Micellization of Sodium Dodecyl Sulfate in Glycerol Aqueous Mixtures

The effect of glycerol on both micellar formation and the structural evolution of the sodium dodecyl sulfate (SDS) aggregates in the context of the action mechanism of the cosolvent has been studied. The critical micelle concentration and the degree of counterion dissociation of the surfactant over a temperature range from 20°C to 40°C were obtained by the conductance method. The thermodynamic parameters of micellization were estimated by using the equilibrium model of micelle formation. The analysis of these parameters indicated that the lower aggregation of the surfactant is mainly due to a minor cohesive energy of the mixed solvent system in relation to the pure water. The effect of glycerol on the mean aggregation number of the micelles of SDS was analyzed by the static quenching method. It was found that the aggregation number decreased with the glycerol content. This reduction in the micellar size seems to be controlled by an increase in the surface area per headgroup, which was ascribed to a participation of glycerol in the micellar solvation layer. Studies on the micropolarity of the aggregates, as sensed by the probe pyrene, indicated that this microenvironmental parameter is almost unaffected by the presence of glycerol in the mixture. However, an increase in the micellar microviscosity at the surface region was observed from the photophysical behavior of two different probes, rhodamine B and auramine O. These results suggest a certain interaction of the cosolvent in the micellar solvation of SDS micelles.     

Aggregation Behavior of Pluronic-L64 in Presence of Sodium Dodecyl Sulphate in Water

The effect of sodium dodecyl sulfate (SDS) on the micellization and aggregation behavior of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic copolymer (Pluronic L64: EO₁₃ PO₃₀ EO₁₃) have been investigated by various techniques like, cloud point, viscosity, isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), fluorescence spectroscopy, room temperature phosphorescence (RTP), and small angle neutron scattering (SANS). Addition of SDS in L64 solutions shows mark alteration of different properties. We observed synergistic interaction between SDS and Pluronic L64. The changes in the critical micelle concentration (CMC), critical micelle temperature (CMT), cloud point (CP), micelle size, and shape has been correlated and reported in terms of structure dynamics and mechanics. The ITC titrations have been used to explore the different stages of binding and interactions of SDS with L64. The enthalpies of aggregation for copolymer-SDS aggregates binding, organizational change of bound aggregates, and the threshold concentrations of SDS in the presence of copolymer were estimated directly from ITC titration curves. The effect of temperature on enthalpy values has been reported in terms of different aggregation state. Fluorescence and RTP for L64 were used to investigate the change in micellar environment on the addition of SDS at different temperature. Appearance and shifting of SANS peaks have been used to monitor the size and inter micellar interaction on addition of SDS in L64 solution. Cloud point and viscosity elaborate the penetration of SDS molecule in L64 micelle and hence changing the micellar architect.     

Polarization of Fluorescence of Asphaltene Containing Systems

Formation of supermolecular structures in petroleum disperse systems is determined by interactions of asphaltenes. Petroleum systems are lyophilic oleocolloids with low polar dispersive media which is in dynamic balance with elements of disperse structure. Supermolecular scale of organization is most important for determining the macroscopic parameters. Levshin-Perrin equation for depolarization of fluorescence was modified for polydispersed systems. Interfacial tension coefficient of model asphaltene solution was calculated in a case of Volmer's function. For technogenic mixtures the temperature dependences of the sizes near the point of phase transition are presented. Enthalpy of asphaltene association per one molecule was calculated. Polarization degree together with macroscopic parameters correlates with appearance of asphaltene dispersed phase in system.     

Synthesis, Crystal Structure and Fluorescent Property of One New Complex [Na2（2-benzoylbenzoato）4（Phen）2（H2O）2]·H2O

One binuclear sodium(Ⅰ) complex [Na2(2-benzoylbenzoato)4(Phen)2(H2O)2]·H2O has been synthesized with 2-benzoylbenzoic acid and 1,10-henanthroline as ligands. The crystal structure was determined by X-ray diffraction. The crystal belongs to the triclinic system with space group P , a = 1.08096(8), b = 1.09619(8), c = 1.09740(8) nm, α = 79.0600(1), β = 71.0450(1), γ = 62.0540(1)o, V = 1.08533(1) nm3, Dc = 1.421 g/cm3, Z = 2, F(000) = 484, GOOF = 1.036, the final R = 0.0363 and wR = 0.0961. The crystal structure shows that two neighboring sodium(Ⅰ) ions are linked together by two bridging water molecules, and each end position is coordinated with one 1,10-phenanthroline molecule and one 2-benzoylbenzoato to form a binuclear structure. Each sodium(Ⅰ) ion in the molecule is coordinated with five atoms to give a distorted trigonal bipyramid. The fluorescence property of the title complex is also discussed.     

The effects of fluorescent probes on model membrane organization: photo-induced lipid sorting and soft structure formation

Liquid crystalline phase behaviour in model cell membranes prepared in-vitro has generated an enormous amount of interest in recent years and the phase diagrams of various bio-mimetic mixtures explored. Most recently photo-induced oxidation in fluorescently labelled membranes has been shown to influence these phase diagrams and can be used to generate interesting membrane-based geometries based on differences in membrane composition. In this article the different phases observed in model membranes will be discussed. Methods used to study these systems and recent developments in photo-stimulated phase changes are described along with areas for future investigation.     

Morphology and molecular organisation of liquid-crystalline perylene-3,4,9,10-tetra-(n-hexylester) deposited on a solid substrate

Liquid-crystalline perylene-3,4,9,10-tetra-(n-hexylester) forms characteristic dendritic or flower-like structures at room temperature when it is deposited on a hydrophilic glass substrate using the zone-casting technique. It was found that such unique structures were not possible to be created simply by recrystallisation of this dye from a liquid-crystalline columnar phase. On the basis of the observations using a confocal microscope and the study of wide angle X-ray scattering (WAXS) as well as the analysis of the absorption and fluorescence spectra, some conclusions, concerning the molecular organisation in the dendritic structure, are drawn. Based on the research, one can assume that the dendrites are formed by columnar molecular aggregates with the column axes parallel to the substrate. Such an organisation of the molecules can be interesting from the point of view of organic electronics.     

Total and inorganic mercury determination in fish tissue by flow injection cold vapour atomic fluorescence spectrometry

A simple and reliable method for Hg determination in fish samples has been developed. Lyophilised fish tissue samples were extracted in a 25% (w/v) tetramethylammonium hydroxide (TMAH) solution; the extracts were then analysed by FI-CVAFS. This method can be used to determine total and inorganic Hg, using the same FI manifold. For total Hg determination, a 0.1% (w/v) KMnO₄ solution was added to the FI manifold at the sample zone, followed by the addition of a 0.5% (w/v) SnCl₂ solution, whereas inorganic Hg was determined by adding a 0.1% (w/v) L-cysteine solution followed by a 1.0% (w/v) SnCl₂ solution to the FI system. The organic fraction was determined as the difference between total and inorganic Hg. Sample preparation, reagent consumption and parameters that can influence the FI-CVAFS performance were also evaluated. The limit of detection for this method is 3.7 ng g^?1 for total Hg and 4.3 ng g^?1 for inorganic Hg. The relative standard deviation for a 1.0 µg L^?1 CH₃Hg standard solution (n = 20) was 1.1%, and 1.3% for a 1.0 µg L^–1 Hg²⁺ standard solution (n = 20). Accuracy was assessed by the analysis of Certified Reference Material (dogfish: DORM-2, NRCC). Recoveries of 99.1% for total Hg and 93.9% inorganic Hg were obtained. Mercury losses were not observed when sample solutions were re-analysed after a seven day period of storage at 4°C.     

Highly sensitive inhibitory kinetics fluorescence method for determination of arsenic

A new and highly sensitive inhibitory kinetic fluorescence method for the determination of arsenic (III) has been established based on its inhibitory effect on the oxidation reaction of Acridine red (ADR) by KBrO₃ in sulphuric acid medium. The reaction has been followed by measuring the enhancement of fluorescence at 550?nm. It relies on the linear relationship where the change in the fluorescence (ΔF) versus added As(III) amounts in the range of 0–0.450?µg?mL^?1 is plotted, under the optimum conditions. The sensitivity of the proposed method, i.e. the limit of detection, is 2.1?×?10^?2?ng?mL^?1. The method is featured with good accuracy and reproducibility for arsenic (III) determination. This method was successfully applied for the quantitative determination of arsenic (III) in food products samples, and the relative standard deviations and the recoveries were in ranges of 2.31–2.83% and 90.0–107.2%, respectively. A review of recently published catalytic or inhibiting kinetic methods for the determination of arsenic (III) has also been presented for comparison. The mechanism of reaction was studied.     

Vibrational spectra and factor group analysis of rare-earth chromium borates,RCr3(BO3)4, with R = La–Ho

Anhydrous orthoborates RM₃(BO₃)₄, where R = Y, La–Lu, M = Al, Ga, Cr, Fe, with huntite structure type are considered as multifunctional laser materials. The crystal structure of these borates is either rhombohedral with space group R32 (D₃⁷) (Z = 3) or monoclinic with space group C2/c (C_2h⁶) (Z = 4) depending on the growth conditions. Both modifications have very close polytypic structures, and it is difficult to identify them by powder diffraction data. In this context, double borates of rare-earth cations and Cr³⁺ have been grown from high-temperature solutions and are characterized by Raman and infrared spectroscopy in a crystalline state in combination with factor group analysis of vibrational modes. The assignment for the stretching and bending vibrations of BO₃³⁻ groups and external modes has been made. Some external modes have been identified by study of mass effect (Al–Cr, La–Ho). Comparison of the Raman spectra of these borates shows redistribution of band intensities of two spectral modifications, related to different symmetry groups. As predicted by factor group analysis, the number of IR-active vibrational modes of stretching and bending vibrations of BO₃³⁻ units significantly increases in infrared spectra of monoclinic borates in comparison with rhombohedral ones. The dependence of the realized borate space group on the crystal growth conditions and the sort of rare-earth atom was revealed. Both GdCr₃(BO₃)₄ and EuCr₃(BO₃)₄ borates crystallize in space group R32 irrespective of growth conditions. The borates with the large rare-earth elements La–Nd always form the monoclinic structures, irrespective of crystallization temperature. The borates SmCr₃(BO₃)₄, TbCr₃(BO₃)₄ and DyCr₃(BO₃)₄ have been obtained in two modifications in dependence of crystalline borate substance/solvent ratio and related temperature of crystallization.     

Infrared and Raman spectra of magnesium ammonium phosphate hexahydrate (struvite) and its isomorphous analogues. IX: Spectra of protiated and partially deuterated cubic magnesium caesium phosphate hexahydrate

Infrared and Raman spectra of cubic magnesium caesium phosphate hexahydrate, MgCsPO₄·6H₂O (cF100), and its partially deuterated analogues were analyzed and compared to the previously studied spectra of the hexagonal analogue, MgCsPO₄·6H₂O (hP50). The vibrational spectra of the cubic and hexagonal dimorphic analogues are similar, especially in the regions of HOH stretching and bending vibrations. In the difference IR spectrum of the slightly deuterated analogue (<5% D), one distinctive band appears at 2260 cm⁻¹ with a small shoulder at around 2170 cm⁻¹, but only one band is expected in the region of the OD stretchings of isotopically isolated HDO molecules. The small weak band could possibly result from second-order transitions (a combination of HDO bending and some libration of the same species) rather than statistical disorder of the water molecules. By comparing the IR spectra in the region of external vibrations of water molecules of the protiated compound recorded at RT (room temperature) and at LNT (liquid nitrogen temperature) and those in the series of the partially deuterated analogues, it can be stated with certainty that the bands at 924 and 817 cm⁻¹ result from librations of water molecules, rocking and wagging respectively. And the band at 429 cm⁻¹ can be safely attributed to a stretching Mg–O_w mode. In the ν₃(PO₄) and ν₄(PO₄) region in the infrared spectra, one band in each is observed, at 995 and 559 cm⁻¹, respectively. In the region of the ν₁ modes, in the Raman spectrum of the protiated compound, one very intense band was observed at 930 cm⁻¹ which is only insignificantly shifted to 929 cm⁻¹ in the spectrum of the perdeuterated compound. The band at 379 cm⁻¹ in the Raman spectrum could be assigned to the ν₂(PO₄) modes. With respect to the phosphate ion vibrations, the comparison between the two polymorphic forms of MgCsPO₄·6H₂O and their deuterated compounds shows that ν₁(PO₄) and ν₃(PO₄) appear at lower wavenumbers in the cubic phase than in the hexagonal phase. These data are in full agreement with the lower repulsion potential at the cubic lattice sites compared with that for the hexagonal lattice sites.