Synthesis and physicochemical characterization of alkanedyil-α-ω-bis(dimethyldodecylammonium) bromide, 12-s-12,2Br(-), surfactants with s=7, 9, 11 in aqueous medium

In this work, three didodecyl dicationic dibromide dimeric surfactants 12-s-12,2Br(-), with different methylene spacer lengths (s=7, 9, and 11) were prepared and characterized and their properties compared to those of 12-s-12,2Br(-) surfactants with s=2, 3, 4, 5, 6, 8, 10, and 12. Information about the critical micelle concentration, the micellar ionization degree, the average aggregation number and the polarity of the interfacial region, and microviscosity of the micellar interior was obtained by using different techniques. Their surface activity was investigated by means of surface tension measurements. Micellization was also studied by using (1)H NMR and diffusion NMR (DOSY) spectroscopy as well as isothermal titration calorimetry. The values of the thermodynamic parameters show that the dimeric surfactants micellization is exothermic and driven by entropy. The occurrence of morphological transitions upon increasing surfactant concentration was studied, and the results indicate that the spacer length, s, plays a key role in the micellar growth of 12-s-12,2Br(-) aggregates. The value of s not only control the magnitude of C(*), the surfactant concentration above which the morphological transition from spherical micelles into elongated ones occurs, but also the sign of the enthalpy change accompanying the sphere-to-rod transition.     

Binary mixtures with novel monomeric and dimeric surfactants: influence of the head group nature and number of hydrophobic chains on non-ideality

The micellization and micellar growth in the mixtures of N,N-dimethyl, N-phenyl,N-dodecylammonium bromide, PH12, N,N-dimethyl,N-ciclohexylmethyl,N-dodecylammonium bromide, CH12, and their two dimeric counterparts m-dimethylphenyl-α-ω-bis(dodecyldimethylammonium) bromide, 12PH12, and m-dimethylciclohexyl-α-ω-bis(dodecyldimethylammonium) bromide, 12CH12, with dodecyltrimethylammoniumbromide, DTAB, and with N-decanoyl N-methylglucamide, MEGA10, were investigated at 303 K. Circular dichroism, CD, experiments showed the formation of mixed micelles. Two-dimensional, 2D, rotating frame nuclear Overhauser effect spectroscopy (ROESY) experiments indicated that the arrangement of the rings in the pure and mixed micelles is similar, with the rings bent into the micelle interior avoiding contact with water. Application of different theoretical approaches shows that PH12 and CH12 mixtures with DTAB and with MEGA10 behave almost ideally. The binary systems of 12PH12 and 12CH12 with DTAB and with MEGA10 show a non-ideal behavior. An increment in the solution mole fraction of MEGA10 and DTAB diminishes the tendency of the micellar aggregates to grow.     

Speciation of arsenic metabolites in the free-living mouse Mus spretus from Do?ana National Park used as a bio-indicator for environmental pollution monitoring

A speciation approach based on orthogonal chromatographic systems coupled to inductively coupled plasma mass spectrometry (ICP-MS) was used to characterise the biological response of free-living mice Mus spretus to environmental pollution caused by arsenic in different areas of the Do?ana National Park (south-west Spain). The relative presence of inorganic and organic forms of arsenic was studied in cytosolic extracts from high metabolic activity organs of Mus spretus mice: kidneys, liver, and brain. An instrumental coupling of size-exclusion chromatography with UV and collision/reaction cell-ICP-MS detectors (SEC-UV-ICP-ORC-MS) both in analytical and preparative scale was used for this purpose. The results showed the presence of low molecular mass (LMM) molecules linked to arsenic in these tissues especially in the kidneys, where the presence of these arsenic metabolites was higher. On the other hand, the presence of these arsenicals varied from one area to the other, which can be related to a different occurrence of contaminants. These low molecular mass fractions were collected by preparative SEC chromatography for later study with ion exchange chromatography and detection by ICP-ORC-MS, using both anionic and cationic columns. The results showed the higher presence of MMA and DMA in kidneys of mice caught in contaminated areas and the existence of small amounts of unidentified arsenicals when cation-exchange chromatography was used, which could be related to the presence of dimethylarsinoylethanol (DMAE), thioarsenic species, or arsenocholine (AsC).     

Geographical origin of Sauvignon Blanc wines predicted by mass spectrometry and metal oxide based electronic nose

Analysis of 34 Sauvignon Blanc wine samples from three different countries and six regions was performed by gas chromatography-mass spectrometry (GC-MS). Linear discriminant analysis (LDA) showed that there were three distinct clusters or classes of wines with different aroma profiles. Wines from the Loire region in France and Australian wines from Tasmania and Western Australia were found to have similar aroma patterns. New Zealand wines from the Marlborough region as well as the Australian ones from Victoria were grouped together based on the volatile composition. Wines from South Australia region formed one discrete class. Seven analytes, most of them esters, were found to be the relevant chemical compounds that characterized the classes. The grouping information obtained by GC-MS, was used to train metal oxide based electronic (MOS-Enose) and mass spectrometry based electronic (MS-Enose) noses. The combined use of solid phase microextraction (SPME) and ethanol removal prior to MOS-Enose analysis, allowed an average error of prediction of the regional origins of Sauvignon Blanc wines of 6.5% compared to 24% when static headspace (SHS) was employed. For MS-Enose, the misclassification rate was higher probably due to the requirement to delimit the m/z range considered.     

Polymer-supported molybdenyl thioglycolate as oxygen atom transfer reagent

Oxo-transfer reactions of a variety of substrates in DMF or methanol using polymer-supported molybdenyl thioglycolate (PSMT) have been investigated. The clean oxidation of Me₂PhP, n-butanethiol or benzoin to yield Me₂PhPO, disulfide or benzil, respectively, occurs in high yield. In the presence of air or pyridine N-oxide, a catalytic cycle is accomplished which goes on until the completion of the substrate.     

Study of the reaction of methyl 4‐nitrobenzenesulfonate and Br− in water–glycerol cationic micellar solutions

The reaction of methyl 4‐nitrobenzenesulfonate (MNB) and Br^? has been studied in water–glycerol (GLY) alkyltrimethylammonium bromide micellar solutions, with the weight percentage of glycerol up to 50%. A pseudophase kinetic model was used for quantitatively discussing the kinetic data. Results showed that the equilibrium‐binding constant for the organic substrate molecules to the cationic micelles decreases upon increasing the amount of glycerol present in the micellar reaction media. The second‐order rate constant of the reaction in the micellar pseudophase is practically independent of wt% of GLY. Similar results were found in other water–organic solvent alkyltrimethylammonium bromide micellar solutions for the same process. However, the dependence of the reaction rate, for a given surfactant concentration, on the wt% of organic solvent is weaker for glycerol than for the other organic solvents. This was explained by considering that the cationic micellar ionization degree is nearly independent of wt% GLY. As a consequence, bromide ions concentration in the interfacial region (the reaction site) does not change by varying wt% of GLY. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 845–582, 2008     

Evaluation of error in the measurement of displacement vector components by using electronic speckle pattern interferometry

We report on the errors obtained by comparing in- and out-of-plane displacements calculated from the sensitivity matrix with all its components, and when only the component from the largest contributing of each one of the three interferometers is considered. Divergent illumination is considered in the evaluation of sensitivity vector to measure displacement vector components. This analysis is performed for a flat elastic target which is loaded in the x-direction and after in the z-direction. The technique applied is electronic speckle pattern interferometry.     

Study of the reaction methyl 4‐nitrobenzene‐sulfonate + Cl− in mixed hexadecyltrimethyl‐ammonium chloride‐triton X‐100 micellar solutions

The reaction methyl 4‐nitrobenzenesulfonate + Cl^? was studied in hexadecyltrimethylammonium chloride (CTAC) in the absence and presence of 0.1 M NaCl, as well as in mixed CTAC/Triton X‐100 (polyoxyethylene(9.5)octylphenyl ether) aqueous micellar solutions with CTAC molar fractions of 0.9, 0.8, 0.7, and 0.6. Conductivity measurements were used to obtain critical micellar concentrations and micellar ionization degrees of the various micellar reaction media. From these data, thermodynamic information on the cationic/nonionic mixed micellar solutions was obtained. Micellar effects on the observed rate constant were explained by pseudophase kinetic models. The estimated second‐order rate constants in the micellar pseudophase of the different micellar reaction media showed that pure CTAC and mixed CTAC/Triton X‐100 micelles, at the high cationic surfactant molar fractions studied, provide reaction sites of similar characteristics at the interfacial region. This was in agreement with previous structural studies carried out on mixed CTAC/Triton X‐100 micellar solutions. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 45–51, 2003     

[CpRu]‐Catalyzed Carbene Insertions into Epoxides: 1,4‐Dioxene Synthesis through SN1‐Like Chemistry with Retention of Configuration

Rather than lead to the usual deoxygenation pathway, metal carbenes derived from α‐diazo‐β‐ketoesters undergo three‐atom insertions into epoxides using a combination of 1,10‐phenanthroline and [CpRu(CH₃CN)₃][BAr_F] as the catalyst. Original 1,4‐dioxene motifs are obtained as single regio‐ and stereoisomers. A perfect syn stereochemistry (retention, e.r. up to 97:3) is observed for the ring opening, which behaves as an S_N1‐like transformation.     

Multifunctional Redox Polymers: Electrochrome,Polyelectrolyte, Sensor,Electrode Modifier,Nanoparticle Stabilizer,and Catalyst Template

Simple “click” polycondensation metallopolymers of redox‐robust bis(ethynyl)biferrocene (biFc) and di(azido) poly(ethylene glycol) (PEG400 and PEG1000) were designed for multiple functions including improvement of water solubility and biocompatibility, the introduction of mixed valency and sensing capabilities, and as nanoparticle stabilizers for catalysis.