Stability Constants Of Metal Ions Research Articles

Changed loading conditions and lysate composition improve the purity of tagged recombinant proteins with tacn-based IMAC adsorbents.

These investigations were designed to improve capture efficiency and selectivity in the immobilized metal ion affinity chromatographic (IMAC) purification of tagged recombinant proteins expressed in Escherichia coli cells, utilizing an alternative and novel class of immobilized metal binding ligands. The impact of loading conditions and lysate composition on the IMAC purification of NT1A- or His6 -tagged green fluorescent protein (GFP), using the ligands 1,4,7-triazacyclononane (tacn) and bis(1,4,7-triazacyclononyl)propane (dtnp), charged with Cu(2+) ions, has thus been explored. These findings were compared to the performance of a commercial adsorbent, IMAC Sepharose™ 6 FF, similarly charged with Cu(2+) ions. With the same loading, wash and elution protocols, the tacn- and dtnp-derived adsorbents showed higher selectivity in terms of removal of E. coli host cell proteins than the commercial adsorbent, while low molecular weight components in the crude lysate had a higher impact on the binding capacities of tacn- and dtnp-derived adsorbents. This effect of lysate composition could be reduced through osmotic shock treatment of the E. coli cells prior to lysis. Additionally, the protein-binding capacities of the tacn-based resins were enhanced by increasing their ligand densities. Because both the tacn- and the dtnp-derived IMAC adsorbents exhibit very high metal ion stability constants, under the chromatographic conditions examined, they could be used several times without re-charging with Cu(2+) ions. The results of these studies thus expand the general application scope of tacn-based IMAC resins for use in the capture and purification of tagged recombinant proteins.

Use of ethylenediamine disuccinic acid in metal surface treatment

Hydrogen embrittlement is a continuing problem in the cleaning of metal surfaces. Furthermore, current processes often use strong acids and can have a poor environmental profile. Work is reported to show that ethylenediamine disuccinic acid (EDDS) offers an alternative process medium for a range of metals. The cleaning of the metal surface is environmentally friendly under mild conditions and does not result in hydrogen embrittlement. Rust removal from an iron surface can be achieved at neutral pH using EDDS at a low concentration. EDDS was found to be effective in hard water whereas the effectiveness of other chelants may be reduced by ions causing hardness. The results are consistent with the stability constants for metal ions which indicate that EDDS is selective for iron. Initial studies on aluminium have demonstrated that EDDS can remove metal deposits from an aluminium surface. Operation in neutral conditions means hydrogen is not generated, removing any risk of embrittlement. EDDS also offers some corrosion inhibition of aluminium and does not produce discoloration of the surface.

Application of an IMAC cassette for the purification of N-terminally tagged proteins

This study documents the use of an IMAC cassette for the purification of N-terminally tagged recombinant proteins. The procedures are based on the application of the immobilised macrocyclic ligand, 1,4,7-triazacyclononance (tacn), with a set of new tags specifically designed to interact with the corresponding immobilised Cu2+- and Ni2+-tacn complexes yet with the propensity to be efficiently removed by diaminopeptidases. The macrocyclic ligand, tacn, displays very high metal ion stability constants, whilst the bound metal ion retains the availability of co-ordination sites for interaction with the N-terminally tagged protein. These studies demonstrate that these new tags exhibit higher affinity and thus improved selectivity with both the immobilised Ni2+- and the Cu2+-tacn complexes compared to control tags, such as [His]6. This study thus documents an alternative IMAC platform for the highly selective, efficient and general purification of recombinant proteins.

The effect on the lanthanide luminescence of structurally simple Eu(iii) cyclen complexes upon deprotonation of metal bound water molecules and amide based pendant arms

A series of substituted 1,4,7,10-tetraazacylcododecane ligands 1-4, possessing sensitizing nitrobenzene or naphthalene antennae, as one of the amide pendant arms, and their complexes with europium(III) were synthesised. The protonation constants and the metal ion stability constants of two of these ligands were determined by potentiometric titration. The pK(a) of the water molecules coordinated to the complexed metal ion were determined by both luminescent and potentiometric measurements. The luminescence pH dependence of a further three Eu(III) complexes, 5-7, which lack any antennae, were also studied with the aim of gaining a better understanding of the role of the metal bound water molecules in the luminescence properties of such complexes upon direct excitation of the lanthanide ion. The results from these luminescent measurements demonstrate that the Eu(III) emission was significantly modulated as a function of pH for all the complexes, which we assigned to changes occurring in the coordination environment of the ion within the cyclen system, caused by deprotonation of metal bound water molecules and/or deprotonation of pendent amide arms.

Parameterization and Validation of Solvation Corrected Atomic Radii

The use of correct ion radii is essential for the calculation of free energies of hydration using continuum models. A simple method for the fitting of the ion radii for ions in aqueous solution, which is a consistently difficult problem for implicit solvent models, is described. A new set of ionic radii based on experimental ionic hydration free energies for use in the integral equation formalism of polarizable continuum model (IEFPCM) is derived using B3LYP calculations with a 6-311++g** basis set for Li, Na, K, Be, Mg, and Ca and a SDD basis set for all other metals. The new radii reproduce the experimental stability constants of metal ions and their pyridine, 2,2'-bipyridine, and 1,10-phenanthroline complexes in aqueous solution significantly better than the results obtained using the default UAHF ion radii. The standard deviation (SD) of binding free energies between the calculations and experiments for the metal-ligand complexes in aqueous solution is 3.7 kcal/mol, while the mean unsigned error (MUE) is 3.1 kcal/mol. These results improve on the standard UFF radii for metal atoms, in which the MUE and the SD are 30.4 and 16.9 kcal/mol, respectively. The new ionic radii greatly improve the computational tools for the study of a variety of metals with ligands such as pyridines or calixarenes, which have found significant interest in materials science and for the removal of toxic metals.

Quantitative Cationic Activity Relationships for Predicting Toxicity of Metal Ions from Physicochemical Properties and Natural Occurrence Levels

AbstractQuantitative Cationic Activity Relationships (QCARs) were developed to predict the toxicity of metal ions from physicochemical properties and natural occurrence levels. In vivo toxicity data for different concentrations of nitrate salts of 17 metal ions were developed based on germination of sunflower seeds (F.1. Helianthus annuus ‘Sunspot’) in distilled water. The EC50 data were reported as the concentration giving 50% inhibition of radicle growth 1 day after emergence. Stepwise regression of the toxicity data produced correlations with some physicochemical properties and natural occurrence levels. For physicochemical properties, good results were obtained with the density of the elements, enthalpy of formation of metal sulphides and the stability constants of metal ions with sulphate ($\rm{ r_{{\rm{adj}}.}^2 }$=0.72−0.81). For natural occurrence levels, good results were obtained with metal concentrations in soil, the median elemental composition of soils and the calculated mean of the elemental content in land plants ($\rm{ r_{{\rm{adj}}.}^2 }$=0.69−0.83).

Comparative stability constants for metal ions with tetraazamacrocycles of various ring sizes carrying a single amine or carboxylate pendant group

Acid dissociation constants for a series of tetraazamonocycloalkanes of {13}–{15} membered ring sizes, as well as for a related ‘reinforced’ {15R} tetraazabicycloalkane, each with one primary amine or carboxylate C-pendant, are reported. Further, formation constants with the metal ions ZnII, CdII, PbII, HgII, MnII and CoII have been determined. The ligands differ in their selection of metal ions, reflected in the formation constants for 1:1 complexation (KML). Differences arise in part from the increasing ring size or rigidity and also from the availability of potential pendant O-donors versus N-donors in stepping from amine to carboxylate pendant ligands, implying a role for the pendants in binding the metal ions.

Use of the ion exchange method for the determination of stability constants of trivalent metal complexes with humic and fulvic acids II. Tb 3+, Yb 3+ and Gd 3+ complexes in weakly alkaline conditions

The conditional stability constants for tracer concentrations of Tb(III), Yb(III), and Gd(III) with three soil humic acids, three soil fulvic acids and a fulvic acid from weathered coal were determined at pH 9.0–9.1 (these values are similar to those in calcareous soils) in the presence of NaHCO 3 by using the anion exchange method. It was found that 1 : 1 and 1 : 2 complexes were simultaneously formed in the weakly alkaline conditions. The conditional stability constants of these 1 : 1 and 1 : 2 complexes were calculated from the distribution coefficients of rare earth elements at various concentrations of humate or fulvate. The stability constants indicate the very high stability of trivalent Tb 3+, Yb 3+ and Gd 3+ complexes with humic substances in weakly alkaline conditions. The key parameters necessary for the experimental determination of the conditional stability constants of metal ions with humic substances in the presence of NaHCO 3 by using an anion exchange method were discussed. The conditional stability constants of these 1 : 1 and 1 : 2 complexes were compared in this paper. It was found that stabilities of Tb 3+ 1 : 1 and 1 : 2 complexes with humic acid are greater than the corresponding ones with fulvic acid from the same soil. In addition, the effect of the presence of Ca 2+ as a competitor on the stabilities of 1 : 1 and 1 : 2 complexes of Yb was examined and no pronounced change of stabilities of 1 : 1 complex was found, even though Ca 2+ is in a 10 3 excess to Yb 3+.

Use of the ion exchange method for the determination of stability constants of trivalent metal complexes with humic and fulvic acids—Part I: Eu 3+ and Am 3+ complexes in weakly acidic conditions

The conditional stability constants for tracer concentrations of Eu(III) and Am(III) with a red earth humic acid (REHA), a red earth fulvic acid (REFA) and a fulvic acid from weathered coal (WFA) were determined at pH 5.2–6.4 (such values are similar to those in non-calcareous soils) in the presence of HAc/NaAc or NaNO 3 by using the cation exchange method. It was found that 1 : 1 complexes were predominately formed in weakly acidic conditions. The total exchangeable proton capacities and the degrees of dissociation of these humic substances were determined by using a potentiometric titration method. The key parameters necessary for the experimental determination of the conditional stability constants of metal ions with humic substances in weakly acidic conditions by using the cation exchange method were discussed. The conditional stability constants of 1 : 1 complexes obtained in this paper were compared with the literature data of Am(III) determined by using the ion exchange method and the solvent extraction method and with the stability constants of 1 : 1 complexes of UO 2 2+ and Th 4+ with the same soil humic substances. These results indicate the great stability of bivalent UO 2 2+, trivalent Eu 3+, Am 3+ and tetravalent Th 4+ complexes with humic and fulvic acids in weakly acidic conditions.

New macrocyclic dicopper(II) complex: synthesis, structure and stability

The macrocyclic ligand of 3,6,9,16,19,22-hexaazatricyclo [22.2.2.2 11,14]-triacoltta-1(26),11(12),13,24,27,29-hexaene(L, BP) was synthesized by [2+2] condensation of p-phthaldehyde and diethylenetriamine. This ligand was used as a building block to synthesize dicopper(II) complex [BPCu 2(II)](ClO 4) 4 ( 1). Protonation constants and metal ion stability constants of the mononuclear and dinuclear copper(II) macrocyclic complexes have been measured potentiometrically. Structural investigation indicated that the two Cu(II) ions are separated in the macrocycle ligand evidenced by the crystallographic structure [BPCu 2(II)(Ph–CO 2 −) 2](ClO 4) 2 ( 2). Complex 2 crystallizes in the triclinic space group P1̄, with cell constants a=9.333(3) Å, b=13.841(4) Å, c=19.025(6) Å, α=102.446(5)°, β=90.929(6)°, γ=93.691(5)°, V=2393.6(13) Å 3 and Z=2.

Metal ion stabilities correlate with electron affinity rather than hardness or softness

Quantitative metal ion hardness values allow a test of their correlation with aqueous metal ion stability constants of four hard ligands: hydroxide, fluoride, acetate and ammonia. For all four ligands the correlation is weak and dependent on the metal ion charge. For all but fluoride the correlation is in the wrong direction. Metal ion electron affinity correlates much better than hardness or softness with metal ion stability constants of all four ligands across metal ions of differing charges. Positive deviations of stability constants from the general trend with electron affinity are often due to a decrease in coordination number from that of the aqueous ion. For metal ion stabilities the hard and soft precept needs to be modified along the following lines. With the proviso that the intrinsic strength of binding (including any change in coordination number) is first accommodated, then hard acids may prefer to coordinate with hard bases and soft acids with soft bases, however, in most cases metal ion stabilities are accounted for mainly by the intrinsic strength. In application to stability constants the hard and soft acids and bases concept is of limited utility and often misleading.

Capillary electrophoretic estimation of sulfate stability constants of metal ions and determination of alkali and alkaline earth metals in waters

We studied the influence of sulfate concentration on the effective mobilities of mono-, di- and tervalent ions and developed a method for the determination of sulfate stability constants. Relative migration times of several cations were determined. Capillary electrophoresis with indirect detection using 4 mmol/l copper(II) sulfate, 18-crown-6 and formic acid in background electrolyte was then applied to the determination of the metal ions in mineral and tap waters samples. The results were compared with those of ion chromatography. The CE detection limits were estimated [signal/noise ratio ( S/ N)=3] in the range from 0.59 (for Li) to 12.9 mg/l (for Ba).

Synthesis, Crystal Structure, and Potentiometry of Pyridine-Containing Tetraaza Macrocyclic Ligands with Acetate Pendant Arms

Tetraazamacrocycles containing the pyridine moiety as part of the cyclic backbone and acetate pendant arms were prepared. The resulting products were characterized by high resolution NMR (‘H and I3C) spectroscopy and single-crystal X-ray diffraction. Single-crystal X-ray diffraction data were obtained for the following compounds: py[l2]aneN4*HC1, C I I H I ~ N ~ C ~ , orthorhombic Pnma (No. 62), a = 10.304(6) A, b = 9.160(2) A, c = 13.552(2) A, Z = 4, Mo Ka, ;1 = 0.710 69, R = 0.037, R, = 0.036; and BP2A.2HC1-3H20, C18H22N404c ~ ~ . ~ H ~ o , triclinic pi (NO. 21, u = 10.201(0) A, b = i3.267(3) A, c = 8.612(6) A, a = 97.676(2)”, p = 105.821(0)”, I. = 86.363(7)”, Z = 2, Mo Ka, = 0.710 69, R = 0.039, R , = 0.038. In addition, protonation constants (log KH~L) and metal ion stability constants (log KML) for BP2A (log KH,-L = 9.57, 5.99, 2.59, 2.22; log KMgL = 8.9; log K c ~ L = 10.0; log KGdL = 14.5) and PC2A (log KH,-~L = 12.5, 5.75, 3,28, 2.38, -1; log KMgL = 8.4, log Kc& = 10.0, log KGdL = 16.6) were determined using potentiometric and NMR pH titrations. These values agree well with previously reported literature values for analogous ligand systems.

Approximation of weak stability constants of paramagnetic complexes by spin-lattice relaxation measurements of water protons

The literature was briefly reviewed concernling the determination of stability constants of metal ions with various complexones using water proton relaxation methods. Experimentally, weak stability constants (Kstab) of ethylenediaminetetraacetic acid (EDTA) and citric acid complexes with several transition and lanthanide ions were obtained at constant pHvia measurements of spin-lattice relaxation times (T1) of water protons. The results were in general agreement with those determined earlier by various methods. In cases where more than one kind of complex was formed, the experimentalKstab reflected an average value of all species. Although this method is limited to measurements of weak complexes, it provides experimentally a simple approach with satisfactory results where neither great accuracy nor knowledge of equilibria and other parameters are required. It is believed that this method could be more widely applied for screening new contrast agents for MRI, and for exploration by MRI of weak low molecular weight complexes derived from biological sources.

Amphoteric polyelectrolytes based on poly- p-aminophenylene thiocyanate

This paper focuses on studies of the synthesis of soluble polyelectrolytes based on new copolymers of styrene with nitrogen-containing monomer: p-aminophenylene thiocyanate and poly- p-aminophenylene thiocyanate. Functional analysis, spectroscopic hydrodynamic and electrochemical studies of aqueous solutions of polymers in comparison with low molecular weight analogs were carried out to confirm the structure of the modified products. Stability constants of ion-exchanger complexes with ions of different metals were determined by the modified Bjerrum method using the program IOS-COMPLEX written in FORTRAN. It was shown, for phosphorylated polyamine, that the metal ion stability constants in the following order: UO 2 2++ > Pr 3+ > Cu 2+ > Ni 2+ > Co 2+ in accord with the stability of the formed complexes.

1-Methyl-3-hydroxy-2-pyridinone and 1,4-dihydroxy-2-pyridinone complexes of the trivalent metal ions of Fe(III), Ga(III), Al(III), In(III) and Gd(III): potentiometric and spectrophotometric determination of stabilities

The trivalent metal ion stability constants for tris bidentate chelates of 1-methyl-3-hydroxy-2-pyridinone (MH2P) and 1,4-dihydroxy-2-pyridinone (DH2P) were determined by potentiometric and spectroscopic methods at 25.0 °C, 0.100 M KCI. The overall log stability constants for Fe(III) complexes (log βFeL 3=[FeL 3]/[Fe][L] 3) are 29.99 and 28.18, respectively, and are lower than that of 1,2-dimethyl-3-hydroxy-4-pyridinone (DMHP), published previously (35.88). The placement of the bidentate hydroxy oxygen donors relative to the pyridyl nitrogen atom of the ligand influences the 3:1 stabilities for each of the trivalent metal ions studied (i.e. Fe(III), Ga(III), Al(III), In(III) and Gd(III)), as the relative order of stability is DMHP>MH2P>DH2P. Among these ligands, the relative order of magnitude of metal ion stability is Fe(III)> Ga(III)>Al(III)>In(III)>Gd(III). Influences of structural and inductive effects (resulting from hydroxyl and methyl substitution of hydroxypyridinone ligands) are evaluated.

2,3-diphosphoglycerate binding of Zn 2+ and Al 3+

The blood red cell contains millimolar amounts of 2,3-diphosphoglycerate, yet no metal ion stability constants appear to have been determined. We show that in the free ligand the 2-phospho group is about six times more basic than the 3-phospho group. We have determined the stability constants for the binding of Zn 2+ which occurs at about 0.2 mM in the red cell, and of Al 3+ which reduces red cell size and inhibits haemoglobin synthesis. At physiological pH both metal ions occur predominantly as MA 2 complexes. The free Zn 2+ concentration permitted within the red cell by the 2:1 complex is about 0.3 μm. 2,3-Diphosphoglycerate binds Al 3+ strongly enough so that at equilibrium there should be comparable concentrations of Al 3+ on both sides of the red cell membrane.

Antiradiation Compounds: XXI. Metal Ion Complexation of Bis(Methylthio) and Methylthio Amino Derivatives of 1-Methylquinolinium-2-dithioacetic Acids

With the assumption that the radiation-protective ability (whole body protection of mice) of the bis(methylthio) and methylthio amino derivatives of the 1-methylquinolinium-2-dithioacetic acids may be due to complexation of copper or zinc ions in vivo, the ability of these compounds to form stable metal complexes has been observed. Metal ion stability constants have been determined for three of the compounds with Al(lll), Cu(ll), Fe(lll), and Zn(ll) ions, and stabilities somewhat larger than those for simple peptides were found. Structures of the Cu(ll) and Fe(lll) complexes are proposed, based on elemental analyses and infrared absorption. The Cu(ll) complexes are 1:1 ligand:metal structures that precipitated as double salts with CuCl2, and the Fe(lll) complexes are 2:1 structures in which the ligands incorporated an additional sulfur atom.

種々の抽出剤によるアンモニウム塩水溶液からの金属イオンの溶媒抽出

Extraction of Cu, Ni, Co(II) and Co(III) from ammoniacal solution was carried out by using Versatic Acid 10, D2EHPA, PC-88A, LIX64N, SME529 and KELEX100 as extractants, in order to investigate the difference in extraction suppresion by the extractants used.When the acidic extractants such as Versatic Acid 10, D2EHPA and PC-88A were applied to the extraction from the aqueous solution containing ammonia at high concentration, the strong extraction suppresion was caused by the formation of stable metal-ammine complexes. Metal ions of Cu, Ni and Co were not extracted at all in the pH region of 7-9.5. On the other hand, the extraction suppresion was weak and the extraction of Cu and Co(II) occurred even in the pH range over 10 when chelating extractants such as LIX64N, SME529 and KELEX100 were used for the extraction from the ammoniacal solution. The extent of extraction suppresion is dependent on the sort of metal ions, the ammonia concentration and the sort of extractants. The difference of the extraction suppresion with the sort of extractants seems to be determined by the relation between stability constants of metal ions and extractants and those of metal ions and ammonia.

Binding sites and stabilities of transition metal ions with nucleosides and related ligands

Stability constant logarithms for Ni 2+, Cu 2+, and Zn 2+ binding at pyridine or purine N1 type nitrogens and imidazole or purine N7 type nitrogens display a linear relationship with pK a for each metal ion and nitrogen type. The slopes of all lines vary only from 0.3 to 0.5. For all three aqueous metal ions and dienPd 2+, at the same pK a, the stability constant for N7 binding is 0.8 to 1.2 log units stronger than for N1 binding. For neutral adenosine the N1 site is intrinsically 320 times more basic than the N7 site. However, for the above three aqueous metal ions the ratio of N1 to N7 bound adenosine complexes is projected to be 3, 2.5, and 1, respectively. Thus solutions of neutral adenosine and these aqueous metal ions contain comparable amounts of N1 metalated and N7 metalated complexes. Intrinsic protonation and metal ion stability constants are compared for adenosine, guanosine and inosine. N7 coordination in purine bases predominates at low pH and gives way to favored N1 coordination for dienPd 2+, Cu 2+, and Zn 2+ between pH 1.5 to 2.7 for adenosine, pH 6.1 to 6.7 for inosine, and pH 6.9 to 7.5 for guanosine. Absolute chemical shifts for both tetramethylammonium ion and acetonitrile are found to be dependent on ionic strength in opposite senses. There seems to be no reliable internal chemical shift reference when ionic strength is varied.