A Highly Selective and Efficient Copper(II) – “Turn-On” Fluorescence Imaging Probe for l-Cysteine

Duraiyarasu Maheshwaran, Thavasilingam Nagendraraj, Paramasivam Manimaran, Balasubramaniem Ashokkumar, Mukesh Kumar, Ramasamy Mayilmurugan

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


A simple copper(II) complex of the anthracenyl-appended terpyridine ligand 4′-(anthracen-9-yl)-2,2′:6′,2′′-terpyridine (L), [Cu(L)Cl2] (1, ESI-MS, m/z = 507.08), is reported as a highly selective “turn-on” optical imaging probe for l-cysteine. Probe 1 shows a CuII/CuIredox potential [E1/2= –0.194 V versus normal hydrogen electrode (NHE)] within a biologically viable range. The copper center in 1 adopts a square-pyramidal geometry (τ = 0.0851), and the Cu–Npybond (1.970 Å) of the middle pyridine (py) ring is shorter than the other two Cu–Npybonds (2.069 and 2.040 Å). The Cu–Cl bonds (2.444 and 2.027 Å) are labile enough to be replaced by solvent molecules. The square-based geometry is further supported by the Avalue of 156.8 × 10–4cm–1determined by electron paramagnetic resonance (EPR) spectroscopy at 70 K. The d–d transition of 1 in acetonitrile/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (acetonitrile/HEPES) buffer at pH 7.34 appears at λ =760 nm (ε = 198 m–1cm–1), and the ligand-based transitions are observed at λ = 327–384 nm. The ligand shows strong fluorescence at λ = 430 nm with a quantum yield of 11 %, but its emission intensity is completely quenched on coordination with Cu2+ions, as in 1. Probe 1 detects l-cysteine selectively through turn-on fluorescence intensity at λem= 431 nm with a limit of detection of 1.9 × 10–8m at pH 7.34. Interestingly, probe 1 is able to visualize exogenously added l-cysteine in Henrietta Lack cervical cancer (HeLa) cells, human liver hepatocellular carcinoma (HepG2) cells, and human embryonic kidney 293 (HEK293) cells under identical conditions at pH 7.4 in confocal microscopy imaging.

Original languageEnglish
Pages (from-to)1007-1016
Number of pages10
JournalEuropean Journal of Inorganic Chemistry
Issue number6
StatePublished - 10 Feb 2017
Externally publishedYes


  • Amino acids
  • Cell imaging
  • Copper
  • Fluorescent probes
  • N ligands

ASJC Scopus subject areas

  • Inorganic Chemistry


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