| Abstract
| - The lability of sequential metal complexes, ML, ML2, ML3, ... , up to a general 1:n metal/ligand stoichiometricratio is considered for the case of metal ions (M) being accumulated at a surface (analytical sensor or organism).The analytical solution for the steady-state diffusion of M within a sequential complexation scheme allowsquantification of the contribution from the dissociation of all of the complex species to the metal flux throughthe so-called lability degree, ξ. A lability degree for each sequential complexation step is also defined which,due to the sequential character of the complexation scheme, depends not only on the proper kinetic constantsof the given complexation step but also on the kinetics of the previous ones. When all contributions from thecomplexes are diffusion limited, the system is fully labile and ξ = 1. To provide simple lability criteria, thereaction layer approximation is extended to specifically deal with this sequential complexation scheme, sothat a reaction layer thickness is defined when the existence of one particular rate-limiting step is assumed.Expressions for the classical lability parameter, L, are formulated using the reaction layer approximation.The change of the lability of the system as the diffusion layer thickness is modified is analyzed in detail. Thecontribution of the complex flux reflects the evolution of the system from labile to inert as the thickness ofthe sensor is appropriately decreased.
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