Terminal group effects on the fluorescence spectra of europium(III) nitrate complexes with a family of amide-based 2,3-dihydroxynaphthalene derivatives

Three ligands 2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diethyl(acetamide)) (L(a)), 2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide)) (L(b)) and 2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-dibutyl(acetamide)) (L(c)) and their europium(III) nitrate complexes were synthesized. The complexes were characterized by elemental analysis, IR, fluorescence spectroscopy and conductivity. The europium atoms are coordinated by O-atoms from CO, Ar-O-C. With the difference of the ligands, the solid fluorescent intensities of the Eu complexes vary regularly. Some factors that influencing the fluorescent intensity were discussed.     

Encapsulation of halides within the cavity of a pentafluorophenyl-substituted tripodal amine receptor

Pentafluorophenyl-substituted tripodal amine L, tris[[(2,3,4,5,6-pentafluorobenzyl)amino]ethyl]amine, is becoming a potential receptor for encapsulation of Cl- and Br- within the pseudo-C3-symmetric tris(2-aminoethyl)amine (L1) cavity upon protonation of the secondary amines. 1H NMR titration results indicate that [H3L]3+ binds with Cl- and Br- strongly compared to the [H3L2]3+ receptor, where L2 is N,N',N' '-tris[(2-benzylamino)ethyl]amine.     

Reactivity of the "yl"-bond in uranyl(VI) complexes. 1. Rates and mechanisms for the exchange between the trans-dioxo oxygen atoms in (UO2)2(OH)2 2+ and mononuclear UO2(OH)n 2-n complexes with solvent water

The stoichiometric mechanism, rate constant, and activation parameters for the exchange of the "yl"-oxygen atoms in the dioxo uranium(VI) ion with solvent water have been studied using 17O NMR spectroscopy. The experimental rate equation, (-->)v= k(2obs)[UO2(2+)]tot2/[H+]2, is consistent with a mechanism where the first step is a rapid equilibrium 2U(17)O2(2+) + 2H2O<==>(U(17)O2)2(OH)2(2+) + 2H+, followed by the rate-determining step (U(17)O2)2(OH)2(2+) + H2O<==>(UO2)2*(OH)2(2+) + H2(17)O, where the back reaction can be neglected because the (17)O enrichment in the water is much lower than in the uranyl ion. This mechanism results in the following rate equation (-->)v= d[(UO2)2(OH)2(2+)]/dt = k(2,2)[(UO2)2(OH)2(2+)] = k(2,2*)beta(2,2)[UO2(2+)]2/[H + ]2; with k(2,2) = (1.88 +/- 0.22) x 10(4) h(-1), corresponding to a half-life of 0.13 s, and the activation parameters DeltaH++ = 119 +/- 13 kJ mol-1 and DeltaS++ = 81 +/- 44 J mol(-1) K(-1). *Beta(2,)2 is the equilibrium constant for the reaction 2UO2(2+) + 2H2O<==>(UO2)2(OH)2(2+) + 2H+. The experimental data show that there is no measurable exchange of the "yl"-oxygen in UO2(2+), UO2(OH)+, and UO2(OH)4(2-)/ UO2(OH)5(3-), indicating that "yl"-exchange only takes place in polynuclear hydroxide complexes. There is no "yl"-exchange in the ternary complex (UO2)2(mu-OH)2(F)2(oxalate)2(4-), indicating that it is also necessary to have coordinated water in the first coordination sphere of the binuclear complex, for exchange to take place. The very large increase in lability of the "yl"-bonds in (UO2)2(OH)2(2+) as compared to those of the other species is presumably a result of proton transfer from coordinated water to the "yl"-oxygen, followed by a rapid exchange of the resulting OH group with the water solvent. "Yl"-exchange through photochemical mediation is well-known for the uranyl(VI) aquo ion. We noted that there was no photochemical exchange in UO2(CO3)3(4-), whereas there was a slow exchange or photo reduction in the UO2(OH)4(2-) / UO2(OH)5(3-) system that eventually led to the appearance of a black precipitate, presumably UO2.     

NMR investigation of the interaction of vanadate with carbasilatranes in aqueous solutions

Reaction of vanadate with carbasilatranes [methoxy{N,N',N' '-2,2',3-[bis(1-methylethanolato)(propyl)]amino}silane (1), methoxy{N,N',N' '-2,2',3-[bis(1-ethanolethanolato)(propyl)]amino}silane (2), and {N,N',N' '-2,2',2-[bis(ethanolato)(glycolpropyl ether)]amino}silane (3)] in aqueous solution results in the formation of vanadosilicates and five-coordinated chelate vanadium(V) complexes as evidenced by 51V, 1H, and 13C NMR spectroscopy. Chiral carbasilatrane S,S-1 was characterized in the solid state by X-ray diffraction, revealing a trigonal bipyramidal geometry around the metal ion, with one unidentate methoxy group and one atrane nitrogen atom at the axial positions and one carbon and two atrane oxygen atoms at the equatorial plane of the bipyramid. Crystal data (Mo Kalpha; 100(2) K) are as follows: orthorhombic space group P2(1)2(1)2(1); a = 8.8751(6), b = 9.7031(7), c = 14.2263(12) A; Z = 4. The complexation of vanadium either with 1 or 2 is stereoselective yielding approximately 94% of the complex containing ligand in the S,R-configuration. The lower ability of the S,S- and R,R-diastereoisomers of 1 and 2 to ligate vanadate was attributed to stereochemical factors, dictating a square pyramidal geometry for the chelated complexes. A dynamic process between the vanadium chelate complexes and the respective carbasilatranes was evaluated by 2D {1H} EXSY NMR spectroscopy. These spectra show that the vanadate complexes with the open carbasilatranes exchange more slowly with the free ligand compared to the respective alcohol aminate complexes.     

Oxidation studies of dipositive actinide ions, An2+ (An = Th, U, Np, Pu, Am) in the gas phase: synthesis and characterization of the isolated uranyl, neptunyl, and plutonyl ions UO2(2+)(g), NpO2(2+)(g), and PuO2(2+)(g)

Reactions of atomic and ligated dipositive actinide ions, An2+, AnO2+, AnOH2+, and AnO2(2+) (An = Th, U, Np, Pu, Am) were systematically studied by Fourier transform ion cyclotron resonance mass spectrometry. Kinetics were measured for reactions with the oxidants, N2O, C2H4O (ethylene oxide), H2O, O2, CO2, NO, and CH2O. Each of the five An2+ ions reacted with one or more of these oxidants to produce AnO2+, and reacted with H2O to produce AnOH2+. The measured pseudo-first-order reaction rate constants, k, revealed disparate reaction efficiencies, k/k(COL): Th2+ was generally the most reactive and Am2+ the least. Whereas each oxidant reacted with Th2+ to give ThO2+, only C2H4O oxidized Am2+ to AmO2+. The other An2+ exhibited intermediate reactivities. Based on the oxidation reactions, bond energies and formation enthalpies were derived for the AnO2+, as were second ionization energies for the monoxides, IE[AnO+]. The bare dipositive actinyl ions, UO2(2+), NpO2(2+), and PuO2(2+), were produced from the oxidation of the corresponding AnO2+ by N2O, and by O2 in the cases of UO2+ and NpO2+. Thermodynamic properties were derived for these three actinyls, including enthalpies of formation and electron affinities. It is concluded that bare UO2(2+), NpO2(2+), and PuO2(2+) are thermodynamically stable toward Coulomb dissociation to [AnO+ + O+] or [An+ + O2+]. It is predicted that bare AmO2(2+) is thermodynamically stable. In accord with the expected instability of Th(VI), ThO(2+) was not oxidized to ThO2(2+) by any of the seven oxidants. The gas-phase results are compared with the aqueous thermochemistry. Hydration enthalpies were derived here for uranyl and plutonyl; our deltaH(hyd)[UO2(2+)] is substantially more negative than the previously reported value, but is essentially the same as our deltaH(hyd)[PuO2(2+)].     

UO22+对某些细胞毒性的初探

建立了由多种金属离子和小分子配体组成的多相细胞液热力学平衡模型,模拟研究了UO22+在组织液和细胞液的形态。体外培养了SD大鼠成骨细胞和人肾小管上皮细胞,通过体外细胞生长抑制实验探索了UO22+对成骨细胞及肾小管上皮细胞的毒性。研究表明,在细胞液中,当各形态UO22+物质总浓度[U]=8.4×10-6mol/L时,当pH为6.0～6.5时,UO22+主要以固相(UO2)3(PO4)2存在,当pH为6.8～7.5时,UO22+主要以水溶性[UO2(CO3)3]4-存在;当[U]=1.3×10-3mol/L时,在整个细胞液pH范围内,固相(UO2)3(PO4)2占主导地位。体外细胞生长抑制实验表明,UO22+对成骨细胞的生长具有抑制作用,能显著降低肾小管上皮细胞的存活率,具有明显的细胞毒性。     

Study of variation in thermophysical properties of RE<Subscript>6</Subscript>UO<Subscript>12</Subscript>(s) along the lanthanide series

The novel ligand N,N,N′′′′,N′′′′-tetrabutyl-N′′′,N′′′-(N″,N″-diethyl)-ethidene bisdiglycolamide (TBEE-BisDGA) and other eight analogous extractants have been synthesized and characterized by NMR and HRMS. The solvent extraction of Th⁴⁺, UO₂ ²⁺ and Eu³⁺ from nitric acid solution using the above BisDGA extractants was investigated in 1-dodecanol at 30 ± 1 °C. The extractants exhibited higher affinity toward Th⁴⁺ than UO₂ ²⁺ and Eu³⁺ in the present system. The maximum value of separation factor SF _Th(IV)/U(VI) and SF _{Th(IV)/Eu(III)} is 78.5 and 53.3 respectively for TBEE-BisDGA, 88.1 and 69.5 respectively in the case of TB ^i-PE-BisDGA at 3 M HNO₃ solution.     

Liquid-liquid extraction of uranium(VI) and thorium(IV) by two open-chain crown ethers with terminal quinolyl groups in chloroform

Two open-chain crown ethers 2,2'-(ethylenedioxy)bis[(8-quinolyloxymethyl)benzene], (L1), and 2,2'-(ethylenedioxy)bis[(8-quinaldyloxymethyl)benzene], (L2) have been prepared and characterized by using elemental analysis, IR spectra, ¹H NMR spectra and positive-ion FAB mass spectra. The extraction of UO₂ ²⁺ and Th⁴⁺ by both open-chain crown ethers, L1 and L2 in chloroform as a diluent was studied at 25 °C. Extraction distribution ratios (D) of UO₂ ²⁺ and Th⁴⁺ were investigated as a function of pH, lithium picrate concentration, and extractant concentration. Based on the expertimental results, it was found that 1 : 1 complexes were formed involving either UO₂ ²⁺ or Th⁴⁺ with L1, and Th⁴⁺ with L2. The extractability of L1 for Th⁴⁺ is significantly higher than that for UO₂ ²⁺, the extractabilities of L1 and L2 for Th⁴⁺ being almost identical. L1 and L2 used here are not feasible for industry because of their relatively low extractabilities for Th⁴⁺ at pH<2.0 and for UO₂ ²⁺ at the extraction conditions used in this work.     

Coordination behavior toward copper(II) and zinc(II) ions of three ligands joining 3-hydroxy-2-pyridinone and polyaza fragments

The synthesis and characterization of new polydentate ligand 2-(N),2'-(N')-bis[2-(3-hydroxy-2-oxo-2H-pyridin-1-yl)acetamido]-1(N'),2(N),2'(N')-trimethyl-2,2'-diaminodiethylamine (L3) is reported. The coordination properties of L3 and of two analogous macrocyclic ligands (L1 and L2) toward Cu(II) and Zn(II) metal ions are reported. All three ligands show the 3-hydroxy-2(1H)-pyridinone (HPO) groups attached as sidearms to a polyaza fragment, which is a macrocyclic framework in the case of L1 and L2 while it is an open chain in the case of L3. The role of the polyaza fragments in preorganizing the two sidearms was investigated. The basicity of L3 and the binding properties of L1-L3 were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). UV-vis spectra as well 1H and 13C NMR experiments were used to understand the role of the HPO and of the polyaza fragments in the stabilization of the cations. While L1 forms stable mono- and dinuclear complexes, L2 and L3 can form only mononuclear species with each of the metal ions investigated. In the main mononuclear species of L2 and L3, the two HPO moieties stabilize the M(II) in a square planar geometry due to the two oxygen atoms of each HPO. The coordination sphere of the metal is completed by adding a secondary ligand such as water molecules in the case of Cu(II) systems or OH- in the Zn(II) systems. These results are confirmed by the crystal structures of the [CuH(-1)L2]+ and [CuH(-1)L3]+ species reported herein. Two conformations of L1 can be hypothesized in the formation of the dinuclear species, as suggested by NMR experiments on the [ZnH(-2)L1] species, which shows two conformers slowly interchanging on the NMR time scale, one of which was found to be more insoluble.     

Rhenium(I) compounds bound by tripodal ligands of pyridine and N-methylimidazole

The reaction of Re(CO)(5)Br with tris(2-pyridyl)methanol (tpmOH) leads to unexpectedly complex chemistry with three new compounds forming instead of a single product. In compound 1, the tpmOH ligand binds to the metal in the N,N',N'-mode; 2 has tpmO(-) bound in the N,N',O-mode; while 3 is a dimer with the tpmO(-) ligand utilizing each of the four donor atoms to bridge the two metal centers. The analogous methyl ether ligands, tris(2-pyridyl)methoxymethane (tpmOMe) or tris[2-(l-methylimidazolyl)]methoxymethane (timmOMe), each yielded a single product, 4 and 5, respectively, bound in the N,N',N'-mode, and are new leads for potential radiotherapeutic agents. All compounds have been structurally characterized.     

Synthesis, crystal structure, and DNA-binding study on the trinitrate{2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide))} gadolinium(III) complex

A 2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide)) ligand (L) and its Gd(III) complex have been prepared and characterized. The crystal and molecular structure of the complex was determined by single-crystal X-ray diffraction. The interactions of complex with calf thymus DNA were investigated by UV-vis, fluorescence and viscosity measurements. Experimental results indicated that the complex can bind to DNA by intercalation modes. Its intrinsic binding constant is 1.03 x 10(6) M(-1).     

Enhancement of hydrolysis through the formation of mixed hetero-metal species: dioxouranium(VI)-cadmium(II) mixtures

In order to continue the investigation on the formation of hetero-metal polynuclear hydrolytic species, in this paper we report some results (at I = 0.16 mol L(-1) in NaNO3, at t = 25 degrees C by potentiometry, ISE-H+, glass electrode) on the hydrolysis of several mixtures (in different ratios) of the dioxouranium(VI) and cadmium(II) cations. The same experimental and calculation procedure of previously investigated systems was followed, and all measurements were performed by two different operators, using completely independent instruments and reagents. Many different speciation models were considered in the calculations, and a simple statistical analysis of obtained results was proposed too. UO2(2+) and Cd2+ form two hetero-metal polynuclear hydrolytic species, namely UO2Cd(OH)3+ and (UO2)2Cd(OH)4(2+), with logbeta(pqr) = -3.25 +/- 0.25 and -13.75 +/- 0.10, respectively. The formation of hetero-metal hydrolytic species is thermodynamically favored with respect to the homo-metal ones, and causes an enhancement of the percentage of hydrolyzed metal cations; comparisons with previously studied systems reveal that the hydrolytic behavior of UO2(2+)/Cd2+ mixtures is more similar to that observed for UO2(2+)/Cu2+ than for UO2(2+)/(C2H5)2Sn2+, and the tendency to form hetero polynuclear hydrolytic species with dioxouranium(VI) by other cations follows the trend (C2H5)2Sn2+ > Cu2+ > or = Cd2+.     

Syntheses and properties of emissive iridium(III) complexes with tridentate benzimidazole derivatives

A series of novel emissive Ir(III) complexes having the coordination environments of [Ir(N--N--N)2]3+, [Ir(N--N--N)(N--N)Cl]2+, and [Ir(N--N--N)(N--C--N)]2+ with 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine (L1, N--N--N), 1,3-bis(1-methyl-benzimidazol-2-yl)benzene (L2H, N--C--N), 4'-(4-methylphenyl)-2,2':6',2' '-terpyridine (ttpy, N--N--N), and 2,2'-bipyridine (bpy, N--N) have been synthesized and their photophysical and electrochemical properties studied. The Ir(III) complexes exhibited phosphorescent emissions in the 500-600 nm region, with lifetimes ranging from approximately 1-10 micros at 295 K. Analysis of the 0-0 energies and the redox potentials indicated that the lowest excited state of [Ir(L1)(L2)]2+ possessed the highest contribution of 3MLCT (MLCT = metal-to-ligand charge transfer) among the Ir(III) complexes, reflecting the sigma-donating ability of the tridentate ligand, ttpy < L1 < L2. The emission quantum yields (phi) of the Ir(III) complexes ranged from 0.037 to 0.19, and the highest phi value (0.19) was obtained for [Ir(L1)(bpy)Cl]2+. Radiative rate constants (k(r)) were 1.2 x 10(4) s(-1) for [Ir(ttpy)2]3+, 3.7 x 10(4) s(-1) for [Ir(L1)(bpy)Cl]2+, 3.8 x 10(4) s(-1) for [Ir(ttpy)(bpy)Cl]2+, 3.9 x 10(4) s(-1) for [Ir(L1)2]3+, and 6.6 x 10(4) s(-1) for [Ir(L1)(L2)]2+. The highest radiative rate for [Ir(L1)(L2)]2+ with the highest contribution of 3MLCT could be explained in terms of the singlet-triplet mixing induced by spin-orbit coupling of 5d electrons in the MLCT electronic configurations.     

Triethylenetetramine penta- and hexa-acetamide ligands and their ytterbium complexes as paraCEST contrast agents for MRI

The ligand triethylenetetramine-N,N,N',N',N',N'-hexaacetamide (ttham) was synthesized with the aim of forming lanthanide complexes suitable as contrast agents for magnetic resonance imaging applications utilizing the chemical exchange-dependent saturation transfer (CEST) effect. It was designed to exclude water molecules from the first coordination sphere and provide a high number of CEST active amide protons per lanthanide ion. The ligand was characterized by its protonation behavior and its complexation properties with ytterbium ions in aqueous solution. The basicity of the ttham backbone amine protons decreases in the order N(central(1)) > N(terminal(1)) > N(terminal(2)) > N(central(2)), as deduced from NMR titration experiments and from a comparison of its protonation constants with those of two ttham derivatives, in which either a terminal (N-benzyl-triethylenetetramine-N,N',N',N',N'-pentaacetamide, 1bttpam) or a central acetamide group (N'-benzyl-triethylenetetramine-N,N,N',N',N'-pentaacetamide, 4bttpam) is substituted with a benzyl group. This protonation sequence results from the combined influence of inductive effects, the intramolecular hydrogen bonding network, and the Coulomb repulsion between protonated ammonium groups. The ytterbium complex of ttham, [Yb(ttham)]Cl(3), is coordinatively frustrated. Due to steric constraints, in addition to the four backbone nitrogen atoms, only three of the four symmetry-equivalent terminal acetamide donors can coordinate simultaneously to the ytterbium ion, and the dangling fourth one exchanges quickly with the other three. The ytterbium complexes of a total of five ligands (ttham, 1bttpam, 4bttpam, 2,2',2'-triaminotriethylaminehexaacetamide (ttaham), and diethylenetriamine-N,N,N',N',N'-pentaacetamide (dtpam)) were studied with respect to their CEST properties. In solution, all of these complexes have a low symmetry. The presence of multiple magnetically different amide groups in each complex prevents the realization of very high CEST effects. These results nevertheless form an excellent basis for a further optimization of this class of ligands.     

Dioxouranium(VI)-carboxylate complexes. Speciation of UO2(2+)-1,2,3-propanetricarboxylate system in NaCl(aq) at different ionic strengths and at t=25 degrees C

The formation constants of dioxouranium(VI)-1,2,3-propanetricarboxylate [tricarballylate (3-), TCA] complexes were determined in NaCl aqueous solutions at 0 < or = I/mol L(-1) < or = 1.0 and t=25 degrees C, by potentiometry, ISE-[H+] glass electrode. The speciation model obtained at each ionic strength includes the following species: ML-, MLH0, ML2(4-) and ML2H3- (M = UO2(2+) and L = TCA). The dependence on ionic strength of protonation constants of 1,2,3-propanetricarboxylate and of the metal-ligand complexes was modeled by the SIT (Specific ion Interaction Theory) approach and by the Pitzer equations. The formation constants at infinite dilution are [for the generic equilibrium p UO22+ + q (L3-) + r H+ = (UO2(2+))p(L)qHr(2p-3q+r); betapqr]: log beta110 = 6.222 +/- 0.030, log beta111 = 11.251 +/- 0.009, log beta121 = 7.75 +/- 0.02, log beta121 = 14.33 +/- 0.06. The sequestering ability of 1,2,3-propanetricarboxylate towards UO2(2+) was quantified by using a sigmoid Boltzman type equation.     

Tetradentate vs pentadentate coordination in copper(II) complexes of pyridylbis(aminophenol) ligands depends on nucleophilicity of phenol donors

The ligand binding preferences of a series of potentially pentadentate pyridylbis(aminophenol) ligands were explored. In addition to the previously reported ligands 2,2'-(2-methyl-2-(pyridin-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)diphenol (H(2)L(1)) and 6,6'-(2-methyl-2-(pyridin-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)bis(2,4-di-tert-butylphenol) (H(2)L(1-tBu)), four new ligands were synthesized: 6,6'-(2-methyl-2(pyridine-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)bis(2,4-dibromophenol) (H(2)L(1-Br)), 6,6'-(2-methyl-2(pyridine-2-yl)propane-1,3diyl)bis(azanediyl)bis(methylene)bis(2-methoxyphenol) (H(2)L(1-MeO)), 2,2'-(2-methyl-2(pyridine-2-yl)propane-1,3diyl)bis(azanediyl)bis(methylene)bis(4-nitrophenol) (H(2)L(1-NO2)), and 2,2'-(2-phenylpropane-1,3-diyl)bis(azanediyl)bis(methylene)diphenol (H(2)L(2)). These ligands, when combined with copper(II) salts and base, form either tricopper(II) species or monocopper(II) species depending on the nucleophilicity of the phenol groups in the ligands. All copper complexes were characterized by X-ray crystallography, cyclic voltammetry, and spectroscopic methods in solution. The ligands in trimeric complexes [{CuL(1)(CH(3)CN)}(2)Cu](ClO(4))(2) (1), [{CuL(1)Cl}(2)Cu] (1a), and [{CuL(2)(CH(3)CN)}(2)Cu](ClO(4))(2) (1b) and monomeric complex [CuL(1-tBu)(CH(3)OH)] (2) coordinate in a tetradentate mode via the amine N atoms and the phenolato O atoms. The pyridyl groups in 1, 1a, and 2 do not coordinate, but instead are involved in hydrogen bonding. Monomeric complexes [CuL(1-Br)] (3a), [CuL(1-NO2)] (3b), and [CuL(1-MeO)Na(CH(3)OH)(2)]ClO(4) (3c) have their ligands coordinated in a pentadentate mode via the amine N atoms, the phenolato O atoms, and the pyridyl N atom. The differences in tetradentate vs pentadentate coordination preferences of the ligands correlate to the nucleophilicity of the phenolate donor groups, and coincide with the electrochemical trends for these complexes.     

二硝酸(N,N,N',N'-四正丁基丁二酰胺)合铀(Ⅱ)酰配合物的合成和结构

合成的配合UO~2[Bu~2NCO(CH~2)~2CONBu~2](NO~3)~2的晶体属四方晶系,a=b=3.3207(8),c=1.0711(4)nm,α=β=γ=90.00(0)°,V=11.811(7)nm^3,D~c=1.65g.cm^-3,Z=16,空间群为14~1/\α.配合物分子中铀酰离子由六个氧原子配位,其中四个来自两个硝酸根,另外两个来自有机配体的两个羰基,两个硝酸根被七原子环排斥而挤在一边,以铀原子为中心的六方双锥结构受到扭曲.     

Molecular design of lipophilic disalicylic acid compounds with varying spacers for selective lead(II) extraction

Lipophilic disalicylic acids 5,5'-decyl-2,2'-[1,2-ethanediylbis(oxy)]bisbenzoic acid (1), 5,5'-decyl-2,2'-[1,3-propanediylbis(oxy)]bisbenzoic acid (2), 5,5'-decyl-2,2'-[oxybis(1,2-ethanediyl-oxy)]bisbenzoic acid (3), 3,5-bis[2'-(2'-carboxyphenoxy)ethyl]-4-oxahexacyclo-[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecane (4), and 1,3-bis[2'-(2'-carboxyphenoxy)ethyl]adamantane (5) are evaluated as selective Pb(II) extractants. The solvent extraction of Pb(II) and of Cu(II) from buffered aqueous solutions of varying pH into chloroform by ligands 1-5 is examined in relation to the molecular structure of the dicarboxylic acid extractant. Ligand 1, with an ethylene spacer between two lipophilic salicylic acid units, exhibits excellent extraction selectivity for Pb(II) over Cu(II). Lengthening the spacer in ligands 2 and 3 diminishes both the extraction efficiency and selectivity. Ligands 4 and 5, with rigid spacer units, show significant reductions in both Pb(II) and Cu(II) extraction. Slope analysis reveals that ligand 1 reacts in a 2:1 stoichiometry with Pb(II) in extraction, which differs from the 1:1 stoichiometries for 2 and 3. The differences in the half extraction pH (DeltapH(1/2)) values for Pb(II) and Cu(II) extraction are 1.29, 0.49, and 0.48 for 1-3, respectively.     

Comparative study of uranyl(VI) and -(V) carbonato complexes in an aqueous solution

Electrochemical, complexation, and electronic properties of uranyl(VI) and -(V) carbonato complexes in an aqueous Na2CO3 solution have been investigated to define the appropriate conditions for preparing pure uranyl(V) samples and to understand the difference in coordination character between UO22+ and UO2+. Cyclic voltammetry using three different working electrodes of platinum, gold, and glassy carbon has suggested that the electrochemical reaction of uranyl(VI) carbonate species proceeds quasi-reversibly. Electrolysis of UO22+ has been performed in Na2CO3 solutions of more than 0.8 M with a limited pH range of 11.7 < pH < 12.0 using a platinum mesh electrode. It produces a high purity of the uranyl(V) carbonate solution, which has been confirmed to be stable for at least 2 weeks in a sealed glass cuvette. Extended X-ray absorption fine structure (EXAFS) measurements revealed the structural arrangement of uranyl(VI) and -(V) tricarbonato complexes, [UO2(CO3)3]n- [n = 4 for uranyl(VI), 5 for uranyl(V)]. The bond distances of U-Oax, U-Oeq, U-C, and U-Odist are determined to be 1.81, 2.44, 2.92, and 4.17 A for the uranyl(VI) complex and 1.91, 2.50, 2.93, and 4.23 A for the uranyl(V) complex, respectively. The validity of the structural parameters obtained from EXAFS has been supported by quantum chemical calculations for the uranyl(VI) complex. The uranium LI- and LIII-edge X-ray absorption near-edge structure spectra have been interpreted in terms of electron transitions and multiple-scattering features.     

Comparison of the self-exchange and interfacial charge-transfer rate constants for methyl- versus tert-butyl-substituted Os(III) polypyridyl complexes

Differences in the self-exchange and interfacial electron-transfer rate constants have been evaluated for a relatively unhindered Os(III/II) redox system, osmium(III/II) tris(4,4'-di-methyl-2,2'-bipyridyl), [Os(Me2bpy)3]3+/2+, relative to those of a relatively hindered system, osmium(III/II) tris(4,4'-di-tert-butyl-2,2'-bipyridyl), [Os(t-Bu2bpy)3]3+/2+. In contrast to the predicted increase in rate constant by a factor of 2-3 due to the difference in reorganization energy of the two complexes, introduction of the tert-butyl functionality decreased the self-exchange rate constant, as measured by NMR line-broadening techniques, by a factor of approximately 50 as compared to that of the analogous methyl-substituted osmium complex. Steady-state current density versus potential measurements, in conjunction with differential capacitance versus potential measurements, were used to compare the interfacial electron-transfer rate constants at n-type ZnO electrodes of [Os(t-Bu2bpy)3]3+/2+ and [Os(Me2bpy)3]3+/2+. The interfacial electron-transfer rate constant for the reduction of [Os(t-Bu2bpy)3]3+ was 100 times smaller than that for [Os(Me2bpy)3]3+. The results indicate that the tert-butyl group can act as a spacer on an outer-sphere redox couple and significantly decrease the electronic coupling of the electron-transfer reaction in both self-exchange and interfacial electron-transfer processes.