Experiments and measurements

After preparation, samples were placed within the stirring device inside the UPLC instrument, with stirring turned on. The system was monitored by subjecting it to periodic UPLC analysis using a Waters Acquity UPLC-H Class system equipped with a photo diode array detector. All analyses were performed using a reversed-phase UPLC column (Aeris Peptide 1.7 µm XB-C18x 2.10 mm, Phenomenex). The column temperature was kept at 35 °C, and the sample chamber was kept at 40 °C. UV absorbance was monitored at 254 nm. Additional occasional column washes were performed. The eluents used in the UPLC separation consist of H₂O and acetonitrile, both are UPLC grade and contain 0.1 vol% trifluoroacetic acid. Gradient and peak integration algorithm are respectively given in Supplementary Note 1 and Supplementary Note 2.

For pre-oxidation experiments, the samples were prepared as described before, with the addition of 0.50 equivalents NaBO₃ so that 50% of the building-block amount is oxidized. Then, the resulting mixture was kept inside the UPLC sample holder and subjected to periodic UPLC analysis as described above. The samples were stirred using the designed device at 200 and 1000 rpm.

Device’s positions used for samples are C2, C7, D2 and D7 (Fig. 1).