3 - DEUTERIUM AND 18O EXCHANGE

Abstract

This chapter describes deuterium and $$ exchange. THE prominent role of the hydrogen atom in modern chemistry makes it an attractive problem to study the binding of this atom. On the assumption that the more strongly a hydrogen atom is bound in a compound, the less is the probability that it will exchange for another, the study of the exchange of deuterium between soluble substances and water should give us some information about the bond strength. In amino acids, peptides, and proteins, the general rule is that hydrogen atoms bound to carbon do not exchange, but those bound to nitrogen, oxygen, or sulphur. However, there are enormous differences in the rates at which individual hydrogen atoms exchange. In amino acids and small peptides all exchangeable hydrogen generally exchanges so rapidly that the rate cannot be measured by our technique. “Deuterium oxide” denotes pure or practically pure (more than 9 9%) D20. “Heavy water” will mean either D2O or H218O, “ordinary water” the naturally occurring isotope mixture. “Enriched water” will stand for any sample richer in heavy isotopes than ordinary water.