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

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

Studies of pyrroloquinoline quinone species in solution and in lanthanide-dependent methanol dehydrogenases

“…S7, ESI †). To avoid formation of Eu-buffer complex species, 36 this experiment was carried out in non-buffered NaCl solution. For the titration experiments, two solutions were prepared: 10 mM Eu-MDH (with only partially occupied Eu-sites) and 3 mM EuCl 3 both in 100 mM NaCl at pH 6.5.…”

Analysis of Anion Binding Effects on the Sensitized Luminescence of Macrocyclic Europium(III) Complexes

“…Under acidic conditions the complexes of the hexadentate Lt ligands were unstable (Figures S56–57). Buffer components may influence Ln(III) luminescence [28] . While TRIS has recently been reported to interact less with hydrated Eu(III) than PIPES, it has a clear influence on EuLc3 s,MOM (Figure S49).…”

Effect of Lipophilicity in Oxyanion‐Responsive Europium(III) Complexes**

“…It is well known in literature that media plays a major effect on the recognition event in host‐guest systems [39,40] . It can either be competitive or not, and no general conclusion should be drawn based on data from a unique media [33–35] .…”

“…It is well known in literature that media plays a major effect on the recognition event in host-guest systems. [39,40] It can either be competitive or not, and no general conclusion should be drawn based on data from a unique media. [33][34][35] We noted that europium(III) complexes and analytes were not fully soluble in mixture of MeOH and water, and that the ternary complexes were not fully soluble in pure buffer.…”

“…[30] We have previously worked on quantifying interactions in lanthanide based supramolecular chemistry, [31][32][33][34][35][36] where quantification required highly alkaline, non-aqueous media. In general, there is a significant focus on media and salt effects in supramolecular chemistry, [37][38][39][40] and in this work we seek an aqueous solvent system that allows us to mitigate the effects of salinity, pH, and any non-specific hydrophobic interactions of guest and host molecules. Our starting point is a recent paper by our group, where luminescent response to bicarbonate of the europium(III) complex of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) was thoroughly studied in various aqueous media.…”