QSAR Study on Solubility of Alkanes in Water and Their Partition Coefficients in Different Solvent Systems Using PI Index Padmakar V. Khadikar, a, * Dheeraj Mandloi, b Amrit V. Bajaj c and Sheela Joshi c a Research Division, Laxmi Fumigation and Pest Control, 3, Khatipura, Indore 452007, India b Institute of Engineering and Technology, D.A. University, Indore 452017, India c School of Chemical Sciences, D.A. University, Indore 452017, India Received 11 September 2002; accepted 31 October 2002 Abstract—The aqueous solubility (S w ) of liquids and solids, expressed as log S w as well as their partition coefficients in different solvent systems viz. P oct (partition coefficient in octanol-water), P 16 (partition coefficient in water-hexadecane), P alk (partition coefficient in water-alkane), and P cyc (partition coefficient in water-cyclohexane), and aqueous solubility (S w ) have been estimated using the PI (Padmakar–Ivan) index and the results compared with those obtained using the widely used Wiener index (W). Regression analysis of the data using n-alkanes show that the PI index gives better results than the W index. # 2002 Elsevier Science Ltd. All rights reserved. Introduction The solubility of liquids and solids in water (S w ) as well as partition coefficient of solutes in different solvents viz. partition coefficient in octanol-water (P oct ), parti- tion coefficient in water-hexadecane (P 16 ), partition coefficient in water-alkane (P alk ), and partition coeffi- cient in water-cyclohexane (P cyc ) are very important molecular properties that influence the release, trans- port, and the extent of absorption of drugs in the body. 1 5 These properties are the key determinants of the environmental fate of agrochemicals and pollutants in the environment. A number of methods are also reported for estimating the aforementioned parameters using molecular descriptors other than topological indices. 6 However, very little work is done for the estimation of aforemen- tioned parameters using topological indices. This has prompted us to undertake the present investigation in that we have used recently introduced the PI (Padma- kar–Ivan) index 7 12 for modeling, monitoring, and esti- mating P oct , P 16 , P alk , P cyc and S w and compared the results with those obtained using widely used Wiener index (W). 13 In doing so we have chosen n-alkanes (Table 1) as all these parameters for this set of com- pounds are easily available in the literature 1,5 which can be adopted. Results and Discussion A perusal of Table 1 shows that all the five properties viz. log P oct , log P 16 , log P alk , log P cyc , and log S w increase with the size of the alkanes. It means that these properties are the function of size, shape, and branching of the molecules. Hence, it appears that Wiener-type indices will be the most appropriate for modeling, monitoring, and estimat- ing these properties. The data presented in Table 2 shows that like the aforementioned properties, the magnitude of W and PI indices also increase with the size of the alkanes under present study. This means, both these indices would be quite suitable for modeling the five properties men- tioned above. The data presented in Tables 2 and 3 indicate that sim- ple regressions are enough to model these five proper- ties. In view of this we have carried out simple regressions and the results are discussed below. The regression parameters and quality of correlations needed for this purpose are given in Table 3. 0960-894X/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(02)00953-8 Bioorganic & Medicinal Chemistry Letters 13 (2003) 419–422 *Corresponding author. Tel./fax: +91-731-531906; e-mail: sachin_g @sancharnet.in