Polarographic studies of complexes of cadmium with chloride and thiocyanate ions in aqueous medium

This is a polarographic study of the system Cd(II)?NaCl?NaSCN in aqueous medium of a constant ionic strength of μ=1.0 M with NaClO₄. Reduction takes place through a reversible bielectronic process. The diffusion magnitudes I_d and D have been determined, and the formation of the mixed complexes CdClSCN, [CdCl₂SCN]^? and [CdCl(SCN)₂]^?, with stability constants of β₁₁=106±101² mol^?2, β₂₁=156±101³ mol^?3 and β₁₂=484±801³ mol^?3, respectively, has been demonstrated. The values of these constants are discussed in the light of statistical aspects and Watters equations.     

Synthesis of 1,1'-binaphthyl-based enantiopure C(60) dimers

The first enantiomerically pure and soluble C(60) dimers have been synthesized from suitably functionalized 1,1'-binaphthyl derivatives by 1,3-dipolar cycloaddition of the respective in situ generated diazo compounds to C(60). These systems exhibit optical and electrochemical activity.     

New Concepts in Tetrathiafulvalene Chemistry

Tetrathiafulvalene (TTF) and its derivatives were originally prepared as strong electron-donor molecules for the development of electrically conducting materials. This Review emphasizes how TTF and its derivatives offer new and in some cases little-exploited possibilities at the molecular to the supramolecular levels, as well as in macromolecular aspects. TTF is a well-established molecule whose interest goes beyond the field of materials chemistry to be considered an important building block in supramolecular chemistry, crystal engineering, and in systems able to operate as machines. At the molecular level, TTF is a readily available molecule which displays a strong electron-donor ability. However, its use as a catalyst for radical-polar crossover reactions, thus mimicking samarium iodide chemistry, has only recently been addressed. Important goals have been achieved in the use of TTF at the macromolecular level where TTF-containing oligomers, polymers, and dendrimers have allowed the preparation of new materials that integrate the unique properties of TTF with the processability and stability that macromolecules display. The TTF molecule has also been successfully used in the construction of redox-active supramolecular systems. Thus, chemical sensors and redox-switchable ligands have been prepared from TTF while molecular shuttles and molecular switches have been prepared from TTF-containing rotaxanes and catenanes. A large synthetic effort has been devoted to the preparation of the so-called organic ferromagnets, many of which are derived from TTF. The main task in these systems is the introduction of ferromagnetic coupling between the conduction electrons and localized electrons. TTF has also played a prominent role in molecular electronics where TTF-containing D-sigma-A molecules have allowed the preparation of the first confirmed unimolecular rectifier. Recently, it has been confirmed that TTF can display efficient nonlinear optic (NLO) responses in the second and third harmonic generation as well as a good thermal stability. These findings can be combined with the redox ability of TTF as an external stimuli to provide a promising strategy for the molecular engineering of switchable NLO materials. Fullerenes endowed with TTF exhibit outstanding photophysical properties leading to charge-separated (CS) states that show remarkable lifetimes.     

Synthesis of photo- and electroactive stilbenoid dendrimers carrying dibutylamino peripheral groups

[structure: see text]. A novel convergent synthetic route for the preparation of functionalized and fluorescent stilbenoid dendrons built on the 1,3,5-benzene core and endowed with a periphery of dibutylamino groups has been developed. Long alkyl chains have been incorporated on the peripheral amino moieties to increase the solubility of the final products. Good donor ability of the new dendrimers has been observed by cyclic voltammetry measurements as a result of the presence of the peripheral dibutylaniline moieties.     

Detection in urine of efaproxiral (RSR13), a potential doping agent, by a routine screening procedure based on methylation followed by gas chromatography/mass spectrometry

Efaproxiral (also known as RSR13) is a synthetic allosteric modifier of hemoglobin. The ability to increase maximal muscle oxygen uptake makes RSR13 a potential performance-enhancing agent for athletes and, therefore, a new agent to be taken into account by the antidoping control laboratories. In this work, a new method for the detection of efaproxiral in urine by gas chromatography/mass spectrometry is described.     

Signal enhancement in laser diode thermal desorption‐triple quadrupole mass spectrometry analysis using microwell surface coatings

Laser‐diode thermal desorption (LDTD) is an ionization source usually coupled to triple quadrupole mass spectrometry (QqQMS) and specifically designed for laboratories requiring high‐throughput analysis. It has been observed that surface coatings on LDTD microwell plates can improve the sensitivity of the analysis of small polar molecules. The objective of the present study is to understand and quantify the effect of microwell surface coatings on signal intensity of small organic molecules of clinical, environmental, and forensic interest. Experiments showed that the peak areas of diclofenac, chloramphenicol, salicylic acid, and 11‐nor‐9‐carboxy‐Δ⁹‐tetrahydrocannabinol obtained by LDTD‐QqQMS increased by up to 3 orders of magnitude when using microwells coated with ethylenediaminetetraacetic acid (EDTA). Tests with different chelating agents and polytetrafluoroethylene as microwell surface coatings showed that nitrilotriacetic acid gave significantly higher peak areas for five out of the nine compounds that showed signal enhancement using chelating agents as coatings. Scanning electron microscopy studies of EDTA‐coated and uncoated microwells showed that analytes deposited in the former formed more uniform and thinner films than in the latter. The enhancement effect of surface coatings in LDTD‐QqQMS was explained mainly by the formation of homogenous and thinner layers of nanocrystals of analytes that are easier to desorb thermally than the layers formed when the analytes dry in direct contact with the bare stainless‐steel surface. Chemisorption of some analytes to the stainless‐steel surface of the microwell plate appeared to be a minor factor. Surface coatings widen the number of compounds analyzable by LDTD‐QqQMS and can also improve sensitivity and limits of detection.     

Investigation of impurity levels inn-type indium selenide by means of Hall effect and deep level transient spectroscopy

We report the results of Hall effect and deep-level-transient-spectroscopy measurements onn-type indium selenide samples cleaved from non-intentionally doped material and from chlorine, tin, gallium sulphide or oxygen doped ingots. Some unidentified shallow and deep levels are found. Impurity levels attributed to Cl (310 meV) and to Sn (44 and 120 meV) are also reported. Anomalous degeneracy of electrons at low temperature is discussed.     

Pressure-induced magnetic switching and linkage isomerism in K0.4Fe4[Cr(CN)6]2.8 x 16 H2O: X-ray absorption and magnetic circular dichroism studies

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% Cr(III)-N[triple bond]C-Fe(II) linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process.     

Identifying minimal and dominant solutions for Kummer recursions

We identify minimal and dominant solutions of three-term recurrence relations for the confluent hypergeometric functions and , where (not both equal to 0). The results are obtained by applying Perron's theorem, together with uniform asymptotic estimates derived by T. M. Dunster for Whittaker functions with large parameter values. The approximations are valid for complex values of , and , with .