The mass of the λ-particles was set to 5 atomic units, and their temperature was main-tained at 300 K by using a separate v-rescale thermostat for the λ coordinates with a time constant of 2.0 ps -1 . For all λ-coordinates the biasing potential V bias i (λ i ) was defined by equation S1 in the SI. The barrier height of the double well potential was set to 5.0 and 7.5 kJ/mol for AA and CG simulations, respectively. The parameters for the double well potential and the pH dependent potential (Equation ) are provided in Table in the SI.