Theoretical and experimental study of the complexation of valinomycin with ammonium cation.
The interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with ammonium cation NH4+ have been investigated. Using quantum mechanical density functional theory (DFT) calculations, the most probable structure of the valinomycin-NH4+ complex species was predicted. In this complex, the ammonium cation is bound partly by three strong hydrogen bonds to three ester carbonyl oxygen atoms of valinomycin and partly by somewhat weaker hydrogen bonds to the remaining three ester carbonyl groups of the valinomycin ligand. The strength of the valinomycin-NH4+ complex was evaluated experimentally by capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the ammonium ion concentration in the background electrolyte, the apparent binding (association, stability) constant (Kb) of the valinomycin-NH4+ complex in methanol was evaluated as log Kb = 1.52 +/- 0.22.
Dybal
Jirí
J
Institute of Macromolecular Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Heyrovského 2, 162 06 Prague 6, Czech Republic.
Ehala
Sille
S
Kasicka
Václav
V
Makrlík
Emanuel
E
D000900:Anti-Bacterial Agents / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D014634:Valinomycin / Q000737:chemistry*
D000900:Anti-Bacterial Agents; D002412:Cations; D000644:Quaternary Ammonium Compounds; D014634:Valinomycin