STRUCTURAL CHARACTERIZATION OF VALINOMYCIN AND NONACTIN AT THE AIR-SOLUTION INTERFACE BY GRAZING-INCIDENCE X-RAY-DIFFRACTION

Grazing incidence X-ray diffraction (GID) has been applied to the stud y of structural characteristics of two-dimensional crystallites of the ionophores valinomycin (VM) and nonactin (NA) when complexed with var ious cations at the air-solution interface. The VM complexes assume a bracelet shape that packs in a two-dimensional hexagonal unit cell. Ot her crystalline phases were formed on potassium iodide and barium perc hlorate solutions. The presence of particular lipids induced ordered s tacking of VM-potassium chloride complexes into three to four layers, NA packs in a pseudotetragonal unit cell on solutions of NH4SCN and KS CN. Upon compression of the NA-NH4SCN film, crystallites seven to eigh t layers thick were detected and the GID data enabled the determinatio n of the structure. The tendency of these complexed ionophores to form multilayer crystallites at interfaces may have bearing on ion transpo rt through membranes, via stacking.