Influence of cationic gemini surfactants on the electrochemical behavior of 2-thiouracil at silver electrodes

Abstract

The voltammetric behavior of 2-thiouracil at a silver electrode is described. 2-Thiouracil can deposit or chemisorb anodically at silver surface; when the potential is made more negative the deposited 2-thiouracil undergoes reductive desorption-process, yielding a cathodic peak at about −1.2 V (vs. SCE) in basic phosphate buffer solution (pH 10.3). In the presence of cationic gemini surfactant C4H8–1,4-(C16H33N+ (CH3)2Br−)2 (C16–C4–C16) the deposition of 2-thiouracil is greatly improved and the cathodic peak is enhanced. Meanwhile, the peak shifts to more negative potential. The role of C16–C4–C16 is thought to combine and coadsorb with 2-thiouracil at silver surface as well as reduce the electrostatic repulse in the deposited film, thus making it more easy to deposit and desorb at more negative potential. With C16–C4–C16 the lateral interaction of deposits reduces, the reductive desorption becomes faster and the cathodic peak becomes sharper. For geminis with different spacer groups and alkyl chains, their influence is mainly determined by their hydrophobicity and adsorbability. It was found that increasing length of alkyl chain was favorable for obtaining a high and sharp desorption peak, whose peak potential is more negative. For comparison, surfactants with single alkyl-chain and double alkyl-chain, such as cetyltrimethyl ammonium bromide and dicetyldimethyl ammonium bromide were studied. They made the desorption peak shift less due to their weaker combination with 2-thiouracil.