Binding Stoichiometry Ratio Research Articles

Linear Schiff-base fluorescence probe with aggregation-induced emission characteristics for Al3+ detection and its application in live cell imaging

A simple Schiff-base derivative with salicylaldehyde moieties as fluorescent probe 1 was reported by aggregation-induced emission (AIE) characterization for the detection of metal ions. Spectral analysis revealed that probe 1 was highly selective and sensitive to Al3+. The probe 1 was also subject to minimal interference from other common competitive metal ions. The detection limit of Al3+ was 0.4 μM, which is considerably lower than the World Health Organization standard (7.41 μM), and the acceptable level of Al3+ (1.85 μM) in drinking water. The Job's plot and the results of 1H-NMR and FT-IR analyses indicated that the binding stoichiometry ratio of probe 1 to Al3+ was 1:2. Probe 1 demonstrated a fluorescence-enhanced response upon binding with Al3+ based on AIE characterization. This response was due to the restricted molecular rotation and increased rigidity of the molecular assembly. Probe 1 exhibited good biocompatibility, and Al3+ was detected in live cells. Therefore, probe 1 is a promising fluorescence probe for Al3+ detection in the environment.

New carbazole-based Schiff base: Colorimetric chemosensor for Fe3+ and fluorescent turn-on chemosensor for Fe3+ and Cr3+

Two novel carbazole-based Schiff-bases L1 and L2 have been synthesized and characterized by 1H NMR, 13C NMR, FT-IR spectroscopy and elemental analysis. L1 can selectively detect Fe3+ by UV–vis spectroscopy and Fe3+/Cr3+ by fluorescent spectroscopy in CH3CN among various metal ions. The addition of Fe3+ ions to a L1 solution results in a significant blue-shift from 410nm to 378nm accompanied with color change from yellowish green to colorless. Upon excitation at 380nm, the addition of Fe3+ or Cr3+ causes a 13-fold or 11-fold fluorescence enhancement. The binding stoichiometry ratio of L1–Fe3+ and L1–Cr3+ is recognized as 2:1 by the method of Job׳s plot, and the possible binding mode of the system also proposes. The results indicate that L1 is an ideal chemosensor for Fe3+ and Cr3+ recognition. However, L2 without hydroxyl in ortho imino group cannot selectively recognize the tasted metal ions, indicating that the introduction of the appropriate coordination binding site to receptor can improve efficiently the selectivity of chemosensor.

Interactions of phenanthroline compounds with i-motif DNA

The interactions of each of three phenanthroline derivatives 1, 2 and 3 with the human telomeric i-motif DNA were investigated. The results suggest these compounds are potent binders. The compounds could stabilize the structure of i-motif DNA by π-π stacking. Moreover, the binding constants of the compounds with i-motif DNA were (2.71–8.12)×104 L·mol−1, and the binding stoichiometry ratio was 1:1. CD studies reveal that the binding by phenanthroline compounds perturbs the conformation of i-motif DNA.