Surface behavior, aggregation and phase separation of aqueous mixtures of dodecyl trimethylammonium bromide and sodium oligoarene sulfonates: the transition to polyelectrolyte/surfactant behavior

The properties and phase diagrams of aqueous mixtures of dodecyltrimethylammonium bromide (C(12)TAB) with the sodium oligoarene sulphonates (POSn), POS2, POS3, POS4, and POS6 have been studied using surface tension and neutron reflectometry to study the surface, and neutron small angle scattering and fluorescence to study the bulk solution. The behavior of POS2 and POS3 is reasonably consistent with mixed micelles of C(12)TAB and POSn-(C(12)TA)(n). These systems exhibit a single critical micelle concentration (CMC) at which the surface tension reaches the usual plateau. This is contrary to a recent report which suggests that the onset of the surface tension plateau does not coincide with the CMC. In the POS3 system, the micelles conform to the core-shell model, are slightly ellipsoidal, and have aggregation numbers in the range 70-100. In addition, the dissociation constant for ionization of the micelles is significantly lower than for free C(12)TAB micelles, indicating binding of the POS3 ion to the micelles. Estimation of the CMCs of the POSn-(C(12)TA)(n) from n = 1-3 assuming ideal mixing of the two component surfactants and the observed values of the mixed CMC gives values that are consistent with the nearest related gemini surfactant. The POS4 and POS6 systems are different. They both phase separate slowly to form a dilute and a concentrated (dense) phase. Fluorescence of POS4 has been used to show that the onset of aggregation of surfactant (critical aggregation concentration, CAC) occurs at the onset of the surface tension plateau and that, at the slightly higher concentration of the phase separation, the concentration of POS4 and C(12)TAB in the dilute phase is at or below its concentration at the CAC, that is, this is a clear case of complex coacervation. The surface layer of the C(12)TA ion in the surface tension plateau region, studied directly by neutron reflectometry, was found to be higher than a simple monolayer (observed for POS2 and POS3) for both the POS4 and POS6 systems. In POS6 this evolved after a few hours to a structure consisting of a monolayer with an attached subsurface bilayer, closely resembling that observed for one class of polyelectrolyte/surfactant mixtures. It is suggested that this structured layer, which must be present on the surface of the dilute phase of the coacervated system, is a thin wetting film of the dense phase. The close resemblance of the properties of the POS6 system to that of one large group of polyelectrolyte/surfactant mixtures shows that the surface behavior of oligoion/surfactant mixtures can quickly become representative of that of true polyelectrolyte/surfactant mixtures. In addition, the more precise characterization possible for the POS6 system identifies an unusual feature of the surface behavior of some polyelectrolyte/surfactant systems and that is that the surface tension can remain low and constant through a precipitation/coacervation region because of the characteristics of two phase wetting. The well-defined fixed charge distribution in POS6 also suggests that rigidity and charge separation are the factors that control whether a given system will exhibit a flat surface tension plateau or the alternative of a peak on the surface tension plateau.     

Synthesis of 2,3-diaryl-5H-imidazo[2,1-a]isoindol-5-ones via the one-pot reaction of 1,2-diketones, 2-formylbenzoic acids, and ammonium acetate

We describe a new one-pot synthesis of 2,3-diaryl-5H-imidazo[2,1-a]isoindol-5-ones via the reaction of 1,2-diketones, 2-formylbenzoic acids, and ammonium acetate in acetic acid under reflux conditions and in the absence of a catalyst.     

Syntheses,Crystal Structures,and Properties of a New Lead(Ⅱ) Complex Involving Holo-and Hemidirected Coordination Spheres with 3,5,6-Tris(2-pyridyl)-1,2,4-triazine Ligand

[Pb(TPT)(μ-I)2PbI2(μ-I)2Pb(TPT)] 1(TPT is the abbreviation of 3,5,6-tris(2-pyridyl)-1,2,4-triazine ligand) has been synthesized and characterized by elemental analysis, IR, 1HNMR spectroscopy and studied by thermal and electrochemical properties as well as X-ray crystallography. The single-crystal X-ray data show two different kinds of Pb2+ ions in 1 with coordination numbers of six, Pb1 = PbI6, and five, Pb2 = PbN3I2, with holodirected and hemidirected coordination spheres, respectively. The supramolecular features in 1 are negotiated through the weak but directional Pb···I, C–H···N and C–H···I interactions and aromatic π-π stacking interactions.     

Palladium-catalyzed oxidative C–H bond coupling of indoles and benzaldehydes: a new approach to the synthesis of 3-benzoylindoles

A palladium-catalyzed dehydrogenative acylation of indoles using easily accessible aldehydes as the acyl source is described. This reaction provides a new approach for the synthesis of 3-acylindoles.     

Catalyst-free synthesis of 3-(alkylamino)-2-arylimidazo[1,2-a]pyridine-8-carboxylic acids via a three-component condensation

The synthesis of a number of 3-(alkylamino)-2-arylimidazo[1,2-a]pyridine-8-carboxylic acids via a facile route involving the reaction between 2-amino-3-pyridinecarboxylic acid, benzaldehyde derivatives, and isonitriles is reported. The structures of the synthesized compounds are proved by X-ray crystallography.     

A PYRIDYL-TRIAZINE COMPLEX OF Co(II): SPECTROSCOPIC,STRUCTURAL, AND DOCKING STUDIES

Journal of Structural Chemistry - A new cobalt(II) complex of 5-phenyl-3-(pyridin-2-yl)-1,2,4-triazine (PPTA), [Co(PPTA)2(NO3)2] (1), is prepared and identified by the elemental analysis, FTIR...     

A molecular orbital rationalization of ligand effects in N2 activation

Molecular orbital theory has been used to study a series of [(micro-N2){ML3}2] complexes as models for dinitrogen activation, with M=Mo, Ta, W, Re and L=NH2, PH2, AsH2, SbH2 and N(BH2)2. The main aims of this study have been to provide a thorough electronic analysis of the complexes and to extend previous work involving molecular orbital analyses. Molecular orbital diagrams have been used to rationalize why for L=NH2 ligand rotation is important for the singlet state but not the triplet, to confirm the effect of ligand pi donation, and to rationalize the importance of the metal d-electron configuration. The outcomes of this study will assist with a more in-depth understanding of the electronic basis for N2 activation and allow clearer predictions to be made about the structure and multiplicity of systems involved in transition-metal catalysis.     

Efficient synthesis of 3,4-dihydropyrano[3,2-c]chromenes catalyzed by Ni(II)-functionalized Li<Superscript>+</Superscript>-Montmorillonite in a one-pot fashion under solvent-free conditions

A family of 3,4-dihydropyrano[3,2-c]chromenes were synthesized from 4-hydroxycoumarin and malononitrile via a one-pot reaction under solvent-free conditions at 100 °C catalyzed by Ni@Imine-Li⁺-MMT. This methodology tolerates most of the substrates and has the merits of lower loading of the catalyst, absence of solvents, excellent yields and reusability of the catalyst. A reasonable mechanism is also proposed. This catalytic system can be reused for at least five times with a negligible loss of activity. The prepared catalyst was characterized by using FTIR, TGA, SEM, TEM, uv-DRS, EDX and XRD.     

Cyclic peptide nanocapsule as ion carrier for halides: a theoretical survey

In this work, the encapsulations of halide ions including F^?, Cl^?, and Br^? by cyclic peptide nanocapsule as ion carrier (F^?, Cl^?, and Br^? @(Ala4...Ala4)) were investigated using the dispersion corrected density functional theory (DFT) employing CAM-B3LYP functional and the 6–311?+?G (d, p) basis set in the gas phase. The electronic binding energy (E_bind), binding enthalpy (H_bind), and binding Gibbs free energy (G_bind) for each anion were calculated and showed that the stability order of the complexes based on their calculated E_bind is F^??>?Cl^??>?Br^? @(Ala4...Ala4). The calculated value of G_bind for F^? @(Ala4...Ala4) was ??29.77 kcal/mol showing the formation of this complex is thermodynamically favorable while the formation of Br^? @(Ala4...Ala4) is 14.35 kcal/mol which shows that the encapsulation of Br^? is not possible. The calculated value of G_bind for Cl^? @(Ala4...Ala4) was ??0.57 kcal/mol which shows that Cl^? ion can be reversibly stored inside the nanocapsule. The NBO analysis was also performed to investigate the charge transfer between two cyclic peptides in the complexes and also between the anion and the nanocapsule. The NBO analysis showed that the strongest hydrogen bonds between two cyclic peptides are in the complex.     

Magnetic Field-Assisted Direct Immersion SPME of Endogenous Aldehydes in Human Urine

Direct immersion solid-phase microextraction (DI-SPME) is an effective microsampling strategy for polar and ionic species in aqueous media. Nevertheless, the fiber coating is in direct contact with sample solution and affected by its conditions. To compensate this limitation and to improve the extraction efficiency, a magnetic fiber coating was prepared and employed for DI-SPME sampling under the enhancing effect of a magnetic field. Magnetic iron oxide core–shell silica nanoparticles were synthesized and embedded in polypyrrole using an in situ electropolymerization method along with simultaneous coating on the surface of a platinized stainless-steel fiber. It was then applied for magnetic-assisted DI-SPME (MA-DI-SPME) sampling of endogenous aldehydes in human urine. Sample solution pH, the magnetic field intensity, ionic strength and extraction time were evaluated as the important affecting variables. Limits of detection were obtained 0.01–0.1 ng mL^?1; the calibration graphs were linear over the range of 0.1–10000 ng mL^?1. The inter-fiber (fiber-to-fiber) reproducibility was found to be 10.7–12.5%. Matrix effect from urine samples was not observed at concentration levels of 0.2, 2, and 8 µg mL^?1. The results showed that magnetic field increased the efficiency of DI-SPME method about two to four times. The developed strategy was successfully applied for the extraction and quantification of hexanal and heptanal (as the most important aldehyde biomarkers) in urine samples.

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