Molecular Engineering of MnII Diamine Diketonate Precursors for the Vapor Deposition of Manganese Oxide Nanostructures.

Molecular engineering of manganese(II) diamine diketonate precursors is a key issue for their use in the vapor deposition of manganese oxide materials. Herein, two closely related ß-diketonate diamine MnII adducts with different fluorine contents in the diketonate ligands are examined. The target compounds were synthesized by a simple procedure and, for the first time, thoroughly characterized by a joint experimental-theoretical approach, to understand the influence of the ligand on their structures, electronic properties, thermal behavior, and reactivity. The target compounds are monomeric and exhibit a pseudo-octahedral coordination of the MnII centers, with differences in their structure and fragmentation processes related to the ligand nature. Both complexes can be readily vaporized without premature side decompositions, a favorable feature for their use as precursors for chemical vapor deposition (CVD) or atomic layer deposition applications. Preliminary CVD experiments at moderate growth temperatures enabled the fabrication of high-purity, single-phase Mn3 O4 nanosystems with tailored morphology, which hold great promise for various technological applications.

A lipophilic ionic liquid based on formamidinium cations and TFSI: the electric response and the effect of CO2 on the conductivity mechanism.

This work describes the preparation of the new lipophilic ionic liquid tetraoctyl-formamidinium bis(trifluoromethanesulfonyl) imide (TOFATFSI), which is miscible with lower alkanes. In particular, this work focuses on the electric behaviour of TOFATFSI in the particularly challenging highly apolar environment of supercritical CO2. The conductivity and relaxation phenomena are revealed through the analysis of the broadband electric spectra with a particular emphasis on the effect of temperature and CO2 uptake on the IL conductivity. It is found that temperature boosts the conductivity via an increase in the charge carrier mobility. Also, CO2 absorption affects both the conductivity and the permittivity of the material due to the presence of CO2-IL interactions that modulate the nanostructure and the size of the TOFATFSI aggregates, which increases both the mobility and the density of the charge carriers.

Nanocomposite membranes based on polybenzimidazole and ZrO2 for high-temperature proton exchange membrane fuel cells.

Owing to the numerous benefits obtained when operating proton exchange membrane fuel cells at elevated temperature (>100 °C), the development of thermally stable proton exchange membranes that demonstrate conductivity under anhydrous conditions remains a significant goal for fuel cell technology. This paper presents composite membranes consisting of poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI4N) impregnated with a ZrO2 nanofiller of varying content (ranging from 0 to 22 wt %). The structure-property relationships of the acid-doped and undoped composite membranes have been studied using thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, wide-angle X-ray scattering, infrared spectroscopy, and broadband electrical spectroscopy. Results indicate that the level of nanofiller has a significant effect on the membrane properties. From 0 to 8 wt %, the acid uptake as well as the thermal and mechanical properties of the membrane increase. As the nanofiller level is increased from 8 to 22 wt % the opposite effect is observed. At 185 °C, the ionic conductivity of [PBI4N(ZrO2 )0.231 ](H3 PO4 )13 is found to be 1.04×10(-1)  S cm(-1) . This renders membranes of this type promising candidates for use in high-temperature proton exchange membrane fuel cells.

Effect of SiO2 on the dynamics of proton conducting [Nafion/(SiO2)X] composite membranes: a solid-state 19F NMR study.

Composite membranes, consisting of Nafion and inorganic oxide additives, are frequently discussed alternative materials to overcome the known low conductivity of pure Nafion at temperatures above 100 °C and at low relative humidity. It has been reported that under dry conditions, these membranes show enhanced water uptake and diffusion as compared to filler-free Nafion. This work focuses on the polymer mobility in Nafion/SiO(2) composites and on the impact of the silica particles on the polymer dynamics. [Nafion/(SiO(2))(X)] composite membranes (with X ranging from 0 to 15 wt%) in the dry and wet states were investigated by variable temperature solid-state (19)F NMR spectroscopy. (19)F T(1) and T(1ρ) relaxation times, and NMR lineshapes (linewidths and spinning sideband intensities) were analyzed to get information about the polymer mobility. It is found that Nafion composite membranes, in general, possess a higher mobility as compared to recast Nafion which is in agreement with previous results from conductivity studies. These findings are attributed to the ability of the SiO(2) particles to keep more water inside the composite membranes which also leads to a higher mobility of the polymer component. The results are further supported by the experimental (19)F{(1)H} CP/MAS NMR spectra. It is also shown that the structure of the composite membranes is more stable after dehydration, and possible condensation reactions are diminished in these membranes. In addition, the decrease in ionic exchange capacity after dehydration is less pronounced for the composite membranes as compared to filler-free Nafion.

Vibrational studies and properties of hybrid inorganic-organic proton conducting membranes based on Nafion and hafnium oxide nanoparticles.

In this report, we will describe the effect of different concentrations of HfO2 nanopowders on the structure and properties of [Nafion/(HfO2)n] membranes with n = 0, 3, 5, 9, 11, 13, and 15 wt %, respectively. Films were prepared by a solvent casting procedure using HfO2 oxoclusters and Nafion. Seven new homogeneous membranes were obtained with thicknesses ranging from 200 to 350 microm. Each membrane is characterized by a rough HfO2-rich surface and a smooth Nafion-rich surface, with different physical-chemical properties. Membrane characterization was accomplished by means of thermogravimetric analysis (TGA), morphological measurements (environmental scanning electron microscopy) and vibrational spectroscopy (Fourier transform infrared attenuated total reflectance spectroscopy and Fourier transform Raman spectroscopy). These systems can be described in terms of five types of water domains, Nafion-HfO2 species with well-defined stoichiometry surrounded by Nafion and hydrated hafnia. The highest conductivity at 125 degrees C (3.2 x 10-2 S x cm(-1)) was measured on the [Nafion/(HfO2)5] film by electrical spectroscopy, with a stability range of conductivity between 5 and 115 degrees C.

Effect of SiO2 on relaxation phenomena and mechanism of ion conductivity of [Nafion/(SiO2)x] composite membranes.

This report describes a study of the effect of SiO2 nanopowders on the mechanism of ionic motion and interactions taking place in hybrid inorganic-organic membranes based on Nafion. Five nanocomposite membranes of the formula [Nafion/(SiO2)x] with SiO2 ranging from 0 to 15 wt % were prepared by a solvent casting procedure. TG measurements demonstrated that the membranes are thermally stable up to 170 degrees C but with the loss water it changes the cluster environments and changes the conductivity properties. MDSC investigations in the 90-300 degrees C temperature range revealed the presence of three intense overlapping endothermal peaks indicated as I, II, and III. Peak I measures the order-disorder molecular rearrangement in hydrophilic polar clusters, II corresponds to the endothermic decomposition of -SO3 groups, and III describes the melting process in microcrystalline regions of hydrophobic fluorocarbon domains of the Nafion moiety. ESEM with EDAX measurements revealed that the membranes are homogeneous materials with smooth surfaces. DMA studies allowed us to measure two relaxation modes. The mechanical relaxation detected at ca. 100 degrees C is attributed to the motion of cluster aggregates of side chains and is diagnostic for R-SO3H...SiO2 nanocluster interactions. DMA disclosed that at SiO2/-SO3H (psi) molar ratios lower than 1.9, the oxoclusters act to restrict chain mobility of hydrophobic domains of Nafion and the dynamics inside polar cages of [Nafion/(SiO2)x] systems; at psi higher than 1.9, the oxoclusters reduce the cohesiveness of hydrophilic polar domains owing to a reduction in the density of cross-links. FT-IR and FT-Raman studies of the [Nafion/(SiO2)x] membranes indicated that the fluorocarbon chains of Nafion hydrophobic domains assume the typical helical conformation structure with a D(14pi/15) symmetry. These analyses revealed four different species of water domains embedded inside polar cages and their interconnecting channels: (a) bulk water [(H2O)n]; (b) water solvating the oxonium ions directly interacting with sulfonic acid groups [H3O+...SO3(-)-].(H2O)n; (c) water aggregates associated with H3O+ ions [H3O+.(H2O)n]; and (d) low associated water species in dimer form [(H2O)2]. The conductivity mechanism and relaxation events were investigated by broadband dielectric spectroscopy (BDS). [Nafion/(SiO2)x] nanocomposite membranes were found to possess two different molecular relaxation phenomena which are associated with the alpha-relaxation mode of PTFE-like fluorocarbon domains and the beta-relaxation mode of acid side groups of the Nafion component. Owing to their strong coupling, both these relaxation modes are diagnostic for the interactions between the polar groups of the Nafion host polymer and the (SiO2)x oxoclusters and play a determining role in the conductivity mechanism of the membranes. The studies support the proposal that long-range proton charge transfer in [Nafion/(SiO2)x] composites takes place due to a mechanism involving exchange of the proton between the four water domains. This latter proton transfer occurs owing to a subsequent combination of domain intersections resulting from the water domain fluctuations induced by the molecular relaxation events of host Nafion polymer.

Effect of peptide ligand dipole moments on the redox potentials of Au38 and Au140 nanoparticles.

Phenylethanethiolate monolayer-protected Au38 and Au140 nanoclusters were modified by ligand place exchange with a series of thiolated peptides. The peptides were homooligomers based on the alpha-aminoisobutyiric acid unit. The effects of changing the peptide concentration and the peptide length in the capping monolayer were studied by differential pulse voltammetry. The results showed that the redox behavior of the nanoparticles can be affected very significantly by such modifications. For example, the first oxidation peak of Au38, a cluster displaying molecule-like behavior, could be shifted positively by as much as 0.7-0.8 V. Detectable redox shifts were noted even when one single oriented peptide was in the Au140 monolayer. These effects were attributed to the molecular dipole moments of the peptide ligands.

Gel-type polyacrylic resins cross-linked with trimethylolpropanetrimethacrylate: the issue of their nanostructure and molecular accessibility unveiled with a combination of inverse steric exclusion chromatography (ISEC), and ESR and CP-MAS 13C NMR spectroscopy.

Six gel-type functional resins, that is, three poly-DMAA-co-TMPTP (DMAA = N,N-dimethylacrylamide, TMPTP = trimethylolpropyltrimethacrylate) samples with different degrees of cross-linking (0.6, 1.2, 1.7 % mol) and three poly-DMAA-co-MA-co-TMPTP (MA = methacrylic acid, ca. 5.5 % mol) samples with 1.7, 3.5, and 7 % mol cross-linking were investigated with ISEC (inverse steric exclusion chromatography), and ESR and CP-MAS (cross polarization magic angle spinning) 13C NMR spectroscopy after swelling in water and other solvents. This unprecedented combination of conceptually independent physicochemical techniques provides a thorough overall consistent picture of the morphology of the resins on the nanometer scale and of the molecular accessibility of the swollen polymer framework to the paramagnetic probe TEMPONE (2,2,6,6-tetramethyl-4-oxo-1-oxypiperidine) and to selected solvents.

A new external EI/CI source-ion trap system devoted to the study of ion-molecule reactions.

A new instrumental arrangement dedicated to the study of ion-molecule reactions and consists of by an electron impact/chemical ionization source mounted 420 mm away from an ion trap is described. It has been designed and developed to exclude diffusion into the ion trap of the neutral reactants from the EI/CI source and so to avoid undesired side-reactions. Its instrumental parameterization is described and some preliminary results are illustrated that show promise for the successful application of the system to the study of ion-molecule reactions.

Low-calcium diet in hypercalciuric enuretic children restores AQP2 excretion and improves clinical symptoms.

In this study, we analyzed the effect of a therapeutic intervention in 46 enuretic children, 26 (57%) of whom were hypercalciuric. All the patients (n = 46) were treated with DDAVP for 3-6 mo. The hypercalciuric patients (n = 26) received a low-calcium diet (approximately 500 mg/day) for the same period. After the therapy, the bed-wetting episodes stopped in 80% of the 46 patients tested. In those patients having low-AVP levels before the therapy, circulating AVP concentration returned to normal (>4 pg/ml), and the hypercalciuria was resolved in the hypercalciuric patients (calcium/creatinine ratio <0.2). Urinary aquaporin-2 (AQP2) levels were semiquantified by densitometric scanning and reported as a ratio between the intensity of the signal in the day vs. the night urine samples (day/night AQP2 ratio). In the hypercalciuric patients, the day/night AQP2 ratio returned to values close to those found in the healthy children (from 1.19 +/- 0.20 before to 0.69 +/- 0.10 after the treatment, n = 26, P = 0.03). In contrast, in the normocalciuric children we saw no significant modulation of AQP2 excretion (from 1.07 +/- 0.14 before to 0.99 +/- 0.14 after the treatment, n = 20). This study clearly demonstrates that urinary calcium levels modulate AQP2 excretion and is likely to be useful for treatment of children with enuresis.

Urinary aquaporin 2 and calciuria correlate with the severity of enuresis in children.

This study examined the hypothesis that nocturnal enuresis might be paralleled by aquaporin 2 (AQP2) urinary excretion. Eighty children who experienced nocturnal enuresis were studied and compared with 9 healthy children. The 24-h urine samples were divided into two portions: night collections and day collections. Creatinine equivalents of urine samples from each patient were analyzed by Western blotting. AQP2 levels were semiquantified by densitometric scanning and reported as a ratio between the intensity of the signal in the day urine sample versus the night urine sample (D/N AQP2 ratio). The D/N AQP2 ratio was 0.59 +/- 0.11 (n = 9) in healthy children and increased to 1.27 +/- 0.24 (n = 10) in a subpopulation of enuretic children who had low nocturnal vasopressin levels. In enuretic children who displayed hypercalciuria and had normal vasopressin levels, the D/N AQP2 ratio was 1.05 +/- 0.27 (n = 8). These data indicate that reduced secretion of vasopressin and absorptive hypercalciuria are independently associated with an approximately twofold increase in the urinary D/N AQP2 ratio. When low nocturnal vasopressin levels were associated with hypercalciuria, a nearly threefold increase in the D/N AQP2 ratio was observed (1. 67 +/- 0.41, n = 11). In addition, in all enuretic patients tested, the urinary D/N AQP2 ratio correlates perfectly with the severity of the disorder (nocturnal polyuria). The findings reported in this article indicate that urinary AQP2 correlates with the severity of enuresis in children.