Ionophoretic studies on mixed metal--nitrilotriacetate--penicillamine complexes
1Department of Chemistry, Faculty of Natural Sciences, University of Guyana, Georgetown. tewari@uog.eud.gy
Journal of Chromatography. A
|March 27, 2001
Summary
Paper ionophoresis effectively determined the stability of mixed ligand complexes. Researchers quantified aluminum and thorium complexes with nitrilotriacetate and penicillamine, yielding key stability constant values.
Area of Science:
- Analytical Chemistry
- Coordination Chemistry
Background:
- Mixed ligand complex systems are crucial in various chemical and biological processes.
- Understanding metal-ligand interactions requires accurate determination of stability constants.
Purpose of the Study:
- To investigate the complexation equilibria of Al3+ and Th4+ with nitrilotriacetate and penicillamine using paper ionophoresis.
- To determine the stability constants (log K) of the ternary complexes formed.
Main Methods:
- Paper ionophoresis was employed to study metal ion movement in an electric field.
- Complexants (nitrilotriacetate and penicillamine) were added to the background electrolyte at pH 8.5.
- The concentration of nitrilotriacetate was constant, while penicillamine concentration was varied.
Main Results:
- The stability constants for Al3+-nitrilotriacetate-penicillamine complexes were determined to be 6.26 ± 0.09 (log K).
- The stability constants for Th4+-nitrilotriacetate-penicillamine complexes were determined to be 6.68 ± 0.13 (log K).
- Measurements were conducted at 35°C and an ionic strength of 0.1 M.
Conclusions:
- Paper ionophoresis is a suitable technique for studying mixed ligand complex systems.
- The study provides quantitative data on the stability of Al3+ and Th4+ ternary complexes.
Related Concept Videos
01:19Complexation Equilibria: The Chelate Effect
In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...
01:22EDTA: Chemistry and Properties
Polydentate ligands are most widely used in complexometric titrations because they form more stable complexes with the metal ions than mono- or bidentate ligands due to the chelate effect. Examples of polydentate ligands are ethylenediaminetetraacetic acid (EDTA), crown ethers, and cryptands. The most important feature of optimal polydentate ligands is the ability to form 1:1 complexes in a single-step process. Amino carboxylic acid derivatives are frequently used as complexing agents. EDTA is...
01:26EDTA: Auxiliary Complexing Reagents
EDTA titrations are usually carried out in highly basic conditions, where the fully deprotonated form of EDTA, Y4−, actively complexes with the free metal ions in the solution. Several metal ions precipitate as hydrous oxide (hydroxides, oxides, or oxyhydroxides) under these conditions, lowering the concentration of free metal ions in the solution. For this reason, auxiliary complexing agents or ligands such as ammonia, tartrate, citrate, or triethanolamine are used in EDTA titrations to...
00:56Extraction: Advanced Methods
Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is formed in...
00:43Complexometric Titration: Ligands
Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in...
01:27Pharmacogenetics of Phase II Enzymes: N-acetyltransferase, Thiopurine S-methyltransferase, UDP-glucuronosyltransferase
Phase II biotransformation reactions are essential for detoxifying and eliminating xenobiotics, including many pharmaceutical compounds. These reactions typically involve conjugation, the covalent attachment of polar endogenous groups such as glucuronic acid, sulfate, methyl, or acetyl moieties to functional groups introduced during Phase I metabolism. The resulting conjugates are more water-soluble, enabling efficient renal or biliary excretion.The major classes of Phase II enzymes include...