The micellization and micellar growth of cationic dimeric surfactant propanediyl-alpha-omega-bis(dodecyldimethylammonium) bromide, 12-3-12,2Br-, have been studied in several water-organic solvent mixtures. The organic solvents were ethylene glycol, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, acetonitrile, dioxane, formamide, and N,N-dimethylformamide. Results showed that the aggregation process was less favored in the binary mixtures than in pure water, which was explained by considering the influence of the solvophobic effect on micellization. The addition of organic solvents was accompanied by a diminution in the average aggregation number, Nagg, of the dimeric micelles. This diminution was due to the decrease in the interfacial Gibbs energy contribution, Delta G0interfacial, to the Gibbs energy of micellization caused by the decrease in the hydrocarbon/bulk-phase interfacial tension. As a result of the micelle size diminution, the concentration at which the sphere-to-rod transition occurred, C*, was higher in the mixtures than in pure water. Micelle size reduction is accompanied by a decrease in the ionic interactions and in the extra packing contribution to the deformation of the surfactants tails, making the formation of cylindrical micelles less favorable.

Noncovalent interactions of anions with electron-deficient aromatic rings that have been studied so far involve non-heteroaromatic or nitrogen-based heteroaromatic systems. Here we report the first case of an organic oxygenated aromatic system, in particular the tri-aryl-pyrylium tetrafluoroborate system, for which noncovalent anion-π interactions of the pyrylium cation with the tetrafluoroborate anion have been experimentally detected and demonstrated by means of (19)F NMR spectroscopy in solution. A series of pyrylium tetrafluoroborate salts were synthesized in the presence of BF3·Et2O, by direct reaction of 4-substituted benzaldehydes with 4-substituted acetophenones or via the previously obtained chalcone of the less reactive ketone. Correlations of (19)F NMR chemical shifts of tetrafluoroborate anion for most of the synthesized tri-arylpyrylium tetrafluoroborate complexes with both the pyrylium cation molecular weight and the standard substituent Hammett constants, demonstrate anion-π(+) interaction to act between the polyatomic anion BF4(-) and the pyrylium aromatic system. DFT calculations reveal that an additional (C-H)(+)-anion hydrogen bond involving the H(5) of pyrylium ring exists for these fluorescent dyes that show a tunable cup-to-cap shape cavity. The strong fluorescence emission observed for some representative pyrylium tetrafluoroborates described herein, makes them a promising class of tunable emission wavelength dyes for laser technology applications.

The synthesis of several non-carbohydrate ligands of cholera toxin based on polyhydroxyalkylfuroate moieties is reported. Some of them have been linked to D-galactose through a stable and well-tolerated S-glycosidic bond. They represent a novel type of non-hydrolyzable bidentate ligand featuring galactose and polyhydroxyalkylfuroic esters as pharmacophoric residues, thus mimicking the GM1 ganglioside. The affinity of the new compounds towards cholera toxin was measured by weak affinity chromatography (WAC). The interaction of the best candidates with this toxin was also studied by saturation transfer difference NMR experiments, which allowed identification of the binding epitopes of the ligands interacting with the protein. Interestingly, the highest affinity was shown by non-carbohydrate mimics based on a polyhydroxyalkylfuroic ester structure.

The origin of the overcharge in the 5 V region observed in lithium-substituted LiM x Mn 2Ϫx O 4ϩ␦ spinels (M ϭ Cr, Ni, Cu; x Ϸ 0.2) prepared at 500°C was analyzed by using accurate analytical spectroscopic techniques ͑mass spectroscopy, nuclear magnetic resonance͒ to examine the electrolyte behavior. The spectra revealed organic solvents to be stable as no decomposition products were detected, thus excluding the electrolyte oxidation as a side reaction accounting for the cell overcharge. However, these spinels contain excess oxygen in an amount that was quantified from thermogravimetric data. The excess oxygen plays a prominent role in the electrochemical response of the spinel. The cyclic voltammetry and galvanostatic results support the assumption that the excess oxygen can be released above 4.5 V. The additional capacity obtained and that required to release the oxygen were quite consistent. This must be the origin of both the overcharge and the poor performance of the cells compared with spinels of similar composition but synthesized at higher temperatures ͑800°C͒, the excess of oxygen in which was smaller. The ability of some Li-Mn based spinels to exhibit high-voltage plateaus at about 5 V has opened up new prospects for lithium batteries such as the possibility of manufacturing high-voltage batteries capable of supplying highly specific energy.1 LiM to Mn 5ϩ or Mn 6ϩ hypothesized for the undoped spinel has not yet been confirmed. Two alternative side reactions can be considered: ͑i͒ electrolyte oxidation above 4.6 V and (ii) a redox process undergone by the oxygen lattice of the spinel framework involving release of oxygen. This latter model can be related with theoretical computations based on either first-principles calculations 10 or the DV-X␣ molecular orbital model.11 Based on such models, when M is substituted by Mn ions, a new O 2p band at a low energy is responsible for the high electrochemical cell voltage observed. Simultaneously, evolved oxygen may oxidize organic solvents. These unwanted side reactions can lead to a premature cell capacity loss. Three recent reports 12-14 have insisted on the origin of the electrochemical activity above 4.5 V. Thus, Wang et al. 12 claim that the high voltage capacity of Li 1ϩx Mn 2Ϫx O 4Ϯz originates from the extraction of Li ϩ at 16d sites, whereas Shin and Manthiram 13,14 ascribe it to the involvement of O 2Ϫ -2p in the redox process. The aim of this work was to help clarify the processes taking place in the high-potential region of 5 V in cation-substituted lithium manganese spinels. For this purpose, Cr-, Ni-, and Cusubstituted spinels containing the doping elements in various oxidation states and prepared at two different temperatures ͑500 and 800°C͒ were examined. The electrolyte decomposition was analyzed using mass spectrometry ͑MS͒ and nuclear magnetic resonance ͑NMR͒ measurements. These measurements, together with thermogravimetric ͑TG͒ data, confirmed the central role played by the excess oxygen ion in the spinel lattice. ExperimentalThree series ...

Site-specific solvation has been determined by intermolecular NOE measurements between solvent and solute. The experimental effect is shown on the four compounds 2-butanol, L-alanyl-L-tryptophan (Ala-Trp), adenosine and the disodium salt of adenosine 5'-monophosphate (5'-AMP) in the two solvents water and dimethyl sulfoxide (DMSO). The strength of NOE transfer correlates with the average distribution of solvent molecules around the corresponding solvation sites represented by the number of solvent molecules in a first solvation sphere, which can be obtained from molecular dynamics simulations in water. Saturation transfer between exchanging protons explains some deviations from this correlation. The NOE transfer measurements provide information on specific solute-solvent interactions and contribute to a better understanding of solvation phenomena. On the basis of a distinct relationship between steric solvation hindrance and the strength of NOE transfer, the application of such measurements for conformational analysis has been demonstrated for the first time.