Sodium deuteroxide

Cobalt(II) acetate (Co(OAc)₂·4H₂O, 99.0%), manganese(II) acetate (Mn(OAc)₂·4H₂O, 99.0%), ammonium hydroxide (NH₃·H₂O, 25%-28%), potassium hydroxide (KOH, 99.99%), sodium hydroxide (NaOH, 99.99%) were purchased from China Medicine Shanghai Chemical Reagent Corporation. Sodium deuteroxide (40 wt% in D₂O, 99 atom% D), deuterium oxide (D₂O, 99.9 atom% D) were obtained from Sigma-Aldrich and used without further purification. Vulcan XC-72 (Cabot Co.), 60 wt% Pt/C (Johnson Matthey Co.), 60 wt% PtRu/C (Johnson Matthey Co.), Nafion (Dupont, 5%) were used as received. The alkaline polymer electrolytes (aQAPS-S_x) were prepared as reported in our previous work^{4 (link)}.

Solvents and reagents, unless otherwise indicated, were analytical-grade commercial products and used as received. L-arginine (≥98.5%), D-arginine (≥99%) and D,L-arginine (≥98.5%), sodium deoxycholate (≥97%), deuterium oxide (D₂O, 99.9%), deuterium chloride (DCl, 99%) and sodium deuteroxide (NaOD, 40 wt % in D₂O) were purchased from Sigma-Aldrich (Milano, Italy), while N,N’-methylenebisacrylamide (MBA, 96%) from Acros Organics (Milano, Italy). 0.3 M HCl and 0.3 M NaOH volumetric standard solutions were purchased from Fluka Analytics (Milano, Italy). Ultrapure water (18 MΩ cm⁻¹), produced with a Millipore Milli-Q^® apparatus (Darmstadt, Hesse, Germany), was used to prepare all solutions, except where stated otherwise (D₂O).

L-Lysine (> 98%, FG), hydrogen chloride (HCl, 37%) and sodium deuteroxide (NaOD) solutions, were purchased from Sigma Aldrich, and sodium hydroxide anhydrous pellets were purchased from Carlo Erba Reagent, ITA. Deuterium chloride (DCl, 20%) was purchased from Cambridge Isotope Laboratories, Inc. Distilled water was used as a solvent.
l-Lysine nanopolymers were obtained by hydrothermal treatment. 0.128 g of l-lysine were solubilized in 10 mL of distilled H₂O (0.87 M). The solutions were placed into a Teflon-lined stainless steel autoclave^{7 (link)} with a capacity of 50 mL and then heated at 130 or 200 °C for 15 h. After the hydrothermal treatment (HT), the obtained products were cooled down to 20 °C and then used for the characterizations. The samples hydrothermally treated at 130 and 200 °C are indicated in the text as HT-130 °C and HT-200 °C.
The pH of the precursor aqueous solutions of l-lysine was measured with a pH meter (pH 80 + DHS, Xs instrument). Four different pH values were used for the experiments: 2.5. 7.3 (obtained by adding 1 M HCl dropwise), 9.7 and 13 (obtained by adding droplets of 1 M NaOH).