Application of long-lived luminescence for detection in liquid chromatography

Summary Quenched and sensitized lanthanide luminescence as detection in liquid chromatography has been investigated. An important advantage in comparison with phosphorescence is that the long-lived luminescence as applied does not require deoxygenation of the samples. In order to obtain a high luminescence intensity Tb(III) complexes with acetylacetonate have been formed, after which indirect excitation of Tb(III) can be realized via the ligands. The potential of Tb(III) luminescence as a detection method in ion chromatography has been shown for chromate, which is an efficient quencher. Sensitizing of the Tb(III) luminescence has been applied for thiol-containing analytes. These compounds are derivatized with maleimidyl salicylic acid to complexes that sensitize the Tb(III) luminescence. From a comparison of the results obtained with normal fluorescence detection and time-resolved sensitized Tb(III) luminescence detection it has become clear that the last method has a higher sensitivity, but in particular a higher selectivity.     

A Highly Sensitive and Recyclable Ln‐MOF Luminescent Sensor for the Efficient Detection of Fe3+ and CrVI Anions

Two new three‐dimensional (3D) Ln^III metal‐organic frameworks (MOFs) were designed and successfully obtained via a solvothermal reaction between lanthanide(III) nitrates and a semi‐flexible carbazole tetracarboxylate acid linker as a high‐performance chromophore. 1 and 2 possess porous 3D networks with channels along the a axis, and more importantly, they show a highly sensitive and selective fluorescence quenching response to Fe³⁺ and Cr^VI anions. The sensing mechanism investigation revealed that the weak interactions of Fe³⁺ with nitrogen atoms of carbazole and deprotonated carboxylic acids protruding into the pores of MOFs quenched the luminescence of 1 and 2 effectively. In addition, the competition absorption also played an important role in the luminescence quenching detection of Fe³⁺ based on 1 , and Cr^VI anions based on 1 and 2 . Therefore, 1 and 2 represent an alternative example of regenerable luminescence based sensors for the quantitative detection of Fe³⁺ and Cr^VI anions.     

Luminescence behavior of a water soluble calix[4]arene derivative complex with terbium ion(III) in gelation solution

The complexation luminescence behavior of a water soluble calix[4]arene derivative, 5,11,17,23-tetra-sulfonate-25,26,27,28-tetra-carboxymethoxycalix[4]arene (L) with lanthanoid ion (Tb(3+)) has been investigated in gelation solution at 25 degrees C by using UV-vis and fluorescence spectra. The results obtained indicated that the water soluble calix[4]arene derivative can form an efficient energy transfer complex with terbium ion(III). The fluorescence of L x Tb(3+)complex is partially quenched by gelatin in gelation solution. The quenching intensity is related to the concentration and the hydrolysis degree of gelatin. Absorption and fluorescence spectra analysis show that the -COO(-) groups on gelatin have a definite binding ability to Tb(3+), and then, gelatin could compete binding with calix[4]arene derivative upon complexation with Tb(3+), leading to the relative fluorescence quenching of the formation complex of terbium(III) ion with calix[4]arene derivative.     

Speciation of Cr(III) and Cr(VI) and separation of common anions by ion pair chromatography with trans-1,2-diaminecyclohexane-N,N,N',N'-tetraacetic acid

A reversed phase ion pair chromatographic method for the simultaneous determination of Cr species and common anions on a C(18)-bonded stationary phase was developed by using acetonitrile-water (2:98 v/v) containing 1.0 mM tetrabutylammonium hydroxide and 0.5 mM trans-1,2-diaminecyclohexane-N,N,N',N'-tetraacetic acid (DCTA) at pH 6.5 as mobile phase and UV-detection at 210 nm. Chromatographic parameters were optimized for separation of Cr(III)-DCTA complex, chromate and other anions. The detection limits were found as 8 ng/ml for Cr(III) and 35 ng/ml for Cr(VI). Under the optimum conditions, most other ions did not interfere. The method can be applied to separate a number of common anions simultaneously with the separation of Cr(III) and Cr(VI).     

Sensitization of Tb<Superscript>3+</Superscript> luminescence with polypyridyl ligands in a nafion membrane

Perfluorosulfonic membranes were modified by terbium(III) polypyridyl complexes by ionexchange sorption of cations followed by addition of ligands. The luminescence sensitization degree is compared with the state of ligands in the grafted complexes. In the case of the terbium(III) 4,7-diphenylphenanthroline complex, strong blue luminescence of the ligand is observed, along with radiation transitions of the cation. The character of luminescence quenching in modified membranes in a wet medium is determined by the ability of ligands to prevent terbium from adsorbing water molecules.     

Terbium Nitrate Luminescence Quenching by Eosin in the Presence of Lithium Perchlorate in Sulfolane Solutions

The quenching of terbium nitrate luminescence by the anionic dye eosin in the presence of lithium perchlorate in sulfolane solutions was examined. The temperature dependence of terbium nitrate luminescence in sulfolane solutions in the presence of perchlorate anions was studied. The energy required for the replacement of a water molecule in the coordination sphere of the Tb(3+) ion by a solvent molecule in an electrolyte solution was determined.     

High luminescence quantum yields and long luminescence lifetime from Eu(III) complex containing two crystal water based on a new beta-diketonate ligand

New members of family of Eu(III) complex based on the thenoylacetophenone have been synthesized and characterized. The compounds were found for high metal luminescence quantum yields and long luminescence lifetime, especially for compound with two crystal water, corresponding with other compounds containing two crystal water. The result is attributed to high molar absorption coefficients of the Eu(III) complex according to UV-vis and emission spectra. The high molar absorption coefficients balance quenching effect from OH oscillators of water contained in compound.     

Luminescence of terbium(III) chloride in porous glass

Terbium(III) chloride (1.5–150 μmol g^?1) was encapsulated in porous glass by impregnation of the support with aqueous solutions of various concentrations. The concentration dependences of the luminescence parameters and luminescence quenching in the course of water vapor adsorption in the salt intercalates were analyzed.     

The Dark Side of Hydrogen Bonds in the Design of Optical Materials: A Charge‐Density Perspective

A combined investigation of the structural, electronic, and optical properties of three crystalline nonaaqualanthanoid(III) triflates, [Ln(H₂O)₉(CF₃SO₃)₃], has provided unambiguous experimental evidence for charge redistribution in the first coordination sphere of a lanthanide ion as a result of hydrogen bonds with outer‐sphere anions. As well as resulting in charge transfer from the noncoordinated anions to the coordinated water molecules, these hydrogen bonds give rise to a new excited state, an hydrogen‐bond‐induced charge‐transfer state, which is observed experimentally for the first time. This state was shown to be responsible for the previously unknown negative aspect of hydrogen bonds with a lanthanide‐bound water molecule: rather than increasing the luminescence efficiency of the complex, they can lead to additional quenching that is unfavorable for the task‐specific design of optical materials.     

Three-component coordination networks based on [Ru(phen)(CN)4(2-) anions, near-infrared luminescent lanthanide(III) cations, and ancillary oligopyridine ligands: structures and photophysical properties

A series of cyanide-bridged coordination networks has been prepared which contain [Ru(phen)(CN)4](2-) anions, Ln(III) cations, and additional oligopyridine ligands (1,10-phenanthroline, 2,2':6',2'-terpyridine or 2,2'-bipyrimidine) which coordinate to the Ln(III) centres. Five structural types have been identified and examples of each type of structure are described: these are hexanuclear Ru4Ln2 clusters; two-dimensional Ru-Ln sheets with a honeycomb pattern of edge-linked Ru6Ln6 hexagons; one-dimensional chains consisting of two parallel cross-linked strands in a ladder-like arrangement; simple single-stranded chains of alternating Ru/Ln components; and a one-dimensional 'chain of squares' in which Ru2Ln2 squares are linked by bipyrimidine bridging ligands which connect to the Ln(III) corners of adjacent squares in the sequence. The 3MLCT luminescence characteristic of the [Ru(phen)(CN)4](2-) units is quenched in those networks containing Ln(III) which have low-lying near-infrared luminescent f-f states [Pr(III), Nd(III), Er(III), Yb(III)], with sensitised Ln(III)-based near-IR luminescence generated by d --> f energy-transfer. The rate of d --> f energy-transfer, and hence the degree of quenching of the 3MLCT luminescence from the [Ru(phen)(CN)4](2-) units, depends on the availability of f-f levels of an appropriate energy on the Ln(III) centre, with Nd(III) (with a high density of low-lying f-f states) being the most effective energy-acceptor and Yb(III) (with a single low-lying f-f state) being the least effective. Rates of d --> f energy-transfer to different Ln(III) centres could be determined from both the residual (partially quenched) lifetimes of the 3MLCT luminescence, and--in the case of the Yb(III) networks--by a rise-time for the sensitised near-IR luminescence. The presence of the 'blocking' polypyridyl ligands, which reduced the number of cyanide and water ligands that would otherwise coordinate to the Ln(III) centres, resulted in increases in the Ln(III)-based emission lifetimes compared to networks where these blocking ligands were not used.     

Determination of medicinal preparations,salts of organic bases,by the effect of their anions on the luminescence of lanthanide complexes

The luminescence parameters of Eu(III) and Tb(III) complexes with fluorinated amide derivatives of hydroxyquinoline carboxylic acid (L_1–8) were studied. It was shown that medicinal preparations, salts of organic bases, can be determined from the effect of their anions on the luminescence of Eu(III)-sensitizing ligand complexes. The Eu(III)-L₁-citrate ion and Eu(III)-L₂-tartrate ion complexes were proposed for the luminescence determination of clomiphene and tamoxifen citrates and platyphyllin tartrate, respectively. The detection limits were 0.30 μg/mL for clomifene (tamoxifen) citrate and 0.85 μg/mL for platyphyllin tartrate.     

Aromatic polyaminocarboxylate ligands for energy transfer luminescence measurements of lanthanide ions in aqueous solutions

The promising ligand candidates for the energy transfer luminescence measurements of lanthanide (Ln) chelates on aqueous matrices are first proposed. The ligands are; 2[(2-amino-5-methyl-phenoxy)methyl]-6-methoxy-8-aminoquinoline-N,N,N',N'-tetraacetate (Quin 2), 1,2-bis(2-amino-phenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA), and 1,2-bis(2-amino-5-fluoro-phenoxy)ethane-N,N,N',N'-tetraacetate (F-BAPTA). The Ln-chelates of these aromatic polyaminocarboxylates show the sensitized emission which results from efficient ligand-centered light absorption, and the interesting selectivity is seen; BAPTA and F-BAPTA form the luminescent chelates only with Tb(III) and Dy(III) ions, whereas the emission from Sm(III) and Eu(III) ions is greatly sensitized with Quin 2. The sufficient emission intensity can be obtained even in slightly alkaline aqueous solutions without any addition of surfactants or organic solvents. These octadentate ligands are fairly capable of shielding central Ln ions from quenching by surrounding water molecules. The luminescence enhancement factors are 1600 for Tb(III) ion with BAPTA (em.544 nm) and 1380 for Eu(III) ion with Quin 2 (em. 615 nm), respectively, being relative to their aqueous chloride solutions.     

Eu(III)-cyclen-phen conjugate as a luminescent copper sensor: the formation of mixed polymetallic macrocyclic complexes in water

The cationic cyclen based Eu(III)-phen conjugated 1.Eu was synthesised as a chemosensor for Cu(II), where the recognition in water at pH 7.4 gave rise to quenching of the Eu(III) luminescence and the formation of tetranuclear polymetallic Cu(II)-Eu(III) macrocyclic complexes in solution where Cu(II) was bound by three 1.Eu conjugates.     

Detection of multiple anions by thin-layer chromatography

A novel detection method for 21 different anions by thin-layer chromatography is presented. Anions on the target plate form salts with amine in a developing solvent and are visualized after staining with citric acid-acetic anhydride reagent as white spots contrasting against a pale red-pink background. This method has particularly high sensitivity for anions of chlorate, sulfate, phosphate, chromate and dichromate (0.02-0.05 microg). The method is demonstrated to efficiently detect toxic arsenite in curry sauce as an example application. The proposed method offers highly efficient indirect detection for a wide range of anions, and serves as a purification procedure for the preparation of anionic sample solutions for other analytical methods.     

Multidentate Europium Chelates as Luminoionophores for Anion Recognition: Impact of Ligand Design on Sensitivity and Selectivity,and Applicability to Enzymatic Assays

The design of photoluminescent molecular probes for the selective recognition of anions is a major challenge for the development of optical chemical sensors. The reversible binding of anions to lanthanide centers is one promising option for the realization of anion sensors, because it leads in some cases to a strong luminescence increase by the replacement of quenching water molecules. Yet, it is an open problem to gain control of the sensitivity and selectivity of the luminescence response. Primarily, the selective detection of (poly)phosphate species such as nucleotides has emerged as a demanding task, because they are involved in many biological processes and enzymatic reactions. We designed a series of pyridyl‐based multidentate europium complexes (seven‐, six‐, and five‐dentate) including sensitizing chromophores and studied their luminescence intensity and lifetime responses to different (poly)phosphates (adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), cyclic adenosine monophosphate (cAMP), pyrophosphate, and phosphate anions), and carboxyanions (citrate, malate, oxalacetate, succinate, α‐ketoglutarate, pyruvate, oxalate, carbonate). The results reveal that the number of free coordination sites has a significant impact on the sensitivity and selectivity of the response. Because of its reversibility, the lanthanide probes can be applied to monitor the activity of ATP‐consuming enzymes such ATPases and apyrases, which is demonstrated by means of the five‐dentate complex.     

Influence of the Nature of Carboxylic Acid on the Luminescence and Spectral Properties of (Carboxylato)bis(dibenzoylmethanato)europium(III) Complexes

A series of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes containing anions of both saturated and unsaturated carboxylic acids were synthesized to compare the luminescence and spectral properties of heteroligand Eu(III) complexes. (Carboxylato)bis(dibenzoylmethanato)europium(III) complexes with unsaturated acid anions were synthesized for the first time. The compounds obtained were characterized using elemental analysis and luminescence and IR spectroscopy. These studies revealed two types of influence of the nature of an acid substituent on the luminescence spectra of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes. The anomalous Stark structure of the luminescence spectra of one group of compounds is attributed to the charge transfer state at 77 K.     

Delayed lanthanide luminescence sensing of aromatic carboxylates using heptadentate triamide Tb(III) cyclen complexes: the recognition of salicylic acid in water

The coordinately unsaturated terbium complexes Tb.1 and Tb.2 possess two labile metal-bound water molecules that can be displaced upon metal chelation to aromatic carboxylic anions such as salicylic acid in water, which gives rise to large enhancements in the Tb(III) luminescence.     

Study of the selectivity of inorganic anions in hydro-organic solvents using indirect capillary electrophoresis

In capillary electrophoresis (CE) analysis of small inorganic anions, the ability to control the electroosmotic flow (EOF) and the ability to alter the electrophoretic mobility of the ions are essential to improve resolution and separation speed. In this work, a CE method for separation of small inorganic anions using indirect detection in mixed methanol/water buffers is presented. The suitability of different UV absorbing probes commonly used for indirect detection including chromate, iodide, phthalate, benzoate, trimellitate, and pyromellitate, in mixed methanol/water buffers is examined. The effect of the electrolyte buffer system, including the pH, buffer concentration and the organic solvent on the electrophoretic mobility of the probes and analytes are also investigated. The EOF was reversed using cationic surfactant, cetyltrimethylammonium bromide (CTAB) so ions were separated under co-EOF mode. The organic solvent alters the electrophoretic mobility of the probes and the analytes differently and hence choice of the appropriate probe is essential to achieve high degree of detection sensitivity. Separations of six anions in less than 2.5 min were accomplished in buffers containing up to 30% MeOH. Adjustment of the methanol content helps to improve the selectivity and resolution of inorganic anions. Limit of detection, reproducibility and application of the method for quantification of anions in water samples will also be discussed.     

Quenching of the long-lived Ru(II)bathophenanthroline luminescence for the detection of supramolecular interactions

A feasibility study based on tailor-made peptide sequences for a new robust luminescence probe-system using the long-lived luminescence of a Ru(II)-bathophenanthroline complex in combination with an efficient anthraquinone-type quencher is presented. Due do their high chemical stability, both dyes can be introduced during solid-phase peptide synthesis avoiding post-synthetic labelling. Photophysical measurements revealed an intense quenching of the luminescence of the Ru-complex (65-68%) which was also confirmed by calculations resulting from decay time measurements. The long-lived luminescence allows for a time-gated detection scheme, which can reduce any luminescence contribution from matrix components.     

Luminescence recognition of different organophosphorus pesticides by the luminescent Eu(III)–pyridine-2,6-dicarboxylic acid probe

Luminescence quenching of a novel long lived Eu(III)–pyridine-2,6-dicarboxylic acid probe of 1:2 stoichiometric ratio has been studied in 0.10 volume fraction ethanol–water mixture at pH 7.5 (HEPES buffer) in the presence of the organophosphorus pesticides chlorfenvinphos (P1), malathion (P2), azinphos (P3), and paraxon ethyl (P4). The luminescence intensity of Eu(III)–(PDCA)₂ probe decreases as the concentration of the pesticide increases. It was observed that the quenching due to P3 and P4 proceeds via both diffusional and static quenching processes. Direct methods for the determination of the pesticides under investigation have been developed using the luminescence quenching of Eu(III)–pyridine-2,6-dicarboxylic acid probe in solution. The linear range for determination of the selected pesticides is 1.0–35.0 μM. The detection limits were 0.24–0.55 μM for P3, P4, and P1 and 2.5 μM for P2, respectively. The binding constants (K), and thermodynamic parameters of the OPs with Eu(III)–(PDCA)₂ were evaluated. Positive and negative values of entropy (ΔS) and enthalpy (ΔH) changes for Eu(III)–(PDCA)₂–P1 ternary complex were calculated. As the waters in this study do not contain the above mentioned OPs over the limit detectable by the method, a recovery study was carried out after the addition of the adequate amounts of the organophosphorus pesticides under investigation.