A new ionic liquid dimethyldinonylammonium bromide as a flow modifier for the simultaneous determination of eight carboxylates by capillary electrophoresis

Two new methods of capillary zone electrophoresis based on aqueous phosphate running buffers with UV spectrophotometric detection were developed and optimized for the determination of eight carboxylates as copper complexes. Metalcomplexes are negatively charged, so measurements were made as anion analyses with flow reversal in the capillary. Two flow modifiers were used: a common tetradecyltrimethylammonium bromide (TTAB) and a new ionic liquid dimethyldinonylammonium bromide (DMDNAB). The methods were compared to each other. Better separation was achieved with DMDNAB as the flow modifier. Method development was done using a fused silica capillary (61 cm x 50 microm i.d.).Optimization was done using 95 mmol L(-1) phosphate buffer with TTAB or DMDNAB in the concentration 0.5 mmol L(-1) at pH 7.1. A -20 kV voltage and direct UV detection at 254 nm was used in measurements. In both CE methods all the peaks in the electropherograms were properly separated, the calibration plots gave good correlation coefficients and all eight carboxylates were detected in less than 7.5 min. The two methods were tested with natural water samples and a paper mill sample, and proved to be feasible.     

Design and self-assembly of ditopic and tetratopic cavitand complexes

The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability.     

Synthesis, characterization and thermal properties of new aromatic quaternary ammonium bromides: precursors for ionic liquids and complexation studies

Series of new aromatic R₂R′₂N⁺Br⁻ (R=benzyl, 4-methylbenzyl, 2-phenylethyl, 3-phenylpropyl; R′=ethyl, methyl, isopropyl) or RR′₂NH⁺Br⁻-type (R=benzyl, R′=isopropyl) quaternary ammonium bromides were prepared by using novel synthetic route in which a formamide (N,N-diethylformamide, N,N-dimethylformamide, N,N-diisopropylformamide) is treated with aralkyl halide in presence of a weak base. The compounds were characterized by ¹H-NMR and ¹³C-NMR spectroscopy and mass spectrometry. Structures of the crystalline compounds were determined by X-ray single crystal diffraction, and in addition the powder diffraction method was used to study the structural similarities between the single crystal and microcrystalline bulk material. Three of the compounds crystallized in monoclinic, two in orthorhombic and one in triclinic crystal system, showing ion pairs, which are interconnected by weak hydrogen bonds and weak π-π interactions between the phenyl rings. Three of the compounds appeared as viscous oil or waxes. Finally, TG/DTA and DSC methods were used to analyze thermal properties of the prepared compounds. The lowest melting points were obtained for diethyldi-(2-phenylethyl)ammonium bromide (122.2 °C) and for diethyldi-(3-phenylpropyl)-ammonium bromide (109.1 °C). In general, decomposition of the compounds started at 170-190 °C without identifiable cleavages, thus liquid ranges of 30-70 °C were observed for some of the compounds.     

Synthesis, characterization and thermal properties of small R2R2NX-type quaternary ammonium halides

Twenty-one R₂R^′₂N⁺X⁻ -type (R=methyl or ethyl, R^′=alkyl, X=Br or I) quaternary ammonium (QA) halides have been prepared by using a novel one-pot synthetic route in which a formamide (dimethyl-, diethylformamide, etc.) is treated with alkyl halide in the presence of sodium or potassium carbonate. The formation of QA halides was verified with ¹H-NMR, ¹³C-NMR, MS and elemental analysis. The crystal structures of four QA halides (two bromide and two iodide) were determined using X-ray single crystal diffraction, and the powder diffraction method was used to study the structural similarities between the single crystal and microcrystalline bulk material. The thermal properties of all compounds were studied using TG/DTA and DSC methods. The smallest compounds decomposed during or before melting. The decreasing trend of melting points was observed when the alkyl chain length was increased. The liquid ranges of 120-180 °C were observed for compounds with 5-6 carbon atoms in the alkyl chain. The low melting points and wide liquid ranges suggest potential applicability of these compounds for example as ionic liquids precursors.     

Gold Decorated Graphene by Laser Ablation for Efficient Electrocatalytic Oxidation of Methanol and Ethanol

A well‐known limitation in the fabrication of metal‐graphene composite has been the use of surfactants that strongly adsorb on the surface and reduce the performance of the catalyst. We demonstrate here a novel one‐pot synthesis of gold nanoparticles by laser ablation of gold strip and in‐situ decoration on graphene substrate. Not only the impregnation of nanoparticles was linker free, but also the synthesis by itself was surfactant‐free. The composite materials were well characterized morphologically and functionally using electron microscopy, X‐ray and electron diffraction, Raman spectroscopy, Zeta potential, electrochemical measurements and UV‐Visible spectroscopic techniques. This linker‐free gold‐graphene based composite has been employed for catalytic applications pertaining to electrooxidation. We have explored the use of this composite as a binder‐free electrode in electrocatalytic oxidation of methanol and ethanol in alkaline medium. Additionally, the onset potential for ethanol oxidation was found to be more negative, ?100 mV, an indication of its promising application in direct ethanol fuel cells.     

Structure-properties relationships in some random copolymers of propylene

Correlations have been investigated between the content of short isotactic segments and thermal properties in some propylene/olefin random copolymers. Polypropylene copolymers modified by ethylene show variations different from those for copolymers modified by ethylene and butene. However, in both cases, the weldability temperature decreases on increasing the comonomer concentration.     

Solvent exchange in thermally stable resorcinarene nanotubes

The assembly of C-methyl resorcinarene into a tubular supramolecular solid-state structure, its thermal stability, and its hosting properties are reported. Careful control of the crystallisation conditions of C-methyl resorcinarene and 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane (1,4-dimethyl DABCO) dibromide leads to a formation of two crystallographically different, but structurally very similar, solid-state nanotube structures. These structures undergo a remarkable variety of supramolecular interactions, which lead to the formation of 0.5 nm diameter nonpolar tubes through the crystal lattice. The formation of these tubes is templated by suitably sized small alcohols, namely, n-propanol, 2-propanol, or n-butanol. The self-assembly involves close pi...pi interactions between the adjacent resorcinarenes, and C--H...pi and cation...pi interactions between the resorcinarenes and the guest 1,4-dimethyl DABCO dications. The crystals of these supramolecular tube structures are thermally very stable and the included solvent alcohol can be removed from the tubes without breaking the single-crystalline structure of the assembly. After removal of the solvent molecules the tubes can be filled with other small, less polar solvent molecules such as dichloromethane.     

A linear Fe–O–Fe unit in bis­(dibenzyl­dimethyl­ammonium) μ‐oxo‐bis­[tribromo­ferrate(III)]

The title compound, (C₁₆H₂₀N)₂[Fe₂Br₆O], crystallizes with one dibenzyl­dimethylammonium cation and one half of a μ‐oxo‐bis­[tribromo­ferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe—O—Fe unit. The iron(III) cations have tetra­hedral geometry, with bond angles in the range 106.8 (1)–112.2 (1)°. The ion pairs are held together by Coulombic forces and C—H⋯Br hydrogen bonds. Each Br⁻ anion forms one hydrogen bond. No C—H⋯O hydrogen bonds are found between the O atom in the Fe—O—Fe unit and surrounding counter‐cations, consistent with the linear configuration of the Fe—O—Fe unit.     

Metal-directed self-assembly of cavitand frameworks

The self-assembly between bidentate cavitand ligands and mono/dinuclear metal precursors to give cavitand frameworks has been explored. For this purpose, two new cavitands bearing AB and AC phenylpyridyl moieties at the upper rim have been synthesized. A series of self-assembled molecular dimers featuring fac-Re(CO)(3)Br as metal corners have been prepared and characterized. Two possible dimeric structures (C-shaped and S-shaped) are possible when AB cavitand 2 is used in the self-assembly reaction; only one is obtained in the case of AC cavitand 3. In addition, the self-assembly of AB-dibridged cavitand 2 with dinuclear Pd/Pt metal precursors 5a and 5b has been studied. At this level of complexity, the self-assembly can lead to more than one structure. Several different final structures have been envisioned and their formation analyzed in silico and in solution. Out of the three possible cyclic structures (dimer, trimer, and tetramer), only the entropically favored dimer 6a (6b) is formed, as predicted from molecular modeling and demonstrated by PGSE NMR experiments.