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Formation of Complex Ions

Formation of Complex Ions

A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...

Extraction: Advanced Methods

Extraction: 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...

Coordination Number and Geometry

Coordination Number and Geometry

For transition metal complexes, the coordination number determines the geometry around the central metal ion. Table 1 compares coordination numbers to molecular geometry. The most common structures of the complexes in coordination compounds are octahedral, tetrahedral, and square planar.

Ladder Diagrams: Complexation Equilibria

Ladder Diagrams: Complexation Equilibria

Ladder diagrams are useful for evaluating equilibria involving metal-ligand complexes. The vertical scale of the ladder diagram represents the concentration of unreacted or free ligand, pL. The horizontal lines on the scale depict the log of stepwise formation constants for metal-ligand complexes and indicate the dominant species in all the regions.
The formation constant, K1, for the formation of Cd(NH3)2+ complex from cadmium and ammonia is 3.55 × 102. Log K1 (i.e. pNH3) is 2.55, and...

Complexation Equilibria: The Chelate Effect

Complexation 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...

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than...

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Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

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The solution structure of the copper clioquinol complex.

M Jake Pushie¹, Kurt H Nienaber¹, Kelly L Summers²

¹Molecular and Environmental Sciences Research Group, Department of Geological Sciences, University of Saskatchewan, SK S7N 5E2, Canada.

Journal of Inorganic Biochemistry

|February 8, 2014

Summary

Clioquinol shows promise for Alzheimer's disease and cancer, potentially due to its copper chelation. However, studies reveal its copper complexes have conventional structures, suggesting other factors drive its therapeutic effects.

Keywords:

Clioquinol Copper chelation Density functional theory X-ray absorption spectroscopy

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Published on: March 20, 2019

Area of Science:

Biochemistry
Medicinal Chemistry
Neuroscience

Background:

Clioquinol (5-chloro-7-iodo-8-hydroxyquinoline) is investigated for Alzheimer's disease and cancer therapy.
Its therapeutic potential is linked to its role as a lipophilic copper chelator.
Past use as an anti-fungal/anti-protozoal drug led to subacute myelo-optic neuropathy (SMON) due to copper deficiency.

Purpose of the Study:

To clarify the chelation chemistry between clioquinol and copper.
To investigate the solution structures of copper-clioquinol complexes.
To determine if novel chelation chemistry underlies clioquinol's therapeutic promise.

Main Methods:

Electron paramagnetic spectroscopy
UV-visible spectroscopy
X-ray absorption spectroscopy

Main Results:

Solution structures of copper complexes with clioquinol are conventional 8-hydroxyquinolate chelates.
No unusual coordination chemistry was identified.
The structures are similar for both stoichiometric and excess clioquinol.

Conclusions:

Clioquinol's therapeutic promise in Alzheimer's disease and cancer is unlikely due to novel chelation chemistry.
Other factors, such as the high lipophilicity of clioquinol and its complexes, may be responsible for its efficacy.
Further research should explore these alternative mechanisms.