Self-Assembling Behavior of Polyglyceryl-Modified Silicone Surfactant in Aqueous Solution

We report interesting self-assembly behavior of a polyglyceryl-modified silicone surfactant in the aqueous solution; the sample has been characterized through measurements of surface tension, transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle x-ray scattering (SAXS). Aqueous solutions of this surfactant had a low critical aggregation concentration (CAC) and surface tension (21.5 mN · m^?1), substantially lower than those reported for polyether-modified silicone surfactants with a similar molecular architecture. DLS and TEM revealed self-assembled spherical micelles with a narrow size distribution. At higher concentrations (10 wt%), linear packing of micelles was observed, while the micelle size distribution remained similar (50–90 nm). SAXS data could be fitted through the use of a core–shell model and implied that the core radius remained roughly 4.3–6.0 nm for all solutions of the surfactant analyzed. The origin of its curious aggregates behavior is attributed to hydrogen bonding, steric effects, and the directionality of bond angle from the polyglyceryl block of this novel class of silicone surfactant. This type of surfactant coupling lipophilic segments assembles the cores of the micelles in water which may find positive factors for potential applications such as microreaction compartmentalization.     

Isolation of Terpenoids from Trichilia quadrijuga (Meliaceae) by Droplet Counter-Current Chromatography

The Trichilia genus (Meliaceae) consists of about 230 species distributed throughout tropical America and its phytochemical profile is rich in terpenic metabolites. Droplet counter-current chromatography (DCCC) was used for the isolation and purification of secondary metabolites obtained from a dichloromethane fraction (2.9 g) of Trichilia quadrijuga stems. A hexane–ethyl acetate–methanol–water (1:2:1.75:1, v/v/v/v) solvent system was chosen to isolate 2β,3β,4β-trihydroxypregnan-16-one (1, 24.5 mg, 0.8%), kudtdiol (2, 45.0 mg, 1.6%) and 3-O-β-d-glucopyranosylsitosterol (3, 6.0 mg, 0.2%). The results showed that DCCC was a very effective tool for the isolation of terpenes from T. quadrijuga.     

Synthesis and Properties of Gluconamide-Based Trisiloxane Surfactant

A gluconamide-based trisiloxane surfactant (Si3N2-GA) was prepared via a two-step method. Structure characterization of the Si3N2-GA was performed by fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (¹H NMR). Surface activity and aggregation behavior in aqueous solution of the Si3N2-GA were investigated by surface tension measurements, dynamic light scattering (DLS), and negative-stained transmission electron microscopy (TEM). The results show that the critical micelle concentration (CAC) and surface tension (γ_CAC) at the cmc in aqueous solution of the Si3N2-GA are 3.77 × 10^?4 M and 20.5 mN · m^?1, respectively, and the surfactants can self-assemble into spherical vesicle with diameters in the range from 50 to 150 nm.     

Sensing water in organic solvent using a polyurethane-silica hybrid membrane doped with a luminescent ruthenium complex

We have prepared an ~1.4 μm thin hybrid film from polyurethane (PU) hydrogel and tetraethylorthosilicate (TEOS) by a sol–gel method, and have incorporated the red-luminescent ruthenium-tris-bipyridyl complex. At an optimized ratio of PU/TEOS (1.5:1; w/w) and annealing temperature (60 °C), the membrane sensor exhibits good capability to extract water from organic solvents but also can well retain the ruthenium dye. If contacted with water-containing organic solvents such as acetone or THF, both the luminescence intensity and wavelength change significantly. The response of luminescence intensity to the water fraction in organics is sigmoidal, which can be well fitted with a modified Stern-Volmer equation. The sensor works in the ranges of 0–6 % and 0–12 % (v/v) of water in acetone and THF, respectively, with detection limits of 0.13 % and 0.486 % (v/v).

Core-corona structure of cubic silsesquioxane-poly(ethylene oxide) in aqueous solution: fluorescence, light scattering, and TEM studies

Well-defined amphiphilic cubic silsesquioxane-poly(ethylene oxide) (CSSQ-PEO) was prepared from octakis (dimethylsiloxy)octasilsesquioxane (Q8M8(H)) and allyl-PEO through a hydrosilylation reaction. The structure of CSSQ-PEO was characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). The amphiphilic properties and aggregation process of CSSQ-PEO in aqueous solution were investigated by fluorescence, dynamic and static light scattering (DLS and SLS), and transmission electron microscopy (TEM). The critical aggregation concentration (CAC) determined by fluorescence measurements was found to be 0.28 mg/mL. Combinations of DLS, SLS, and TEM studies showed the existence of core-corona micelle with hydrophobic CSSQ as the core and hydrophilic PEO as the corona in aqueous solution. The observation of two size distribution peaks from DLS measurements revealed the coexistence of small amounts of unassociated unimolecular micelles (approximately 10% of the scattered intensity) together with micellar aggregates when the CSSQ-PEO concentration was < or = 2 mg/mL. The hydrodynamic radii (R(h)) of unassociated unimolecular micelle and micellar aggregates were found to be 26 and 79 nm, respectively. A large R(g)/R(h) ratio (1.46) and the extremely small value of average chain density (4 x 10(-4) g/cm3) indicate the small hydrophobic CSSQ core was surrounded by the extended PEO coronae. The aggregation number (N(agg)) of CSSQ-PEO in aqueous solution was found to be 38 +/- 2 from SLS and 31-40 from TEM, respectively. The long PEO segments act as a spacer between the spherical aggregates, which facilitate the formation of a network-like structure at high concentration.     

Formation of Vesicles and Micelles in Aqueous Systems of Tetrameric Acids as Determined by Dynamic Light Scattering

A comprehensive dynamic light scattering (DLS) study on the system BP10Na₄/water is presented. BP 10Na₄ is a tetrameric fatty acid in sodium form. In order to change molecular packing conditions both electrolyte (NaCl) and alcohol (1-butanol, 1-pentanol) are added to the surfactant system. Phase diagrams of the systems reveal not only an extensive micellization, but also the occurrence of a lamellar liquid crystalline D phase. The DLS study shows an existence of vesicles at very dilute BP10Na₄ concentrations ( ?cmc) and also a co-existence of micelles and vesicles at higher BP10Na₄ concentrations. Cryo-TEM pictures verify the existence of the vesicles. Based on the DLS and SLS experiments the weight-average molar mass of the micelles are estimated to be 13500 g/mol at 100 mM NaCl and 22700 g/mol at 600 mM. The corresponding aggregation numbers are 13 and 22, respectively.     

Hydrophobic and electrostatic interactions in the mixture hydrolyzed polyacrylamide–N-dodecylpyridinium chloride (AD37–DPC) in aqueous solution

The interactions of oppositely charged polyelectrolyte and surfactant (anionic polyacrylamide AD37 and dodecylpyridinium chloride DPC, respectively) in aqueous solution were studied at 25 °C by measurement of viscosity and conductivity. The system was investigated in aqueous medium in the absence and presence of NaCl. The AD37 interacts strongly with the DPC surfactant of the opposite charge. The interactions are electrostatic and hydrophobic. Thus, they are manifested in the formation of hydrophobic aggregates. The critical aggregation concentration (CAC) is much lower than the critical micellar concentration (CMC) of the surfactant alone. However, the value of the saturation concentration X ₂ is higher. The ionic strength of the medium after addition of salt explains an important part of these interactions. In fact, the electrolyte charge affects the CMC and the CAC values.     

The surface and solution properties of dihexadecyl dimethylammonium bromide

The surface adsorption behavior and solution aggregate microstructure of the dichain cationic surfactant dihexadecyl dimethylammonium bromide (DHDAB) have been studied using small angle neutron scattering (SANS), light scattering, neutron reflectivity (NR), and surface tension (ST). Using a combination of surface tension and neutron reflectivity, the DHDAB equilibrium surface excess at saturation adsorption has been measured as 2.60 +/- 0.05 x 10 (-10) mol.cm (-2). The values obtained by both methods are in good agreement and are consistent with the values reported for other dialkyl chain surfactants. The critical aggregation concentration (CAC) values obtained from both methods (NR and ST) are also in good agreement, with a mean value for the CAC of 4 +/- 2 x 10 (-5) M. The surface equilibrium is relatively slow, and this is attributed to monomer depletion in the near surface region, as a consequence of the long monomer residence times in the surfactant aggregates. The solution aggregate morphology has been determined using a combination of SANS, dynamic light scattering (DLS), cryogenic transmission electron microscopy (CryoTEM), and ultrasmall angle neutron scattering (USANS). Within the concentration range 1.5-80 mM, the aggregates are in the form of bilamellar vesicles with a lamellar " d-spacing" of the order of 900 A. The vesicles are relatively polydisperse with a particle size in the range 2000-4000 A. Above 80 mM, the bilamellar vesicles coexist with an additional L beta lamellar phase.     

Influence of aquo-organic solvent media on the self-aggregation of sodium dodecyl sulfate (SDS) and its interaction with polyvinylpyrrolidone (PVP)

Influence of mixed aquo-organic solvents viz. water-dimethyl sulfoxide (DMSO), water-formamide (FA), water-dioxane (DX), and water-ethylene glycol (EG) on the micellization of sodium dodecylsulfate (SDS) alone and in presence of neutral polymer polyvinyl pyrrolidone (PVP) was studied. Interaction with PVP initially witnessed formation of critical aggregation concentration (CAC) in the favor of formation of induced small micelles of SDS at a concentration lower than the normal critical micelle concentration (CMC), and later found the formation of normal micelles with extended critical micelle concentrations (CMC_e) in solution. The SDS-PVP interaction depended on the nature and composition of the mixed solvents. Besides CAC and CMC_e, the maximum Gibbs surface excess at the interface (Γ _max), the minimum area (A _min) of the dissociated amphiphile anion, and enthalpy of micellization (ΔH _m ⁰ ) were also determined. Configurational state of PVP in aquo-organic media was investigated by the methods of viscometry, dynamic light scattering (DLS), and scanning electron microscope (SEM) methods. The [η] and Huggins constant (k _H) were considered to ascertain the overall configuration of PVP in solution. The complexes were formed and aggregated at different stages of their molecular composition. The aggregate sizes were determined by DLS, and the surface morphologies in the solvent removed states were examined by SEM. With reference to bulk and interfacial phenomena, polymer-surfactant interaction is thus considered to be important, and the detailed study herein under taken for SDS-PVP combination and PVP alone in mixed aquo-organic solvent media is a new sort of attempt. Figure

DX and DMSO influenced [η] of PVP, SDS interacted PVP enthalpogram and the SEM image of the PVP in 10 wt% DX     

Colorimetric detection of lead (II) based on silver nanoparticles capped with iminodiacetic acid

We report on a colorimetric probe for the determination of Pb(II). It is based on the use of silver nanoparticles that have been functionalizd with iminodiacetic acid (IDA-Ag NPs). The absorption spectrum and solution color of IDA-Ag NPs undergo dramatic changes on exposure to Pb(II) with a new absorption peak appearing at 650 nm and a concomitant color change from yellow to green. This is assumed to result from the aggregation of IDA-Ag NPs induced by Pb(II). Under optimum conditions, there is a linear relationship between the ratio of the absorbances at 650 and 396 nm, respectively, and the concentration of Pb(II) in the 0.4 to 8.0 μM concentration range, with a detection limit of 13 nM. The method was applied to the determination of Pb(II) in tap water and urea samples, and recoveries ranged from 93.7 % to 98.6 %.

Aggregation and complexation in a series of tetramethylenesulfonate-substituted calix[4]resorcinarenes

NMR methods are employed to study the effects of inorganic salts, solvents, and guest molecules of methylviologen (MV²⁺) and choline (Ch⁺) on the aggregation properties of water-soluble tetramethylene-sulfonate-substituted calix[4]resorcinarenes containing methyl (1), amyl (2), and heptyl (3) substituents in the lower rim. It is established that, in aqueous solutions at concentrations of 1?C10 mM, compound 1 exists in the monomeric form; the size of aggregates of amphiphilic compound 2 gradually increases (aggregation number varies from 1 to 20); and hydrophobic compound 3 dissolves only in slightly alkaline aqueous solutions to form large micellar aggregates. For macrocycles 2 and 3, which are inclined to aggregation, the aggregate sizes depend on the concentration, pH, and ionic strength of solutions, as well as on the presence of organic solvents. Macrocycle 1 binds guest molecules Ch⁺ and MV²⁺ to yield inclusion complexes. In the presence of aggregates of substance 2, the binding of guest molecules is more efficient and they are encapsulated between the rim of one molecule and the tail of another molecule of compound 2. The presence of guest molecules enhances the aggregation of macrocycle 2. In the case of compound 3 solutions, guest Ch⁺ molecules are predominantly localized in the hydrophobic environment of alkyl substituents of the host.     

Ultrasound-assisted emulsification–microextraction for the sensitive determination of ethyl carbamate in alcoholic beverages

A method based on ultrasound-assisted emulsification–microextraction (USAEME) was proposed in this contribution for the determination of ethyl carbamate (EC) in alcoholic beverages using gas chromatography coupled to triple quadrupole mass spectrometry. To achieve the determination of EC in alcoholic beverages, the influences on the extraction efficiency of type and volume of extraction solvent, temperature, ionic strength, alcohol content, and extraction time were studied, once the extraction solvent had been selected. The optimized conditions were 200.0 μL of chloroform at 30 °C during 5 min with 15 % (m/v) sodium chloride addition. The detection limit, relative standard deviations, linear range, and recoveries under the optimized conditions were 0.03 μg L^?1, 4.2–6.1 %, 0.1–50.0 μg L^?1, and 80.5–87.9 %, respectively. Moreover, the feasibility of the present method was also validated by real samples. To the best of our knowledge, this is the first time that USAEME has been applied to determine a strongly hydrophilic compound in alcoholic beverages.

Preparative Isolation and Purification of Two Phenylpropanoids from Daphne giraldii Nitsche by HSCCC

Preparative high-speed counter-current chromatography (HSCCC) was successfully applied to purify phenylpropanoids from the stem and root bark of Daphne giraldii Nitsche, a traditional Chinese medicine. Their structures were identified on the basis of ¹H NMR and ¹³C NMR technology. The two-phase solvent system composed of n -hexane–ethyl acetate–methanol–water (2: 3: 0.5: 4, v/v/v/v) was selected for HSCCC. A total of 8.0 mg woonenoside XI (1) and 18.0 mg daphnetin (2) were obtained in one-step separation from 200 mg of the crude extract with purity of 96.0 and 99.1%, respectively, as determined by LC. And the major compound (2) showed antithrombotic activity in vitro.     

Application of nano-baskets in metabolomics

A novel approach for inclusion extraction and fingerprinting of metabolite was introduced base upon the emulsion liquid membrane-nuclear magnetic resonance (ELM-NMR) technique. The objective of this method is optimizing the fingerprints, minimizing the metabolic variation from analysis, increasing the likelihood differences, and obtaining the maximum extraction yield. Low molecular weight metabolites in rat serum were recovered by ELMs using three nano-baskets of calix[4]crowns-3 as emulsifier and carrier. The yields of ELMs were optimized by the method of once at a time. According to the NMR data, the maximum metabolic variation was achieved using scaffold 4 (4 wt%), n-decane membrane, stirring rate of 300 rpm, treat and phase ratios of 0.3 and 0.8, respectively. According to the NMR data, the results revealed that calixcrowns 6 and 9 tend to extract non-specific macromolecules and the repeatability of fingerprints for 4-mediated ELM was more than two others. The yield of extractions was obtained to be higher for n-decane and lower for carbon tetrachloride. Using different membrane types, the fingerprints by chlorinated liquid membranes were more repeatable than toluene or n-decane.     

Adsorption and Aggregation Behavior of n-Undecyl Ammonium Acetate Ionic Liquid in Aqueous Solution

A surface active ionic liquid (IL), [CH₃(CH₂)₁₀NH₃][OOCCH₃], was synthesized and characterized by FTIR, ¹H NMR, and ¹³C NMR. Its surface activity and aggregation behavior in aqueous solution were investigated using surface tension measurements, conductivity measurements, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The results reveal that the CAC and γ_cac of this IL are 15.3 mM and 23.1 mN/m, respectively. We observed a strong interaction between the counter-ions, leading to ion pairs that self-assemble into spherical vesicles in aqueous solution, with an average diameter in the range of 120 to 130nm.     

萘和丹酰基修饰的扇形树枝状分子聚集体的能量转移行为

分别对1-3代聚(酰胺-胺)(PAMAM)结构的dendron分子的外端基和focal point进行了修饰,得到了外端基为萘(给体)色团、焦点(focal point)为丹酰(受体)色团的树枝状化合物Dan-ABπ-Nap(n=2,4,8).利用荧光光谱测定了不同浓度下所得一系列树枝状分子在水中的荧光强度,并计算了它...     

Comparison of HPLC and MEEKC for Miconazole Nitrate Determination in Pharmaceutical Formulation

A simple solid phase extraction (SPE) method coupled with high performance liquid chromatography (HPLC) using UV detector and microemulsion electrokinetic chromatography (MEEKC) has been developed and compared for the quantitative determination of miconazole nitrate in pharmaceutical formulation. For HPLC method, two parameters were optimized, namely, the wavelength and the mobile phases. The optimized condition was at the 225 nm wavelength and the mobile phase of ACN:MeOH (90:10 v/v). There are seven MEEKC parameters that were optimized, in this research, which were applied to voltage, temperature, wavelength, sodium dodecyl sulfate (SDS) concentration, buffer pH, buffer concentration and butan-1-ol concentration. The optimum MEEKC condition was obtained using 86.35 % (w/w) 2.5 mM borate buffer pH 9, 0.25 % (w/w) SDS, 0.8 % (w/w) ethyl acetate, 6.6 % w/w butan-1-ol and 6.0 % (w/w) acetonitrile. The combination of SPE using a diol column with HPLC–UV and the MEEKC methods were successfully applied for the determination of miconazole nitrate in a pharmaceutical formulation with the recovery percentage of 98.35 and 92.50 %, respectively.

     

Aggregation behavior of a model ionic liquid surfactant in monosaccharide + water solutions

Alkylimidazolium salts are a very important class of ionic liquids (ILs). The ILs containing long alkyl chains are a kind of model surfactants. In this paper, the aggregation behavior of 1-decyl-3-methylimidazolium chloride ([C(10)mim]Cl) was investigated for the first time in aqueous monosaccharide (glucose, galactose, xylose and arabinose) solutions by conductivity, fluorescence, NMR and dynamic light scattering (DLS). Thus a series of physico-chemical parameters for the aggregation of [C(10)mim]Cl-the critical aggregation concentration (CAC), ionization degree of the aggregates (α), the standard Gibbs energy of aggregation (ΔG(m)(0)), and the aggregation number (N) were derived from the experimental data. The results show that addition of small amounts of monosaccharides in aqueous solution can cause a variation in aggregation properties of the IL. The CAC values decrease with increasing molality of monosaccharides. In particular for different kinds of monosaccharides, we found that the CAC values are in the order: glucose>galactose (hexoses), xylose>arabinose (pentoses); xylose>glucose (1e2e3e4e), arabinose>galactoses (1e2e3e4a). These trends may be attributed to the slight difference in the stereo-structure of monosaccharide molecules. Finally a mechanism for the interaction of these monosaccharides with [C(10)mim]Cl was proposed.     

Light scattering and luminescence studies on self-aggregation behavior of amphiphilic copolymer micelles

The self-aggregation behavior of three amphiphilic graft copolymers, oligo(9,9-dihexyl)fluorence-graft-poly(ethylene oxide) (OHF-g-PEO), with different architectures was studied by dynamic and static light scattering (DLS and SLS) in combination with fluorescence spectroscopy and transmission electron microscopy (TEM). The formation of self-assembled polymeric micelles was confirmed by SLS and TEM. DLS and SLS analyses showed that the architecture of graft copolymers has a dramatic effect on critical aggregation concentration (CAC), micelle size distribution, apparent aggregation number (Nagg app), and apparent molecular weight of polymer aggregates (Mw,agg app). An architecture-dependent excimer emission, resulting from the pi-pi stacking of the oligofluorene backbones, was also observed from the photoluminescence spectra of the micelle aqueous solutions, which indicated a strong intermolecular interaction among the polymeric molecules. The excimer emission was further investigated by time-resolved fluorescence spectroscopy.     

Detection of catecholamines in single specimens of groundwater amphipods

Catecholamines play essential roles in several physiological processes in vertebrates as well as in invertebrates. While several studies have shown the presence of these substances in surface water invertebrates, their occurrence in groundwater fauna is unproven. In the present study, the presence of different catecholamines (i.e., noradrenaline, adrenaline, and dopamine) in individual specimens of groundwater amphipods of the genus Niphargus (mostly Niphargus inopinatus) was investigated via two independent analytical methods: HPLC/EcD and UPLC/TOF-MS. Mean values for catecholamine levels were 533 pg mg^?1 fresh weight for noradrenaline, 314 pg mg^?1 for adrenaline, and 16.4 ng mg^?1 for dopamine. The optimized protocol allowed the detection of CAs in single organisms of less than 1 mg fresh weight. Catecholamine concentration patterns in groundwater invertebrates are briefly discussed here with respect to their evolutionary adaptation to an environmentally stable, energy-poor habitat.