Development and electrochemical characterization of functional self-assembled monolayrs

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(1) Hydroxylalkanetiols (HAT), carboxylalkanethiols (CAT) and aminoalkanethiols (AAT) having different alkyl chain-length were synthesized and a gold electrode was modified with the self-assembled monolayrs (SAMs) of these thiols. Ferrocene derivatives having different chargeable side chain unit were also prepared for the electrochemical reduction and oxidation species. From the dependence of the SAM terminal charges on the voltammetric response of the ferrocenedimethanol, the effect of the terminal charges on the electrical double layr potential was quantitatively estimated. As compared to the neutral HAT modified electrode (HAT/Au), it was found that the change of the double layr potential is in the ranges of 15 - 45 mV and -15 --45 mV for the AAT/Au and CAT/Au, respectively. Based on these results, SAM/Au was utilized as the selective electrode for the catechol derivatives.(2) By using the reactivity of the amino unit of the AAT,quinone derivatives were immobilized on the AAT/Au surface and its electrochemical response was studied. In the case of naphtoquinone, the chargetransfer rate between the NQ and Au surface was decreased exponentially with increasing the alkyl chain-length of the AAT.In the case of quinolinequinone, electrochemically reversible responses were observed independent of the alkyl chain-length.(3) Cysteine containing dipeptides having two side chains were modified on a gold electrode as the SAM.Then the effect of the co-existing ions on the voltammetric response of Fe (CN)_6^3 was studied. In the case of the longer side-chains monolayr, the voltammetric response was considerably affected by the kind of co-existing ion. In the case of shorter side-chains monolayr, the effect of type of co-existing ion was scare as compared to the longer side-chains monolayr.