Fluorescence Probe Method Research Articles

Self-Assembly and Emulsification of Poly{[styrene-alt-maleic acid]-co-[styrene-alt-(N-3,4-dihydroxyphenylethyl-maleamic acid)

Self-assembled polymeric micelles can be used as efficient particulate emulsifiers. To explore the relationship between the structure and the oil-water interfacial behavior of the micelle emulsifiers, a new type of amphiphilic random copolymer, poly{(styrene-alt-maleic acid)-co-[styrene-alt-(N-3,4-dihydroxyphenylethyl-maleamic acid)]} (SMA-Dopa), was synthesized, self-assembled into micelles, and used as emulsifiers. SMA-Dopa was synthesized via an aminolysis reaction between dopamine and commercial alternating copolymer poly(styrene-alt-maleic anhydride) (SMA). Dopamine moiety facilitated the self-assembly of the SMA-Dopa in selective-solvent into stable micelles, and increased the adsorption of the SMA-Dopa at the oil-water interface. Additionally, the structural transition of the self-assembled SMA-Dopa52 micelles in response to pH and salinity changes were confirmed by means of TEM, AFM, DLS, aqueous electrophoresis techniques, potentiometric titration, and pyrene fluorescence probe methods. Micelles shrunk with increasing salinity, and flocculation of the shrunken primary micelles occurred at salt concentration exceeding 0.1 M. The micelles swelled with increasing pH, and the disassociation of the SMA-Dopa52 micelles occurred at pH above approximately 6.5. The structure of the micelles plays a crucial role in the oil-water interfacial performance. Micelles with various structures were used as emulsifiers to adsorb at the styrene-water and toluene-water interfaces. The emulsifying characteristics demonstrated that self-assembled SMA-Dopa52 micelles with moderately swollen structure (at 2 < pH < 6) combine the advantages of the solid particulate emulsifiers and polymeric surfactants, possessing excellent emulsifying efficiency and good emulsion stability. Moreover, the emulsifying performance of the SMA-Dopa52 micelles could be enhanced by the addition of salt.

Effects of High Hydrostatic Pressure Treatment on Physicochemical Characteristics of Sea Cucumber

The effects of high hydrostatic pressure (HHP) treatment on sea cucumber qualities, such as shelf-life, autoenzyme, total volatile basic nitrogen (TVB-N), mucopolysaccha ride and protein, were investigated experimentally. The shelf-life of sea cucumber was greatly prolonged by HHP treatment. High pressure treatment of sea cucumber significantly reduced the activity of autoenzyme at 550 MPa. The TVB-N content was 8.4 mg/100 g in the HHP-treated samples after 38 days' storage at 4 °C, while it had already reached 11.2 mg/100 g in the untreated ones after 5 days' storage under the same condition. The relative mucopolysaccharide content of the HHP-treated samples was 94.3%, while that of the heat-treated ones was only 35.5%. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Differential scanning calorimetric (DSC), ANS fluorescence probe method and fourier-transform infrared (FTIR) spectroscopy results indicated some changes in protein subunits, denaturation, surface hydrophobicity and secondary structure of sea cucumber protein. This study has provided complementary information of pressure-induced structural changes on both the molecular and the sub-molecular level of sea cucumber protein.

Biochemical evaluation of a synthesized isoflavone-selenium complex by molecular spectra

A coordination compound of 5, 7-dihydrox-4'-methoxyisoflavone and selenium was synthesized and its structure was identified by IR, LC-MS and (1)H-NMR. Its biochemical effects were investigated using bovine serum albumin (BSA) as a target protein molecule, in which process three-dimensional (3D) fluorescence spectra, ultraviolet spectra, circular dichroism (CD) spectra and fluorescence probe techniques were employed. The interaction of SEIF and BSA was discussed by fluorescence quenching method and Förster non-radiation energy transfer theory. The thermodynamic parameters ΔH (θ), ΔG (θ), ΔS (θ) at different temperatures were calculated according to Van't Hoff isobaric equation and the results indicated the interaction was an exothermic as well as a spontaneous process. The binding site was explored by fluorescence probe method using warfarin and ibuprofen as markers. Intramolecular forces which are responsible for maintaining the binding were mainly hydrogen bond and van der Waals power. The average distance from the tryptophan residue in domain II of BSA (donor) to SEIF (acceptor) is 3.57 nm at body temperature. The conformation changes of BSA were investigated by 3D fluorescence and CD spectra.

Cytomimetic Large-Scale Vesicle Aggregation and Fusion Based on Host–Guest Interaction

Herein, we have shown a large-scale cell-mimetic (cytomimetic) aggregation process by using cell-sized polymer vesicles as the building blocks and intervesicular host-guest molecular recognition interactions as the driving force. We first prepared the hyperbranched polymer vesicles named branched polymersomes (BPs) around 5-10 μm through the aqueous self-assembly of a hyperbranched multiarm copolymer of HBPO-star-PEO [HBPO = hyperbranched poly(3-ethyl-3-oxetanemethanol); PEO = poly(ethylene oxide)]. Subsequently, adamantane-functionalized BPs (Ada-BPs) or β-cyclodextrin-functionalized BPs (CD-BPs) were prepared through the coassembly of HBPO-star-PEO and Ada-modified HBPO-star-PEO (HBPO-star-PEO-Ada), or of HBPO-star-PEO and CD-modified HBPO-star-PEO (HBPO-star-PEO-CD), respectively. Macroscopic vesicle aggregates were obtained by mixing CD-BPs and Ada-BPs. The intervesicular host-guest recognition interactions between β-CD units in CD-BPs and Ada units in Ada-BPs, which were proved by (1)H nuclear Overhauser effect spectroscopy (NOESY) spectrum and the fluorescence probe method, are responsible for the vesicle aggregation. Additionally, the vesicle fusion events happened frequently in the process of vesicle aggregation, which were certified by double-labeling fluorescent assay, real-time observation, content mixing assay, and component mixing assay.

Drug solubilization by amino acid based polymeric nanoparticles: Characterization and biocompatibility studies

Three novel amino acid based amphiphilic copolymers, poly(sodium N acryloyl-l-aminoacidate-co-dodecylacrylamide) (where aminoacidate=glycinate, leucinate, and phenylalaninate) were synthesized and characterized. These hydrophobically modified polyelectrolytes (HMPs) formed spheroidal nanoparticular aggregates above a critical aggregation concentration with average diameter 20–200nm and overall negative charges as indicated by dynamic light scattering (DLS) and zeta-potential (ζ≈−10.2 to −25.2) measurements, respectively. The size and shape of the nanostructures was confirmed by transmission electron microscopic images. The micropolarity and microviscosity of the nanosize aggregates were investigated by fluorescence probe method using extrinsic probes like N-phenyl-1-naphthylamine, pyrene, and 1,6-diphenyl-1,3,5-hexatriene. The stability of the copolymer micelles was investigated as a function of pH and temperature using fluorescence and DLS techniques. Both fluorescence probe and DLS data suggest that the copolymer micelles are highly stable under physiological condition (pH 7.4, 37.4°C). These HMP micelles were evaluated primarily as a drug delivery system. The ability of the copolymers to encapsulate hydrophobic drug was investigated using a poorly water-soluble antifungal drug, griseofulvin. Biocompability of the HMPs were examined by hemolytic and cytotoxicity assay. All three HMPs were non-hemolytic up to the tested concentration of about 1.0g/L. In vitro biological assay indicated that these new copolymers were also less toxic against 3T3 mammalian cell line. The studies suggest that these newly conceived amino acid based biocompatible polymeric nanoparticles might have potential application as injectible drug delivery systems which can enhance the therapeutic index of poorly water-soluble clinically challenging drugs.

Characterization of the interaction between surfactants and enzymes by fluorescence probe

In order to investigate the mechanism of the different stimulatory effects of the biosurfactant rhamnolipid and the chemical surfactant Tween 80 on enzymatic hydrolysis of lignocellulose, the interaction between surfactants and enzymes was analyzed by the fluorescence probe method using pyrene as probe. Based on the evolution law of pyrene fluorescence spectroscopy in the “surfactants–enzymes” systems, the interaction relationship between surfactants and enzymes was analyzed and discussed in this paper. The results show that enzyme molecules bind with rhamnolipid molecules, participate in the formation of rhamnolipid micelles, and increase the inner hydrophobic polarity of micelles, but do not change the properties of rhamnolipid micelles above the CMC (Critical Micelle Concentration). Nevertheless, for Tween 80, enzyme molecules also participate in the forming of micelles, however, they exhibit a stronger interaction with enzymes above the CMC. Both rhamnolipid and Tween 80 bind more strongly with xylanase than cellulase. Considering also previous experimental results, it can be concluded that the interaction between surfactants and enzymes improve enzyme stability and activity, and, therefore, the efficiency of enzymatic hydrolysis of lignocellulose is enhanced. The findings further provide theoretical knowledge about the mechanism of the stimulative effects of surfactants on enzymatic hydrolysis of lignocellulose.

Microstructure of Polyelectrolyte Nanoaggregates Studied by Fluorescence Probe Method

The microstructure of water soluble nanoaggregates based on polyelectrolyte complex formed by the cationic comb-type copolymer poly(acrylamide -co-[3- (methacryloyl-amino)propyl] trimethylammonium chloride)-graft- polyacrylamide [P(AM-co-MAPTAC)-g-PAM] and the anionic linear polyelectrolyte sodium polyacrylate (NaPA) was investigated using the fluorescence probe technique. The fluorescence probe were 1-anilinonaphthalene-8-sulfonic acid (ANS), pyrene (Py) and 1,10-bis(1-pyrene) decane (PD). The fluorescence properties in polyelectrolyte complex solutions, which are sensitive to either micropolarity (ANS, Py) or microviscosity (PD), were related to the quantities obtained in different pure or mixed solvents. Micropolarities were quantified utilizing the polarity common index (Reichardt) E(T)(30). ANS and Py showed a variation of the micropolarity with the charge ratio of the two polymers, with the lowest polarity reached at the complex neutralization. The PD probe, by its excimer-to-monomer fluorescence intensities ratio, enabled us to evidence the effect of the composition and the comb-type copolymer grafting density on the microviscosity of the interpolyelectrolytes aggregates. It has been found that the microviscosity increased with the density of the grafting PAM chains.

Chemicobiological effects of herbicide MCPA-Na on plasma proteins

Under physiological conditions, the potential hematological toxicity of herbicide 2-methyl-4-chlorophenoxyacetic acid sodium (MCPA-Na) was discussed by fluorescence probe technology and spectroscopy methods including three-dimensional (3D) fluorescence, UV absorption and circular dichroism (CD) spectra. In vitro, MCPA-Na bound with bovine serum albumin (BSA) and formed new complex at ground state by electrostatic force and hydrogen bond. During the process, non-radiation energy transfer from BSA to MCPA-Na occurred and the distance r between donor and acceptor was obtained based on Förster theory. The binding site was investigated by fluorescence probe method and the results implied MCPA-Na was absorbed on domain II of BSA molecule. The enthalpy change (ΔH(θ)), Gibbs free energy change (ΔG(θ)) and entropy change (ΔS(θ)) were calculated at four different temperatures according to Van't Hoff isobar equation and Gibbs-Helmholtz equation. Negative value of ΔG(θ) indicated the process of binding was a spontaneous and irreversible process, which gave a broad hint that MCPA-Na was likely to be poisonous. CD spectra exhibited significant changes of secondary structures in BSA molecule and three-dimensional fluorescence spectra indicated the tryptophan residue in BSA was placed in a less hydrophobic environment, which presented additional evidence to caution the danger of MCPA-Na residue in food. Meanwhile, the mechanism and geometry of the binding was analyzed at molecular level.

The stabilization mechanism of latanoprost

The content of latanoprost is likely to decrease in solution because of the adsorption to eye drop containers and hydrolysis. We reduced these problems and established a formulation of latanoprost eye drops which is stable at room temperature. We assume that the additive surfactants form micelles and stabilize latanoprost in this formulation. In this study, we elucidated the latanoprost stabilization mechanism. It was revealed by Arrhenius analysis that the adsorption to eye drop containers and hydrolysis of latanoprost were temperature-dependent. In addition, polyethylene glycol monostearates inhibited the adsorption and hydrolysis of latanoprost at 1 mg/mL, which exceeded the critical micelle concentration. By the fluorescent probe method, it was suggested that the surfactants were associated with benzalkonium chloride and formed complex micelles consisting of about 10 molecules, and latanoprost interacted with the micelles at 1:1. By 1H NMR, it was revealed that adsorption was inhibited by arranging the hydrophobic group toward the center of complex micelles and that hydrolysis was inhibited by interaction between the ester group and the complex micelles. It was shown that the latanoprost is stabilized by the interaction with complex micelles. It was effective for the inhibition of both adsorption and degradation.

A Novel Zwitterionic Imidazolium‐Based Ionic Liquid Surfactant: 1‐Carboxymethyl‐3‐Dodecylimidazolium Inner Salt

AbstractA novel zwitterionic imidazolium‐based ionic liquid (IL) surfactant, 1‐carboxymethyl‐3‐dodecylimidazolium inner salt, was synthesized. The molecule structure was confirmed by means of electrospray ionization mass spectrometry, 1H nuclear magnetic resonance and elemental analysis. The isoelectric point (pI) is 3.8 ± 0.1 at 35 ± 0.1 °C. The other important physicochemical parameters such as the critical micelle concentration (CMC), the surface tension at CMC (γCMC), the adsorption efficiency (pC20), the surface pressure at CMC (ΠCMC), the maximum surface excess (Γm), the minimum molecular cross‐sectional area (Amin), the value of CMC/C20 and the average number of aggregation (Nm) were determined by surface tension and steady‐state fluorescence probe methods, respectively.

Detection of OH Radicals Generated in Polymer Electrolyte Membranes of Fuel Cells

OH radicals formed during the PEFC operation of a single cell were detected by means of a fluorescence probe method with coumarin. The coumarin molecules impregnated in the polymer electrolyte membrane react with OH radicals to form a highly fluorescent product, umbelliferone. After PEFC operation under various conditions, the cross section of the membrane for five positions was monitored by a fluorescence microscope and the distribution of the OH radical density in the membrane was evaluated. The difference among the radical densities at the five positions was large for each membrane. The observations suggest that the crossleak of oxygen gas is a main process of the OH radical formation.

Development of a Novel PPARγ Ligand Screening System Using Pinpoint Fluorescence-Probed Protein

The activation of peroxisome-proliferator-activated receptor-γ (PPARγ), which plays a central role in adipocyte differentiation, depends on ligand-dependent co-activator recruitment. In this study, we developed a novel method of PPARγ ligand screening by measuring the increase in fluorescent polarization accompanied by the interaction of a fluorescent co-activator and PPARγ. Sterol receptor co-activator-1 (SRC-1), a major PPARγ co-activator, was probed by fluorescent TAMRA by the Amber codon fluorescence probe method. Polarization was increased by adding PPARγ ligands to a solution containing labeled SRC-1 (designated TAMRA-SRC-S) and PPARγ. The disassociation constants (Kd) of the PPARγ synthesized ligands, pioglitazone (221 nM), troglitazone (83.0 nM), and 15-deoxy-Δ12,14-prostaglandin J(2) (15d-ΔPGJ(2)) (156 nM), were determined by this method. Farnesol (2.89 µM) and bixin (21.1 µM), which we have reported to be PPARγ ligands, increased the fluorescent polarization. Their Kd values were in agreement with the ED(50) values obtained in the luciferase assay. The results indicate that the method is valuable for screening natural PPARγ ligands.

Synthesis and Critical Micelle Concentration of a Series of Gemini Alkylphenol Polyoxyethylene Nonionic Surfactants

AbstractA series of gemini n‐alkylphenol polyoxyethylene surfactants (GAP) were successfully synthesized and their molecular structure were confirmed by NMR and FTIR spectrum. Using the same synthesis route, a gemini nonylphenol polyoxyethylene surfactant (GNP) was synthesized using an industrial nonylphenol product and paraformaldehyde, and its molecular structure was also characterized by 1H‐NMR and FTIR spectra. The optimal reaction conditions were established. The critical micelle concentration (CMC) values of GAP were determined by means of Wilhelmy plate method and steady‐state fluorescence probe method. The experimental results show how the lengths of the hydrophilic polyoxyethylene chain and the hydrophobic tail alter the CMC values. The CMC values of the GAP are found to be much lower than those of corresponding conventional single tail nonionic surfactants of the polyethoxylated alkylphenol type, which indicates that the gemini species exhibit a better surface activity.

Aqueous Solution Properties of Disulfide-Linked Fluorinated Gemini and Cleaved Monomeric Thiol Surfactants

We prepared a fluorinated gemini surfactant containing a disulfide bond in its spacer chain, [C₈F₁₇(CH₂)₃N(CH₃)₂CH₂CH₂SSCH₂CH₂N(CH₃)₂(CH₂)₃C₈F₁₇]2Cl, and its analogue with a hexamethylene spacer. Monomeric thiol surfactant, [C₈F₁₇(CH₂)₃N(CH₃)₂CH₂CH₂SH]Cl, was readily produced by the cleavage of the gemini surfactant using dithiothreitol in water. The critical micelle concentration was determined using surface tension, conductivity, and fluorescence probe methods. The critical micelle concentration of the monomeric surfactant was significantly larger than that of the gemini surfactant. The surface tension of aqueous solution for the cleaved monomeric thiol surfactant returned gradually to the original value through the formation of the disulfide bond via air oxidation.

Aqueous Solution Behavior of Cationic Surfactants Containing Sulfide Linked Alkyl Chain

Cationic surfactants containing a thioether group in the hydrophobic chain were prepared by the reaction of alkanethiol and bromocholine bromide. The aqueous solution properties of the thio-surfactants were investigated and compared with conventional cationic surfactants. The Krafft temperatures of the thio-surfactants were lower than that of alkyltrimethylammonium bromide. The critical micelle concentrations were determined by the conductivity method, and pyrene and SPQ fluorescence probe methods. A linear relation was observed for the plots of cmc vs. chain length. However, the cmc of the thio-surfactants depended on the position of the thioether group in the hydrophobic alkyl chain. It was found that the thioether group exhibited quenching ability toward SPQ fluorescence. The variation of the surfactant monomer concentration in equilibrium with micelles can be estimated from Stern-Volmer plots.

Effects of Soybean Isoflavones on In vitro Antioxidative Capacity of Satellite Cells of Porcine Skeletal Muscles

Abstract A synthetic isoflavone (ISO-S) or genistein was added in culture medium at different concentrations (0, 10, 20, 30, 40, and 80 μmol L −1) to investigate the effects of soybean isoflavones on antioxidative capacity of porcine skeletal muscle satellite cells. After 48 h incubation, the suspension was cryopreserved for the determination of Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) activities, and malondialdehyde (MDA) content. The mRNA levels of SOD, CAT, and GSH-Px gene in cells were detected with Taqman fluorescent probe method. The results showed that the content of MDA and the activities and the mRNA levels of SOD of porcine skeletal muscle satellite cells were influenced by supplemented soybean isoflavone (P<0.05) when adding 10-80 μmol L −1 ISO-S or genistein in the medium. The MDA contents, SOD and CAT activities and their mRNA expression levels of porcine skeletal muscle cells responded quadratically ( P <0.05) as the level of ISO-S or genistein increased. Pre-incubation of porcine skeletal muscle satellite cells with ISO-S or genistein at 10-40 μmol L −1 elevated the activities and the mRNA expression levels of SOD and CAT in cells concurrently and decreased the cellular content of MDA (P<0.05). The results indicated that pre-incubation of ISO-S or genistein at 10-40 μmol L −1 could improve the antioxidative capacity of porcine skeletal muscle satellite cells.

The preparation of phosphorylcholine-containing poly(Llactide) nanoparticles with solvent evaporation method

AbstractPhosphorylcholine-containing poly(L-lactide) (PLLA-PC) is a kind of amphiphilic copolymer synthesized with L-lactide (LLA) as monomer and glycerophosphorylcholine as ring-opening reagent. In this paper, self-assembly nanoparticles of PLLA-PC were prepared with solvent evaporation method. The factors that affected the properties and stability of nanoparticles were investigated. Transmission electron microscope (TEM) indicated that PLLA-PC nanoparticles presented typical core/shell structure. The critical micelle concentration (CMC) was determined with fluorescent probe method. The results showed that the CMCs were quite low (&lt; 1×10-3 g/l) and were dependent on LLA units in the copolymer. The size of the nanoparticles was detected by dynamic light scattering (DLS). The results indicated that the size could be affected by LLA units, the amount of solvent and water in the preparation process. On the other hand, the obtained nanoparticles were stable while being stored at 4 °C, and hardly changed over the dilution with water, which was of great importance in venous injection. The solubility of clofazimine was better in aqueous solution of PLLA-PC nanoparticles than in pure water. This preliminary study suggested that PLLA-PC nanoparticles had a great potential as delivery system for hydrophobic drug.

Effect of ghrelin on angiotensin II induced human umbilicus vein endothelial cell oxidative stress and endothelial cell injury.

To determine the effect of ghrelin on protecting the human umbilical vein endothelial cells (HUVEC) from injury by angiotensin II (Ang II) in vitro. (1) HUVEC was incubated for 24 h with AngII whose final concentration in the medium varied from 10⁻⁹ to 10⁻⁶ mol/L or pretreated with 10⁻⁹ to 10⁻⁶ mol/L ghrelin for 2 h before incubation for 24 h with Ang II whose final concentration in the medium was 10⁻⁶ mol/L. HUVECs were harvested to measure the cell vitality and cell apoptosis. The cell vitality was determined by MTT and cell apoptosis rates were measured by Annexin V-FITC apoptosis detection kit. (2) HUVECs were incubated for 3, 6, 12, or 24 h with 10⁻⁹, 10⁻⁸, 10⁻⁷, or 10⁻⁶ mol/L Ang II, respectively. Before HUVECs were incubated with 10⁻⁶ mol/L Ang II for 24 h, ghrelin (10⁻⁹, 10⁻⁸, 10⁻⁷, and 10⁻⁶ mol/L) was used to pretreat the cells for 2 h. Growth hormone secregogue receptor 1a blocker [D-Lys³]GHRP-6 was added to the cells which were incubated for 24 h with 10⁻⁶ mol/L Ang II and pretreated with 10⁻⁶ mol/L ghrelin for 2 h. Cell reactive oxygen species were measured by dichlorofluorescin (DCF) fluorescence probe method. (3) HUVECs were incubated for 24 h with 10⁻⁹, 10⁻⁸, 10⁻⁷, or 10⁻⁶ mol/L Ang II and ghrelin, respectively,and then were incubated with 10⁻⁶ mol/L of Ang II for 3, 6, 12, or 24 h. Furthermore, HUVECs were pretreated with 10⁻⁹, 10⁻⁸, 10⁻⁷, or 10⁻⁶ mol/L ghrelin for 30 min,1 h, or 2 h, and then were incubated with the inhibitor of mitogen-activated protein kinase /extracellular regulated kinase (MAPK/ERK1/2),PD98059, the inhibitor of phosphoinositide-3-kinase/serine threonine kinase( PI3K/Akt)wortmannin, and [D-Lys³]GHRP-6 for 24 h. NO production was compared among groups. HUVECs were pretreated with ghrelin, PD98059, wortmannin, and [D-Lys³]GHRP-6 for 2 h and co-cultured with 10⁻⁶ mol/L Ang II for 24 h, or pretreated with ghrelin plus PD98059, wortmannin, and [D-Lys³]GHRP-6 before incubation with Ang II for 24 h. NO was measured in the endothelial cell supernatants by Griess method. (4) HUVECs were cultivated with blank or Ang II with or without pretreatment with ghrelin or both ghrelin and wortmannin. The protein expression of eNOS and phospho-protein expression of Akt were measured by Western blot analysis. Ang II injuried the endothelial cell vitality,increased the cell apoptosis rates in HUVECs, and decreased NO production in HUVEC supernatants,whereas ghrelin protected HUVECs from Ang II injury. Ghrelin decreased the reactive oxygen species in HUVECs induced by Ang II. The effect could be attenuated by [D-Lys³]GHRP-6 pretreatment; PD98059 alleviated Ang II inhibition of NO production in HUVEC supernatants. Wortmannin and [D-Lys³]GHRP-6 could abolish protection of ghrelin from reducing NO production in HUVEC supernatants. Ang II reduced the expression of eNOS,but ghrelin increased eNOS expression. Wortmannin could cancel this effect of ghrelin. Ghrelin increased p-Akt expression and reached the peak in 10 and 20 min. Ghrelin may protect HUVECs from Ang II induced injury, which is related to decreasing oxidative stress, increasing the protein expression of eNOS, and activating PI3K/Akt signal pathway through GHSR1a receptor.

Detection of OH Radicals Generated in Polymer Membranes of PEFC

OH radicals formed during the PEFC operation of a single cell were detected by means of a fluorescence probe method with coumarin. In polymer electrolyte, coumarin molecules were impregnated to react with OH radicals to form a highly fluorescent product, umbelliferone. By measuring the fluorescence intensity of the cross section of the membrane with a fluorescence microscope, the distribution of the OH radical density in the membrane could be evaluated for various operational conditions.

Synthesis and surface activity properties of alkylphenol polyoxyethylene nonionic trimeric surfactants

A series of trimeric n-alkylphenol polyoxyethylene surfactants (TAP) were successfully synthesized and the molecular structure were confirmed by NMR, FTIR spectrum and elemental analysis. Using the same synthesis route, the trimeric nonylphenol polyoxyethylene surfactant (TNP) was synthesized using industrial product nonylphenol and paraformaldehyde, and its molecular structure was characterized by 1HNMR, FTIR spectrum and elemental analysis. The optimal reaction conditions were established. The surface activity properties of TAP and TNP (such as the critical micelle concentration (cmc), the values of surface tension at the cmc ( γ cmc), the maximum surface excess concentration ( Γ cmc), and the minimum surface area per surfactant molecule ( A cmc)), were determined by means of Wilhelmy plate method and steady-state fluorescence probe method, respectively. The experimental results show that the lengths of the hydrophilic group oxyethylene (EO) chains and hydrophobic group methylene chains have an influence on the cmc, γ cmc, Γ cmc, and A cmc of series of surfactants. Furthermore, TAP are arranged to staggered three-dimensional array mode at the air–water interface, which has exhibited better surface properties, such as low cmc values, strong adsorption affinities and wet abilities.