Bioinspired Luminescent Europium-Based Probe Capable of Discrimination between Ag⁺ and Cu⁺

Abstract

Due to their similar coordination properties, discrimination of Cu + and Ag + by water-soluble luminescent probes is challenging. We have synthesized LCC4 Eu , an 18 amino acid cyclic peptide bearing a europium complex, that is able to bind one Cu + or Ag + ion by the side chains of two methionines, a histidine and a 3-(1-naphthyl)-Lalanine. In this system, the naphthyl moiety establishes a cation- interaction with these cations. It also acts as an antenna for the sensitization of Eu 3+ luminescence. Interestingly, when excited at 280 nm behaves as a turn-on probe for Ag + (+150 % Eu emission) and as a turn-off probe for Cu + (-50% Eu 3+ emission). Shifting the excitation wavelength to 305 nm makes the probe responsive to Ag + (+380% Eu 3+ emission) but not to Cu + or other physiological cations. Thus, LCC4 Eu is uniquely capable of discriminating Ag + from Cu + . A detailed spectroscopic characterization based on steady state and time-resolved measurements clearly demonstrates that Eu 3+ sensitization relies on electronic energy transfer from the naphthalene triplet state to the Eu 3+ excited states and that the cation- interaction lowers the energy of this triplet state by 700 cm -1 and 2400 cm -1 for Ag + and Cu + , respectively. Spectroscopic data point to a modulation of the efficiency of the electronic energy transfer caused by the differential red-shift of the naphthalene triplet, deciphering the differential luminescence response of LCC4 Eu toward Ag + and Cu + .

Versatile Macrocyclic Platform for the Complexation of [natY/90Y]Yttrium and Lanthanide Ions

“…The value of 6.55 ms found for τ R is similar to those reported in the literature for nine-coordinated Eu III complexes. 76 − 80 The quantum yield of the luminescence step (ϕ Eu ) can be subsequently obtained using eq 2 since the lifetime of the Eu complex in water (τ H 2 O ) is known ( Table 2 ). …”

Ratiometric Luminescence Detection of Copper(I) by a Resonant System Comprising Two Antenna/Lanthanide Pairs

“…Indeed, Cu + - or Ag + -bound probes of the LCC1 Tb family exist in two forms in equilibrium: one with the tryptophan engaged in a cation−π interaction that is not fluorescent and the other one where the tryptophan is not engaged in the cation−π interaction, which is fluorescent. , At the microsecond time scale, a broad emission is detected in the 400–700 nm range in the case of metal-free LCCR GdGd that decays monoexponentially with a time constant of 46 ± 2 μs, homogeneous over the whole spectral range (Figure S14 in the Supporting Information). This emission could correspond to naphthalene triplet emission, since tryptophan emission was never detected in the Cu + - or Ag + -free forms for compounds of the LCC1 Tb family. , Addition of Ag + red-shifts the emission, and the decay time is not homogeneous on the whole 400–700 nm range, which could account for additional tryptophan­(T 1 ) emission. At 450 nm, the decay could be fit with a monoexponential and a time constant of 25 μs, while, at 570 nm, a monoexponential with a longer 49 μs decay time could be satisfyingly used to fit the decay.…”

“…20,21 At the microsecond time scale, a broad emission is detected in the 400−700 nm range in the case of metal-free LCCR GdGd that decays monoexponentially with a time constant of 46 ± 2 μs, homogeneous over the whole spectral range (Figure S14 in the Supporting Information). This emission could correspond to naphthalene triplet emission, 50 since tryptophan emission was never detected in the Cu + -or Ag + -free forms for compounds of the LCC1 Tb family. 20,21 Addition of Ag + red-shifts the emission, and the decay time is not homogeneous on the whole 400−700 nm range, which could account for additional tryptophan(T 1 ) emission.…”