A laser-induced europium (III) ion luminescence study of the interaction of this ion with phospholipid bilayer vesicles above and below the gel to liquid-crystalline phase transition temperature

Multiphoton Ligand-Enhanced Excitation of Lanthanides

We describe multiphoton excitation of the lanthanides europium (Eu³⁺) and terbium (Tb³⁺) when these ions are complexed with nucleic acids, proteins, and fluorescent chelators. In all cases excitation occurs by multiphoton absorption of the sensitizers. For the nucleotide GDP and an oligonucleotide with several guanines, the sensitized emission of Tb³⁺ excited at 776 nm indicated a three-photon process. For Tb³⁺ bound to the wild-type troponin C and a single tryptophan mutant (26W), excitation at 794 nm was also close to a three-photon process. For lanthanide chelators containing various sensitizers, we observed three-photon excitation in the case of methyl anthranilate, a mixuture of two- and three-photon excitation for carbostyril 124, and a two-photon process with a coumarin derivative. In the case of coumarin-sensitized emission of Eu³⁺ varied from a two- to a three-photon process at wavelengths ranging from 780 to 880 nm. The sensitized luminescence also shows significantly higher photostability compared to the fluorescence from the organic fluorophores alone. These results suggest the use of multiphoton-induced sensitized lanthanide fluorescence in biochemistry and cellular imaging.

Gd3+ vibronic side band spectroscopy. New optical probe of Ca2+ binding sites applied to biological macromolecules

A new spectroscopic technique is presented for obtaining infraredlike spectra of the binding sites of Ca2+ and other metals in biological macromolecules. The technique, based on the Ca(2+)-like binding properties of Gd3+, utilizes vibronic side bands (VSB) that appear in Gd3+ fluorescence. In the fluorescence spectrum of Gd3+, the separation in photon frequency between a VSB and its electronic origin at approximately 32,150 cm-1 (approximately 311 nm) is a direct measure of the vibrational frequency of a ligand coordinated to Gd3+ ion. As a consequence, the VSB are uncomplicated by molecular vibrations distant from the Gd3+ binding site. The vibrational spectra resulting from the VSB of Gd3+ coordinated to a Ca2+ binding protein, a phospholipid, and DNA are presented.

Physical characterization of and ionophore-mediated europium(III) transport through unilamellar phosphatidylcholine vesicles. A laser-induced europium(III) luminescence spectroscopy study

A continuation of the study of phospholipid bilayer vesicles as model membrane systems by laser-induced europium(III) luminescence spectroscopy is presented here (B.M. Cader and W. DeW. Horrocks, Jr, Biophys. Chem. 32 (1988) 97). This spectroscopic technique was used to characterize further the physical properties of small and large vesicles composed of dipalmitoylphosphatidylcholine and egg phosphatidylcholine, respectively. Unilamellar preparations were confirmed and internal aqueous volumes were calculated. The calcium-binding carboxylic ionophores, lasalocid A and A23187, were incorporated into the lipid bilayers of these vesicles for the purpose of modeling the mobile carrier mechanism of ion transport across cell membranes. Spectroscopic data implicate the presence of 1:1 and 1:2 europium(III)/lasalocid A complexes within the hydrophobic region, both capable of efficient transport and containing no water molecules in the inner sphere of europium(III). First-order rate constants for lasalocid A-mediated europium(III) transport were determined at 37 and 62 degrees C (0.018 and 0.11 min-1, respectively) using EGTA as a 'flag' to bind and detect the post-transported metal ion.