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 (O(2)NCH(2)CO(2)H) 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.