Time-programmable pH: decarboxylation of nitroacetic acid allows the time-controlled rising of pH to a definite value

In this report it is shown that nitroacetic acid 1 (O₂NCH₂CO₂H) can be conveniently used to control the pH of a water solution over time. Time-programmable sequences of the kind pH_1(high)-pH_2(low)-pH_3(high) can be achieved, where both the extent of the initial pH jump (pH_1(high)-pH_2(low)) and the time required for the subsequent pH rising (pH_2(low)-pH_3(high)) can be predictably controlled by a judicious choice of the absolute and relative concentrations of the reagents (acid 1 and NaOH). Successive pH_1(high)-pH_2(low)-pH_3(high) sequences can be obtained by subsequent additions of acid 1. As a proof of concept, the method is applied to control over time the pH-dependent host-guest interaction between alpha-cyclodextrin and p-aminobenzoic acid.