Chmistry Essay Example | Topics and Well Written Essays - 1500 words

Chmistry - Essay Example The molecule is "locked" into a conformation with the isopropyl groups on the exterior. 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 (Metzeler 2001) Question 1b Valinomycin is a dodecadepsipeptide, that is, it is made of twelve alternating amino acids and esters to form a macro cyclic molecule. The twelve carbonyl groups are essential for the binding of metal ions, and also for solvation in polar solvent. The isopropyl and methyl groups are responsible for solvation in nonpolar solvents. Along with its shape and size this molecular duality is the main reason for its binding properties. K+ ions are octahedral coordinated in a square bi-pyramidal geometry by 6 carbonyl bonds in this space of 1.33 Angstrom, leading to a 10,000x selectivity for K+ ions. For polar solvents, valinomycin will mainly expose the carbonyls to the solvent and in nonpolar solven ts 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. 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. Conformational and ionophoric properties of 3 valinomycin analogs cyclo n (n = 2, 3, 4) were studied by spectral and extraction methods. Conformations of dodeca- and hexadecaisoleucinomycins in nonpolar media practically do not differ from that of valinomycin, whereas for octaisoleucinomycin and octavalinomycin the conformations change significantly. Spatial structures of complexes of the investigated compounds are analogous to structures of complexes of valinomycin cyclopolymerhomologs (Metzeler 2001) The presence of isoleucine residues in dodeca- and hexadecaisole ucinomycins results in substantial increase in their ability of transfer the cat ions from aqueous to organic phase. Each complex has a characteristic spectrum which differs from that of uncomplexed valinomycin, suggesting several distinct structures for each of the metal-valinomycin complexes. The biologically active K complex shows the most significant changes in its spectrum, especially in the intensity of the symmetric C-H stretching vibration of CH3 and the convergence of the 2 ester carbonyl stretching vibration bands into 1 upon complex formation. These results are due to the unique orientation of the ester carbonyl groups toward the caged K ion and the resulting more free rotation of isopropyl side chains, thus they are poor cat ions transporters, assumptions made are that valinomycin has a complex structure as compared to octa-isoleucinomycin and hexadecaisoleucinomycin, differs in bonding in the methyl groups and the space in orientation make it superior in terms of bondin g and having a chelate effect as compared to its