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The shielding properties of the terphenyl-based complex L·Eu³⁺ in methanol solution have been studied by computer simulations with an emphasis on the influence of small amounts of water on the shielding properties. The theoretical studies were carried out in explicit solvent models by molecular mechanics and dynamics simulations (up to 2000 ps), Monte Carlo free energy perturbations, and a potential of mean force calculation. In dry methanol solutions, complex L·Eu³⁺ is predicted to have one methanol coordinated to the Eu³⁺. The presence of 1.0 ± 0.5 OH groups (from methanol) is in agreement with fluorescence measurements. Millimolar concentrations of water lead to a monohydrated complex and possibly to a dihydrated complex. At these concentrations of water in the methanol solutions of L·Eu³⁺, the luminescence intensities decrease, which supports the conclusion that one and possibly two waters are preferentially coordinated to the Eu³⁺ ion. This study also shows that molecular dynamics runs of 1 ns or more are needed to allow major transitions in the first coordination sphere of Eu³⁺ to occur, but even simulations up to 2 ns do not guarantee that the global energy minimum is calculated.

Rare earth ions, with relatively long luminescence lifetimes, have significant advantages for application in fields as varied as diagnostics and optical amplification. In diagnostics the long luminescence lifetimes allow for extremely sensitive time-gated detection, where the difference in temporal behavior of scatter and background fluorescence and the long-lived rare earth luminescence is utilized. In optical amplification the long excited-state lifetime makes it easier to obtain population inversion, a requirement for effective stimulated emission. Unfortunately the absorption cross section of rare earth ion transitions is extremely low. However, via sensitized excitation by means of a suitable organic molecule, efficient excitation is obtained. It is shown that excitation in the visible part of the spectrum can be used to excite rare earth ions which luminesce in the near-IR, such as ytterbium, neodymium, and erbium, via a fluorescein-derivative as sensitizer. The advantages of this approach are manifold. Low-cost light sources are available for the visible part of the spectrum, and interferences from the matrix (scatter, absorption) are minimal. Detection in the near-IR is almost interference-free. For optical amplification the wavelength regions around 1300 and 1550 nm, which can be covered with the neodymium and erbium complexes, respectively, are the most important for applications in optical telecommunication.

Biliary secretion of phospholipids (PL) and cholesterol (CH) is regulated by bile acids (BA). However, a number of organic anions (OA) has been shown to inhibit PL and CH secretion without affecting that of BA. The mechanism of this OA-effect is unclear. We studied this uncoupling phenomenon with 3 different OA in normal Wistar (NW) rats and Groningen Yellow (GY) Wistar rats. The GY strain has a genetic defect in biliary secretions of various OA (JCI 81: 1593-9, 1988). NW and GY rats with 8-day bile diversion were injected intravenously with ampicillin (18 mol.100 g BW), sufated taurolithocholic acid (STLC, 1.0 umol/100gBW) or idocyanine green (ICG, 0.6 umol/100g BW). At 1 hr after injection recoveries in bile were: ampicillin, 4.1% and 0.5%; STLC 98% and 32%; ICG, 39% and 9%, in NW and GY rats, respectively. Ampicillin and STLC caused a strong uncoupling in NW rats (maximal BA.(PL+CH) -ratio+ 70% (ampicillin) and +147%(STLC), but no (ampicillin) or a much smaller (STLC +65%) uncoupling in GY rats. ICG injections did not induce an uncoupling, either in NW rats or in GY rats. The hetatic uptake of the used OA appeared to be unaffected in GY rats. Gel filtration chromatography (Sepharose CL-4B) showed that ampicillin and STLC coeluted with BA, while ICG coeluted with the PL and CH fraction. We conclude that the uncoupling of biliary PL and CH from BA secretion by ampicillin and STLC is not due to disturbance of processes at intracellular or bile canalicular membrane level, but to interactions with BA inside the canalicular lumen which disturb PL and CH solubilization.