Green synthesis of Schiff base based on thiadiazolyl and recognition of arginine and ascorbic acid

Arginine (Arg) and ascorbic acid (AA) are biologically essential compounds that play a key role in human development and disease resistance. Consequently, it is imperative to detect these molecules expeditiously and efficiently. In the present study, 5-phenyl-1,3,4-thiadizole-2-amine and 2-((5-phenyl-1,3,4-thiadizole-2-yl)imino) methyl) phenol (henceforth designated Probe L) were synthesised catalytically by low eutectic solvent. Subsequently, probe L was utilised as a fluorescence sensor for the detection of Arg and AA. Specifically, the solution of probe L undergoes a colour change from yellow to orange-red in the presence of Arg, and fades when interacting with AA. However, under the fluorescence spectrum, the fluorescence intensity of the probe L solution significantly increases after the addition of Arg and AA. The experiments on the influence of time on the recognition of probe L demonstrated that Arg and AA could be recognised at different times. In the experiments on the influence of pH on the recognition of probe L, it was shown that Arg and AA could be effectively detected within the pH range of 4-12. The curve analysis of Job indicates that 2:3 (probe L: Arg) and 3:2 (probe L: AA) are combined with the stoichiometric ratio. The binding constants of Arg and AA were determined to be 7.43 × 10³ M^-1 and 14.11 × 10⁴ M^-1, respectively. The detection limits (LOD) were calculated to be 1.05 × 10^-5 M and 9.37 × 10^-6 M, respectively. In conclusion, this work presents the synthesis of probe L, promoted by DES, and establishes its practicality as a highly selective and stable optical sensor for Arg and AA, which is of great significance for biomedical and environmental monitoring.