Models for biological ion exchangers. I. Proton magnetic resonance studies of water structure in Bio-Rex 70.
Bio-Rex 70, a carboxylic acid cation exchanger, is studied as a biological ion-exchanger resin model for cellular cytoplasm. High-resolution proton magnetic resonance spectra of 1l ionic forms of Bio-Rex 70 are determined. From measured cation exchange capacities, water contents, and chemical shifts for the resin-phase water protons, the dependence of the chemical shift on the counter ion is calculated. The observed chemical shifts (Hz/geq/kg internal water, referred to the Ba2+ form) for each ionic form are: H+, --0.5; Li+, --0.2; Na+, 1.2; K+, 2; Rb+, 2.1; Ag+, --0.4; NH4+, --2.0; NMe4+, 1.2; NEt4+, 1.8; Mg2+, --2.0; Ca2+, --1.5; Sr2+, --0.6; Ba2+, 0.0 Zn2+, --2.3; Cd2+, --4.7; and La3+, --3.3. The results are in good agreement with earlier studies on Dowex 50, indicating that the carboxylate ion exchanger behaves like a concentrated polyelectrolyte. The widths at half-height for the internal water peaks of the polyvalent forms are quite large, ranging from 40 to 100 Hz.
Models for biological ion exchangers. I. Proton magnetic resonance studies of water structure in Bio-Rex 70. Bio-Rex 70, a carboxylic acid cation exchanger, is studied as a biological ion-exchanger resin model for cellular cytoplasm. High-resolution proton magnetic resonance spectra of 1l ionic forms of Bio-Rex 70 are determined. From measured cation exchange capacities, water contents, and chemical shifts for the resin-phase water protons, the dependence of the chemical shift on the counter ion is calculated. The observed chemical shifts (Hz/geq/kg internal water, referred to the Ba2+ form) for each ionic form are: H+, --0.5; Li+, --0.2; Na+, 1.2; K+, 2; Rb+, 2.1; Ag+, --0.4; NH4+, --2.0; NMe4+, 1.2; NEt4+, 1.8; Mg2+, --2.0; Ca2+, --1.5; Sr2+, --0.6; Ba2+, 0.0 Zn2+, --2.3; Cd2+, --4.7; and La3+, --3.3. The results are in good agreement with earlier studies on Dowex 50, indicating that the carboxylate ion exchanger behaves like a concentrated polyelectrolyte. The widths at half-height for the internal water peaks of the polyvalent forms are quite large, ranging from 40 to 100 Hz.