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Computational determination of pKa values. A comparison of different theoretical approaches and a novel procedure by Elena Soriano; Sebastián Cerdán; Paloma Ballesteros is a Chemistry article available to read on EtoBox.

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We have estimated the pK a values of different series of imidazol-1-ylalcanoic acid derivatives using combinations of semiempirical or ab initio methods and two semiempirical solvation models SM2 and SM5.4. None of these procedures was able to describe the zwitterionic structure of the carboxylic monoacids series as their most stable form determined experimentally in solution. Under these conditions, a comparison of the theoretical and experimental pK a values showed RMS differences ranging from 1.43 to 3.04 pK a units. As an alternative strategy we describe here a mathematical model for pK a determination based on quantitative structure-property relationships. The model uses two quantum chemical descriptors, the natural atomic charge on the N3 proton (q H C ) and the frontier orbital energy (3 L ), allowing the determination of pK a values for every compound of a given series with a reasonable computational effort. A linear relationship is described among pK a , q H C , 3 L and the number of ester groups in the molecule n. Multiple linear regression analysis of the available series of imidazol-1ylalcanoic compounds allowed to obtain the expression pK a ZK119:435 !q C H C 0:612 !3

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Author

Elena Soriano; Sebastián Cerdán; Paloma Ballesteros

Publisher

Elsevier Science; Elsevier ; Elsevier BV (ISSN 0166-1280)

Published

2004

Language

EN

Field

Chemistry (Physical Sciences)