Simultaneous determination of gasoline oxygenates and benzene, toluene, ethylbenzene and xylene in water samples using headspace-programmed temperature vaporization-fast gas chromatography-mass spectrometry

A sensitive method is presented for the fast analysis of seven fuel oxygenates (methanol, ethanol, tert-butyl alcohol (TBA), methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) and diisopropyl ether (DIPE)) and benzene, toluene, ethylbenzene and p-xylene (BTEX) in water samples. The applicability of a headspace (HS) autosampler in combination with a GC device equipped with a programmable temperature vaporizer (PTV) and a MS detector is explored. The proposed method achieves a clear improvement in sensitivity with respect to conventional headspace methods due to the use of the PTV. Two different packed liners with materials of different trapping strengths (glass wool and Tenax-TA) were compared. The benefits of using Tenax-TA instead of glass wool as packed material for the measurement of the 11 compounds emerged as better signal-to-noise ratios and hence better detection limits. The proposed method is extremely sensitive. The limits of detection are of the order of ng/L for six of the compounds studied and of the order of microg/L for the rest, with the exception of the most polar and volatile compound: methanol. Precision (measured as the relative standard deviation for a level with an S/N ratio close to 3) was equal to or lower than 15% in all cases. The method was applied to the determination of the analytes in natural matrixes (tap, river and sea water) and the results obtained can be considered highly satisfactory. The methodology has much lower detection limits than the concentration limits proposed in drinking water by the US Environmental Protection Agency (EPA) and the European Union for compounds under regulation.     

The photophysical determination of the minimum hydrotrope concentration of aromatic hydrotropes

A method based on the aggregate to monomol emission ratio, I(aggr)/I(monomol), was used to determine the minimal hydrotropic concentration (MHC) of aromatic hydrotropes. The main advantage of this method is that it does not require the use of probes or other additives, which might disrupt the aggregation process. Also, it relies on spectrophotometric measurements, which are more sensitive and less arduous than others, like conductivity, light scattering and surface tension.     

Photoinduced electron transfer in a hexaphenylbenzene-based self-assembled porphyrin-fullerene triad

A hexaphenylbenzene-based zinc porphyrin dyad forms a 1:1 complex with a fullerene bearing two pyridyl groups via coordination of the pyridyl nitrogens with the zinc atoms. The fullerene is symmetrically located between the two zinc porphyrins. The binding constant for the complex is 7.3 x 10(4) M(-1) in 1,2-difluorobenzene. Photoinduced electron transfer from a porphyrin first excited singlet state to the fullerene occurs with a time constant of 3 ps, and the resulting charge-separated state has a lifetime of 230 ps. This self-assembled construct should form a basis for the construction of more elaborate model photosynthetic antenna-reaction center systems.     

Palladium-catalyzed aryl-aryl cross-coupling reaction using ortho-substituted arylindium reagents

A range of biaryl compounds (aryl-aryl, aryl-heteroaryl, and heteroaryl-heteroaryl) can be efficiently prepared by a palladium-catalyzed cross-coupling reaction between ortho-substituted triarylindium reagents and aryl halides. The triarylindium reagents are prepared by directed ortho-lithiation and transmetallation to indium from the corresponding benzene derivatives using various directed metallation groups (DMGs). The reaction proceeds smoothly in high yields and short reaction times with high atom economy (the three aryl groups attached to indium are efficiently transferred).     

Synthesis of 2-iodoglycals, glycals, and 1,1'-disaccharides from 2-Deoxy-2-iodopyranoses under dehydrative glycosylation conditions

Treatment of 2-deoxy-2-iodopyranoses under dehydrative glycosylation conditions afforded pyranose glycals, 2-iodoglycals, and 1,1'-disaccharides instead of the expected glycoside products. While the product distribution revealed that this reaction is very sensitive to the configuration of the 2-deoxy-2-iodopyranose, 2-iodopyranoid glycals can be obtained almost exclusively in good yields by employing 3,4-O-isopropylidene as a cyclic bifunctional protecting group. The behavior of 2-deoxy-2-iodopyranoses during the dehydrative elimination reaction has been analyzed in detail.     

J-aggregation of a water-soluble tetracationic porphyrin in mixed LB films with a calix[8]arene carboxylic acid derivative

The molecular organization of a mixed film, containing a water-soluble tetracationic porphyrin (TMPyP) and a p-tert-butyl calix[8]arene octacarboxylic acid derivative (C8A), at the air-water interface and on a solid support (LB film), has been investigated. Although the TMPyP aggregation was not detected at the air-water interface, TMPyP J-aggregates have been found in the LB films (Y-type). Unlike tetraanionic porphyrins, for example TSPP, the TMPyP J-aggregates are not induced by a zwitterion formation. The TMPyP J-aggregation is a result of a "double comb" configuration, where porphyrins from opposite layers are interwoven in a linear infinite J-aggregate. Our results confirm that TMPyP molecules tend to self-aggregate strongly, provided the electrostatic repulsions of their peripheral groups are cancelled by the anionic groups of the C8A matrix.     

Langmuir-Blodgett films of a Mo-blue nanoring [Mo(142)O(429)H(10)(H(2)O)(49)(CH(3)CO(2))(5)(CH(3)CH(2)CO(2))](30)(-) (Mo(142)) by the semiamphiphilic method

Langmuir monolayers and LB films of the ring-shaped mixed-valence polyoxomolybdate [Mo142O429H10(H2O)49(CH3CO2)5(CH3CH2CO2)](30-) (Mo142) dissolved in the aqueous subphase have been successfully fabricated by using the adsorption properties of a DODA monolayer. Infrared and ultraviolet-visible spectroscopy of the LB films indicates that Mo142 and DODA molecules are incorporated within these LB films. X-ray reflectivity experiments indicate that the LB films exhibit a well-defined lamellar structure formed by bilayers of DODA molecules alternating with monolayers of Mo142. Using behenic acid-modified hydrophobic quartz substrate is critical for the formation of the well-defined lamellar structure. From the values of the periodicity obtained by these experiments it is clear that the Mo142 clusters lie flat along the charged organic layers. AFM images also showed the flat and homogeneous films on the quartz substrates treated with behenic acid. Cyclic voltammograms of Mo142-LB films deposited on ITO substrates showed quasi-reversible oxidation/reduction waves with positive shift of the potential compared to the case of solution.     

4,2-Ribbon like ferromagnetic cyano-bridged Fe(III)2Ni(II) chains: a magneto-structural study

The low-spin iron(III) complex AsPh(4)[Fe(III)(bpy)(CN)(4)].CH(3)CN (1) [AsPh(4) = tetraphenylarsonium cation] and the heterobimetallic chains [{Fe(III)(L)(CN)(4)}(2)Ni(II)(H(2)O)(2)].4H(2)O with L = bpy (2) and phen (3) [bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline] have been prepared and their structures determined by X-ray diffraction methods. The structure of 1 consists of mononuclear [Fe(bpy)(CN)(4)](-) anions, tetraphenylarsonium cations and acetonitrile molecules of crystallization. The iron(III) is hexacoordinated with two nitrogen atoms of the bidentate bpy and four carbon atoms of four terminal cyanide groups building a distorted octahedral surrounding around the metal atom. 2 and 3 are isomorphous compounds whose structure is made up of neutral 4,2-ribbon like bimetallic chains of formula [{Fe(III)(L)(CN)(4)}(2)Ni(II)(H(2)O)(2)] where the [Fe(III)(L)(CN)(4)](-) unit acts as a bis-monodentate bridging ligand toward the trans-diaquanickel(II) units through two of its four cyanide groups in cis positions. The chains exhibit two orientations in the unit cell and they interact with each other through hydrogen bonds involving the coordination and crystallization water molecules together with the uncoordinated cyanide nitrogen atoms of the [Fe(L)(CN)(4)](-) units. Compounds 2 and 3 behave as ferromagnetic Fe(III)(2)Ni(II) chains which interact ferromagnetically at very low temperatures in the case of 2, whereas metamagnetic-like behaviour is observed for with a critical field (H(c)) around 200 G. For H > H(c) the ferromagnetic Fe(III)(2)Ni(II) chains of 3 exhibit a frequency dependence of the out-of-phase ac susceptibility signal at T < 3.5 K.     

Metamorphosis of a butterfly: synthesis, structural, thermal, magnetic and DFT characterisation of a ferromagnetically coupled tetranuclear copper(II) complex

The reaction in water of Cu(OH)(2) with 2,2'-bipyridine (bipy) and (NH(4))(2)HPO(4) in a 4 : 4 : 2 molar ratio under an inert atmosphere leads to the formation of a tetranuclear copper(II) complex of formula {[(H(2)O)(2)Cu(4)(bipy)(4)(mu(4)-PO(4))(2)(mu(2)-OH)] x 0.5 HPO(4) x 15.5 H(2)O}, 1, with butterfly topology. The structure of the tetranuclear core in 1 consists of four crystallographically unique copper(II) ions in approximate square-pyramidal geometry with each coordinated to a bipy ligand and interacting through two mu(4)-O,O',O'-phosphate bridges. Additional bridging between Cu(3) and Cu(4) is provided by a hydroxide ligand, whereas two water molecules cap the Cu(1) and Cu(2) square pyramids to yield a N(2)O(3) chromophore at each copper atom. Adjacent tetranuclear units align in anti-parallel fashion where proximate metal-bound water molecules interact with each other through both intra- and inter-molecular H-bonding to link two such clusters. These pairs then further associate through pi[...]pi interactions between bipy ligands to form a 2D sheet with neighbouring sheets separated by H-bonded lattice water molecules, which form a 2D H-bonded network. Variable-temperature magnetic susceptibility measurements performed upon 1 reveal net intramolecular ferromagnetic coupling between the copper(II) ions and this is supported and rationalized by a DFT study.