Self-assembled Triple Helical Bioprobes

Crystal structures are only available for [Ln2(L30a)3] (Ln = Eu, Tb). They show the two metal ions lying on a pseudo-C axis, at a distance of about 9 A, and the three ligand strands helically wrapped around them, forming protective NsOa nine-coordinate environments (Fig. 4.17, left). 

This structure is maintained in solution, as demonstrated by lanthanide-induced shift analysis on eight different helicates [165]. Although quite precise, the procedure is somewhat long and involved so that the structure of the other dinuclear bioprobes has simply been ascertained by the NMR spectra of the chelates with diamagnetic Ln ions, which point to 

Relevant photophysical parameters for the [Eu2(L)3] helicates are reported in Table 4.6. The most striking characteristics are the large molar absorption coefficients, around 

85 000 cm that are far larger than those exhibited by most lanthanide bioprobes, long lifetimes, and sizeable quantum yields in aqueous solution. Among the helicates tested, the one with H2L30b proved to be the best, especially that the ligand sensitises also Tb  

Another important information to unravel is where the luminescent helicates are located within the cytosol of the live cells. To this end, co-localisation experiments have been conducted with organic stains known to localise in specific compartments of the cells, such as acridine orange (AO), which stains the cell nuclei. In the top part of Fig. 4.18, the helicate is shown to be entrapped into isolated vesicles which diffuse into the cytoplasm and the size of which is usually around 0.5-1.5 pm, with shapes ranging from flecks, spheres to ellipsoids. After 1 h incubation, vesicles have concentrated around the nucleus, as ascertained by the counter-staining experiment with AO (Fig. 4.18). In fact, other counter-staining experiments 

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