Potential and structure controlled interfacial behavior of uracil derivatives

The adsorption and related interfacial behavior of uracil, various methylated uracil derivatives, uridine, uridine-5'-monophosphate and uridine-3'5'-cyclic monophosphate has been studied by surface electrochemical measurements at a mercury electrode. All uracil derivatives exhibit an initial "dilute" adsorption region where the virtually flat uracil residue is absorbed flat on the electrode surface. In the case of uracil and its methylated derivatives the area occupied by one molecule is about 60-70 A2. Uracil, thymine and 1,5-dimethyluracil exhibit a second adsorption region where they rearrange on the surface and adopt a perpendicular orientation and occupy about 40 A2 per molecule. In this perpendicular orientation the uracils are bound to the electrode through the N(3)-H or perhaps N(1)-H functions in a manner similar to their Watson-Crick bonding in nucleic acids. When in the perpendicular orientation the adsorbed molecules undergo extensive stacking (association) interactions, again similar to those observed between adjacent bases in nucleic acids. The ability of a uracil derivative to undergo a surface reorientation is critically dependent on electrode potential, bulk-solution concentration and molecular structure.