Estrada correlation

Correlation of Estrada Estrada [22] derived the following simple, linear correlation between (cm3 mol-1) and the e index for alkanes (C5-C9) (eq. 2.3.6) ... 

The direct summation of vertex degree products in M2 has been changed in (G) to a summation of inverse-square-root terms. This specific function selection has been made to provide better correlations of with the properties of isomeric alkanes. This shows the high sensitivity of the new molecular descriptor to variations in molecular structure. More recently, some restrictions in the applicability of the inverse-square-root function to compounds with large numbers of atoms (Gutman and Lepovic, 2001) and new values for the exponent were investigated (Gutman and Lepovic, 2001 Estrada, 2002). 

Pang S, Wang M, Jeffries S, Riddick L, Clark A, Estrada E. Normal and elevated 3 alpha-androstanediol glucuronide concentrations in women with various causes of hirsutism and its correlation with degree of hirsutism and androgen levels. J Clin Endocrinol Metab 1992 75 243-8. 

It can be noted that function i was used by Ivanciuc to define the —> distance-valency matrices, function was used by Kier-Hall to define the —> electrotopological state indices, function y was proposed by Randic to calculate the —> alimented valence of vertices, and function y was proposed by Estrada in the generalized molecular-graph matrix, where x is a user-defined parameter or a parameter to be optimized during the searching for the best QSAR correlations. 

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