PPO Chain Research Articles

Artificial Chaperone-Assisted Refolding of Bovine Carbonic Anhydrase Using Molecular Assemblies of Stimuli-Responsive Polymers

An artificial chaperone, which can decrease the protein aggregation and increase the reactivation yield of denatured protein in a fashion similar to natural chaperone, was newly developed using stimuli-responsive polymers. It has previously been reported that the addition of poly(propylene oxide)-phenyl-poly(ethylene glycol) (PPOn-Ph-PEG) with the unit number of PPO (n) 33 could enhance the refolding of bovine carbonic anhydrase (Kuboi et al. J. Chromatogr. B 2000, 243, 213). PPO-Ph-PEG with a large PPO chain (n = 50) was synthesized and the surface properties were characterized by both the relative fluorescence intensity of 1-anilino-8-naphthalene sulfonate (ANS) and the fluidity determined by diphenylhexatriene (DPH). The variation of ANS intensity and DPH fluidity is shown in a diagram as functions of temperature and polymer concentration. The high values of ANS intensity and fluidity of PPO50-Ph-PEG were obtained in a relatively wide conditional range (more than 0.08 mM and more than 15 degrees C) although the conditions showing the high values of PPO33-Ph-PEG were restricted (more than 0.1 mM and more than 40 degrees C). It was also found that molecular assemblies of PPOn-Ph-PEG with diameters of 7-18 nm were formed in the above conditions. On the basis of the surface properties of their polymer self-assemblies, the possibility of using them as an artificial chaperone was investigated. The effect of the addition of PPOn-Ph-PEG on the reactivation yield of a model protein, carbonic anhydrase from bovine (CAB), and the optical density of the solution was examined at various temperatures and concentrations. The reactivation yield of CAB was strongly enhanced and the aggregate formation (the optical density) was suppressed by adding PPOn-Ph-PEG in the above conditions, which show high ANS intensity and DPH fluidity. Especially in the presence of 0.1 mM PPO50-Ph-PEG, the reactivation yield of CAB reached approximately 100% at 40-55 degrees C. It was thus found that self-assemblies of the present polymer could be utilized as an artificial chaperone by selecting suitable stimuli conditions.

Small-angle X-ray scattering study of the interaction of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers with lipid bilayers.

The relationship between molecular architecture and the nature of interactions with lipid bilayers has been studied for a series of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers using small-angle X-ray scattering (SAXS) and thermal analysis (differential scanning calorimetry, DSC). The number of molecular repeat units in the hydrophobic poly(propylene oxide), PPO, block has been found to be a critical determinant of the nature of triblock copolymer-lipid bilayer association. For dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-based biomembrane structures, polymers possessing a PPO chain length commensurate with the acyl chain dimensions of the lipid bilayer yield highly ordered, swollen lamellar structures consistent with well-integrated (into the lipid bilayer) PPO blocks. Triblock copolymers of lesser PPO chain length yield materials with structural characteristics similar to a simple dispersion of DMPC in water. Increasing the concentration (from 4 to 12 mol %) of well-integrated triblock copolymers enhances the structural ordering of the lamellar phase, while concentrations exceeding 16 mol % result in the formation of a hexagonal phase. Examination of temperature-induced changes in the structure of these mesophases (complex fluids) reveals that if the temperature is reduced sufficiently, all compositions exclude polymer and thus exhibit the characteristic SAXS pattern for hydrated DMPC bilayers. Increasing the temperature promotes better insertion of the polymers possessing PPO chain lengths sufficient for membrane insertion. No temperature-induced structural changes are observed in compositions prepared with PEO-PPO-PEO polymers that feature PPO length insufficient to permit full incorporation into the lipid bilayer.

Crystallization and orientation behaviors in isotactic polystyrene and poly(2,6-dimethylphenylene oxide) blends

The crystallization and orientation behavior in the miscible iPS/PPO blends were studied aiming at producing oriented materials consisting of iPS crystals and amorphous PPO chains. Oriented films of iPS/PPO blends were prepared by drawing the melt-quenched blend films. The films were heat-treated under constraint at the drawing temperature so as to crystallize the molecular chains of iPS in the oriented state. The crystallinity and the crystal orientation in the drawn annealed films were studied by the wide-angle X-ray diffraction (WAXD), and the orientation behaviors of molecular chains were analyzed by polarized FTIR spectroscopy. WAXD diagrams show the presence of the highly oriented crystalline structure of iPS in the drawn annealed films of pure iPS and iPS/PPO=7/3 blend. The polarized FTIR spectra of drawn annealed films suggest that the molecular orientation of the amorphous chains of PPO and iPS is markedly relaxed by the heat treatment, although the orientation of iPS with 3 1 helical structure was retained during the oriented crystallization. It was concluded that the drawn annealed samples of the iPS/PPO=7/3 blend consist of highly oriented iPS crystals and nearly isotropic amorphous materials. The mechanical properties of the oriented iPS/PPO blends were measured not only in the stretching direction but also perpendicular to the stretching direction. It was shown that the ultimate strength in the perpendicular direction is 4–5 times higher in the drawn annealed film of iPS/PPO=7/3 blend than in the drawn annealed iPS. The improvement in the vertical strength in the blend is discussed in relation to the structural characteristics of the iPS/PPO blend.

Preparation and characterization of polypseudorotaxanes based on block-selected inclusion complexation between poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) triblock copolymers and alpha-cyclodextrin.

A series of new polypseudorotaxanes were synthesized in high yields when the middle poly(ethylene oxide) (PEO) block of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) triblock copolymers was selectively recognized and included by alpha-cyclodextrin (alpha-CD) to form crystalline inclusion complexes (ICs), although the middle PEO block was flanked by two thicker PPO blocks, and a PPO chain had been previously thought to be impenetrable to alpha-CD. X-ray diffraction studies demonstrated that the IC domains of the polypseudorotaxanes assumed a channel-type structure similar to the necklace-like ICs formed by alpha-CD and PEO homopolymers. Solid-state CP/MAS (13)C NMR studies showed that the alpha-CD molecules in the polypseudorotaxanes adopted a symmetrical conformation due to the formation of ICs. The compositions and stoichiometry of the polypseudorotaxanes were studied using (1)H NMR, and a 2:1 (ethylene oxide unit to alpha-CD) stoichiometry was found for all polypseudorotaxanes although the PPO-PEO-PPO triblock copolymers had different compositions and block lengths, suggesting that only the PEO block was closely included by alpha-CD molecules, whereas the PPO blocks were uncovered. The hypothesis was further supported by the differential scanning calorimetry (DSC) studies of the polypseudorotaxanes. The glass transitions of the PPO blocks in the polypseudorotaxanes were clearly observed because they were uncovered by alpha-CD and remained amorphous, whereas the glass-transition temperatures increased, because the molecular motion of the PPO blocks was restricted by the hard crystalline phases of the IC domains formed by alpha-CD and the PEO blocks. The thermogravimetric analysis (TGA) revealed that the polypseudorotaxanes had better thermal stability than their free components due to the inclusion complexation. Finally, the kinetics of the threading process of alpha-CD onto the copolymers was also studied. The findings reported in this article suggested interesting possibilities in designing other cyclodextrin ICs and polypseudorotaxanes with block structures.

Intercalation of poly(propyleneoxide) amines (Jeffamines) in synthetic layered silicas derived from ilerite, magadiite, and kenyaite

The synthetic layered silicates Na+-ilerite (Na2Si8O17·nH2O), Na+-magadiite (Na2Si14O29·nH2O), and K+-kenyaite (K2Si20O41·nH2O) were converted to the corresponding layered silicic acids (silicas) through the stoichiometric replacement of the gallery alkali metal ions with protons. The protonated derivatives were subsequently used as hosts for the intercalation of poly(propyleneoxide) amines that are normally used as curing agents for thermoset polymers. The amines of interest were the commercially available α,ω-diamines known as Jeffamine D-series amines and Jeffamine T-series glycolitic triamines with molecular weights in the range 400–5000. Low molecular weight Jeffamines (MW∼400) intercalate in all three layered silicas as lateral monolayers in which the PPO chains are oriented parallel to the silica sheets and the gallery heights are restricted to values of 4.0–4.9 A. Amines with MW values of 1000–5000 afford intercalates in which the gallery heights are 2.6–9.0 times as large as the thickness of the host layers and the PPO chains adopt coiled conformations in the galleries. Substantial de-intercalation of the high MW amines occurs upon mild extraction with ethanol–water mixtures, as expected for an intercalation mechanism that involves hydrogen bonding between the amine head groups and silanol groups on the basal surfaces of the host silicas. The ability to control the amine to silica ratios in these intercalates should prove to be advantageous in applying these materials for the preparation of epoxy-layered silicates nanocomposites and other thermoset nanocomposites derived from amine monomers.

Structure and Electrical Properties of Potassium-Doped Siloxane-Poly(oxypropylene) Ormolytes

The structure and the ionic conduction properties of siloxane-poly(oxypropylene) (PPO) hybrids doped with different potassium salts (KCF3SO3, KI, KClO4 and KNO2) are reported for two polymer molecular weights (300 and 4000 g/mol), labelled PPO300 and PPO4000, respectively. The doping concentration, related to the concentration of the ether type oxygen of the PPO chain, is the same whatever the salt and verifies [O]/[K] = 20. Ionic room temperature conductivity shows the highest value for the KCF3SO3 doped PPO4000 hybrid (4 × 10−7 Ω−1 ċcm−1). The structure of these hybrids was investigated by X-ray powder diffraction (XRPD) and X-ray absorption spectroscopy (EXAFS and XANES) at the potassium K-edge (3607 eV). XRPD results show that the hybrid matrix is always amorphous and the formation of secondary potassium phases is observed for all the samples, except for the KCF3SO3 doped PPO4000 hybrid. EXAFS results evidence a good correlation between the ionic conductivity and the presence of oxygen atoms as first neighbours around potassium.

Normal and Segmental Mode Dynamics of End-Functionalized Poly(propylene oxide) by Dielectric Relaxation Spectroscopy and Dynamic Mechanical Spectroscopy

An investigation was carried out of the normal and segmental dynamics of poly(propylene oxide) (PPO) chains with (1) symmetrical dipole inversion and (2) three-arm star configuration. PPO chains exhibit, in addition to the transverse dipole moment component (μ⊥) that gives rise to segmental (α) process, a persistent cumulative dipole moment along the chain contour (μ∥) that can be relaxed via the normal mode (αN) process. Data were generated by broad-band dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS), and the findings were contrasted. In comparison with the previous studies of PPO dynamics, our DRS and DMS results were generated over a broader range of frequency and temperature and on samples of a wider range of molecular architecture (molecular weight, type, and functionality of end group). Segmental and normal mode spectra were thermodielectrically simple (with the KWW β parameter of ca. 0.51). The average relaxation times for the segmental mode (τS) from DRS and DMS...

Siloxane–polypropyleneoxide hybrid ormolytes: structure–ionic conductivity relationships

Siloxane–polypropyleneoxide (PPO) hybrids doped with sodium perchlorate (NaClO 4) obtained by the sol–gel process were prepared with two PPO molecular weights (2000 and 4000 g/mol) and two sodium concentrations such as [O]/[Na]=4 and 15 (O being the ether-type oxygen of PPO chains). The structure of these hybrids was investigated by 23 Na nuclear magnetic resonance (NMR) and X-ray absorption spectroscopy at the sodium K-edge (1071.8 eV) whereas complex impedance spectroscopy was used to determine their ionic conductivity. Three sodium sites were determined by NMR. The conjunction of NMR and X-ray absorption results allows us to identify one site in which Na is in a NaCl structure, a second one in which Na is in contact with perchlorate anions. The third site is attributed to mobile sodium species in interaction with the polymeric chain. The relative proportion of the different sites in the materials determines the ionic conductivity of the materials at room temperature: the largest ionic conductivity is 8.9×10 −6 Ω −1 cm −1 and is observed on the material with the larger amount (at least 85%) of sites in which sodium interacts with the polymer.

Thermal degradation of poly(ethylene oxide–propylene oxide–ethylene oxide) triblock copolymer: comparative study by SEC/NMR, SEC/MALDI-TOF-MS and SPME/GC-MS

By comparing size exclusion chromatography/matrix assisted laser desorption ionisation (SEC/MALDI) and SEC/NMR spectra from virgin poly(ethylene oxide–propylene oxide–ethylene oxide) triblock copolymer, we were able to understand the bimodal distribution observed in poloxamer 407. Propylene oxide, isomerised to allyl alcohol during polymerisation, eventually forms a Poly(ethylene oxide–propylene oxide) diblock copolymer when EO is added to the feed. The oxidative thermal degradation of poloxamer 407 at 80°C in air was studied. We found by MALDI that degradation starts after 21 days in the PPO block of the copolymer. This result was confirmed by solid phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS): The first volatile degradation product to appear is 1,2-propanediol,1-acetate,2-formate. The structure of this molecule suggests that a six-ring intramolecular decomposition reaction of the PPO chain occurs at the very beginning of the polymer breakdown. Thus, the secondary hydroperoxide formed on the PPO chain plays a major role on the thermoxidation of poloxamer materials.

Study of laser action of Coumarine-153 incorporated in sol–gel made silica/poly(propylene oxide) nanocomposite gels

Coumarin-153 (C-153) has been incorporated by the sol–gel method into transparent nanocomposite matrices made by using a precursor composed of a poly(propylene oxide) (PPO) chain covalently linked by urea bridges with two end triethoxysilane groups. The solid gels can be used without any further treatment as active components in a dye laser, providing a rather wide range of laser emission. This range is further widened by exploiting the solvatochromic effect of coumarin and the different polarity of the solubilization sites provided by nanocomposites of various PPO chain sizes.

Orientation and relaxation study of polystyrene: Polystyrene/poly(phenylene oxide) blends

Polarization modulation infrared linear dichroism has been used to study the molecular orientation and relaxation of polystyrene/poly(2,6-dimethyl 1,4-phenylene oxide) (PS/PPO) miscible blends, containing up to 20% PPO, during and after a rapid uniaxial deformation above Tg. In general, it is found that both the PS and PPO chain orientation functions increase with stretching rate and PPO content, and decrease with temperature. For all blends investigated, between Tg + 5 and Tg + 13 °C, the relaxation occurs at the same rate for PS and PPO and, therefore, the relaxation times calculated are similar indicating, under those conditions, a strong relaxation coupling between the two polymers at both short and long times. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1405–1415, 2000

NOVEL CERAMER MATERIALS BASED ON JEFFAMINE® POLY(PROPYLENE OXIDE) OLIGOMERS AND TETRAMETHOXYSILANE

Novel hybrid organic–inorganic network materials have been generated based on poly(propylene oxide) (PPO) and tetramethoxysilane (TMOS). The PPO source chosen for this study was the family of JEFFAMINE®s often employed as epoxy curing agents. These materials were end–functionalized with trialkoxysilane groups which later were exploited in the sol–gel reaction. The sol–gel variables of water and acid catalyst concentration had little influence on the final structure and properties of the resulting network materials for the ranges probed. Increasing the TMOS content, however, generated a structure that angle X-ray scattering revealed a correlation length associated with a silicate phase separated by PPO chains, which increased with PPO molecular weight, as expected.

Thermally-stimulated depolarization current studies in chemically doped poly(2,6-dimethyl-1,4-phenylene oxide)

The electret properties of solution-grown poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) films doped with 7,7,8,8-tetracyanoquinodimethane, tetracyanoethylene, 2,4,7-trinitro-9-fluorenone and I 2 have been studied by measuring thermally-stimulated depolarization currents (TSDC) as a function of dopant concentration varying from 0.25 to 1.00 wt% for identical conditions of polarizing field, temperature and time. The depolarization behaviour of poled doped PPO film exhibits a dopant-concentration dependent single relaxation around 438 K maximum in the TSDC spectra. This is attributed to formation of charge-transfer complexes with the PPO chain by interstitially placed dopants. The existence of such a complex is confirmed by ultraviolet-visible and infrared absorption spectral measurements. The dopant-concentration dependent increase in the magnitude of the TSDC peak is attributed to the enhanced aligned dipole density.

Structure of grafted products of maleic anhydride and poly(propylene oxide)

Poly(propylene oxide) (PPO) is widely applied for the preparation of thermoplastic elastomers, surfactants and additives. A well-defined polar modification of poly(propylene oxide) was achieved by radical grafting with maleic anhydride (MAn). A protection of hydroxyl end-groups of PPO was realized by acetylation to prevent side-reactions of these groups with MAn. An isolation of highly grafted parts from the reaction products was carried out to obtain suitable samples for a structure characterization. FTIR spectroscopy proved a characteristic shift of the carbonyl valence vibrations of cyclic anhydrides to higher wave numbers due to grafting reactions. It was proven by 13C NMR spectroscopy that the grafting of MAn occurs onto both methine and methylene carbons of the PPO chain. Monosubstituted succinic anhydrides were formed as graft units. Furthermore, in products synthesized with a high initial concentration of MAn (20 wt.-%) beside single units a small amount of oligo(maleic anhydride) grafts was formed.

Structure of grafted products of maleic anhydride and poly(propylene oxide)

Poly(propylene oxide) (PPO) is widely applied for the preparation of thermoplastic elastomers, surfactants and additives. A well-defined polar modification of poly(propylene oxide) was achieved by radical grafting with maleic anhydride (MAn). A protection of hydroxyl end-groups of PPO was realized by acetylation to prevent side-reactions of these groups with MAn. An isolation of highly grafted parts from the reaction products was carried out to obtain suitable samples for a structure characterization. FTIR spectroscopy proved a characteristic shift of the carbonyl valence vibrations of cyclic anhydrides to higher wave numbers due to grafting reactions. It was proven by 13C NMR spectroscopy that the grafting of MAn occurs onto both methine and methylene carbons of the PPO chain. Monosubstituted succinic anhydrides were formed as graft units. Furthermore, in products synthesized with a high initial concentration of MAn (20 wt.-%) beside single units a small amount of oligo(maleic anhydride) grafts was formed.

Adsorption of PEO−PPO−PEO Triblock Copolymers at the Solid/Liquid Interface: A Surface Plasmon Resonance Study

Poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) triblock copolymers are used in a wide range of industrial applications from detergents to pharmaceutical materials. We have employed surface plasmon resonance (SPR) to monitor the adsorption of these materials, from aqueous solutions to a model hydrophobic surface. The effect of varying the PPO or PEO block size of the copolymer on adsorption has been investigated, and a linear increase in SPR angle shift with increasing PPO or PEO chain length is observed. The SPR angle shifts show a greater increase in SPR angle with increasing PPO block size compared to an equivalent increase in PEO block size. This has been explained by considering the effect each block has on the dielectric properties of the adsorbed polymer at the interface. The presence of micelles in solution and their influence on Pluronic adsorption has also been considered, and adsorption from micellar solutions has been determined to be dependent on the PPO content ...

H NMR Relaxation Studies of the Micellization of a Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Triblock Copolymer in Aqueous Solution

1H nuclear magnetic resonance (NMR) relaxation studies of the temperature-induced micellization of a poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide), PEO−PPO−PEO, block copolymer in aqueous solution were performed in the range 280−345 K. 1H NMR spectra of the block copolymer were well resolved, thus allowing us to probe specifically the methyl and methylene relaxation processes in the PPO and PEO blocks, respectively. Interpretation of the relaxation data in terms of the Hall−Helfand correlation function leads to four distinct correlation times for the PPO and PEO blocks. The slower correlation time in the PPO block was identified as the Zimm−Rouse first normal mode of the copolymer and served to determine the hydrodynamic radius, RH, of the unimers and the micelles. On a more local scale, the behavior of the correlation time for segmental motions in the PPO block indicates an extension of the PPO chains in micelles relative to the unimers. This conformational change is related to the form...

Thermotropic liquid‐crystalline aromatic polyester‐graft‐poly(2,6‐dimethyl‐1,4‐phenylene oxide) copolymers

AbstractDicarboxy‐terminated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) macromonomers were prepared and subjected to the preparation of tailor‐made aromatic thermotropic liquid‐crystalline (LC) polyester‐graft‐PPO copolymers. The macromonomers were obtained by hydrolysis of dimethyl carboxylate‐terminated PPO macromonomers without cleavage of the PPO chains, which were derived from PPO oligomers with a terminal phenolic OH‐group and a bromo derivative of isophthalate. The tailor‐made aromatic thermotropic LC graft copolymers were prepared by direct polycondensation from the dicarboxy‐terminated macromonomers, p‐hydroxybenzoic acid, aromatic dicarboxylic acids and diphenols at definite mole ratios in pyridine in the presence of diphenyl chlorophosphate as a condensation reagent. The polyester‐graft‐PPO copolymers are thermally stable up to 280–300°C and show a thermotropic LC nematic phase in spite of introduction of PPO grafts on the polyester backbones.

Ionic conduction in LiScn/Dimethylformamide/Poly(propylene oxide) system II. Mobility of lithium and thiocyanate ions

AbstractIonic conductivity σ, shear viscosity η, and glass transition temperature Tg were measured on systems composed of lithiumthiocyanate LiSCN, N,N‐dimethylformamide (DMF), and poly (propylene oxide) (PPO) over wide ranges of LiSCN concentration C and DMF content Φ. Using the dissociation constant of LiSCN reported in Part I, we have determined the concentration n of Li+ and SCN− ions and then the mobility μ from σ. Data indicate that in the binary system of LiSCN/PPO, the σ versus C curve exhibits a maximum ca. C = 0.3 mol/L. In low C range, μ is independent of C but decreases with C in the range of C > 0.3 mol/L. Similar n dependence of μ is seen in the ternary systems containing DMF. The ratio of μ0/μ (C) is lower than the ratio of viscosity η(C)/η0 where μ0 and η0 indicate the values at infinite dilution of LiSCN. Thus the friction coefficient ςion for the translational diffusion of the ions is not proportional to the macroscopic viscosity. Relationship between μ and the monomeric friction ςp for the segmental motion of the PPO chains is also discussed based on the data of Tg and the Williams‐Landel‐Ferry equation. ©1995 John Wiley & Sons, Inc.

Differential Anomalous X-ray Scattering from an Amorphous Polymer Electrolyte: [PPO]xZnBr2

Differential anomalous X-ray scattering (DAS) and extended X-ray absorption fine structure (EXAFS) were used to determine the local structure surrounding the ions in amorphous polymer electrolyte complexes of poly(propylene oxide) and ZnBr 2 : [PPO] 6 ZnBr 2 and [PPO] 16 ZnBr 2 . On the basis of our results, we propose that ZnBr 2 dissociates to form mainly ZnBr 4 2- and Zn(O) 4 2+ , where (O) is an ether oxygen on a PPO chain. This observation is contrasted with aqueous ZnBr 2 , where ZnBr 2 , ZnBr 3 - , and ZnBr 4 2- are all observed in the estimated proportions of 2:4:3, respectively. This paper describes the DAS method and its application to structure determination in a multicomponent, amorphous system. In systems with n components, where one or more of the species is a heavy atom, DAS reduces the scattering intensity from a weighted sum of n(n+1)/2 partial structure factors to a sum of partial structure factors which only include the heavy atom of interest