The Hydrogen Perturbation in Molecular Connectivity Indices and their Application to a QSPR Study
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The Hydrogen Perturbation in Molecular Connectivity Indices and their Application to a QSPR Study Morteza Atabati • Reza Emamalizadeh
Received: 30 August 2011 / Accepted: 13 January 2012 / Published online: 22 November 2012 Springer Science+Business Media New York 2012
Abstract Although chemical graphs do not show the difference between various atoms and electron lone pairs, the use of pseudo-graphs is a remedy. Modified molecular connectivity indices (mMCIs) have been suggested as showing the role of hydrogen atoms that are also useful in distinguishing isomers. A new algorithm for the dv number, the basic parameter of molecular connectivity indices (MCIs), has recently been proposed. This algorithm, which is centered on graph concepts such as complete graphs and general graphs, encodes the information of the bonded hydrogen atom on different atoms through a perturbation parameter that requires no new graph concepts. In this study, hydrogen perturbations in valence molecular connectivity indices were applied as structural descriptors for organic compounds in quantitative structure property relationship studies on the molar volume and molar refraction of liquid alkanes, alkenes and alcohols. The results show that, in most cases, these indices give improved correlations compared with the original MCIs. Keywords Hydrogen perturbation QSPR Molecular connectivity indices Molar volume Molar refraction
1 Introduction Quantitative structure property/activity relationship (QSPR/QSAR) studies are powerful tools for predicting physic–chemical properties, biological activities, and pharmacological and toxicological properties of organic compounds. Many structure–property/activity studies use graph theoretical indices that are based on the topological properties of a molecule viewed as a graph. Since topological indices can be derived directly from the molecular structure, they provide a simple and straightforward method for property prediction. A variety of topological indices have been proposed, such as the molecular connectivity index (MCI) [1, 2], Hosoya’s index (Z) [3], Balaban’s index (J) [4], Schultz’s
M. Atabati (&) R. Emamalizadeh School of Chemistry, Damghan University, Damghan, Iran e-mail: [email protected]; [email protected]
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J Solution Chem (2012) 41:1922–1936
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index (MTI) [5], Wiener’s index (W) [6] and the electrotopological index (S) [7], and a great number of investigations have been made to extend and apply them [8–17]. Among the existing topological indices, the MCI is one of the most commonly used indices and has found wide applications in both simple and complex systems [1, 2, 13, 16, 17]. Recently, a modified connectivity index was proposed in which the contribution of the hydrogen atoms to the overall connectivity index was parametrized as nH/6, where nH is the number of hydrogen atoms attached to a non-hydrogen atom, which can better distinguish the atoms in a compound [18]. The previous algorithms of molecular connectivity do not encode the bonded hydrogen atoms and do not all
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