Why Is the Spontaneous Deprotonation of [Cu(uracil)₂]²⁺Complexes Accompanied by Enolization of the System?

Abstract

The reaction-force formalism is applied to carry out a detailed analysis of the mechanisms behind the enolization processes undergone by the complexes formed on interaction of uracil dimers with Cu(2+) ions after spontaneous deprotonation of the resulting complexes. These enolization processes apparently involve a single proton transfer (PT) from an NH group to a carbonyl group of the same uracil moiety, which should involve a rather high activation barrier that prevents the process occurring. However, the reaction-force, chemical-potential, and electronic-flux profiles unambiguously indicate that the actual mechanism involves three low-barrier elementary steps, and this explains why enolization of the [Cu(uracil-H)(uracil)](+) complexes is a highly facile, assisted PT process. All of the observed PT processes show a typical profile for both the chemical potential and the electronic flux associated with the bond-breaking and the bond-formation processes.

Effects of the ionization in the tautomerism of uracil: A reaction electronic flux perspective

“…Uracil molecule, as a part of the RNA helix, is one of the most studied compounds due to its relevance in pharmacy and biochemistry . Consequently, its acidity, basicity solvation by water molecules, its fragmentation in mass spectrometry, and its reactivity with respect to different reactants and metal ions have been investigated. Their tautomeric forms attracted the attention of many scientists along the years as they are suspected to be behind the genetic mutations .…”

“…The tautomerism of uracil has been investigated extensively. Recently, we have performed systematic studies on the effects that different transition and alkaline‐earth metal ions, namely Cu + , Cu 2+ , and Ca 2+ have on these processes, by paying particular attention to changes on the relative stability of the enolic form and on the height of the tautomerization barrier on metal cation association. These effects were found to depend strongly on the nature of the interaction between the metal cation and the uracil molecule.…”