一种新型的荧光探针及其在表面活性剂溶液胶束形成过程中的应用

一种新型的荧光探针及其在表面活性剂溶液胶束形成过程中的应用姜永才，汪鹏飞，吴世康（中国科学院感光化学研究所，北京１００１０１）关键词荧光探针，表面活性剂，分子集合体，极性，粘度近年来，具有分子内共轭的电荷转移化合物用作荧光探针来研究微环境的特性得到较...     

Poly[2,7-(9,9-dihexylfluorene)]-block-poly[3-(trimethoxysilyl)propyl methacrylate] (PF-b-PTMSPMA) rod-coil block copolymers: Synthesis,morphology and photophysical properties in mixed solvents

We report the synthesis, morphology, and photophysical properties of poly[2,7-(9,9-dihexylfluorene)]-block-poly[3-(trimethoxysilyl)propyl methacrylate] (PF-b-PTMSPMA) with two different coil lengths. Ethyl acetate (EA) and methanol (MeOH) are used as selective solvents for the PF rod and PTMSPMA coil blocks, respectively, while THF as the common solvent. Micelle morphologies of the PF-b-PTMSPMA in THF/MeOH or THF/EA mixed solvents are characterized by transmission electron microscopy (TEM) and scanning force microscopy (SFM). In the THF/MeOH mixed solvent, PF-b-PTMSPMA assembles into diverse morphologies of sphere, short cylinder, cylinder, and cylinder bundles. Besides the selective effects, the strong π–π interaction of PF contributes partially to the above morphologies. In the THF/EA mixed solvent, morphologies of the PF-b-PTMSPMA changes from large compound micelles (LCM) to hollow spherical micelles due to the strong core chain stretching. Stable micelles are obtained by crosslink Si(OR)₃ groups of the PTMSPMA block by triethylamine (TEA). The micellar morphology significantly affects the photophysical properties. In the THF/MeOH mixed solvent, blue shifts on the UV-vis and fluorescence spectra are observed probably attributed to the formation of the H-aggregation in the PF core. However, the photophysical properties are insensitive to the different ratios of THF/EA, due to the insignificant aggregation of short PF corona. The present study reveals that the morphology and photophysical properties of fluorene-based rod-coil polymers could be significantly manipulated through solvent, rod/coil ratio, and π–π interaction.     

Detecting Cysteine in Bioimaging with a Near-Infrared Probe Based on a Novel Fluorescence Quenching Mechanism

Near-infrared (NIR) fluorescent probes are very significant for detecting cysteine in biological systems. Herein, we report a highly selective and sensitive NIR turn-on fluorescent probe (BDP-NIR) based on BODIPY with large Stokes shift (105 nm) for detecting Cys. We clarified the sensing mechanism based on the different thiol-induced S_NAr substitution/rearrangement reaction of the probe with cysteine and homocysteine/glutathione, which leads to the corresponding amino- and thiol-BODIPY dyes with distinct photophysical properties. Moreover, a novel mechanism of fluorescence quenching was demonstrated by density functional theory calculation. The reason for the fluorescence quenching of the probe might be intersystem crossing (from singlet to triplet excited state). Moreover, BDP-NIR had a high linear dynamic range of 0–500 μM, which was promising for detecting cysteine quantificationally. Significantly, BDP-NIR was capable of sensing endogenous cysteine in living cells and in vivo.     

Enzymatic esterification of DL‐menthol with propionic acid by lipase from Candida cylindracea

This work deals with the resolution of DL ‐menthol with propionic acid by Candida cylindracea lipase (Ccl) in organic solvent reaction systems and a reverse micelles system of sodium 1,4‐bis (2‐ethylhexyl) sulfosuccinate (AOT). The activity and stability as well as enantioselectivity of the lipase in two systems were studied. The results indicate that the lipase showed higher stability in reverse micelles than in organic solvent, which proved that the reverse micelles system has potential application for maintaining the activity of the enzyme for a long time. This is because lipase molecules can be entrapped in water‐containing micro‐drops of reverse micelles, avoiding direct‐contract with unfavorable organic medium. The enantioselectivity (E > 30, ee_p = 92.5) in the two systems is relatively high, although the conversion is moderate. The influence of the characteristic parameters of the two systems, such as pH, temperature, w₀ (molar ratio of water to AOT in reverse micelles systems) and water content (organic solvent) on the conversion of DL ‐menthol was also investigated. Copyright © 2005 Society of Chemical Industry     

Formation of reverse micelles in supercritical carbon dioxide and its thermodynamics

The solubilization behavior of methyl orange as a solvation probe in multiple systems composed of supercritical carbon dioxide, surfactants and co-solvents, is studied. It is concluded that some surfactants, such as sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) and isooctyl phenol polyethoxylate (TX-10), could form reverse micelles in supercritical carbon dioxide under the action of butanol. The formation of reverse micelles is a spontaneous process thermodynamically. Specifically for the nonionic surfactant TX-10, the formation of reverse micelles is dependent on the entropy increase in the system, while for the anionic surfactant AOT, the micellization is mainly dominated by the increase in enthalpy at higher temperatures, but by the increase in entropy at lower temperatures. Translated from Journal of South China University of Technology (Natural Science Edition), 2006, 34(8): 66–69 [译自: 华南理工大学学报 (自然科学版)]     

Self-Assembly,Surface Activity and Structure of n-Octyl-β-D-thioglucopyranoside in Ethylene Glycol-Water Mixtures

The effect of the addition of ethylene glycol (EG) on the interfacial adsorption and micellar properties of the alkylglucoside surfactant n-octyl-β-d-thioglucopyranoside (OTG) has been investigated. Critical micelle concentrations (cmc) upon EG addition were obtained by both surface tension measurements and the pyrene 1:3 ratio method. A systematic increase in the cmc induced by the presence of the co-solvent was observed. This behavior was attributed to a reduction in the cohesive energy of the mixed solvent with respect to pure water, which favors an increase in the solubility of the surfactant with EG content. Static light scattering measurements revealed a decrease in the mean aggregation number of the OTG micelles with EG addition. Moreover, dynamic light scattering data showed that the effect of the surfactant concentration on micellar size is also controlled by the content of the co-solvent in the system. Finally, the effect of EG addition on the microstructure of OTG micelles was investigated using the hydrophobic probe Coumarin 153 (C153). Time-resolved fluorescence anisotropy decay curves of the probe solubilized in micelles were analyzed using the two-step model. The results indicate a slight reduction of the average reorientation time of the probe molecule with increasing EG in the mixed solvent system, thereby suggesting a lesser compactness induced by the presence of the co-solvent.     

CMC and dynamic properties of poly(VA-<Emphasis Type="Italic">b</Emphasis>-St) copolymer micelles for drug delivery

The polymeric micelles from amphiphilic block copolymer poly(vinyl alcohol-b-styrene) (poly(VA-b-St)) with different syndiotacticity of poly(vinyl alcohol) (PVA) block were prepared by dialysis against water. Critical micelle concentration (CMC) and dynamic properties of poly(VA-b-St) copolymeric micelles were investigated by fluorescence techniques. From the fluorescence emission spectrum measurements using pyrene as a fluorescence probe, the observed CMC value was in the range of 0.125–4.47 mg/L. The CMC value increased with decreasing the weight ratio of PS to PVA block and with increasing the syndiotacticity of PVA block. The rate of pyrene release was very slow for block copolymers containing PVA block with higher syndiotacticity, which indicates that their micelles have increased kinetic stability. This work was presented at 13 ^th YABEC symposium held at Seoul, Korea, October 20–22, 2007.     

Probe Molecules for Pulsed-Field-Gradient Diffusion Nuclear Magnetic Resonance Experiments on Micelles

Nuclear magnetic resonance (NMR) diffusion measurements of surfactants suffer from fast exchange of the surfactant between the micellar aggregate and bulk solution. Therefore, hydrophobic probe molecules are commonly used to directly measure aggregate diffusion under the assumption that the probe molecules remain solubilized inside the micelles. Aggregate size is then determined or estimated from the aggregate diffusion value. Unfortunately, the probe molecule also experiences rapid exchange between the aggregate and bulk, leading to inaccurate or unreasonable micelle diffusion values, a fact that has often been ignored in the literature. In this article, we present a systematic evaluation of probe molecules in cationic and anionic surfactants, obtained by measuring the diffusion of probe molecules with varying hydrophobicity. We find that an octanol–water partition coefficient of at least ~5 is required for correct measurements of aggregate diffusion in the systems studied. Notably, some commonly used probes have a partition coefficient much lower than five and are therefore not suitable for aggregate diffusion measurements. Consideration of these results will help researchers obtain accurate results for micelle sizing or partitioning studies with pulsed-field-gradient NMR.     

单分散二氧化硅超细颗粒的制备

利用3种不同类型的表面活性剂反胶团体系制备SiO2超细颗粒,并与传统的Stober制备方法进行了对比. 在阴离子表面活性剂AOT和非离子表面活性剂TritonX-100两类体系中,得到了单分散的SiO2超细颗粒．在AOT体系中颗粒粒径随体系水含量w。的增大而增大;而TritonX-100体系中,颗粒粒径随w。的增大而减小;在阳离子表面活性剂(如CTAB,TOMAC)体系中无法得到SiO2超细颗粒．对不同体系所得颗粒的粒径标准偏差及粒度分布进行了对比,结果表明制备粒径小于100 nm的SiO2颗粒,反胶团法明显优于Stober方法,粒径相对标准偏差较低, 而对粒径大于100 nm的颗粒,Stober方法仍不失为一种很好的制备途径．     

Hydroformylation in reverse micellar systems

Different micellar systems are characterized. Hydroformylation reactions are carried out in the most appropriate ones and are compared with hydroformylations in a non-micellar system. Reaction rates and selectivities for aldehydes are higher than the micelles. In addition to this, olefins between C₆ and C₁₆ are successfully hydroformylated in the micellar system, whereas C₈ is the highest olefin that can be hydroformylated without micelles. The behavior of the reaction in the micellar system is very sensitive to the initial composition and reaction conditions.     

Aqueous solution properties of a silicone surfactant and its mixed surfactant systems

The aqueous solution properties of a nonionic silicone surfactant of dimethylpolysiloxane and its mixed surfactant systems were studied. It was found that the silicone surfactant has a high surface activity and forms micelles in two steps: premicelles in dilute concentrations and polymolecular micelles above 3.7 × 10⁻⁷ mol dm⁻³. In mixed systems of the silicone surfactant with anionic hydrocarbon or fluorocarbon surfactant, weak intermicellar interactions were found. They are due to electrostatic interaction between hydrophilic groups of the respective micelles. Dye solubilization measurements showed that the solubilized amount of Yellow-OB is greater than predicted by ideal systems. Hydrazo-azo tautomerism is observed in fluorocarbon-silicone surfactant systems, while Yellow-OB is solubilized only in the azo-form in the hydrocarbon-silicone surfactant system.     

Fluorescein Derivatives as Fluorescent Probes for pH Monitoring along Recent Biological Applications

Potential of hydrogen (pH) is one of the most relevant parameters characterizing aqueous solutions. In biology, pH is intrinsically linked to cellular life since all metabolic pathways are implicated into ionic flows. In that way, determination of local pH offers a unique and major opportunity to increase our understanding of biological systems. Whereas the most common technique to obtain these data in analytical chemistry is to directly measure potential between two electrodes, in biological systems, this information has to be recovered in-situ without any physical interaction. Based on their non-invasive optical properties, fluorescent pH-sensitive probe are pertinent tools to develop. One of the most notorious pH-sensitive probes is fluorescein. In addition to excellent photophysical properties, this fluorophore presents a pH-sensitivity around neutral and physiologic domains. This review intends to shed new light on the recent use of fluorescein as pH-sensitive probes for biological applications, including targeted probes for specific imaging, flexible monitoring of bacterial growth, and biomedical applications.     

Vibrational spectroscopy of water at interfaces

Understanding liquid water's behavior at the molecular level is essential to progress in fields as disparate as biology and atmospheric sciences. Moreover, the properties of water in bulk and water at interfaces can be very different, making the study of the hydrogen-bonding networks therein very important. With recent experimental advances in vibrational spectroscopy, such as ultrafast pulses and heterodyne detection, it is now possible to probe the structure and dynamics of bulk and interfacial water in unprecedented detail. We consider here three aqueous interfaces: the water liquid-vapor interface, the interface between water and the surfactant headgroups of reverse micelles, and the interface between water and the lipid headgroups of aligned multi-bilayers. In the first case, sum-frequency spectroscopy is used to probe the interface. In the second and third cases, the confined water pools are sufficiently small that techniques of bulk spectroscopy (such as FTIR, pump-probe, two-dimensional IR, and the like) can be used to probe the interfacial water. In this Account, we discuss our attempts to model these three systems and interpret the existing experiments. For the water liquid-vapor interface, we find that three-body interactions are essential for reproducing the experimental sum-frequency spectrum, and presumably for the structure of the interface as well. The observed spectrum is interpreted as arising from overlapping and canceling positive and negative contributions from molecules in different hydrogen-bonding environments. For the reverse micelles, our theoretical models confirm that the experimentally observed blue shift of the water OD stretch (for dilute HOD in H(2)O) arises from weaker hydrogen bonding to sulfonate oxygens. We interpret the observed slow-down in water rotational dynamics as arising from curvature-induced frustration. For the water confined between lipid bilayers, our theoretical models confirm that the experimentally observed red shift of the water OD stretch arises from stronger hydrogen bonding to phosphate oxygens. We develop a model for heterogeneous vibrational lifetime distributions, and we implement the model to calculate isotropic and anisotropic pump-probe decays. We then compare these results with experimental data. Clearly, recent experimental advances in vibrational spectroscopy have led to beautiful new results, providing information about the structure and dynamics of water at interfaces. These experimental and concomitant theoretical advances (particularly the unified theoretical framework of non-linear response functions) have greatly contributed to our understanding of this unique and important substance.     

Photophysical properties and self-assembly of triblock copolymer with complexes of positively charged PDMAEMA and oppositely charged chromophores

The self-assembly and photophysical properties of a triblock copolymer with complex mid-block in THF and aqueous solution were investigated in this research. Poly(poly(ethylene glycol) methyl ether methacrylate)-block-poly(2-(dimethylamino ethyl methacrylate)-block- poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA–b–PDMAEMA–b–PPEGMA) triblock copolymer was synthesized by subsequent atom transfer radical polymerizations (ATRP) of DMAEMA and PEGMA. The PDMAEMA blocks were quaternized by a reaction with iodomethane. The complex of the positively charged PDMAEMA chain unit and sodium salt of 1-pyrenebutyric acid was prepared by mixing equimolar amount of the two components in THF/water mixture. Transmission electron microscopy and fluorescence technique results show that the triblock copolymer chains self-assemble into micelles in THF at high concentration. The critical aggregation concentration (CAC) of the triblock copolymer in THF determined by fluorescence technique is 6.8 × 10^?5 M. The triblock copolymer was also able to self-assemble into micelles in water. The value of CAC of the triblock copolymer in water is 2.0 × 10^?5 M. The photophysical properties and self-assembly structures of the triblock copolymer in aqueous solutions were influenced by added sodium chloride. After salt addition, a transition of the assembled structures from micelles to hollow structures was observed.     

Effects of sodium glycocholate and sodium taurocholate on the mixed micelles of bile salts and nonionic surfactant

Effects of sodium glycocholate (NaGC) and sodium taurocholate (NaTC) on the mixed micelles for two systems consisting of NaGC-octaoxyethylene glycol monon-decyl ether (C₁₀E₈) and NaTC-C₁₀E₈ have been studied as a function of the mixed micelles’ compositions, polarities of the micelles’ interior and mean aggregation numbers. The compositions of the mixed micelles are calculated from critical micelle concentration (CMC) data by using excess thermodynamic quantities. The polarities and mean aggregation numbers are determined from pyrene fluorescence in the mixed micelles. Both mixed systems were nonideal, and the mole fraction of NaGC or NaTC in a mixed micelle near the CMC was less than that in the aqueous mixed solution. However, the mixed micelle of the NaTC-C₁₀E₈ system contained more bile salt molecules than that of the NaGC-C₁₀E₈ system because of a good miscibility of NaTC and C₁₀E₈ molecules. The pyrene fluorescence results suggested that the mixed micelles changed from C₁₀E₈-rich micelles to NaGC- or NaTC-rich micelles, and mean aggregation numbers of the mixed micelles decreased abruptly with increasing mole fraction of bile salts. In the low mole fraction range of bile salts, however, both the polarities and the mean aggregation numbers for the NaTC-C₁₀E₈ system are lower than those for the NaGC-C₁₀E₈ system because of the high mole fraction of NaTC in a mixed micelle, and also because of the different effect of the conjugated group between NaTC and NaGC molecules in the mixed micelles.     

Physiochemical insight into the solution behavior of cationic gemini surfactant in water and ethanol–water systems

Surfactants in water and both alcohol-water mixed solutions are used extensively in a host of industrial applications. This work presents the solution behavior and micellar transition of a cationic gemini surfactant (GS): N,N′-dihexadecyl-N,N,N′,N′-tetramethyl-N,N′-ethanediyl-diammonium dibromide (16-2-16) in water and mixed water-ethanol media. Phase behavior for 16-2-16 in the ethanol–water system was investigated at ambient temperature. The rheological data obtained for these systems at varying alcohol concentrations showed that the system viscosity (η) decreased with as the ethanol concentration increased. Small-angle neutron scattering (SANS) was used to probe the structural details of the cationic micelles as a function of ethanol concentration and temperature. The scattering data inferred a structural transition from unilamellar vesicles (ULV) through rod-like micelles to ellipsoidal micelles occurs that is dependent on the solvent composition and temperature indicating the behavior of ethanol molecules as a cosolvent in the process of micelle breaking. The plausible physicochemical interactions in the 16-2-16-ethanol mixed system were further investigated using a computational simulation study employing density functional theory (DFT)/B3LYP (Gauss View 5.0.9) utilizing a 3-21G basis set.     

Synergistic Rheological Behavior of Mixed Micellar Solutions of Surfactin and Cetyl Trimethyl Ammonium Bromide

This paper investigated the rheological properties of novel viscoelastic thickening micelle system formed by surfactin and cetyl trimethyl ammonium bromide (CTAB). The total concentration of surfactin and CTAB was maintained at 12 wt%. The rheological behavior of the surfactin/CTAB synergistic micelles with different mass ratio and pH was systematically investigated. For the surfactin/CTAB micellar system with a mass ratio varied from 1/11 to 4/8, the viscosity of the micelles rose to a maximum with increasing pH, and then decreased with a further increase of pH. When the mass ratio was surfactin:CTAB = 2.5:9.5 (pH 5.72), the maximum viscosity of the micelle solution reached 8170 mPa. s. Meanwhile, the viscosity curve of the surfactin/CTAB systems was described by the nonlinear co-rotational Jeffreys model. This work sets a rheological foundation for the application of surfactin/CTAB systems. The thixotropic loop area of the micelles was basically zero. Through viscoelasticity measurements, the results demonstrated that the appropriate surfactin/CTAB mass ratio would favor the stability of the network structure of the synergistic thickening system. The value of G″(viscous modulus) is always higher than the value of G′ (elastic modulus).     

Photophysikalische Meßverfahren zur Untersuchung von Gas/Flüssig-Reaktoren

Photophysical measuring techniques for the study of gas/liquid reactors . After a brief account of the fundamentals of photophysics, the authors describe various photophysical measuring procedures, with reference to available instrumentation, including prices. The measuring methods permit contactless and intertialess determination of various quantities in very small volumes (temperature, viscosity, concentration, pH, orientation of molecules, etc.). The authors examine which methods are available for the study of gas/liquid reactors. The most promising studies seem to involve the heat effects accompanying absorption with chemical reaction, study of interfacial effects (slowing mass transfer by accumulation of surface-active impurities, Marangoni effect), and the observation of complex reaction systems. Photophysical measuring techniques can also be used for measurements in industrial reactors; some of the known applications are described.     

The Formation of pH-Sensitive Wormlike Micelles in Ionic Liquids Driven by the Binding Ability of Anthranilic Acid

Wormlike micelles are typically formed by mixing cationic and anionic surfactants because of attractive interactions in oppositely charged head-groups. The structural transitions of wormlike micelles triggered by pH in ionic liquids composed of N-alkyl-N-methylpyrrolidinium bromide-based ILs (ionic liquids) and anthranilic acid were investigated. These structures were found responsible for the variations in flow properties identified by rheology and dynamic light scattering, and account for the structures observed with cryogenic transmission electron microscopy (Cryo-TEM). High-viscosity, shear-thinning behavior, and Maxwell-type dynamic rheology shown by the system at certain pH values suggested that spherical micelles grow into entangled wormlike micelles. Light scattering profiles also supported the notion of pH-sensitive microstructural transitions in the solution. Cryo-TEM images confirmed the presence of spherical micelles in the low-viscosity sample and entangled wormlike micelles in the peak viscosity sample. Nuclear magnetic resonance spectroscopy analysis revealed that the pH sensitivity of ionic liquid systems originated from the pH-dependent binding ability of anthranilic acid to the cationic headgroup of ionic liquids.