Covalent versus Self-assembled Ln-receptor Design

2 Covalent versus Self-assembled Ln-receptor Design 

Typically an antenna can bind to the Ln via anionic sites such as carboxylates and phosphinates it is important to note that such a process is reversible and the kinetic robustness of the assembly will be determined by the local environment and competing binding events with endogenous ions/species. However, this apparent limitation can be used advantageously if, for example, the target analyte is chromophoric (i.e. the binding event switches on Ln emission) or a non-chromophoric residue displaces an antenna unit (i.e. the binding event switches off Ln emission Fig. 6.3). 

Of course, other scenarios are possible whereby a coordinatively unsaturated Ln complex already incorporates a covalently attached antenna. In such cases, binding events (displacement of coordinated water/solvent molecules) at the Ln ion are reported more subtly via changes in lifetime, quantum yield and observable changes in the form of the structured emission profiles, due to the hypersensitivity of certain/-/transitions (e.g. Eu ). Finally, it should be noted that reports of displacement assays based on lanthanide complexes are often conceptually directly related to the points above regarding reversible binding events at Ln the principle of a Ln -based displacement assay owes much to the discussion of self-assembled arrays. 

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