Phase evolution,structural characteristics and mechanism of vesicle formation from a synthetic amphiphile: Controlled morphology by tuning solution phase parameters

We report herein, the aggregation behavior of 3, 4-di(dodecyloxy)benzoic acid-4-hydroxy phenyl ester (DDBE), a synthetic amphiphile and a true non-ionic surfactant system as per the geometrical considerations. The true surfactant nature of the system stems from its hydrophilic-lipophilic-balance (HLB?=?4.7), comparable to that of Span-60, also a true non-ionic surfactant. This compound undergoes spontaneous vesicle formation in THF:water binary solvent mixtures which further underwent fission at lower DDBE concentrations and fusion at higher concentrations, leading to giant vesicles of the order of 3000?nm. These vesicles are sensitive to the polarity of their environment. The predominant mode of interaction as observed from the molecular dynamics simulations were found to be π-π stacking with the phenyl rings of the molecule. Further, the system, upon complete extraction into water, formed spherical aggregates of size 50?nm based on the good solvent-poor solvent combination as the necessary condition for the vesicle formation.GRAPHICAL ABSTRACT     

Equilibria in ion exchanger-aqueous salt solution systems and clathrate formation

Russian Journal of General Chemistry - The new approach has been developed for the analysis of the data on the equilibria in the systems ionite-aqueous salt solution, based on the application of...     

Biosorption of lead from aqueous solution by seed powder of Strychnos potatorum L.

In the present study, Pb(II) removal efficiency of Strychnos potatorum seed powder (SPSP) from aqueous solution has been investigated. Batch mode adsorption experiments have been conducted by varying pH, contact time, adsorbent dose and Pb(II) concentration. Pb(II) removal was pH dependent and found to be maximum at pH 5.0. The maximum removal of Pb(II) was achieved within 360 min. The Lagergren first-order model was less applicable than pseudo-second-order reaction model. The equilibrium adsorption data was fitted to Langmuir and Freundlich adsorption isotherm models to evaluate the model parameters. Both models represented the experimental data satisfactorily. The monolayer adsorption capacities of SPSP as obtained from Langmuir isotherm was found to be 16.420 mg/g. The FTIR study revealed the presence of various functional groups which are responsible for the adsorption process.     

CdS and Cd carboxylate nanoclusters dispersed in polymer matrix produced by a freeze drying method

Cadmium sulfide (CdS) nanoclusters were prepared by a freeze drying method from two types of cadmium carboxylates. One was cadmium methacrylates that were part of poly(methyl methacrylate) (PMMA) ionomer. The other was cadmium acetates that were dispersed in PMMA. X-ray diffraction was mainly used to study the formation and the size of nanoclusters. The size of CdS made from the ionomer was 0.9 nm, whereas that from the composite of cadmium acetate and PMMA was 2 nm. This was consistent with the size difference of the precursors of CdS: i.e., Cd carboxylate nanoclusters (ionic aggregates) were smaller in the ionomer than in the PMMA mixture, because ionic groups in the ionomer were constrained due to their connectivity to backbone chains and thus forming smaller ionic aggregates. Once stabilized, however, CdS nanocluster sizes were unchanged despite thermal treatments at up to 220 °C for 24 h for both systems. Structural transformations from a freeze dried cadmium carboxylate powder, to a CdS-containing powder, and to a heat-treated CdS-containing sample are speculated for both types of systems.     

Structurally tailored carbon xerogels produced through a sol–gel process in a water–methanol–inorganic salt solution

The impact of solvent composition as well as inorganic salt content and type on carbon xerogel structure was investigated. Carbon xerogels were derived from the sol–gel polycondensation of resorcinol with furfural in a water–methanol–inorganic salt solution. As inorganic salts, NaCl, NH₄ClO₄ and FeCl₃ were used. In order to conduct an accurate examination of the carbon xerogel structures and textures, inorganic salts were removed prior to carbonization. The xerogel structures can be tailored according to the water/methanol ratio and, to a lesser extent, according to the inorganic salt content and type in the starting solution. As a result, a significant amount of salt can be introduced to the gel network of the desired structure. The morphology and physical properties of the organic xerogels, carbon xerogels and their composites were characterized by means of SEM, N₂ sorption and XRD. It was found that samples derived from mixtures with FeCl₃ manifest well developed mesoporosity and depleated microporosity in comparison to samples prepared from mixtures with NaCl and NH₄ClO₄. Iron ions chemically bond to the xerogel matrix and cause its partial graphitization during the carbonization process, resulting in enhanced mesoporosity.     

Possibilities of powder X-ray diffraction methods in determining structural characteristics of carbon materials

The possibilities of using powder X-ray diffraction methods in the study of carbon materials are discussed. To determine the phase composition of the crystalline materials the X-ray phase analysis is employed; the real structure is established by the harmonic analysis of diffraction profiles; the structural features and phase composition of the nanomaterials are found by the radial electron density distribution function.     

Chemical and structural modification of polymers by matrix polymerization

The condensation polymerization of urea and formaldehyde in water in the presence of a macromolecular matrix, polyacrylic acid, as well as properties of composites obtained by the matrix polymerization, have been studied. The chemical structure of the urea-formaldehyde polymer was changed by the presence of the matrix. The products of matrix polymerization are composites consisting of a stoichiometric polycomplex of polyacrylic acid with the urea-formaldehyde polymer and an excess of one of the components, depending on the initial composition of the system. Introduction of matrix macromolecules into the reacting system leads to a fibrillized structure of the urea-formaldehyde polymer. The polycomplex, as well as composites with high content of polyacrylic acid, are glasses characterized by high compressive strength and ability to forced elastic deformation. They swell in water. The highly cooperative character of potentiometric titration curves for swollen gels and the quantitative yield in intermolecular amidation indicate an ideal structure of the polycomplex stabilized by hydrogen and ionic-type bonds.     

Influence of solution composition and iron powder characteristics on reduction of 2,4,6-trinitrophenol

Kinetics of the 2,4,6-trinitrophenol reaction with iron powder was investigated voltammetrically. The process was found to be mainly governed both by the iron powder characteristics and by the solution composition. Degradation kinetics was generally represented by a pseudo-first-order rate law. Consecutively, the 2,4,6-trinitrophenol reduction reaction rates for three fractions of iron powder as well as the effect of individual ions presented in the reaction system were evaluated. A correlation between the reaction rate and both the grain size of iron particles and the state of their surface was found. The effect of the reaction system composition was investigated for two types of buffered medium: Britton-Robinson buffer (boric acid, orthophosphoric acid, and glacial acetic acid) and acetate buffer solution (sodium acetate and acetic acid).     

Preparation of silver nanoparticles in solution from a silver salt by laser irradiation

A new method is proposed for the fabrication of a well-defined size and shape distribution of silver nanoparticles in solution; the method employs direct laser irradiation of an aqueous solution containing a silver salt and a surfactant in the absence of reducing agents.     

Electrochemical synthesis of lead fluoroborate by anodic dissolution of lead in fluoroboric acid solution

Lead fluoroborate solution was prepared by anodic dissolution of lead in fluoroboric acid solution. The optimal current density could reach 2 A/dm² with a current efficiency over 90%. The exchange current density of this system was found to be 0.649 A/dm² and to follow the Tafel Equation.Polarography shows that the cathodic reaction of lead fluoroborate involves only free lead ions with a charge transfer number equal to 2.     

Phase evolution in lithium disilicate glass-ceramics based on non-stoichiometric compositions of a multi-component system: structural studies by 29Si single and double resonance solid state NMR

The crystallization mechanism of a high-strength lithium disilicate glass-ceramic in the SiO(2)-Li(2)O-P(2)O(5)-Al(2)O(3)-K(2)O-(ZrO(2)) system, used as restorative dentistry material, has been examined on the basis of quantitative (29)Si magic angle spinning (MAS) and (29)Si{(7)Li} rotational echo double resonance (REDOR) NMR spectroscopy. Crystallization occurs in two stages: near 650 °C a significant fraction of the Q(3) units disproportionates into crystalline Li(2)SiO(3) and Q(4) units. Upon further annealing of this glass-ceramic to 850 °C the crystalline Li(2)SiO(3) phase reacts with the Q(4) units of the softened residual glass matrix, resulting in the crystallization of Li(2)Si(2)O(5). The NMR experiments provide detailed insight into the spatial distribution of the lithium ions suggesting the absence of lithium ion clustering in the residual glassy component of the final glass-ceramic. (31)P MAS-NMR spectra indicate that phosphate acts as a lithium ion scavenger, resulting in the predominant formation of orthophosphate (P(0)) and some pyrophosphate (P(1)) groups. Crystallization of Li(2)SiO(3) occurs concomitantly with the formation of a highly disordered Li(3)PO(4) phase as evidenced from strong linebroadening effects in the (31)P MAS-NMR spectra. Well-crystallized Li(3)PO(4) is only formed at annealing conditions resulting in the formation of crystalline lithium disilicate. These results argue against an epitaxial nucleation process previously proposed in the literature and rather suggest that the nucleation of both lithium metasilicate and lithium disilicate starts at the phase boundary between the disordered lithium phosphate phase and the glass matrix.     

Label-free fluorescent probing of G-quadruplex formation and real-time monitoring of DNA folding by a quaternized tetraphenylethene salt with aggregation-induced emission characteristics

Biosensing processes such as molecular beacons require non-trivial effort to covalently label or mark biomolecules. We report here a label-free DNA assay system with a simple dye with aggregation-induced emission (AIE) characteristics as the fluorescent bioprobe. 1,1,2,2-Tetrakis[4-(2-bromoethoxy)phenyl]ethene is nonemissive in solution but becomes highly emissive when aggregated. This AIE effect is caused by restriction of intramolecular rotation, as verified by a large increase in the emission intensity by increasing viscosity and decreasing temperature of the aqueous buffer solution of 1,1,2,2-tetrakis[4-(2-triethylammonioethoxy)phenyl]ethene tetrabromide (TTAPE). When TTAPE is bound to a guanine-rich DNA strand (G1) via electrostatic attraction, its intramolecular rotation is restricted and its emission is turned on. When a competitive cation is added to the G1 solution, TTAPE is detached and its emission is turned off. TTAPE works as a sensitive poststaining agent for poly(acrylamide) gel electrophoresis (PAGE) visualization of G1. The dye is highly affinitive to a secondary structure of G1 called the G-quadruplex. The bathochromic shift involved in the G1 folding process allows spectral discrimination of the G-quadruplex from other DNA structures. The strong affinity of TTAPE dye to the G-quadruplex structure is associated with a geometric fit aided by the electrostatic attraction. The distinct AIE feature of TTAPE enables real-time monitoring of folding process of G1 in the absence of any pre-attached fluorogenic labels on the DNA strand. TTAPE can be used as a K+ ion biosensor because of its specificity to K+-induced and -stabilized quadruplex structure.     

Formation of the solid solution CdS/CdSe from CdS and Se and its thermal stability a thermogravimetric investigation

Selenium and cadmium sulphide react in the temperature range 250–350 to form a solid solution CdSe/CdS. Thermogravimetric (in N₂) and chemical analyses show that this reaction occurs with the elimination of equimolecular amounts of Se and S. The thermal stability of the s.s. (2CdS · CdSe) in an atmosphere of N₂ was studied.

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Zusammenfassung Selen und Kadmiumsulfid reagierten miteinander im Temperaturbereich von 250 bis zu 350 unter Bildung einer festen Lösung CdSe/CdS. Thermogravimetrische (unter N₂) und chemische Untersuchungen bewiesen, da\ die Reaktion unter Elimination Äquimolekularer Mengen von Se und S verlÄuft. Die thermische StabilitÄt der festen Lösung (2CdS · CdSe) in Stickstoff wurde geprüft.

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Résumé Le sélénium et le sulfure de cadmium réagissent entre 250 et 350C en formant une solution solide CdSe/CdS. Les analyses thermogravimétrique (dans l'azote) et chimique montrent que cette réation se produit avec élimination de Se et de S suivant un rapport équimoléculaire. On a contrÔlé la stabilité thermique de la solution solide [2CdS · CdSe] dans l'azote.

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250–350 C, CdSe/CdS; ( ) , Se S; 2 CdS·CdSe N₂.

     

ICP-OES and SEM-EDX Analysis of dust and powder produced by the laser-processing of a Cr-Ni-Steel alloy

In this investigation we compared the analytical results obtained by inductively coupled plasma optical emission spectroscopy (ICP-OES) and a scanning electron microscope with an energy dispersive X-ray analysis system (SEM-EDX). The powder and dust, obtained by laser-processing of CRN-14301 steel, was analysed to classify the powder and dust for its final waste disposal. For this reason we analysed the elemental content of the samples. The samples consisted of a mixture of metals and their oxides.The solid powder and dust was analysed directly by SEM-EDX, the ICP-OES analysis was carried out after the solid was dissolved in an acid solution. Both analytical methods were in good agreement.ICP-OES showed a higher precision and lower detection limit than EDX, but SEM-EDX showed a higher amount of information regarding the sample composition.     

Quantitative characteristics of active sites on the surface of sorbents produced by the modification of kaolinite with chlorosilanes

The amount of hydroxyl and alkyl groups on the surface of sorbents synthesized by chemical modification is determined. The interaction of chlorosilanes and organosilanes with the kaolinite surface is investigated. A correlation between the pH value of a suspension of the obtained sorbent and the amount of active sites on its surface is established.     

Optical and electroluminescent characteristics of CdS nanoparticles stabilized by guanidine-containing dendrimers

Colloidal CdS nanoparticles measuring 1.9-2.3 nm and stabilized by guanidine-containing dendrimers were produced. It was established that such nanoparticles are characterized by photoluminescence in a wide spectral range (2.1-3.2 eV) with an average radiative lifetime of 55-85 ns depending on the energy of the emitted quanta and also by electroluminescence in the visible region of the spectrum (1.8-2.8 eV).     

Development of a certified reference material for lead in noodles powder

Accreditation and Quality Assurance - Food Safety and Standards Authority of India has set maximum permissible level of lead in noodle at 2.5 mg/kg. The standardized lead measurement is of high...     

Precise determination of cadmium and lead isotopic compositions in river sediments

A method for the accurate determination of Cd and Pb isotope compositions in sediment samples is presented. Separation of Cd and Pb was designed by using an anionic exchange chromatographic procedure. Measurements of Cd isotopic compositions were carried out by multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS), by using standard-sample bracketing technology for mass bias correction and Pb isotopic ratios were determined by thermal ionization mass spectrometry (TIMS). The factors that affect the accurate and precise Cd isotope compositions analysis, such as instrumental mass fractionation and isobaric interferences, were carefully evaluated and corrected. The Cd isotopic results were reported relative to an internal Cd solution and expressed as the δ^114/110Cd. Five Cd reference solutions and one Pb standard were repeatedly measured in order to assess the accuracy of the measurements. Uncertainties obtained were estimated to be lesser than 0.11‰ (2s) for the δ^114/110Cd value. Analytical uncertainties in 2s for Pb isotopic ratios were better than 0.5‰. The method has been successfully applied to the investigation of Cd and Pb isotope compositions in sediment samples collected from North River in south China.     

Phase transitions in a solution of solvated oligomers

Phase diagrams of oligomer solutions have been constructed within the mean-field approximation. The free energy includes the configuration entropy and the formation free energy of both solvation shells of the oligomers and bonds between them, where this formation free energy depends upon the oligomer-solvent and solvent-solvent bonding energies. The equations for spinodal (phase separation boundary) and percolation threshold (solution-to-gel transition) in the oligomer concentration-temperature coordinates have been found. The model makes it possible to determine the position of phase boundaries by quantum-chemical calculations of these energies and to explain the change in the composition of colloid particles and gel, depending on the solvent. The phase separation region has been predicted to narrow and to be displaced toward higher oligomer concentrations in a series of solvents with progressively increasing intermolecular bond energy.