Surface-enhanced resonance Raman spectra of water-insoluble tetraphenylporphyrin and chlorophyll a on silver hydrosols with a dioxane molecular spacer

A surface-enhanced resonance Raman spectroscopic (SERRS) study of tetraphenylporphyrin (TTP) on a silver hydrosol, obtained by mixing a dioxane solution of the water-insoluble TPP with the hydrosol, indicates that there is no metallation of the porphyrin. By contrast, water-soluble porphyrins such as tetra-N-methylpyridylporphyrin (TMPyP) have been shown to undergo metallation. We suggest that the TPP is encapsulated within a dioxane envelope which is co-adsorbed to the surface of the silver hydrosol and functions as a molecular spacer. This spacer does not eliminate the analytical advantages afforded by SERRS, but does prevent significant perturbation from the native conformation, as is demonstrated by results obtained using chlorophyll a.