Biologically active Schiff bases as potentiometric sensor for the selective determination of Nd3+ ion

Novel multidentate Schiff bases 5-((1-(3-(3-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)-1H-indol-1-yl)propyl)-1H-indol-3-yl)methyleneamino)-1,3,4-thiadiazole-2-thiol (S1) and N-((1-(3-(3-((thiazol-2-ylimino)methyl)-1H-indol-1-yl)propyl)-1H-indol-3-yl)methylene)thiazol-2-amine (S2) were synthesized for the construction of Nd3+ ion-selective electrode. The polymeric membrane electrodes (PME) were fabricated along with various plasticizers and additive. It is found that the PME based on S1 having the composition (S1: (potassium tetrakis p-(chloro phenyl)borate) KTpClPB: (o-nitrophenyloctyl ether) o-NPOE: PVC ≡ 4:2:58:36, w/w, mg) is found to be better. Thus, the coated graphite electrode (CGE) was constructed with the same composition and the results were compared with PME. The CGE is found to be better in comparison to PME with respect to all the potentiometric characteristics such as low detection limit (1.1 × 10−8 mol L−1), wide working concentration range (3.1 × 10−8-1.0 × 10−1 mol L−1), near Nernstian slope (19.8 ± 0.3 mV decade−1 of activity), low response time (10 s), shelf life time (105 days) and wide pH range (3.5-8.0). Both the PME and CGE were used for the quantifying the Nd3+ ion in various samples such as water, soil samples, binary mixtures and as an indicator electrode using EDTA. PME and CGE were also used for the determination of F− ion in mouth wash solution and tooth paste sample. Further the antibacterial activity of Schiff bases were examined by broth micro-dilution method and found that these are antibiotics against Staphylococcus aureus (Gram positive) and Escherichia coli (ATCC25922) (Gram negative).