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

The 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?

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The interaction of native calf thymus DNA with FeIII-dipyrido[3,2-a:2\u2019,3\u2019-c]phenazine

The mono and bis dipyrido[3,2-a:20,30-c]phenazine (dppz) adducts of iron(III) chloride, i.e. [Fe(dppz)]Cl3 and [Fe(dppz)2]Cl3, have been synthesized and characterized. The interaction of the FeIIIdppz hydrolyzed aquo complex with native calf thymus DNA has been monitored as a function of the metal complex\u2013DNA molar ratio, by variable temperature UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The results obtained in solution at various ionic strength values give support for a tight intercalative binding of the FeIIIdppz cation with DNA. In particular, the appearance of induced CD bands, caused by the addition of FeIIIdppz, indicate the existence of a rigid metal complex\u2013DNA-binding leading to dominating chiral organization of FeIIIdppz species within the DNA double helix. The trend of selected CD bands with the molar concentration of FeIIIdppz emphasizes that the presence of high amounts of metal complex induces also the formation of DNA\u2013FeIIIdppz supramolecular aggregates in solution. The analysis of fluorescence measurements allowed us to calculate a value of the intercalative binding constant comparable to that obtained by UV spectrophotometric titration. Finally, the temperature dependence of the absorbance at 258 nm shows that the metal complex strongly increases the DNA melting temperature already at metal complex\u2013DNA molar ratio equal to 0.25 suggesting that metal complex intercalation effectively hinders DNA denaturation. Overall, the results of the present study point out that the FeIIIdppz aquo complex has DNA-binding properties analogous to those previously reported for the tris-chelate FeII(phen)2dppz complex (phen = 1,10-phenantroline)

Sodium bis-(2-ethylhexyl) sulfosuccinate sepf-aggregation in vacuo: Molecular Dynamics simulation

Molecular 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

COUPLING ELECTROCHEMISTRY TO ELECTROSPRAY: A NOVEL PREPARATION OF GOLD NANOSTRUCTURES

nanoparticles on ITO (Indium tin oxide) coated glass using the electrospray (ESI) method Method:The starting point of this study is that the ESI/MS spectrum (Figure 1) of an ethanolic solution of HAuCl 4 shows a reduction process of Au (III) strongly dependent on the Cone Voltage (CV) values (20, 80, 150 V), affording to the ion at m/z 197 (Au+). Further, the decrease of the abundance of this ion at the highest cone voltage suggests the subsequent its reduction with the formation of Au 0 . Figure 1: ESI/MS spectra of an ethanolic solution of HAuCl4 at various cone voltages: Conclusion: Such experimental evidence leads us to use electrospray technique as a preparative tool to obtain the formation and deposition of gold nanoparticles in a single step. In fact, using a home-made electrospray apparatus, we sprayed an ethanolic solution of HAuCl4, forming a very thin aerosol that has been uniformly deposited on ITO coated glass. Then, the deposit by SEM, UV-Vis, Optical-Microscopy and XPS has been characterized4,5. In particular, SEM micrographs show rod-like structures, while XPS spectra show that the deposited nanoparticles contain about 23% of Au0

Surfactant self-assembling in the gas phase: bis(2-ethylhexyl)- sulfosuccinate divalent metal ion anionic aggregates

RATIONALE: 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 mL/min. Low energy collision-induced dissociations were carried out by using helium with collision energy in the range 1\u20135 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]\u2013, a stability order Ca> Mn>Mg>Ni. Their decomposition pathways show the unusual formation of the radical anions [C4HO6SMIICl]\u2013\u2022. CONCLUSIONS: This study shed some light on the assembling and chelating properties of AOT\u2013 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]\u2013

Self-assembly in surfactant-based liquid mixtures: Bis(2-ethylhexyl)phosphoric acid/bis(2- ethylhexyl)amine systems

Surfactant-based liquid mixtures constitute an interesting class of nanostructured materials with promising potential in specialized applications. Here, structural and conductometric properties of liquid mixtures composed of bis(2-ethylhexyl)amine (BEEA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) have been thoroughly investigated with the aim to correlate structural features with system charge transport capability. The evolution of self-assembled local nanostructures with system composition has been investigated by FT-IR and XRD while the conductometric properties were probed by conventional AC complex impedance. Both pure components exhibit nano-segregation due to their amphiphilic nature but with only very low proton conductivities. However their mixtures, characterized by local organization of polar and apolar domains driven by acid–base interactions between HDEHP PO4H and BEEA NH groups, show enhanced structural order and proton conductivity