| Abstract
| - Processes of adsorption and metalation of a cationic water-soluble free base porphyrin, i.e., 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP) on Ag colloids have been monitored by surface enhanced resonanceRaman spectroscopy (SERRS) as a function of time and porphyrin concentrations. Ag colloids employedwere prepared either by laser ablation or by chemical reduction (by sodium borohydride and citrate) of Agsalts. SERRS intensities of TMPyP depend on the morphology of the colloidal aggregates in each system;aggregation, in turn, is governed by a balance between the so-called “diffusion limited aggregation” and“contact limited aggregation” processes, strongly influenced by the TMPyP concentration and the initial stateof the colloidal particles (i.e. the residuals ions stuck at the substrate surface). The time evolution of theoverall SERRS intensities is thus a function of the colloid preparation procedure. On the other hand, thekinetics of metalation reflects primarily the accessibility of the substrate surface for porphyrin adsorption.Consequently, it is highly sensitive to porphyrin concentration, the covering of the colloid surface by porphyrinmolecules being the main qualitative limiting factor. Moreover, the process of metalation is controlled byresidual ions at the substrate surface and therefore completely different for laser-ablated and chemically preparedAg colloids. In the former, the amount of the metalated species is only limited by the adsorbate concentrationwhile in the latter it is also mediated by the removal of residual ions from the colloidal surface by porphyrinmolecules.
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