Using the cationic surfactants N-cetyl-N-methylpyrrolidinium bromide and 1-cetyl-3-methylimidazolium bromide for sweeping–micellar electrokinetic chromatography

This paper describes a sweeping–micellar electrokinetic chromatography (sweeping–MEKC) technique for the determination of seven benzodiazepines, using, as sweeping carriers, the ionic liquid-type cationic surfactants 1-cetyl-3-methylimidazolium bromide (C₁₆MIMBr) and N-cetyl-N-methylpyrrolidinium bromide (C₁₆MPYB). These surfactants resemble the commonly employed cationic surfactant cetyltrimethylammonium bromide (CTAB), but they provide different separation efficiencies. We optimized the separation and sweeping conditions, including the pH, the concentrations of organic modifier and surfactant, and the sample injection volume. Adding C₁₆MIMBr or C₁₆MPYB to the background electrolyte enhanced the separation efficiency and detection sensitivity during the sweeping–MEKC analyses of the benzodiazepines. C₁₆MIMBr enhanced the sensitivity for each benzodiazepine 31–59-fold; C₁₆MPYB, 86–165-fold. In the presence of C₁₆MPYB, the limits of detection for the seven analytes ranged from 4.68 to 9.75 ng/mL. We adopted the sweeping–MEKC conditions optimized for C₁₆MPYB to satisfactorily analyze a human urine sample spiked with the seven benzodiazepines. To minimize the matrix effects, we subjected this urine sample to off-line solid phase extraction (SPE) prior to analysis. The recoveries of the analytes after SPE were satisfactory (ca. 77.0–88.3%). Our experimental results reveal that the cationic surfactant C₁₆MPYB exhibits superior sweeping power relative to those of C₁₆MIMBr and CTAB and that it can be applied in sweeping–MEKC analyses for the on-line concentrating and analyzing of benzodiazepines present in real samples at nanogram-per-milliliter concentrations.     

Modulation of the aggregation behaviour and physicochemical properties of 1-dodecyl-3-methylimidazolium bromide in aqueous solutions by β-CD

The modulation of aggregation behaviour of ionic liquids (ILs) in aqueous media is one of the important research topics. In the present work, aggregation behaviour of 1-dodecyl-3-methylimidazolium bromide ([C₁₂mim]Br) modulated by beta-cyclodextrin (β-CD) has been investigated by using conductivity, volume, fluorescence, dynamic light scattering and transmission electron microscopy techniques. The results suggested that the addition of β-CD significantly affects the aggregation of [C₁₂mim]Br in aqueous solutions. For example, the apparent critical micelle concentration increases with the increase of β-CD concentration; the average micellar size reduced with the increasing concentration of β-CD, and the process for micelle formation of [C₁₂mim]Br in aqueous β-CD solution is driven by entropy at lower temperature, while driven by enthalpy at higher temperature. It is expected that findings in this study would shed light on the potential applications of IL in supramolecular chemistry.     

Effect of cationic surfactants on the enzymatic activity of α-chymotrypsin

The hydrolysis of p-nitrophenyl benzoate catalyzed by α-chymotrypsin in the presence of cetyltriphenylphosphonium bromide, cetyltributylphosphonium bromide and cetyltrimethylammonium bromide (pre and post micellar regions) has been studied. The ester is hydrolyzed readily by α-chymotrypsin in all the surfactants with the highest activity shown in cetyltributylphosphonium bromide. The dependences of the Michaelis constant and the catalytic constant with surfactant concentration have also been discussed.     

Sugar surfactants — aggregation,interfacial, and adsorption phenomena

The latest research work provides us with basic knowledge about some selected properties of systems containing sugar surfactants. Now we are able to understand the behavior of aqueous solutions reasonably well and very recently progress was made with respect to the properties of microemulsions. However, little is still known about the adsorption properties. Apart from the need for more fundamental research, the future task will be to handle more complex systems. Here complex refers to multi-component mixtures used in technical applications, but also to biotechnological applications where the structure of the surfactant is more complex. Promising future developments in this field are outlined.     

Thermodynamic stability and retinol binding property of β-lactoglobulin in the presence of cationic surfactants

In this work the stability parameters of bovine β-lactoglobulin, variant A (BLG-A), with regard to their transition curves induced by dodecyltrimethylammonium bromide (C₁₂TAB), tetradecyltrimethylammonium bromide (C₁₄TAB) and hexadecyltrimethylammonium bromide (C₁₆TAB) as cationic surfactants, were determined at 298 K. For each transition curve, the conventional method of analysis which assumes a linear concentration dependence of the pre- and post-transition base lines, gave the most realistic values for ΔG_D(H₂O). The results represent the increase in the denaturating power of surfactants with an increase in hydrocarbon chain length. The value of about 22.27 kJ · mol^?1 was obtained for ΔG_D(H₂O) from transition curves. Subsequently, the retinol binding property of BLG as its functional indicator was investigated in the presence of these surfactants using the spectrofluorimeter titration method. The results represent the substantial enhancement of retinol binding affinity of BLG in the presence of these surfactants.     

Interactions and influence of α-cyclodextrin on the aggregation and interfacial properties of mixtures of nonionic and zwitterionic surfactants

The interactions of α-cyclodextrin (α-CD) with the nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) and the zwitterionic surfactant dimethyldodecylammoniopropanesulfonate (DPS) in their mixed system have been studied using interfacial tension, fluorescence, and nuclear magnetic resonance measurements. From the plots of interfacial tension vs. log of total surfactant concentration, we have obtained values of the surface excess of surfactant, the critical micellar concentration (cmc), the standard free energy of micelle formation, and association constant of surfactant/α-CD inclusion complexes (assuming a 1:1 stoichiometry). A comparison of the K _a values obtained for the interaction between α-CD and DPS and Mega-10, respectively, shows that DPS interacts stronger with α-CD than Mega-10. The experimental mixed cmc was analyzed by the pseudophase separation model and regular solution theory for the evaluation of ideality or nonideality of the mixed micelle formation. The interaction parameters in the mixed micelle and the micelle composition at different mole fractions of DPS were also computed. The fluorescence anisotropy (r) values of rhodamine B decreases with the increase of α-CD concentrations.     

Effect of cationic and anionic surfactants on the addition–elimination-type interaction between o-toluidine and d-glucose

The kinetics of the o-toluidine–d-glucose reaction has been studied as a function of [o-toluidine], [d-glucose], [acetic acid], and temperature by UV–visible spectrophotometry at 630 nm in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The reaction follows second-order kinetics, being unity in each of the reactants in both media. The effect of added surfactants has also been investigated. The model of micellar catalysis, such as the Menger–Portony model modified by Bunton, is applied to explain the catalytic role of CTAB and SDS micelles. The association/incorporation constants (K _s and K _n), the rate constant in micellar media (k _m), and the activation parameters of this system have been calculated and discussed. The value of the rate constant is found to be higher in SDS than in CTAB. Hydrophobic and electrostatic interactions are responsible for higher reaction rates in SDS. From all observed facts, a reaction mechanism involving a nucleophilic addition–elimination path has been suggested.     

Experimental and theoretical study of the charge transport property of 4,4′-N,N′-dicarbazole-biphenyl

The hole and electron mobilities of the amorphous films of the organic semiconductor 4,4′-N,N′-dicarbazole-biphenyl (CBP) at different electric fields were measured through the time of flight (TOF) method. Based on its crystalline structure, the hole and electron mobilities of CBP were calculated. A detailed comparison between experimental and theoretical results is necessary for further understanding its charge transport properties. In order to do this, charge mobilities at zero electric field, μ(0), were deduced from experimental data as a link between experimental and theoretical data. It was found that the electron transport of CBP is less affected by traps compared with its hole transport. This unusual phenomenon can be understood through the distributions of frontier molecular orbitals. We showed that designing materials with frontier molecular orbitals localized at the center of the molecule has the potency to reduce the influence of traps on charge transport and provide new insights into designing high mobility charge transport materials.     

Biophysical analysis of partially folded state of α-lactalbumin in the presence of cationic and anionic surfactants

The role of different types of interactions and their contribution in the stabilization of bovine α-lactalbumin (α-LA) molten globule in presence of cationic surfactant, hexadecyl trimethyl ammonium bromide (HTAB) and anionic surfactant, sodium dodecyl sulphate (SDS) have been examined using a combination of spectroscopic, light scattering and calorimetric techniques. The results correlated well with each other and were used to characterize the partially folded states of the protein both qualitatively and quantitatively. At lower concentration of the surfactants, the thermodynamic parameters obtained from UV-visible spectroscopy suggested an increased exposure of non-polar groups in HTAB while a possible restructuring of non-polar groups were indicated in SDS. The fluorescence and circular dichroism spectroscopy showed the formation of an intermediate state at various concentrations of HTAB and SDS while the lifetime measurements supported the assumption of protein-surfactant complex stability in HTAB as compared to SDS. The hydrodynamic diameter and the ζ-potential were analyzed by dynamic light scattering (DLS) which also implicated the combined influence of electrostatic and hydrophobic interactions in protein unfolding in HTAB and only hydrophobic interactions in SDS. The binding parameters for ANS obtained from isothermal titration calorimetric (ITC) measurements suggested a high stability of α-LA molten globule and the role of enthalpic and entropic contribution in the binding of ANS in HTAB. It also indicated the fragility of α-LA molten globule in SDS. The possible binding sites as well as the interactions of ANS with the partially folded protein were also studied from the thermodynamic parameters obtained from the ITC.     

The properties of 4′-N,N-dimethylaminoflavonol in the ground and excited states

The mechanism of protonation of 4-N,N-dimethylaminoflavonol and the structure of its protolytic forms in the ground and excited states were studied by electron absorption and fluorescence (steady-state and time-resolved) spectroscopy and with the use of the RM1 quantum-chemical method. A comparison of equilibrium constants and the theoretical enthalpies of formation showed that excitation should be accompanied by the inversion of the basicity of the electron acceptor groups of this compound and, as a consequence, changes in the structure of its monocationic form. An analysis of the spectral parameters of the protolytic 4-N,N-dimethylaminoflavonol forms, however, showed that their structure and the sequence of protonation in the excited state were the same as in the ground state. Changes in the structure of the monocation in the excited state were not observed because of the fast radiationless deactivation of this form and the occurrence of excited state intramolecular proton transfer in aprotic solvents.     

Coordination behaviour of 2,2′-bipyridine towards the dichloroacetates of zinc and cadmium

The coordiantion compounds [Zn(C₁₀H₈N₂)(Cl₂HCCOO)(H₂O)₃]⁻·[Zn(C₁₀H₈N₂)(Cl₂HCCOO)₃]⁺ and [Cd(C₁₀H₈N₂)₂(Cl₂CHCOO)₂] were synthesised and characterised by elemental and thermal analysis, IR and UV–VIS spectroscopy, and X-ray crystallography. The complexes are air stable and well-soluble in water. The zinc atoms are five and six coordinated and the cadmium atom is six coordinated. The coordination polyhedra of central atoms can be described as trapezoidal pyramid and octahedron in zinc compound and as rectangular bipyramid strongly distorted towards skew trapezoidal bipyramid in cadmium compound. In both compounds all dichloroacetate groups are monodentate. The bond valences considerations show that all 2,2′-bipyridine molecules are bonded almost 2 times stronger than carboxylate groups. In the structure of zinc compound exist O–H···O hydrogen bonds and in both structures can be found weak C–H···O hydrogen bonds. Additionally, both compounds are pile-stacked by π···π interactions. The IR spectra show typical vibrations for chelating 2,2′-bipyridine molecules and terminal monodentate carboxylate groups. The thermal decomposition studies show zinc compound decomposes in 4 steps and cadmium compound decomposes in 5 steps with formation of oxides as a final products. The ligands decompose gradually, first dichloroacetates and next 2,2′-bipyridine.     

Synthesis,structures, thermal behaviour,luminescence and magnetic properties of lanthanide complexes constructed from 2,6-dimethylbenzoic acid and 5,5′-dimethyl-2,2′-bipyridine

Six new lanthanide complexes, with the formula [La(2,6-DMBA)₃(5,5′-DM-2,2′-bipy)(H₂O)]₂ (1) and [Ln(2,6-DMBA)₃(5,5′-DM-2,2′-bipy)]₂ (Ln = Tb(2), Dy(3), Ho(4), Pr(5), Nd(6)) (2,6-DMBA = 2,6-dimethylbenzoate, 5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine) have been successfully synthesized and characterized. These title complexes have three different structural types. The structure of complex 1(type I) contains coordination water molecules, and the coordination number is 8. The coordination numbers of complexes 2–4 and 5–6 are 8 and 9, showing a distorted square antiprism geometry and distorted monocapped square anti-prismatic geometry, respectively. However they have the same general formula and they can be all assembled into the same 1D, 2D supramolecular structures via the C-H···O hydrogen bonding interactions, which is interesting in previous lanthanide complexes. The complexes were analyzed by TG-DSC/FTIR. In addition, the visible light luminescence experiments of Tb (III) complex was carried out, and the characteristic luminescence behavior of strong green color was shown. And the fluorescence lifetime and intrinsic quantum yield were calculated. The magnetic properties of complexes 2–4 were also studied, and the results showed that complex 3 and complexes 2, 4 have ferromagnetic interactions and antiferromagnetic interactions, respectively.     

Structures and NMR spectra of N-(ω-alkoxyethyl)N-(2-hydroxyethyl)-N,N-dimethylammonium chlorides

Russian Chemical Bulletin - Homoand heteronuclear NMR experiments (COSY, HSQC, and HMBC) were used for the attribution of the proton and carbon atom signals in the 1H and 13C NMR spectra of...     

Synthesis of 1,1′-Dibenzo- and 1,1′-Dinaphtho-2,2′-Dithiols from the Respective Thiophenes

The title compounds 1 and 2 were prepared from the respective, inexpensive and readily available thiophenes via reaction with lithium and sulfur monochloride, followed by reduction with lithium aluminium hydride.     

Study on the effect of chain-length compatibility of mixed anionic–cationic surfactants on the cloud-point extraction of selected organophosphorus pesticides

The chain-length compatibility of mixed anionic-cationic surfactants was investigated for the extraction of organophosphorus pesticides (OPPs). Cationic surfactants with different chain lengths (n = 12 and 16) were mixed with sodium dodecyl sulfate (SDS; n = 12) for the mixed anionic-cationic surfactants-based extraction. Six OPPs were studied including azinphos-methyl, parathion-methyl, fenitrothion, diazinon, chlorpyrifos, and prothiophos. Reversed-phase high-performance liquid chromatography was used for the determination of the studied OPPs. The extraction was performed using mixtures of SDS and cationic surfactants including dodecyltrimethyl ammonium bromide or dodecyltrimethylammonium bromide (DTAB; n = 12) and cetyltrimethyl ammonium bromide or cetyltrimethyl ammonium bromide (CTAB; n = 16). The parameters affecting the extraction efficiencies of two extraction systems were studied and discussed. The optimum condition for SDS-DTAB was 15 mmol L(-1) SDS and 1 mmol L(-1) DTAB in the presence of 15% (w/v) sodium chloride (NaCl). Meanwhile, the condition for SDS-CTAB was 10 mmol L(-1) SDS and 1.0 mmol L(-1) CTAB with 10% (w/v) NaCl. Under the optimum conditions, the extraction efficiency of SDS-DTAB (66-85%) was slightly higher than that of SDS-CTAB (61-82%). In addition, the SDS-DTAB system also gave greater enrichment factor than SDS-CTAB for all the studied OPPs. This result may be due to the compatibility of chain length between SDS and DTAB. The extraction using SDS-DTAB was successfully applied to determine OPPs in fruit samples (i.e., pomelo, apple, and pineapple). No contamination by the studied OPPs in samples was observed. Good accuracy with recoveries ranging from 77 to 105% was obtained. Low limits of detection were in the range of 0.003-0.01 mg kg(-1) which are below the MRLs established by EU-MRLs for the OPPs residues in fruit samples.     

The synthesis of 2′-homouridine,its incorporation into a dinucleoside monophosphate and hydrolytic behaviour of the dimer

An efficient route to 2′-homouridine (1), a new nucleoside analogue, is reported that is based on an ene reaction. This nucleoside has been incorporated into a dinucleoside monophosphate and hydrolytic studies on the dimer show that it does not behave like a ribonucleotide.     

Synthesis and Characterization of Polymers Derived from the Copolymerization of 1,1′-Dihydroxyethyl-2,2′-Biimidazole and the Diglycidyl Ether of Bisphenol A

Abstract

1,1′-Dihydroxyethyl-2,2′-biimidazole has been used as a copolymerizing monomer with the diglycidyl ether of bisphenol A in the preparation of biimidazole-containing epoxy polymers. Polymerization reactions were studied in bulk, with and without catalyst, and in N,N-dimethylforma-mide and anisole solvents, with and without catalyst. FT-IR and NMR spectra, molecular weight, thermal and solubility characteristics were obtained. Polymers isolated as amorphous light brown solids were found to be only sparingly soluble in THF or in highly polar nitrogen-containing solvents (DMF, NMP, pyridine). These materials exhibited molecular weights up to 37 000 for SnC1₄-catalyzed polymerization carried out in DMF. A glass-transition temperature of 391°C was observed for polymers obtained under uncatalyzed solventless conditions. The glass transition temperature was 373°C for product obtained under SnC1₄-catalyzed, solventless conditions. Thermogravimetric analysis in air of polymers obtained under varying solvent and catalyst conditions showed less than 25% weight loss below 330°C and greater than 75% weight loss above 400°C.     

Formation of TiO2 ceramic foams from the integration of the sol–gel method with surfactants assembly and emulsion

A general and potentially easy method for synthesizing TiO₂ ceramic foams presenting hierarchical architecture of meso and macropores is presented here. The ceramics foaming method is based on the integration of the sol?Cgel process with sodium dodecyl sulfate (SDS) surfactant and oil droplets of isopropyl myristate (IPM) as dual pore templates. The main aim of this study was to evaluate the effect of ionic surfactant on the porous structure and specific surface area. The structural feature of these materials was characterized by analyzes of X-ray diffraction, nitrogen absorption/desorption isotherms, Hg porosimetry, He and Dried-Fluid^? picnometers. Mercury intrusion porosimetry shows that SDS and IPM induce the formation of hierarchical structure composed of two families of pores, namely macro and mesopores. The relative population of each family and the average size of macropores could be finely tuned by adjusting the SDS quantity. In the presence of this surfactant, a single anatase crystalline phase was observed for titania foams fired at 600?°C.