Synthesis of 7-amino-4-trifluoromethyl-2-(1H)-quinolinone and its use as an antenna molecule for luminescent europium polyaminocarboxylates chelates

Visible-Light-Active Coumarin- and Quinolinone-Based Photocatalysts and Their Applications in Chemical Transformations

Organic dyes have been actively studied as useful photocatalysts because they allow access to versatile structural flexibility and green synthetic applications. The identification of a new class of robust organic chromophores is, therefore, in high demand to increase structural diversity and variability. Although coumarins and quinolinones have long been acknowledged as organic chromophores, their ability to participate in photoinduced transformations is somewhat less familiar. Fascinated by their chromophoric features and adaptable platform, our group is interested in the identification of fluorescent bioactive molecules and in the development of new photoinduced synthetic methods using coumarins and quinolinones as photocatalysts. This account provides an overview of our recent progress in the discovery and application of light-absorbing coumarin and quinolinone derivatives in photochemistry and medicinal chemistry.

An expeditious synthesis of 6,7-dihydrodibenzo[b,j][4,7] phenanthroline derivatives as fluorescent materials

A rapid and efficient method has been developed for the synthesis of 13,14-dimethyl-6,7-dihydrodibenzo[b,j][4,7]phenanthroline derivatives (3a-d) through the Friedländer condensation of 2-aminoarylketone with 1,4-cyclohexanedione under solvent-free conditions using p-toluenesulphonic acid. The synthetic utility of compounds 3a, 3b, and 3c was demonstrated by synthesizing compounds 6a-kvia Suzuki coupling, 8 by Buchwald-Hartwig amination, and 9a-bvia NBS bromination. Significantly, the emission band corresponding to the π-π* electronic transition of compounds 3a, 6a, 6d, 6f, and 8 showed a redshift with increasing polarity of the solvents. Molar extinction coefficient (ε), Stoke's shift (Δ[italic small upsilon, Greek, macron]), and quantum yield (Φ f) were calculated for all these compounds.

Lanthanide-Based Optical Probes of Biological Systems

The unique photophysical properties of lanthanides, such as europium, terbium, and ytterbium, make them versatile molecular probes of biological systems. In particular, their long-lived photoluminescence, narrow bandwidth emissions, and large Stokes shifts enable experiments that are infeasible with organic fluorophores and fluorescent proteins. The ability of these metal ions to undergo luminescence resonance energy transfer, and photon upconversion further expands the capabilities of lanthanide probes. In this review, we describe recent advances in the design of lanthanide luminophores and their application in biological research. We also summarize the latest detection systems that have been developed to fully exploit the optical properties of lanthanide luminophores. We conclude with a discussion of remaining challenges and new frontiers in lanthanide technologies. The unprecedented levels of sensitivity and multiplexing afforded by rare-earth elements illustrate how chemistry can enable new approaches in biology.

Ultrasensitive optical imaging with lanthanide lumiphores

In principle, the millisecond emission lifetimes of lanthanide chelates should enable their ultrasensitive detection in biological systems by time-resolved optical microscopy. In practice, however, lanthanide imaging techniques have provided no better sensitivity than conventional fluorescence microscopy. Here, we identified three fundamental problems that have impeded lanthanide microscopy: low photon flux, inefficient excitation, and optics-derived background luminescence. We overcame these limitations with a new lanthanide imaging modality, transreflected illumination with luminescence resonance energy transfer (trLRET), which increases the time-integrated signal intensities of lanthanide lumiphores by 170-fold and the signal-to-background ratios by 75-fold. We demonstrate that trLRET provides at least an order-of-magnitude increase in detection sensitivity over that of conventional epifluorescence microscopy when used to visualize endogenous protein expression in zebrafish embryos. We also show that trLRET can be used to optically detect molecular interactions in vivo. trLRET promises to unlock the full potential of lanthanide lumiphores for ultrasensitive, autofluorescence-free biological imaging.

Photophysics of Coumarin and Carbostyril-Sensitized Luminescent Lanthanide Complexes: Implications for Complex Design in Multiplex Detection

Luminescent lanthanide (Ln(III)) complexes with coumarin or carbostyril antennae were synthesized and their photophysical properties evaluated using steady-state and time-resolved UV-vis spectroscopy. Ligands bearing distant hydroxycoumarin-derived antennae attached through triazole linkers were modest sensitizers for Eu(III) and Tb(III), whereas ligands with 7-amidocarbostyrils directly linked to the coordination site could reach good quantum yields for multiple Ln(III), including the visible emitters Sm(III) and Dy(III), and the near-infrared emitters Nd(III) and Yb(III). The highest lanthanide-centered luminescence quantum yields were 35% (Tb), 7.9% (Eu), 0.67% (Dy), and 0.18% (Sm). Antennae providing similar luminescence intensities with 2-4 Ln-emitters were identified. Photoredox quenching of the carbostyril antenna excited states was observed for all Eu(III)-complexes and should be sensitizing in the case of Yb(III); the scope of the process extends to Ln(III) for which it has not been seen previously, specifically Dy(III) and Sm(III). The proposed process is supported by photophysical and electrochemical data. A FRET-type mechanism was identified in architectures with both distant and close antennae for all of the Lns. This mechanism seems to be the only sensitizing one at long distance and probably contributes to the sensitization at shorter distances along with the triplet pathway. The complexes were nontoxic to either bacterial or mammalian cells. Complexes of an ester-functionalized ligand were taken up by bacteria in a concentration-dependent manner. Our results suggest that the effects of FRET and photoredox quenching should be taken into consideration when designing luminescent Ln complexes. These results also establish these Ln(III)-complexes for multiplex detection beyond the available two-color systems.

Brightly Luminescent and Kinetically Inert Lanthanide Bioprobes Based on Linear and Preorganized Chelators

The synthesis, photophysical properties, and kinetic stability of a series of water-soluble, highly emissive Tb(III) and Eu(III) complexes featuring triethylenetetraamine hexaacetic acid (TTHA) and cyclohexyl triethylenetetraamine hexaacetic acid (cyTTHA) chelator scaffolds and carbostyril sensitizers are reported. The unique and modular design of the chelators gives rise to striking quantum yields of emission in aqueous solutions (up to 54%) as well as the characteristic lanthanides' photophysical properties (long excited-state lifetimes, large effective Stokes shifts, and narrow emission peaks). Furthermore, the preorganized chelators (L3, L4, and L6) bind metal within minutes at ambient temperature yet exhibit substantial resistance to transchelation in the presence of a challenge solution (EDTA, 1 mM). Moreover, the Eu(III) complex of L4 remains stably luminescent in HeLa cells over hours, demonstrating the suitability of these compounds for live-cell imaging applications. Representative chelators suitable for derivatization and protein bioconjugation were also prepared that were functionalized with clickable azide and alkyne moieties, biotin, and trimethoprim (TMP). With exceptional long-wavelength brightness, enhanced kinetic inertness, and an adaptable synthetic route, the reported lanthanide complexes are promising probes and labels for time-gated bioanalysis, biosensing, and optical microscopy.

Silver nanoparticles-enhanced rare earth co-luminescence effect of Tb(III)-Y(III)-dopamine system

It was found that silver nanoparticles (AgNPs) could enhance co-luminescence effect of rare earths ions Tb(3+) and Y(3+). Based on this, a sensitive fluorescence detection method for the determination of dopamine (DA) was proposed. Moreover, the detection limit for DA was very low (down to nM). This is because DA can remarkably enhance the luminescence intensity of the Tb(3+) ion by Y(3+) in the colloidal solution of AgNPs, forming a new co-luminescence system. Furthermore, based on the metal enhanced fluorescence (MEF), AgNPs can sensitize the co-luminescence effect of the complex of Tb(3+)-Y(3+)-DA. In a neutral buffer solution (pH 7.50), the luminescence intensity of the system was linearly related to the concentration of DA in the range of 2.0-100 nM, with a limit of detection as low as 0.57 nM. The proposed method was applied for the determination of DA in dopamine hydrochloride injections and human serum samples with good accuracy and satisfactory recovery.

Energy transfer in coumarin-sensitised lanthanide luminescence: investigation of the nature of the sensitiser and its distance to the lanthanide ion

A series of lanthanide complexes [Ln(dpxCy)3](3-) have been synthesised. The ligands are composed of a coordinating dipicolinic acid backbone decorated with a polyoxyethylene arm fitted with a coumarin moiety at its extremity. The nature of the coumarin as well as the length of the linker have been varied. Upon excitation at 320 nm, the coumarin exclusively acts as an antenna while the dipicolinic acid core is not excited. Upon excitation below 300 nm, both parts are excited. With europium as a metal centre, the relaxation of the europium ion (intrinsic quantum yield Φ(Eu)(Eu) and radiative lifetime τr) is constant for all the studied ligands. Therefore, the observed differences in overall quantum yield (Φ(Eu)(L)) in such systems come exclusively from the variation of the terminal coumarin. The overall quantum yields of the studied complexes are low (Φ(Eu)(L) < 2% in aqueous solution). In order to rationalise the mechanism of the energy transfer and to improve the sensitisation efficiency (ηsens), the distance between the coumarin sensitiser and the lanthanide centre was explored in solution and compared to the solid state. In the solid state, a dramatic effect was confirmed, with an improvement of 80% in the quantum yield Φ(Eu)(L) for short linkers ((-CH2CH2O-)n with n = 1 compared to n = 3). By monitoring the lifetime decay of the excited state of the lanthanide cation with nanosecond vs. microsecond time-resolved spectroscopy at low temperature, the sensitisation of the lanthanide ions by coumarin derivatives was demonstrated to mainly occur through the singlet excited state of the coumarin and not via the usual triplet pathway. No evidence of a different behaviour at room temperature was found by transient triplet-triplet absorption spectroscopy.

New quinolone-based thiol-reactive lanthanide luminescent probes

Luminescent lanthanide ion complexes are distinguished by unique light emitting properties that enable both highly sensitive detection of lanthanide labels attached to biomolecules and contrast imaging of various micro objects (cells, nanoparticles, etc.). Previously, we synthesized amine-reactive cs124-based luminescent lanthanide chelates with improved brightness and metal retention. Here we report the synthesis of new thiol-reactive derivatives of the same compounds including bromoacetamido-, and maleimido- forms of cs124 and cs124CF₃ fluorophores. Maleimido-compounds displayed exceptional reactivity instantaneously coupling to thiols at physiological conditions at micromolar probes concentrations. Surprisingly, they displayed strong quenching by adjacent maleimido-group, which was completely eliminated after reaction with thiols, thereby enabling their simple detection by monitoring the light emission of the reaction mixture. This reaction can be used for hyper-sensitive determination of biologically important sulphydryl compounds (e.g. glutathione, co-enzyme A, etc.) in time-resolved mode.

Simple no-chromatography procedure for amine-reactive Eu3+ luminescent chelates optimal for bioconjugation

Lanthanide ions luminescence has long life time enabling highly sensitive detection in time-gated mode. The synthesis of reactive lanthanide probes for covalent labeling of the objects of interest is cumbersome task due to the large size of the probes, complex multi-step procedures and the presence of sensitive groups, which often prevents introduction of reactive cross-linking functions optimal for conjugation. We suggest simple synthetic protocol for luminescent europium chelates based on serendipitous reaction yielding acylating compounds, whose reactivity is comparable to that of commonly used N-hydroxysuccinimide (NHS) esters. The probes react with proteins at pH 7.0 within several minutes at ambient temperature displaying high coupling efficiency. The resulting conjugates survive electrophoretic separation under denaturing conditions, which makes the labels useful in proteomic studies that rely on high detection sensitivity.

New cross-linking quinoline and quinolone derivatives for sensitive fluorescent labeling

A variety of contemporary analytical platforms, utilized in technical and biological applications, take advantage of labeling the objects of interest with fluorescent tracers-compounds that can be easily and sensitively detected. Here we describe the synthesis of new fluorescent quinoline and quinolone compounds, whose light emission can be conveniently tuned by simple structural modifications. Some of these compounds can be used as sensitizers for lanthanide emission in design of highly sensitive luminescent probes. In addition, we also describe simple efficient derivatization reactions that allow introduction of amine- or click-reactive cross-linking groups into the fluorophores. The reactivity of synthesized compounds was confirmed in reactions with low molecular weight nucleophiles, or alkynes, as well as with click-reactive DNA-oligonucleotide containing synthetically introduced alkyne groups. These reactive derivatives can be used for covalent attachment of the fluorophores to various biomolecules of interest including nucleic acids, proteins, living cells and small cellular metabolites. Obtained compounds are characterized using NMR, steady-state fluorescence spectroscopy as well as UV absorption spectroscopy.

Luminescent trimethoprim-polyaminocarboxylate lanthanide complex conjugates for selective protein labeling and time-resolved bioassays

Labeling proteins with long-lifetime emitting lanthanide (III) chelate reporters enables sensitive, time-resolved luminescence bioaffinity assays. Heterodimers of trimethoprim (TMP) covalently linked to various cs124-sensitized, polyaminocarboxylate chelates stably retain lanthanide ions and exhibit quantum yields of europium emission up to 20% in water. A time-resolved, luminescence resonance energy transfer (LRET) assay showed that TMP-polyaminocarboxylates bind to Escherichia coli dihydrofolate reductase (eDHFR) fusion proteins with nanomolar affinity in purified solutions and in bacterial lysates. The ability to selectively impart terbium or europium luminescence to fusion proteins in complex physiological mixtures bypasses the need for specific antibodies and simplifies sample preparation.

Eu(III) complexes as anion-responsive luminescent sensors and paramagnetic chemical exchange saturation transfer agents

The Eu(III) complex of (1S,4S,7S,10S)-1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (S-THP) is studied as a sensor for biologically relevant anions. Anion interactions produce changes in the luminescence emission spectrum of the Eu(III) complex, in the (1)H NMR spectrum, and correspondingly, in the PARACEST spectrum of the complex (PARACEST = paramagnetic chemical exchange saturation transfer). Direct excitation spectroscopy and luminescence lifetime studies of Eu(S-THP) give information about the speciation and nature of anion interactions including carbonate, acetate, lactate, citrate, phosphate, and methylphosphate at pH 7.2. Data is consistent with the formation of both innersphere and outersphere complexes of Eu(S-THP) with acetate, lactate, and carbonate. These anions have weak dissociation constants that range from 19 to 38 mM. Citrate binding to Eu(S-THP) is predominantly innersphere with a dissociation constant of 17 μM. Luminescence emission peak changes upon addition of anion to Eu(S-THP) show that there are two distinct binding events for phosphate and methylphosphate with dissociation constants of 0.3 mM and 3.0 mM for phosphate and 0.6 mM and 9.8 mM for methyl phosphate. Eu(THPC) contains an appended carbostyril derivative as an antenna to sensitize Eu(III) luminescence. Eu(THPC) binds phosphate and citrate with dissociation constants that are 10-fold less than that of the Eu(S-THP) parent, suggesting that functionalization through a pendent group disrupts the anion binding site. Eu(S-THP) functions as an anion responsive PARACEST agent through exchange of the alcohol protons with bulk water. The alcohol proton resonances of Eu(S-THP) shift downfield in the presence of acetate, lactate, citrate, and methylphosphate, giving rise to distinct PARACEST peaks. In contrast, phosphate binds to Eu(S-THP) to suppress the PARACEST alcohol OH peak and carbonate does not markedly change the alcohol peak at 5 mM Eu(S-THP), 15 mM carbonate at pH 6.5 or 7.2. This work shows that the Eu(S-THP) complex has unique selectivity toward binding of biologically relevant anions and that anion binding results in changes in both the luminescence and the PARACEST spectra of the complex.

Luminescent probes for ultrasensitive detection of nucleic acids

Novel amino-reactive derivatives of lanthanide-based luminescent labels of enhanced brightness and metal retention were synthesized and used for the detection of cDNA oligonucleotides by molecular beacons. Time-resolved acquisition of the luminescent signal that occurs upon hybridization of the probe to the target enabled the avoidance of short-lived background fluorescence, markedly enhancing the sensitivity of detection, which was less than 1 pM. This value is about 50 to 100 times more sensitive than the level achieved with conventional fluorescence-based molecular beacons, and is 10 to 60 times more sensitive than previously reported for other lanthanide-based hybridization probes. These novel luminescent labels should significantly enhance the sensitivity of all type of nucleic acid hybridization probes, and could dramatically improve the detection limit of other biopolymers and small compounds that are used in a variety of biological applications.

Synthesis, enzymatic evaluation, and docking studies of fluorogenic caspase 8 tetrapeptide substrates

The synthesis, enzymatic evaluation, and molecular modeling studies of new fluorogenic tetrapeptide-based substrates selective for caspase 8, having the general structure Ac-IETD-AXX, are described. Various fluorescent reporter groups (AXX), i.e., 3- and 4-substituted coumarins and quinolin-2(1H)-ones were synthesized by von Pechmann condensation. They were subsequently coupled with the caspase-8-selective tetrapeptide Ac-IETD-OH under newly developed synthetic conditions to give the desired substrates in good yields and in high enantiomeric purity. Based on K(M) and V(max) values, the new compounds proved to be excellent substrates for recombinant human caspase 8. In contrast, the K(M) values for the same compounds as substrates for human caspase 3 were approximately 10-20-fold higher. Molecular modeling studies based on the X-ray crystal structures of both human caspases 3 and 8 revealed that there is sufficient room within both active sites to accommodate substrates with moderately bulky substituents in the 3- and 4-positions of the fluorogenic coumarins and quinolin-2(1H)-ones. Automated docking of the substrates into the active sites of both human caspases 3 and 8 with the program AutoDock 3 gave structures similar to the published crystallographic structures for the same tetrapeptide bound to caspase 8 in the form of an irreversible inhibitor. The calculated binding energies for the new substrates to either caspase 3 or 8 showed little difference between the substrates, consistent with the K(M) data. In addition, the calculated binding energies (DeltaG) to caspase 8 were considerably more negative than those to caspase 3, also consistent with the K(M) data. A possible molecular interaction that might explain the selectivity of the IETD tetrapeptide motif for caspase 8 over caspase 3 is discussed.

Synthesis and characterization of coumarin-based europium complexes and luminescence measurements in aqueous media

A series of new ligands suitable for the formation of luminescent lanthanide complexes in water is described. The chelates are designed for analyte labeling and play the role of fluorescent donor in homogeneous time-resolved fluorescence assays using LEDs as a light source for excitation at 370 nm. Ligands are constructed from a coumarin nucleus, for lanthanide sensitization, and different aminomethylenecarboxy moieties are introduced in positions 7 and 5, 6, or 8 of the sensitizer. A reactive spacer arm under biocompatible conditions (maleimide, azide) is introduced at position 3 for ultimate bioconjugation purposes. The synthesis and characterization of the ligands are described, together with the preparation of their corresponding europium complexes. Photophysical properties of the complexes are investigated in water by means of UV-vis and luminescence spectroscopy.

Predicting efficient antenna ligands for Tb(III) emission

A series of highly luminescent Tb(III) complexes of para-substituted 2-hydroxyisophthalamide ligands (5LI-IAM-X) has been prepared (X = H, CH(3), (CO)NHCH(3), SO(3)(-), NO(2), OCH(3), F, Cl, Br) to probe the effect of substituting the isophthalamide ring on ligand and Tb(III) emission in order to establish a method for predicting the effects of chromophore modification on Tb(III) luminescence. The energies of the ligand singlet and triplet excited states are found to increase linearly with the pi-withdrawing ability of the substituent. The experimental results are supported by time-dependent density functional theory calculations performed on model systems, which predict ligand singlet and triplet energies within approximately 5% of the experimental values. The quantum yield (Phi) values of the Tb(III) complexes increase with the triplet energy of the ligand, which is in part due to decreased non-radiative deactivation caused by thermal repopulation of the triplet. Together, the experimental and theoretical results serve as a predictive tool that can guide the synthesis of ligands used to sensitize lanthanide luminescence.

"Cymothoe sangaris": an extremely stable and highly luminescent 1,2-hydroxypyridinonate chelate of Eu(III)

The synthesis, structure, and characterization of a new class of luminescent agents based on the 1,2-hydroxypyridinone chelator are reported. The prototype complex, [Eu(5LIO-1,2-HOPO)2]-, demonstrates superb aqueous stability [pEu = 18.64(10)] and is highly emissive [Phit = 0.21(3)], emitting almost pure "red" light (lambdaem = 612 nm). The crystal structure reveals a coordination geometry reminiscent of a "butterfly", hence the soubriquet of "Cymothoe sangaris" to identify with the unique species of red butterfly found only in Central Africa.

Enhanced fluorescence of 3-(naphthalene-2-ylimino)-1-phenylbutan-1-one-Tb with 1,10-phenanthroline ternary system and its analytical application

A new Schiff base ligand: 3-(naphthalene-2-ylimino)-1-phenylbutan-1-one (NPB) was synthesized. Its fluorescence intensity with terbium(III) was greatly enhanced by the addition of 1,10-phenanthroline (Phen) in the chloroform solution. The mechanism of fluorescence enhancement was studied. The results indicate the formation of a ternary NPB-Phen-Tb complex. In the ternary system, Phen can transfer the energy absorbed by Phen and NPB to Tb(3+).

Cocktails of Tb3+ and Eu3+ Complexes: A General Platform for the Design of Ratiometric Optical Probes

Fluorescent and luminescent reporters that signal molecular events of interest by modulating the ratio of peaks in their emission profile have advantages over reporters that simply modulate their emission intensity, since ratiometric measurement is concentration-independent and allows them to be effective in complex contexts, such as living cells or sensor microarrays. We herein describe a general platform for the design of ratiometric probes based on a heterometallic Tb(3+)/Eu(3+) bis-lanthanide ensemble, consisting of a mixture, or "cocktail", of otherwise identical heterometalated chelates. The chelate contains an organic photon antenna that sensitizes the Tb(3+)/Eu(3+) luminescence. The contributions of the two metals to the composite luminescence spectrum can be tuned to the same relative scale by adjusting the stoichiometry of the cocktail, allowing subtle changes in their ratio to be accurately measured. Importantly, the ratio responds to chemical and environmental changes experienced by the photon antenna, making the system an ideal platform for the design of chemical and enzymatic probes. As proofs of concept, we describe a ratiometric probe for esterase activity and a polarity-responsive ratiometric sensor.

Luminescence quenching of Eu(III) carboxylates by Cu(II) in a composite polymer xerogel film

Three Eu(III) luminescent compounds were separately entrapped in a xerogel porous silica matrix and finely ground particles of it were deposited on a glass support with polyvinylacetate (PVAc) as a binder to build a thin film sensor. These 3 devices were immersed in aqueous solutions of Cu(II) and the content of this metal was evaluated by emission-quenching experiments. The sensor containing the highly luminescent antenna chelate of diethylenetriaminepentaacetic acid (dtpa) sensitized with Coumarin120 rendered the largest Stern-Volmer constant (K(SV) = 1.49 x 10(4) M(-1)), showing no leaching of the Eu(III) complex to the aqueous solution and a reproducible value of the luminescence ratio between water and Cu(II) solution. The in situ sensor we developed can measure the concentration of Cu(II) in aqueous media down to the ppm level by emission-quenching experiments. This methodology permits a simple calibration of the sensor and an easy to use reusable device.

Modulation of Luminescence Intensity of Lanthanide Complexes by Photoinduced Electron Transfer and Its Application to a Long-Lived Protease Probe

Luminescent lanthanide complexes (Tb(3+), Eu(3+), etc.) have excellent properties for biological applications, including extraordinarily long lifetimes and large Stokes shifts. However, there have been few reports of lanthanide-based functional probes, because of the difficulty in designing suitable complexes with a luminescent on/off switch. Here, we have synthesized a series of complexes which consist of three moieties: a lanthanide chelate, an antenna, and a luminescence off/on switch. The antenna is an aromatic ring which absorbs light and transmits its energy to the metal, and the switch is a benzene derivative with a different HOMO level. If the HOMO level is higher than a certain threshold, the complex emits no luminescence at all, which indicates that the lanthanide luminescence can be modulated by photoinduced electron transfer (PeT) from the switch to the sensitizer. This approach to control lanthanide luminescence makes possible the rational design of functional lanthanide complexes, in which the luminescence property is altered by a biological reaction. To exemplify the utility of our approach to the design of lanthanide complexes with a switch, we have developed a novel protease probe, which undergoes a significant change in luminescence intensity upon enzymatic cleavage of the substrate peptide. This probe, combined with time-resolved measurements, was confirmed in model experiments to be useful for the screening of inhibitors, as well as for clinical diagnosis.

Combinatorial method for the study of new co-fluorescence enhancement system

The new co-fluorescence enhancement system was found in polymer matrix and studied with a combinatorial approach based on Re(DBM)3phen (Re3+: Tb3+, La3+, Gd3+, Y3+; dbm: dibenzoylmethane; phen: phenanthroline) and Sm3+ complex co-doped poly(methyl methacrylate)(PMMA). We have presents a new methodology for the rapid optimization of the luminescence conditions of thin-film sample in arrays of microwells. Two libraries were generated in order to study the effect of the species and content of enhancing ions on the luminescence enhancing efficiency, respectively. At the optimal content of 20 wt.% Sm(DBM)3phen, the maximum sensitization efficiency of Tb(DBM)3phen is about nine times. The intramolecular and intermolecular energy transfer processes in rare-earth complex-doped PMMA are discussed. The energy transfer processes make the co-fluorescence effect come true. Although, the methodology described here was implemented for optimization of co-fluorescence conditions, it is can be further implemented for a variety of applications in which optimization of parameters can be studied in situ using spectroscopic tool.

Combinatorial Study of Cofluorescence of Rare Earth Organic Complexes Doped in the Poly(Methyl Methacrylate) Matrix

The luminescence enhancement effect of different kinds and contents of rare earth complexe (RE(DBM)3Phen, RE = Dy, La, Gd, Sm, Y; DBM = dibenzoylmethane; Phen = 1,10-phenanthroline) sensitized Eu(DBM)3Phen doped in poly(methyl methacrylate) (PMMA) matrix was investigated using the combinatorial method. The efficiency of the luminescence enhancement increases with a decrease in the weight percentage of the Eu(DBM)3Phen and an increase in the molecular weight of the PMMA in the systems. Among these sensitization ion complexes, La(DBM)3Phen shows the highest sensitization efficiency. At the optimal content of 5 wt % Eu(DBM)3Phen and 350,000 g/mol weight average molecular weight (Mw) of PMMA, the maximum sensitization efficiency of La(DBM)3Phen is approximately 20 times. We believe that the PMMA with high molecular weight enwraps the rare earth complexes and keeps the donors and acceptors close, which results in the effective intermolecular energy transfer and, consequently, the high sensitization efficiency.

Carbostyril Derivatives as Antenna Molecules for Luminescent Lanthanide Chelates

Luminescent lanthanide complexes consisting of a lanthanide-binding chelate and organic-based antenna molecule have unusual emission properties, including millisecond excited state lifetimes and sharply spiked spectra, compared to standard organic fluorophores. We have previously used carbostyril (cs124, 7-amino-4-methyl-2(1H)-quinolinone) as an antenna molecule (Li and Selvin, J. Am. Chem. Soc., 1995) attached to a polyaminocarboxylate chelate such as DTPA. Here, we report the chelate syntheses of DTPA conjugated with cs124 derivatives substituted on the 1-, 3-, 4-, 5-, 6-, and 8-position. Among them, the DTPA chelate of cs124-6-SO(3)H has similar lifetime and brightness for both Tb(3+) and Eu(3+) compared to the corresponding DTPA-cs124 complexes, yet it is significantly more soluble in water. The Tb(3+) complex of DTPA-cs124-8-CH(3) has significantly longer lifetime compared to DTPA-cs124 (1.74 vs 1.5 ms), indicating higher lanthanide quantum yield resulting from the elimination of back emission energy transfer from Tb(3+) to the antenna molecule. Thiol-reactive forms of chelates were made for coupling to proteins. These lanthanide complexes are anticipated to be useful in a variety of fluorescence-based bioassays.

Engineering of Highly Luminescent Lanthanide Tags Suitable for Protein Labeling and Time-Resolved Luminescence Imaging

The synthesis of a new ligand LH(4) based on a glutamic acid skeleton bis-functionalized on its nitrogen atom by 6-methylene-6'-carboxy-2,2'-bipyridine chromophoric units is described. UV-vis spectrophotometric titrations revealed the formation of 1:1 M:L complexes with lanthanide(III) cations, and complexation of LH(4) with equimolar amounts of hydrated LnCl(3) salts (Ln = Eu, Gd, and Tb) gave water-soluble and stable complexes of the general formula [LnL(H(2)O)]Na, which were characterized by elemental analysis, IR, UV-vis absorption spectroscopy, (1)H NMR (Ln = Eu), and mass spectrometry. The conditional stability constant for formation of the [EuL(H(2)O)]Na complex was determined by competitive complexation experiments to be log K = 16.5 +/- 0.6 in 0.01 M TRIS/HCl buffer (pH = 7.0). In water solution, the [EuL(H(2)O)]Na and [TbL(H(2)O)]Na complexes were highly luminescent with quantum yields of 8% and 31%, respectively, despite the presence of ca. one water molecule in the first coordination sphere of the metal ions. Activation of the appended carboxylate function of the glutamate moiety in the form of an N-hydroxysuccinimidyl ester allows for the covalent linking of the complexes to primary amino groups of biological compounds. Bovine serum albumin (BSA) was labeled with both Eu or Tb complexes, and the Ln-BSA conjugates were characterized by UV-vis absorption and emission spectroscopy and MALDI-TOF mass spectrometry. Labeling ratios (number of complex molecules per BSA) of ca. 8:1 and 7:1 were established for Eu-BSA and Tb-BSA, respectively. The suitability of the tagged compound for use in bioanalytical time-resolved luminescence microscopy was established by comparison with fluorescein-labeled probes.

Synthesis of novel macrocyclic lanthanide chelates derived from bis-pyrazolylpyridine

[structure: see text] New macrocyclic chelates based on bis-pyrazolylpyridine and diethylenetriaminepentaacetic acid are synthesized, and the remarkable luminescence properties of their lanthanide chelates are reported.