Electrochemical, spectroscopic, and mass spectrometric studies of the interaction of silver species with polyamidoamine dendrimers

Electrochemical, spectroscopic, and mass spectrometric (MS) methods were used to probe the interaction (complexation) of silver ions and zerovalent silver species with polyamidoamine generation 1 amine-terminated (PAMA-MG1NH(2)) and generation 2 hydroxy-terminated (PAMA-MG2OH) dendrimers (DDMs). Stability constants (K-q(+)) and stoichiometries (q) (i.e., the number of silver ions complexed per DDM molecule) were determined from the voltammetric data, that is, shifts in potential and changes in peak or limiting current with addition of DDM. When the mole ratio of DDM to Ag+ is >= 1, Ag+ binds with PAMAMG2OH to form a dominant 1:1 complex with a el value of 1.1 x 10(7) M-1. Under similar conditions, Ag+ binds with PAMAMG1NH(2), yielding a 1:1 complex with K-1(+) = 4 x 10(9) M-1, which is consistent with the finding of the NIS experiments. When the mole ratio is < 1, q >= 2. The E(0')of the Ag-PAMAMG1NH(2)(+/0) couple shifted to a more negative value than that of die Ag+/0 couple. The negative shift in the halfwave potential also suggests that DDM binds more strongly with Ag+ than with zerovalent silver species. Spectroscopic results suggest that hydroxyl-terminated PAMAMG2OH favors the formation of small zerovalent silver clusters after reduction while amine-terminated PAMAMG1NH(2) allows for simultaneous formation of both clusters and larger nanoparticles at similar conditions. Other quantities, such as diffusion coefficients of the complexes and molar absorptivity of the Ag+ DDMs, are also reported.