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Related Concept Videos

Complexation Equilibria: The Chelate Effect01:19

Complexation Equilibria: The Chelate Effect

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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...
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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...
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Complexation reactions take place when dative or coordinate covalent bonds form between metal ions and ligands. The compounds formed in these reactions are called coordination compounds. The number of bonds formed between the metal ion and the ligands is called its coordination number. Generally, most metal ions in an aqueous solution are solvated by water molecules and thus exist as aqua complexes.
The equilibrium constant of the complexation reaction is represented as the formation constant...
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EDTA: Auxiliary Complexing Reagents01:26

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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...
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Complexation Equilibria: Factors Influencing Stability of Complexes01:09

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In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
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Complexometric titration involves the formation of a complex by reacting a metal ion with one or more ligands. A visual indicator often detects the end point of a complexometric titration. It is added to the metal solution before the titration, forming a stable metal–indicator complex and imparting color to the solution. As the titration approaches the equivalence point, the excess of the added ligand displaces the indicator from the metal–indicator complex, releasing the free...
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Preparation, Purification, and Characterization of Lanthanide Complexes for Use as Contrast Agents for Magnetic Resonance Imaging
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Caffeic Acid/Eu(III) Complexes: Solution Equilibrium Studies, Structure Characterization and Biological Activity.

Żaneta Arciszewska1, Sofia Gama1, Monika Kalinowska2

  • 1Department of Analytical and Inorganic Chemistry, Faculty of Chemistry, University of Bialystok, K. Ciołkowskiego 1K, 15-245 Białystok, Poland.

International Journal of Molecular Sciences
|January 21, 2022
PubMed
Summary

This study investigated the properties of caffeic acid (CFA) complexed with Europium(III) (Eu(III)). While Eu(III)/CFA showed lower antioxidant activity than CFA alone, it demonstrated enhanced antibacterial properties against common pathogens.

Keywords:
antimicrobial activityantioxidant activitychemical speciationlanthanidesmetal complexesmicroelectrophoretic mobilitypolyphenolssequestering abilitysolution equilibria

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Area of Science:

  • Coordination Chemistry
  • Bioinorganic Chemistry
  • Analytical Chemistry

Background:

  • Caffeic acid (CFA) is a natural antioxidant with known biological roles.
  • Research on CFA complexes with lanthanide metals, like Europium(III) (Eu(III)), is limited.
  • Understanding the structure-property relationships of metal complexes is crucial for their applications.

Purpose of the Study:

  • To synthesize and characterize the Eu(III)/CFA complex.
  • To investigate the chemical speciation of Eu(III)/CFA in aqueous solutions.
  • To evaluate the biological activities, including antioxidant and antimicrobial properties, of the Eu(III)/CFA complex.

Main Methods:

  • Multi-analytical techniques: FT-IR, FT-Raman, elemental analysis, TGA.
  • Solution behavior studies: Potentiometric and UV-Vis titrations, 1H-NMR, ESI-MS.
  • Biological assays: Electrophoretic mobility, antioxidant capacity tests, minimum inhibitory concentration (MIC).

Main Results:

  • The solid-state complex has a 1:3 metal-to-ligand ratio: [Eu(CFA)3(H2O)3]·2H2O.
  • In aqueous solution (pH 6-10), 1:1 species ([Eu(CFA)] and [Eu(CFA)(OH)]-) were predominant.
  • Eu(III)/CFA exhibited reduced antioxidant activity but increased antibacterial efficacy compared to free CFA.

Conclusions:

  • The study elucidates the structural and solution behavior of the Eu(III)/CFA complex.
  • The enhanced lipophilicity of the Eu(III) complex likely contributes to its improved antibacterial activity.
  • This research provides foundational chemical and biological data for lanthanide-caffeic acid systems.