二甲酰对苯二胺(PPTA), 采用N-烷基化方法制备了系列PPTACns(烷基侧链碳原子数n=8, 10, 12, 14, 16, 18)刚性主链梳状高分子, 利用DSC, XRD和FTIR等方法研究了其主链堆积行为、 分子链构象及热性能等与烷基侧链长度及结晶特性之间的关系. XRD和DSC结果表明, 当烷基侧链碳原子数达到14时, 烷基侧链发生结晶. XRD结果显示, PPTACns具有层状结构, 烷基侧链长度对主链层间距影响显著. FTIR研究发现, 烷基侧链的聚集状态对PPTACns分子链的构象产生较大影响, 伴随着烷基侧链结晶的熔融, PPTACns的分子链构象发生显著改变. 烷基侧链处于熔融状态的PPTACns的ν_C=O和γ_C-H谱带峰位与烷基侧链不结晶的PPTACn接近.     

Role of the in‐plane orientation of polyimide films in graphitization

Poly(amide acid) labeled with perylenetetracarboxydiimide (PEDI) was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), p‐phenylenediamine (PDA), and diamino‐PEDI. Poly(amide acid) was then reacted with sodium hydride and various kinds of alkyl iodides for transformation into various poly(amide ester)s. The cast films were imidized while fixed on glass substrates to give BPDA/PDA polyimide films. The degree of in‐plane molecular orientation (f) of the polyimides and their precursors, poly(amide acid) and poly(amide ester)s, were determined via measurements of the visible dichroic absorption at an incidence angle for a rodlike dye (PEDI) bound to the main chain. All precursor films showed relatively low degrees of in‐plane orientation. After imidization of the precursors fixed on glasses, however, striking spontaneous in‐plane orientation behavior was observed. The f value for polyimide film from a poly(amide acid) precursor was as high as 0.7–0.8. The f value for polyimide film from a methyl ester precursor, however, was lowered to 0.4–0.5, but it increased with the increasing size of the alkyl groups. Good correlations of the in‐plane orientation of the polyimide films with the tensile modulus of the films and the in‐plane orientation of the graphitized films were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3011–3019, 2001     

Preparation of Silk‐Like Fibers Designed by Self‐Assembled Ionic Polypeptides

Natural protein fibers, such as silk, having high‐performance characteristics have been important materials in biopolymer research. This article reports the development of a silk‐like extensible poly(α,L ‐amino acid) fiber inspired by self‐assembly of polypeptides in living systems. Electrostatic interaction was employed as the driving force for building the fiber, and we succeeded in spinning the fiber from an aqueous solution interface between poly(α,L ‐lysine) (PLL) and poly(α,L ‐glutamic acid) (PLG). When the PLL/PLG fiber was formed, the conformations of PLL and PLG were changed from random to β‐structures. A remarkable feature of the PLL/PLG fiber is the high extensibility. Mechanical stretching of the PLL/PLG fiber resulted in a change from an extensible fiber to a rigid and strong fiber. These features depend on the molecular conformation and the deviation in the amino acid composition of the PLL/PLG fibers. This concept and the poly(α,L ‐amino acid) fibers themselves allow the production of new protein fibers and aid the development of the science of protein folding as well as giving insight into the noncovalent interactions involved in self‐assembly.

SEM micrograph showing that the surface of the stretched fiber is smooth.     

Poly(epsilon-caprolactone)-poly(oxyethylene) multiblock copolymers bearing along the chain regularly spaced pendant amino groups

Poly(epsilon-caprolactone) (PCL) macromers (M(n) = 1.7-3.8 kDa) which contain one Z-protected -NH2 group per chain were synthesized by ring-opening polymerization of epsilon-caprolactone in the presence of Sn(oct)2 using as initiator a diamine prepared by condensation of N-Boc-1,6-hexanediamine and N(alpha)-Boc-N(epsilon)-Z-L-Lysine. The coupling of these macromers with -COCl end-capped poly(oxyethylene) (PEO), M(n) = 1.0 kDa, afforded amphiphilic multiblock poly(ether ester)s (PEEs) which have, along the chain, regularly spaced pendant protected amino groups. Deprotection, accomplished without chain degradation, yielded -NH2 groups available for further reactions. The molecular structure of macromers and PEEs was investigated by 1H NMR and SEC. DSC and WAXS analyses showed that macromers and copolymers were semicrystalline and their T(m) increased with increase in the molecular weight of PCL segments. The inherent viscosity values (0.25-0.30 dL x g(-1)), together with SEC analysis results, indicated moderate polymerization degrees.     

Synthesis and hydrolysis behaviour of poly(ester anhydrides) from polylactone precursors containing alkenyl moieties

Hydroxyl-group functional polylactones were prepared and converted to acid- terminated polyesters in a reaction with a series of alkenylsuccinic anhydrides containing 8, 12, or 18 carbons in their alkenyl chains. These polyester precursors were then linked into higher molecular weight poly(ester anhydrides) containing alkenyl moieties in their polyester blocks. The hydrolysis behaviour of the poly(ester anhydrides) was found to depend on the thermal properties of the polyester precursors. For poly(ester anhydrides) prepared from low molecular weight prepolymers with thermal transitions below 37 degrees C, the presence of hydrophobic alkenyl chains in the polyester precursors slowed the rate of weight loss. Poly(ester anhydrides) prepared from higher molecular weight prepolymers showed the opposite weight-loss behaviour; i.e., the crystallinity and thermal transitions of the alkenyl chain-containing poly(ester anhydrides) were low, and the weight loss was faster than for poly(ester anhydrides) without the alkenyl chains. The differences in length of the alkenyl chain, as such, had little effect on the hydrolysis behaviour and thermal properties of the poly(ester anhydrides).     

Convenient esterification of poly(γ-glutamic acid) produced by microorganism with alkyl halides and their thermal properties

The esterification of poly(γ-glutamic acid) (γ-PGA) produced by Bacillus subtilis F2-01 with alkyl halides was carried out at 60°C in N-methyl-2-pyrrolidinone (NMP) in the presence of sodium bicarbonate to obtain the corresponding esterified γ-PGA. The thermal properties of these γ-PGA esters were examined by differential scanning calorimetry and thermogravimetry. γ-PGA esters were more stable than free acid type γ-PGA, which decomposed at 210°C. Melting temperature (T_m) of γ-PGA esters could be observed at 230-250°C. T_m of γ-PGA n-alkyl esters reached a maximum at an alkyl chain length of n = 3. © 1995 John Wiley & Sons, Inc.     

Preparation of novel poly(ethylene oxide‐co‐glycidol)‐graft‐poly(ε‐caprolactone) copolymers and inclusion complexation of the grafted chains with α‐cyclodextrin

A well‐defined comblike copolymer of poly(ethylene oxide‐co‐glycidol) [(poly(EO‐co‐Gly)] as the main chain and poly(ε‐caprolactone) (PCL) as the side chain was successfully prepared by the combination of anionic polymerization and ring‐opening polymerization. The glycidol was protected by ethyl vinyl ether to form 2,3‐epoxypropyl‐1‐ethoxyethyl ether (EPEE) first, and then ethylene oxide was copolymerized with EPEE by an anionic mechanism. The EPEE segments of the copolymer were deprotected by formic acid, and the glycidol segments of the copolymers were recovered after saponification. Poly(EO‐co‐Gly) with multihydroxyls was used further to initiate the ring‐opening polymerization of ε‐caprolactone in the presence of stannous octoate. When the grafted copolymer was mixed with α‐cyclodextrin, crystalline inclusion complexes (ICs) were formed, and the intermediate and final products, poly(ethylene oxide‐co‐glycidol)‐graft‐poly(ε‐caprolactone) and ICs, were characterized with gel permeation chromatography, NMR, differential scanning calorimetry, X‐ray diffraction, and thermogravimetric analysis in detail. The obtained ICs had a channel‐type crystalline structure, and the ratio of ε‐caprolactone units to α‐cyclodextrin for the ICs was higher than 1:1. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3684–3691, 2006     

Synthesis of Polyelectrolytes Bearing Phosphorylcholine Moieties

We report on the modification of the polyelectrolytes poly(L ‐glutamic acid) (PGA), poly(acrylic acid) (PAA), and poly(L ‐lysine) (PLL) with side groups bearing phosphorylcholine (PC) groups. Two different side chains were synthesized from monoamino tri‐ or tetraethylene glycol, both with PC group linked to the OH end: the tert‐butyloxycarbonyl protected compounds BOCNH(EO)_nPC (n = 2, 3) and the succinylated compound SucNH(EO)₃PC. BOCNH(EO)_nPC was deprotected and the resulting amine was condensed with PGA or PAA and SucNH(EO)₃PC was directly coupled to PLL. Degrees of substitution as high as 80% were obtained with the method described. These polyelectrolytes are potential candidates to fabricate multilayers with protein repellent properties.

     

Mechanism of high thermal stability of commercial polyesters and polyethers conjugated with bio‐based caffeic acid

In previous report, we discovered that a novel improvement technique to enhance the thermal properties of poly(L ‐lactide)s (PLLAs) by terminal conjugation with 3,4‐diacetoxycinnamic acid (DACA). In this study, we clarified the mechanism of the enhancement of thermal stability by using commercial polyesters and polyethers. The effect of thermal improvement by the terminal conjugation of DACA on poly(DL ‐lactide), poly(ε‐caprolactone), and poly(ethylene glycol) was almost the same as about 100 °C increase. The amount of residual tin catalyst, which enhances the thermal degradation of polyesters, was reduced at undetected level after the terminal conjugation of DACA probably due to the removal of tin during DACA conjugation process. Furthermore, the π‐π stacking interactions of DACA units and the chemical protection of terminal hydroxyl groups, which enhances intramolecular scission, were also important for the high thermal stability. We clarified that the extreme high thermal stability by DACA conjugation was induced by these above mechanisms. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Semi‐Interpenetrated Hydrogels‐Microfibers Electroactive Assemblies for Release and Real‐Time Monitoring of Drugs

Simultaneous drug release and monitoring using a single polymeric platform represents a significant advance in the utilization of biomaterials for therapeutic use. Tracking drug release by real‐time electrochemical detection using the same platform is a simple way to guide the dosage of the drug, improve the desired therapeutic effect, and reduce the adverse side effects. The platform developed in this work takes advantage of the flexibility and loading capacity of hydrogels, the mechanical strength of microfibers, and the capacity of conducting polymers to detect the redox properties of drugs. The engineered platform is prepared by assembling two spin‐coated layers of poly‐γ‐glutamic acid hydrogel, loaded with poly(3,4‐ethylenedioxythiophene) (PEDOT) microparticles, and separated by a electrospun layer of poly‐ε‐caprolactone microfibers. Loaded PEDOT microparticles are used as reaction nuclei for the polymerization of poly(hydroxymethyl‐3,4‐ethylenedioxythiophene) (PHMeDOT), that semi‐interpenetrate the whole three layered system while forming a dense network of electrical conduction paths. After demonstrating its properties, the platform is loaded with levofloxacin and its release monitored externally by UV–vis spectroscopy and in situ by using the PHMeDOT network. In situ real‐time electrochemical monitoring of the drug release from the engineered platform holds great promise for the development of multi‐functional devices for advanced biomedical applications.     

Novel π-Conjugated Poly（Schiff base） Containing Thiazole and Tetrathiatetrahyd ropentalene Moieties

A new kind of π-conjugated heterocyclic poly(Schiff base) was firstly prepared by the condensation reaction between tetrathiatetrahydropentalene-type diketone and bithiazole-diamine in good yields. The polymers were characterized by VPO, FTIR and ^1H NMR spectroscopy. A large bathochromic shift was observed in UV-Vis spectra for these polymers due to the π-π* transition in the conjugated main chain. Brief examination indicated that the nitrogen-and sulfur-containing polymers exhibited an excellent chelating tendency to metal ions and the corresponding polymeric complexes would be expected to have potential in applications.     

Water‐Soluble Polypeptides at Aqueous Interface Produce Extensible Silk‐Like Fiber

A silk‐like extensible poly(α,L ‐amino acid) fiber is created by self‐assembly of poly(α,L ‐lysine) and poly(α,L ‐glutamic acid) at their aqueous solutions' interface. Distinguishing features of the PLL/PLG fiber are the high extensibility and good stretch. Stretching after spinning changes this fiber to a rigid and strong one. The concept and the poly(α,L ‐amino acid) fibers themselves open doors for the production of new protein fibers which are more silk‐ and wool‐like.     

Blend of electroactive poly(3-dodecylthiophene) with comb-like alkylated polyacrylate

The conformational mode change of the stiff alkylated polymer, poly(3-dodecyl thiophene) (PDDT), with a flexible comb-like coil poly(octadecyl acrylate) (PODA), and the effect of intermolecular interaction between these two alkylated polymers with different chemical structure of the backbone were investigated using UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimeter (DSC), and wide-angle x-ray diffraction (WAXD). In addition to the characteristics of thermochromism, a homogeneous one phase was observed above 175°C when the PODA content was 10 wt % or less. Increased conductivity in the PDDT/PODA blend due to the highly conjugated π-system of PDDT backbone was observed in the presence of nonelectroactive PODA. A red-shift of absorption maximum of PDDT/PODA blend observed in solid state at room temperature. From the FTIR spectra, the gauche-trans conformational structure change of methylene units was investigated in two alkylated polymer blends. The increase of combined heat of fusion of the alkyl side chain melting of PDDT and the endothermic peak of PODA, as well as the interlayer d-spacing of PDDT main chain were also observed with the addition of PODA in blends. A more ordered conformational structure of rigid rod backbone of PDDT was induced due to the attractive intermolecular interaction which can cause cocrystallization between the alkylated side chains of two polymers. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 :1025–1041, 1997