On a Class of Multitime Evolution Equations with Nonlocal Initial Conditions

The existence and uniqueness of the strong solution for a multitime evolution equation with nonlocal initial conditions are proved. The proof is essentially based on a priori estimates and on the density of the range of the operator generated by the considered problem

Immobilization of complexes of some heavy metals with a 2-(4-pyridylazo)-resorcinol “PAR” on Algerian hydrothermal clay

International audienc

Independent of local properties mathematical models for the calculation of retention indices in programmed temperature gas chromatography

Retention indices of some phthalates separated in temperature programming on SE-30 packed column were calculated by smoothing calibration data with Bezier curves, and from 2 to 6 order B-splines. The values thus obtained were compared to the corresponding ones calculated in a classical way. Whatever the standard n-alkane mixtures used (homologous series, alternate members with even or odd carbon atoms, any mixture with consecutive members not exceeding 4 carbon atoms between each two) the B-splines interpolations lead to retention indices values in better agreement with these ones, although Bezier curve smoothing still leads to values more consistent with the scheme of retention indices. Referring the phthalates to n-alkane standard mixtures, with consecutive members not exceeding 3 or 4 carbon atoms between each 2, connecting the calibration data by B-splines, with orders from 2 to 5, and selecting the set of retention indices corresponding to the smallest value of the sum of squared second divided differences one may recover, with a good accuracy, classical programmed retention indices

Effect of the chelating agents on bio-sorption of hexavalent chromium using Agave sisalana fibers

International audienc

Crystallographic elucidation of purely structural, thermal and light-induced spin transitions in an iron(ii) binuclear complex

The intricate phase diagram of the binuclear iron(ii) spin-crossover complex [{Fe(3-bpp)(NCS)2}2(4,4�-bypiridine)] ·2CH3OH where 3-bpp is 2,6-bis(pyrazol-3-yl)pyridine has been investigated by variable temperature single crystal X-ray diffraction including a study into the effect of photo-irradiation. This sample is known to exhibit an incomplete spin transition at low temperature. At room temperature, in phase I, iron ions are all crystallographically equivalent, adopting the high spin state (HS). X-Ray structural investigation has revealed two phase transitions in the range (300-30 K). The first transition (T�161 K) leading to phase II is of a purely structural nature and corresponds to a break in symmetry as a result of a twist of the two rings of 4,4�-bipyridine; the two iron sites of the binuclear unit becoming crystallographically independent but remaining all HS. The second structural transition corresponds to the spin crossover, one of the two Fe(ii) ions of the binuclear complex being in the low spin state (LS) in phase III. The crystal structure shows an ordered HS-LS crystal packing where HS and LS sites are clearly identified and not randomly distributed in the metal ion sites as often observed. Moreover, light irradiation of single crystals in phase III at 30 K, leading to phase III*, induces a light-induced spin-state trapping (LIESST) effect corresponding to the full conversion of all the iron sites to HS. The crystal packing in phase III* is closer to that of phase III than to those observed in the other HS phases, I and II. This reveals an unusual differentiation between the thermal and light-induced HS states. A deeper analysis of the structural properties first demonstrates the key role of the bipyridine bridge in the peculiar preliminary pure structural transition shown by the title compound. Elsewhere, it also shows that the molecular packing is strongly dependent on the nature of the external perturbation contrary to the iron coordination sphere geometry that appears to be only dependent on the spin state. Moreover, in the HS phase II, the distortion of the iron sites that will subsequently undergo a spin crossover demonstrates some differences with the distortion of the iron sites that remain HS. The predominant role of the iron environment distortion in the spin crossover phenomenon is thus clearly evidenced. © 2010 The Royal Society of Chemistry