Not just a background: pH buffers do interact with lanthanide ions\u2014a Europium(III) case study

Jerome Kretzschmar,Poulami Mandal,Björn Drobot

doi:10.1007/s00775-022-01930-x

Abstract

The interaction between Eu(III) ion and different pH buffers, popular in biology and biochemistry, viz. HEPES, PIPES, MES, MOPS, and TRIS, has been studied by solution nuclear magnetic resonance spectroscopy (NMR) and time-resolved laser-induced fluorescence spectroscopy (TRLFS) techniques. The Good’s buffers reveal non-negligible interaction with Eu(III) as determined from their complex stability constants, where the sites of interaction are the morpholine and piperazine nitrogen atoms, respectively. In contrast, TRIS buffer shows practically no affinity towards Eu(III). Therefore, when investigating lanthanides, TRIS buffer should be preferred over Good’s buffers.Graphical abstract

Highlights

A ubiquitous feature of many aqueous, chemical and biological reactions is their pH sensitivity
The provided complex stability constants are based on complex structure and buffer pKa, so these thermodynamic parameters can be used to calculate speciation of Eu(III)–buffer-systems with different composition
The results indicate that all the chosen buffers except TRIS interact significantly with Eu(III)

Summary

Introduction

A ubiquitous feature of many aqueous, chemical and biological reactions is their pH sensitivity. Chemical reactions involving complex formation [1, 2], oxidation–reduction [3, 4], catalytic reactions [5, 6] or acid–base reactions [7, 8] significantly depend on the solution’s hydrogen ion concentration. The buffer concept is based upon the protonation–deprotonation equilibrium of a weak acid–base pair. Close to their pKa values, buffer molecules exist simultaneously in both forms. This enables the buffer to scavenge or release protons and thereby stabilizes the pH value against changes in total proton concentration

Methods

Results

Conclusion