Copper(II) complexes of diaminodiamides in aqueous solution

The basicity constants of N,N′-bis(β-carbamoylethyl)ethylenediamine, N,N′-bis(β-carbamoylethyl)trimethylenediamine, N,N′-bis(β-carbamoylethyl)-1,2-propylenediamine, and N,N′-bis-(β-carbamoylethyl)-2-hydroxyltrimethylenediamine were determined potentiometrically in 0.10 mol dm^?3 NaNO₃ at 25.0°C. The formation of Cu(II) complexes of these ligands and the CuO to CuN bond rearrangements at the two amide sites of these complexes were investigated quantitatively by potentiometric and spectrophotometric techniques under the same conditions. Electronic spectra of the Cu(II) complexes of these ligands and their deprotonated species formed in aqueous solution were measured and discussed.     

Cyclo(L-histidyl-L-histidyl)copper(II) complexes in aqueous solution

Summary The structure of the copper(II) complex cation with HISH₂ [HISH₂ = cyclo(L-histidyl-L-histidyl)] was determined from molecular weight data and n.m.r. and c.d. spectra in aqueous solution. Two HISH₂ moieties ligate to coppervia two nitrogen atoms of the imidazole rings giving rise to two 13-membered chelate rings in solution, a situation seen previously in the crystal.     

Mercury(II) cysteine complexes in alkaline aqueous solution

Mercury(II) complexes with l-cysteine (H(2)Cys) in alkaline aqueous solutions have been structurally characterized by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. The distribution of [Hg(Cys)(n)] (n = 2, 3, and 4) species in approximately 0.09 mol dm(-3) mercury(II) solutions with H(2)Cys/Hg(II) ratios varying from 2.2 to 10.1 has been evaluated by fitting linear combinations of simulated EXAFS functions for the separate complexes to the experimental EXAFS data, aided by (199)Hg NMR and Raman results. For the [Hg(Cys)(2)](2-) and [Hg(Cys)(3)](4-) complexes and the novel four-coordinated Hg(Cys)(4) species that dominates in solutions with excess of cysteine (H(2)Cys/Hg(II) > 5), the mean Hg-S bond distances were found to be 2.35(2), 2.44(2), and 2.52(2) Angstroms, respectively. The minor amount of the linear [Hg(Cys)(2)](2-) complex that can still be discerned in solutions with ratios up to H(2)Cys/Hg(II) = 5 was derived from the distinct S-Hg-S symmetric stretching Raman band at 334 cm(-1). From (199)Hg NMR spectra, the chemical shift of the Hg(Cys)(4) species was estimated to -340 ppm with an amount exceeding 85% in the highest excess of cysteine, consistent with the EXAFS data.     

Cadmium(II) N-acetylcysteine complex formation in aqueous solution

The complex formation between Cd(II) ions and N-acetylcysteine (H(2)NAC) in aqueous solution was investigated using Cd K- and L(3)-edge X-ray absorption and (113)Cd NMR spectroscopic techniques. Two series of 0.1 M Cd(II) solutions with the total N-acetylcysteine concentration c(H2NAC) varied between 0.2-2 M were studied at pH 7.5 and 11.0, respectively. At pH = 11 a novel mononuclear [Cd(NAC)(4)](6-) complex with the average Cd-S distance 2.53(2) ? and the chemical shift δ((113)Cd) = 677 ppm was found to dominate at a concentration of the free deprotonated ligand [NAC(2-)] > 0.1 M, consistent with our previous reports on cadmium tetrathiolate complex formation with cysteine and glutathione. At pH 7.5 much higher ligand excess ([HNAC(-)] > 0.6 M) is required to make this tetrathiolate complex the major species. The (113)Cd NMR spectrum of a solution containing c(Cd(II)) = 0.5 M and c(H2NAC) = 1.0 M measured at 288 K showed three broad signals at 421, 583 and 642 ppm, which can be attributed to CdS(3)O(3), CdS(3)O and CdS(4) coordination sites, respectively, in oligomeric Cd(II)-NAC species with single thiolate bridges between the cadmium ions.     

Thermodynamics of copper(II) dicarboxylate coordination in aqueous solution

Summary The association of H⁺ and Cu²⁺ with malonate, maleate, succinate and phthalate ions has been investigated both potentiometrically and calorimetrically at 25° and I = 0.1 mol dm^–3 (NaClO₄).The structures of the complexes existing in aqueous solution are proposed on the basis of thermodynamic data.     

Mercury(II) penicillamine complex formation in alkaline aqueous solution

The complex formation between mercury(II) and penicillamine (H(2)Pen = 3,3'-dimethyl cysteine) in alkaline aqueous solutions (pH approximately 2) has been investigated with extended X-ray absorption fine structure (EXAFS) and 199Hg NMR spectroscopy. By varying the penicillamine concentration (C(H(2)Pen) = 0.2-1.25 M) in approximately 0.1 M Hg(II) solutions, two coexisting major species [Hg(Pen)2](2-) and [Hg(Pen)3](4-) were characterized with mean Hg-S bond distances 2.34(2) and 2.44(2) A, respectively. The [Hg(Pen)2](2-) complex with two deprotonated penicillamine ligands forms an almost linear S-Hg-S entity with two weak chelating Hg-N interactions at the mean Hg-N distance 2.52(2) A. The same type of coordination is also found for the corresponding [Hg(Cys)2](2-) complex in alkaline aqueous solution with the mean bond distances Hg-S 2.34(2) A and Hg-N 2.56(2) A. The relative amounts of the [Hg(Pen)2](2-) and [Hg(Pen)3](4-) complexes were estimated by fitting linear combinations of the EXAFS oscillations to the experimental spectra. Also their (199)Hg NMR chemical shifts were used to evaluate the complex formation, showing that the [Hg(Pen)3](4-) complex dominates already at moderate excess of the free ligand ([Pen(2-)] > approximately 0.1 M).     

Interaction of palladium(II) with DL-selenamethionine in acidic aqueous solution

Summary The interaction of Pd^II with DL-selenamethionine (SeMet) in acidic aqueous solution was investigated. SeMet was found to act as a bidentate ligand, forming a stable complex with Pd^II. Binding of the metal ion to the selenoether group creates a new chiral centre, which generates two sets of¹H and¹³C n.m.r. methyl resonances for the two diastereoisomers. The²J values for (⁷⁷Se–Me) decreased upon complex formation.     

Binding of hexacyanoferrate(II) by aliphatic amines in aqueous solution

The stability of hexacyanoferrate(II)-amine(methylamine, ethylenediamine, diethylenetriamine and tetraethylenepentamine) was determined potentiometrically. Species Fe(CN)₆(A)H _j ^(j–4) (A=amine) are formed in all the systems investigated, with j=1...n+2 (n=number of aminogroups). Some other complexes Fe(CN)₆(A)_iH_j (with i>1) were also found. The stability of these complexes is fairly high: the full protonated amine species, show for the reaction Fe(CN)₆ ^4- + H_nAⁿ⁺ = Fe(CN)₆(A)H_n ^(n-4) an equilibrium constant given by logK=0.686+2.10n. Factors affecting the stability are discussed in comparison with similar systems, together with the importance of interferences.     

On the structure of Zn(II) and Cu(II) cyanin complexes in aqueous solution

B3LYP/6-31++G(d,p) optimizations on models for the metal cyanin, Cy, complexes [MCy(H₂O) _n ]⁺, (M = Zn(II), Cu(II); n = 2, 3, 4) in aqueous solution indicate that 4 is the most favoured coordination number in both cases. SP -4 and T -4 geometries are nearly isoenergetic for the former, while SP -4 is the only one obtained for the latter. Anionic cyanin displays higher affinity for Cu(II) than for Zn(II) or Mg(II). The electron density reorganization of cyanin model accompanying the complexation process was analyzed by means of the quantum theory of atoms in molecules. This analysis reveals that: (1) the O4′–M bond is stronger than O3′–M; (2) anionic cyanin displays a dual character between 4′-keto-quinoidal and 3′,4′-dienolate resonance forms; (3) Cu(II) takes more electron density than Zn(II) from Cy^? and water ligands; (4) when the coordination number increases, each ligand (Cy^? or water) transfers less electron density; (5) complex formation modifies the electron density in all the atoms of the ligands, but the largest modifications are displayed within the AC bicycle of Cy^?; and (6) a third part of density lost by the Cy^? ligand is removed from hydrogens.     

Electric polarizability of DNA in aqueous salt solution

Monte Carlo simulations are performed to determine the anisotropy of the electric polarizability of a model DNA fragment in aqueous salt solution. By taking into consideration the participation of coions in the electroneutrality condition, at every simulation step, we obtain a list of counterions constituting the net charge arranged in increasing order of their distance from the DNA and calculate the contribution to the dipole moment from the first n counterions in the list. We define a partial polarizability tensor due to these n counterions to understand the origin of the polarizability in close relation to the solution structure. The ionic distributions are described by the counterion condensation theory. Characteristic features of the electric properties of polyelectrolytes are reproduced. The anisotropy of the electric polarizability Deltaalpha of DNA decreases with the addition of salt, yielding values comparable to experiment. The effect of electrophoretic motion of the polyion is examined by estimating its upper limit.     

Fe(II) hydrolysis in aqueous solution: A DFT study

Species arising from Fe(II) hydrolysis in aqueous solution have been investigated using density-functional methods (DFT). The different tautomers and multiplicities of each species have been calculated. The solvation energy has been estimated using the UAHF–PCM method. The hydrolysis free energies have been estimated and compared with the available experimental data. The different hydrolysis species have distinct geometries and electronic structures. The estimated ionization potential of the hydrolyzed species is linearly dependent to the number of hydroxyls present in the complex. The estimated Fe(II)/Fe(III) oxidation potential is in good agreement with previously published results about 0.29 V larger than the experimental value. The results highlight the importance of the chemical speciation in describing electron transfer processes at a molecular level. The PBE/TZVP/UAHF–PCM method has been found to describe correctly the hydrolysis free energies of Fe(II) with an average error about 5 kcal mol⁻¹ from the experimental values.     

Tridentate lysine-based fluorescent sensor for Hg(II) in aqueous solution

A novel homoplastic podand fluorescent sensor based on flexible hydrophilic lysine was prepared. Lysine with two dansyl groups-appended at both ends supplied a possibility for a tridentate binding toward Hg(II) and finally resulted in a unique selectivity to Hg(II) over other transition-metal ions with a hypersensitivity (detection limit 2.0 nM) in neutral buffered aqueous solutions. Notably, the coordination of chloride ion to the complex of sensor-Hg(II) brought forth that the trend in the NMR chemical shift for hydrogen and carbon atoms of the sensor was contrary to the findings in the former reports, which shows upfield shifts for the hydrogens and the alkane carbons but downfield shifts for the dansyl carbons, respectively.     

The kinetics of complexation of nickel(II) and cobalt(II) with cinchomeronate in aqueous solution

The pressure-jump method has been used to determine the rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with cinchomeronate in aqueous solution at zero ionic strength. The forward and reverse rate constants obtained are k_f = 2.27 × 10⁶ M^?1 s^?1 and k_r = 3.81 × 10¹ s^?1 for the nickel(II) complex and k_f = 1.23 × 10⁷ M^?1 s^?1 and k_r = 2.66 × 10² s^?1 for the cobalt(II) complex at 25°C. The activation parameters of the reactions have also been obtained from the temperature variation study. The results indicate that the rate determining step of the reaction is a loss of a water molecule from the inner coordination sphere of the cation for the nickel(II) complex and the chelate ring closure for the cobalt(II) complex. The influence of the pyridine ring nitrogen atom of the cinchomeronate ligand on the complexation of cobalt(II) ion is also discussed.     

Copper (II) adsorption from aqueous solution by herbaceous peat

In this research, the herbaceous peat collected from Gavurgolu peatlands, one of the biggest Turkish peatlands, was utilized as an adsorbent for the removal of copper (II) ions from aqueous solution. Adsorption experiments were conducted under various conditions, i.e., initial concentration, temperature, and pH. While the amount of Cu (II) adsorbed on the peat increased with increasing concentration of Cu (II) ions, it was not markedly affected by temperature and pH. Percentage removal was higher at lower concentration. For example, the maximum percentage removal of Cu (II) ions for initial concentration of 3 x 10(-4) M was 97.04% at 21 degrees C and pH 5.5. The adsorption capacity (Q(0)) of the peat was 4.84 mgg(-1) from Langmuir adsorption isotherm for the concentration range of 3 x 10(-4)-6 x 10(-4) M at 21 degrees C and pH 5.5. The equilibrium time of adsorption of Cu (II) ions was 150 min and independent of concentration and temperature. The amount of Cu (II) adsorbed at equilibrium time did not considerably change with temperature and pH. It was also determined that adsorption isotherm followed both Freundlich and Langmuir. Uptake mechanism of Cu (II) ions by the peat occurs via cation exchange (especially by means of Ca(2+) and Mg(2+)) as well as copper/peat complexation. Adsorption kinetic was consistent with the pseudo-second-order model.     

Complex formation equilibria of some beta-amino-alcohols with lead(II) and cadmium(II) in aqueous solution

A study of complex formation equilibria of some beta-amino-alcohols with lead(II) and cadmium(II) ions at 25 degrees C and in 0.5 M KNO(3) is reported. The amino-alcohols considered are 2-amino-1-propanol, 2-amino-1-butanol, 2-amino-1-pentanol and 2-amino-1,3-propanediol. sec-Buthylamine and 2-amino-1-methoxy-propane have been also considered for comparison. The results are discussed in terms of ligand structure, paying attention to the number of hydroxyl groups and to the length of the alkyl residual. A weak contribution of the alcoholic oxygen in the coordination of cadmium(II) and the presence of a mixed hydroxyl species in lead(II) containing systems are hypothesized.