Although widely used in bioassays, the spectrofluorimetric method described here uses the antenna effect as a tool to probe the thermodynamic parameters of ligands that sensitize lanthanide luminescence. The Eu(3+) coordination chemistry, solution thermodynamic stability, and photophysical properties of the spermine-based hydroxypyridonate octadentate chelator 3,4,3-LI(1,2-HOPO) are reported. The complex [Eu(III)(3,4,3-LI(1,2-HOPO))](-) luminesces with a long lifetime (805 mus) and a quantum yield of 7.0% in aqueous solution, at pH 7.4. These remarkable optical properties were exploited to determine the high (and proton-independent) stability of the complex (log beta(110) = 20.2(2)) and to define the influence of the ligand scaffold on the stability and photophysical properties.
4 Figures and Tables
Figure 1. Structures of the octadentate hydroxypyridonate ligands 3,4,3- LI(1,2-HOPO) (1, left) and H(2,2)-1,2-HOPO (2, right); the metalcoordinating oxygen atoms are indicated in red.
Table 1. Summary of Photophysical Parameters for [EuIII(1)]- a
Figure 2. Electronic absorption (solid, left) and normalized steady-state emission spectra (solid, right, λexc = 325 nm) of [EuIII(1)]-, and electronic absorption spectrum (dash) of [EuIII(2)]0, in 0.1 M TRIS buffer (pH 7.4).
Table 2. Protonation and Eu Complex Formation Constants for Ligand 1a
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