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Capillary affinity electrophoresis and ab initio calculation studies of valinomycin complexation with Na + ion
Author(s) -
Ehala Sille,
Dybal Jirí,
Makrlík Emanuel,
Kašička Václav
Publication year - 2009
Publication title -
journal of separation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.72
H-Index - 102
eISSN - 1615-9314
pISSN - 1615-9306
DOI - 10.1002/jssc.200800555
Subject(s) - chemistry , valinomycin , ionophore , capillary electrophoresis , ligand (biochemistry) , molecule , density functional theory , proton affinity , crystallography , stability constants of complexes , inorganic chemistry , analytical chemistry (journal) , ion , membrane , computational chemistry , chromatography , protonation , organic chemistry , biochemistry , receptor
In a combined experimental and theoretical approach, the interactions of valinomycin (Val), macrocyclic depsipeptide antibiotic ionophore, with sodium cation Na + have been investigated. The strength of the Val–Na + complex was evaluated experimentally by means of capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the sodium ion concentration in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, 0–40 mM NaCl), the apparent binding (stability) constant ( K b ) of the Val–Na + complex in methanol was evaluated as log K b = 1.71 ± 0.16. Besides, using quantum mechanical density functional theory (DFT) calculations, the most probable structures of the nonhydrated Val–Na + as well as hydrated Val–Na + ·H 2 O complex species were proposed. Compared to Val–Na + , the optimized structure of Val–Na + ·H 2 O complex appears to be more realistic as follows from the substantially higher binding energy (118.4 kcal/mol) of the hydrated complex than that of the nonhydrated complex (102.8 kcal/mol). In the hydrated complex, the central Na + cation is bound by strong bonds to one oxygen atom of the respective water molecule and to four oxygens of the corresponding C=O groups of the parent valinomycin ligand.