The pH measurements (DrDAQ data logger board, PicoLog 6 software, Pico Technology, Cambridgeshire, UK) were performed every 1 s for the entire duration of the experiment. The scattering data were collected at 10 s/frame. The time scales of all the measurements/experiments were aligned according to the following convention: the measurement finishing at 0 s (thus starting at negative 10 s) represents a structure of an unmixed solution (i.e. only DAP), the measurement at 10 s represents the averaged structure of the solution until the end of the injection, the measurement at 20 s corresponds to stoichiometrically mixed solutions.