Two new silver(I) complexes, formulated as [Ag2(L1)2](picrate)2 (1), {[Ag2(L2)2(terephthalate)](C2H5OH)3(H2O)}n (2) (L1 = 1,3‐bis(2‐benzimidazyl)benzene, L2 = 1,3‐bis(1‐methylbenzimidazol‐2‐yl)‐2‐thiapropane), were synthesized and characterized by X‐ray crystallography, elemental analysis, infrared, and UV–Vis spectroscopy. The crystal analysis results showed that the complexes exhibited different structures: binuclear for 1 and one‐dimensional polymeric for 2. Their Ag(I) centers displayed different coordination geometric structures: two‐coordinated linear in 1, whereas four‐coordinated distorted tetrahedron in 2. The electrochemical sensing performance of Ag(I) complexes modified carbon paste electrode (CPE‐1 and CPE‐2) toward hydrogen peroxide (H2O2) was evaluated by chronoamperometry in 0.2 M phosphate buffer saline (pH = 6) at −0.2 V. The CPE‐1 was found to have a wide linear response from 1.0 × 10−5 to 4.0 × 10−3 M, lower detection limit of 1.73 μM, excellent anti‐interference ability, and stability. The CPE‐2 does not have recognition properties for H2O2, which may be due to the large steric hindrance around Ag(I) centers that is not easy to combine with H2O2 to form a catalytic transition state. The above studies proved that Ag(I) complexes can be used as effective components of electrode materials for the electrochemical recognition of H2O2.
A highly sensitive fluorescence “turn‐on” 1,8‐naphthalimide Schiff base probe: N‐allyl‐4‐(ethylenediamine‐salicylidene)‐1,8‐naphthalimide (HL) for Hg2+ was designed, synthesized and characterized. In addition, the sensing behavior of HL towards various transition metal ions has been investigated in solution (DMF/Tris–HCl buffer, 1:1, vol/vol, pH = 7.2). The HL exhibited high selectivity for Hg2+ over other metal ions with obvious fluorescence enhancement. Moreover, the fluorescence intensity of HL showed good linearity with a correlation coefficient (R2) of 0.99, confirming that HL could be applied to detect the quantification of Hg2+ in a linear fashion from 0.5 to 4 μM and the detection limit reach at 0.16 μM. Meanwhile, the association constant (Ka) between Hg2+ and HL achieves 1.23 × 1012 M−1. Moreover, the fluorescence titration experiment and Job plot analysis indicate the formation of a 2:1 stoichiometric complex of HL with Hg2+. The fluorescence enhancement of HL response to Hg2+ ions could be attributed to the photoinduced electron transfer (PET) mechanism.
A new fluorescent sensor, N-allyl-4-[(2-(3-methoxysalicylaldimino)ethylamino]-1,8-naphthalimide (HL), for Hg2+ has been developed where the Schiff base substituent acts as a recognition group. This sensor shows a large Stokes shift of 3535–4042 cm−1 and a general fluorescence quantum yield of 0.05, 249–0.11, 866 in organic solvents of different polarity as expected. It also exhibits highly selective and a sensitive response to Hg2+ (Ф
Hg+HL/Ф
HL = 2.28) over other metal ions (Na+, K+, Ca2+, Mg2+, Al3+, Pb2+, Fe3+, Ni2+, Zn2+, Cu2+, Ag+, Co2+, Cr3+, Mn2+ and Cd2+) in solution (DMF/Tris-HCl buffer, 1:1, v/v, pH = 7.2). The Hg2+-induced fluorescence enhancement at 526 nm is proportional to the concentration of Hg2+ in the range of 0.5–4.0 µm with a detection limit of 0.18 µm. Based on the fluorescence titration and a Job’s plot analysis, the metal-to-ligand ratio of the complex is 2:1 with a binding constant of 1.56 × 1012 m
−1.
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