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Exploring Theoretical Origins of the Toxicity of Organic Quaternary Ammonium Salts towards Escherichia coli Using Machine Learning Approaches
[Thesis]. Manchester, UK: The University of Manchester; 2014.
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Abstract
Quaternary ammonium salts are surface active bactericides. A mechanism oftheir biological activity has been well studied experimentally, and itencompasses two stages. The first stage involves electrostatic interactions ofpolar functional groups of the salts with oppositely charged functional groupson a bacterial cell surface, and the second stage includes incorporation oftheir lipophilic groups into a bacterial cell membrane. However, despitenumerous experimental studies, computational modelling of this mechanismwith the aim to support experimental observations with theoreticalconclusions, to the author’s knowledge, has not yet been reported.In the current study, linear regression models correlating theoreticaldescriptors of lipophilicity and electronic properties of mono- and disubstitutedimidazolium carboxylates with their biological activity towardsEscherichia coli have been developed. These models established thatbiological activity of these salts is governed by the chemical structures ofimidazolium cations, and that the centre of this biological activity is located inthe long alkyl side chains of the cations. It was also found that these sidechains have an intrinsic electronic potential to form internal C-H- -H-Celectrostatic interactions when their lengths reach seven carbon atoms.Additionally, the nature of the C-H- -O-C inter-ionic electrostaticinteractions in imidazolium carboxylates has been explored via a topologicalanalysis of these interactions in 1-ethyl-3-methylimidazolium acetate. Thus, itwas established that these electrostatic interactions are hydrogen bonds.
Keyword(s)
QSAR; QTMS; agar diffusion test; dipole; hydrogen bond; quaternary ammonium salts