Expanded Pyridiniums: Bis‐cyclization of Branched Pyridiniums into Their Fused Polycyclic and Positively Charged Derivatives—Assessing the Impact of Pericondensation on Structural,Electrochemical, Electronic,and Photophysical Features

This study evaluates the impact of the extension of the π‐conjugated system of pyridiniums on their various properties. The molecular scaffold of aryl‐substituted expanded pyridiniums (referred to as branched species) can be photochemically bis‐cyclized into the corresponding fused polycyclic derivatives (referred to as pericondensed species). The representative 1,2,4,6‐tetraphenylpyridinium ( 1^H ) and 1,2,3,5,6‐pentaphenyl‐4‐(p‐tolyl)pyridinium ( 2^Me ) tetra‐ and hexa‐branched pyridiniums are herein compared with their corresponding pericondensed derivatives, the fully fused 9‐phenylbenzo[1,2]quinolizino[3,4,5,6‐def]phenanthridinium ( 1^H f ) and the hitherto unknown hemifused 9‐methyl‐1,2,3‐triphenylbenzo[h]phenanthro[9,10,1‐def]isoquinolinium ( 2^Me f ). Combined solid‐state X‐ray crystallography and solution NMR experiments showed that stacking interactions are barely efficient when the pericondensed pyridiniums are not appropriately substituted. The electrochemical study revealed that the first reduction process of all the expanded pyridiniums occurs at around ?1 V vs. SCE, which indicates that the lowest unoccupied molecular orbital (LUMO) remains essentially localized on the pyridinium core regardless of pericondensation. In contrast, the electronic and photophysical properties are significantly affected on going from branched to pericondensed pyridiniums. Typically, the number of absorption bands increases with extended activity towards the visible region (down to ca. 450 nm in MeCN), whereas emission quantum yields are increased by three orders of magnitude (at ca. 0.25 on average). A relationship is established between the observed differential impact of the pericondensation and the importance of the localized LUMO on the properties considered: predominant for the first reduction process compared with secondary for the optical and photophysical properties.     

Structure and electrical properties of single-phase cobalt manganese oxide spinels Mn3−xCoxO4 sintered classically and by spark plasma sintering (SPS)

Cobalt manganese oxide spinels Mn_3−xCo_xO₄ (with 0.98?x?3) were prepared by the thermal decomposition in air of oxalate precursors. The influence of the thermal treatments on the structure of these materials is emphasized. Single-phase ceramics were obtained after optimization of the sintering parameters. A precise phase diagram for the Co-Mn-O system is proposed according to thermal stability and structure of oxide powders. The electrical measurements on single-phase ceramics show that low values of resistivity can be achieved. The conduction could take place through jumps of polarons between Mn³⁺ and Mn⁴⁺ on octahedral sites. These compounds present interesting electrical characteristics for negative temperature coefficient (NTC) thermistor applications.     

Calix[4]arenes as Molecular Platforms for Magnetic Resonance Imaging (MRI) Contrast Agents

The novel amphipilic conjugate of a calix[4]arene with four Gd–1,4,7,10‐ tetra(carboxymethyl)‐1,4,7,10‐tetraazacyclododecane (DOTA) chelates has potential as a magnetic resonance imaging contrast agent, both in its monomeric and in its micellar form. The system, illustrated here with its nuclear magnetic relaxation profile, shows good relaxivities, thanks to its high rigidity.

     

Bis(tetraphenylphosphonium) (hexasulfido‐2κ2S1,S6)di‐μ‐sulfido‐disulfido‐1κ2S‐tungsten(VI)zinc(II) acetone solvate

The title complex, (C₂₄H₂₀P)₂[WZnS₄(S₆)]·C₃H₆O or (Ph₄P)₂[WS₂(μ‐S)₂{Zn(S₆)}]·Me₂CO, was unexpectedly obtained on attempted recrystallization of a mixed tungten–zinc complex of a tris(pyrazolato)borate ligand. The two metal centres of the anion have distorted tetrahedral coordination and the two tetrahedra share one S...S edge; tungsten is additionally coordinated by two terminal sulfide ligands and zinc by a chelating S₆²⁻ ligand, which has one central S—S bond significantly longer than the other four, a pattern found to be consistent for this ligand. This is the first reported example of a tetrahedral zinc centre bridging an edge of a single tetrathiotungstate(VI) or tetrathiomolybdate(VI) anion, although there are many previous examples with other metals.     

Design of metal oxide nanoparticles: Control of size,shape, crystalline structure and functionalization by aqueous chemistry

The aim of this paper is to show that a very simple but well controlled chemistry in an aqueous medium allows one to efficiently control the main characteristics of oxide nanoparticles. Examples concerning titania, alumina, iron and manganese oxides are discussed to illustrate various effects on the control of size, shape and structure of nanoparticles. Some examples of functionalization of these particles are also illustrated. Experimental data, procedures and detailed references can be found in the cited literature.     

Electrochemical approach to detect the presence of peroxynitrite in aerobic neutral solution

This work describes the conditions of use of bare gold electrode to detect electrochemically the presence of peroxynitrite ONOO^? in phosphate buffer solution at pH 7.1. As ONOO^? is extremely unstable in neutral solution, current–potential curve was reconstructed between ?0.5 and 0.7 V vs SCE by amperometry experiments at rotating disk electrode at different potentials. Comparison of this reconstructed curve with voltammograms of the common interfering species (dopamine, hydrogen peroxide, nitrite, ascorbic acid and glutamate) shows that the presence of ONOO^? can be selectively determined at ?0.1 V vs SCE. This detection occurs through the electrochemical reduction of peroxynitrous acid ONOOH, the conjugated acid of ONOO^?. Detection of ONOO^? produced in situ by the reaction of nitric oxide with superoxide was also achieved.     

Octupolar Derivatives Functionalized with Superacceptor Peripheral Groups: Synthesis and Evaluation of the Electron‐Withdrawing Ability of Potent Unusual Groups

Novel tripodal derivatives with a triphenylamine core and that bear “superacidifiers” (i.e., fluorinated sulfoximinyl blocks) or novel sulfiliminyl moieties as peripheral groups were synthesized. These new chromophores show strong absorption in the near‐UV region and emission in the visible region. The fluorinated sulfoximinyl moieties were found to behave as potent auxochromic and electron‐withdrawing (EW) groups, thus leading to redshifted absorption and emission. These moieties promote a core‐to‐periphery intramolecular charge transfer (ctp‐ICT) transition, the energy of which was found to be correlated to their EW strength. In this study, we provide evidence of a linear correlation between the Hammett constant (σ_p) values and the electronic gap between the ground and first excited state of the three‐branched derivatives. This in turn was used to derive σ_p values of fluorinated sulfoximinyl moieties. These EWGs show unprecedentedly high σ_p values, up to 1.45 relative to 0.8 for NO₂. Also, by using this method, the sulfiliminyl moiety was shown to exhibit similar EW strength as NO₂, while promoting improved transparency and solubility. Finally, the superior EW strength of the fluorinated sulfoximine peripheral moieties was shown to induce significant enhancement of the two‐photon absorption responses in the red near‐IR region of the three‐branched derivatives relative to similar octupoles that bear more usual strong EW groups. These characteristics (improved nonlinear responses or transparency) open new routes for the design of nonlinear optical (NLO) chromophores for optical limiting or electro‐optical modulation. Such building blocks could also be of interest for optoelectronic applications, including the development of solar cells.     

Electrochemical Characterization of Stainless Steel as a New Electrode Material in a Medical Device for the Diagnosis of Sudomotor Dysfunction

An electrochemical sensor detects the risk of diabetes and prediabetes; low potentials are applied to nickel electrodes and electrical responses are measured. Although the contact of nickel with skin is short, the risk of allergical reactions cannot be discarded. SS 304L, with lower Ni content, was tested in carbonate buffer solutions containing chloride, lactate and urea to investigate its sensitivity to different parameters in sweat and compare it to nickel. The results show that SS 304L is a suitable material for the assessment of sudomotor dysfunction due to its high capacity to detect the deviation in Cl^? concentration. Sensitivity of SS 304L to Cl^? is much higher than for nickel.     

Asymmetric base-mediated epoxide isomerisation

The base-mediated rearrangement of epoxides into allylic alcohols is a well-known synthetic transformation. The first enantioselective version of the reaction using a chiral base was reported in 1980. Since then, the reaction has received a lot of attention mostly due to the great usefulness of chiral allylic alcohols in organic synthesis. Major breakthroughs in the area were the first report on using a sub-stoichiometric amount of chiral base, and the development of chiral bases for a true catalytic reaction protocol. The present review covers the time from when the first asymmetric epoxide isomerisation reaction was reported (1980) up to now, focusing on the period 1997-2001.