Transport of 125I−, 137Cs+ and 85Sr2+ in granitoidic rock and soil columns

Transport of ¹²⁵I^?, ¹³⁷Cs⁺ and ⁸⁵Sr²⁺ radionuclides in crushed granitoidic rocks and homogenized soils was studied. Two simple methods for calculation of breakthrough curves in flow column experiments with groundwater as transport medium have been described. The first method, so called non-linear approach, is derived on the assumption of a reversible non-linear sorption isotherm described with Freundlich equation, i.e., with non-constant distribution and retardation coefficients. The second method, so-called linear approach, is applied for reference only, and is based on the assumption of a reversible sorption characterized with linear sorption isotherm, i.e., with constant distribution and retardation coefficients. Both methods model the experimental breakthrough curves with the integrated form of the simple 1-D advection–dispersion equation (ADE) expressed analytically for pulse application of radiotracer to the liquid phase before entering the columns. The integrated form of the ADE equation was modified by the so-called peak position and peak height correction coefficients the advantage of which consists among others in the elimination of the influence of starting concentration. The comparison of both approaches has shown that fitting by means of non-linear approach has given rather reliable values of the transport parameters and calculated dependences, especially in a case of ¹³⁷Cs system characterized evidently with non-linear type of sorption isotherms. As for ¹²⁵I^?, the sorption capacity of all solid samples studied is nearly on the zero level and ¹²⁵I^? is practically not retarded, and from this point of view it behaves as non-interacting component. In addition, it was found that the modified ADE gives rather better results than the classical one.     

Michael addition of thiols to alpha-enones in ionic liquids with and without organocatalysts

Seventeen organocatalyts were tested for their ability to catalyst the addition of thiophenols to chalcones in [bmim]PF6. The products were isolated in high yield after a short reaction time, but no stereoselectivity was observed. The reactions also proceeded (without any stereoselectivity) in four other ionic liquids. In contrast, 16% and 26% ee were observed when L-proline and cinchonine, respectively, were used as the catalysts in CH2Cl2. Addition of thiophenols is also catalysed by HCl, as well as D-mandelic and L-tartaric acids. Addition of thiophenols to chalcones also occurred in neat ionic liquids, without any additional catalyst, but the rate of the reaction depended considerably on the structure of ionic liquid. The scope of the non-catalysed reaction in ionic liquids was tested by the reactions of 5 different thiols and 3 different alpha-enones.     

Absorption and Luminescence Spectra of Tetra (3-Pyridyl)Porphyrazine: A Convergent Spectroscopic Method for the Elucidation of Association Reactions in Solution

Tetra(3-pyridyl)porphyrazine is soluble in trifluoroethanol yielding intense blue solutions. The electronic spectra exhibit the characteristic Soret and Q bands around 330 and 610 nm, respectively; however, the absorption profile is strongly dependent on the concentration, reflecting the occurrence of an association process. The system has been elucidated by solving the equilibrium and the absorbance-concentration equations for all the wavelengths in the spectral range, according to a variational procedure. In this way the consistent spectra of the individual species have been generated. The study has also been extended to the luminescence properties of the porphyrazine molecule, and discussed in terms of the ground state association and the exciplex formation involving the monomeric species.     

Adsorption, association and precipitation in hexadecyltrimethylammonium bromide/sodium dodecyl sulfate mixtures

The phase equilibria of surfactant aqueous mixtures, hexadecyltrimethylammonium bromide and sodium dodecyl sulfate, have been studied by polarizing microscopy, quasielastic light scattering, conductivity, potentiometric, electrophoretic, and surface tension measurements. Adsorption at the air/solution interface, association and precipitation in bulk solution strongly depended on the molar ratio and the concentration of surfactants. Catanionic vesicles coexisted with crystalline catanionic salts in a broad concentration range. The relative proportions of crystallites and vesicles varied according to the concentration and the molar ratio of the surfactants. The solid crystalline phase was progressively converted to catanionic vesicles with increasing surfactant molar ratio. At the highest excess of one of the surfactants transition from catanionic vesicles to mixed micelles occurred. The formation and stability of different phases are discussed in terms of surfactant molecular packing constraints and electrostatic interactions in the headgroup region. Surfactant tail-length asymmetry and the change of electrostatic interactions in the headgroup region from attractive to repulsive are governing factors for the transition from planar to curved bilayers. Received: 9 June 1998 Accepted: 18 August 1998     

mer-[Fe III(bpca)(CN)3]-: a new low-spin iron(III) complex to build heterometallic ladder-like chains

The novel mononuclear complex PPh(4)-mer-[Fe(III)(bpca)(3)(CN)(3)].H(2)O (1) [PPh(4)(+) = tetraphenylphosphonium cation and bpca = bis(2-pyridylcarbonyl)amidate anion] and ladder-like chain compound [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)] [Fe(III)(bpca)(CN)(3)]].3H(2)O (2) have been prepared and characterized by X-ray diffraction analysis. Compound 1 is a low-spin iron(III) compound with three cyanide ligands in mer arrangement and a tridentate N-donor ligand building a distorted octahedral environment around the iron atom. Compound 2 is an ionic salt made up of cationic ladder-like chains [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)]](+) and uncoordinated anions [Fe(III)(bpca)(3)(CN)(3)](-). The magnetic properties of 2 correspond to those of a ferrimagnetic chain with significant intrachain antiferromagnetic coupling between the low-spin iron(III) centers and the high-spin manganese(II) cations. This compound exhibits ferrimagnetic ordering below 2.0 K.     

Spectroscopic study of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles and their N-allylbenzothiazolium bromides. Solvent and substituent effects on their ultraviolet-visible and fluorescence spectra.

UV-vis and fluorescence spectra of 2-[2-(4-cyclaminophenyl)ethen-1-yl] benzothiazoles 1 and their N-allylbenzothiazolium bromides 2 have been measured and interpreted. The substitution and solvent effects on electronic structure and spectra have been investigated. The benzothiazolium salts substituted with saturated cyclamines show strong push-pull character and can be used as potential NLO materials. Formation of aggregated structures was observed at higher concentrations of the benzothiazolium bromides.     

Gas-chromatographic determination of volatile sulfur-containing impurities in industrial emissions and aqueous solutions

Procedures are developed for determining volatile sulfur-containing impurities, hydrogen sulfide, simple mercaptans, sulfides, and disulfides in air and aqueous solutions. The procedures are based on the principle’s headspace gas chromatography and equilibrium preconcentration. The procedures differ from the officially approved ones in that the operations of sampling and sample preparation to gas-chromatographic analysis considerably reduce the loss of hydrogen sulfide and mercaptans unstable in humid air. The procedures provide the determination of sulfur-containing substances at the level of their maximum permissible concentrations (MPC) in industrial emissions and natural waters and the analytical range of four orders of magnitude; they can be implemented on gas chromatographs with flame ionization and flame photometric detectors, a quartz capillary column, and a thermostated gas-sampling valve.     

Synthesis and nmr analysis of cyclo-[85% 13C-asp]-pro: 13C-13C vicinal coupling constants and conformation

The dipeptide cyclo(Asp-Pro) where the aspartic acid residue was 85% ¹³C enriched, was synthesized with the aim of analyzing its conformation in solution by using ¹C-¹H, ¹³H-¹H and ¹³C-¹³C coupling constant parameters. The values of these couplings agree well with each other and show that the side chain of the aspartic acid residue adopts privileged conformations the proportions of which vary somewhat with pH, and more weakly, with a change in solvent. The ¹³C-¹³C interresidue coupling constants ³J_Cl'–_C2^β and ³J_Cl'–_C2^γ obtained after long accumulation of the signals of unenriched carbons, have different values; they show puckering in the pyrrolidine ring similar to that found in cyclo(Leu-Pro) in the solid state. It was concluded that ¹³C-¹³C coupling constants represent an excellent means of determining the side chain conformation (whenever the incorporation of an enriched amino acid into the peptide is possible) that will find applications particularly in the case of peptides with complicated proton spectra.     

Separation of131I by isotopic and non-isotopic liquid ion exchange

A study is presented on the use of isotopic and non-isotopic ion exchange in a heterogeneous liquid-liquid system for the separation of¹³¹I from water. The method is based on the reaction between radioiodide in the aqueous phase and trioctylmethylammonium iodide or chloride in the organic phase. The effect of some important experimental parameters on the separation efficiency is discussed. It has been found that under optimum conditions the method of isotopic ion exchange can be used for the radiochemical determination of iodine in water.