Brief Introduction to Molecular Descriptors Used in SAR

In SAR research, the purpose is to connect the biological activities of a series of compounds with their physico-chemical properties by using regression analysis, pattern recognition methods, or other sophisticated data processing methods. Generally speaking, the activities and properties are connected by a function F as follows for QSAR problems  

In SAR work, the biological activity of compounds is usually expressed by the values of IC50 or ED50. Physico-chemical properties used in SAR can be broadly classified into three general tjq)es electronic parameters, steric parameters and hydrophobic parameters. Electronic parameters include Hammett constants o ,(7, 7 ), Swain and Lupton field parameter (F), Swain and Lupton resonance parameter (R), etc. Steric parameters include Taft s steric parameter (Eg), molecular volume (Vm), molecular surface area (Area), molecular weight (MW), van der Waals radius (r), molar refractivity (MR), parachor (Pr), etc. Hydrophobic parameters include partition coefficient (LogP), distribution coefficient (LogD), substituent constant ( ), solubility 

HOMO is the highest energy level of the molecule that contains electrons. It is crucially important in governing molecular reactivity and other properties. When a molecule acts as a Lewis base (an electron pair 

The molecular surface area (Area) descriptor is a 3D spatial descriptor that describes the van der Waals area of a molecule. The molecular surface area determines the extent to which a molecule exposes itself to the external environment. This descriptor is related to the binding, transport properties and the solubility of compounds. 

The molecular volume (Vm) is a 3D spatial descriptor that defines the molecular volume inside the contact surface. The molecular volume is calculated as a function of conformation. Molecular volume is related to the binding and transport properties of compounds. 

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