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Hydration Number (hydration + number)
Selected AbstractsFluorinated ,-Diketones for the Extraction of Lanthanide Ions: Photophysical Properties and Hydration Numbers of Their EuIII ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2006Anne-Sophie Chauvin Abstract Tris(,-diketonato)europium(III) with a series of variably fluorinated ligands derived from 3,5-heptanedione were synthesised with the aim of determining their hydration state under extraction conditions. The number of coordinated water molecules was determined by measuring the lifetime of the Eu(5D0) excited level in water and deuterated water. The hydration gain (,q = q , q0) after shaking chloroform solutions during 10 min with 0.1 M NaClO4 aqueous solutions depends on the fluorination extent of the diketonates: fluorination of one methyl group leads to a decrease in ,q of ca. 0.5 unit, while fluorination of one ethyl group results in a decrease of ca. 1.3 units. Highly fluorinated complexes (i.e with hexafluoroacetylacetonate and related ligands) display a hydration number close to one while poorly fluorinated compounds (or nonfluorinated ones, such as the acetylacetonate complex) have a hydration state close to two. Photophysical properties of the EuIII ,-diketonates are also described and the synthesis of the fluorinated ,-diketones is re-investigated and discussed in details. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Molecular modeling of metal complexation by a fluoroquinolone antibioticENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2008Ludmilla Aristilde Abstract An understanding of the factors controlling the chemodynamics of fluoroquinolone antibiotics in different environmental matrices is a necessary prerequisite to the assessment of their potential impact on nontarget organisms in soils and receiving waters. Of particular interest are the complexes formed between fluoroquinolones and metal cations, which are believed to be important in the mechanism of sequestration of the antibiotic by minerals and natural organic matter. The structures of these complexes have not been fully resolved by conventional spectroscopy; therefore, molecular simulations may provide useful complementary insights. We present results from apparently the first molecular dynamics simulations of a widely used fluoroquinolone antibiotic, ciprofloxacin (Cipro), in aqueous complexes with five metal cations typically found in soils and surface waters: Ca2+, Mg2+, Fe2+, Na+, and K+. The interatomic potential functions employed in the simulations were validated by comparison with available structural data for solid-phase Cipro-hexahydrate and for the metal cations in aqueous solution. Although no comprehensive structural data on the aqueous complexes appear to be available, properties of the metal complexes predicted by our simulations agree with available data for solid-phase metal,Cipro complexes. Our results indicate that the ionic potential of the metal cation controls the stability of the complex formed and that the hydration number of the metal cation in aqueous solution determines its coordination number with O atoms in the metal,Cipro complex. In respect to environmental chemodynamics, our results imply that Cipro will form two configurations of bidendate chelates with metal centers on exposed surfaces of mineral oxides, water-bridged surface complexes with exchangeable cations in clay mineral interlayers, and cation-bridged complexes with functional groups in natural organic matter. [source] Hydration of Lanthanoid(III) Ions in Aqueous Solution and Crystalline Hydrates Studied by EXAFS Spectroscopy and Crystallography: The Myth of the "Gadolinium Break"CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2008Ingmar Persson Prof. Abstract The structures of the hydrated lanthanoid(III) ions including lanthanum(III) have been characterized in aqueous solution and in the solid trifluoromethanesulfonate salts by extended X-ray absorption fine structure (EXAFS) spectroscopy. At ambient temperature the water oxygen atoms appear as a tricapped trigonal prism around the lanthanoid(III) ions in the solid nonaaqualanthanoid(III) trifluoromethanesulfonates. Water deficiency in the capping positions for the smallest ions starts at Ho and increases with increasing atomic number in the [Ln(H2O)9,x](CF3SO3)3 compounds with x=0.8 at Lu. The crystal structures of [Ho(H2O)8.91](CF3SO3)3 and [Lu(H2O)8.2](CF3SO3)3 were re-determined by X-ray crystallography at room temperature, and the latter also at 100,K after a phase-transition at about 190,K. The very similar Ln K- and L3 -edge EXAFS spectra of each solid compound and its aqueous solution indicate indistinguishable structures of the hydrated lanthanoid(III) ions in aqueous solution and in the hydrated trifluoromethanesulfonate salt. The mean LnO bond lengths obtained from the EXAFS spectra for the largest ions, La,Nd, agree with estimates from the tabulated ionic radii for ninefold coordination but become shorter than expected starting at samarium. The deviation increases gradually with increasing atomic number, reaches the mean LnO bond length expected for eightfold coordination at Ho, and increases further for the smallest lanthanoid(III) ions, Er,Lu, which have an increasing water deficit. The low-temperature crystal structure of [Lu(H2O)8.2](CF3SO3)3 shows one strongly bound capping water molecule (LuO 2.395(4),Å) and two more distant capping sites corresponding to LuO at 2.56(1),Å, with occupancy factors of 0.58(1) and 0.59(1). There is no indication of a sudden change in hydration number, as proposed in the "gadolinium break" hypothesis. [source] Unexpected Aggregation of Neutral, Xylene-Cored Dinuclear GdIII Chelates in Aqueous SolutionCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2006Jérôme Costa Dr. Abstract We have synthesized ditopic ligands L1, L2, and L3 that contain two DO3A3, metal-chelating units with a xylene core as a noncoordinating linker (DO3A3, = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate; L1 = 1,4-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzene; L2 = 1,3-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzene; L3 = 3,5-bis{[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]methyl}benzoic acid). Aqueous solutions of the dinuclear GdIII complexes formed with the three ligands have been investigated in a variable-temperature, multiple-field 17O NMR and 1H relaxivity study. The 17O longitudinal relaxation rates measured for the [Gd2L1,3(H2O)2] complexes show strong field dependence (2.35,9.4 T), which unambiguously proves the presence of slowly tumbling entities in solution. The proton relaxivities of the complexes, which are unexpectedly high for their molecular weight, and in particular the relaxivity peaks observed at 40,50 MHz also constitute experimental evidences of slow rotational motion. This was explained in terms of self-aggregation related to hydrophobic interactions, , stacking between the aromatic linkers, or possible hydrogen bonding between the chelates. The longitudinal 17O relaxation rates of the [Gd2L1,3(H2O)2] complexes have been analysed with the Lipari,Szabo approach, leading to local rotational correlation times of 150,250 ps and global rotational correlation times of 1.6,3.4 ns (cGd: 20,50 mM), where is attributed to local motions of the Gd segments, while describes the overall motion of the aggregates. The aggregates can be partially disrupted by phosphate addition; however, at high concentrations phosphate interferes in the first coordination sphere by replacing the coordinated water. In contrast to the parent [Gd(DO3A)(H2O)1.9], which presents a hydration equilibrium between mono- and dihydrated species, a hydration number of q = 1 was established for the [Ln2L1,3(H2O)2] chelates by 17O chemical shift measurements on Ln = Gd and UV/Vis spectrophotometry for Ln = Eu. The exchange rate of the coordinated water is higher for [Gd2L1,3(H2O)2] complexes ( = 7.5,12.0×106 s,1) than for [Gd(DOTA)(H2O)],. The proton relaxivity of the [Gd2L1,3(H2O)2] complexes strongly decreases with increasing pH. This is related to the deprotonation of the inner-sphere water, which has also been characterized by pH potentiometry. The protonation constants determined for this process are logKOH = 9.50 and 10.37 for [Gd2L1(H2O)2] and [Gd2L3(H2O)2], respectively. [source] | ||||||||||