Fig. 3.10  Trichloroethane

A A

A

A

A A

A

AAA A A A A A A A AA

AA AA A A A AA AA AA

A A A A A A AA A

Ko/w = 7/33

Fig. 3.11  Solvent’s partition coefficient

that measures the proportion of the substance within each of both phases proposed. In common practice we use water (as phase of aqueous nature) and octanol (as phase of lipidic type) (Fig. 3.11).

Therefore, the partition coefficient enables to foresee with figures the behavior of a given substance (the solute) in a hydrophilic or lipophilic solvent environment. Some examples of partition coefficients are given in Fig. 3.12.

3.2.2.6  Chelating Function or Complexation

Chelation (literally pliers or pincers) is the formation of a complex made of a chelating agent, a ligand, and a cation or a metallic atom that is set in the center of the complex. The atom or cation is connected by at least two connections called coordination bonds. Illustrations of important chelating reactions found in ocular corrosive damages: the calcium and magnesium ions with oxalic acid or with the fluor ion of hydrofluoric acid (Fig. 3.13).

Fig. 3.12  Values of some partition coefficients

Fig. 3.13  Chelator agents

Energy Scale of Chelation Reactions

The molecular complexation constant expresses the strength of the bond. A weak chelation results in an unsteady and labile complex. A high constant results in a very stable compound that will not tend to dissociate.

3.2.2.7  Alkylation Reaction

The notion of alkylation is linked to the concept of adduct and therefore to the mechanism of addition of a substrate to another one. An adduct is a piece of chemical covalently bonded to another molecule. If the adduct concern DNA, it can cause carcinogenesis.