Ab Initio Investigation of Interactions between Local Anesthetics and Receptor. Complexes Involving Amine, Phosphate, Amide, Na+, K+, Ca2+ and Cl-

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Ab initio molecular orbital methods are used to study the interactions between models of local anesthetic molecules and the putative receptors within the nerve membrane: phospholipids and lipoproteins. The tertiary amine terminus of local anesthetics was modeled by ionized and un-ionized trimethylamine, while phosphate monoanion and formamide emulated the appropriate portions of the receptor. The protonated amine forms a very strong complex with the phosphate anion in which the charge is transferred to the phosphate. While somewhat weaker than this, the complex involving the amine (in either its ionized or un-ionized state) and peptide is considerably stronger than interpeptide H bonds, suggesting the anesthetic can disrupt the normal H-bond patterns in a protein. On the other hand, such interactions must compete with the rather tight binding of the anesthetic with the Na+ K+ Ca2+ and Cl ions present in vivo.

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