Hybridization Assay by Time-Resolved Capillary Gel Electrophoresis with a Lanthanide Chelate

Capillary electrophoresis of crude biological samples with time-resolved fluorescence (TRF) detection enables elimination of interference from organic fluorophores and from light scattering. Because the fluorescence lifetime of biological substances and impurities overlaps the fluorescence lifetime of conventional labeling dyes, TRF detection with conventional organic labeling dyes suffers from background fluorescence. In this work, we synthesized a luminescent lanthanide chelating reagent to covalently bind the 5′-end of DNA through its dichroic functional group while retaining the unique luminescent properties of the lanthanide chelate, i.e. large Stokes shift, sharp emission, and a long luminescence lifetime in the microsecond to millisecond range. The luminescence of lanthanide chelates is inherently quenched by dissociation of the central metals in typical biological buffers containing a strong chelator, for example EDTA or phosphate; the synthesized Eu³⁺ chelate reagent, however, was stable even in EDTA solutions. In addition to stability in biological buffer solution, the synthesized Eu³⁺ chelate reagent enabled direct labeling of single-stranded oligonucleotides, and was used for DNA hybridization assay by time-resolved capillary gel electrophoresis. DNA hybridization assay in fetal bovine serum was also demonstrated.     

DNA binding and antibacterial properties of ternary lanthanide complexes with salicylic acid and phenanthroline

Twelve ternary lanthanide complexes RE(sal)₃phen (RE³⁺ = La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Yb³⁺, Lu³⁺, sal = salicylic acid, phen = phenanthroline) were prepared. Interactions between the complexes and calf thymus DNA (ct‐DNA) were investigated using UV–visible spectrophotometry, fluorescence quench experiment and viscosity measurement. Hypochromicity and red shift of the absorption spectra of complexes were observed in the presence of DNA. The enhanced emission intensity of ethidium bromide (EB) in the presence of DNA was quenched by the addition of lanthanide complexes, which indicated that the lanthanide complexes displaced EB from its binding sites in DNA. Based on the systematic research of the binding constant (K_b) and the fluorescence quenching constant (K_q) of the 12 complexes, we found that the complexes with smaller lanthanide ion radius had stronger binding abilities with DNA. Viscosity measurement showed that the relative viscosity of the DNA solution was enhanced with increasing the amounts of the complexes. All these results suggested that the complexes could bind to DNA and the major binding mode was intercalative binding. Moreover, all these complexes exhibited excellent antibacterial abilities against Escherichia coli. Also, the antibacterial activities of complexes with heavy rare earth were higher than those of complexes with light rare earth. Copyright © 2014 John Wiley & Sons, Ltd.     

DNA Intercalating Near-Infrared Luminescent Lanthanide Complexes Containing Dipyrido[3,2-a:2′,3′-c]phenazine (dppz) Ligands: Synthesis,Crystal Structures,Stability, Luminescence Properties and CT-DNA Interaction

In order to create near-infrared (NIR) luminescent lanthanide complexes suitable for DNA-interaction, novel lanthanide dppz complexes with general formula [Ln(NO₃)₃(dppz)₂] (Ln = Nd³⁺, Er³⁺ and Yb³⁺; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) were synthesized, characterized and their luminescence properties were investigated. In addition, analogous compounds with other lanthanide ions (Ln = Ce³⁺, Pr³⁺, Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Lu³⁺) were prepared. All complexes were characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction analysis of the complexes (Ln = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Er³⁺, Yb³⁺, Lu³⁺) showed that the lanthanide’s first coordination sphere can be described as a bicapped dodecahedron, made up of two bidentate dppz ligands and three bidentate-coordinating nitrate anions. Efficient energy transfer was observed from the dppz ligand to the lanthanide ion (Nd³⁺, Er³⁺ and Yb³⁺), while relatively high luminescence lifetimes were detected for these complexes. In their excitation spectra, the maximum of the strong broad band is located at around 385 nm and this wavelength was further used for excitation of the chosen complexes. In their emission spectra, the following characteristic NIR emission peaks were observed: for a) Nd³⁺: ⁴F_3/2 → ⁴I_9/2 (870.8 nm), ⁴F_3/2 → ⁴I_11/2 (1052.7 nm) and ⁴F_3/2 → ⁴I_13/2 (1334.5 nm); b) Er³⁺: ⁴I_13/2 → ⁴I_15/2 (1529.0 nm) c) Yb³⁺: ²F_5/2 → ²F_7/2 (977.6 nm). While its low triplet energy level is ideally suited for efficient sensitization of Nd³⁺ and Er³⁺, the dppz ligand is considered not favorable as a sensitizer for most of the visible emitting lanthanide ions, due to its low-lying triplet level, which is too low for the accepting levels of most visible emitting lanthanides. Furthermore, the DNA intercalation ability of the [Nd(NO₃)₃(dppz)₂] complex with calf thymus DNA (CT-DNA) was confirmed using fluorescence spectroscopy.     

Lanthanide complexes of new polyaminocarboxylate complexes with two chromophores derived from bispyrazolylpyridine and aceto or benzophenone: synthesis, characterization and photophysical properties

New ionophores derived from 2,6-bis(N-pyrazolyl)pyridine and aceto/benzophenone have been synthesized and fully characterized. The lanthanide complexes of these new ligands were studied from their UV-vis and fluorescence data. Eu³⁺ and Tb³⁺ complexes were easily formed and their photophysical properties measured. In all cases, lanthanide emission lifetimes were in the range of ms albeit quantum yields were relatively low. Possible flaws in the energy-transfer mechanisms are discussed.     

Absorption and luminescence of yttrium and lanthanide octaethylporphin complexes

Absorption spectra of yttrium octaethylporphin complex and of seven lanthanide complexes are quite similar, but emission properties vary greatly. The closed shell complexes, Y and Lu (f¹⁴), show moderately strong porphyrin fluorescence and phosphorescence, with the latter having decay times 55 ms (Y) and 7.8 ms (Lu) at 77 K. All six open shell lanthanides studied show weak porphyrin fluorescence. In addition, the Gd complex (f⁷) shows a very strong porphyrin phosphorescence at 702 nm, with decay time 103 μs at 77 K, and the Yb complex (f¹³) shows both a weak, non-exponential porphyrin phosphorescence at 704 nm and an f-shell emission, ²F → ²F , at 975 nm.     

Fluorescence properties of novel rare earth complexes using carboxyl-containing polyaryletherketones as macromolecular ligands

The fluorescence properties of a series of rare earth (Re³⁺ = Eu³⁺, Tb³⁺) polymeric complexes (PEK-Re³⁺-HLs) using three high-T_g novel carboxyl-containing polyaryletherketones (PEK) as macromolecular ligands and small molecules (HL) such as 1,10-phenanthroline (Phen), dibenzoylmethane (DBM) and 8-hydroxyquinoline (HQ) as co-ligands were investigated by means of fluorescence excitation and emission spectroscopy as well as fluorescence lifetime measurement methods. Among them, PEK-1-Re³⁺-Phens, in which the Re³⁺ ions were coordinated simultaneously with Phen and PEK-1 containing both carboxyl and bulky isopropyl groups on the polymer backbone, exhibited strong fluorescence intensities, long lifetimes, and good film-formation properties. The smooth films of PEK-1-Eu³⁺-Phen and PEK-1-Tb³⁺-Phen, cast from their DMF solutions, could emit bright red and green light under the UV lamp of 365 nm, respectively, which characteristics are of great significance for their potential applications in the large area display material fields. The excellent fluorescence properties of complexes in this study were attributed to the synergistic effects of PEK-1 ligand and Phen co-ligand. Especially, the rigid twisted structure and the bulky isopropyl substituents on PEK-1 backbone forced the coordinated rare earth ion moieties apart, and thus the probability of non-radiative decay rate of Re³⁺ ions at the excited levels were decreased to a large extent.     

Photophysical Properties of Lanthanide (Eu3+, Tb3+) Hybrid Soft Gels of Double Functional Linker of Ionic Liquid–Modified Silane

Four kinds of luminescent hybrid soft gels have been assembled by introducing the lanthanide (Eu³⁺, Tb³⁺) tetrakis β‐diketonate into the covalently bonded imidazolium‐based silica through electrostatic interactions. Here, the imidazolium‐based silica matrices are prepared from imidazolium‐derived organotriethoxysilanes by the sol–gel process, in which the imidazolium cations are strongly anchored within the silica matrices while anions can still be exchanged following application for functionalization of lanthanide complexes. The photoluminescence measurements indicated that these hybrid soft gels exhibit characteristic red and green luminescence originating from the corresponding ternary lanthanide ions (Eu³⁺, Tb³⁺). Further investigation of photophysical properties reveals that these soft gels have inherited the outstanding luminescent properties from the lanthanide tetrakis β‐diketonate complexes such as strong luminescence intensities, long lifetimes and high luminescence quantum efficiencies.     

Lanthanide metal polymer complexes. Synthesis,characterization and application

Our recent results on the investigation of lanthanide metal polymer complexes were presented. Luminescence properties of Tb³⁺ or Eu³⁺ -polycarboxylate complexes in aqueous solution were investigated. The excitation band near 300 nm for Tb or Eu(polyacrylate) solutions were drastically enhanced by the addition of hydroxy radical generating reagents as well as ultrasonic irradiation. These spectral changes were attributed to the energy transfer from chromophore molecules formed by generated hydroxy radicals in both systems. Since the increase in the luminescence intensity was proportional to the hydroxy radical concentration, the Eu³⁺ or Tb³⁺ (PAA) system can provide a convenient method for the determination of hydroxy radical concentration in aqueous solution. We have also utilized lanthanide metal ion complexes as a luminescent emitter in electroluminescence (EL) devices. The configuration of the EL cell and experimental results were discussed.     

Fluorescent Complexes of Nucleic Acids/8-Hydroxyquinoline/Lanthanum(III) and the Fluorometry of Nucleic Acids

Abstract

The ternary fluorescent complexes of nucleic acids/8-hydroxyquinoline/ lanthanum (III) were studied. Nucleic acids in the study involve natured and thermally denatured calf thymus DNA, fish sperm DNA and yeast RNA. In the range of pH 8.0–8.4 (controlled by NH₃-NH₄Cl buffer) ternary fluorescent complexes are formed which emit at 485.0 nm for calf thymus DNA and at 480.0 nm for yeast RNA (when excited at 267.0 nm) and emits at 483.0 nm for fish sperm DNA when excited at 265.0 nm. Based on the fluorescence reactions sensitive fluorometric methods for nucleic acids were proposed. Using optimal conditions, the calibration curves were linear in the range of 0.4–3.6 μg˙ml^?1 for calf thymus DNA, 0.4–4.0 μg-ml^?1 for fish sperm DNA and 0.4–4.0 μg˙ml^?1 for yeast RNA, respectively. The limits of determination (3σ) were 0.076 μg˙ml^?1 for calf thymus DNA, 0.068 μg˙ml^?1 for fish sperm DNA and 0.329 μg˙ml^?1 for yeast RNA, respectively. Five synthetic samples were determined with satisfaction.

     

Terpyridine-Functionalized Calixarenes: Synthesis,Characterization and Anion Sensing Applications

Lanthanide complexes have been developed and are reported herein. These complexes were derived from a terpyridine-functionalized calix[4]arene ligand, chelated with Tb³⁺ and Eu³⁺. Synthesis of these complexes was achieved in two steps from a calix[4]arene derivative: (1) amide coupling of a calix[4]arene bearing carboxylic acid functionalities and (2) metallation with a lanthanide triflate salt. The ligand and its complexes were characterized by NMR (¹H and ¹³C), fluorescence and UV-vis spectroscopy as well as MS. The photophysical properties of these complexes were studied; high molar absorptivity values, modest quantum yields and luminescence lifetimes on the ms timescale were obtained. Anion binding results in a change in the photophysical properties of the complexes. The anion sensing ability of the Tb(III) complex was evaluated via visual detection, UV-vis and fluorescence studies. The sensor was found to be responsive towards a variety of anions, and large binding constants were obtained for the coordination of anions to the sensor.     

Fluorescence characteristics of europium ions stabilized in solid polymer electrolytes containing polyether structure

Polyethylene oxide (PEO) oligomers can dissolve lanthanide salts. The terminal hydroxyl groups of PEO affect the solubility of the lanthanide salts in the PEO considerably. However, no intensive fluorescence was observed from Eu³⁺ dispersed in PEO or other ion-conductive polymers containing terminal hydroxyl groups, because of the quenching effect of the terminal hydroxyl groups. Copolymer of ω-methoxy oligo(oxyethylene) methacrylate and methyl methacrylate (P(MEOM-co-MMA)) could dissolve small amount of Eu(NO₃)₃, but the copolymer film containing Eu³⁺ shows intensive fluorescence (Ex = 269.0 nm, Em = 570.0 nm). This was prepared as a soft film, and there was a clear dependence of the Eu³⁺ concentration on the fluorescence intensity. A linear relation between the film thickness and the fluorescence intensity was also observed. Little fluorescence was found for Eu³⁺ in the blend of the corresponding two homopolymers, i.e. poly-(ω-methoxy oligo (oxyethylene) methacrylate) (PMEOM) and poly(α-methyl methacrylate) (PMMA). This strongly suggests that intensive fluorescence requires a mixed state of MEOM and MMA units at molecular level.     

Synthesis, characterization and spectroscopic studies of copolymer of styrene with 4-oxe-4(P-hydroxyl phenylamino) but-2-enoic acid and corresponding fluorescent macromolecular lanthanide(III) complexes

Copolymer of styrene with 4-oxe-4(P-hydroxyl phenylamino) but-2-enoic acid (PSHPEA) and its luminescent lanthanide complexes Ln-PSHPEA (Ln = La, Eu, Tb and Y) were synthesized and characterized by means of elemental analysis, FT-IR, thermogravimetric analysis and fluorescence determination. The results showed that the carboxylic groups on the chain of the copolymer acted as bidentate ligands coordinated to lanthanide ions, but the amido carbonyl groups, amino N and hydroxy groups had not taken part in coordination; the coordination degree of -COO⁻/Ln³⁺ which determined the content of metal ions in the macromolecular complexes, was closely dependent on both the pH value of the solution and the molar ratio of St to 4-oxe-4(P-hydroxyl phenylamino) but-2-enoic acid in the polymer ligand. The fluorescence determination showed that the complexes exhibited characteristic fluorescence with comparatively high brightness and good mono-chromaticity. Typical relationship between emission intensity and Ln³⁺ ions content in macromolecular complexes exhibited some extent of fluorescence concentration quenching in our studies. The emission intensity of Tb-PSHPEA complexes was much stronger than that of Eu-PSHPEA complexes, which was attributed to especial effectivity in transferring energy from the lowest triplet energy level of the ligand onto the excited state (⁵D₀) of Tb³⁺ ion than that (⁵D₄) of Eu³⁺ ion.     

Bioconjugation of Proteins with a Paramagnetic NMR and Fluorescent Tag

Site‐specific labeling of proteins with lanthanide ions offers great opportunities for investigating the structure, function, and dynamics of proteins by virtue of the unique properties of lanthanides. Lanthanide‐tagged proteins can be studied by NMR, X‐ray, fluorescence, and EPR spectroscopy. However, the rigidity of a lanthanide tag in labeling of proteins plays a key role in the determination of protein structures and interactions. Pseudocontact shift (PCS) and paramagnetic relaxation enhancement (PRE) are valuable long‐range structure restraints in structural‐biology NMR spectroscopy. Generation of these paramagnetic restraints generally relies on site‐specific tagging of the target proteins with paramagnetic species. To avoid nonspecific interaction between the target protein and paramagnetic tag and achieve reliable paramagnetic effects, the rigidity, stability, and size of lanthanide tag is highly important in paramagnetic labeling of proteins. Here 4′‐mercapto‐2,2′: 6′,2′′‐terpyridine‐6,6′′‐dicarboxylic acid (4MTDA) is introduced as a a rigid paramagnetic and fluorescent tag which can be site‐specifically attached to a protein by formation of a disulfide bond. 4MTDA can be readily immobilized by coordination of the protein side chain to the lanthanide ion. Large PCSs and RDCs were observed for 4MTDA‐tagged proteins in complexes with paramagnetic lanthanide ions. At an excitation wavelength of 340 nm, the complex formed by protein–4MTDA and Tb³⁺ produces high fluorescence with the main emission at 545 nm. These interesting features of 4MTDA make it a very promising tag that can be exploited in NMR, fluorescence, and EPR spectroscopic studies on protein structure, interaction, and dynamics.     

Spectroscopic studies on the interaction of cilostazole with iodine and 2,3-dichloro-5,6-dicyanobenzoquinone

Lanthanide sensitized luminescence and chemiluminescence (CL) are of great importance because of the unique spectral properties, such as long lifetime, large Stokes shifts, and narrow emission bands characteristic to lanthanide ions (Ln³⁺). With the fluoroquinolone (FQ) compounds including enoxacin (ENX), norfloxacin (NFLX), lomefloxacin (LMFX), fleroxacin (FLRX), ofloxacin (OFLX), rufloxacin (RFX), gatifloxacin (GFLX) and sparfloxacin (SPFX), the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes have been investigated in this contribution. Ce⁴⁺–SO₃²⁻ in acidic conditions was taken as the CL system and sensitized CL intensities of Tb³⁺–FQ and Eu³⁺–FQ complexes were determined by flow-injection analysis. The luminescence and CL spectra of Tb³⁺–FQ complexes show characteristic peaks of Tb³⁺ at 490 nm, 545 nm, 585 nm and 620 nm. Complexes of Tb³⁺–ENX, Tb³⁺–NFLX, Tb³⁺–LMFX and Tb³⁺–FLRX display relatively strong emission intensity compared with Tb³⁺–OFLX, Tb³⁺–RFX, Tb³⁺–GFLX and Tb³⁺–SPFX. Quite weak peaks with unique characters of Eu³⁺ at 590 nm and 617 nm appear in the luminescence and CL spectra of Eu³⁺–ENX, but no notable sensitized luminescence and CL of Eu³⁺ could be observed when Eu³⁺ is added into other FQ. The distinct differences on emission intensity of Tb³⁺–FQ and Eu³⁺–FQ might originate from the different energy gap between the triplet levels of FQ and the excited levels of the Ln³⁺. The different sensitized luminescence and CL signals among Tb³⁺–FQ complexes could be attributed to different optical properties and substituents of these FQ compounds. The detailed mechanism involved in the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes has been investigated by analyzing the luminescence and CL spectra, quantum yields, and theoretical calculation results.     

Study on the new fluorescence enhancement system of Tb-1,10-bis(2′-carboxylphenyl)-1,4,7,10-tetraoxadecane in silver chloride collosol and its analytical application

A new salicylic-based open-chain crown ether ligand, 1,10-bis(2′-carboxylphenyl)-1,4,7,10-tetraoxadecane (BCPTD) was synthesized. Solutions of its complex with Tb³⁺ can emit the intrinsic fluorescence of Tb³⁺. The fluorescence intensity of the complex in KCl solution was enhanced by the addition of silver(I), leading to a new fluorescence enhancement phenomenon. The spectrofluorimetric determination of traces of silver(I) based on the above phenomenon was carried out. The excitation and emission wavelengths are 298 and 545 nm, respectively. Under optimal conditions, the differential value of fluorescence intensity in the absence and presence of Ag⁺ was proportional to the concentration of silver(I) in the range 0.5-20 μg ml⁻¹. The method was applied to the determination of silver(I) in a standard ore sample. The analytical performance is investigated in detail by using common aromatic carboxylic acids or synthetic analogues of BCPTD as ligands to replace BCPTD. It was found that Tb-aromatic acid complexes did not result in fluorescence enhancement of Tb³⁺ in AgCl collosol. The phenomenon was only observed in Tb(III) with BCPTD or its open-chain crown ether analogues solutions.In addition, the enhancement of the fluorescence intensity of terbium(III) in these complexes depends on the extent of formation of the AgCl collosol.     

Synthesis,Structures, and Luminescent Properties of Lanthanide Complexes with Triphenylphospine Oxide

Seven lanthanide complexes [Ln(OPPh₃)₃(NO₃)₃] ( 1 – 3 ) (OPPh₃ = triphenylphosphine oxide, Ln = Nd, Sm, Gd), [Dy(OPPh₃)₄(NO₃)₂](NO₃) ( 4 ), [Ln(OPPh₃)₃(NO₃)₃]₂ ( 5 – 7 ) (Ln = Pr, Eu, Gd) were synthesized by the reactions of different lanthanide salts and OPPh₃ ligand in the air. These complexes were characterized by single‐crystal X‐ray diffraction analysis, elemental analysis, IR and fluorescence spectra. Structure analysis shows that complexes 1 – 4 are mononuclear complexes formed by OPPh₃ ligands and nitrates. The asymmetric units of complexes 5 – 7 consist of two crystallographic‐separate molecules. Complex 1 is self‐assembled to construct a 2D layer‐structure of (4,4) net topology by hydrogen bond interactions. The other complexes show a 1D chain‐like structure that was assembled by OPPh₃ ligands and nitrate ions through C–H ··· O interactions. Solid emission spectra of compounds 4 and 6 are assigned to the characteristic fluorescence of Tb³⁺ (λ_em = 480, 574 nm) and Eu³⁺ (λ_em = 552, 593, 619, 668 nm).     

Synthesis,DNA interaction and photocleavage studies of ruthenium(II) complexes with 2-(pyrrole) imidazo[4,5-f]-1,10-phenanthroline as an intercalative ligand

Three Ru(II) complexes, namely [Ru(bipy)₂PRIP]²⁺ (1), [Ru(dmb)₂PRIP]²⁺ (2), and [Ru(phen)₂PRIP]²⁺ (3) (dmb = 4,4′-dimethyl-2,2′-bipyridine; PRIP = 2-(pyrrole) imidazo [4,5-f]-1,10-phenanthroline) have been synthesized and characterized by elemental analysis, mass spectra, IR, ¹H NMR and ¹³C NMR. The DNA-binding properties of the three complexes with calf-thymus DNA (CT-DNA) were investigated by spectrophotometry, fluorescence methods and viscosity measurements. The results suggest that all three complexes bind to CT-DNA through intercalation. Also, when irradiated at 365 nm, the three complexes promote the photocleavage of plasmid pBR-322 DNA. Under comparable experimental conditions, complex 3 cleaves DNA more effectively than complexes 1 and 2.     

Efficient Luminescence from Fluorene‐ and Spirobifluorene‐Based Lanthanide Complexes upon Near‐Visible Irradiation

We describe herein the synthesis and photophysical characterization of new lanthanide complexes that consist of a (9,9‐dimethylfluoren‐2‐yl)‐2‐oxoethyl or a (9,9′‐spirobifluoren‐2‐yl)‐2‐oxoethyl unit as the antenna, covalently linked to a 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid (DO3A) unit as the Ln³⁺ (Gd³⁺, Eu³⁺, Sm³⁺, Tb³⁺, Dy³⁺) coordination site. We were able to translate the spectroscopic properties of the innovative bipartite ligands into the formation of highly luminescent europium complexes that exhibit efficient emission (?_se>0.1) upon sensitization in the near‐visible region, that is, with an excitation wavelength above 350 nm. The luminescence of the Eu³⁺complexes is clearly detectable at concentrations as low as 10 pM . Furthermore, the structural organization of these bipartite ligands makes the complexes highly soluble in aqueous solutions and chemically stable over time.     

Using Native Chemical Ligation for Site-Specific Synthesis of Hetero-bis-lanthanide Peptide Conjugates: Application to Ratiometric Visible or Near-Infrared Detection of Zn2+

The interest in ratiometric luminescent probes that detect and quantify a specific analyte is growing. Owing to their special luminescence properties, lanthanide(III) cations offer attractive opportunities for the design of dual-color ratiometric probes. Here, the design principle of hetero-bis-lanthanide peptide conjugates by using native chemical ligation is described for perfect control of the localization of each lanthanide cation within the molecule. Two zinc-responsive probes, r-LZF1^Tb|Cs124|Eu and r-LZF1^Eu|Cs124|Tb are described on the basis of a zinc finger peptide and two DOTA (DOTA=1,4,7,10-tetraaza-cyclododecane-1,4,7,10-tetraacetic acid) complexes of terbium and europium. Both display dual-color ratiometric emission in response to the presence of Zn²⁺. By using a screening approach, anthracene was identified for the sensitization of the luminescence of two near-infrared-emitting lanthanides, Yb³⁺ and Nd³⁺. Thus, two novel zinc-responsive hetero-bis-lanthanide probes, r-LZF3^Yb|Anthra|Nd and r-LZF3^Nd|Anthra|Yb were assembled, the former offering a neat ratiometric response to Zn²⁺ with emission in the near-infrared around 1000 nm, which is unprecedented.     

Cationic Biphotonic Lanthanide Luminescent Bioprobes Based on Functionalized Cross-Bridged Cyclam Macrocycles

Cationic lanthanide complexes are generally able to spontaneously internalize into living cells. Following our previous works based on a diMe-cyclen framework, a second generation of cationic water-soluble lanthanide complexes based on a constrained cross-bridged cyclam macrocycle functionalized with donor-π-conjugated picolinate antennas was prepared with europium(III) and ytterbium(III). Their spectroscopic properties were thoroughly investigated in various solvents and rationalized with the help of DFT calculations. A significant improvement was observed in the case of the Eu³⁺ complex, while the Yb³⁺ analogue conserved photophysical properties in aqueous solvent. Two-photon (2P) microscopy imaging experiments on living T24 human cancer cells confirmed the spontaneous internalization of the probes and images with good signal-to-noise ratio were obtained in the classic NIR-to-visible configuration with the Eu³⁺ luminescent bioprobe and in the NIR-to-NIR with the Yb³⁺ one.