Thermodynamics of the Extraction of U(VI) by N,N′-Didecanoylpiperazine

A novel extractant, N, N-didecanoylpiperazine (DDPEZ), was synthesized for the first time. The extraction of U(VI) by DDPEZ from aqueous nitric acid media in carbon tetrachloride has been studied. The dependence of extraction distribution ratio on concentration of aqueous nitric acid, extractant, salting-out agent and temperature was investigated and the enthalpy of the extraction was calculated.     

Kinetics and mechanism of the anation of (αβ)-hydroxo(tetraethylenepentamine)cobalt(III) by thiosulfate, the base hydrolysis of the (sulfur-bonded) thiosulfato(tetraethylenepentamine)-cobalt(III) and photochemistry of oxygen and sulfur-bonded thiosulfato complexes

Summary The reaction of ()-(tetren)CoOH²⁺ with S₂O ₃ ^2- in the 7.25–8.28 pH range at 20–40 °C yielded S- (yellow) and O- (purple) bonded thiosulfato(tetren)cobalt(III) complexes, the former in larger quantities. The rate determining step is preceded by diffusion-controlled ion-pair [(tetren)CoOH²⁺,S₂O ₃ ^2- ] formation. Replacement of coordinated OH^- by S₂O ₃ ^2- is interpreted in terms of an internal conjugate base mechanism: (tetren)CoOH²⁺ (tetren-H)CoOH ₂ ²⁺ , the reactive amido conjugate base being generated by intramolecular proton transfer from the coordinated NH site.In acid medium the S-bonded (tetren)Co(S₂O₃)⁺ is highly stable to redox decomposition, in contrast to its pentaammine analogue. The complex however, undergoes base hydrolysis yielding the corresponding hydroxo complex. The rate and activation parameters for the base hydrolysis have been reported. Photolysis of O- and S-bonded isomers of [(tetren)CoS₂O₃]⁺ in acidic medium at 254 and 313 nm, respectively, yielded aquation products accompanied by some decomposition of S₂O ₃ ^2- .     

Analysis of pigments and coverings by X-ray diffraction (XRD) and micro Raman spectroscopy (MRS) in the cemetery of Tutugi (Galera, Granada, Spain) and the settlement convento 2 (Montemayor, Córdoba, Spain)

This paper focuses on the identification of the composition of the coverings and pigments of two archaeological sites. The sites researched here lie in Andalusia and show two contexts, which have a highly symbolic and ritual meaning. The first, Convento 2 (Montemayor, Córdoba), dates back to the period of formation of the Iberian Culture (VIIth century b.c.). The second is the cemetery of Tutugi (Galera, Granada), of the mid-Iberian period (IVth century b.c.). The analytical procedure consisted in combined and complementary use of XRD and MRS. This allowed to identify the materials used, namely hematite, goethite, coal, gypsum and calcite. Identification of these materials proves essential for the restoration and musealization of both archaeological sites.     

Co-crystal of (R,R)-1,2-cyclohexanediol with (R,R)-tartaric acid,a key structure in resolution of the (±)-trans-diol by supercritical extraction,and the related ternary phase system

A novel co-crystal of trans-(R,R)-1,2-cyclohexanediol and (R,R)-tartaric acid (with 1:1 molar ratio, 1) has been found to be a key crystalline compound in the improved resolution of (±)-trans-1,2-cyclohexanediol by supercritical fluid extraction. The molecular and crystal structure of this co-crystal, which crystallizes in orthorhombic crystal system (space group P2₁2₁2₁, a = 6.7033(13) Å, b = 7.2643(16), c = 24.863(5), Z = 4), has been solved by single crystal X-ray diffraction (R = 0.064). The packing arrangement consists of two dimensional layers of sandwich-like sheets, where the inner part is constructed by double layers of tartaric acids which hydrophilicity is “covered” on both upper and bottom side by cyclohexanediols with the hydrophobic cyclohexane rings pointing outward. Thus, a rather complex hydrogen bonding pattern is constructed. The relatively high melting point (133 °C) observed by both simultaneous TG/DTA and DSC, and the main features of FTIR-spectrum of 1 are explained by the increased stability of this crystal structure. DSC studies on binary mixtures of co-crystal 1 with (R,R)-1,2-cyclohexanediol or (R,R)-tartaric acid, revealed eutectic temperatures of T_eu = 100 or 131 °C, respectively. Between (S,S)-1,2-cyclohexanediol and (R,R)-tartaric acid a eutectic temperature of T_eu = 85 °C have also been observed. The phase relations have been confirmed by powder X-ray diffraction, as well.     

Unprecedented water addition to the α,β-unsaturated enone bond, mediated by the combination of carbonate and platinum(II)

The cytostatic compounds cis-[Pt(A9pyp)(dmso)Cl(2)] (1) and [Pt(A9pyp)(dmso)(cbdca)] (2) (A9pyp=(E)-[1-(9-anthryl)-3-(2-pyridyl)-2-propenone) as carrier ligand; cbdca=cyclobutane dicarboxylate) have been found to add water across the enone C==C bond of the ligand A9pyp. The water addition occurs in the presence of carbonate buffer, and has been followed in detail using NMR and ESI-MS spectroscopy. The spectroscopic data clearly indicate that the platinum(II) ion, the carbonate species, and the proximity of the enone C==C bond to the metal ion, are all required for this unusual hydration. A difference in kinetics is observed between chloride and cbdca, showing that the Pt-ligand dissociation plays an important role in the hydration kinetics.     

Modulating the light switch by (3)MLCT-(3)ππ* state interconversion

The spectroscopic, electronic, and DNA-binding characteristics of two novel ruthenium complexes based on the dialkynyl ligands 2,3-bis(phenylethynyl)-1,4,8,9-tetraaza-triphenylene (bptt, 1) and 2,3-bis(4-tert-butyl-phenylethynyl)-1,4,8,9-tetraaza-triphenylene (tbptt, 2) have been investigated. Electronic structure calculations of bptt reveal that the frontier molecular orbitals are localized on the pyrazine-dialkynyl portion of the free ligand, a property that is reflected in a red shift of the lowest energy electronic transition (1: λ(max) = 393 nm) upon substitution at the terminal phenyl groups (2: λ(max) = 398 nm). Upon coordination to ruthenium, the low-energy ligand-centered transitions of 1 and 2 are retained, and metal-to-ligand charge transfer transitions (MLCT) centered at λ(max) = 450 nm are observed for [Ru(phen)(2)bptt](2+)(3) and [Ru(phen)(2)tbptt](2+)(4). The photophysical characteristics of 3 and 4 in ethanol closely parallel those observed for [Ru(bpy)(3)](2+) and [Ru(phen)(3)](2+), indicating that the MLCT excited state is primarily localized within the [Ru(phen)(3)](2+) manifold of 3 and 4, and is only sparingly affected by the extended conjugation of the bptt framework. In an aqueous environment, 3 and 4 possess notably small luminescence quantum yields (3: ?(H(2)O) = 0.005, 4: ?(H(2)O) = 0.011) and biexponential decay kinetics (3: τ(1) = 40 ns, τ(2) = 230 ns; 4: τ(1) ～ 26 ns, τ(2) = 150 ns). Addition of CT-DNA to an aqueous solution of 3 causes a significant increase in the luminescence quantum yield (?(DNA) = 0.045), while the quantum yield of 4 is relatively unaffected (?(DNA) = 0.013). The differential behavior demonstrates that tert-butyl substitution on the terminal phenyl groups inhibits the ability of 4 to intercalate with DNA. Such changes in intrinsic luminescence demonstrate that 3 binds to DNA via intercalation (K(b) = 3.3 × 10(4) M(-1)). The origin of this light switch behavior involves two competing (3)MLCT states similar to that of the extensively studied light switch molecule [Ru(phen)(2)dppz](2+). The solvent- and temperature-dependence of the luminescence of 3 reveal that the extended ligand aromaticity lowers the energy of the (3)ππ* excited state into competition with the emitting (3)MLCT state. Interconversion between these two states plays a significant role in the observed photophysics and is responsible for the dual emission in aqueous environments.     

A Further Investigation into Intramolecular Process of Mg( Ⅱ )-, Sc( Ⅲ )-, Y( Ⅲ )-, In ( Ⅲ )-and Pb( Ⅲ )-CyDTA Complexes by the Method of Dynamic NMR

The intramolecular process of Mg ( Ⅱ ) - , Sc ( Ⅲ ) - , Y ( Ⅲ ) - , In(Ⅲ)-and Pb ( Ⅱ )-trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA) complexes was studied by the method of proton dynamic NMR(DNMR). The top limit of. the experimental temperature range of deuterium oxide solutions was extended from 100℃ to 167 ℃ instead of the previous 100 ℃ by using sealed, thick-walled tubes to observe experimental phenomena further. It was found that another intramolecular process, i. e. B, R (Bonded State, Rotational State) conversion, exists in these complexes formed by polyaminepolycarboxylic ligands in addition to △,A conversion and nitrogen inversion. A quantitative treatment was proposed to estimate the relative populations of acetate groups in B and R states.     

(E)-Selective hydrolysis of (E,Z)-α,β-unsaturated nitriles by the recombinant nitrilase AtNIT1 from Arabidopsis thaliana

From stereoisomeric α,β-unsaturated nitriles (E,Z)-1, the recombinant nitrilase AtNIT1 from Arabidopsis thaliana hydrolyses the (E)-isomers exclusively to the corresponding (E)-carboxylic acids (E)-2 with high specificity. The (E)-selectivity can also be utilised for the preparation of the isomerically pure nitriles (Z)-1. From (E,Z)-2-hydroxycinnamonitrile (E,Z)-3, the otherwise difficult obtainable (Z)-3 was prepared in 66% isolated yield. With β,γ-unsaturated (E,Z)-3-heptenenitrile (E,Z)-4, however, (E)-selectivity was not observed. AtNIT1 exhibits not only diastereoselectivity but also regioselectivity. From a mixture of the four isomers A–D of 3-(2-cyanocyclohex-3-enyl)propenenitrile 6, exclusively isomer D ((E)-cis-6) was hydrolysed to 3-(2-cyanocyclohex-3-enyl)propenoic acid (E)-cis-7, as stated by X-ray crystal structure. Only after complete conversion of D and high enzyme concentrations, isomer C ((E)-trans-6) was hydrolysed to a small extent.     

Kinetics and mechanism of the oxidation of L-ascorbic acid by the N,N′-ethylenebis(salicylideneiminato)manganese(III) complex in aqueous solution

Summary The kinetics of oxidation of l-ascorbic acid by the N,N-ethylenebis(salicylideneiminato) manganese(III) complex have been studied over the 4.5–9.3 pH range. An intermediate ascorbate complex was formed which had an inhibiting effect on the rate of the redox reaction. The rapid formation of this intermediate was followed using the stopped-flow technique, whereas its slow decomposition was monitored using a conventional spectrophotometer. The formation of this intermediate was strongly pH dependent. Addition of sodium perchlorate and sodium dodecyl sulphate (anionic surfactant) affected the reaction rate. A probable mechanism comprising both the intermediate formation and the overall redox reaction is discussed.     

Kinetic study on the ligand exchange reactions between bis(alkylxanthato)palladium(II)and bis(N,N-dialkyldithiocarbamato)palladium(II)by high-performance liquid chromatography

The rate constants and equilibrium constants of ligand exchange reactions between his(alkylxanthato)palladium(Ⅱ),Pd(S_2COR)_2(R=Am,n-Hex,Bz),and bis(N,N-dialkyldithiocarbamato)palladium(Ⅱ),Pd(S_2CNR_2)_2(K=Et,n-Pr,n-Bu),in chloroform solution have been determined ina temperature range of 20—50°C by means of high-performance liquid chromatography.It was foundthat both the forward and reverse reactions are of second order.All of the equilibrium constants Kdetermined are 10.3±1.0,much greater than the value(K=4)calculated statistically which indicatesthat the ternary complexes are more stable than the binary complexes.The experimental resultsrevealed that the reaction rate decreases with the increase in the size of R and R~1 groups and the latterare more remarkable,consistent with the deduction of steric effect.The activation parameters ofthe reactions have been calculated.In reaction series(11)and(12)(in the text)the isokinetic tempera-tures B=390±8K and β=346±15 K have been observed respectively.A plausiblemechanism in-volving an eight-membered ring intermediate has been proposed on the basis of experimental results.     

Tuning the Photoluminescence of Zn(Ⅱ) Coordination Polymers by Changing the Coordinated Solvent

By using solvothermal method,two new Zn(Ⅱ) coordination polymers based on 2,5-furandicarboxylic acid(H_2FDA) ligand,[Zn(FDA)(CH_3OH)]_n(1) and [Zn_2(FDA)_2(CH_3CH_2OH)_2]_n(2),were synthesized and structurally characterized by single-crystal X-ray diffraction as well as elemental analysis and IR.Complexes 1 and 2 are isostructural coordination polymers with two-dimensional sheet structures bridged by the protonated carboxylates ligands.The 2D network can be rationalized as a 3-c net with Schl?fli symbol is 82·10.Although 1 and 2 are isostructural,the photoluminescent intensity of 2 is almost twice that of 1 due to the difference of coordinated solvents.     

Ternary surface complexes by the E(%)-pH curve method

A new method for the study of ternary surface complexes at liquid-solid interface,the E(%)-pH curve method,was proposed.Four types of E(%)-pH curves,namely,phenomenon of left-right shifts of S-shaped curve,V-shaped curve,monodirection shift curve and X-shaped curve,were discovered.Correspondingly,apart fromtype (Ⅰ) ternary surface complex -S-O-M-L and type (Ⅱ) ternary surface complex -S-L-M,a newtype of ternary surface complex -S-O-L-M was discovered.     

Structural Relationships Afforded by the Coordination of 2,2′-Bipyridine to the (Iminodiacetato)Copper(II) Chelate: Synthesis,Structure and Properties of (2,2′-Bipyridine) (N-(2-Hydroxyethyl)Iminodiacetato) Copper(II)Tetrahydrate

Abstract

The stoichiometric reaction of copper(II) hydroxycarbonate, N-(2-hydroxyethyl)iminodiacetic acid [H₂heida?HOCH₂CH₂N(CH₂CO₂H)₂)] and 2,2′-bipyridine (bipy) in water yields crystalline (2,2′-bipyridine)(N-(2-hydroxyethyl)iminodiacetato)copper(II) tetrahydrate, [Cu(heida)-(bipy)] · 4H₂O (compound I). This was studied by TG analysis (with FT-IR study of evolved gases), IR, electronic and ESR spectra, magnetic susceptibility data and single crystal X-ray diffraction methods. The compound crystallises in the triclinic system, space group P1, a = 7.011(2), b = 12.586(3), c = 13.052(3) Å, α = 62.14(1), β = 80.51(2), γ = 77.09(2)°, Z = 2, final R ₁ = 0.051 for 3900 independent reflections. The Cu(II) atom exhibits an asymmetric, elongated, octahedral coordination (type 4+1 + 1), and bipy acts as an N,N-bidentate ligand supplying two among the four closest donor atoms of the metal (Cu-N bond lengths of 1.994(2) and 2.053(2) Å); heida plays an N,O,O′,O″-tetradentate chelating role (bond lengths Cu?N = 2.075(2), Cu-O(carboxyl) = 1.958(2), Cu-O′(carboxyl) = 2.337(2) and Cu-O″(hydroxyl) = 2.459(2) Å). The effective bidentate chelation of bipy imposes fac-chelation to the iminodiace-tate moiety of heida in I, as previously reported in mixed-ligand complexes having a 1:1:2 Cu(II)/IDA/N(heterocyclic) or a 1/1/(1 + 1) Cu/IDA/(N-heterocyclic + N-aliphatic) donor ratio. The tetradentate role of heida in I reveals its noticeable conformational flexibility. The crystal features a hydrogen bond network forming supra-molecular chains extending along the a axis. These are linked by two symmetry-related hydrogen bonds of the type O(hydroxyl)-H…O′(carboxyl) between two adjacent complex units (symmetry code i=-x, -y+1, -z+1), related to each other by an inversion centre.     

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-S(CH(2) )(3) S] (PNP(R) ={Ph(2) PCH(2) }(2) NR, R=Me, Ph)

The behavior of [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-pdt)] (PNP(R) =(Ph(2) PCH(2) )(2) NR, R=Me (1), Ph (2); pdt=S(CH(2) )(3) S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3) SO(3) H or CH(3) SO(3) H; the cation with a bridging hydride ligand, 1?μH(+) (R=Me) or 2?μH(+) (R=Ph) is obtained rapidly. Only 1?μH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4) ?Et(2) O or CF(3) SO(3) H, which results in a positive shift of the proton reduction by approximately 0.15?V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2) -H(2) species in the Fe(I) Fe(II) state. When R=Ph, the bridging hydride cation 2?μH(+) cannot be protonated at the amine function by HBF(4) ?Et(2) O or CF(3) SO(3) H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2?μH(+) . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7?s(-1) ) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.     

Measurement of isomeric-yield ratios for the 197Au(γ,n)196m,gAu reactions induced by bremsstrahlung

We measured isomeric-yield ratios for the ¹⁹⁷Au(γ,n)^196m,gAu reactions with bremsstrahlung energies of 50-, 60-, 70- MeV, and 2.5-GeV at the two different electron linac of the Pohang accelerator laboratory by using the activation method. The photons were produced when a pulsed electron beam hit a thin tungsten target. The well-known photoactivation method was used and hence the induced activities in the irradiated foils were measured with the high-resolution γ-ray spectrometric system consisting of lithium drifted high-purity Germanium detector and a multichannel analyzer. The measured isomeric-yield ratios for the ¹⁹⁷Au(γ,n)^196m,gAu reactions were (4.95 ± 0.51) × 10^?4, (5.72 ± 0.72) × 10^?4, (6.03 ± 0.50) × 10^?4, and (9.27 ± 0.83) × 10^?4 for 50-, 60-, 70-MeV, and 2.5-GeV bremsstrahlung energies, respectively. The present results measured with the bremsstrahlung energy higher than 60-MeV are the first measurement.     

Relative reactivities of halogen-substituted substrates (R-Br,R-C1) toward the halophilic attack by a carbanion

Relative reactivities of bromine-substituted substrates (R-Br) or chlorine-substituted substrates (R-CI) toward bromophilic or chlorophilic attack by a carbanion have been evaluated by the intermolecular competition kinetics. Relative reactivity orders are CF3CFBr2 >CF3CBr3≥CBr4 > CHBr3 > CF3CFBrCF2Br > CF2Br2 > BrCF2CF2Br > BrCH2CO2Et≥ BrCF2CFHBr > CH2Br2 > BrCH2CH2Br, and CI3CNO2 > CI3CCN > CI3CCOPh > cyclo-C5CI6> CI3CCOCI > CCI3CF2CI > CCI3CF3 ≥ CCI4 > CCI3CCI3 ≥ CCI3(CF2)2CI > CI3CCOCCI3 > CCI3(CF2)6CI > CI3CCO2Et > CI3CF > CI3CPh>CI3CCH2O2CCH3.     

Synthesis of pyrazolines by the reactions ofα,β-enones with diazomethane and hydrazines (review)

The first representatives of pyrazolines were synthesized in the last century. These nitrogen-containing heterocyclic compounds became important in the development of different bioactive substances. For this reason, various procedures have been worked out for their synthesis. In the present article we summarize those synthetic methods providing 1- or 2-pyrazolines by the reactions of ,-unsaturated ketones with diazomethane or hydrazine derivatives.Department of Organic Chemistry, Kossuth Lajos University, Egyetem ter I, H 4010 Debrecen, Hungary. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 747–759, June, 1997.     

Study of the copper(II)-Aztreonam™ system by potentiometry and spectrophotometry,and structural characterization by 13C NMR relaxation

Potentiometric and spectrophotometric results obtained for the Cu(II)-Aztreonam system give a clear indication of the cheating properties of this antibiotic toward the Cu²⁺ ion, coordinated already at pH ≌ 2. Only one single complex of 1:1 stoichiometry is formed. Measurements of ¹³C relaxation rates allow us to attribute a coordination scheme via the carboxylic and aminic groups.