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Complexometric Titration: Ligands00:43

Complexometric Titration: Ligands

2.2K
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...
2.2K
Complexation Equilibria: The Chelate Effect01:19

Complexation Equilibria: The Chelate Effect

1.2K
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...
1.2K
Metal-Ligand Bonds02:51

Metal-Ligand Bonds

23.9K
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
23.9K
EDTA: Auxiliary Complexing Reagents01:26

EDTA: Auxiliary Complexing Reagents

1.2K
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...
1.2K
EDTA: Chemistry and Properties01:22

EDTA: Chemistry and Properties

3.2K
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...
3.2K
Oxidation of Phenols to Quinones01:17

Oxidation of Phenols to Quinones

4.5K
In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox...
4.5K

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Effective Antioxidants as Plausible Ligands in Chromium(III) Supplementation: How Complexation Modulates

Hanna Lewandowska1,2, Zhe Chen3, Krystian Marszałek3

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Summary

Metal coordination significantly alters the antioxidant and pro-oxidant effects of 3,4-dihydroxybenzoic acid (3,4-DHBA) and caffeic acid (CA). Chromium (Cr(III)) chelation, in particular, shows complex, ligand-dependent impacts on their biological activity.

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Area of Science:

  • Biochemistry
  • Medicinal Chemistry
  • Inorganic Chemistry

Background:

  • 3,4-dihydroxybenzoic acid (3,4-DHBA) and caffeic acid (CA) are phenolic compounds with known antioxidant properties.
  • Metal ion coordination can modulate the biological activity of organic molecules.
  • Understanding these modulations is crucial for developing novel therapeutic agents.

Purpose of the Study:

  • To investigate the influence of sodium (Na(I)), potassium (K(I)), and chromium (Cr(III)) coordination on the antioxidant and pro-oxidant activities of 3,4-DHBA and CA.
  • To elucidate the mechanisms behind metal-induced changes in redox properties.

Main Methods:

  • In vitro evaluation of radical scavenging using ABTS, DPPH, hydroxyl, and superoxide assays.
  • Assessment of ferric- and cupric-reducing power.
  • Determination of inhibition of linoleic acid peroxidation.

Main Results:

  • Alkali metal coordination generally reduced radical scavenging but improved lipid peroxidation inhibition in some cases (K complexes, Cr-3,4-DHBA).
  • Cr(III) chelation exhibited ligand-dependent effects, increasing CA reducing power while decreasing 3,4-DHBA reducing power.
  • Cr(III)-CA complexes uniquely displayed pro-oxidant behavior under superoxide conditions.

Conclusions:

  • Metal coordination, especially with Cr(III), significantly alters the antioxidant and pro-oxidant profiles of 3,4-DHBA and CA.
  • Chromium chelation influences electronic distribution and charge transfer, leading to enhanced reducing power and potential redox cycling.
  • The biological significance of these compounds is dual and highly dependent on the specific metal ligand interactions.