Interaction of europium(III) with phospholipid vesicles as monitored by laser-excited europium(III) luminescence

Abstract

The technique of laser-excited Eu(III) luminescence was applied to monitor Eu(III) binding to a variety of phospholipids. Eu(III) excitation spectra were similar with and without the presence of neutral phospholipids, while acidic phospholipids changed the spectrum in a concentration-dependent manner. Eu(III) appears to bind to the phosphate moiety with at least a 2:1 phospholipid:metal ion stoichiometry. Analysis of luminescence lifetimes reveals that only one or two waters of hydration are removed from Eu(III) by addition of neutral phospholipids, whereas acidic phospholipids and inorganic phosphate strip off all but one or two waters. Implications with regard to fusion and use of lanthanides as probes in membrane preparations are discussed.

High-speed atomic force microscopy for nano-visualization of dynamic biomolecular processes

“…So far, spectroscopy experiments have revealed that metal cations specifically interact with negatively charged moieties of the lipid headgroups [212][213][214][215]. These experiments, together with theoretical simulations [216], have led to an idea that individual ions may interact with multiple headgroups to form complex "lipid-ion networks".…”

Subnanometer-Resolution Frequency Modulation Atomic Force Microscopy in Liquid for Biological Applications

“…To date, spectroscopy experiments have revealed that metal cations specifically interact with negatively charged moieties of the lipid headgroups. [40][41][42][43] These experiments, together with theoretical simulations, 44) support the idea that individual ions may interact with multiple headgroups to form complex "lipid-ion networks." This concept has been used to explain the previously observed effects of the ions, such as the enhancement of the mechanical strength of membranes 45) and the reduction of the mobility of the lipid molecules therein.…”

Ion-Channel – Mimetic Sensors Based on Self-Assembled Monolayers of Phosphate Esters: High Selectivity for Trivalent Cations

“…2, the phosphate monoester 1, diester 2, and triester 3 may be formed in monolayers prepared according to the above procedure. While all three compounds can be expected to bind Ca 2 and the other cations used in this study, binding strengths are expected to increase in the order of 3 < 2 < 1 [17]. No attempt to determine the molecular ratios of 1, 2, and 3 on the electrode was made.…”

“…Indeed, it has been shown that cation binding to phosphate esters at phospholipid membrane interfaces is accompanied by partial dehydration of the cation and the phosphate groups [17,21,22]. Therefore, it appears reasonable to explain the weaker responses to the more hydrophilic dications by the energetically unfavorable partial dehydration that is required for the formation of interfacial complexes of these ions.…”

“…[27] and references cited therein). However, while binding of Ca 2 to phospholipid monolayers indeed seems to occur by interfacial 1:1 complexation [20,28], binding of larger cations such as Tb 3 has been reported to occur by formation of 1:2 complexes between the cation and the phosphate groups [17,20]. Differences in binding stoichiometries may explain why the alkaline earth metal ion selectivity of the sensor reported here differs from the selectivity reported previously for binding to phospholipid aggregates (Ca 2 b Mg 2 b Sr 2 b Ba 2 ) [19].…”