Electrophoretic measurement of water charge density and ion hydration

다국어 초록 (Multilingual Abstract)

Water exchange between bulk water and water‐ion complexes will be at equilibrium when the charge density of the complex surface equals the charge density of bulk water, producing a constant radius water‐ion complex. This complex will migrate in an electric field at a velocity proportional to the complex radius. CE velocity is the sum of the complex charge‐dependent velocity and the buffer electro‐osmotic flow. Simultaneous use of both a base (1.07 mM imidazole) and an acid (1.5 mM MOPS) buffer negates EOF at pH 7.4. Electric fields below 300 V/cm (potassium, calcium) and 400 V/cm (magnesium) yield migration velocities with no dehydration of the water‐ion complexes. The number of waters per complex increase with the ion charge density: K+ 1.90, Ca++ 5.90, Mg++ 6.59 waters/ion. The charge densities of the complexes are similar: K+ 1.24, Ca++ 1.43, Mg++ 1.21 e/nm2, for an average bulk water charge density of 1.29 ± 0.11 (SD) e/nm2. The addition of 0.1% Triton increases the number of waters for Mg++ to 25.33 and lowers the charge density to 0.497 e/nm2. High electric field dehydration shows that calcium will be fully dehydrated at 638.3 V/cm and magnesium fully dehydrated at 925.5 V/cm, which occur at 6.15 and 5.78 nm from the membrane. Dehydrated magnesium will then bind to calcium channels leading to decreased smooth muscle activation.