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Electrophoretic measurement of water charge density and ion hydration
Author(s) -
Barger James P.,
Dillon Patrick F.
Publication year - 2020
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.201900467
Subject(s) - chemistry , electric field , ion , analytical chemistry (journal) , charge density , magnesium , surface charge , electrophoresis , radius , dehydration , potassium , chromatography , biochemistry , physics , computer security , organic chemistry , quantum mechanics , computer science
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 /nm 2 , for an average bulk water charge density of 1.29 ± 0.11 (SD) e/nm 2 . 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 /nm 2 . 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.