Cation Transport across Bulk Liquid Organic Membranes with Oligomers of (R)‐3‐Hydroxybutanoic Acid

Several oligomeric derivatives 1–5 of (R)‐3‐hydroxybutanoic acid and a cyclic trimer of (R)‐3‐hydroxypentanoic acid (6) were used as ionophores to transport potassium picrate across a bulk liquid CH2Cl2 membrane. Using the cyclic trimer 1 and an oligomer mixture of (R)‐3‐hydroxybutanoic acid, 5 (ca. 28‐mer), for the transport experiments, the alkali‐metal ions from Li+ to Cs+ and the alkaline‐earth‐metal ions from Mg2+ to Ba2+ were also shown to be transported through the organic phase. Although a pronounced enhancement of the transport rates was observed in the presence of 3‐hydroxyalkanoate oligomers, no special selectivity for one ion was detected. The ionophore properties of the investigated oligomers and oligolides derived from 3‐hydroxybutanoic acid are compatible with the alleged role of oligo(3‐hydroxybutanoate) (c‐PHB; ca. 120‐mer) as component of ion channels through cell membranes.