Crystal and molecular structure of K+ complex of meso-valinomycin, cyclo[-(D-Val-L-Hyi-L-Val-D-Hyi)(3)-]center dot KAuCl4

Crystal structure of the complex of meso-valinomycin with KAuCl4 (C60H102N6O18KAuCl4) was determined using direct X-ray diffraction analysis. The conformational state of the complex is similar to that determined earlier for free meso-valinomycin. Characteristic of it is the centrosymmetric bracelet shape stabilized by six intramolecular NH...OC hydrogen bonds of 4 --> 1 type. The K+ ion is located in an inner negatively charged octahedral cavity formed by six carbonyl oxygen atoms of ester groups. The observed differences in conformational angles of the complex and free forms are caused by readjustment of the geometry of the ion-binding cavity to the size of the ion bound during complexation.