Glutamine-binding protein (GlnBP) from Escherichia coli is a prototypical periplasmic binding pro... more Glutamine-binding protein (GlnBP) from Escherichia coli is a prototypical periplasmic binding protein that has been crystallized in an apo, "open" conformation, with its two domains far apart, and a holo, "closed" form, with proximal domains that engulf the cognate L-Gln ligand. A fundamental question about such large-scale conformational transitions-whether the closed state exists in the absence of ligand-is a matter of controversy in the case of GlnBP. Previously, NMR observations have indicated no evidence of the closed form, whereas experimentally validated computations have suggested a remarkable ~40% population. Here, a paramagnetic NMR strategy designed to specifically detect the putative apo-closed species shows that a major population of the latter is highly improbable. Further, NMR residual dipolar couplings collected under three anisotropic conditions fail to reveal differential domain alignment (which would otherwise signal interdomain dynamics) and establish that the average solution conformation is satisfied by the apo-open crystal structure. Our results indicate that the computational prediction of large-scale interdomain motions is far from trivial and may lead to grossly erroneous conclusions without proper experimental validation.
Colloids and surfaces. B, Biointerfaces, Jan 2, 2018
The present study was aimed to examine the interaction of two bile salts viz. sodium cholate (NaC... more The present study was aimed to examine the interaction of two bile salts viz. sodium cholate (NaC) and sodium deoxycholate (NaDC) with three ethylene polyoxide-polypropylene polyoxide (PEO-PPO-PEO) triblock copolymers with similar PPO but varying PEO micelles with a focus on the effect of pH on mixed micelles. Mixed micelles of moderately hydrophobic PluronicP123 were examined in the presence of two bile salts and compared with those from very hydrophobic L121 and very hydrophilic F127. Both the bile salts increase the cloud point (CP) of copolymer solution and decreased apparent micelle hydrodynamic diameter (D). SANS study revealed that P123 forms small spherical micelles showing a decrease in size on progressive addition of bile salts. The negatively charged mixed micelles contained fewer P123 molecules but progressively rich in bile salt. NaDC being more hydrophobic displays more pronounced effect than NaC. Interestingly, NaC shows micellar growth in acidic media which has been ...
The micellization, intermolecular interaction and microenvironment of molecular segments in the m... more The micellization, intermolecular interaction and microenvironment of molecular segments in the mixed aqueous solution of PEO-PPO-PEO triblock copolymer (Pluronic(superscript ®) F88, P84 and P123) and Surfynol(superscript ®) 104 (S1O4) were studied by nuclear magnetic resonance method. The results showed that the addition of S1O4 decreased the critical micellization temperature of copolymer. When its concentration was 0.5g/L, the most reduction was up to more than 10℃ for F88, which was most hydrophilic in the selected copolymers. This reduction was caused by the hydrophobic interaction between S1O4 molecules and PPO segments. The addition of S104 enhanced the hydration of PEO segments most obviously for P123. And S104 slightly increased the hydration of PPO segments before the micellization, but obviously decreased their hydration after micellization, which was attributed to the hydrophobic interaction mentioned above and temperature rising. This effect was most observable for F88.
FTIR spectroscopy was applied to investigate the interaction of anionic surfactant Sodium Dodecyl... more FTIR spectroscopy was applied to investigate the interaction of anionic surfactant Sodium Dodecyl Sulfate (SDS) and Bovine Serum Albumin (BSA). Amide band I of BSA was analyzed to obtain the change in secondary structure of BSA when different concentration of SDS was added and during different interaction period. In short interaction period and at low concentration of SDS, the alpha-helixes increased and the random coil decreased. In long interaction period or at high concentration of SDS, SDS unfolded the protein by decreasing the alpha-helix structure and increasing the random coil.
The micellization of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-P... more The micellization of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer (Pluronic L64: EO 13 PO 30 EO 13) with the presence of various sodium halides (NaF, NaCl, NaBr and NaI) was studied by Fourier transform infrared (FTIR) spectroscopy. The critical micelle temperature (CMT) of Pluronic L64 in the salt solution decreased with the addition of salt and the anion effect followed the sequence: F À > Cl À > Br À > I À. The deconvolution method was used to resolve the overlapping bands in the CO stretching region. The deconvoluted spectra provide information about the microenvironmental changes of ethylene oxide (EO) and propylene oxide (PO) blocks in the salt solution. Both the PEO and PPO blocks are dehydrated at lower temperature in the salt solution. The standard enthalpies (DH 0) and entropies (DS 0) of micellization for copolymer, PEO and PPO blocks, decreased by the addition of salt. Thus, it is deduced that the salt-induced decrease of enthalpy of micellization contributes to the decrease of CMT. The results reveal the leading role of saltwater interaction in promoting the micellization of PEO-PPO-PEO copolymer on addition of salt.
A novel method has been developed to prepare vesicles from aqueous solutions of poly(ethylene oxi... more A novel method has been developed to prepare vesicles from aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, by adding anionic surfactant sodium dodecyl sulfate (SDS) and inorganic salt NaF. As determined by TEM and dynamic light scattering (DLS) measurements, the average diameter of vesicles is about 800 nm having 50 nm outer shell thickness. Identifying hydrophobic interactions between the block copolymers and the microenvironments around the vesicles using FTIR, 1H NMR, and fluorescence spectroscopy techniques revealed the vesicle formation mechanism. The spontaneously formed vesicles were further cross-linked by converting the terminal hydroxyl groups of block copolymers into aldehydes, and then chemically bridging the polymer chains by the reaction between aldehydes and diamine compounds. The cross-linked vesicles are proved much more stable than free vesicles even at higher dilutions. The obtained vesicles with good stability and biocompatibility are promising candidates for widespread applications.
The acid effect on the aggregation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene ox... more The acid effect on the aggregation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers EO(20)PO(70)EO(20) has been investigated by transmission electron microscopy (TEM), particle size analyzer (PSA), Fourier transformed infrared, and fluorescence spectroscopy. The critical micellization temperature for Pluronic P123 in different HCl aqueous solutions increases with the increase of acid concentration. Additionally, the hydrolysis degradation of PEO blocks is observed in strong acid concentrations at higher temperatures. When the acid concentration is low, TEM and PSA show the increase of the micelle mean diameter and the decrease of the micelle polydispersity at room temperature, which demonstrate the extension of EO corona and tendency of uniform micelle size because of the charge repulsion. When under strong acid conditions, the aggregation of micelles through the protonated water bridges was observed.
Solution 1H NMR techniques were used to characterize the interaction of urea with poly(ethylene o... more Solution 1H NMR techniques were used to characterize the interaction of urea with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. The urea was established to interact selectively with the PEO blocks of the block copolymer, and the interaction sites were found not to change with increasing temperature. Such interactions influence the self-assembly properties of the block copolymer in solution by increasing the hydration of the block copolymers and stabilizing the gauche conformation of the PPO chain. Therefore, urea increases the critical micellization temperature (CMT) values of PEO-PPO-PEO copolymers, and the effect of urea on the CMT is more pronounced for copolymers with higher PEO contents and lower for those with increased contents of PPO segments.
Effect of 1-butyl-3-methyl-imidazolium bromide (BmimBr) on the aggregation behavior of PEO-PPO-PE... more Effect of 1-butyl-3-methyl-imidazolium bromide (BmimBr) on the aggregation behavior of PEO-PPO-PEO Pluronic P104 aqueous solution was studied by Fourier transform infrared (FTIR) spectroscopy, freeze fracture transmission electron microscopy (FF-TEM), dynamic light scattering (DLS), and NMR spectroscopy. When the BmimBr concentration was below 1.232 mol/L, the critical micelle temperature (CMT) of Pluronic P104 remained constant, while the size of micelles increased with increasing the BmimBr concentration; above this concentration, the CMT of Pluronic P104 decreased abruptly, and bigger clusters of BmimBr were formed. The selective nuclear Overhauser effect (NOE) spectrum indicates that the PO block of the P104 interacts with the butyl group of the Bmim + cation by hydrophobic interaction. It suggests that when the concentration of BmimBr is below 1.232 mol/L, there are P104 micelles in the aqueous solution with BmimBr embedding to the micellar core, while above this concentration, P104 micelles and BmimBr clusters coexist in the system.
By using a combination of 1 H NMR spectroscopy, two-dimensional heteronuclear single-quantum cohe... more By using a combination of 1 H NMR spectroscopy, two-dimensional heteronuclear single-quantum coherenceresolved 1 H{ 13 C} and homonuclear rotating-frame Overhauser enhancement NMR correlation experiments with diffusion ordered spectroscopy (DOSY), the location and distribution of a hydrophobic drug, paeonol, have been established with respect to the methyl groups of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The interaction between them is adjustable according to the different temperature-dependent hydrophilicities or hydrophobicities of the triblock copolymer components. On the other hand, such interactions influence the self-assembly properties of the block copolymer amphiphiles in solution. The amount of anhydrous methyl groups of PPO segments shows an increase with increasing paeonol concentration. It was also demonstrated that the shell-crosslinking of the Pluronic polymer has an effect in increasing the amount of anhydrous methyl groups and thus increasing the hydrophobicity of Pluronic micelles. This might be the deeper reason underlying the increase in drug-loading capacity and prolongation in release time of Pluronic micelles for drug delivery after the shell-crosslinking. Changes in self-diffusion coefficients of paeonol with varying copolymer concentrations and types were also determined by the diffusion-based NMR DOSY technique, and values of K a , ∆G, and n were calculated.
In this study, temperature-responsive magnetite/polymer nanoparticles were developed from iron ox... more In this study, temperature-responsive magnetite/polymer nanoparticles were developed from iron oxide nanoparticles and poly(ethyleneimine)-modified poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer. The particles were characterized by TEM, XRD, DLS, VSM, FTIR, and TGA. A typical product has an ∼20 nm magnetite core and an ∼40 nm hydrodynamic diameter with a narrow size distribution and is superparamagnetic with large saturation magnetization (51.34 emu/g) at room temperature. The most attractive feature of the nanoparticles is their temperature-responsive volume-transition property. DLS results indicated that their average hydrodynamic diameter underwent a sharp decrease from 45 to 25 nm while evaluating the temperature from 20 to 35°C. The temperature-dependent evolution of the CO stretching band in the FTIR spectra of the aqueous nanoparticles solution revealed that thermo-induced self-assembly of the immobilized block copolymers occurred on the magnetite solid surfaces, which is accompanied by a conformational change from a fully extended state to a highly coiled state of the copolymer. Consequently, the copolymer shell could act as a temperature-controlled "gate" for the transit of guest substance. The uptake and release of both hydrophobic and hydrophilic model drugs were well controlled by switching the transient opening and closing of the polymer shell at different temperatures. A sustained release of about 3 days was achieved in simulated human body conditions. In primary mouse experiments, drugentrapped magnetic nanoparticles showed good biocompatibility and effective therapy for spinal cord damage. Such intelligent magnetic nanoparticles are attractive candidates for widespread biomedical applications, particularly in controlled drug-targeting delivery.
Journal of Dispersion Science and Technology, 2008
The effect of potassium chloride on the micellization of a poly(ethylene oxide)‐poly(propylene ox... more The effect of potassium chloride on the micellization of a poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblock copolymer (Pluronic F88: EO103PO39EO103.) in water was studied by fluorescence, FTIR, 1H NMR, dynamic light scattering, and dye solubilization. The critical micellization temperature (CMT) values of the copolymer decreased with an increase of KCl concentration while micellar core gets progressively dehydrated. The results reveal the leading role of salt‐water interaction in promoting the micellization of PEO‐PPO‐PEO copolymer by the addition of salt. No significant micellar growth was seen even at temperatures close to cloud point.
Industrial & Engineering Chemistry Research, 2008
Here, we have reported a new approach for utilizing oleic acid-Pluronic L-64 block copolymer coat... more Here, we have reported a new approach for utilizing oleic acid-Pluronic L-64 block copolymer coated iron oxide nanoparticles as supports for enzyme immobilization. Iron oxide nanoparticles were prepared by a coprecipitation method and were coated with oleic acid and Pluronic to achieve higher stability and dispersibility. The surface morphology and size of the particle, as determined by transmission electron microscopy (TEM), was (10 nm. X-ray diffraction (XRD) patterns were taken over a range from 10°to 90°2 θ, using Cu KR radiation. Saturation magnetization values, measured at 300 K, varied from 34.6 emu/g to 60.8 emu/g. The possible interaction behavior of oleic acid and Pluronic was observed by Fourier transform infrared (FTIR) analysis and nuclear magnetic resonance (NMR) studies. Further potential of this material as a support for lipase immobilization and enzymatic hydrolysis at the oil/water interface was also investigated. The features of the surface-coated magnetic particles enable the adsorption of lipase from Candida cylindraces via strong hydrophobic interactions, which enhances the stability of the adsorbed enzyme molecules. The stability of the catalyst and, hence, its industrial applicability was tested by performing subsequent reaction cycles for the hydrolysis of olive oil. The activity of the immobilized lipase, pretreated with its substrate, was 510 U/g-matrix and was observed to be maintained at levels as high as 90% of its original activity for up to at least seven reuses.
The aqueous solution behavior of an ethylene oxide-propylene oxide triblock copolymer Pluronic ® ... more The aqueous solution behavior of an ethylene oxide-propylene oxide triblock copolymer Pluronic ® P123 [(EO) 20 (PO) 70 (EO) 20 ] was investigated in the presence of various n-alkanols (C 1-C 6) by cloud-point, viscosity, dynamic light scattering (DLS) and spectroscopic (FTIR, NMR) measurements. For lower alkanols (methanol, ethanol and 1-propanol), the cloud-points (CPs) increased with increase in alkanol concentration. The reverse eVect was found for higher alkanols (C 4-C 6) where both the CPs and critical micelle temperatures (CMTs) decreased with increase in concentration. This behavior is explained in terms of a cooperative association of higher alkanols and block copolymers by replacing water molecules in the PPO core and inducing micellar growth in aqueous P123 solution. Lower alkanols are likely to be good solvents for both PEO and PPO blocks and the eVect on PPO blocks predominates indicating an increase in CP and CMT with increase in alkanol concentration.
Symmetrical poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, tribloc... more Symmetrical poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, triblock copolymers with 80% polyethylene oxide (PEO, the hydrophilic end blocks) and polypropylene oxide (PPO, the hydrophobic middle block) usually remain as molecularly dissolved at ambient temperature even at fairly high-concentrations (2 wt.% or more). However, the micellization is induced at lower concentration/temperature in the presence of salts. The results on salt induced micellization from four such hydrophilic copolymers Pluronic Ò F38, F68, F88 and F108 obtained from several independent techniques are described. FTIR and fluorescence results provide essentially identical critical micelle temperatures (CMTs) showing marked decrease with increase in PPO molecular weight and in the presence of salt. These copolymers were weakly surface active and did not show a clear break point in surface tension concentration plot typical of surfactants. While addition of salt decreases the cloud point, no significant micelle growth was observed even at temperature close to cloud point (CP). Marked increased in solubilization of an oil dye was observed in presence of KCl. Different methods showed good agreement in temperature/salt-induced micellization of these hydrophilic copolymers.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010
Calorimetric and spectroscopic studies have been carried out to investigate the thermodynamics of... more Calorimetric and spectroscopic studies have been carried out to investigate the thermodynamics of temperature-induced micellization of Tetronic® T904 [(EO15PO17)2NCH2CH2N (PO17EO15)2] in aqueous salt solutions. High-sensitivity differential scanning calorimetry (HSDSC), nuclear magnetic resonance (NMR) and Fourier transfer infrared (FTIR) measurements were used to evaluate the critical micellization temperature (CMT). The critical micellization concentration (CMC) and the thermodynamic parameters of micelle formations,
The micellar behavior of a polyethylene oxide block-polypropylene oxide block-polyethylene oxide ... more The micellar behavior of a polyethylene oxide block-polypropylene oxide block-polyethylene oxide copolymer Pluronic L64 in aqueous urea solutions (urea concentrations 0, 1, 2, 3, 4, and 6 M) by physical methods, viz. cloud point and viscosity, spectral techniques (Fourier transform infrared, fluorescence, and nuclear magnetic resonance), differential scanning calorimetry, and dynamic light scattering is reported. The presence of urea causes an increase in the clouding temperature, critical micellization temperature, and the structural transition (spherical micelles to ellipsoid/rod) temperature; different methods showed good agreement. Urea induces demicellization of L64, enhancing accumulation of water molecules surrounding micelles. L64 micelles show growth at high temperatures, but this micellar transition is suppressed by urea, as proven by calorimetric and viscometric methods. The results are discussed in terms of the molecular mechanism underlying the effects of urea.
Wu (2010). The Fas-FADD death domain complex structure reveals the basis of DISC assembly and dis... more Wu (2010). The Fas-FADD death domain complex structure reveals the basis of DISC assembly and disease mutations''. Nature Struct. Mol. Biol. in press. [3] Su-Chang Lin, Yu-Chih Lo and Hao Wu (2010). Helical assembly in the MyD88-IRAK4-IRAK2 complex in TLR/IL-1R signaling. Nature, 465: 885-90.
(1)H nuclear magnetic resonance (NMR) spectroscopy has been applied to study the temperature and ... more (1)H nuclear magnetic resonance (NMR) spectroscopy has been applied to study the temperature and concentration-induced micellization of a poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymer, Pluronic P105, in D(2)O solutions in the temperature range from 5 to 45 degrees C and the concentration range from 0.01 to 15% (w/v). The intrinsic probes, the chemical shift, and the half-height width of the PO CH(3) signal are very sensitive to the local environment and can be used to characterize the temperature and concentration-dependent aggregation process. When the temperature approaches the critical micellization temperature or the polymer concentration reaches the critical micellization concentration, the chemical shift of the PO CH(3) signal moves toward lower ppm values and the half-height width of the PO CH(3) signal shows a sudden increase. It indicates that the methyl groups are experiencing a progressively less polar environment and transferring from water to the hydrophobic micellar core. The hydrodynamic radius of the unimers and the micelles are determined as be 1.8 and 5.0 nm by means of pulsed-field gradient spin-echo (PGSE) NMR. They were independent of temperature and concentration. The drastic shortening of spin-lattice relaxation time T(1) for the PO CH(3)/CH(2) protons in the transition region suggested that the PPO blocks are located in a "liquid-like" micellar core, whereas the exponential increase of T(1) for the PEO CH(2) protons implied that the PEO blocks are still keeping in contact with surrounding water. Thermodynamics analysis according to a closed association model shows that the micellization process is entropy-driven and has an endothermic micellization enthalpy.
Glutamine-binding protein (GlnBP) from Escherichia coli is a prototypical periplasmic binding pro... more Glutamine-binding protein (GlnBP) from Escherichia coli is a prototypical periplasmic binding protein that has been crystallized in an apo, "open" conformation, with its two domains far apart, and a holo, "closed" form, with proximal domains that engulf the cognate L-Gln ligand. A fundamental question about such large-scale conformational transitions-whether the closed state exists in the absence of ligand-is a matter of controversy in the case of GlnBP. Previously, NMR observations have indicated no evidence of the closed form, whereas experimentally validated computations have suggested a remarkable ~40% population. Here, a paramagnetic NMR strategy designed to specifically detect the putative apo-closed species shows that a major population of the latter is highly improbable. Further, NMR residual dipolar couplings collected under three anisotropic conditions fail to reveal differential domain alignment (which would otherwise signal interdomain dynamics) and establish that the average solution conformation is satisfied by the apo-open crystal structure. Our results indicate that the computational prediction of large-scale interdomain motions is far from trivial and may lead to grossly erroneous conclusions without proper experimental validation.
Colloids and surfaces. B, Biointerfaces, Jan 2, 2018
The present study was aimed to examine the interaction of two bile salts viz. sodium cholate (NaC... more The present study was aimed to examine the interaction of two bile salts viz. sodium cholate (NaC) and sodium deoxycholate (NaDC) with three ethylene polyoxide-polypropylene polyoxide (PEO-PPO-PEO) triblock copolymers with similar PPO but varying PEO micelles with a focus on the effect of pH on mixed micelles. Mixed micelles of moderately hydrophobic PluronicP123 were examined in the presence of two bile salts and compared with those from very hydrophobic L121 and very hydrophilic F127. Both the bile salts increase the cloud point (CP) of copolymer solution and decreased apparent micelle hydrodynamic diameter (D). SANS study revealed that P123 forms small spherical micelles showing a decrease in size on progressive addition of bile salts. The negatively charged mixed micelles contained fewer P123 molecules but progressively rich in bile salt. NaDC being more hydrophobic displays more pronounced effect than NaC. Interestingly, NaC shows micellar growth in acidic media which has been ...
The micellization, intermolecular interaction and microenvironment of molecular segments in the m... more The micellization, intermolecular interaction and microenvironment of molecular segments in the mixed aqueous solution of PEO-PPO-PEO triblock copolymer (Pluronic(superscript ®) F88, P84 and P123) and Surfynol(superscript ®) 104 (S1O4) were studied by nuclear magnetic resonance method. The results showed that the addition of S1O4 decreased the critical micellization temperature of copolymer. When its concentration was 0.5g/L, the most reduction was up to more than 10℃ for F88, which was most hydrophilic in the selected copolymers. This reduction was caused by the hydrophobic interaction between S1O4 molecules and PPO segments. The addition of S104 enhanced the hydration of PEO segments most obviously for P123. And S104 slightly increased the hydration of PPO segments before the micellization, but obviously decreased their hydration after micellization, which was attributed to the hydrophobic interaction mentioned above and temperature rising. This effect was most observable for F88.
FTIR spectroscopy was applied to investigate the interaction of anionic surfactant Sodium Dodecyl... more FTIR spectroscopy was applied to investigate the interaction of anionic surfactant Sodium Dodecyl Sulfate (SDS) and Bovine Serum Albumin (BSA). Amide band I of BSA was analyzed to obtain the change in secondary structure of BSA when different concentration of SDS was added and during different interaction period. In short interaction period and at low concentration of SDS, the alpha-helixes increased and the random coil decreased. In long interaction period or at high concentration of SDS, SDS unfolded the protein by decreasing the alpha-helix structure and increasing the random coil.
The micellization of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-P... more The micellization of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer (Pluronic L64: EO 13 PO 30 EO 13) with the presence of various sodium halides (NaF, NaCl, NaBr and NaI) was studied by Fourier transform infrared (FTIR) spectroscopy. The critical micelle temperature (CMT) of Pluronic L64 in the salt solution decreased with the addition of salt and the anion effect followed the sequence: F À > Cl À > Br À > I À. The deconvolution method was used to resolve the overlapping bands in the CO stretching region. The deconvoluted spectra provide information about the microenvironmental changes of ethylene oxide (EO) and propylene oxide (PO) blocks in the salt solution. Both the PEO and PPO blocks are dehydrated at lower temperature in the salt solution. The standard enthalpies (DH 0) and entropies (DS 0) of micellization for copolymer, PEO and PPO blocks, decreased by the addition of salt. Thus, it is deduced that the salt-induced decrease of enthalpy of micellization contributes to the decrease of CMT. The results reveal the leading role of saltwater interaction in promoting the micellization of PEO-PPO-PEO copolymer on addition of salt.
A novel method has been developed to prepare vesicles from aqueous solutions of poly(ethylene oxi... more A novel method has been developed to prepare vesicles from aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, by adding anionic surfactant sodium dodecyl sulfate (SDS) and inorganic salt NaF. As determined by TEM and dynamic light scattering (DLS) measurements, the average diameter of vesicles is about 800 nm having 50 nm outer shell thickness. Identifying hydrophobic interactions between the block copolymers and the microenvironments around the vesicles using FTIR, 1H NMR, and fluorescence spectroscopy techniques revealed the vesicle formation mechanism. The spontaneously formed vesicles were further cross-linked by converting the terminal hydroxyl groups of block copolymers into aldehydes, and then chemically bridging the polymer chains by the reaction between aldehydes and diamine compounds. The cross-linked vesicles are proved much more stable than free vesicles even at higher dilutions. The obtained vesicles with good stability and biocompatibility are promising candidates for widespread applications.
The acid effect on the aggregation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene ox... more The acid effect on the aggregation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers EO(20)PO(70)EO(20) has been investigated by transmission electron microscopy (TEM), particle size analyzer (PSA), Fourier transformed infrared, and fluorescence spectroscopy. The critical micellization temperature for Pluronic P123 in different HCl aqueous solutions increases with the increase of acid concentration. Additionally, the hydrolysis degradation of PEO blocks is observed in strong acid concentrations at higher temperatures. When the acid concentration is low, TEM and PSA show the increase of the micelle mean diameter and the decrease of the micelle polydispersity at room temperature, which demonstrate the extension of EO corona and tendency of uniform micelle size because of the charge repulsion. When under strong acid conditions, the aggregation of micelles through the protonated water bridges was observed.
Solution 1H NMR techniques were used to characterize the interaction of urea with poly(ethylene o... more Solution 1H NMR techniques were used to characterize the interaction of urea with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. The urea was established to interact selectively with the PEO blocks of the block copolymer, and the interaction sites were found not to change with increasing temperature. Such interactions influence the self-assembly properties of the block copolymer in solution by increasing the hydration of the block copolymers and stabilizing the gauche conformation of the PPO chain. Therefore, urea increases the critical micellization temperature (CMT) values of PEO-PPO-PEO copolymers, and the effect of urea on the CMT is more pronounced for copolymers with higher PEO contents and lower for those with increased contents of PPO segments.
Effect of 1-butyl-3-methyl-imidazolium bromide (BmimBr) on the aggregation behavior of PEO-PPO-PE... more Effect of 1-butyl-3-methyl-imidazolium bromide (BmimBr) on the aggregation behavior of PEO-PPO-PEO Pluronic P104 aqueous solution was studied by Fourier transform infrared (FTIR) spectroscopy, freeze fracture transmission electron microscopy (FF-TEM), dynamic light scattering (DLS), and NMR spectroscopy. When the BmimBr concentration was below 1.232 mol/L, the critical micelle temperature (CMT) of Pluronic P104 remained constant, while the size of micelles increased with increasing the BmimBr concentration; above this concentration, the CMT of Pluronic P104 decreased abruptly, and bigger clusters of BmimBr were formed. The selective nuclear Overhauser effect (NOE) spectrum indicates that the PO block of the P104 interacts with the butyl group of the Bmim + cation by hydrophobic interaction. It suggests that when the concentration of BmimBr is below 1.232 mol/L, there are P104 micelles in the aqueous solution with BmimBr embedding to the micellar core, while above this concentration, P104 micelles and BmimBr clusters coexist in the system.
By using a combination of 1 H NMR spectroscopy, two-dimensional heteronuclear single-quantum cohe... more By using a combination of 1 H NMR spectroscopy, two-dimensional heteronuclear single-quantum coherenceresolved 1 H{ 13 C} and homonuclear rotating-frame Overhauser enhancement NMR correlation experiments with diffusion ordered spectroscopy (DOSY), the location and distribution of a hydrophobic drug, paeonol, have been established with respect to the methyl groups of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The interaction between them is adjustable according to the different temperature-dependent hydrophilicities or hydrophobicities of the triblock copolymer components. On the other hand, such interactions influence the self-assembly properties of the block copolymer amphiphiles in solution. The amount of anhydrous methyl groups of PPO segments shows an increase with increasing paeonol concentration. It was also demonstrated that the shell-crosslinking of the Pluronic polymer has an effect in increasing the amount of anhydrous methyl groups and thus increasing the hydrophobicity of Pluronic micelles. This might be the deeper reason underlying the increase in drug-loading capacity and prolongation in release time of Pluronic micelles for drug delivery after the shell-crosslinking. Changes in self-diffusion coefficients of paeonol with varying copolymer concentrations and types were also determined by the diffusion-based NMR DOSY technique, and values of K a , ∆G, and n were calculated.
In this study, temperature-responsive magnetite/polymer nanoparticles were developed from iron ox... more In this study, temperature-responsive magnetite/polymer nanoparticles were developed from iron oxide nanoparticles and poly(ethyleneimine)-modified poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer. The particles were characterized by TEM, XRD, DLS, VSM, FTIR, and TGA. A typical product has an ∼20 nm magnetite core and an ∼40 nm hydrodynamic diameter with a narrow size distribution and is superparamagnetic with large saturation magnetization (51.34 emu/g) at room temperature. The most attractive feature of the nanoparticles is their temperature-responsive volume-transition property. DLS results indicated that their average hydrodynamic diameter underwent a sharp decrease from 45 to 25 nm while evaluating the temperature from 20 to 35°C. The temperature-dependent evolution of the CO stretching band in the FTIR spectra of the aqueous nanoparticles solution revealed that thermo-induced self-assembly of the immobilized block copolymers occurred on the magnetite solid surfaces, which is accompanied by a conformational change from a fully extended state to a highly coiled state of the copolymer. Consequently, the copolymer shell could act as a temperature-controlled "gate" for the transit of guest substance. The uptake and release of both hydrophobic and hydrophilic model drugs were well controlled by switching the transient opening and closing of the polymer shell at different temperatures. A sustained release of about 3 days was achieved in simulated human body conditions. In primary mouse experiments, drugentrapped magnetic nanoparticles showed good biocompatibility and effective therapy for spinal cord damage. Such intelligent magnetic nanoparticles are attractive candidates for widespread biomedical applications, particularly in controlled drug-targeting delivery.
Journal of Dispersion Science and Technology, 2008
The effect of potassium chloride on the micellization of a poly(ethylene oxide)‐poly(propylene ox... more The effect of potassium chloride on the micellization of a poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblock copolymer (Pluronic F88: EO103PO39EO103.) in water was studied by fluorescence, FTIR, 1H NMR, dynamic light scattering, and dye solubilization. The critical micellization temperature (CMT) values of the copolymer decreased with an increase of KCl concentration while micellar core gets progressively dehydrated. The results reveal the leading role of salt‐water interaction in promoting the micellization of PEO‐PPO‐PEO copolymer by the addition of salt. No significant micellar growth was seen even at temperatures close to cloud point.
Industrial & Engineering Chemistry Research, 2008
Here, we have reported a new approach for utilizing oleic acid-Pluronic L-64 block copolymer coat... more Here, we have reported a new approach for utilizing oleic acid-Pluronic L-64 block copolymer coated iron oxide nanoparticles as supports for enzyme immobilization. Iron oxide nanoparticles were prepared by a coprecipitation method and were coated with oleic acid and Pluronic to achieve higher stability and dispersibility. The surface morphology and size of the particle, as determined by transmission electron microscopy (TEM), was (10 nm. X-ray diffraction (XRD) patterns were taken over a range from 10°to 90°2 θ, using Cu KR radiation. Saturation magnetization values, measured at 300 K, varied from 34.6 emu/g to 60.8 emu/g. The possible interaction behavior of oleic acid and Pluronic was observed by Fourier transform infrared (FTIR) analysis and nuclear magnetic resonance (NMR) studies. Further potential of this material as a support for lipase immobilization and enzymatic hydrolysis at the oil/water interface was also investigated. The features of the surface-coated magnetic particles enable the adsorption of lipase from Candida cylindraces via strong hydrophobic interactions, which enhances the stability of the adsorbed enzyme molecules. The stability of the catalyst and, hence, its industrial applicability was tested by performing subsequent reaction cycles for the hydrolysis of olive oil. The activity of the immobilized lipase, pretreated with its substrate, was 510 U/g-matrix and was observed to be maintained at levels as high as 90% of its original activity for up to at least seven reuses.
The aqueous solution behavior of an ethylene oxide-propylene oxide triblock copolymer Pluronic ® ... more The aqueous solution behavior of an ethylene oxide-propylene oxide triblock copolymer Pluronic ® P123 [(EO) 20 (PO) 70 (EO) 20 ] was investigated in the presence of various n-alkanols (C 1-C 6) by cloud-point, viscosity, dynamic light scattering (DLS) and spectroscopic (FTIR, NMR) measurements. For lower alkanols (methanol, ethanol and 1-propanol), the cloud-points (CPs) increased with increase in alkanol concentration. The reverse eVect was found for higher alkanols (C 4-C 6) where both the CPs and critical micelle temperatures (CMTs) decreased with increase in concentration. This behavior is explained in terms of a cooperative association of higher alkanols and block copolymers by replacing water molecules in the PPO core and inducing micellar growth in aqueous P123 solution. Lower alkanols are likely to be good solvents for both PEO and PPO blocks and the eVect on PPO blocks predominates indicating an increase in CP and CMT with increase in alkanol concentration.
Symmetrical poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, tribloc... more Symmetrical poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, triblock copolymers with 80% polyethylene oxide (PEO, the hydrophilic end blocks) and polypropylene oxide (PPO, the hydrophobic middle block) usually remain as molecularly dissolved at ambient temperature even at fairly high-concentrations (2 wt.% or more). However, the micellization is induced at lower concentration/temperature in the presence of salts. The results on salt induced micellization from four such hydrophilic copolymers Pluronic Ò F38, F68, F88 and F108 obtained from several independent techniques are described. FTIR and fluorescence results provide essentially identical critical micelle temperatures (CMTs) showing marked decrease with increase in PPO molecular weight and in the presence of salt. These copolymers were weakly surface active and did not show a clear break point in surface tension concentration plot typical of surfactants. While addition of salt decreases the cloud point, no significant micelle growth was observed even at temperature close to cloud point (CP). Marked increased in solubilization of an oil dye was observed in presence of KCl. Different methods showed good agreement in temperature/salt-induced micellization of these hydrophilic copolymers.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010
Calorimetric and spectroscopic studies have been carried out to investigate the thermodynamics of... more Calorimetric and spectroscopic studies have been carried out to investigate the thermodynamics of temperature-induced micellization of Tetronic® T904 [(EO15PO17)2NCH2CH2N (PO17EO15)2] in aqueous salt solutions. High-sensitivity differential scanning calorimetry (HSDSC), nuclear magnetic resonance (NMR) and Fourier transfer infrared (FTIR) measurements were used to evaluate the critical micellization temperature (CMT). The critical micellization concentration (CMC) and the thermodynamic parameters of micelle formations,
The micellar behavior of a polyethylene oxide block-polypropylene oxide block-polyethylene oxide ... more The micellar behavior of a polyethylene oxide block-polypropylene oxide block-polyethylene oxide copolymer Pluronic L64 in aqueous urea solutions (urea concentrations 0, 1, 2, 3, 4, and 6 M) by physical methods, viz. cloud point and viscosity, spectral techniques (Fourier transform infrared, fluorescence, and nuclear magnetic resonance), differential scanning calorimetry, and dynamic light scattering is reported. The presence of urea causes an increase in the clouding temperature, critical micellization temperature, and the structural transition (spherical micelles to ellipsoid/rod) temperature; different methods showed good agreement. Urea induces demicellization of L64, enhancing accumulation of water molecules surrounding micelles. L64 micelles show growth at high temperatures, but this micellar transition is suppressed by urea, as proven by calorimetric and viscometric methods. The results are discussed in terms of the molecular mechanism underlying the effects of urea.
Wu (2010). The Fas-FADD death domain complex structure reveals the basis of DISC assembly and dis... more Wu (2010). The Fas-FADD death domain complex structure reveals the basis of DISC assembly and disease mutations''. Nature Struct. Mol. Biol. in press. [3] Su-Chang Lin, Yu-Chih Lo and Hao Wu (2010). Helical assembly in the MyD88-IRAK4-IRAK2 complex in TLR/IL-1R signaling. Nature, 465: 885-90.
(1)H nuclear magnetic resonance (NMR) spectroscopy has been applied to study the temperature and ... more (1)H nuclear magnetic resonance (NMR) spectroscopy has been applied to study the temperature and concentration-induced micellization of a poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymer, Pluronic P105, in D(2)O solutions in the temperature range from 5 to 45 degrees C and the concentration range from 0.01 to 15% (w/v). The intrinsic probes, the chemical shift, and the half-height width of the PO CH(3) signal are very sensitive to the local environment and can be used to characterize the temperature and concentration-dependent aggregation process. When the temperature approaches the critical micellization temperature or the polymer concentration reaches the critical micellization concentration, the chemical shift of the PO CH(3) signal moves toward lower ppm values and the half-height width of the PO CH(3) signal shows a sudden increase. It indicates that the methyl groups are experiencing a progressively less polar environment and transferring from water to the hydrophobic micellar core. The hydrodynamic radius of the unimers and the micelles are determined as be 1.8 and 5.0 nm by means of pulsed-field gradient spin-echo (PGSE) NMR. They were independent of temperature and concentration. The drastic shortening of spin-lattice relaxation time T(1) for the PO CH(3)/CH(2) protons in the transition region suggested that the PPO blocks are located in a "liquid-like" micellar core, whereas the exponential increase of T(1) for the PEO CH(2) protons implied that the PEO blocks are still keeping in contact with surrounding water. Thermodynamics analysis according to a closed association model shows that the micellization process is entropy-driven and has an endothermic micellization enthalpy.
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