A Fluorescent 18-Crown-6 Based Luminescence Sensor for Lanthanide Ions

A turn-on fluorescent probe for Lu3+ recognition and bio-imaging in live cells and zebrafish

A new Lu3+ selective fluorescent probe L was synthesized and characterized. The optical properties of L were investigated by using absorption and fluorescence spectral studies in 7 : 3 (v/v) aqueous dimethyl sulphoxide. Upon addition of Lu3+ in a pH 4 (acetate buffer) solution of L, the weakly fluorescent probe L became highly fluorescent. The fluorescence intensity increased five-fold at 490 nm with excitation at 437 nm. The formation of 2 : 1 complexation between L and Lu3+ was confirmed by Job's plot. The binding constant (Ka, 1.43 × 104 M-1) was determined by the Benesi-Hildebrand (BH) method. The limit of detection (LOD) of Lu3+ using L was found to be 23 nM. The binding mechanism of L with Lu3+ was studied by 1H-NMR, ESI mass spectroscopy, and theoretical studies. Further, the probe L was successfully used to bioimage Lu3+ in a zebrafish gill cell line (DrG) and in the yolk, papillae of the eyes, and head of zebrafish embryos (Danio rerio), therefore providing a powerful live imaging approach for investigating chemical signaling in complex multicellular systems.

Highly selective CHEF-type chemosensor for lutetium (III) recognition in semi-aqueous media

A simple phosphoryl quinolone (L) based sensor has been synthesized for the selective recognition of Lu³⁺ by spectrofluorimetric method. In methanol-water (1:1, v/v), the ligand L exhibits a weak emission peak at 400 nm upon excitation at 280 nm. Upon interaction with various f-metal and other selected metals from s, p, and d-block elements, the fluorescence of L is selectively enhanced in the presence of Lu³⁺ due to the chelation enhanced fluorescence (CHEF) effects. The quantum yield (φ) of L (φ = 0.063) is enhanced to φ = 0.118 upon chelation with Lu³⁺ ion. From the titration experiment, the limit of detection (LOD) of sensor L to recognize Lu³⁺ is estimated down to 24.2 nM, which is much lower than the WHO guidelines (76 μM) in drinking water. The formation of host-guest complexation between L and Lu³⁺ in 2:1 binding stoichiometry is studied by Job's method and the binding constant is estimated by band fit analysis (logK_f = 5.1). Further, the coordination behaviour between L and Lu³⁺ is well supported by FT-IR, ¹H NMR, ¹³C NMR, ³¹P NMR, ESI mass spectral data and the theoretical results.

Bispyrene/surfactant-assembly-based fluorescent sensor array for discriminating lanthanide ions in aqueous solution

Lanthanides are valuable nonrenewable resources and widely used in a variety of industries. Detection and identification of lanthanide ions are in high demand but challenging because of the similarity among lanthanide ions. In the present work, a fluorescent sensor array of three cationic bispyrene derivatives mixed with anionic surfactant assemblies was developed. The sensor array exhibits cross-reactive responses to lanthanide ions when tested in aqueous solution. The combination of fluorescence variations at both monomer and excimer emission of each of the bispyrene sensor elements provides a six-signal recognition pattern for lanthanide ions. Principle component analysis illustrates that the sensor array could at least identify 6 of the 14 similar lanthanide ions including La(3+), Pr(3+), Nd(3+), Eu(3+), Ho(3+), and Er(3+). UV-vis absorption measurements rule out the possibility of binding lanthanides with fluorophores. Fluorescence titration experiments in both cationic and neutral surfactant aqueous solutions reveal that the three fluorophores show slight fluorescence responses to the lanthanide ions, indicating that electrostatic attraction between lanthanide ions and anionic surfactant plays an important role in the sensing behavior of the sensor array. Control experiments with divalent metal ions find no cross-reactive responses, suggesting that the stronger electrostatic interaction with trivalent lanthanide ions is responsible for the multiple fluorescence responses.

A new Tb3+-selective fluorescent sensor based on 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamide

A novel fluorescent chemosensor 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission intensity quenching upon binding to terbium ions in MeCN solution. The fluorescence quenching of L is attributed to the 1:1 complex formation between L and Tb(III) which has been utilized as the basis for the selective detection of Tb(III). The linear response range covers a concentration range of Tb(III) from 4.0 x 10(-7) to 1.0 x 10(-5) M and the detection limit is 1.4 x 10(-7) M. The association constant of the 1:1 complex formation for L-Tb(+3) was calculated to be 6.01 x 10(6) M(-1), and the fluorescent probe exhibits high selectivity over other common metal ions mono-, di-, and trivalent cations indicate good selectivity for Tb(III) ions over a large number of interfering cations.

Abnormal behavior in Stern-Volmer luminescence quenching measurements via apparent lifetime methods

Luminescence lifetimes are widely used as an analysis tool. Since decays in analytical systems are frequently complex decays rather than single exponentials, apparent lifetime methods based on the rapid lifetime determination (RLD) method or single frequency phase shift (SFPS) measurements are frequently used to reduce cost and simplify data analysis. It is demonstrated here that these methods can produce large errors under the right conditions. Both methods can give unexpected and uncharacteristic Stern-Volmer quenching plots (SVQPs) in two-component systems. Behaviors include bimodal quenching curves as well as "anti-quenching" curves. These phenomena are exacerbated by small fractions of long unquenched components.

Molecular Design of Luminescence Ion Probes for Various Cations Based on Weak Gold(I)···Gold(I) Interactions in Dinuclear Gold(I) Complexes

A series of luminescent dinuclear gold(I) complexes with different crown ether pendants, [Au(2)(PwedgeP)(S-B15C5)(2)] [S-B15C5 = 4'-mercaptobenzo-15-crown-5, P(wedge)P = bis(dicyclohexylphosphino)methane (dcpm) (1), bis(diphenylphosphino)methane (dppm) (2)] and [Au(2)(P(wedge)P)(S-B18C6)(2)] [S-B18C6 = 4'-mercaptobenzo-18-crown-6, P(wedge)P = dcpm (3), dppm (4)], and their related crown-free complexes, [Au(2)(P(wedge)P)(SC(6)H(3)(OMe)(2)-3,4)(2)] [P(wedge)P = dcpm (5), dppm (6)], were synthesized. The low-energy emission of the mercaptocrown ether-containing gold(I) complexes are tentatively assigned as originated from states derived from a S --> Au ligand-to-metal charge transfer (LMCT) transition. The crown ether-containing gold(I) complexes showed specific binding abilities toward various metal cations according to the ring size of the crown pendants. Spectroscopic evidence was provided for the metal-ion-induced switching on of the gold...gold interactions upon the binding of particular metal ions in a sandwich binding mode.