125 research outputs found
Self-assembly in surfactant-based mixtures driven by acidâbase reactions: bis(2-ethylhexyl) phosphoric acidâ n-octylamine systems
Structural and dynamic features of bis(2-ethylhexyl) phosphoric acid (HDEHP)ân-octylamine (NOA)
mixtures as a function of the NOA mole fraction (XNOA) have been investigated by SAXS, WAXS, IR,
dielectric spectroscopy and polarized optical microscopy. In the 0 ÂĄ XNOA , 0.5 range, mixtures are
transparent liquids, while the abrupt formation of a waxy solid characterized by an hexagonal
bidimensional structure occurs at XNOA = 0.5. Such a composition-induced phase transition results from
the synergetic effect of the progressive increase in number density of ordered HDEHPâNOA nanodomains
with XNOA. Mainly driven by an HDEHP to NOA proton transfer, the increase of structural order with XNOA
arises from the progressive substitution of loosely hydrogen bonded HDEHPâHDEHP aggregates with
strongly bonded NOAâHDEHP ones. Analysis of SAXS patterns at temperatures in the 10â70 uC range
emphasized that these local structures are scarcely impacted by an increase of thermal fluctuations. Effects
due to the steric compatibility between HDEHP and NOA apolar moieties have been highlighted. Overall,
the results allow us to emphasize the role of specific polar and apolar interactions joined to steric effects in
regulating the molecular organization in surfactant mixtures and can be used to design novel materials
with planned physico-chemical properties
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]â anions
Structure and properties of even-electron anionic species formed by bis(2-ethylhexyl)sulfosuccinate (AOT) and divalentmetal ions
(MII) with stoichiometry [AOTMIICl2]â 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]ââą 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
Dibutyl phosphate/propylamine mixtures show supra-molecular slow building up under magnetic field
Liquids with anisotropic local nanostructures which are able to be oriented by a magnetic field can give birefringence. Usually magnetically-induced birefringence is low owing to the low magnetic energy of molecules and to the averaging effect due to thermal agitation. At the same time, the response is usually very fast given the typical timescales of molecular orientational dynamics (nanoseconds). However, we show that the dibutyl phosphate/propylamine liquid mixture is characterized by an extremely slow response (hours) to the magnetic field and by an intense overall effect (În/λ â â0.1m-1at 1 Tesla).This surprising behavior has been interpreted as a manifestation of a novel phenomenon of progressive building up of larger and larger internally ordered hetero-associates driven by the magnetic field and involving strongly interacting amphiphiles
Degrees of freedom effect on fragmentation in tandem mass spectrometry of singly charged supramolecular aggregates of sodium sulfonates
The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged non-covalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine-enkephalin. Positively and negatively charged aggregates behave similarly, but the slope of the CCE vs DoF plot is steeper for positive ions, suggesting that these are more stable than their negative counterparts
The interaction of native DNA with Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene orto-phenylendiimine
The interaction of native calf thymus DNA with the Zn(II) and Cu(II) complexes of 5-triethyl ammonium methyl salicylidene ortophenylendiimine (ZnL2+ and CuL2+), in 1 mM Tris-HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectro photometry, circular dichroism (CD) and fluorescence spectroscopy. The results support for an intercalative interaction of both ZnL2+ and CuL2+ with DNA, showing CuL2+ an affinity of approximately 10 times higher than ZnL2+. In particular, the values of the binding constant, determined by UV spectrophotometric titration, equal to 7.3 x 10(4) and 1.3 x 10(6) M-1. for ZnL2+ and CuL2+, respectively, indicate the occurrence of a marked interaction with a binding size of about 0.7 in base pairs. The temperature dependence of the absorbance at 258 nm suggests that both complexes strongly increase the DNA melting temperature (Tm) already at metal complex-DNA molar ratios equal to 0.1. As evidenced by the quenching of the fluorescence of ethidium bromide-DNA solutions in the presence of increasing amounts of metal complex, ZnL2+ and CuL2+ are able to displace the ethidium cation intercalated into DNA. A tight ZnL2+-DNA and CuL2+-DNA binding has been also proven by the appearance, in both metal complex-DNA solutions, of a broad induced CD band in the range 350-450 nm. In the case of the CuL2+-DNA system, the shape of the CD spectrum, at high CuL2+ content, is similar to that observed for psi-DNA solutions. Such result allowed us to hypothesize that CuL2+ induces the formation of supramolecular aggregates of DNA in aqueous solutions
Molecular dynamics of electrosprayed water nanodroplets containing sodium bis(2-ethylhexyl)sulfosuccinate
The 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), N0
AOT AOT anions (N0
AOT = 0, 5, 10) and N0
Na sodium ions (N0
Na = 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, N0
AOT and N0
Na 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 theMD trajectories allows to evidencemolecular details potentially useful in designing
future ESI experimental conditions
Inclusion complexes of cyclomaltooligosaccharides (cyclodextrins) with melatonin in solid phase
Fourier transform infrared spectrometry (FT-IR) and X-Ray diffraction (XRD) investigations were carried out on MLT plus α-, ÎČ- and Îł-CD physical mixtures and lyophilized or crystalline MLT/α-, ÎČ-, Îł-CD complexes. Inclusion complexes formation between MLT and cyclodextrins in solid phase has been emphasized by the significant differences between IR and XRD spectra of physical mixtures with respect to those of the complexes. The structure of MLT CDs complexes in the solid state as well as the biochemical and pharmaceutical implications are discussed
Effects of the net charge on abundance and stability of supramolecular surfactant aggregates in gas phase
Self-assembling of amphiphilic molecules under electrospray ionization (ESI) conditions is characterized by quite unexpected phenomenology. The noticeable differences with respect to the condensed phase are attributable to the absence of the surfactant-solvent interactions, the presence of net charge in the aggregates, and the strong deviation from equilibrium conditions. Aiming to investigate the effects of the net charge on abundance and stability of supramolecular surfactant aggregates, positively and negatively charged aggregates of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium methane sulfonate (MetS), butane sulfonate (ButS) and octane sulfonate (OctS) have been studied by ESI mass spectrometry, energy resolved mass spectrometry and density functional theory calculations. The negatively charged aggregates are found to be less stable than their positive counterparts. The results are consistent with a self-assembling pattern dominated by electrostatic interactions involving the counterions and head groups of the investigated amphiphilic compounds while the alkyl chains point outwards, protecting the aggregates from unlimited growth processes
1H-NMR and FT-IR study of the state of melatonin confined in membrane models: location and interactions of melatonin in water free lecithin and AOT reversed micelles
The state of melatonin confined either in dry lecithin or bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) reversed micelles has been investigated by H-1-NMR and FT-IR spectroscopies as a function of the melatonin to surfactant molar ratio (R). The analysis of experimental results leads to hypothesize that, independently of R and the surfactant nature and as a consequence of anisotropic melatonin/surfactant interactions, melatonin is totally solubilized in reversed micelles and mainly located by opportune orientation in the nanodomain constituted by the surfactant head groups. The absence of significant spectral changes related to the protons linked to the first carbon atoms of surfactant alkyl chain, indicates a scarce insertion of melatonin into the so-called micellar palisade layer. The possible biological implications of the peculiar solubilization state of melatonin in reversed micelles are discussed
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