Application of affinity capillary electrophoresis and density functional theory to the investigation of benzo-18-crown-6-ether complex with ammonium cation.
Affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations have been employed for investigation of non-covalent interactions between macrocyclic ligand, benzo-18-crown-6-ether (B18C6) and ammonium cation, NH(4)(+). Firstly, by means of ACE, the strength of the B18C6-NH(4)(+) complex in mixed binary hydro-organic solvent system, methanol-water (50/50, v/v), was determined from the dependence of effective electrophoretic mobility of B18C6 (corrected to reference temperature 25 degrees C and constant ionic strength, 10mM) on the concentration of ammonium ion in the background electrolyte (BGE) using non-linear regression analysis. The logarithmic form of the apparent binding (stability) constant (logK(b)) of B18C6-NH(4)(+) complex in the above binary solvent system was found to be equal to logK(b)=1.63+/-0.10. Secondly, the structural characteristics of B18C6-NH(4)(+) complex were described by quantum mechanical density functional theory (DFT) calculations. According to these calculations, in the energetically most favoured form of the B18C6-NH(4)(+) complex, three strong hydrogen bonds are formed between central ammonium ion and B18C6 ligand, one of them is directed to aryl-O-alkyl (Ar-O-CH(2)) ethereal oxygen and the other two hydrogen bonds are oriented to alkyl-O-alkyl (CH(2)-O-CH(2)) ethereal oxygen atoms of the macrocyclic crown ligand.
Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo 2, 166 10, Prague 6, Czech Republic.
Sille
S
Ehala
Petr
P
Toman
Emanuel
E
Makrlík
Václav
V
Kasicka
D002412:Cations / Q000737:chemistry*; D043844:Crown Ethers / Q000737:chemistry*; D019075:Electrophoresis, Capillary / Q000379:methods*; D007700:Kinetics; D008958:Models, Molecular; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*
D002412:Cations; D043844:Crown Ethers; D000644:Quaternary Ammonium Compounds