KCl, and an aqueous NaOH solution at a fixed pH. The adopted conditions for each kinetic experiment are provided in the ESI. The 1 mL of each solution was directly mixed in a spectrophotometric agitated disposable cuvette. Absorption spectra (300-500 nm) were collected at fixed time intervals (Agilent, Cary 60). Absorption data at 400 nm were converted to PNP concentration. Calibration was carried out using different aqueous solutions at a known concentration of PNP at the same methanol and KCl concentrations and pH of the tested solutions. PNPA concentrations were calculated as its initial concentration minus the concentration of the formed product according to the literature , since no by-products formation was reported under the adopted conditions.