Electrode reduction mechanism of aromatic nitriles in aprotic solvents: Benzonitrile

The electrode reaction mechanism of benzonitrile in anhydrous DMF has been studied by polarography, potential sweep voltammetry, macroscale electrolysis, e.p.r. spectrometry and kinetic analysis. The relatively stable radical anion formed by one-electron addition decays according to a first order kinetic law, with formation of benzene and CN^? as final products together with substantial amounts of the alkene and alkylamine corresponding to the tetraalkylammonium salt used as background electrolyte. The results are interpreted in terms of a mechanism involving protonation of the anion radical by the solvent and the back-ground electrolyte, followed by dismutation of the resulting neutral radical with the anion radical and elimination of CN^? ions from the anionic species thus formed. By phenol addition CN^? elimination is prevented and the reduction proceeds to 1-cyclohexene-1-nitrile or to cyclohexane-nitrile, depending on the reduction potential.     

The structures of europium(III)- and uranium(IV) derivatives of [P5w3oo110]15-: Evidence for “cryptohydration”

The crystal structures of (Nh₄)_11.5K_0.5[ Eu(OH₂)P₅W₃₀O₁₁₀] ·24 H₂O, K₅H₅ [Eu(OH₂)P₅W₃₀O₁₁₀] ·31 H₂O, and (NH₄)₁₁[U(OH₂)P₅Wn₃₀O₁₁₀ ·12 H₂O have been determined. In each case, the anion has the overall virtual C_5v symmetry previously observed for the sodium derivative, [NaP₅W_{30 110}]14- The encrypted Eu³⁺ and U⁴⁺cations lie on the C₅ axis, but are displaced further than the Na⁺ from the equatorial plane defined by the five phosphorus atoms. Only minor differences are observed between the structures of the two salts of the europium derivative, although solutions of these display³¹P NMR spectra with chemical shifts differing by 10 ppm, provisionally attributed to the effects of protonation of the anion, The most significant feature of the three new structures is the presence of a water molecule within the central cavity and coor-dinated to the Eu³⁺ or U⁴⁺ cation.The coordination spheres of the central cations can therefore be described as monocapped pentagonal antiprisms.     

Quantification of theophylline in human plasma by reversed-phase ion-interaction high-performance liquid chromatography and comparison with the TDx fluorescence polarization immunoassay procedure.

A new method for the determination of theophylline (1,3-dimethyl-1H-purine-2,6-dione) in human plasma is described, free from interference by theobromine (3,7-dimethyl-1H-purine-2,6-dione) and caffeine (1,3,7-trimethyl-1H-purine-2,6-dione). The method makes use of ion-interaction reversed-phase high-performance liquid chromatography (octylamine-orthophosphate being the interaction reagent and a C18 reversed-phase column the stationary phase) with spectrophotometric detection at 274 nm. The quantitative results obtained in the analysis of samples of plasma from patients undergoing treatment with theophylline were compared with those obtained for the same samples with the TDx fluorescence polarization immunoassay procedure (using the Abbot Therapeutic Drug Monitoring system), which is generally employed in hospitals and clinical laboratories. Statistical F-test and t-test for multiple samples were applied to the data obtained by the two methods. The results showed no significant difference between the two methods at the 95% confidence level.     

Synthesis of N-1 and ribose modified inosine analogues on solid support

Herein, we report the synthesis and the use of new N-1-dinitrophenyl-inosine based solid supports, in which the C-2 of the purine base is strongly activated toward the attack of N-nucleophiles. The synthesized supports, binding the nucleoside by a 5′-O-monomethoxytrityl function, have been used to accomplish the synthesis of a small library of N-1 alkylated inosine and AICAR derivatives. In addition, cleavage of the 2′-3′ ribose bond of N-1 alkylated inosine derivatives anchored to the supports allowed to prepare a new set of N-1 alkylated-2′,3′-secoinosine derivatives in high yields.     

Sulfate determination in lagoon water (venice) by reversed-phase ion-interaction chromatography — a method validation

The validation of a new ion-interaction chromatographic method for sulfate determination is presented by the comparison with results obtained by ionchromatography. The two procedures were employed to quantify sulfate in model solutions and in samples of Venice lagoon water. The statistical t-test for multiple samples showed no significant difference between the two methods, at the 99% confidence level.     

Ab initio evaluation of the thermodynamic and electrochemical properties of alkyl halides and radicals and their mechanistic implications for atom transfer radical polymerization

High-level ab initio molecular orbital calculations are used to study the thermodynamics and electrochemistry relevant to the mechanism of atom transfer radical polymerization (ATRP). Homolytic bond dissociation energies (BDEs) and standard reduction potentials (SRPs) are reported for a series of alkyl halides (R-X; R = CH 2CN, CH(CH 3)CN, C(CH 3) 2CN, CH 2COOC 2H 5, CH(CH 3)COOCH 3, C(CH 3) 2COOCH 3, C(CH 3) 2COOC 2H 5, CH 2Ph, CH(CH 3)Ph, CH(CH 3)Cl, CH(CH 3)OCOCH 3, CH(Ph)COOCH 3, SO 2Ph, Ph; X = Cl, Br, I) both in the gas phase and in two common organic solvents, acetonitrile and dimethylformamide. The SRPs of the corresponding alkyl radicals, R (*), are also examined. The computational results are in a very good agreement with the experimental data. For all alkyl halides examined, it is found that, in the solution phase, one-electron reduction results in the fragmentation of the R-X bond to the corresponding alkyl radical and halide anion; hence it may be concluded that a hypothetical outer-sphere electron transfer (OSET) in ATRP should occur via concerted dissociative electron transfer rather than a two-step process with radical anion intermediates. Both the homolytic and heterolytic reactions are favored by electron-withdrawing substituents and/or those that stabilize the product alkyl radical, which explains why monomers such as acrylonitrile and styrene require less active ATRP catalysts than vinyl chloride and vinyl acetate. The rate constant of the hypothetical OSET reaction between bromoacetonitrile and Cu (I)/TPMA complex was estimated using Marcus theory for the electron-transfer processes. The estimated rate constant k OSET = approximately 10 (-11) M (-1) s (-1) is significantly smaller than the experimentally measured activation rate constant ( k ISET = approximately 82 M (-1) s (-1) at 25 degrees C in acetonitrile) for the concerted atom transfer mechanism (inner-sphere electron transfer, ISET), implying that the ISET mechanism is preferred. For monomers bearing electron-withdrawing groups, the one-electron reduction of the propagating alkyl radical to the carbanion is thermodynamically and kinetically favored over the one-electron reduction of the corresponding alkyl halide unless the monomer bears strong radical-stabilizing groups. Thus, for monomers such as acrylates, catalysts favoring ISET over OSET are required in order to avoid chain-breaking side reactions.     

Multistate Aggregation-Induced Chiroptical Properties of Enantiopure Disulfide-Mediated Bispyrene Macrocycles

A chiral bispyrene macrocycle designed for exclusive intermolecular excimer fluorescence upon aggregation was synthesized by a double hydrothiolation of a bis-enol ether macrocycle followed by intramolecular oxidation of free thiols. Unusually high stereoselectivity was achieved for the thiol-ene additions under templated conditions and Et₃B/O₂ radical initiation. After enantiomer separation (chiral stationary phase HPLC), aqueous conditions provoked aggregation. Detailed structural evolution was afforded by ECD/CPL monitoring. Three regimes can be observed and characterized by strong modifications in chiroptical patterns under, at, or above a 70 % H₂O : THF threshold. In luminescence, high g_lum dissymmetry factors values were obtained, up to 0.022, as well as a double sign inversion of CPL signals during the aggregation, a behavior rationalized by time-dependent density functional theory (TDDFT) calculations. Langmuir layers of enantiopure disulfide macrocycles were formed at the air–water interface and transferred onto solid substrates to afford Langmuir–Blodgett films, which were then studied by AFM and UV/ECD/fluorescence/CPL.     

Magnetic Circularly Polarized Luminescence of Organic Compounds

Achiral purely organic molecules can show selectivity towards circularly polarized light in emission in the presence of a magnetic field. This phenomenon is called magnetic circularly polarized luminescence (MCPL). Recently a few examples of MCPL from organic molecules have appeared in the literature. Through this technique, interesting photophysical information can be inferred and, moreover, a few technological applications can be devised based on this principle. This short review has the purpose to give a general introduction to this recent field of research and some critical insights on the reported examples.     

Short‐Range Interactions in Na Coadsorption with CO and O on Ni(111)

The coadsorption of Na with CO and O on Ni(111) is studied by high‐resolution electron energy loss spectroscopy. Experimental evidence for a very short‐range interaction between Na and coadsorbates is reported, in contrast with recent theoretical predictions overestimating nonlocal alkali‐induced effects. Loss spectra show distinct features, as a consequence of different local [CO]:[Na] and [O]:[Na] stoichiometries.