Metal ion transfers among biological metabolites or proteins can be difficult to measure because of the spectroscopic signatures or the conditions of the measurement. Cu(II) and Zn(II) are two essential elements which are involved in metal ion transfer reactions between proteins and peptides in biology. Both elements have been implicated in Alzheimer’s disease development with the amyloid-beta peptide chelation resulting in deposits of these metal ions in amyloid plaques within the brain. We have used tryptophan fluorescence quenching to measure inter- and intra-peptidic Cu(II) exchange rate constants in some Aβ binding models, and motifs found in blood serum such as GHK and DAHK, by substituting non-coordinating lysine with tryptophan, GHW and DAHW (1). These exchanges had second-order kinetic rate constants that could be determined by fluorescence using the method of initial rates (k ~ x 102 / x 101 M-1s-1). Similarly, we measured Zn(II) transfer at the nanoscale. In a reverse micellar system, composed of a self-assembling surfactant, AOT, in isolated small water droplets within a membrane-like interface we investigated Zn(II) chelation reactions (2). To mimic metal ion bursts which are observed in biology, a Zn(II) photocage was used to release ions induced by photolysis. We followed the release of Zn(II) using a second ligand, Zincon, by measuring the absorption spectroscopy of Zincon as it chelated Zn(II). The interface of the reverse micelle slowed the coordination reaction of Zincon binding Zn(II) compared to corresponding coordination reaction in aqueous buffered solution. The rate decrease was observed despite the proximity of the reactants and was attributed to the association of the reaction components at the interface, resulting in an overall decrease in rates. This methodology can potentially be used to monitor fast metal ion transfers at the nanoscale, without the interference of the diverse metabolites present in living cells.

Measuring transition metal ion transfer of the essential ions Cu(II)and Zn(II) in complex systems

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.