Application of a weakly basic dimethylamino-modified silica ion exchanger to the separation of oligonucleotides

Abstract

LiChrosorb RP-8, RP-18 and Diol as well as a newly synthesized basic dimethylamino-modified silica ion-exchanger (DMA-silica) were applied for the separation of adenylic acid, cytidylic acid and uridylic acid oligoribonucleotides. On LiChrosorb RP-8 and RP-18, respectively, in aqueous buffered eluents (K 2HPO 4- H 3PO 4), the retention of oligonucleotides was increased with decreasing number of nucleotide units in the solute, i.e., with increasing hydrophobic character. The elution behaviour of ologonucleotides on LiChrosorb Diol followed the same order but took place according to a size-exclusion mechanism. The retention of oligonucleotides on DMA-silica is assumed to be based on electrostatic interactions between the charged. solute and the ionic surface sites of DMA. This is evidenced by (i) the exponential decrease of k′ of the solute with increasing salt concentration of buffer, and (ii) the increase of log k′ of the solute with the number of nucleotide units, i.e., negative charges in the oligoribonucleotide solute. The relative contribution of ionic and molecular interactions to total retention of the solutes is descussed.