Cys-AE, a new electroactive compound, has been synthesized using a two-step process involving the reaction of aloe-emodin with phosphorus tribromide and then cysteine in a 1.0 M NaOH solution. The resulting compound has been characterized using various analytical techniques, including NMR, HRMS, and UV-Vis spectroscopy. Compared to aloe-emodin, Cys-AE exhibits improved solubility, with a solubility ratio of 3:1 in 1.0 M KOH solution. The introduction of the amino acid group in Cys-AE induces an asymmetric charge distribution, leading to higher polarizability and increased intermolecular interactions.
Electrochemical analysis of Cys-AE and aloe-emodin shows that Cys-AE exhibits a redox potential of -0.51 V and a peak separation of 69 mV for 2 electrons, similar to aloe-emodin. However, the pair of Cys-AE and potassium ferrocyanide yields an equilibrium cell voltage of ~1.01 V. The study also investigates the stability of the molecules in 1.0 M KOH solution, with no noticeable changes in their 1H NMR spectra over 14 days. Additionally, DFT simulations and UV-Vis absorption spectra are presented, revealing the differences in the molecular orbitals and energy gaps between the two compounds. The results support the potential of Cys-AE as a promising material for alkaline membrane fuel cells.