CARRIERS FOR LIQUID MEMBRANE-TRANSPORT OF NUCLEOTIDE 5'-TRIPHOSPHATES

The transport of the nucleotide triphosphates adenosine 5'-triphosphate (ATP), cytidine 5'-triphosphate (CTP), 2',3'-dideoxythymidine 5'-triphosphate (ddTTP), and 3'-azido-2'-deoxythymidine 5'-triphosphate (AZTTP) across a liquid organic membrane mediated by cationic DABCO-derived carriers was studied. With their branched aliphatic chains, these compounds, which bear two (2), three (3), or four (4) quaternary ammonium centers show excellent solubility in chloroform, the solvent chosen as liquid organic membrane. The bisquaternary mono(DABCO) derivative 2 was found to be the most efficient carrier for all nucleotides. Concentration-dependent extraction studies showed that 2 undergoes formation of a 2:1 carrier-nucleotide complex in the chloroform phase. This stoichiometry differs from the 1:1 stoichiometry previously suggested by Tabushi et al. for the association between nucleotide 5'-triphosphates and a bisquaternary DABCO derivative. The tricationic compound 3 is generally inferior to 2 in its carrier properties but shows an unexpectedly high selectivity for transporting ddTTP. The tetracationic bis(DABCO) derivative 4 shows poor carrier properties since it forms highly water-soluble associations which prefer distribution into the aqueous phase rather than into the liquid membrane.