Exchange algebra and the Drinfeld-Sokolov theorem

We analyse the relation between the exchange algebra and the separation of the chiralities in classical Toda field theory. We show that there exists a conformally covariant Bloch wave basis such that the two chiralities commute. In terms of this basis we then reconstruct the periodic and local solution of Toda field theory.Work supported by Fondazione Angelo Della Riccia     

F 2-FDG NMR imaging of the brain in rat

Images of the rat head reflecting glucose utilization were obtained using 2-fluoro-2-deoxy-D-glucose (2-FDG) and ¹⁹F nuclear magnetic resonance (NMR) imaging. Spatial heterogeneity of glucose utilization in the rat head was clearly demonstrated showing significantly higher glucose utilization in the brain as compared to the surrounding tissues. Although the potential adverse effects of the high doses of 2-FDG (400 mg/kg) needed to perform the study preclude immediate application of this technique to clinical quantitative glucose utilization studies, the present study shows potential for future development of glucose utilization imaging by NMR.     

Adapted numerical modelling of the Belousov–Zhabotinsky reaction

Adapted numerical schemes for the integration of differential equations generating periodic wavefronts have reported benefits in terms of accuracy and stability. This work is focused on differential equations modelling chemical phenomena which are characterized by an oscillatory dynamics. The adaptation is carried out through the exponential fitting technique, which is specially suitable to follow the apriori known qualitative behavior of the solution. In particular, we have merged this strategy with the information coming from existing theoretical studies and especially the observation of time series. Numerical tests will be provided to show the effectiveness of this problem-oriented approach.     

A Biomimetic Nickel Complex with a Reduced CO2 Ligand Generated by Formate Deprotonation and Its Behaviour towards CO2

Reduced CO₂ species are key intermediates in a variety of natural and synthetic processes. In the majority of systems, however, they elude isolation or characterisation owing to high reactivity or limited accessibility (heterogeneous systems), and their formulations thus often remain uncertain or are based on calculations only. We herein report on a Ni?CO₂^2? complex that is unique in many ways. While its structural and electronic features help understand the CO₂‐bound state in Ni,Fe carbon monoxide dehydrogenases, its reactivity sheds light on how CO₂ can be converted into CO/CO₃^2? by nickel complexes. In addition, the complex was generated by a rare example of formate β‐deprotonation, a mechanistic step relevant to the nickel‐catalysed conversion of H_xCO_y^z? at electrodes and formate oxidation in formate dehydrogenases.     

Exclusive Free Radical Mechanisms of Cellular Photosensitization

In order to determine the specific effects of radical-induced reactions in the absence of complicating excited-state pathways, four different thiohydroxamic esters and their parent molecule, N-hydroxypyridine-2(1H)-thione, have been studied in murine L1210 leukemia cells for their ability to produce photobiological damage. Irradiation (X_exc= 355 nm) of cells in the presence of thiopyridone esters, specific photolytic precursors of sulfur-, carbon- and oxygen-centered radicals, caused toxicity that was unambiguously demonstrated to result from radical photosensitization mechanisms. Cellular morphological changes were observed following irradiation but apoptosis was not found to take place. A good correlation was evident between lipid peroxidation, measured by the thiobarbituric acid method, and phototoxicity, assessed by the trypan blue exclusion assay, indicating that the ester derivatives exert their effects mainly in plasma and/ or subcellular membranes. Irradiation performed under deaerated conditions also induced significant phototoxicity but the effects of deaeration were dependent on the ester used and are discussed in terms of the nature of the primary radical species generated in each case. Irradiation of L1210 cells in the presence of N-hydroxypyridine-2(1H)-thione, a nonspecific, photochemical source of hydroxyl radical, was also found to trigger phototoxicity and lipid peroxidation. However in this case, photodamage cannot yet be definitely attributed to a radical or type II mechanism although the apparent oxygen independence of phototoxicity would indicate that type II contribution is not significant.     

Determination of triazines and dinitroanilines in waters by high-performance liquid chromatography after solid-phase extraction

A rapid and selective method for the simultaneous determination of triazines and dinitroanilines in real water matrices is suggested based on a preliminary adsorption on an RP-18 cartridge, an elution step using acetonitrile and HPLC separation with a Lichrosorb RP- Select B column and UV detection. The washing step cartridge is critical for triazines: terbutryn is eluted with quantitative recovery only after washing with an NH₃ solution. The degree of enrichment of the compounds studied has been determined: triazine recoveries are quantitative, while dinitroaniline recoveries are between 66% and 78% at the lowest fortification level. The detection limits for the ten herbicides are in the range 0.03-0.1 μg/l. The analysis time is 2 h.     

Preparation and characterization of a europium(II) bromide-chloride phase EuBr1.5Cl0.5

A divalent europium chloride-bromide phase, EuBr_1.56(7)Cl_0.46(2) has been prepared and identified on the basis of analytical, X-ray powder diffraction and single-crystal data. Although the phase is considered isostructural with EuCl₂ (PbCl₂ structure type, a = 0.9230 (5), b = 0.7890 (4), c = 0.4613 (3) nm, space group Pbnm), the single-crystal data indicate long-range order in the form of a superstructure which doubles the b parameter. In the pseudocell the square pyramidal anion sites are occupied principally by bromide ions, the tetrahedral sites almost equally by bromide and chlorine ions. Structural details and the long-range order are discussed. Evidence is presented for the existence of another europium(II) mixed halide phase, EuBr_1.8(2)Cl_0.16(2).     

Short and diverse route toward complex natural product-like macrocycles

[reaction: see text] A general strategy toward macrocyclic compounds using multicomponent reaction (MCR) chemistry, e.g., Passerini and Ugi variants, and ring-closing metathesis (RCM) is introduced. The corresponding bifunctional isocyanides carboxylic acids bearing a terminal olefin are easy to prepare from the corresponding commercially available starting materials. Advantageously, this strategy allows fast access to a diverse conformational space of natural product-like macrocycles and could thus be of interest in the discovery of novel bioactive agents.     

Ordered binary crystals via cocrystallisation of quasiracemic Pd(II) complexes in a borderline regime between inertness and lability

Square planar complexes of the type [2-(1-aminoethyl)phenyl-kappa(2)C(1),N]chloro(py-kappaN)palladium(II)(py = pyridine derivative) have been prepared by cyclopalladation of 1-phenylethylamine. When opposite enantiomers of the chiral amine and different pyridine ligands were coordinated to the metal, quasiracemic complexes were obtained. The racemisation speed of solutions containing equimolar amounts of such quasiracemic complexes was used to test the compounds for inertness: slow ligand exchange was found for methylated pyridines. Enantiomerically pure complexes of opposite chirality with the electron rich ligands 2,6-collidine and 2,4,6-lutidine were successfully cocrystallised: they form a well-ordered binary solid in which four independent molecules, two of each constituent, are related by pseudo symmetry operations. This quasiracemate as well as its components and the true racemates of the latter were characterised by single crystal X-ray diffraction. The heterochiral crystals, both the cocrystal as well as the racemates, show better space filling than the homochiral solids.