Cu(i) and Ag(i) complex formation with the hydrophilic phosphine 1,3,5-triaza-7-phosphadamantane in different ionic media. How to estimate the effect of a complexing medium

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. \ua9 2017 The Royal Society of Chemistry

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe

Yield of Magnesium Isotopes by Intermediate-energy, Photon-induced, Spallation in Natural Chlorine.

Targets of LiCl (natural Cl) were irradiated with bremsstrahlung beams in the energy range 0.3-1 GeV and the mean cross-sections per photon were deduced for the prodn. of 27Mg and 28Mg from 35,37Cl. Comptete agreement was found between the experimentally determined yields and those calculaied by using a modified CDMD Rudstam formula

A calorimetric study of the hydrolysis and peroxide complex formation of the uranyl(vi) ion

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(O-2)(OH)](-) and [(UO2)(2)(O-2)(2)(OH)](-)} have been determined from calorimetric titrations at 25 degrees 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. Fanghanel, 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

Thermodynamic and Spectroscopic Studies on the Complexation of Silver(I) by Mixed Phosphorus-Sulfur Compounds in Propylene Carbonate. Crystal and Molecular Structure of a Silver(I)-Thiophosphine Complex.

The thermodynamic parameters for complexation of silver(I) with the mixed-donor compounds Ph(2)PCH(2)SPh and Ph(2)P(CH2)(2)SR (R = Me, Et or Ph) have been determined by potentiometric and calorimetric techniques in propylene carbonate at 25 degrees C and 0.1 mol dm(-3) ionic strength (NEt(4)ClO(4)). Within the silver(I) concentration range investigated, Ph(2)PCH(2)SPh forms three successive mononuclear complexes whereas also polynuclear species are formed by the other thiophosphines. All the complexes are strongly enthalpy stabilized, the entropy changes being unfavourable. The ligands behave as either monodentate (through P) or bidentate. depending upon the length of the aliphatic chain between the donor atoms and on the stoichiometry of the species formed. The influence of R on the stabilities of the complexes is discussed. The crystal structure of the 1:1 Ag-Ph(2)P(CH2)(2)SEt complex has been determined: monoclinic. space group P2(1)/c, a = 8.924(2), b = 9.620(1), c = 44.797(6) Angstrom, beta = 93.41(1)degrees and Z = 4. Phosphorus-31 NMR studies have also been performed to obtain additional information on the nature and structure of the species formed. Comparison of the thermodynamic data for formation of the silver(I) complexes with the same ligands in dimethyl sulfoxide evidences a different behaviour of the ligands in the two media: the results are discussed in terms of the different physicochemical properties of the two solvents

Thermodynamic Properties of Actinide Complexes. IV. Thorium(IV)- and Uranyl(VI) - Malonate Systems.

The stability consts. and thermodn. of formation of Th4+ and UO22+ malonate complexes were detd. by potentiometric and calorimetric titrns. in 1.00 M NaClO4 at 25\ub0. All complexes formed were stabilized by a large entropy gain. Stability const. values agreed with an ionic bonding model in which the malonate behaved as a bidentate ligand forming only chelate complexes