ELECTROCHEMICAL PROPERTIES OF LANGMUIR-BLODGETT MIXED FILMS CONSISTING OF A WATER-SOLUBLE PORPHYRIN AND A PHOSPHOLIPID

Films of a water-soluble tetracationic porphyrin (TMPyP) and an insolu ble phospholipid (DMPA), in a molar ratio TMPyP:DMPA = 1:4, were trans ferred onto optically transparent indium tin oxide (ITO) electrodes, a nd cyclic voltammetry and visible spectroscopy were used to detected a nd quantify the presence of porphyrin on the ITO supports. We found th e surface density of porphyrin deposited ranges from that correspondin g to a monolayer of porphyrin monomers lying parallel to the electrode surface to the total amount of porphyrin (partially as dimer) present in the compressed monolayer at the air-water interface. Also, the ele ctrochemical properties of the films were analyzed in terms of experim ental variables including the nature and concentration of the electrol yte and the scan rate, used to obtain the voltammetric recordings. Whe n the reduction of TMPyP is a two-electron process and the salt concen tration moderate, porphyrin remains anchored to the phospholipid film, which makes the system highly stable and reversible in successive oxi dation-reduction cycles.