Self-assembly of well-defined mono and dual end-capped C(60) containing polyacrylic acids in aqueous solution

Well-defined stimuli-responsive mono and dual fullerene (C(60)) end-capped poly(acrylic acid)s (PAA-C(60) and C(60)-PAA-C(60)) were synthesized by reacting C(60) with well-defined mono and dual azide end-functionalized poly(tert-butyl acrylate)s, followed by hydrolysis. The aggregation behaviors of these C(60) end-capped polymers in aqueous solution were examined using potentiometric and conductometric titrations and static and dynamic light scattering as well as transmission electron microscopy (TEM). Both PAA-C(60) and C(60)-PAA-C(60) show pH-responsive and water-soluble properties at high pH. Both polymers self-assemble to form large compound micelles (LCMs) in aqueous solutions. The LCMs of PAA-C(60) exist as "compact aggregates", whereas the LCMs of C(60)-PAA-C(60) possess a "core-shell" structure with a larger size and aggregation number. The micelles for both polymers swell upon neutralization, where the R(h) of PAA-C(60) micelles increases from approximately 44 to approximately 102 nm and the R(h) of C(60)-PAA-C(60) aggregates varies from approximately 89 to approximately 128 nm with increasing degree of neutralization. The lower swelling of the dual end-capped C(60)-PAA-C(60) system is related to its higher C(60) content, which enhances the interpolymer chain hydrophobic association that restrains the swelling of micellar aggregates.     

Morphological transformation of [60]fullerene-containing poly(acrylic acid) induced by the binding of surfactant

Water-soluble pH-responsive [60]fullerene end-capped poly(acrylic acid) (PAA85-b-C60) was synthesized using atom-transfer radical polymerization (ATRP) technique. The unusual morphological transformation of the polymer induced by the binding of nonionic surfactant Triton X-100 (TX100) at different degrees of neutralization (alpha) was investigated using isothermal titration calorimetry (ITC), UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). For the 5 mM (monomer concentration) polymer solution at pH < 4, approximately 1.3 mM TX100 binds specifically to C60 domains of the polymeric micelles driven by hydrophobic interaction, which induces a structural transformation of the polymer from a large compound micelle with a radius of 110 nm to a dense precipitated spherical polymer/surfactant complex (PSC) with a radius of 500 nm. The precipitates are resolubilized by a wetting layer of TX100 in excess surfactant (> 1.7 mM in the polymer solution). The binding is significantly weakened and the complexation is disrupted with increasing pH, where the interaction completely ceased at pH > 6.     

Phase behavior of DOPE/TritonX100 (reduced) in dilute aqueous solution: aggregate structure and pH-dependence

The phase behavior of dilute mixtures of dioleoylphosphatidylethanolamine (DOPE) and reduced TritonX100 (TX100(r)) has been investigated at pH 7.4 and 10. Using simple turbidity measurements and optical observations, together with cryo-transmission electron microscopy (cryo-TEM), we estimate the phase boundaries. We show that at both pH 7.4 and 10, a very large amount of surfactant is needed for the onset of micelle formation (X(TX100(r)) approximately 0.60-0.70) as well as for a complete solubilization of DOPE into mixed micelles (X(TX100(r)) > 0.94). We find that the micelles that are formed at high TX100(r) concentrations are of spherical shape. Increasing the pH from 7.4 to 10 has a comparably small effect on the transition from a lamellar (Lalpha) to a micellar (L1) phase. However, the reversed hexagonal phase (H(II)) that is present at low surfactant content at pH 7.4 is absent at pH 10. This is due to the partial negative charge of DOPE at pH 10. We determine the fraction of charged DOPE (alpha = 0.34) at pH 10 in a 150 mM NaCl buffer using zeta-potential (zeta-potential) measurements in combination with a Poisson-Boltzmann (PB) model. The intrinsic pK(a) of the primary amino group of DOPE, in a pure DOPE membrane, is estimated to 9.15 +/- 0.2.     

Nanostructured thermosensitive polymers with radical scavenging ability

The thermosensitive [60]fullerene end-capped poly(N-isopropylacrylamide) was successfully synthesized by the reaction of C(60) with dithiobenzoate-terminated poly(N-isopropylacrylamide), which was prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization in the presence of azobisisobutyronitrile (AIBN). Its structure was determined by FTIR, UV/Vis, and carbon and proton NMR spectroscopy as well as by size exclusion chromatography (SEC). The novel fullerenated polymer retained the thermosensitivity of poly(N-isopropylacrylamide). Moreover, it is soluble in water and most of the common organic solvents. Interestingly, it was able to form nanoparticle clusters in methanol and exhibited significant radical scavenging ability in cell viability and metabolic activity tests with fibroblasts and NOR-3 radicals.     

Properties of mixed micelles of cationic gemini surfactants and nonionic surfactant triton X-100: effects of the surfactant composition and the spacer length

The mixed micelles of cationic gemini surfactants C12C(S)C12Br2 (S=3, 6, and 12) with the nonionic surfactant Triton X-100 (TX100) have been studied by steady-state fluorescence, time-resolved fluorescence quenching, electrophoretic light scattering, and electron spin resonance. Both the surfactant composition and the spacer length are found to influence the properties of mixed micelles markedly. The total aggregation number of alkyl chains per micelle (N(T)) goes through a minimum at X(TX100)=0.8. Meanwhile, the micropolarity of the mixed micelles decreases with increasing X(TX100), while the microviscosity increases. The presence of minimum in N(T) is explained in terms of the competition of the reduction of electrostatic repulsion between headgroups of cationic gemini surfactant with the enhancement of steric repulsion between hydrophilic headgroups of TX100 caused by the addition of TX100. The variations of micropolarity and microviscosity indicate that the incorporation of TX100 to the gemini surfactants leads to a more compact and hydrophobic micellar structure. Moreover, for the C12C3C12Br2/TX100 mixed micelle containing C12C3C12Br2 with a shorter spacer, the more pronounced decrease of N(T) at X(TX100) lower than 0.8 may be attributed to the larger steric repulsion between headgroups of TX100. Meanwhile, the increase of microviscosity and the decrease of micropolarity are more marked for the C12C12C12Br2/TX100 mixed micelle, owing to the looped conformation of the longer spacer of C12C12C12Br2.     

Polymer-induced fractal patterns of [60]fullerene containing poly(methacrylic acid) in salt solutions

Well-defined water-soluble pH-responsive [60]fullerene (C60) containing poly(methacrylic acid) (PMAA-b-C60) was synthesized using the atom transfer radical polymerization technique. By varying pH and salt concentration, different types of fractal patterns at nano- to microscopic dimensions were observed for negatively charged PMAA-b-C60, while such structure was not observed for positively charged poly(2-dimethylaminoethyl methacrylate)-b-C60. We demonstrated that negatively charged fullerene containing polymeric systems can serve as excellent nanotemplates for the controlled growth of inorganic crystals at the nano- to micrometer length scale, and the possible mechanism was proposed.     

Self-assembly of stimuli-responsive water-soluble [60]fullerene end-capped ampholytic block copolymer

A well-defined, water-soluble, pH and temperature stimuli-responsive [60]fullerene (C(60)) containing ampholytic block copolymer of poly((methacrylic acid)-block-(2-(dimethylamino)ethyl methacrylate))-block-C(60) (P(MAA-b-DMAEMA)-b-C(60)) was synthesized by the atom transfer radical polymerization (ATRP) technique. The self-assembly behavior of the C(60) containing polyampholyte in aqueous solution was characterized by potentiometric and conductometric titration, dynamic light scattering (DLS), and transmission electron microscopy. This amphiphilic mono-C(60) end-capped block copolymer shows enhanced solubility in aqueous medium at room and elevated temperatures and at low and high pH but phase separates at intermediate pH between 5.4 and 8.8. The self-assembly of the copolymer is different from that of P(MAA-b-DMAEMA). Examination of the association behavior using DLS revealed the coexistence of unimers and aggregates at low pH at all temperatures studied, with the association being driven by the balance of hydrophobic and electrostatic interactions. Unimers and aggregates of different microstructures are also observed at high pH and at temperatures below the lower critical solution temperature (LCST) of PDMAEMA. At high pH and at temperatures above the LCST of PDMAEMA, the formation of micelles and aggregates coexisting in solution is driven by the combination of hydrophobic, electrostatic, and charge-transfer interactions.     

Salt effect on the complex formation between cationic gemini surfactant and anionic polyelectrolyte in aqueous solution

Salt effect on the interaction of anionic polyelectrolyte sodium carboxymethylcellulose (NaCMC) with cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) [C12H25(CH3)2N(CH2)6N(CH3)2C12H25]Br2 (C12C6C12Br2) has been investigated using turbidimetric titration, steady-state fluorescence, and mobility measurement. It is found that the critical aggregation concentration(cac) for C12C6C12Br2/NaCMC complexes depends little on addition of sodium bromide (NaBr). However, in the presence of nonionic surfactant Triton X-100 (TX100), the critical ionic surfactant mole fraction for the onset of complex formation (Yc) increases markedly with increasing NaBr concentration. These salt effects are supposed as the overall result from competition between the increase of interaction and the screening of interaction. The increase of interaction is referred to as the effect that the larger micelle with higher surface charge density induced by salt has a stronger interaction with oppositely charged polyelectrolyte. The screening of interaction is referred to as the salt screening of electrostatic attraction between the polymer chain and the surfactant. For complex formation between C12C6C12Br2 and NaCMC, the increase of interaction probably compensates the screening of interaction, leading to constant cac values at different salt concentrations. For complex formation between the C12C6C12Br2/TX100 mixed micelle and NaCMC, the screening of interaction probably plays a dominant role, leading to higher suppression of electrostatic binding of micelles to polyelectrolyte.     

Effect of surfactant type on surfactant-maltodextrin interactions: isothermal titration calorimetry, surface tensiometry, and ultrasonic velocimetry study

Isothermal titration calorimetry (ITC), surface tensiometry, and ultrasonic velocimetry were used to characterize surfactant-maltodextrin interactions in buffer solutions (pH 7.0, 10 mM NaCl, 20 mM Trizma base, 30.0 degrees C). Experiments were carried out using three surfactants with similar nonpolar tail groups (C12) but different charged headgroups: anionic (sodium dodecyl sulfate, SDS), cationic (dodecyl trimethylammonium bromide, DTAB), and nonionic (polyoxyethylene 23 lauryl ether, Brij35). All three surfactants bound to maltodextrin, with the binding characteristics depending on whether the surfactant headgroup was ionic or nonionic. The amounts of surfactant bound to 0.5% w/v maltodextrin (DE 5) at saturation were < 0.3 mM Brij35, approximately 1-1.6 mM SDS, and approximately 1.5 mM DTAB. ITC measurements indicated that surfactant binding to maltodextrin was exothermic. Surface tension measurements indicated that the DTAB-maltodextrin complex was more surface active than DTAB alone but that SDS- and Brij35- maltodextrin complexes were less surface active than the surfactants alone.     

用多官能团引发剂合成超支化聚苯乙烯及其C60衍生物

通过α-溴丙酰溴与Z5(季戊四醇与2,2-二羟甲基丙酸缩聚的产物)酯化反应制得超支化原子转移自由基聚合(ATRP)引发剂Z5-B(约含19个引发点).在100℃及CuCl/N,N,N,N",N"-五甲基二亚乙基三胺催化下,用Z5-B引发苯乙烯的ATRP聚合(环己酮为溶剂,体积分数为50%),得到超支化的聚苯乙烯,将溴端基叠氮化后与C60反应,获得超支化聚苯乙烯C60衍生物.该超支化C60衍生物可用于光限制材料.     

Molecular state and distribution of fullerenes entrapped in sol-gel samples

A novel synthetic method that can encapsulate fullerene molecules (pure C60, pure C70, or their mixture) over a wide range of concentrations ranging from micromolar to millimolar in hybrid glass by a sol-gel method without any time-consuming, complicated, and unwanted extra steps (e.g., addition of a surfactant or derivatization of the fullerenes) has been successfully developed. The molecular state and distribution of encapsulated fullerene molecules in these sol-gel samples were unequivocally characterized using newly developed multispectral imaging techniques. The high sensitivity (single-pixel resolution) and ability of these instruments to record multispectral images at different spatial resolutions (approximately 10 microm with the macroscopic instrument and approximately 0.8 microm with the microscopic instrument) make them uniquely suited for this task. Specifically, the imaging instruments can be used to simultaneously measure multispectral images of sol-gel-encapsulated C60 and C70 molecules at many different positions within a sol-gel sample in an area either as large as 3 mm x 4 mm (with the macroscopic imaging instrument) or as small as 0.8 microm x 0.8 microm (with the microscopic instrument). The absorption spectrum of the fullerene molecule at each position can then be calculated either by averaging the intensity of a 15 x 15 square of pixels (which corresponds to an area of 3 mm x 4 mm) or from the intensity of a single pixel (i.e., an area of about 0.8 microm x 0.8 microm), respectively. The molecular state and distribution of fullerene molecules within sol-gel samples can then be determined from the calculated spectra. It was found that spectra of encapsulated C60 and C70 measured at five different positions within a sol-gel sample were similar not only to one another but also to spectra measured at six different times during the sol-gel reaction process (from t = 0 to 10 days). Furthermore, these spectra are similar to the corresponding spectra of monomeric C60 or C70 molecules in solution. Similarly, spectra of sol-gel samples containing a mixture of C60 and C70 were found to be the same at five different positions, as well as similar to spectra calculated from an average of the spectra of C60 and C70 either encapsulated in a sol-gel or in solution. It is evident from these results that C60 and C70 molecules do not undergo aggregation upon encapsulation into a sol-gel but rather remain in their monomeric state. Furthermore, entrapped C60 and C70 molecules in their monomeric state were distributed homogeneously throughout the entire sol-gel samples. Such a conclusion can be readily, quickly, and easily obtained, not with traditional spectroscopic techniques based on the use of a single-channel detector (absorption, fluorescence, infrared, Raman) but rather with the newly developed multispectral imaging technique. More importantly, the novel synthetic method reported here makes it possible, for the first time, to homogenously entrap monomeric fullerene molecules (C60, C70, or their mixture) in a sol-gel at various concentrations ranging from as low as 2.2 mM C60 (or 190 microM C70) to as high as 4.2 mM C60 (or 360 microM C70).     

Wettability of polymeric solids by ternary mixtures composed of hydrocarbon and fluorocarbon nonionic surfactants

Contact angle (θ) measurements on poly(tetrafluoroethylene) (PTFE) and polymethyl methacrylate (PMMA) surface were carried out for the systems containing ternary mixtures of surfactants composed of: p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycols), Triton X-100 (TX100), Triton X-165 (TX165) and Triton X-114 (TX114), and fluorocarbon surfactants, Zonyl FSN100 (FSN100) and Zonyl FSO100 (FSO100). The aqueous solutions of ternary surfactant mixtures were prepared by adding TX114, FSN100 or FSO100 to binary mixtures of TX100+TX165, where the synergistic effect in the reduction of the surface tension of water (γ(LV)) was determined. From the obtained contact angle values, the relationships between cosθ, the adhesion tension and surface tension of solutions, cosθ and the reciprocal of the surface tension were determined. On the basis of these relationships, the correlation between the critical surface tension of PTFE and PMMA wetting and the surface tension of these polymers as well as the work of adhesion of aqueous solutions of ternary surfactant mixtures to PTFE and PMMA surface were discussed. The critical surface tension of PTFE and PMMA wetting, γ(C), determined from the contact angle measurements of aqueous solutions of surfactants including FSN100 or FSO100 was also discussed in the light of the surface tension changes of PTFE and PMMA under the influence of film formation by fluorocarbon surfactants on the surface of these polymers. The γ(C) values of the studied polymeric solids were found to be different for the mixtures composed of hydrocarbon surfactants in comparison with those of hydrocarbon and fluorocarbon surfactants. In the solutions containing fluorocarbon surfactants, the γ(C) values were different taking into account the contact angle in the range of FSN100 and FSO100 concentration corresponding to their unsaturated monolayer at water-air interface or to that saturated.     

富勒烯衍生物引发的富勒烯末端封端聚己内酯的合成

利用带活性羟基的N-取代3,4-富勒烯吡咯烷作为引发剂,引发ε-己内酯开环聚合,制备了一种具有新型结构的富勒烯末端封端聚己内酯,通过核磁共振(1H NMR,13C NMR)、红外光谱(FTIR)和基质辅助激光解吸电离飞行时间质谱(MALDI-TOF-MS)等手段对产物进行了结构表征,并用热重(TG)分析和差示扫描量热(DSC)分析的方法进行了热学性能分析.结果表明,与聚己内酯相比产物热稳定性增加.     

Self-assembly behavior of a stimuli-responsive water-soluble [60]fullerene-containing polymer

A novel pH- and temperature-responsive water-soluble [60]fullerene-containing poly[2-(dimethylamino)ethyl methacrylate] (C60-b-PDMAEMA) was synthesized by atom transfer radical polymerization. The pH and temperature dependence of the physical properties of the aqueous C60-b-PDMAEMA solution was studied by potentiometric and conductometric titrations, UV-vis transmittance, and laser light scattering techniques. At low pH and at temperatures ranging from 25 to 55 degrees C, in addition to C60-b-PDMAEMA unimers, micelle-like aggregates are produced in the aqueous solution containing C60 hydrophobic cores and protonated PDMAEMA shells. Only unimeric C60-b-PDMAEMAs are found to exist in solution at high pH and low temperature, where PDMAEMA segments form a charge-transfer complex with C60 molecules. However, C60-b-PDMAEMA precipitates from aqueous solution at temperatures exceeding the lower critical solution temperature of PDMAEMA of approximately 45 degrees C. The pH and temperature stimuli-responsive properties of the [60]fullerene-containing polymer in aqueous solution are completely reversible.     

Scanning tunnelling microscopic investigation of fullerene monolayers

C(60) fullerene monolayers have been investigated by scanning tunnelling microscopy/spectroscopy. Single C(60) molecules have been resolved and a regular surface lattice structure of fullerene - in - surfactant is observed. Tunnel electron spectroscopic measurements results in typical I(V) curves which are interpreted in terms of the two-junction Coulomb blockade effect.     

Temperature responsive complex coacervate core micelles with a PEO and PNIPAAm corona

In aqueous solutions at room temperature, poly( N-methyl-2-vinyl pyridinium iodide)- block-poly(ethylene oxide), P2MVP 38- b-PEO 211 and poly(acrylic acid)- block-poly(isopropyl acrylamide), PAA 55- b-PNIPAAm 88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO 3, T = 25, and 60 degrees C, that is, below and above the LCST of approximately 32 degrees C. At T = 25 degrees C, C3Ms were observed for 7 < pH < 12 and NaNO 3 concentrations below approximately 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 degrees C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona.     

Binding of a surfactant counterion to low-charge-density poly(acrylic acid) and poly(methacrylic acid)

The binding of a cationic surfactant, dodecylpyridinium (C12Py) chloride, with a low-charge-density poly (methacrylic acid) (PMA) was investigated in buffer solutions under the condition of constant pH. The binding isotherms with PMA consisted of two and three steps at a pH lower and higher than 3.2, respectively. Bindings in the first step were independent of pH and this step was considered to correspond to the solubilization of the hydrocarbon chains of C12Py into the nonpolar region of the compact form of PMA. This is the indication of the compact form from the binding isotherm. At pH higher than 3.2, the second step was discriminated and it depended on the pH. In the third step, a sharp rise in the degree of binding (β) was observed accompanying the solubilization of the precipitates of the PMA–C12Py complex. The binding with poly(acrylic acid) (PAA) and PMA in conventional unbuffered NaCl solutions was also examined and the pH profile of the solution during the binding process was determined. In the case of unbuffered NaCl solutions, the binding with PAA took place cooperatively at the critical association concentration (cac). The binding isotherm consisted of two steps and the pH decreased with the increase in β. The binding isotherm of PMA, on the other hand, consisted of three steps: the pH decreased slightly in the first step and considerably in the second step with the increase in β but it increased with β in the third step, exhibiting a pH minimum around 3.2. The binding in the first step coincided with that obtained in the buffered solutions. Linear relationships between β and the pH were found for both polymers. In the case of PMA, no cac was observed in both buffered and unbuffered NaCl solutions. Received: 24 January 2001 Accepted: 23 May 2001     

Liquid-crystalline fullerodendrimers which display columnar phases

[structure: see text] The title compounds were synthesized by applying the 1,3-dipolar cycloaddition reaction of aldehyde-based poly(benzyl ether) dendrimers and sarcosine (N-methylglycine) to [60]fullerene (C(60)). The dendritic building blocks used to functionalize C(60) displayed cubic and hexagonal columnar phases. The fullerene derivatives showed rectangular columnar phases of c2mm symmetry.     

Study of the interaction between polyphenol,quercetin and three micelles with different electric charges in acidic and aqueous media

The interactions between the polyphenol quercetin, Q, with three surfactant aggregates with different electric charges named micelles, were studied in aqueous solutions with pH values 4.7 and 7.0, to determine the following parameters: critical micellar concentration (CMC), micelle size and binding constant of the complex (Q-Micelle) proposing interaction sites for the formation of the complex. The surfactants used were: hexadecyltrimethyl ammonium bromide (cationic surfactant), CTAB, sodium dodecyl sulfate (anionic surfactant), SDS, and triton X-100 (non-ionic surfactant), TX100, used as Q fluorescence promoters to determine the CMC. The CMC values of the above surfactants at pH 4.7 were: 0.80 ± 0.10, 1.39 ± 0.07 and 0.59 ± 0.05 mM respectively, being lower than those reported in the water. With dynamic light scattering measurements, the hydrodynamic diameters of each micelle were calculated resulting in values of: 2.4 ± 0.5, 5.0 ± 1.1 and 8.4 ± 4.3 nm at pH 4.7 and: 2.1 ± 0.4, 4.9 ± 1.1 and 11.5 ± 4.1 nm at pH 7.0 respectively. In addition, the binding constants of the complex (Q-Micelle) with 1:1 stoichiometry were calculated from emission fluorescence data giving Log K values: 2.94 ± 0.02, 2.54 ± 0.02, and 3.63 ± 0.05 M^-1 respectively. Finally, from the experimental data by UV–Vis spectrophotometry, the change in the behavior of the Q spectrum upon the addition of each of the surfactants to the system was analyzed, showing a decrease in absorbance when SDS and TX100 were added in an acidic medium, as a consequence of the photo-instability of the drug, suggesting that Q interacts with the outside of these micelles and is not fully incorporated inside them.     

Microchip micellar electrokinetic chromatography based on one functionalized ionic liquid and its excellent performance on proteins separation

Herein, one water-soluble functionalized ionic liquid (IL), 1-butyl-3-methylimidazolium dodecanesulfonate (BAS), was designed, investigated and successfully applied to microchip micellar electrokinetic chromatography (MEKC) construction. It possessed the properties of both IL and surfactant. A fairly stable pH value approximately 7.4, which was fit to pH values of general biological buffers, was nicely placed at the optimum concentration of 20mM BAS solution. While applying BAS solution as running buffer in poly(dimethylsiloxane) (PDMS) microfluidic systems, significantly enhanced electroosmotic flow (8-fold) and resolutions between analytes were obtained than that using other supporting electrolytes or surfactants. Pure BAS solution could conveniently complete the task of MEKC establishment: not only the ionic strength of the running buffer was guaranteed, but also the analytes adsorption to PDMS surface was conquered, as was demonstrated in the sensitive determination of fluorescent dyes and well-separated protein mixtures.