Surface-Promoted Thioether Linkage between Proto- or Hemato porphyrins and Thiol-Silanized Quartz: Formation of Self-Assembled Monolayers and Interaction with Imidazole and Carbon Monoxide

Abstract

Free base protoporphyrin IX (PP),1 Zn(II)protoporphyrin IX (Zn(II)PP), Fe(III)protoporphyrin IX (Fe(III)PP), and Fe(III)protoporphyrin IX dimethylester (Fe(III)PPDME) as well as free base hematoporphyrin were selectively chemisorbed onto thiol-silanized quartz in aqueous media at neutral pH values and at room temperature. The self-assembled monolayers (SAMs) were characterized by UV/vis absorption and fluorescence spectroscopy. Evidence for chemisorption through the formation of thioether linkages between the immobilized thiols at the surface and the vinyl or the hydroxyethyl groups of the porphyrins is as follows: (1) Only porphyrins that possess either vinyl or hydroxyethyl groups show the characteristic absorption and properties of a SAM; porphyrins free of vinyl or hydroxyethyl groups do not form SAMs. (2) Attachment to the surface through the propionates of the metal is ruled out since the presence of both metal and propionates is not mandatory for the formation of SAMs. (3) None of the porphyrins f...