Proton exchange in aqueous solutions of polyfunctional electrolytes

Atherton, John Norman (1977) Proton exchange in aqueous solutions of polyfunctional electrolytes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The adiabatic half passage experiment was used to measure the rates of proton exchange reactions in acidified aqueous solutions of piperazine, N,N'-dimethylpiperazine and histamine. All of the reactions which were detected -involved participation by water molecules. Reactions detected for piperazine included (a) the transfer of a proton from a piperazine species to a water molecule and (b) the transfer of a proton from one piperazine species to another piperazine species via at least one water molecule. For N,N'-dimethylpiperazine, reactions of type (b) could not be detected. -- In the case of histamine, proton exchange from two different types of N-H site was distinguished. Reactions of types (a) and (b) were detected for proton transfer from both imidazolium and ammonium sites. An intramolecular proton exchange was also found in which a proton was transferred from an ammonium site to an-imidazole slte of the same histamine molecule with one or two water molecules participating. The rate costant for this reaction is j1 = (1 .87 ± 0,09) x 10 to the power of 5 sec.-1. -- Since, the distances between active centers in enzymes is sometimes comparable to that in histamine, it follows that intramolecular proton transfer in enzymes is possible and perhaps even probable. If such an intramolecular reaction does occur in enzymes at about the same rate as it occurs in histamine then it will compete favourably with bi molecular reactions at physiological pH. The ability of the hydrogen bonded water molecules to fit the contours of the enzyme, could result in an intramolecularproton transfer even between centers which are severely sterically crowded.

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