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The role of trivalent rare-earth dopants on the cerium oxidation state has been systematically studied by in situ photoemission spectroscopy with synchrotron radiation for 10 mol % rare-earth doped epitaxial ceria films. It was found that dopant rare-earths with smaller ionic radius foster the formation of Ce3+ by releasing the stress strength induced by the cation substitution. With a decrease of the dopant ionic radius from La3+ to Yb3+, the out-of-plane axis parameter of the crystal lattice decreases without introducing macroscopic defects. The high crystal quality of our films allowed us to comparatively study both the ionic conductivity and surface reactivity ruling out the influence of structural defects. The measured increase in the activation energy of films and their enhanced surface reactivity can be explained in terms of the dopant ionic radius effects on the Ce4+ -> Ce3+ reduction as a result of lattice relaxation. Such findings open new perspectives in designing ceria-based materials with tailored properties by choosing suitable cation substitution.

The phenyl–iron complex of 5,10,15-tritolylcorrole was prepared by reaction of the starting chloro–iron complex with phenylmagnesium bromide in dichloromethane. The organometallic complex was fully characterized by a combination of spectroscopic methods, X-ray crystallography, and density functional theory (DFT) calculations. All of these techniques support the description of the electronic structure of this phenyl–iron derivative as a low-spin iron(IV) coordinated to a closed-shell corrolate trianion and to a phenyl monoanion. Complete assignments of the 1H and 13C NMR spectra of the phenyl–iron derivative and the starting chloro–iron complex were performed on the basis of the NMR spectra of the regioselectively β-substituted bromo derivatives and the DFT calculations., The preparation of complex 1 fills a gap in the series of triarylcorrole iron derivatives. The spectroscopic and theoretical characterization of this complex indicates that it can be described as an Fe(IV) derivative, with a nonoxidized corrole species, acting as a trianionic ligand. However also in this case significant spin density is present on the corrole ring, as predicted by DFT calculations and confirmed by the 1H NMR isotropic shifts.

Nafion/Faujasite zeolite composite membranes have been prepared by solution casting at a zeolite content ranging from 0.98 to 21.4 wt %. The effect of the zeolite loading on the mobility of both liquid and vapor water through the Nafion membrane has been investigated by using two complementary techniques, that is, differential scanning calorimetry and dynamic vapor sorption. The relationship between water mobility, proton conductivity, and direct methanol fuel cell (DMFC) performance of composites is also discussed. The addition of zeolite contributes to the enhancement of the water mobility degree in the composite membrane due to both the surface composition of the additive and the introduction of porosity at the polymer/filler interface. Nafion/zeolite composites having higher proton conductivity and DMFC performance than bare Nafion can thus be fabricated by fine-tuning of the additive content and the membrane morphology.

Spider silk is a fascinating natural composite material. Its combination of strength and toughness is unrivalled in nature, and as a result, it has gained considerable interest from the medical, physics, and materials communities. Most of this attention has focused on the one to tens of nanometer scale: predominantly the primary (peptide sequences) and secondary (β sheets, helices, and amorphous domains) structure, with some insights into tertiary structure (the arrangement of these secondary structures) to describe the origins of the mechanical and biological performance. Starting with spider silk, and relating our findings to collagen fibrils, we describe toughening mechanisms at the hundreds of nanometer scale, namely, the fibril morphology and its consequences for mechanical behavior and the dissipation of energy. Under normal conditions, this morphology creates a nonslip fibril kinematics, restricting shearing between fibrils, yet allowing controlled local slipping under high shear stress, dissipating energy without bulk fracturing. This mechanism provides a relatively simple target for biomimicry and, thus, can potentially be used to increase fracture resistance in synthetic materials. © 2012 American Chemical Society.

Sulfonated poly(ether ether ketone) (SPEEK) membranes were thermally treated at temperatures between 120 and 160 degrees C. Water uptake measured at different relative humidity values or by full immersion in water between 25 and 145 degrees C was found to depend very strongly on previous thermal treatment and casting solvent. Water-uptake coefficient values as low as 10-15 even upon immersion in water at 100 degrees C were obtained with membranes treated at 160 degrees C. This effect is related to cross-linking by SO2 bridges between macromolecular chains. An important role is also played by the casting solvent: among the investigated solvents, dimethylsulfoxide (DMSO) gave the best results. A chemical kinetics model is outlined that permits the estimation of the relevant kinetic parameters, especially the activation energy of the cross-linking reaction, which was found to be about 60 kJ/mol. These results are of significant importance for the improvement of proton-exchange membrane fuel cells.

The reaction of meso-triarylcorroles with AgNO2 proceeds with concomitant metalation and peripheral substitution to give the corresponding nitro-substituted silverIII corrole complex. The substitution is highly regioselective, giving only the corresponding 3-nitro derivative, among the different possible isomers. The results obtained indicate that the reaction intermediate is the pi-cation radical of the complex, which is then attacked by nitrite ion. This was proven by the reaction of the copper corrole complexes with NaNO2: in this case, the nitration reaction proceeded without the addition of an oxidant, because of the pi-cation radical character of the copper complex. The reaction is also successful in the case of 2,3,17,18-tetraethyl-8,12-diacetoxymethyl-7,13-dimethylcorrole (AMCorH3), with the formation of the meso-substituted silver corrole derivative (NO2)3AMCorAg (fully characterized by X-ray crystallography), the first of its kind to be reported. Two of the corroles are characterized by cyclic voltammetry and spectroelectrochemistry in dichloromethane, and the site of electron transfer is elucidated.

The development of proton exchange membranes as electrolytes for polymer electrolyte fuel cells operating at intermediate temperatures has been achieved combining two approaches: the preparation of a cross-linked polymer and the formation of covalent organic/inorganic hybrids. A covalently crosslinked sulfonated polyetheretherketone with elevated degree of sulfonation (DS ) 0.8) was prepared by reaction with HSO3Cl (SOPEEK). No degradation of PEEK was detected upon sulfonation, but only cross-linking via sulfonic groups with formation of SO2 moieties was observed. The extent of ramification was calculated by analyzing the 1 H nuclear magnetic resonance (NMR) spectra of the products and resulted in 20% of the total amount of -SO3H groups present in the polymer. The solubility of the -SO2Cl precursor in organic solvents allowed easy carrying out of functionalization reactions in homogeneous conditions by lithiation and subsequent reaction with SiCl 4, thus introducing covalenly linked silicon moieties (SOSiPEEK) at the ratios 1:0.25 and 1:0.50 per monomeric unit. The products were characterized by 1 H and 13 C NMR, attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.

The proton NMR spectra of a variety of low-spin and high-spin ferric complexes of the naturally occurring chlorin derivative pyropheophorbide a methyl ester have been recorded and assigned. The complete assignments for the low-spin, dicyano complex were effected by a combination of partial isotope labeling, paramagnetic relaxation, multiplet structure, and nuclear Overhauser measurements in viscous solvent. The resulting contact shift pattern reflects I€ spin delocalization into both the highest filled MO equivalent to the porphyrin 3eI€(xz,yz), as well as into the former a1u orbital of the porphyrin. The saturation of a pyrrole ring to produce a chlorin is concluded to uniquely stabilize the orbital ground state of the iron, which allows the lone spin to I€ bond to the two unmodified trans-pyrroles. The pattern of contact shift asymmetry of the pyrroles adjacent to the saturated ring provides a potential model for interpreting NMR spectra of iron chlorin enzymes. Ferric pyropheophorbide a methyl ester yields a six-coordinate high-spin complex in dimethyl sulfoxide in both the presence and absence of chloride, indicating that high-spin ferric chlorins have a greater affinity for weak-field ligands than do analogous porphyrins. The ∼103 acceleration of the rate of macrocycle "inversion" of pyropheophorbide-iron chloride, as induced by associative halide exchange, supports a more flexible core for chlorins relative to porphyrins. © 1989 American Chemical Society.