Single-particle and collective excitations of polar water molecules confined in nano-pores within a cordierite crystal lattice.

Recently, the low-temperature phase of water molecules confined within nanocages formed by the crystalline lattice of water-containing cordierite crystals has been reported to comprise domains with ferroelectrically ordered dipoles within the a, b-planes which are antiferroelectrically alternating along the c-axis. In the present work, comprehensive broad-band dielectric spectroscopy is combined with specific heat studies and molecular dynamics and Monte Carlo simulations in order to investigate in more detail the collective modes and single-particle excitations of nanoconfined water molecules. From DFT-MD simulations we reconstruct the potential-energy landscape experienced by the H2O molecules. A rich set of anisotropic temperature-dependent excitations is observed in the terahertz frequency range. Their origin is associated with the complex rotational/translational vibrations of confined H2O molecules. A strongly temperature dependent relaxational excitation, observed at radio-microwave frequencies for the electric field parallel to the crystallographic a-axis, E||a is analyzed in detail. The temperature dependences of loss-peak frequency and dielectric strength of the excitation together with specific heat data confirm a ferroelectric order-disorder phase transition at T0 ≈ 3 K in the network of H2O dipoles. Additional dielectric data are also provided for polarization E||b, too. Overall, these combined experimental investigations enable detailed conclusions concerning the dynamics of the confined water molecules that develop within their microscopic energy landscapes.

Dielectric ordering of water molecules arranged in a dipolar lattice.

Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine H2O molecules in nanosized cages formed by ions of a dielectric crystal. Arranging them in channels at a distance of ~5 Å with an interchannel separation of ~10 Å prevents the formation of hydrogen networks while electric dipole-dipole interactions remain effective. Here, we present measurements of the temperature-dependent dielectric permittivity, pyrocurrent, electric polarization and specific heat that indicate an order-disorder ferroelectric phase transition at T0 ≈ 3 K in the water dipolar lattice. Ab initio molecular dynamics and classical Monte Carlo simulations reveal that at low temperatures the water molecules form ferroelectric domains in the ab-plane that order antiferroelectrically along the channel direction. This way we achieve the long-standing goal of arranging water molecules in polar order. This is not only of high relevance in various natural systems but might open an avenue towards future applications in biocompatible nanoelectronics.

Redox chemistry in the pigment eumelanin as a function of temperature using broadband dielectric spectroscopy.

Conductive biomolecular systems are investigated for their promise of new technologies. One biomolecular material that has garnered interest for device applications is eumelanin. Its unusual properties have led to its incorporation in a wide set of platforms including transistor devices and batteries. Much of eumelanin's conductive properties are due to a solid state redox comproportionation reaction. However, most of the work that has been done to demonstrate the role of the redox chemistry in eumelanin has been via control of eumelanin's hydration content with scant attention given to temperature dependent behavior. Here we demonstrate for the first time consistency between hydration and temperature effects for the comproportionation conductivity model utilizing dielectric spectroscopy, heat capacity measurements, frequency scaling phenomena and recognizing that activation energies in the range of ∼0.5 eV correspond to proton dissociation events. Our results demonstrate that biomolecular conductivity models should account for temperature and hydration effects coherently.

Systemic sclerosis in Argentina: evaluation of a large cohort from a single centre and comparison with other international series.

OBJECTIVES: Prevalence of systemic sclerosis (SSc) and different clinical subsets varies across the world. Few data have been published on SSc patients in Latin America. Our objective was to describe a SSc cohort in Argentina and to compare clinical findings, disease subsets and antibodies with other international SSc populations. METHODS: Patients with SSc (n=234) seen at the Rheumatology section of the Hospital Italiano de Buenos Aires between 2000-2011 were retrospectively analysed. Data on clinical manifestations, disease subsets and antibodies were obtained. Patients were classified into diffuse cutaneous (dc) and limited cutaneous (lc) subsets. Comparison with other cohorts (France, United States, Germany, Italy, Mexico, EUSTAR and Brazil) was made based on published information. RESULTS: A higher female:male ratio (12:1) and a higher limited subset prevalence (76.1%) was found in this Argentine cohort comparing with others. We also found a lower prevalence of diffuse disease, anti Scl-70 (antitopoisomerase) and nucleolar pattern antinuclear antibodies. Within each subset, clinical findings were similar with other SSc populations except for a very low prevalence in renal crisis (0.02% of dc SS). CONCLUSIONS: With slight variations perhaps due to genetic, environmental or referral factors, SSc in this cohort appears to be similar to that described in other parts of the world.