Swelling of Lamellar Gel from Catanionic Hydro- and Perfluoro-Carbon Surfactant Mixtures by Refractive-Index Matching

Bilayer swelling behavior of cationic and anionic surfactant mixtures in solution induced by adding glycerin was investigated. The measurements were performed a system, cationic tetradecyltrimetylammonium bromide (TTABr), and anionic sodium perfluorodecanoate (C₉F₁₉CO₂Na) surfactant mixtures with their stoichiometric mole ratio being exactly 1 in aqueous solution. The non-precipitated phase of cationic and anionic hydro- and perfluoro-carbon surfactant mixtures being the mole ratio of 1:1 could be identified to be lamellar gel phase, which was characterized by freeze-fracture transmission electron microscopy (FF-TEM) and x-ray diffraction (XRD) measurements. Deuterium nuclear magnetic resonance (²H NMR) and rheology were used to characterize the phase transition from the lamellar gel to smaller vesicles. Phase transition from lamellar gel to smaller vesicles can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by matching of refractive index between solvent and bilayers.     

Highly concentrated emulsions as novel reaction media

Synthesis of a cationic surfactant, N^α-lauroyl arginine methyl ester hydrochloride (LAM) has been carried out in gel emulsions of the system water/C₁₄E₄/decane. The yields of LAM synthesized in gel emulsions are comparable to those obtained in conventional dimethylformamide (DMF) media. The rate of LAM formation is faster in gel emulsions at short times, the reaction taking place without mechanical energy input and at 25°C.     

Surface characterization and heats of adsorption of chromatographic alumina gel

The porous nature of chromatographic alumina gel has been investigated by adsorption/condensation processes and electron microscopy. Having 63% porosity, the gel is very porous. Total pore volume as determined by the fluid-displacement method is 0.497 cm³ g^–1. Its specific surface area, as determined by water vapor adsorption, is 225 m² g^–1. Micropore volume, as determined by utilizing Gurwitsch's rule, turns out to be 0.262 cm³ g^–1. The greater portion of the surface area and pore volume occurs in small and transitional pores, with average pore radii (hydraulic) less than 2.1 nm.Organic vapors, such as methyl ethyl ketone, acetone, methyl acetate, and methyl alcohol, were adsorbed on the gel between 0 and 36°C under vacuum, and the data were recorded on a Cahn-1000 electrobalance device. Isosteric heats of adsorption were calculated by applying the Clausius Clapeyron equation to the adsorption isosters at different surface coverages. Two types of adsorption processes, one with low activation energy and other with high activation energy can be distinguished. The increase in values ofq _st indicates that increasing temperature changes physical adsorption into chemisorption.     

Catalytic reactions of metalloporphyrins.: II. Activation and catalytic aldol condensation of ketone with rhodium(III)-porphyrin perchlorate under neutral and mild conditions

Acetone and methyl ethyl kektone undergo facile and direct metalation at the methyl groups by a cationic (octaethylporphyrinato) rhodium (III) complex with a non-coordinating perchlorate counteranion, (OEP)Rh^III(ClO₄), under mild conditions. Acetylacetone and ethyl acetoacetate are similarly metalated at the internal methylene groups. The metalation of acetone is firs-order with respect to both rhodium complex and ketone, and involves the (OEP)Rh^III(ClO₄)-assisted, rate-determining enolization of the ketone. The resulting 2-oxopropyl-rhodium derivative undergoes facile cleavage of the CRh bond with electrophiles such as H⁺ and Br₂. When cyclohexanone is used as substrate, on the other hand, (OEP)Rh^III(ClO₄) catalyzes the aldol condensation of the ketone effectively, where the intermediate cyclohexanone enolate reacts with the ketone or other carbonyl compound present and regenerates the Rh^III complex. An essential aspect of the present reaction is the remarkable ability of (OEP)Rh^III(ClO₄) to promote enolization of simple ketones by activation with charge-separated [(OEP)Rh^III+ (a Lewis acid) under mild and neutral conditions. The second-order rate constant of (OEP)Rh^III(ClO₄)-assisted enolization of acetone at 30°C (k₂ = 2.6 × 10⁻⁴ M⁻¹ sec⁻¹) is 10⁷ times as large as that of its spontaneous enolization in water, where water is both acid and bse.     

The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H₂C?N(CH₃)₂]⁺ and [N(CH₃)₃]^+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Application of FTIR spectra for evaluating interfacial reactions in metal matrix composites

Manufacturing of Saffil/MgLi metal matrix composites by the melt infiltration process is accompanied by extensive interfacial redox reaction between δ-Al₂O₃ fibers (Saffil) and lithium. The present paper deals with the Fourier transform infrared spectroscopy examination of Saffil fibers isolated from Mg–8 wt% Li alloy by the bromine/methylacetate agent focusing on the insertion of Li⁺ ions into δ-Al₂O₃ and their influence on water adsorption. Insertion of Li⁺ into δ-Al₂O₃ is monitored by gradual change of Al–O stretching bands (400–900 cm⁻¹) towards more simple patterns of a spinel-like product assigned as δ(Li) which transforms to LiAl₅O₈ during subsequent annealing. Rapid increase in the water adsorption with increase in Li content, indicated by the changes in H–O–H bending (about 1,650 cm⁻¹) and O–H stretching (about 3,500 cm⁻¹), is connected with the ionicity of the δ(Li) phase, which attracts polar water molecules.     

Cationic Ruthenium(II) Carbonyl Complexes with Nitrile Ligands

Stable cationic complexes of the type [RuCO(PPh₃)₂(L)(RCN)]⁺[ClO₄]^? derived from acetonitrile and acrylonitrile have been synthesized. The bidentate ligands (LH) used are acetylacetone, benzoylacetone, dibenzoylmethane, trifluorothenoyl acetone and 8-hydroxyquinoline. The complexes have been characterized by elemental analysis, IR, conductivity, ¹H and ³¹P NMR and ESCA studies, and possible stereochemistry has been established.     

Solvent-induced molecular gel formation at room temperature and the preparation of related gel-emulsions

The gelation behaviors of four recently reported amphiphilic cholesteryl derivatives (1, 2, 3 and 4) have been evaluated. It was found that the gel formation process can be controlled by introduction of water at room temperature. Addition of water to an acetone solution of 4 immediately results in the system becoming turbid, and a gel subsequently forms within a few minutes. Interestingly, 4 is a super-gelator for a mixed solvent of acetone and water at room temperature, in particular when their volume ratio is close to 1:1 at which the critical gelation concentration (CGC) is 0.06% (w/v). It was found that the introduction of water favors the formation of gel networks, and the gel possesses smart and reversible thixotropic properties. FTIR and 1H NMR spectroscopy confirmed that hydrogen bonding is one of the main driving forces for the gelation of the solvents. XRD demonstrated that 4 self-assembled into a layered structure within the acetone-water mixed solvent gel. Furthermore, 1 and 2 can be used as excellent stabilizers for gel emulsions of alkanes and water. The maximum of the dispersed phase, water, in one of the gel-emulsions can be as high as 97% (v/v).     

Insights into Functional‐Group‐Tolerant Polymerization Catalysis with Phosphine–Sulfonamide Palladium(II) Complexes

Two series of cationic palladium(II) methyl complexes {[(2‐MeOC₆H₄)₂PC₆H₄SO₂NHC₆H₃(2,6‐R¹,R²)]PdMe}₂[A]₂ ( ^X 1⁺‐A : R¹=R²=H: ^H 1⁺‐A ; R¹=R²=CH(CH₃)₂: ^DIPP 1⁺‐A ; R¹=H, R²=CF₃: ^CF3 1⁺‐A ; A =BF₄ or SbF₆) and neutral palladium(II) methyl complexes {[(2‐MeOC₆H₄)₂PC₆H₄SO₂NC₆H₃(2,6‐R¹,R²)]PdMe(L)} ( ^X 1‐acetone : L=acetone; ^X 1‐dmso : L=dimethyl sulfoxide; ^X 1‐pyr : L=pyridine) chelated by a phosphine–sulfonamide were synthesized and fully characterized. Stoichiometric insertion of methyl acrylate (MA) into all complexes revealed that a 2,1 regiochemistry dominates in the first insertion of MA. Subsequently, for the cationic complexes ^X 1⁺‐A , β‐H elimination from the 2,1‐insertion product ^X 2⁺‐A_MA‐2,1 is overwhelmingly favored over a second MA insertion to yield two major products ^X 4⁺‐A_MA‐1,2 and ^X 5⁺‐A_MA . By contrast, for the weakly coordinated neutral complexes ^X 1‐acetone and ^X 1‐dmso , a second MA insertion of the 2,1‐insertion product ^X 2_MA‐2,1 is faster than β‐H elimination and gives ^X 3_MA as major products. For the strongly coordinated neutral complexes ^X 1‐pyr , no second MA insertion and no β‐H elimination (except for ^DIPP 2‐pyr_MA‐2,1 ) were observed for the 2,1‐insertion product ^X 2‐pyr_MA‐2,1 . The cationic complexes ^X 1⁺‐A exhibited high catalytic activities for ethylene dimerization, affording butenes (C₄) with a high selectivity of up to 97.7 % (1‐butene: 99.3 %). Differences in activities and selectivities suggest that the phosphine–sulfonamide ligands remain coordinated to the metal center in a bidentate fashion in the catalytically active species. By comparison, the neutral complexes ^X 1‐acetone , ^X 1‐dmso , and ^X 1‐pyr showed very low activity towards ethylene to give traces of oligomers. DFT analyses taking into account the two possible coordination modes (O or N) of the sulfonamide ligand for the cationic system ^CF3 1⁺ suggested that the experimentally observed high activity in ethylene dimerization is the result of a facile first ethylene insertion into the O‐coordinated PdMe isomer and a subsequent favored β‐H elimination from the N‐coordinated isomer formed by isomerization of the insertion product. Steric hindrance by the N‐aryl substituent in the neutral systems ^CF3 1 and ^H 1 appears to contribute significantly to a higher barrier of insertion, which accounts for the experimentally observed low activity towards ethylene oligomerization.     

Spectrophotometric Determination of Sulfate Ion Through Copper(II)-azide System

Abstract

An indirect and alternative method for the determination of sulfate ion has been established by spectrophotometry. The procedure is based on the formation of copper(II) monoazido species, in water/acetone medium, in which a discoloration effect of system is caused by sulfate presence. In the recommended conditions, sulfate ions can be determined in the concentration range from 40 to 5000 mg/l (ppm), at 375 nm, in natural samples of waters. The best experimental conditions were determined analysing the different factors involved. Studies about the formation equilibria of the CuN₃ ⁺ and CuSO₄ species were realized in water and their respective stability constants (β₁ = 225 M^?1 and 7.15 M^?1) were determined by spectrophotometry at 25.0° C and ionic strength 1.0 M (NaClO₄). Equilibrium investigations were also made in presence of acetone. Additional studies on the ternary system Cu(II)/N₃ ^?/SO₄ ^2-) indicated some evidences of mixed complexes.     

Direct Electrochemistry of Horseradish Peroxidase Immobilized in a Low Molecular Weight Gel

The ternary system of dodecylpyridinium bromide (DDPB)/acetone/H₂O with appropriate composition can form a gel spontaneously and the gel is stable in hydrophobic ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim]PF₆). Based on the gelation phenomenon we observed, the low molecular weight gelator (LMWG) was first tried to immobilize horseradish peroxidase (HRP) on glassy carbon electrode (GCE). The scanning electron microscope (SEM) images, the UV‐Vis spectra and the bioactivity measurement indicate that the gel is suitable for the immobilization of HRP. The direct electrochemistry of the HRP‐gel modified GCE (HRP‐gel/GCE) in [Bmim]PF₆ shows a pair of well‐defined and quasi‐reversible redox peaks with the heterogeneous electron transfer rate constant (k_s) being 14.4 s^?1, indicating that the direct electron transfer between HRP and GCE is fast. The HRP‐gel/GCE is stable and reproducible. Also the electrode exhibits good electrocatalytic effect on the reduction of trichloroacetic acid (TCA), showing good promise in bioelectrocatalysis.     

Drawing with Iron on a Gel Containing a Supramolecular Siderophore

Guanosine‐5′‐hydroxamic acid ( 3 ) forms hydrogels when mixed with guanosine ( 1 ) and KCl. The 5′‐hydroxamic acid (HA) unit is pH‐responsive and also chelates Fe³⁺. When gels are prepared under basic conditions, the 5′‐HA groups are deprotonated and the anionic hydrogel binds cationic thiazole orange (TO), signaled by enhanced fluorescence. The HA nucleoside 3 , when immobilized in the G‐quartet gel, acts as a supramolecular siderophore to form red complexes with Fe³⁺. We patterned the hydrogel's surface with FeCl₃, by hand and by using a 3D printer. Patterns form instantly, are visible by eye, and can be erased using vitamin C. This hydrogel, combining self‐assembled G‐quartet and siderophore–Fe³⁺ motifs, is strong, can be molded into different shapes, and is stable on the bench or under salt water.     

Gemini Surfactants as New,Low Molecular Weight Gelators of Organic Solvents and Water

As many as 1200 solvent molecules can be entrapped by one molecule of the cationic dimeric surfactants 1 to form a gel in CHCl₃. These new gelators contain chiral counterions and form gels with both organic solvents and water upon their assembly into helical aggregates, which have similar structures in both media.     

Fluorescence of auramine O and its binding to poly(vinylbenzo-18-crown-6) and to polyvinylbenzoglyme in water

Binding of the cationic dye auramine O (AuO) to the polysoap-type polymers poly(vinylbenzo-18-crown-6) (P18C6) and polyvinylbenzoglyme (PVBG) in water were studied by fluorimetry and dialysis. The quantum yield of P18C6-bound AuO was found to be 0.028, the value being 0.018 for AuO bound to PVBG. The intrinsic binding constants were found to be 2.2 × 10⁴M^?1 (P18C6) and 1.2 × 10⁴M^?1 (PVBG), the respective first binding constants being 317 and 63M^?1. Addition of crown-ether-complexable cations such as K⁺, Tl⁺, or Cs⁺ converts the neutral poly(crown ether) into a polycation, causing repulsion of the cationic dye and a strong decrease in the AuO fluorescence. AuO fluorescence was also studied in the absence of polymer in ether solvents, giving θ values of 0.011 and 0.018 in THF and dioxane. Traces of water rapidly form a nonfluorescent species. Solutions of AuO in water without polymer present exhibit very strong fluorescence on addition of BPh₄ anions owing to formation of AuO⁺, BPh₄^? ion pairs and higher aggregates.     

Cationic Lanthanide Luminescent Copolymer: Design,Synthesis and Interaction with DNA

Polymerizable rare earth complex Eu(AA)₃Phen was synthesized by complexion of europium ion, acrylic acid (AA), and 1,10-phenanthroline (Phen). The structure and fluorescence properties of the complex were studied by elemental analysis, ¹H-NMR spectroscopy, and fluorescence spectroscopy. Eu-containing copolymer poly(PEGMA-co-MMA-co-METAC-co-Eu(AA)₃Phen) (PPMMEu) was then synthesized by free radical copolymerization of Eu(AA)₃Phen and other functional monomers including poly(ethylene glycol) methyl ether methacrylate (PEGMA) and [2-(Methacryloyloxy) ethyl] trimethylammonium chloride (METAC). ¹H-NMR spectroscopy and fluorescence spectroscopy were used to characterize the copolymer and the interactions between the copolymer and DNA was investigated by TEM, fluorescence spectroscopy, and agarose gel electrophoresis. The desired luminescent cationic copolymer was successfully obtained. The copolymer can form micelles in water solution and can efficiently bind to DNA molecules through electrostatic interaction. The results suggest the potential use of PPMMEu in bioprobes and gene vectors.     

Fabrication of silicon oxycarbide fibers from alkoxide solutions along the sol–gel process

Spinnable solutions are obtained in the sol–gel system of tetraethoxide (TEOS, Si(OC₂H₅)₄) and vinyltrimethoxysilane (VTMS, CH₂=CHSi(OCH₃)₃) under aqueous condition (water) with acid catalysts (HNO₃ and HCl). Polysiloxane (PSO) fibers are drawn from the solution and characterized by spectroscopic and structural analyses. ²⁹Si-nuclear magnetic resonance NMR) spectral analysis of the PSO fiber indicates the incorporation of atomic carbon in the silica network. ¹³C-NMR analysis shows the existence of considerable amount of hydroxyl groups in the PSO fiber. The spinnablity of the solution is studied by varying the mole ratios of the alkoxides, solvents and catalysts as well as precursor chemistries. The amount of water and catalysts are found to be important for the attaining of a spinnable state in the solution. SiOC fibers are obtained after pyrolysis of the PSO fibers with a high ceramic yield (88 wt%). The high ceramic yield attributes to the incorporation of vinyl-groups in the gel fiber that enhances crosslinking during pyrolysis. The SiOC fiber has a tensile strength of 776 MPa and electrical conductivity of 3.6 × 10⁻⁴ S/m.     

Anion receptor-coated separator for lithium-ion polymer battery

Anion receptor-coated separators were prepared by coating poly(ethylene glycol) borate ester (PEGB) as an anion receptor and poly(vinyl acetate) (PVAc) as a good adhesive material towards electrodes onto microporous polyethylene (PE) separators. Gel polymer electrolytes were fabricated by soaking them in an liquid electrolyte, 1 M LiPF₆ in EC/DEC/PC (30/65/5, wt.%). As the weight ratio of PEGB to PVAc in a coating layer increased, gel polymer electrolytes showed higher cationic conductivity and electrochemical stability. The cationic conductivity and electrochemical stability of the gel polymer electrolyte based on coated separator with PVAc/PEGB (2/5, weight ratio) could reach 2.8 × 10^–4 S cm^–1 and 4.8 V, respectively. Lithium-ion polymer cells (LiCoO₂/graphite) based on gel polymer electrolytes with and without PEGB were assembled, and their electrochemical performances were evaluated.     

Characterization of low molecular-weight gelator methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside hydrogels and water diffusion in their networks

This paper focuses on the thermal properties, the microstructure, and the molecular dynamics of water in the hydrogels (1.5, 2, 3, 4, and 5% [g mL⁻¹]) formed by sugar-based low molecular-weight gelator methyl-4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside. The energy needed to break the non-covalent interactions such as the hydrophobic, dipole-dipole, and π-π stacking interactions responsible for the gel formation was calculated to be 43 kJ mol⁻¹. The microstructure of the 4% [g mL⁻¹] hydrogel shows a characteristic fibril structure of the gel network with individual gel fibers, the junction points of thicker fibers, and pores occupied by water. The single mode diffusion of water molecules inside the gel network was detected irrespective of the diffusion time Δ (8-75 ms) and hydrogel concentration. For Δ of 10 ms the water diffusion is almost free and characterized by the diffusion coefficient in the range from 2.17×10⁻⁹ to 1.84×10⁻⁹ m² s⁻¹ for studied hydrogels. For larger Δ values, so-called restricted diffusions are observed and manifested in the linear decreases of the diffusion coefficient with diffusing time Δ, as shown for 5% gel. Only the one average proton spin-lattice relaxation time T₁ of water was determined for the studied hydrogels, irrespective of gelator concentration.     

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).

Terpyridine-based smart organic-inorganic hybrid gel as potential dye-adsorbing agent for water purification

A terpyridine-based organic-inorganic hybrid gelator possessing triethoxylsilane moiety was synthesized and its adsorption capacity for aromatic dyes in the absence and the presence of metal ions such as Zn²⁺ and Cu²⁺ was measured by UV-vis spectroscopy. From aqueous solutions of dyes, the hybrid gel, in the absence of metal ions, adsorbed 97.4% for basic blue 41, 94.2% for crystal violet, and 41.5% for bromocresol green. When metal ion was present, the adsorption capacity of dried hybrid gel 1 for the anionic dye bromocresol green significantly increased due to the enhanced electrostatic interaction between cationic gel and anionic dye. Thus, this hybrid gel can efficiently adsorb various toxic dyes in water.