1,721,099 research outputs found
Characterization of gas phase aggregates of bis(2-ethylhexyl)-sulfosuccinate (AOT) and divalent metal ions: elimination of radical species in the decomposition pathways of even-electron [AOTMIICl2]– anions
No full textStructure and properties of even-electron anionic species formed by bis(2-ethylhexyl)sulfosuccinate (AOT) and divalent metal ions (MII) with stoichiometry [AOTMIICl2] have been investigated by using electrospray ionization and different mass spectrometry techniques, such as high resolution, accurate mass measurements, collision-induced dissociation (CID) multiple-stage mass spectrometry. Owing to CID, eliminations of neutrals, mainly consisting in hydrochloric acid, 2-ethyl-1-hexene and 2-ethylhexanol, and an unexpected loss of an alkyl radical have been observed. The radical anions [C4HO6SMIICl] so produced have been characterized by MS3 experiments. Density functional theory calculations have been carried out for investigating structure and stability of the ionic species formed in the decomposition pathways. Copyright (c) 2012 John Wiley & Sons, Ltd
Surfactant Self-Assembling in the Gas Phase: Bis(2-ethylhexyl)sulfosuccinate-Divalent Metal Ion Anionic Aggregates
No full textRATIONALE Investigation of fundamental aspects driving surfactant self-assembling and of the capability of including guest molecules or ions in their micellar aggregates is an exciting research field for theoretical and technological reasons. In this light, assembling and chelating properties of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) towards divalent metal ion chlorides have been investigated in the gas phase by electrospray ionization mass spectrometry in negative ion mode, tandem mass spectrometry and energy-resolved mass spectrometry. METHODS Water/methanol solutions of AOTNa and chloride salts of nickel, magnesium, calcium and manganese, with different AOTNa/metal salt ratios, were infused into the electrospray source of a LCQ DECA ion trap mass spectrometer, operating in negative ion mode, at a flow rate of 5 mu L/min. Low energy collision-induced dissociations were carried out by using helium with collision energy in the range 15?eV. RESULTS A variety of negatively singly charged monometallated and mixed metal aggregates have been observed, some of which were able to incorporate the metal counter ion of the inorganic salt used. The stability of these aggregates was evaluated by energy-resolved mass spectrometry which showed, for the anions [AOTMIICl2], a stability order Ca?>?Mn?>?Mg?>?Ni. Their decomposition pathways show the unusual formation of the radical anions [C4HO6SMIICl]. CONCLUSIONS This study shed some light on the assembling and chelating properties of AOT towards divalent metal ions to form negatively charged assemblies, some of them incorporating the metal counter ion of the inorganic salt used. Differently from what was observed with positively charged AOT-MII aggregates, solvated species were not detectable. An exception to the even-electron rule was observed in the decomposition pathway of [AOTMIICl2]. Copyright (c) 2012 John Wiley & Sons, Ltd
Study of Confined 5-Aza[5]helicene in Ytterbium(III) Bis(2-ethylhexyl) Sulfosuccinate Reversed Micelles
No full textSome relevant physicochemical properties of 5-aza[5]helicene (H5) in solutions of ytterbium bis(2-ethylhexyl) sulfosuccinate (Yb(DEHSS)3) reversed micelles have been investigated by UV-vis-NIR, photoluminescence, and FT-IR techniques with the aim of emphasizing the role played by specific Yb(III)/H5 interactions and confinement effects as driving forces of its binding to reversed micelles, preferential solubilization site, and local photophysical properties. It has been found that the binding strength of 5-aza[5]helicene to reversed micelles, triggered by steric and orientational constrains as well as the water content, is mainly regulated by its interaction with the Yb(III) counterion. Moreover, when H5 is entrapped in Yb(DEHSS)3 reversed micelles, the combined action of this interaction and of confinement effects leads to marked changes of its photophysical properties with respect to those of H5 molecularly dispersed in apolar medium. The influence of the entrapment of finite amounts of H5 on the reversed micelle structure was investigated by SAXS. The analysis of experimental results brings to the hypothesis that H5 is preferentially solubilized and opportunely oriented in the micellar palisade layer and that its insertion causes an unidimensional growth of reversed micelles. From an analysis of WAXS spectra of H5/Yb(DEHSS)3 composites, obtained by complete evaporation of the volatile components of the H5/water/Yb(DEHSS)3/n-heptane solutions, it was ascertained that also on these systems H5 is dispersed molecularly or in a quite amorphous state in the surfactant liquid crystals without forming a separate crystalline nanophase
Confinement of Chiral Molecules in Reverse Micelles: FT-IR, polarimetric and VCD investigation on the state of dimethyl tartrate in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles dispersed in carbon tetrachloride
No full textThe state of d and l-dimethyl tartrate confined within dry sodium bis(2-ethylhexyl) sulfosuccinate
(AOT) reverse micelles dispersed in CCl4 has been investigated by FT-IR spectroscopy, polarimetry, and
vibrational circular dichroism (VCD). Measurements have been performed at 25 ◦C as a function of the
solubilizate-to-surfactant molar ratio (R) at a fixed AOT concentration (0.158 M). The analysis of experimental
data is consistent with the hypothesis that both enantiomers of dimethyl tartrate are mainly
entrapped in the reverse micelles and located in proximity to the surfactant head-group region. The
formation of this interesting self-organized chiral nanostructure involves some changes of the typical
H-bonding of dimethyl tartrates in the pure solid state or as monomers dispersed in CCl4 attributable to
the establishment of specific solubilizate/surfactant head-group interactions and confinement effects
Do electrospray mass spectra of surfactants mirror their aggregation state in solution?
No full textOne important feature in the gas phase chemistry of surfactants is to ascertain whether their aggregates produced by electrospray
ionization reflect those formed in the starting solution. With this aim, we have performed ESI-MS, ESI-MS/MS and
ER-MS spectra of bis(2-ethylhexyl)sulfosuccinate (AOTNa) solutions in different solvents, i.e. water, water/methanol,
methanol and n-hexane. The results clearly indicate that, notwithstanding the strongly different aggregation state in solution
(direct micelles in water and in water/methanol, molecular dispersion in methanol and reverse micelles in n-hexane) and
marked effects of the solvent polarity on the total ionic current, the surfactant aggregates in gas phase show identical
structural features. Analogous conclusions can be drawn analyzing the infrared multiple photon dissociation (IRMPD) spectra
of AOTNa solutions in water/methanol and n-hexane. Moreover, according to the idea that gas phase can be considered an
apolar environment par excellence, data consistently suggest a reverse micelle-like aggregation. Some peculiarities of the
mechanisms leading to aggregate formation through electrospray ionization of surfactant solutions in solvent media with
different polarity have been also discussed
Analysis of melatonin interaction with receptioral models of biological interest: alfa, beta and gamma-cyclodextrins
No full textMolecular dynamics of electrosprayed water nanodroplets containing sodium bis(2-ethylhexyl)sulfosuccinate
No full textThe behavior of aqueous solutions of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) subject to electrospray ionization (ESI) has been investigated by molecular dynamics (MD) simulations at three temperatures (350, 500 and 800 K). We consider several types of water nanodroplets containing AOTNa molecules and composed of a fixed number of water molecules (1000), N0AOT AOT− anions (N0AOT = 0, 5, 10) and N0Na sodium ions (N0Na = 0, 5, 10, 15, 20): in a short time scale (less than 1 ns), the AOTNa molecules, initially forming direct micelles in the interior of the water nanodroplets, are observed in all cases to diffuse nearby the nanodroplet surface, so that the hydrophilic heads and sodium ions become surrounded by water molecules, whereas the alkyl chains lay at the droplet surface. Meanwhile, evaporation of water molecules and of solvated sodium ions occurs, leading to a decrease of the droplet size and charge. At 350 K, no ejection of neutral or charged surfactant molecules is observed, whereas at 500 K, some fragmentation occurs, and at 800 K, this event becomes more frequent. The interplay of all these processes, which depend on the values of temperature, N0AOT and N0Na eventually leads to anhydrous charged surfactant aggregates with prevalence of monocharged ones, in agreement with experimental results of ESI mass spectrometry. The quantitative analysis of the MD trajectories allows to evidence molecular details potentially useful in designing future ESI experimental conditions
Sodium bis-(2-ethylhexyl) sulfosuccinate sepf-aggregation in vacuo: Molecular Dynamics simulation
No full textMolecular dynamics (MD) simulations were conducted for systems in vacuo consisting of n AOT
anions (bis(2-ethylhexyl)sulfosuccinate ions) and n 1 or n Na+ ions up to n = 20. For n = 15,
positively charged systems with Li+, K+, and Cs+ cations were also considered. All systems were
observed to form reverse micelle-like aggregates whose centre is occupied by cations and polar
heads in a very compact solid-like way, while globally the aggregate has the form of an elongated
and rather flat ellipsoid. Various types of statistical analyses were carried out on the systems to
enlighten structural and dynamical properties including gyration radius, atomic pair correlation
functions, atomic B-factor and moment of inertia tensor. For completeness and comparison the
stability of reverse micelle is tested in the case of neutral n = 20 system in CCl4 solution
Electrospray ion mobility mass spectrometry of positively charged sodium bis(2-ethylhexyl)sulfosuccinate aggregates.
No full textCollision cross-sections (CCS) of positively singly and multiply charged aggregates of the surfactant sodium bis(2-ethythexyl)sulfosuccinate (AOTNa) in the gas phase have been measured by quadrupole ion mobility time-of-flight mass spectrometry. Calibration of the observed drift times to the CCS of the AOTNa non-covalent aggregates was achieved by collecting, under the same experimental conditions, the drift times of a range of singly and multiply charged polyalanine peptides whose CCS had been obtained by conventional ion mobility spectrometry. Together with an obvious increase of the aggregate cross-section with the aggregation number, it was found that the aggregate cross-section increases with the charge state due to the sodium counterions steric effect and the augmented electrostatic repulsion. This finding is consistent with the result of a previous molecular dynamics study on positively charged AOTNa aggregates in the gas phase showing that, by increasing the charge state, the aggregates become progressively more oblate; implying a rise of their CCS. Moreover, the occurrence at each aggregation number and extra charge of a unique value of cross section points toward aggregates whose conformations do not show discernible shape change in the experiment time scale
Triggering Dissymmetry in Achiral Dye Molecules by Chiral Solvents: Circular Dichroism Experiments and DFT Calculations
No full textThe electronic circular dichroism spectra of achiral product ‘‘Lumogen F Red’’
(ROT-300) in four different chiral solvents are recorded at different temperatures. DFT calculations
allow to identify two enantiomeric conformers for ROT-300. In vacuo they are equally
populated; in chiral solvents one enantiomer prevails. Thermodynamic quantities involved in
the chiral preference are derived
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