Fig. 7.

The Na⁺ counter-ion drags its strongly-bound hydration shell towards SO₃⁻ terminal group, top left, and bonds by ionic contacts both to the terminal group and water, top right. A Cl⁻ counter-ion drags its weakly-bound hydration shell towards the NH₃⁺ terminal group, bottom left, and bonds by hydrogen bonds both to water and the terminal group, bottom right. A cutoff distance 0.35 nm and a cutoff angle of 30° was considered for the hydrogen bonds two values were taken from Ref. 50). Color code: S, yellow; O, red; C, cyan; white; N, blue; Na⁺, blue; Cl⁻, purple; hydrogen bonds, white.