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1.
Alessandro de Robertis Concetta de Stefano Rosario Scarcella Carmelo Rigano 《Thermochimica Acta》1984,80(2):197-208
The formation constants for the complexes Mg2+ -, Ca2+ -, Sr2+ - and Ba2+ - succinate (succ2−) have been determined by potentiometric measurements, in aqueous solution, at different temperatures and ionic strengths. The species [M(succ)]0 and [M(succ)H]+ were found for all systems. For the stability constant the ionic strength dependence has been found, and general parameters for the relation log β = f(I) have been obtained. From the temperature dependence of stability constants ΔH values have been deduced. The procedure adopted in calculating all the thermodynamic parameters for the systems under study, where weak complexes are formed, is discussed. The stability of the complexes follows the order Mg < Ca Sr ≈ Ba. 相似文献
2.
The 17O and 14N paramagnetic relaxation rates and chemical shifts of glycine as well as of water, in aqueous solutions of Co(II), Cu(II), and Mn(II) were measured as a function of pH, temperature and metal ion concentration; the relaxation results were fitted to a theoretical equation linking the Swift-Connick equation to the stability constants of all major complexes in equilibrium. As a result, the stability constants of all major complexes were determined, and from the temperature-dependent measurements the thermodynamic parameters for some of these complexes were also calculated. In addition to the bidentate complexes ML+, ML2 and ML3−, monodentate complexes of the type MHL2+ and M(HL)22+, mixed complexes of the type MHL2+ and MHL3 were also considered. In the case of the Cu(II)-glycine system at pH> 12 two additional species were considered, namely ML2(OH)− and ML2(OH)22−, suggested by the drastic reduction of the paramagnetic broadening in that pH range. 相似文献
3.
The ion-pair extraction equilibria of dibenzo-18-crown-6 (DB18C6) complexes of Na+, K+, Rb+ and Cs+ (M+) with picrate ion (Pic−) into 1,2-dichloroethane (1,2-DCE) have been studied at 25.0°C. In the case of the Rb+ and Cs+ systems, the extraction results were interpreted by taking into consideration the formation of a (DB18C6)2 -M+ complex in 1,2-DCE. The thermodynamic constants of extraction,
, and ion-pair formation in 1,2-DCE,
, of ion pairs of the DB18C6-M+ complexes with Pic− were determined. By using the distribution coefficient of M+·Pic− the thermodynamic formation constants of the DB18C6-M+ complexes in 1,2-DCE,
, were evaluated. Consequently the component equilibrium constants of the ion-pair extraction were completely determined and a contribution of these constants to the difference of
value was discussed. The
value in 1,2-DCE is quite high compared with that in solvating solvents and log
decreases linearly with increasing Gutmann donor number of solvents. 相似文献
4.
Ion-pair formation constants (KMLA mol−1 dm3) of Na+– and K+–18-crown-6 ether (18C6) complexes with MnO4− in water (w) were determined potentiometrically at 25 °C. Simultaneously, extraction constants (Kex mol−2 dm6) of the permanganates with 18C6 from w into 1,2-dichloroethane at 25 °C were obtained from the spectrophotometric determination of distribution ratios of the permanganates. These Kex values were divided into KMLA and other three component equilibrium constants and thereby extraction-selectivity and -ability were discussed in comparison with corresponding metal picrate–18C6 extraction systems reported before. 相似文献
5.
The stability constants of the Cu2+, Zn2+, Ni2+ and Mu2+ complexes of N-phenyl-o-methoxybenzohydroxamic acid at 30° in 50% v/v aqueous dioxan are: log K1 10·45, 8·16, 7·52, 6·33; log K2 8·90, 6·70, 6·01, 5·59 (for the ions in the order given). 相似文献
6.
The ligand monoaza-12-crown-4 ether (A12C4) was studied in aqueous solution at 298 K and an ionic strength of 0.5 mol dm−3 in the presence of an excess of sodium ion (0.5 mol dm−3 NaNO3). The protonation constant of A12C4, determined by glass electrode potentiometry (GEP) in the same background electrolyte, was found to be log K=9.36±0.03. Polarographic experimental and calculated complex formation curves (ECFC and CCFC) for labile metal–ligand systems, studied at a fixed total ligand (LT) to total metal (MT) concentration ratio and varied pH, were used for the modelling of the metal species formed and the refinement of their stability constants. The metal–ligand model and formation constants are optimised by solving mass-balance equations written for the assumed model and by fitting the CCFC to the ECFC. The CCFC can be generated for any metal–ligand model, including polynuclear metal species, for any LT:MT ratio, and for more than one ligand competing in the complex formation reaction. Three lead complexes with the ligand A12C4, viz. PbL2+, PbL(OH)+ and PbL(OH)2, were found and their overall stability constants from differential pulse polarography (DPP), as log β, were estimated to be 3.75±0.03, 9.30±0.05 and 12.70±0.05, respectively. Two copper complexes CuL2+ and CuL(OH)2 are reported and their stability constants (from DPP) were estimated to be 6.00±0.05 and 21.77±0.1, respectively. Two cadmium complexes CdL2+ and CdL(OH)+ are reported. The stability constant for CdL2+ was estimated from DPP and GEP as 2.80±0.05 and 2.68±0.03 (the latter value was obtained from a few potentiometric experimental points), respectively, and the stability constant for CdL(OH)+ from DPP was estimated to be 7.88±0.05. GEP could not be used for the stability constants determination of other metal complexes studied because of precipitation occurring prior the completion of a complex formation reaction. 相似文献
7.
J. M. Gonzlez LaFuente E. Fernndez Martínez J. A. Vicente Prez S. Fernndez Fernndez A. J. Miranda Ordieres J. E. Snchez Uría M. L. Fernndez Snchez A. Sanz-Medel 《Analytica chimica acta》2000,410(1-2):135-142
The proposed method for cyanide determination at the ultratrace level by differential pulse voltammetry is based in the sensitivity enhancement obtained when both Cu(II) and EDTA are present in the background electrolyte. Comparison of the detection limits and linear dynamic ranges using the conventional borate (pH 9.75), and the proposed borate-EDTA–Cu(II) background electrolytes was carried out. Best results have been obtained with the addition of 0.5 mmol l−1 EDTA and 0.02 mmol l−1 of Cu(II), which allow a detection limit of 1.7 μg l−1 CN− (65 nmol l−1 — absolute detection limit 34 ng) with a precision better than ±2% for a 40 μg l−1 level. Calibration range extended from detection limit up to 100 μg l−1. Cyclic voltammetry indicates that the measured cyanide peak is obtained when the electrogenerated CuCN adsorbed onto the hanging mercury drop electrode surface, is oxidised at positive going potential scan. The method has been successfully applied to various industrial waste waters such as metal-finishing waste waters, water/sand mixtures from cleaning processes of coke production, leachates from wastes obtained from electrolytic cells of aluminium production, and liquors from gold extraction industry. Results obtained by the proposed method showed good agreement with those obtained by the standard methods (ion-selective potentiometry and the spectrophotometric pyridine method). 相似文献
8.
Sarka Langer Evert Ljungstr m Thomas Ellermann Ole J. Nielsen Jens Sehested 《Chemical physics letters》1995,240(5-6):499-505
UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF6 by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σR = (2.6 ± 0.4) × 10−18 cm2 molecule−1 and σRO2 = (4.1 ± 0.6) × 10−18 cm2 molecule−1 (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10−11 cm3 molecule−1 s−1. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO2 are (9.1 ± 1.5) × 10−13, (4.3 ± 1.6) × 10−12 and (1.2 ± 0.3) × 10−11 cm3 molecule−1 s−1, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule. 相似文献
9.
A study on transport, kinetic selectivity and stability in SLM operations using a new carrier, the molecule 2-hydroxy-5-dodecylbenzaldehyde (2H5DBA) in kerosene, is described. A simple transport model is derived to evaluate the mass transfer coefficient in the membrane. Finally a comparison with the di-(2-ethylhexyl) phosphoric acid (D2EHPA) carrier in kerosene is made. The SLM system was employed and tested in the removal of Cu2+ from wastewater by using the operating conditions obtained from L–L extraction tests. Studies on the kinetics of copper extraction by using the 2H5DBA showed that complexation reaction is very fast. Transport tests were performed at different carrier concentrations (10%, 30%, 50% (v/v)) showing the improvement of SLM performance with increasing its concentration. Operating the SLM at optimum conditions (50% (v/v) 2H5DBA concentration in kerosene, feed pH 5, strip pH 2.2) final copper concentrations in the feed and strip phases were, respectively, 2.0 and 47.0 mg L−1, starting from 50 mg L−1 in the feed, meaning a significant up-hill transport. The fluxes (J) were calculated by fitting the experimental data of copper concentration in the feed by an exponential equation. They were used to calculate the transport (kinetic) selectivities of Cu2+ SLM separation over Ni2+, Zn2+ and Mn2+, given by the ratio J0(Cu)/J0(M), where M = Ni, Zn and Mn. The values were 37.4, 48.2 and 42.1, respectively. Transport and stability tests at the optimal carrier concentration by using the 2H5DBA and the D2EHPA in kerosene were carried out to compare them in terms of flux, lifetime and mass transfer coefficients. Experimental data evidenced for 2H5DBA a lower copper flux (8.67 mmol h−1 m−2 versus 36.71 mmol h−1 m−2), a lower lifetime (20 h versus 57 h) and lower mass transfer coefficient in the membrane (3.00 × 10−7 m s−1 versus 2.00 × 10−6 m s−1) but the selectivity of the separation process can overcome the disadvantages. 相似文献
10.
Hayrettin Türk Turgay Tay Hüseyin Berber 《Journal of molecular catalysis. A, Chemical》2000,160(2):323-330
This article gives the degradation rate constants of meso-tetrakis(3,5-disulfonatomesityl)porphinatomanganese(III) X (where X=H2O and/or OH− depending on pH) (MnTMSP) and its β-brominated analogue (MnTMSPBr8) toward the oxidants NaOCl, H2O2, and (CH3)3COOH at various pHs, I=0.2 M and 30°C. In addition, the degradation rate constants of MnTMSP was determined when it was bound to cationic supports — namely, CTAB, a poly(vinylbenzyltrimethylammonium chloride) latex, 2,6-ionene and 2,10-ionene. MnTMSP showed high structural stability toward the peroxides in strong acidic medium and the degradation rate constants were found as low as 10−4 min−1 at pH<1.50. When NaOCl was employed as the oxidant, the pH dependence of the stability of MnTMSP was vice versa and its degradation rate constant was determined as 1.43×10−4 min−1 at pH 14.10. In strong acidic solution, the supports CTAB and latex made the stability of MnTMSP toward the peroxides improve significantly. In strong basic solution, only latex-bound MnTMSP showed higher stability toward NaOCl than the homogeneous MnTMSP. Because MnTMSPBr8 was not stable in solutions having pH higher than 9 and containing no oxidant, its stability was investigated at pH<9 and it showed slightly lower stability toward the peroxides than the non-brominated analogue. 相似文献
11.
Equilibrium constants relative to the binding of Cl− by nine open chain polyammonium cations (di, tri and tetra) were determined by potentiometric measurements (H+-glass electrode), at T=25°C. To this end the protonation constants of these amines were measured in NaCl aqueous solutions, in the ionic strength range 0.1<I≤1 mol dm−3. The different amines (some of which are N-alkyl substituted) were chosen in order to consider several factors affecting the values of protonation constants, the chloride complex formation constants and the dependence on ionic strength of apparent protonation constants. As concerns these last two points, it was found that fully N-alkyl substituted amines behave in a very similar way, with respect to partially or non-substituted ones. Simple linear relationships are reported involving chloride formation constants, parameters for the dependence on ionic strength of protonation constants and charges in polyammonium cations. The complexes formed by two linear polyamines with NO3− have also been studied for comparison. Literature data are examined. 相似文献
12.
Mozaffar Asadi Elham Safaei Bijan Ranjbar Leila Hasani 《Journal of Molecular Structure》2005,754(1-3):116-123
Interaction of N,N′,N″,N-tetramethyltetra-2,3-pyridinoporphyrazinatocopper(II), ([Cu(2,3-tmtppa)]4+) and N,N′,N″,N-tetramethyltetra-3,4-pyridinoporphyrazinatocopper(II), ([Cu(3,4-tmtppa)]4+) with calf thymus DNA was studied in 1 mM phosphate buffer and low ionic strength (5 mM NaCl) at various temperatures by UV-visible and circular dichroism (CD) spectroscopies and viscometric method. The binding constants were determined from the changes in the visible part of porphyrazine complexes spectra using SQUAD software. The values of K have been obtained (7.9±0.4)×104 and (2.2±0.1)×105 M−1 for [Cu(2,3-tmtppa)]4+ and [Cu(3,4-tmtppa)]4+, respectively at 27 °C. The higher affinity of 3,4-isomer of Cu complex towards DNA with respect to the 2,3-isomer was attributed to favorable external positioning of the cationic charges in former, which enables superior interaction with the DNA duplex. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated by van't Hoff equation. The enthalpy and entropy changes were determined, +34.2±3.6 kJ mol−1 and +207.8±12.70 J mol−1 K−1 for [Cu(2,3-tmtppa)]4+ and +49.7±2.1 kJ mol−1 and +267.8±7.9 J mol−1 K−1 for [Cu(3,4-tmtppa)]4+. The existence of extensive hypochromicity, large red shift and negative CD in the visible part of [Cu(3,4-tmtppa)]4+ spectra suggested an intercalation binding mode. Analysis of the moderate hypochromicity, red shift and bisignate CD in the Q-band absorption region of [Cu(2,3-tmtppa)]4+ spectra possibly led us to the coexistence of intercalation and outside binding modes. The influence of the ionic strength on the binding parameters and binding modes was investigated. The results show that increase in ionic strength causes the decrease in the binding constants. It was also concluded that increase in ionic strength affects the binding characteristics of positively charged complexes with DNA.
The increase in DNA viscosity in the presence of Cu–tmtppa complexes is attributed to the lengthening of DNA helix due to the intercalation. This result is consistent with conclusions obtained from the spectroscopic techniques. 相似文献
13.
《Journal of Molecular Structure》2003,650(1-3):49-56
Two novel hydrogen maleato (HL) bridged Cu(II) complexes ∞1[Cu(phen)Cl(HL)2/2] 1 and ∞1[Cu(phen)(NO3)(HL)2/2] 2 were obtained from reactions of 1,10-phenanthroline, maleic acid with CuCl2·2H2O and Cu(NO3)2·3H2O, respectively, in CH3OH/H2O (1:1 v/v) at pH=2.0 and the crystal structures were determined by single crystal X-ray diffraction methods. Both complexes crystallize isostructurally in the monoclinic space group P21/n with cell dimensions: 1 a=8.639(2) Å, b=15.614(3) Å, c=11.326(2) Å, β=94.67(3)°, Z=4, Dcalc=1.720 g/cm3 and 2 a=8.544(1) Å, b=15.517(2) Å, c=12.160(1) Å, β=90.84(8)°, Z=4, Dcalc=1.734 g/cm3. In both complexes, the square pyramidally coordinated Cu atoms are bridged by hydrogen maleato ligands into 1D chains with the coordinating phen ligands parallel on one side. Interdigitation of the chelating phen ligands of two neighbouring chains via π–π stacking interactions forms supramolecular double chains, which are then arranged in the crystal structures according to pseudo 1D close packing patterns. Both complexes exhibit similar paramagnetic behavior obeying Curie–Weiss laws χm(T−θ)=0.414 cm3 mol−1 K with the Weiss constants θ=−1.45, −1.0 K for 1 and 2, respectively. 相似文献
14.
Fluorescence reaction and complexation equilibria between norfloxacin and aluminium (III) ion in chloride medium 总被引:2,自引:0,他引:2
Predrag T. Djurdjevic Milena Jelikic-Stankov Dejan Stankov 《Analytica chimica acta》1995,300(1-3):253-259
Norfloxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid (NORH), reacts with aluminium(III) ion forming the strongly fluorescent complex [Al(HNOR)]3+, in slightly acidic medium. The complex shows maximum emission at 440 nm with excitation at 320 nm. The fluorescence intensity is enhanced upon addition of 0.5% sodium dodecylsulphate. Fluorescence properties of the Al-NOR complex were used for the direct determination of trace amounts of NOR in serum. The linear dependence of fluorescence intensity on NOR concentration, at a NOR to Al concentration ratio of 1:10, was found in the concentration range 0.001–2 μg/ml NOR with a detection limit of 0.1 ng/ml. The ability of aluminium (III) ion to form complexes with NOR was investigated by titrations in 0.1 M LiCl medium, using a glass electrode, at 298 K, in the concentration range: 2 × 10−4 ≤ [Al] ≤ 8 × 10−4; 5 × 10−4 ≤ [NOR] ≤ 9 × 10−4 mol/dm3; 2.8 ≤ pH ≤ 8.3. The experimental data were explained by the following complexes and their respective stability constants, log(β ± σ): [Al(HNOR)], (14.60 ± 0.05); [Al(NOR)], (8.83 ± 0.08); [A1(OH)3(NOR)], (−14.9 ± 0.1), as well as several pure hydrolytic complexes of A13+. The structure of the [Al(HNOR)] complex is discussed, with respect to its fluorescence properties. 相似文献
15.
Reaction of L {L = [24]aneS8, [28]aneS8} with two molar equivalents of [Cu(NCMe)4]X (X− = ClO4−, BF4−, PF6−) in MeCN affords the white binuclear copper(I) complexes [Cu2(L)]2+. A single crystal X-ray structure determination of [CU2([24]aneS8)](BF4)2 shows two tetrahedral copper(I) centres, each of which is coordinated to four thioether sulphur-donors, Cu---S(1) = 2.263(3), Cu---S(4) = 2.363(3), Cu---S(7) = 2.349(3), Cu---S(10) = 2.261(3) Å. The Cu … Cu distance is 5.172(3) Å. A single crystal X-ray structure determination Of [CU2([28]aneS8)](ClO4)2 shows that this complex also contain two tetrahedral copper(I) centres, each coordinated to four thioether sulphur-donors, Cu---S(1) = 2.278(5), Cu---S(4) = 2.333(5), Cu---S(8) = 2.328(5), CU---S(11) = 2.268(5) Å. The Cu … Cu distance of 6.454(3) Å is greater than in [CU2([24]aneS8)]2+ , reflecting the greater cavity size in [CU2([28]aneS8)]2+. Cyclic voltammetry of [CU2([24]aneS8)]2+ and [CU2([28]aneS8)]2+ at platinum electrodes in MeCN (0.1 M nBU4NPF6) shows irreversible oxidations at Epa, = +0.88 V, +0.92 V vs Fc/Fc+, respectively, at a scan rate of 200 mV s−1. Coulometric measurements in MeCN confirm these oxidations to be two-electron (one electron per copper) processes to give binuclear copper(II) species. Oxidation of the binuclear copper(I) precursors with H2SO4 or HNO3 affords ESR-active copper(II) species which presumably incorporate SO42− and NO3− bridges. 相似文献
16.
Vesicles formed from the polymerizable phospholipid, 1,2-diacyl-sn-glycero-3-(N-2(methacryloyloxy)ethyl)-phosphocholine, and the crosslinker, 1,2-dihydroxyethylene-bis-acrylamide, exhibit significantly enhanced stability relative to egg phosphatidylcholine (PC) vesicles. As evidenced by absorbance measurements, methacrylate PC vesicles with a 1 : 75 crosslinker-to-lipid molar ratio retain their integrity in up to 20% (v/v) ethanol as opposed to <10% (v/v) for egg PC vesicles. These crosslinked-polymerized vesicles also remain impermeable to Cd2+ (in the absence of ionophore) for up to 15 mM octyl glucoside. Furthermore, the crosslinked-polymerized vesicles show enhanced stability under osmotic stress. These inprovements in vesicle robustness are attained without dramatic loss in A23187-mediated Cd2+ permeability. The initial Cd2+ permeability of crosslinked-polymerized (1 : 75 crosslinker-to-lipid molar ratio) and egg PC vesicles, with A23187 as ionophore, measured 6.0 × 10−5 and 9.8 × 10−5 cm s−1, respectively. 相似文献
17.
Catherine D. Clark Morton Z. Hoffman D. Paul Rillema Quinto G. Mulazzani 《Journal of photochemistry and photobiology. A, Chemistry》1997,110(3):285-290
The photophysics of three complexes of the form Ru(bpy)3−(pypm)2+ (where bpy2,2′-bipyridine, pypm 2-(2′-pyridyl)pyrimidine and P=1, 2 or 3) was examined in H2O, propylene carbonate, CH3CN and 4:1 (v/v) C2H5OH---CH3OH; comparison was made with the well-known photophysical behavior of Ru(bpy)32+. The lifetimes of the luminescent metal-to-ligand charge transfer (MLCT) excited states were determined as a function of temperature (between −103 and 90 °C, depending on the solvent), from which were extracted the rate constants for radiative and non-radiative decay and ΔE, the energy gap between the MLCT and metal-centered (MC) excited states. The results indicate that *Ru(bpy)2(pypm)2+ decays via a higher lying MLCT state, whereas *Ru(pypm)32+ and *Ru(pypm)2(bpy)2+ decay predominantly via the MC state. 相似文献
18.
The complexation reactions between murexide and Co2+, Ni2+ and Cu2+ in C2H5OH-H2O mixtures have been investigated spectrophotometrically. The formation constants of the 1:1 complexes formed increase in the order Co2+ < Ni2+ < Cu2+ for all solvent mixtures studied, and log Kf is a linear function of the mole fraction of ethanol. The heat of complexation was determined calorimetrically for the nickel and copper complexes. The values of ΔH° and ΔS° are solvent-dependent, and all three complexes have negative ΔH° and positive ΔS° values. 相似文献
19.
A sensitive spectrophotometric method for the determination of uranium with Pyrogallol Red (PGR) and cetyltrimethylammonium bromide (CTAB) is described. The sensitivity of the colour reaction between uranium and Pyrogallol Red is greatly increased in the presence of cetyltrimethylammonium bromide. The blue ternary complex (λmax580 nm) has composition 1:2:4 [U(VI):PGR:CTAB] at pH 5.6. Beer's law is obeyed over the range 19.0-0.24 ppm of uranium and the molar absorptivity is 3.3 × 104 l.mole−1.cm−1 at 620 nm. A tentative structure for the ternary complex is suggested. A simple method is suggested for evaluation of stability constants of such ternary complexes. 相似文献
20.
Tapan Kumar Lal John F. Richardson Mark S. Mashuta Robert M. Buchanan Rabindranath Mukherjee 《Polyhedron》1997,16(24):1248-4336
Synthesis and characterization of a nitrite-bound copper(II) compound [CuL4)2(ONO)]ClO4 have been achieved (L4 = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine]. The bidentate ligand L4 provides a pyridine and a pyrazole donor site; however, they are separated by a methylene spacer. The complex has been structurally characterized and it belongs to only a handful of complexes having nitrito-bound mononuclear copper(II) centre. The metal atom has a distorted square pyramidal geometry with the copper atom displaced from the equatorial plane by 0.25 Å. In MeCN solution the green complex exhibits a broad ligand-field transition at 655 nm with a shoulder at 675 nm and in dichloromethane-toluene glass (80 K) it exhibits an EPR spectral feature characteristic of the unpaired electron in the dx2−y2 orbital. Variable-temperature (80–300 K) magnetic susceptibility measurements in the solid state as well as room temperature measurement in MeCN solution reveal mononuclear magnetically dilute copper(II) centre. When examined by cyclic voltammetry (MeCN solution) it displays electrochemically irreversible CuII---CuI response [cathodic peak potential, Epc (V vs saturated calomel electrode (SCE)): −0.32]. An oxidative response is observed at 1.14 V, probably due to bound-nitrite oxidation and is partially removed to generate a solvated complex at the electrode surface. The latter species gives rise to reversible CuII---CuI redox response [
]. 相似文献