Y. Temerk, M. Kamal
Dec 1, 1983
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Journal
Journal of Electroanalytical Chemistry
Abstract
Abstract The adsorption stages and association of 2-methylguanosine in solutions of varying pH have been studied at the hanging mercury drop electrode by phase-sensitive a.c. voltammetry. The adsorption equilibrium and its attainment have been investigated as a function of various parameters such as pH, adsorption potential U s , adsorption time t s , temperature and the bulk concentration of 2-methylguanosine. Over a wide potential range, 2-methylguanosine exhibits a dilute adsorption region where it is adsorbed with the base flat on the electrode surface. At elevated bulk concentrations above a threshold value, 2-methylguanosine appears to undergo surface reorientation around U e.c.m. and adopts a perpendicular position. In this new orientation it is concluded that the stacking interactions between vertically oriented molecules of 2-methylguanosine lead to the association and formation of a compact layer in the pit region. Characteristic properties and adsorption parameters of the dilute and compact layers of 2-methylguanosine were evaluated from -the obtained two-step Frumkin isotherm and from the potential dependence of adsorption. The resulting adsorption parameters of 2-methylguanosine have been computed at various pH's and at different temperatures, and compared with those of guanosine. Methylation increases the surface activity of guanosine and decreases the value of the interaction coefficient a .