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The complexes of Cu(i) and Ag(i) with 1,3,5-triaza-7-phosphadamantane (PTA) are currently studied for their potential clinical use as anticancer agents, given the cytotoxicity they exhibited in vitro towards a panel of several human tumor cell lines. These metallodrugs are prepared in the form of [M(PTA)4]+ (M = Cu+, Ag+) compounds and dissolved in physiological solution for their administration. However, the nature of the species involved in the cytotoxic activity of the compounds is often unknown. In the present work, the thermodynamics of formation of the complexes of Cu(i) and Ag(i) with PTA in aqueous solution is investigated by means of potentiometric, spectrophotometric and microcalorimetric methods. The results show that both metal(i) ions form up to four successive complexes with PTA. The formation of Ag(i) complexes is studied at 298.15 K in 0.1 M NaNO3 whereas the formation of the Cu(i) one is studied in 1 M NaCl, where Cu(i) is stabilized by the formation of three successive chloro-complexes. Therefore, for this latter system, conditional stability constants and thermodynamic data are obtained. To estimate the affinity of Cu(i) for PTA in the absence of chloride, Density Functional Theory (DFT) calculations have been done to obtain the stoichiometry and the relative stability of the possible Cu/PTA/Cl species. Results indicate that one chloride ion is involved in the formation of the first two complexes of Cu(i) ([CuCl(PTA)] and [CuCl(PTA)2]) whereas it is absent in the successive ones ([Cu(PTA)3]+ and [Cu(PTA)4]+). The combination of DFT results and thermodynamic experimental data has been used to estimate the stability constants of the four [Cu(PTA)n]+ (n = 1–4) complexes in an ideal non-complexing medium. The calculated stability constants are higher than the corresponding conditional values and show that PTA prefers Cu(i) to the Ag(i) ion. The approach used here to estimate the hidden role of chloride on the conditional stability constants of Cu(i) complexes may be applied to any Cu(i)/ligand system, provided that the stoichiometry of the species in NaCl solution is known. The speciation for the two systems shows that the [M(PTA)4]+ (M = Cu+, Ag+) complexes present in the metallodrugs are dissociated into lower stoichiometry species when diluted to the micromolar concentration range, typical of the in vitro biological testing. Accordingly, [Cu(PTA)2]+, [Cu(PTA)3]+ and [Ag(PTA)2]+ are predicted to be the species actually involved in the cytotoxic activity of these compounds. [ABSTRACT FROM AUTHOR]

Sorption of U(VI) and other metal ions on amine-functionalized silica was studied, including aminopropylsilica (APS), 3-(ethylenediamino)propyl silica (ENPS), and 3-[2-(2-aminoethylamino)ethylamino]propyl silica (DIENPS). DIENPS showed the strongest and fastest sorption for U(VI) that can be described by Langmuir isotherm, suggesting U(VI) was sorbed at well-defined and energetically identical sites independent from each other. The sorption efficiency of DIENPS follows the order: U(VI) > Fe(III) > Cu(II) > Pb(II) > Ni(II) > Mg(II) > Sr(II). Results demonstrate that the amine-functionalized silica materials could be used as efficient sorbents to remove uranium and hazardous metal ions in environmental remediation. [ABSTRACT FROM PUBLISHER]

The constitution and equilibrium constants of ternary uranyl(vi) peroxide carbonate complexes [(UO2)p(O2)q(CO3)r]2(p−q−r) have been determined at 0 °C in 0.50 M MNO3, M = Li, K, and TMA (tetramethyl ammonium), ionic media using potentiometric and spectrophotometric data; 17O NMR data were used to determine the number of complexes present. The formation of cyclic oligomers, “[(UO2)(O2)(CO3)]n”, n = 4, 5, 6, with different stoichiometries depending on the ionic medium used, suggests that Li+, Na+, K+ and TMA ions act as templates for the formation of uranyl peroxide rings where the uranyl-units are linked by μ–η2–η2 bridged peroxide-ions. The templating effect is due to the coordination of the M+-ions to the uranyl oxygen atoms, where the coordination of Li+ results in the formation of Li[(UO2)(O2)(CO3)]47−, Na+ and K+ in the formation of Na/K[(UO2)(O2)(CO3)]59− complexes, while the large tetramethyl ammonium ion promotes the formation of two oligomers, TMA[(UO2)(O2)(CO3)]59− and TMA[(UO2)(O2)(CO3)]611−. The NMR spectra demonstrate that the coordination of Na+ in the five- and six-membered oligomers is significantly stronger than that of TMA+; these observations suggest that the templating effect is similar to the one observed in the synthesis of crown-ethers. The NMR experiments also demonstrate that the exchange between TMA[(UO2)(O2)(CO3)]59− and TMA[(UO2)(O2)(CO3)]611− is slow on the 17O chemical shift time-scale, while the exchange between TMA[(UO2)(O2)(CO3)]611− and Na[(UO2)(O2)(CO3)]611− is fast. There was no indication of the presence of large clusters of the type identified by Burns and Nyman (M. Nyman and P. C. Burns, Chem. Soc. Rev., 2012, 41, 7314–7367) and possible reasons for this and the implications for the synthesis of large clusters are briefly discussed. [ABSTRACT FROM AUTHOR]

The alkali metal ions Li+, Na+ and K+ have a profound influence on the stoichiometry of the complexes formed in uranyl(vi)–peroxide–hydroxide systems, presumably as a result of a templating effect, resulting in the formation of two complexes, M[(UO2)(O2)(OH)]2− where the uranyl units are linked by one peroxide bridge, μ–η2–η2, with the second peroxide coordinated “end-on”, η2, to one of the uranyl groups, and M[(UO2)(O2)(OH)]43−, with a four-membered ring of uranyl ions linked by μ–η2–η2 peroxide bridges. The stoichiometry and equilibrium constants for the reactions: M+ + 2UO22+ + 2HO2− + 2H2O → M[(UO2)(O2)(OH)]2− + 4H+ (1) and M+ + 4UO22+ + 4HO2− + 4H2O → M[(UO2)(O2)(OH)]43− + 8H+ (2) have been measured at 25 °C in 0.10 M (tetramethyl ammonium/M+)NO3 ionic media using reaction calorimetry. Both reactions are strongly enthalpy driven with large negative entropies of reaction; the observation that ΔH(2) ≈ 2ΔH(1) suggests that the enthalpy of reaction is approximately the same when peroxide is added in bridging and “end-on” positions. The thermodynamic driving force in the reactions is the formation of strong peroxide bridges and the role of M+ cations is to provide a pathway with a low activation barrier between the reactants and in this way “guide” them to form peroxide bridged complexes; they play a similar role as in the synthesis of crown-ethers. Quantum chemical (QC) methods were used to determine the structure of the complexes, and to demonstrate how the size of the M+-ions affects their coordination geometry. There are several isomers of Na[(UO2)(O2)(OH)]2− and QC energy calculations show that the ones with a peroxide bridge are substantially more stable than the ones with hydroxide bridges. There are isomers with different coordination sites for Na+ and the one with coordination to the peroxide bridge and two uranyl oxygen atoms is the most stable one. [ABSTRACT FROM AUTHOR]

The enthalpies of reaction for the formation of uranyl(VI) hydroxide {[(UO2)2(OH)2]2+, [(UO2]3(OH)4]2+, [(UO2]3(OH)5]+, [(UO2]3(OH)6](aq), [(UO2]3(OH)7]-, [(UO2]3(OH)8]2-, [(UO2)(OH)3]-, [(UO2)(OH)4]2-} and peroxide complexes {[UO2(O2)(OH)]- and [(UO2)2(O2)2(OH)]-} have been determined from calorimetric titrations at 25 °C in a 0.100 M tetramethyl ammonium nitrate ionic medium. The hydroxide data have been used to test the consistency of the extensive thermodynamic database published by the Nuclear Energy Agency (I. Grenthe, J. Fuger, R. J. M. Konings, R. J. Lemire, A. B. Mueller, C. Nguyen-Trung and H. Wanner, Chemical Thermodynamics of Uranium, North-Holland, Amsterdam, 1992 and R. Guillaumont, T. Fanghänel, J. Fuger, I. Grenthe, V. Neck, D. J. Palmer and M. R. Rand, Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, Amsterdam, 2003). A brief discussion is given about a possible structural relationship between the trinuclear complexes [(UO2]3(OH)n]6-n, n = 4-8. [ABSTRACT FROM AUTHOR]

The focus of this study is on the relationship between uranyl(vi) poly-peroxo clusters in the solid state and their possible precursors in solution. For this purpose, the complex formation in the ternary U(vi)–H2O2–F− system has been studied by potentiometric titrations, measuring p[H+] and p[F−], revealing that significant amounts of ternary uranyl(vi)–peroxide–fluoride complexes are formed. Based on the analysis of these data we find that there are two models consistent with structure data and previous speciation in the uranyl(vi)–peroxide–carbonate system (Dalton. Trans., 2012, 41, 11635–11641). One model contains ternary complexes (UO2)4(O2)4F− and (UO2)4(O2)4F22− and the other (UO2)4(O2)4F− and (UO2)5(O2)5F33−; we have chosen the second model as the one most consistent with available information. We suggest that (UO2)4(O2)4F− is a building block in the U-24 cluster, [Na6(OH2)8]@[UO2(O2)F]2418− identified in a single-crystal X-ray diffraction study of the solid phase that slowly precipitates from the slightly acidic test solutions. At p[H+] ≈ 9.5, a new solid phase is formed that contains the cluster [Na6(OH2)8]@[UO2(O2)OH]2418−, also identified from an X-ray structure. Both structures contain η2–η2 bridging peroxide and η2 bridging fluoride or hydroxide ions, respectively. As fluoride bridges are unknown in solution coordination chemistry, it is unlikely that the U-24 fluoride cluster is formed in solution. We suggest that both the solid state fluoride and hydroxide clusters are formed in the crystallization from smaller precursors identified in solution. The study illustrates the importance of accurate control of the solution chemistry when preparing poly-peroxo-metallate clusters and also that the mechanism of their formation is still an open field of research. [ABSTRACT FROM AUTHOR]

The thermodynamics of the complexation between uranium(VI) and acetate in dimethyl sulfoxide (DMSO) was studied at 298 K in an ionic medium of 0.1 mol dm-3 tetrabutyl ammonium Perchlorate. The results show that the urartyl ion forms three strong successive mononuclear complexes with acetate. The complexes, both enthalpically and entropically stabilized, are significantly more stable in DMSO than in water. This feature can be ascribed to the weak solvation of acetate in DMSO. The thermodynamic parameters for the formation of the uranium(VI) complexes with acetate in DMSO are compared with those with ethylenediamine in the same solvent. The difference between the two ligand systems reveals that, for the complexation reactions involving charge neutralization, the reorganization of the solvent gives a very important contribution to the overall complexation energetics. The coordination mode of acetate in the uranyl complexes and the changes of the solvation sphere of UO22+ upon complexation were investigated by FT-IR spectroscopy in DMSO and in acetonitrile/DMSO mixtures. In addition, DFT calculations were performed to provide an accurate description of the complexation at the molecular level. The experimental and calculated results suggest that acetate is solely bidentate to UO22+ in the 1:1 and 1:3 complexes but mono- and bidentate in the 1:2 complexes. The DFT calculations also indicate that the medium effects must always be taken into account in order to gain accurate information on the complex formation in solution. In fact, the relative stability of the reaction products changes markedly when the DFT calculations are carried out in vacuum or in DMSO solution. [ABSTRACT FROM AUTHOR]

The applicability of spectrophotometry or H + -potentiometry to the studies of the complexation of thorium(IV) in aqueous solutions is limited because Th(IV) does not have characteristic optical absorption in UV/Vis/Near IR region and H + -electrode is not sensitive in solutions of high acidity that needs to be maintained to prevent the hydrolysis of Th(IV). In the present work, the technique of calorimetric titration was used to determine the heat of reaction for the complexation of Th(IV) with sulfate in the temperature range of 10–70 °C. The equilibrium constants and enthalpy of complexation were determined simultaneously from the calorimetric data. It was observed that the enthalpy of complexation is endothermic at 10 °C, and become more endothermic as the temperature is increased. Despite of this, the complexes, Th(SO 4 ) 2+ and Th(SO 4 ) 2 (aq), become more stable at higher temperatures due to the increasingly more positive entropy of complexation that exceeds the increase of enthalpy. The trends in the stability of sulfate complexes with tetravalent actinides (Th 4+ , U 4+ , Np 4+ , and Pu 4+ ) are discussed in terms of electrostatic interactions that correlate with the ionic radii of the metal cations. [ABSTRACT FROM AUTHOR]

The interaction of La(III), Gd(III), and Yb(III) with Tris((2,3-dihydroxybenzylamino)ethyl)amine) (TRENCAT) was investigated by means of potentiometric measurements in 0.1 mol dm−3 aqueous solution of sodium perchlorate at 25 °C. The formation of complexes between the partially protonated ligand and lanthanides has been observed and the values of their formation constants are reported. [Copyright &y& Elsevier]