M. Freda

Transmittance Fourier Transform Infrared Spectra of Liquid Water in the Whole Mid-Infrared Region: Temperature Dependence and Structural Analysis:

Transmittance Fourier transform infrared (FT-IR) spectra of liquid water in the 4–80 °C temperature range are reported in the whole mid-infrared (MIR) region (4000–360 cm−1). The spectra were recorded by using a newly developed, home-made transmittance cell, working in light vacuum conditions (pressures of the order of 3–4 millibar). This permits the elimination of the aqueous vapor bands from the liquid spectra, particularly in the bending region, and the rapid collection of data without fluxing large amounts of nitrogen through the interferometer sample chamber. The temperature evolution of the OH stretching and HOH deformation bands is discussed in terms of Gaussian components analysis and a two-state model describing the equilibrium between different H-bond structures of liquid water. From this picture, structural and thermodynamic information about the hydrogen-bonding network of water is obtained.

Hydration and dynamics of Aerosol OT reverse micelles

Abstract We report results of a detailed dielectric, IR and elastic neutron scattering study of bis(2-ethylhexyl)sulfosuccinate (AOT) based micellar systems in CCl4 as a function of the molar ratio W=[H2O]/[AOT]. The aim is to explore the connection between hydration and dynamical properties of the reverse AOT micelles. We restricted our analysis to the region of small amounts of water added (0

Infrared and dielectric spectroscopy study of the water perturbation induced by two small organic solutes

Abstract This work concerns a comparison of the hydration properties of two simple molecules of biological relevance: trimethyl-amine- N -oxide (TMAO) and tert -butyl alcohol (TBA). These molecules are geometrically very similar, having the same hydrophobic moiety and different polar groups. Both molecules have been used as a model to study hydrophobic behaviour in water solutions. In the present work, dielectric relaxation of water/TBA and water/TMAO mixtures have been studied at a cosolvent mole fraction, x 2 =0.02. Water perturbation induced by TBA and TMAO molecules has been studied also at x 2 =0.02 and 0.05 by using the absorption bands due to the vibrational modes of water in the infrared region. The data show, in agreement with molecular dynamics simulation results, that TMAO and TBA interaction with water are remarkably different and that water molecules are more tightly coordinated by TMAO than by TBA.

Hydrophobic hydration and hydrophobic interaction in aqueous solutions of tert-butyl alcohol and trimethylamine-N-oxide: a correlation with the effect of these two solutes on the micellization process

We report the study of the effect of tert-butyl alcohol (TBA) and trimethylamine-N-oxide (TMAO) on a typical process governed by the hydrophobic interaction, such as the micellization of a surfactant in aqueous solution. The behaviour of the critical micelle concentration (c.m.c.) of the sodium dodecyl sulfate (SDS) was investigated as a function of the added amounts of TBA or TMAO by conductivity measurements. The hydration properties of the two solutes was studied by IR spectroscopy, in the region of the frequency of the O–H stretching band for H2O and of the methylic band for TBA and TMAO. The overall behaviour of the TBA/H2O and TMAO/H2O solutions is also studied by compressibility measurements. The data were discussed in terms of the hydration properties of TBA and TMAO and of the thermodynamical properties of the mixtures. Significant correlations between these properties and the effect of TBA and TMAO on the micellization process are shown.

Influence of hydration on dynamical properties of reverse micelles

Abstract We performed dielectric measurements on sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles in CCl4 as a function of the molar ratio W=[D2O]/[AOT], for a small amount of deuterated water (0.2

Hydration and dynamics of bis(2-ethylhexyl)sulfosuccinate microemulsions: effect of change in counterion

We report results of a detailed dielectric and IR study of bis(2-ethylhexyl)sulfosuccinate based micellar systems in CCl4, where the Na+ counterion of the surfactant was replaced by the divalent cations Ca2+, Cu2+ and Mg2+. In all these micellar systems a relaxation phenomenon was found, whose behaviour strongly depends on the degree of hydration of the micellar aggregate. This relaxation process reflects complex intrinsic dynamics of the reverse micelles, which can be activated above a threshold in the degree of hydration of the same aggregates. The connection between hydration and dynamical properties of the reverse micelles can be considered to be a possible model to explain more complex biological phenomena, for example, the starting of protein functionality above a defined degree of hydration.