13C relaxation studies of the structure and flexibility of the carboxylic ionophore lasalocid A

Abstract

Carbon-13 spin lattice relaxation times (T1) were determined for all the protonated carbon atoms of the carboxylic ionophore lasalocid A in non-hydroxylic (CDCl3) and hydroxylic (CD3OD) media. In CDCl3, the motions of the protonated backbone carbon atoms C-4 to C-24 (inclusive) are all equally restricted. The correlation time for overall molecular reorientation, τeff, calculated from an average NT1 value of 565 ms, is 8.6 × 10–11 s, where N is the number of attached protons. The carbon atoms in the side chains are more mobile than those in the backbone. The carbon backbone in CD3OD is characterized by segmental motion at the aromatic end, as evidenced by increased NT1, values for C-4, C-5, C-7, and C-8. The reminder of the backbone appears to be rigid and to have a τeff virtually identical with that observed for the entire backbone in CDCl3. These results are discussed in terms of the mechanism that has been proposed for ion complexation and transport by carboxylic ionophores in biomembranes.