Editing Valinomycin (section)

==Structure==
Valinomycin is a dodecadepsipeptide, that is, it is made of twelve alternating [[amino acid]]s and [[ester]]s to form a macrocyclic molecule. The twelve [[carbonyl]] groups are essential for the binding of metal ions, and also for [[solvation]] in [[solvent|polar solvents]]. The [[isopropyl]] and [[methyl]] groups are responsible for solvation in [[solvent|nonpolar solvent]]s.
<ref>{{cite journal |vauthors=Thompson M, Krull UJ|title=The electroanalytical response of the bilayer lipid membrane to valinomycin: membrane cholesterol content | journal=[[Anal. Chim. Acta]] | year=1982 | volume=141 | pages=33–47 | doi=10.1016/S0003-2670(01)95308-5|bibcode=1982AcAC..141...33T }}</ref> Along with its shape and size this molecular duality is the main reason for its binding properties. K ions must give up their water of hydration to pass through the pore. K<sup>+</sup> ions are octahedrally coordinated in a square bipyramidal geometry by 6 carbonyl bonds from Val. In this space of 1.33 Angstrom, Na<sup>+</sup> with its 0.95 Angstrom radius, is significantly smaller than the channel, meaning that Na<sup>+</sup> cannot form ionic bonds with the amino acids of the pore at equivalent energy as those it gives up with the water molecules. This leads to a 10,000x selectivity for K<sup>+</sup> ions over Na<sup>+</sup>. For polar solvents, valinomycin will mainly expose the carbonyls to the solvent and in nonpolar solvents the isopropyl groups are located predominantly on the exterior of the molecule. This conformation changes when valinomycin is bound to a potassium ion. The molecule is "locked" into a conformation with the isopropyl groups on the exterior [Citation Needed]. It is not actually locked into configuration because the size of the molecule makes it highly flexible, but the potassium ion gives some degree of coordination to the macromolecule.