Structure of valinomycin-K+ complex and cryptate-k+ complex in solution by extended x-ray absorption fine structure
Wang, C. C.
Master of Arts
A new tool used to study the structure of molecules is Extended X-ray Absorption Fine Structure (EXAFS). EXAFS is small oscillatory signals added on to the smooth x-ray absorption structure curve produced from the excitation of an inner electron out of its bound inner shell into a free electron state. The oscillations are produced from scattering of the excited electron from surrounding atoms. These oscillations, EXAFS, contain molecular structure information, such as the distances between atoms. Since EXAFS can be used for crystals, amorphous solids, solutions and gases it has a strong advantage over x-ray crystallography in many cases for determining local structural information. I used EXAFS to determine what structural changes occur between the known crystalline states and the unknown solution states of K+ complexed with the ionophores cryptate and valinomycin. Ionophores are organic molecules which have a polar oxygen and nitrogen cage in the center of the molecule and a hydrophobic organic exterior. These ionophores are capable of trapping a potassium ion within the cage. The hydrophobic exterior allows the ionophore to dissolve in organic solvents. For the K+-cryptate complex I found no differences in the structure between the crystalline and acetone solution states. For the K+-valinomycin complex I found the K+- distances increased by .3 ± .2 A in the solutions as compared to the crystalline state.