The Structure of Valinomycin Cesium Picrate

The structure by X-ray crystallography of the valinomycin–cesium picrate complex has been determined by the heavy atom method. The crystal class was trigonal, space group P31, with unit cell dimensions a = b = 14.028(4) â, 31.888(10) Ǎ, Z = 3, filtered Mo radiation; the final value of R was 0.111 for 4088 reflections measured at − 170 °C. The enclosed cation was found to be too large for the cavity, causing the valinomycin to be incompletely closed and forming a weak bond with the picrate at the D-valyl end, which was the same end as had been previously found to be involved in the sodium complex. This result is in agreement with the proposal that the cation enters and exits by the D-valyl end.