Every drug has certain level of biological activity. The biological activity of any drug depends on a number of parameter. The equation that describes the relation between the drug’s biological activities to various physiochemical parameters is referred as hansch equation.
The quantitative structure-activity relationship or commonly known QSAR is a model that attempts to find relationships among various molecular properties that are consistent in nature. These molecular properties tend to affect the biological activity of the drug.
In the given QSAR equation that was derived for a pesticide the meanings of different terms has been discussed as follows:
1. The term ‘log 1/C’ represents the biological activity of any drug molecule. The term ‘C’ represents the concentration of the drug molecule that is needed to bring out the necessary biological activity.
2. The term ‘πx’ represents the hydrophobicity constant.
3. ‘Fx’ refers to the Fischer’s test value.
4. ‘Rx’ refers to the resonating value of the drug molecule.
5. The term ‘MRx’ refers to the molar refractivity of the drug compound.
Further the terms ‘n’, ‘r2’ and ‘s’ represents the number of compound, regression coefficient and the value for standard deviation. The equation that is described in the question is valid as it relates the biological activity of a drug molecule to various parameters that might affect its effectiveness.
The substances that would be best for the QSAR activities are the ones with high level of biological activity on small amount of concentration. The drug molecules that show high biological activity even at low concentration do not interferes with the normal body functioning and show less toxicological effects.