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Issue 34, 2017
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Copper(II)-benzimidazole complexes as efficient fluorescent probes for L-cysteine in water

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Copper(II) complexes [Cu(L1)(H2O)2](SO3CF3)21 and [Cu(L2)(H2O)2](SO3CF3)22 based on 2,6-bis(benzimidazolyl)pyridine were synthesized and are reported herein as highly selective “turn-on” optical probes for L-cysteine. The Cu(II)/Cu(I) redox potential of probe 1 (0.14 V vs. NHE) was lower than that of 2 (0.233 V vs. NHE) in water. The molecular structure of 2 adopted a square pyramidal geometry (τ = 0.2545), with the Cu–Npy bond (1.958 Å) of its middle pyridine unit being shorter than the other two Cu–Nbenzim bonds (Cu–N, 1.995, 2.000 Å). The axial Cu–O2 bond distance (2.247 Å) was slightly longer than the equatorial Cu–O1 bond distance (1.953 Å). The square-based geometry was further supported by the A value of 156 × 10−4 cm−1 in EPR at 70 K. The d–d and ligand-based transitions appeared at 662 and 314–356 nm for 1 and 651 and 313–360 nm for 2, respectively, in HEPES buffer at pH 7.34. These probes showed selective and efficient “turn-on” fluorescence behaviour towards Cys over other natural amino acids with a binding constant for 1 of 5.4 × 104 and 1.30 × 104 M−1 for 2 and a limit of detection of 2.9 × 10−8 M and 3.32 × 10−8 M, respectively, for 1 and 2 at pH 7.34. The quantum yield for the detection of Cys by 1 (14.7%) was much lower than by 2 (23%). The fluorescence intensity of 1 and 2 were also slightly enhanced by histidine, but at a relatively lower level than that exhibited by Cys.

Graphical abstract: Copper(ii)-benzimidazole complexes as efficient fluorescent probes for l-cysteine in water

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Publication details

The article was received on 24 May 2017, accepted on 02 Aug 2017 and first published on 03 Aug 2017

Article type: Paper
DOI: 10.1039/C7DT01895A
Citation: Dalton Trans., 2017,46, 11408-11417
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    Copper(II)-benzimidazole complexes as efficient fluorescent probes for L-cysteine in water

    D. Maheshwaran, S. Priyanga and R. Mayilmurugan, Dalton Trans., 2017, 46, 11408
    DOI: 10.1039/C7DT01895A

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