Job plot
Encyclopedia
A Job plot is used to determine the stoichiometry
of a binding event. This method is widely used in analytical chemistry
, instrumental analysis, and advanced chemical equilibrium
texts and research articles.
In solutions where two species are present (i.e. species A and species B), one species (A) may bind to the other species (B). In some cases, more than one A will bind with a single B. One way to determine the amount of A binding to B is by using a Job plot.
In this method, the total molar concentration of the two binding partners (e.g. a protein
and ligand
or a metal and a ligand) are held constant, but their mole fractions are varied. An observable that is proportional to complex formation (such as absorption signal or enzymatic activity) is plotted against the mole fractions of these two components. The maximum (or minimum) on the plot corresponds to the stoichiometry of the two species if sufficiently high concentrations are used. This method is named after P. Job, who first introduced this methodology in 1928.
There are several conditions that must be met in order for Job's method to be applicable:
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
of a binding event. This method is widely used in analytical chemistry
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
, instrumental analysis, and advanced chemical equilibrium
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
texts and research articles.
In solutions where two species are present (i.e. species A and species B), one species (A) may bind to the other species (B). In some cases, more than one A will bind with a single B. One way to determine the amount of A binding to B is by using a Job plot.
In this method, the total molar concentration of the two binding partners (e.g. a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
and ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
or a metal and a ligand) are held constant, but their mole fractions are varied. An observable that is proportional to complex formation (such as absorption signal or enzymatic activity) is plotted against the mole fractions of these two components. The maximum (or minimum) on the plot corresponds to the stoichiometry of the two species if sufficiently high concentrations are used. This method is named after P. Job, who first introduced this methodology in 1928.
There are several conditions that must be met in order for Job's method to be applicable:
- The system must conform to Beer's law
- One complex must predominate under the conditions of the experiment
- The Total concentration of the two binding partners must be maintained constant
- pH and ionic strength must be maintained constant