[Chemistry Class Notes] on Chelate Pdf for Exam

Chelation is a very common term used in different branches of science like chemistry, biology, and medical sciences. The process of chelation is widely used in the detoxification of toxicants and in making complexes. Let us come to our main question, what is chelation?

Let us discuss the chelate meaning, a chelate is a compound that has two or more coordinate or dative bonds between a ligand (usually organic) and a central metal atom.

Chelation Definition- Chelation is a phenomenon or the ability of ions and molecules to form bonds with metal ions. Between a polydentate ligand and a single central atom, two or more different coordinate bonds are formed or present. Let us discuss the terms used in the chelation definition for a better understanding of the definition.

Ligand- A ligand is an ion or molecule that forms a coordination complex by donating a pair of electrons to the central metal atom or ion.

Polydentate- The number of atoms used to bind to a central metal atom or ion varies among polydentate ligands. Hexadentate ligands, such as EDTA, have six donor atoms with electron pairs that can bind to a central metal atom or ion.

What is Chelation in Chemistry?

The chelate effect is when chelating ligands have a higher affinity for a metal ion than equivalent non-chelating (monodentate) ligands. Let’s take a look at how the chelation mechanism works. The chelate effect is supported by certain thermodynamic concepts. Let’s take a look at an example: Copper(II) affinities for ethylenediamine (en) and methylamine are compared.

1. [Cu^{2+} + en rightleftharpoons  Cu(en)^{2+}]

2. [Cu^{2+} + 2 MeNH_{2} rightleftharpoons  [Cu(MeNH_{2})_{2}]^{2+}]

The copper ion forms a chelate complex with ethylenediamine in the first equation. Chelation results in the creation of a [CuC_{2}N_{2}] chelate ring with five members. The bidentate ligand is substituted by two monodentate methylamine ligands with roughly the same donor strength in the second reaction, suggesting that the Cu–N bonds are similar in both reactions.

The equilibrium constant for the reaction is taken into account in the thermodynamic approach in explaining the chelate effect. The higher the equilibrium constant, the higher the complex concentration.

For the sake of clarity, electrical charges have been removed. The subscripts to the stability constants show the stoichiometry of the complex, and the square brackets indicate concentration. The concentration Cu(en) is much higher than the concentration [[Cu(MeNH_{2})_{2}]] because the analytical concentration of methylamine is double that of ethylenediamine and the concentration of copper is the same in both reactions.

As we know, ΔG = ΔH – TΔS 

The discrepancy between the two stability constants is due to the effects of entropy since the enthalpy should be about the same for the two reactions. There are two particles on the left and one on the right in equation one, while there are three particles on the left and one on the right in equation two.

This distinction suggests that when a chelate complex is formed with a bidentate ligand, less entropy of disorder is lost than when a complex is formed with monodentate ligands. One of the variables that contribute to the entropy gap is this. Solvation shifts and chelate ring formation are two other factors to consider. 

The enthalpy changes for the two reactions are nearly equal, indicating that the entropy expression, which is much less unfavorable, is the key reason for the chelate complex’s greater stability. It’s difficult to account for thermodynamic values in terms of changes in solution at the molecular level exactly, but it is apparent that the chelate effect is primarily an entropy effect.

Chelate Complex

The ligands (electron donors) used in the chelation process are known as chelants, chelators, chelating agents, and sequestering agents. These molecules are generally organic compounds, but this is not a necessity. As there are some cases of zinc and other inorganic molecules that are used as chelants. 

Chelate Example

Some of the examples of chelates are given below:

Chelate Compound Uses

• Chelation is useful in providing nutritional supplements.

• It is used in chelation therapy to remove toxic metals from the body.

• Chelate compounds are used as contrast agents in MRI scanning.

• These compounds are used in the manufacturing of homogeneous catalysts.

• It is used in chemical water treatment to assist the removal of metals and in fertilizers.

• The chelation process is used by plants for the removal of heavy metals.

Natural Chelating Agent & Cosmetic Industry

Chelating agents are compounds that form multiple bonds with metal ions. The compound hence formed is used in a variety of applications. But the natural chelating agent is mostly used in the cosmetic industry. As they do not react with any other element present in the substance. Natural chelating agents are biodegradable and free from toxic elements. Due to their organic nature, they are mostly used for producing cosmetics. These agents are derived from microorganisms. Due to the constant demand amongst the consumers for using eco-friendly products, natural chelating agents are now being consumed on a large scale. 

The usage of chelating agents helps to increase the shelf life of products and make it less harmful to the environment. Unsaturated oils can be obtained from these natural chelating agents when used with antioxidants such as tocopherol.

Advantages of Using Natural Chelating Agents:

• Helps to increase shelf life of products

• Work as a natural alternative to EDTA

• Used for skin brightening functions

• Effective for making metal ions inactive

• Is color stable

• Comes in easy to use the form

• Is biodegradable and environment friendly

• Free from toxic elements

• Derived from natural animals such as microorganisms. 

Examples:

• In the chelation process, monodentate and polydentate ligands bend over to form bonds and ring structures.

• Polydentae ligands such as amino acids, proteins, poly nucleic acids are used to form bonds.

• Most molecules dissolve metal cations to form chelate complexes

• Ethylenediamine, a bidentate ligand, forms a chelate complex with copper. And this gives a five-membered ring of CuC2N2. 

• Peptides, prosthetic groups or cofactors belong to metalloenzymes. 

• Organic chelates help to extract metal ions from rocks or minerals help in hot chemical weathering.

• Using chelating metal ions, nutritional supplements are formed

• These supplements help to prevent the formation of complexes insoluble in salts for the stomach.

• Moreover, these supplements have a higher capacity for absorption 

• Common chelating agents used for the softening process of eaters are EDTA and phosphorus. 

• Some frequent chelated completions include ruthenium chloride with bidentate phosphine. 

Sample Questions:

1. What are chelating agents? Give examples.

2. Explain the process of chelating with one example.

3. Give some uses of chelating agents.

4. How does the chelate effect take place?

5. Draw a structure of ethylenediamine and explain its uses.

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