CARBOXYLATION OF FORMIC ACID IN AQUEOUS SOLUTIONS UNDER THE INFLUENCE OF U.V.-LIGHT

Abstract— Carboxylation of various organic substances by dissolved carbon dioxide or bicarbonate is achieved by the action of U.V. -Light of 184.9 and 253.1 mμ on water. The transformation of formic acid to oxalic acid was investigated in more detail as a function of u.v.-dose, pH-values and the formate concentration. For an irradiation period of 12 hr of 0.1 M formate, a yield of about 2 m mol.1^--¹ oxalic acid was obtained. A reaction mechanism for the photochemical carboxylation process is presented. The results are of some interest in respect of the synthesis of organic compounds under the primitive earth conditions.     

Structure, magnetism and optical properties of achiral and chiral two-dimensional oxalate-bridged anionic networks with symmetric and asymmetric ammonium cations

A series of two-dimensional (2D) oxalate-based compounds, namely [N(n-C4H9)4][M(II)Cr(III)(ox)3] (M(II) = Mn, Fe; ox = C2O4(2-)) and [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][M(II)M(III)(ox)(3)] ((M(II), M(III)) =(Mn, Cr), (Fe, Cr), (Mn, Fe)) were synthesised starting from racemic tris(oxalato)metalate: rac-[M(III)(ox)3]3- (M(III) = Cr, Fe). For Cr(III), the synthesis has been undertaken starting from resolved (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. The natural circular dichroism measurements assess the enantioselectivity of the synthesis. X-Ray powder diffraction analysis has revealed that, when racemic reagents are used to synthesise Mn(II) containing compounds, a R3c achiral space group is found. In contrast a P6(3) chiral space group is found when starting from (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. Surprisingly, whatever the optical purity of the starting building block, all Fe(II) containing compounds crystallise in the P6(3) chiral space group. The magnetic properties of the synthesised compounds confirm that these compounds are ferromagnets for M(III)= Cr. For M(II)= Mn, Theta ranges between 9 and 11 K and T(c) equals 6 K. For M(II)= Fe, Theta ranges between 14 and 16 K and Tc between 11 and 12 K. [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][Mn(II)Fe(III)(ox)3] is an antiferromagnet with Theta = - 107 K and T(N) = 29 K.     

Unequal-sphere packing model for simulation of the uniaxially compressed iodine adlayer on Au(111)

A simple unequal-sphere packing (USP) model, based on pure geometrical principles, was applied to study the centered-rectangular iodine c(px radical3)R30 degrees adlayer on the Au(111) surface, well-known from surface X-ray structure (SXS), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM) experiments. To reproduce the exact patterns observed in experiments, two selective conditions-minimum average adsorbate height and minimum adlayer roughness-were imposed. As a result, a series of adlayer patterns with c(px radical3)R30 degrees symmetry (2.3 < p < 3), with precise structural details, including atomic registry and identification of the p-bisector as the most likely trajectory for the iodine adatom movement during the so-called uniaxial compression phenomenon, were identified. In addition, using the same model, the difference between the iodine adlayer arranged in hexagonal and centered-rectangular c(px radical3)R30 degrees patterns, as in the case of Pt(111) and Au(111) surfaces, was investigated. Qualitative and quantitative comparison shows that iodine adatoms in these two arrangements differ significantly in atomic registry, distance from the substrate, and the adlayer corrugation. Our findings could be of special interest in the study of the nature of the iodine adatom bonding to different substrates (i.e., Au vs Pt).     

Absolute and relative emission cross sections for electron impact on CH3F,CH2F2 and CHF3

Emission spectra following electron impact on CH₃F, CH₂F₂ and CHF₃ at various energies have been investigated in the spectral region from 200 nm to 700 nm. Emission thresholds and excitation functions for atomic and molecular fragments have been determined. Absolute emission cross sections were obtained for two band systems, ^{A 2} Δ → X ² Π, C ² Σ⁺ → X ² Π, observed in the emission spectrum of CH₃F and for the H-Balmer radiation, H _α ? H _γ, in the spectra of all compounds. The continuous emission between 200 nm and 400 nm in the spectra of CH₂F₂ and CHF₃ has been examined systematically. It was found that CF₂(Ã) is the main precursor in both spectra.     

Mechanism of oxidation of 1-benzyl-1,4-dihydronicotinamide by the biologically active p-benzoquinone derivative, avarone, in a cationic micellar medium: An electrochemical approach

The electrochemical reduction of avarone (Q), an antitumor sesquiterpenoid quinone, was investigated at various pH in aqueous ethanol containing a cationic surfactant, cetyltrimethylammonium bromide (CTAB) by cyclic and rotating disc electrode voltammetry, using a glassy carbon electrode. Comparison of the electrochemical reduction of Q in presence of CTAB with the same process in a homogeneous water + ethanol solution shows an anodic shift of the reduction potential in the presence of CTAB; at pH > 9.5 and in presence of CTAB, two well-defined reduction peaks are observed, thus confirming one-electron reduction of Q, whereby the intermediate radical-anion is stabilized by the cationic micellar medium. The electrochemical oxidation of BNAH was investigated by cyclic voltammetry, and the anodic shift of the peak potential in presence of CTAB was observed. From the electrochemical behaviour of Q and BNAH, and the kinetics of the oxidation of BNAH with Q, it is suggested that the reaction takes place in two successive one-electron transfer steps. The application of the Marcus theory gives additional proof that, in this case, the first electron transfer is the rate determining step.     

The Synthesis of Novel Iodinated Iminodiacetic Acid Analogues as Hepatobiliary Imaging Agents

The synthesis and characterization of N-[2-[[4-iodo-2,6-bis(1-methylethyl)phenyl]amino]-2-oxoethyl]-N-(carboxymethyl)glycine and N-[2-[(4-iodo-2,6-diethylphenyl)amino]-2-oxoethyl]-N-(carboxymethyl)glycine is presented, as well as a modified and improved synthesis of N-[2-[(2,4-diiodo-6-methylphenyl)amino]-2-oxoethyl]-N-(carboxymethyl)glycine. These compounds are new agents for hepatobiliary imaging.     

Complexation of fluoride anion and its ion pairs with alkali metal cations by tetra-substituted lower rim calix[4]arene tryptophan derivative

Abstract

Selective binding of fluoride anion and its alkali metal cation ion pairs by a fluorescent calix[4]arene (L) derivative bearing tryptophan moieties was studied in acetonitrile at 25 °C. It was found that LF^? and LF₂^2? complexes were formed and their stability constants were determined by means of UV and ¹H NMR titrations. Both amide and indole NH groups were involved in the stabilisation of the fluoride complexes, i.e. L afforded two anion-binding sites. ¹H NMR titrations provided evidence of simultaneous complexation of both Na⁺ cation and fluoride anion resulting in the formation of a ternary NaLF complex. In this ion pair complex, the Na⁺ cation was most probably bound primarily by the calixarene ether and amide oxygen atoms, whereas the indole NH groups interacted with the fluoride ion. A highly favourable ion pairing between Na⁺ and F^– in acetonitrile was studied using potentiometric measurements. The results pointed out the importance of fluoride pairing with alkali metal cations in aprotic organic solvents and the necessity of taking these reactions into account in the course of speciation studies of such solutions.     

Measurement of surface potential at silver chloride aqueous interface with single-crystal AgCl electrode

The surface potential at the silver chloride aqueous interface was measured by means of a single-crystal silver chloride electrode (SCr-AgCl). The measurements were conducted by titration of the KCl solution with AgNO3, and vice versa. The SCr-AgCl electrode potentials were converted to surface potentials psi(0) by setting zero at the point of zero charge at pCl = 5.2. The psi(0)(pCl) function was linear, with a slope 12% lower with respect to the Nernst equation. It was demonstrated that the surface potential at the silver halide aqueous interface could be interpreted by means of the surface complexation model, originally developed for metal oxides.     

Double-quantum biased covariance spectroscopy: application to the 2D INADEQUATE experiment

A novel processing scheme is presented that converts a two-dimensional double-quantum NMR spectrum into a single-quantum correlation spectrum. The covariance-like spectrum is computed from the 2D Fourier transform spectrum by emphasizing contributions that fulfill the double-quantum condition resulting in a symmetric spectrum that is easier to analyze. The method is demonstrated for the 2D INADEQUATE experiment.