08-12-2012, 03:34 PM
COORDINATION CHEMISTRY (COMPLEXATION)
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WHY IS CHEMICAL SPECIATION SO IMPORTANT?
The biological availability (bioavailability) of metals and their physiological and toxicological effects depend on the actual species present.
Example: CuCO30, Cu(en)20, and Cu2+ all affect the growth of algae differently
Example: Methylmercury (CH3Hg+) is readily formed in biological processes, kinetically inert, and readily passes through cell walls. It is far more toxic than inorganic forms.
Solubility and mobility depend on speciation.
METAL-ION TITRATIONS
Metal ions can be titrated by ligands in the same way that acids and bases can be titrated.
According to the Lewis definition, metal ions are acids because they accept electrons; ligands are bases because they donate electrons.
HYDROLYSIS
The waters surrounding a cation may function as acids. The acidity is expected to increase with decreasing ionic radius and increasing ionic charge. For example:
Zn(H2O)62+ Zn(H2O)5(OH)+ + H+
Hydrolysis products may range from cationic to anionic. For example:
Zn2+ ZnOH+ Zn(OH)20 (ZnO0)
Zn(OH)3- (HZnO2-) Zn(OH)42- (ZnO22-)
May also get polynuclear species.
Kinetics of formation of mononuclear hydrolysis products is rather fast, polynuclear formation may be slow.
[attachment=43098]
WHY IS CHEMICAL SPECIATION SO IMPORTANT?
The biological availability (bioavailability) of metals and their physiological and toxicological effects depend on the actual species present.
Example: CuCO30, Cu(en)20, and Cu2+ all affect the growth of algae differently
Example: Methylmercury (CH3Hg+) is readily formed in biological processes, kinetically inert, and readily passes through cell walls. It is far more toxic than inorganic forms.
Solubility and mobility depend on speciation.
METAL-ION TITRATIONS
Metal ions can be titrated by ligands in the same way that acids and bases can be titrated.
According to the Lewis definition, metal ions are acids because they accept electrons; ligands are bases because they donate electrons.
HYDROLYSIS
The waters surrounding a cation may function as acids. The acidity is expected to increase with decreasing ionic radius and increasing ionic charge. For example:
Zn(H2O)62+ Zn(H2O)5(OH)+ + H+
Hydrolysis products may range from cationic to anionic. For example:
Zn2+ ZnOH+ Zn(OH)20 (ZnO0)
Zn(OH)3- (HZnO2-) Zn(OH)42- (ZnO22-)
May also get polynuclear species.
Kinetics of formation of mononuclear hydrolysis products is rather fast, polynuclear formation may be slow.