Straightforward synthesis of gold nanoparticles by adding water to an engineered small dendrimer.

A small water-soluble phosphorus-containing dendrimer was engineered for the complexation of gold(I) and for its reduction under mild conditions. Gold nanoparticles were obtained as colloidal suspensions simply and only when the powdered form of this dendrimer was dissolved in water, as shown by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) analyses. The dendrimers acted simultaneously as mild reducers and as nanoreactors, favoring the self-assembly of gold atoms and promoting the growth and stabilization of isolated gold nanoparticles. Thus, an unprecedented method for the synthesis of colloidal suspensions of water-soluble gold nanoparticles was proposed in this work.

Tunable Redox Potential, Optical Properties, and Enhanced Stability of Modified Ferrocene-Based Complexes.

We report a series of ferrocene-based derivatives and their corresponding oxidized forms in which the introduction of simple electron donating groups like methyl or tert-butyl units on cyclopentadienyl-rings afford great tunability of Fe+III/Fe+II redox potentials from +0.403 V down to -0.096 V versus saturated calomel electrode. The spin forbidden d-d transitions of ferrocene derivatives shift slightly toward the blue region with an increasing number of electron-donating groups on the cyclopentadienyl-rings with very little change in absorptivity values, whereas the ligand-to-metal transitions of the corresponding ferricinium salts move significantly to the near-IR region. The electron-donating groups also contribute in the strengthening of electron density of Fe+III d-orbitals, which therefore improves the chemical stability against the oxygen reaction. Further, density functional theory calculations show a reducing trend in outer shell reorganization energy with an increasing number of the electron donating units.

Cholesteryl and diosgenyl glycosteroids: synthesis and characterization of new smectic liquid crystals.

While present in large numbers in nature, studies on the physical chemical aspects of glycosteroids are quite rare and focused on cholesterol, and all compounds studied thus far have shown liquid crystalline properties in a narrow temperature range. New glycosteroids composed by cholesterol or diosgenin and different glycosidic moieties have been synthesized here in order to analyze the influence of the structure on the formation of mesophases. These compounds have been studied by crossed polarized optical microscopy. These studies have revealed that these new glycosteroids form Smetic A liquid crystals in a broad temperature range.

The formation mechanism of fluorescent metal complexes at the Li(x)Ni(0.5)Mn(1.5)O(4-δ)/carbonate ester electrolyte interface.

Electrochemical oxidation of carbonate esters at the Li(x)Ni(0.5)Mn(1.5)O(4-δ)/electrolyte interface results in Ni/Mn dissolution and surface film formation, which negatively affect the electrochemical performance of Li-ion batteries. Ex situ X-ray absorption (XRF/XANES), Raman, and fluorescence spectroscopy, along with imaging of Li(x)Ni(0.5)Mn(1.5)O(4-δ) positive and graphite negative electrodes from tested Li-ion batteries, reveal the formation of a variety of Mn(II/III) and Ni(II) complexes with ß-diketonate ligands. These metal complexes, which are generated upon anodic oxidation of ethyl and diethyl carbonates at Li(x)Ni(0.5)Mn(1.5)O(4-δ), form a surface film that partially dissolves in the electrolyte. The dissolved Mn(III) complexes are reduced to their Mn(II) analogues, which are incorporated into the solid electrolyte interphase surface layer at the graphite negative electrode. This work elucidates possible reaction pathways and evaluates their implications for Li(+) transport kinetics in Li-ion batteries.

Influence of alkyl chain length on the mesomorphism of 5-S-alkyl-5-thiopentonolactones and 5-S-alkyl-5-thiopentitols.

Mesomorphic properties of S-alkylthiopentonolactones (d-ribono, d-arabinono and d-xylono) and corresponding alditol derivatives with the general formula Su-SR (R=CnH2n+1; n=5-12) are studied. It was shown that the thermotropic and lyotropic phase transition temperatures are influenced by the following structural parameters: alkyl chain length, cyclic or acyclic Su structure and alditol conformation. Besides, it seems that n parity affects thermotropic phase transition temperatures.

Voltage gain in lithiated enolate-based organic cathode materials by isomeric effect.

Li-ion batteries (LIBs) appear nowadays as flagship technology able to power an increasing range of applications starting from small portable electronic devices to advanced electric vehicles. Over the past two decades, the discoveries of new metal-based host structures, together with substantial technical developments, have considerably improved their electrochemical performance, particularly in terms of energy density. To further promote electrochemical storage systems while limiting the demand on metal-based raw materials, a possible parallel research to inorganic-based batteries consists in developing efficient and low-polluting organic electrode materials. For a long time, this class of redox-active materials has been disregarded mainly due to stability issues but, in recent years, progress has been made demonstrating that organics undeniably exhibit considerable assets. On the basis of our ongoing research aiming at elaborating lithiated organic cathode materials, we report herein on a chemical approach that takes advantage of the positive potential shift when switching from para to ortho-position in the dihydroxyterephthaloyl system. In practice, dilithium (2,3-dilithium-oxy)-terephthalate compound (Li4C8H2O6) was first produced through an eco-friendly synthesis scheme based on CO2 sequestration, then characterized, and finally tested electrochemically as lithiated cathode material vs. Li. This new organic salt shows promising electrochemical performance, notably fast kinetics, good cycling stability and above all an average operating potential of 2.85 V vs. Li(+)/Li(0) (i.e., +300 mV in comparison with its para-regioisomer), verifying the relevance of the followed strategy.

High-potential reversible Li deintercalation in a substituted tetrahydroxy-p-benzoquinone dilithium salt: an experimental and theoretical study.

Efficient organic Li-ion batteries require air-stable lithiated organic structures that can reversibly deintercalate Li at sufficiently high potentials. To date, most of the cathode materials reported in the literature are typically synthesized in their fully oxidized form, which restricts the operating potential of such materials and requires use of an anode material in its lithiated state. Reduced forms of quinonic structures could represent examples of lithiated organic-based cathodes that can deintercalate Li(+) at potentials higher than 3 V thanks to substituent effects. Having previously recognized the unique electrochemical properties of the C(6)O(6)-type ring, we have now designed and then elaborated, through a simple three-step method, lithiated 3,6-dihydroxy-2,5-dimethoxy-p-benzoquinone, a new redox amphoteric system derived from the tetralithium salt of tetrahydroxy-p-benzoquinone. Electrochemical investigations revealed that such an air-stable salt can reversibly deintercalate one Li(+) ion on charging with a practical capacity of about 100 mAh g(-1) at about 3 V, albeit with a polarization effect. Better capacity retention was obtained by simply adding an adsorbing additive. A tetrahydrated form of the studied salt was also characterized by XRD and first-principles calculations. Various levels of theory were probed, including DFT with classical functionals (LDA, GGA, PBEsol, revPBE) and models for dispersion corrections to DFT. One of the modified dispersion-corrected DFT schemes, related to a rescaling of both van der Waals radii and s(6) parameter, provides significant improvements to the description of this kind of crystal over other treatments. We then applied this optimized approach to the screening of hypothetical frameworks for the delithiated phases and to search for the anhydrous structure.