Luminescence kinetic inertness

In addition to the features relevant to energy-transfer processes and minimization of nonradia-tive deactivation discussed above, the Lnm environment in a lanthanide-containing luminescent probe must also fulfill several other requirements high thermodynamic stability, kinetic inertness, and a saturated coordination sphere. Furthermore, in case of bio-analyses, the luminescent probe has to comply with biochemical aspects as well, especially if the probe is to be... 

A viable luminescent bioprobehas to meet several stringent requirements, among which are adequate photophysical properties, thermodynamic stability and kinetic inertness at physiological... 

Elhabiri et al., 2004a). The ultimate fixation of the third ligand in the neutral helicate [f 2(L13%] induces a considerable entropic gain to the overall complexation process, which is responsible for both extreme thermodynamic stability (Elhabiri et al., 1999) and kinetic inertness (Elhabiri et al., 2004b, Figure 59), which make these helicates promising building blocks for the development of luminescent bioprobes (see Section 6). 

Isolation of enantiomerically pure helicates. One disadvantage of Zn is its relatively large lability with respect to transmetallation, so that successful attempts have been made to replace it with Cr which, in addition to be optically active (see point 4 below), is kinetically inert, opening the way to designing chiral helical luminescent probes (Cantuel et al., 2004). Another possibility to produce inert 3d-4f helicates is to insert Co ions into the self-assembled edifices, followed by a mild and selective oxidation into the low-spin diamagnetic, and kinetically inert Co ion (Rigault et al., 1998). 

Cellular imaging has become a topic of intensive research in recent years, and luminescent metal-based probes have been intensively utilized for such a process. The transition metal ions of ruthenium(II), rhenium(I), and iridium(III) have been particularly effective as luminescent intracellular imaging agents owing to their kinetic inertness (low rates of ligand exchange), attractive photophysical properties (large... 

The competition titrations presented in the previous paragraph are interesting to establish the stability of a given complex compared to another. They are also useful tools to ensure the kinetic inertness of the complex over time. Any decrease of intensity would iudicate a modificatiou of the coordination sphere. On release of any ligand, the lanthanide ion would be exposed to water molecules in its vicinity, thus causing a decay of its luminescence intensity. Nevertheless, in snch long experiments, one has to ensure that the lamp is stable over time, that no evaporation of the solution or precipitation takes place over time, etc. 

With these experiments, it was possible to ascertain good stabihty of the helicate not only in solution (water or buffered solution or culture media) but also in the stringent conditions that can be found in biological media. Having estabhshed the thermodynamic stability of the complexes as well as their kinetic inertness, it is time to study their luminescent properties in detail. 

Following some detailed studies of kinetically inert complexes of yttrium - for targeted radiotherapy - and of gadolinium, for use as contrast agents in magnetic resonance imaging, we were attracted by the chemical versatility of single component, luminescent lanthanide complexes. The monoanionic tetracarboxylate and... 

In radiolysis, a significant proportion of excited states is produced by ion neutralization. Generally speaking, much more is known about the kinetics of the process than about the nature of the excited states produced. In inert gases at pressures of a few torr or more, the positive ion X+ converts to the diatomic ion X2+ very rapidly. On neutralization, dissociation occurs with production of X. Apparently there is no repulsive He2 state crossing the He2+ potential curve near the minimum. Thus, without He2+ in a vibrationally excited state, dissociative neutralization does not occur instead, neutralization is accompanied by a col-lisional radiative process. Luminescences from both He and He2 are known to occur via such a mechanism (Brocklehurst, 1968). 

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