Stability constants for metal arsenates

2007 ◽  
Vol 4 (2) ◽  
pp. 123 ◽  
Author(s):  
Janice S. Lee ◽  
Jerome O. Nriagu
Keyword(s):  
Metal Ions ◽  
Current Knowledge ◽  
Ion Pairs ◽  
Fate And Transport ◽  
Solid Metal ◽  
Association Constants ◽  
Arsenic Acid ◽  
Arsenic Compounds ◽  
Solubility Products ◽  
Metal Arsenates

Environmental context. The behaviour of arsenic compounds is controlled by their solubility, which in turn controls both the forms and mobility of arsenic in the environment. Current knowledge on arsenic chemistry may be distorted because information available on the solubility of arsenic compounds usually does not include possible formation of metal–arsenate complexes. Our results show the formation of stable metal–arsenate complexes that have not been considered before, and this new data can be used to further examine the effect of these complexes on controlling the fate and transport of arsenic in the environment. Abstract. The formation of solid metal arsenates could conceivably reduce the concentrations of arsenate and metal ions in natural and contaminated aqueous ecosystems, and possibly in human body fluids. In this study, solid metal arsenates were dissolved isothermally in solutions with different molar concentrations of arsenic acid. The saturated solutions were analysed and the results processed to derive the solubility products (Ksp) for solid phases and association constants (K) for metal arsenate ion-pairs. Ion chromatography was used to confirm the presence of ion-pairs, some of which had never before been considered. Association constants were determined for the following ion-pairs: FeHAsO4+ (log K = 4.88), CoHAsO40 (log K = 1.50), ZnHAsO40 (log K = 3.28), SrH2AsO4+ (log K = 1.72), and Ag2H2AsO4+ (log K = 4.50). The following metal ions apparently do not form stable complexes with HAsO42–: Cd2+, Cr3+, Cu2+, Mg2+, Mn2+, Ni2+, Pb2+, and Sn2+. Standard state solubility products (Ksp°) were redetermined for the following compounds: Ag3AsO4, Cd3(AsO4)2, Co3(AsO4)2, CrAsO4, Cu3(AsO4)2, FeAsO4, Mg3(AsO4)2, MnHAsO4, NiHAsO4, PbHAsO4, Sn3(AsO4)2, Sr3(AsO4)2, Zn3(AsO4)2·Zn3(AsO4)2·8H2O (koettigite), Cu2Al7(AsO4)4(OH)13·12H2O (ceruleite), and Pb2CuAsO4CrO4OH (fornacite). Our results show the formation of ion-pairs for some metal arsenates and indicate that previous studies have overestimated the solubilities of many arsenates.

Association constants for ion pairs

1986 ◽  
Vol 15 (3) ◽  
pp. 231-235 ◽  
Author(s):  
Raymond M. Fuoss
Keyword(s):  
Ion Pairs ◽  
Association Constants

scholarly journals Functional characterization of the dimerization domain of the ferric uptake regulator (Fur) of Pseudomonas aeruginosa

2006 ◽  
Vol 400 (3) ◽  
pp. 385-392 ◽  
Author(s):  
Erdeni Bai ◽  
Federico I. Rosell ◽  
Bao Lige ◽  
Marcia R. Mauk ◽  
Barbara Lelj-Garolla ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Metal Ions ◽  
Binding Site ◽  
Metal Ion ◽  
Association Constants ◽  
Ion Binding ◽  
Ferric Uptake Regulator ◽  
Metal Ion Binding ◽  
Dimerization Domain ◽  
High Affinity

The functional properties of the recombinant C-terminal dimerization domain of the Pseudomonas aeruginosa Fur (ferric uptake regulator) protein expressed in and purified from Escherichia coli have been evaluated. Sedimentation velocity measurements demonstrate that this domain is dimeric, and the UV CD spectrum is consistent with a secondary structure similar to that observed for the corresponding region of the crystallographically characterized wild-type protein. The thermal stability of the domain as determined by CD spectroscopy decreases significantly as pH is increased and increases significantly as metal ions are added. Potentiometric titrations (pH 6.5) establish that the domain possesses a high-affinity and a low-affinity binding site for metal ions. The high-affinity (sensory) binding site demonstrates association constants (KA) of 10(±7)×106, 5.7(±3)×106, 2.0(±2)×106 and 2.0(±3)×104 M−1 for Ni2+, Zn2+, Co2+ and Mn2+ respectively, while the low-affinity (structural) site exhibits association constants of 1.3(±2)×106, 3.2(±2)×104, 1.76(±1)×105 and 1.5(±2)×103 M−1 respectively for the same metal ions (pH 6.5, 300 mM NaCl, 25 °C). The stability of metal ion binding to the sensory site follows the Irving–Williams order, while metal ion binding to the partial sensory site present in the domain does not. Fluorescence experiments indicate that the quenching resulting from binding of Co2+ is reversed by subsequent titration with Zn2+. We conclude that the domain is a reasonable model for many properties of the full-length protein and is amenable to some analyses that the limited solubility of the full-length protein prevents.

Solution Properties of Tetraalkylammonium Halide and Alkali-Metal Halide Ion Pairs. The Relationship Between Dissociation Constants and Solubility Products

1987 ◽  
Vol 40 (7) ◽  
pp. 1201 ◽  
Author(s):  
W Mizerski ◽  
MK Kalinowski
Keyword(s):  
Alkali Metal ◽  
Solubility Product ◽  
Dissociation Constants ◽  
Ion Pairs ◽  
Empirical Relation ◽  
Alkali Metal Halide ◽  
Alkali Metal Cations ◽  
Solubility Products ◽  
The Relationship ◽  
Dissociation Constant Kd

An empirical relation describing the effect of solvent on the dissociation constant ( Kd ) of ion pairs is described. An equation of the form pKd = apKso + bD-1 + c ( Kso and D stand for the solubility product of a given salt and for the electric permittivity of a solvent, respectively) has been tested with 13 sets of experimental data for salts containing tetraalkylammonium and alkali-metal cations. A successful correlation was obtained in 100% of the cases considered.

Octahedral cobalt(III) complexes in dipolar aprotic solvents. II. Association between cis- and trans-dichlorobisethylenediamine cobalt(III) cations,[Co en2 Cl2]+, and chloride and bromide ions in the solvents NN-dimethylformamide, dimethyl sulphoxide, and LVN-dimethylacetamide

1966 ◽  
Vol 19 (1) ◽  
pp. 43 ◽  
Author(s):  
WA Millen ◽  
DW Watts
Keyword(s):  
Spectrophotometric Method ◽  
Ion Pairs ◽  
Ion Association ◽  
Ion Pair ◽  
Association Constants ◽  
Dimethyl Sulphoxide ◽  
Aprotic Solvents ◽  
Ion Association Constants ◽  
Cis And Trans ◽  
Dipolar Aprotic Solvents

Ion association constants at 30� have been determined for the cis-[Co en, Cl2]+Cl- ion pair in NN-dimethylformamide (DMF), NN-dimethylacetamide (DMA), and at 20.0�, 25.0�, and 30.0� in dimethyl sulphoxide (DMSO), by a spectrophotometric method. Association constants for the cis-[Co en2 Cl2]+Br- and the trans- [Co en2 Cl2]+Cl- ion pairs have also been determined in DMF at 30�.

scholarly journals The Biochemical Properties of Manganese in Plants

Plants ◽  
2019 ◽  
Vol 8 (10) ◽  
pp. 381 ◽  
Author(s):  
Schmidt ◽  
Husted
Keyword(s):  
Metal Ions ◽  
Oxidation State ◽  
Metal Binding ◽  
Molecular Mechanisms ◽  
Current Knowledge ◽  
Biochemical Properties ◽  
Oxygen Evolving Complex ◽  
Functional Roles ◽  
Catalyzed Reactions ◽  
Enzyme Catalyzed Reactions

Manganese (Mn) is an essential micronutrient with many functional roles in plant metabolism. Manganese acts as an activator and co-factor of hundreds of metalloenzymes in plants. Because of its ability to readily change oxidation state in biological systems, Mn plays and important role in a broad range of enzyme-catalyzed reactions, including redox reactions, phosphorylation, decarboxylation, and hydrolysis. Manganese(II) is the prevalent oxidation state of Mn in plants and exhibits fast ligand exchange kinetics, which means that Mn can often be substituted by other metal ions, such as Mg(II), which has similar ion characteristics and requirements to the ligand environment of the metal binding sites. Knowledge of the molecular mechanisms catalyzed by Mn and regulation of Mn insertion into the active site of Mn-dependent enzymes, in the presence of other metals, is gradually evolving. This review presents an overview of the chemistry and biochemistry of Mn in plants, including an updated list of known Mn-dependent enzymes, together with enzymes where Mn has been shown to exchange with other metal ions. Furthermore, the current knowledge of the structure and functional role of the three most well characterized Mn-containing metalloenzymes in plants; the oxygen evolving complex of photosystem II, Mn superoxide dismutase, and oxalate oxidase is summarized.

scholarly journals When spectroscopy fails: The measurement of ion pairing

2006 ◽  
Vol 78 (8) ◽  
pp. 1571-1586 ◽  
Author(s):  
Glenn Hefter
Keyword(s):  
Metal Ion ◽  
Chemical Speciation ◽  
Ion Pairs ◽  
Ion Association ◽  
Ion Pair ◽  
Association Constants ◽  
Spectroscopic Techniques ◽  
Association Equilibria ◽  
Solvent Molecules ◽  
Contact Ion Pairs

Spectroscopic techniques such as UV/vis, NMR, and Raman are powerful tools for the investigation of chemical speciation in solution. However, it is not widely recognized that such techniques do not always provide reliable information about ion association equilibria. Specifically, spectroscopic measurements do not in general produce thermodynamically meaningful association constants for non-contact ion pairs, where the ions are separated by one or more solvent molecules. Such systems can only be properly quantified by techniques such as dielectric or ultrasonic relaxation, which can detect all ion-pair types (or equilibria), or by traditional thermodynamic methods, which detect the overall level of association. Various types of quantitative data are presented for metal ion/sulfate systems in aqueous solution that demonstrate the inadequacy of the major spectroscopic techniques for the investigation of systems that involve solvent-separated ion pairs. The implications for ion association equilibria in general are briefly discussed.

Sign in / Sign up

Export Citation Format

Share Document