A Developed QSPR Model for the Melting Points of Isatin Derivatives

Abstract

This paper suggests a developed quantitative structure property relationship (QSPR) model for coping the melting point (M.P) which is considered as the main and important physical property of solid state. The development was based on the decreasing in number of descriptors in order to be statistically intensive with excellent values of statistical parameters. The model was applied successfully to the already published data of M.P for 32 biologically active molecules derived from 4-(1-aryl-2-oxo-1,2-dihydro-indol-3-ylideneamino)-N-substituted benzene sulfonamides. The calculations of descriptors were carried out using density functional theory (DFT) with bases set of 6-311G (d, P). A statistically intensive QSPR model contains only three descriptors with physical meaning has been introduced. Two of them are belonging to the direct theoretical calculations but the third was considered as three dimensional correcting term of which depending on the chemical structure of the substituent. The theoretically calculated descriptors were the total connectivity (TC) and the average charge on the aryl group (AQArH) as both depending on the packing of molecules and responsible on M.P. The last descriptor was suggested as a correction term with respect to the packing of molecules of which depending on their three dimensional chemical structure which only taking the values of -1, 0 and 1. A relatively excellent statistical parameters for the developed model were obtained with square regression coefficient (r2), cross-validation (q2) and root mean squared error (RMSE) are equal to 0.925, 0.903 and 15.26oC, respectively. It was concluded that the developed model gives more confidence results in addition to physical significance which can be considered as a helpful tool for understanding the factors affecting the melting point.