ACE in a free solution and quantum mechanical density functional theory have been applied to the investigation of interactions of glycine-6-antamanide ([Gly ]AA), a synthetic derivative of cyclic decapeptide antamanide isolated from the highly poisonous mushroom Amanita phalloides, with sodium or potassium ions in methanol. First, from the dependence of effective electrophoretic mobility of [Gly ]AA on Na or K ions concentration in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, pH 7.8, containing 0-50 mM NaCl or 0-40 mM KCl), the apparent binding (stability) constants of [Gly ]AA-Na and [Gly ]AA-K complexes were evaluated as 26 ± 1 and 14 ± 1 L/mol, respectively. The employed ACE method included correction of the effective mobilities measured at ambient temperature and at variable ionic strength of the BGEs to the mobilities related to the reference temperature 25°C and to the constant ionic strength 10 mM. Second, the interaction energies of the [Gly ]AA-Na and [Gly ]AA-K complexes (-466.3 and -345.2 kJ/mol, respectively) and the structural details of these complexes, such as position of the Na and K ions in the cavity of the [Gly ]AA molecule and the interatomic distances within these complexes, were determined by the density functional theory calculations.
Affinity capillary electrophoresis (ACE) and pressure‐assisted ACE were employed to study the noncovalent molecular interactions of antamanide (AA), cyclic decapeptide from the deadly poisonous fungus Amanita phalloides, with univalent (Li+, Na+, K+, and NH4+) and divalent (Mg2+ and Ca2+) cations in methanol. The strength of these interactions was quantified by the apparent stability constants of the appropriate AA‐cation complexes. The stability constants were calculated using the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of AA on the concentration of the above ions in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, pHMeOH 7.8, containing 0–50 mM concentrations of the above ions added in the form of chlorides). Prior to stability constant calculation, the AA effective mobilities measured at actual temperature inside the capillary and at variable ionic strength of the BGEs were corrected to the values corresponding to the reference temperature of 25°C and to the constant ionic strength of 10 mM. From the above ions, sodium cation interacted with AA moderately strong with the stability constant 362 ± 16 L/mol. K+, Mg2+, and Ca2+ cations formed with AA weak complexes with stability constants in the range 37–31 L/mol decreasing in the order K+ > Ca2+ > Mg2+. No interactions were observed between AA and small Li+ and large NH4+ cations.
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