Time-resolved Laser-induced Fluorescence Spectroscopy Research Articles

Uranyl sorption onto gibbsite studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite ( γ-Al(OH) 3). The experiments were performed under ambient conditions in 0.1 M NaClO 4 solution in the pH range from 5.0 to 8.5 using a total uranium concentration of 1 × 10 −5 M , and a solid concentration of 0.5 g/40 ml. Two uranyl surface species with fluorescence lifetimes of 330 ± 115 and 5600 ± 1640 ns , respectively, were identified. The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1 , 497.4 ± 0.8 , 518.7 ± 1.0 , 541.6 ± 0.7 , 563.9 ± 1.2 , and 585.8 ± 2.1 nm . The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH − groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be log β 210 = 7.33 ± 0.10 at an ionic strength of 0.1 mol/l (NaClO 4) and at 21 °C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.

Stabilities of the Aqueous Complexes Cm(CO3)33- and Am(CO3)33- in the Temperature Range 10−70 °C

The carbonate complexation of curium(III) in aqueous solutions with high ionic strength was investigated below solubility limits in the 10-70 degrees C temperature range using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The equilibrium constant, K(3), for the Cm(CO(3))(2-) + CO(3)(2-) right harpoon over left harpoon Cm(CO(3))(3)(3-) reaction was determined (log K(3) = 2.01 +/- 0.05 at 25 degrees C, I = 3 M (NaClO(4))) and compared to scattered previously published values. The log K(3) value for Cm(III) was found to increase linearly with 1/T, reflecting a negligible temperature influence on the corresponding molar enthalpy change, Delta(r)H(3) = 12.2 +/- 4.4 kJ mol(-1), and molar entropy change, Delta(r)S(3) = 79 +/- 16 J mol(-1) K(-1). These values were extrapolated to I = 0 with the SIT formula (Delta(r)H(3) degrees = 9.4 +/- 4.8 kJ mol(-1), Delta(r)S(3) degrees = 48 +/- 23 J mol(-1) K(-1), log K(3) degrees = 0.88 +/- 0.05 at 25 degrees C). Virtually the same values were obtained from the solubility data for the analogous Am(III) complexes, which were reinterpreted considering the transformation of the solubility-controlling solid. The reaction studied was found to be driven by the entropy. This was interpreted as a result of hydration changes. As expected, excess energy changes of the reaction showed that the ionic strength had a greater influence on Delta(r)S(3) than it did on Delta(r)H(3).

Curium(III) species and the coordination states in concentrated LiCl-aqueous solutions studied by time-resolved laser-induced fluorescence spectroscopy

Study on Cm(III) species and the coordination states in concentrated LiCl-aqueous solutions were performed by using time-resolved laser-induced fluorescence spectroscopy. The inner-sphere hydration number, N H 2 O and average chloride coordination number, N Cl, of Cm(III) were determined from the luminescence lifetimes and emission spectra, respectively. While the inner-sphere coordination sites of Cm(III) was fully occupied by water molecules in the C LiCl range less than 4 M, the inner-sphere chloro complexation of Cm(III) was observed in the C LiCl range more than 6 M. The total coordination number, defined as the sum of N H 2 O and N Cl, was kept constant in the C LiCl range up to 10 M, and then decreased gradually with an increase of C LiCl. This indicates that one chloride ion excludes more than one water molecule through the inner-sphere chloro complexation in the extremely concentrated LiCl-aqueous solutions.

Interactions of rare earth elements with bacteria and organic ligands

We investigated the interactions of rare earth elements (REEs) Eu(III) and/or Ce(III, IV) with the common soil bacterium Pseudomonas fluorescens and organic ligands, such as malic acid, citric acid, a siderophore (DFO), cellulose, chitin, and chitosan. Malic acid formed complexes with Eu(III), but degradation of malic acid was observed when the ratio of malic acid to Eu(III) was higher than 100. Citric acid formed a stoichiometric complex with Eu(III) that was not degraded by P. fluorescens. Adsorption of Eu(III) from the DFO complex occurred as a free ion dissociated from DFO and not as the Eu(III)–DFO complex. Cerium(III) was oxidized to Ce(IV) during complexation with DFO to form the Ce(IV)–DFO complex. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) analysis showed that cellulose, chitin, and chitosan, respectively, formed a weak complex, an inner-spherical complex, and an outer-spherical complex with Eu(III). This method also demonstrated that the coordination environment of Eu(III) adsorbed on P. fluorescens possessed similar characteristics to that of chitin, and revealed that adsorption of Eu(III) on P. fluorescens was through a multidentate and predominantly inner-spherical coordination.

In vivo detection of macrophages in a rabbit atherosclerotic model by time-resolved laser-induced fluorescence spectroscopy

Accumulation of numerous macrophages in the fibrous cap is a key identifying feature of plaque inflammation and vulnerability. This study investigates the use of time-resolved laser-induced fluorescence spectroscopy (TR-LIFS) as a potential tool for detection of macrophage foam cells in the intima of atherosclerotic plaques. Experiments were conducted in vivo on 14 New Zealand rabbits (6 control, 8 hypercholesterolemic) following aortotomy to expose the intimal luminal surface of the aorta. Tissue autofluorescence was induced with a nitrogen pulse laser (337 nm, 1 ns). Lesions were histologically classified by the percent of collagen or macrophage foam cells as well as thickness of the intima. Using parameters derived from the time-resolved fluorescence emission of plaques, we determined that intima rich in macrophage foam cells can be distinguished from intima rich in collagen with high sensitivity (>85%) and specificity (>95%). This study demonstrates, for the first time, that a time-resolved fluorescence-based technique can differentiate and demark macrophage content versus collagen content in vivo. Our results suggest that TR-LIFS technique can be used in clinical applications for identification of inflammatory cells important in plaque formation and rupture.

Cryogenic Laser Induced U(VI) Fluorescence Studies of a U(VI) Substituted Natural Calcite: Implications to U(VI) Speciation in Contaminated Hanford Sediments

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and imaging spectromicroscopy (TRLFISM) were used to examine the chemical speciation of uranyl in contaminated subsurface sediments from the U.S. Department of Energy (U.S. DOE) Hanford Site, Washington. Spectroscopic measurements for contaminant U(VI) were compared to those from a natural, uranyl-bearing calcite (NUC) that had been found via X-ray absorption spectroscopy (XAS) to include uranyl in the same coordination environment as calcium. Spectral deconvolution of TRLFS measurements on the NUC revealed the unexpected presence of two distinct chemical environments consistent with published spectra of U(VI)-substituted synthetic calcite and aragonite. Apparently, some U(VI) substitution sites in calcite distorted to exhibit a local, more energetically favorable aragonite structure. TRLFS measurements of the Hanford sediments NP4-1 and NP1-6 were similar to the NUC in terms of peak positions and intensity, despite a small CaCO3 content (1.0 to 3.2 mass %). Spectral deconvolution of the sediments revealed the presence of U(VI) in calcite and aragonite structural environments. A third, unidentified U(VI) species was also present in the NP1-6 sediment. TRLFISM measurements at multiple locations in the different sediments displayed only minor variation, indicating a uniform speciation pattern. Collectively, the measurements implied that waste U(VI), long-resident beneath the sampled disposal pond (32 y), had coprecipitated within carbonates. These findings have major implications for the solubility and fate of contaminant U(VI).

Complexation of curium(III) by adenosine 5′-triphosphate (ATP): A time-resolved laser-induced fluorescence spectroscopy (TRLFS) study

The complex formation of curium(III) with adenosine 5′-triphosphate (ATP) was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS). The interaction between soluble species of curium(III) with ATP was studied at trace Cm(III) concentrations (3 × 10 −7 M). The concentrations of ATP were varied between 6.0 × 10 −7 and 1.5 × 10 −4 M in the pH range of 1.5–7.0 using 0.154 M NaCl as background electrolyte. Three Cm–ATP species, M pH qL r, could be identified from the fluorescence emission spectra: (i) CmH 2ATP + with a peak maximum at 598.6 nm, (ii) CmHATP with a peak maximum at 600.3 nm, and (iii) CmATP − with a peak maximum at 601.0 nm. The formation constants of these complexes were calculated from TRLFS measurements to be log β 121 = 16.86 ± 0.09, log β 111 = 13.23 ± 0.10, and log β 101 = 8.19 ± 0.16. The hydrated Cm–ATP species showed fluorescence lifetimes between 88 and 96 μs; whereas the CmATP − complex has a significantly longer fluorescence lifetime of 187 ± 7 μs.

Associations of Eu (III) with Gram-Negative Bacteria, Alcaligenes faecalis, Shewanella putrefaciens, and Paracoccus denitrificans

with bacteria in that these elements may be leaked out of radioactive contaminants. In this study, we used Eu(III) because of its informative fluorescence properties. Europium(III) is a good analogue of Am(III) and Cm(III), and a study on the association of Eu(III) with bacteria is of great help in assessing that of Am(III) and Cm(III), whose long half-lives and high-energy αparticle emission can pose high risks to human health. Time-resolved laser-induced fluorescence spectroscopy is a powerful tool to characterize the coordination environment of Eu(III) with regard to the number of water molecules in the inner-sphere of Eu(III) and the strength of its ligand field both in the inner- and outer-sphere. 14 Previously, we used this technique and successfully characterized the association of Eu(III) with biopolymers (cellulose, chitin, and chitosan) and a unicellular alga Chlorella vulgaris. 15, 16 In the present study, we examined the adsorption behavior of Eu(III) on Gram-negative bacteria A. faecalis, S. putrefaciens, and P. denitrificans by a batch method. Using timeresolved laser-induced fluorescence spectroscopy (TRLFS), we examined the coordination environment of Eu(III) adsorbed on them.

Study on Stabilization Effect of Neutral Soft Donor on Trivalent Lanthanide and Actinide Dicarboxylate Complexes by Time-Resolved Laser-Induced Fluorescence Spectroscopy

Study on Stabilization Effect of Neutral Soft Donor on Trivalent Lanthanide and Actinide Dicarboxylate Complexes by Time-Resolved Laser-Induced Fluorescence Spectroscopy

Eu(CO3)33? and the limiting carbonate complexes of other M3+ f-elements in aqueous solutions: a solubility and TRLFS study

Within the framework of environmental studies regarding radioactive waste management, the speciation of M3+ f-elements in concentrated carbonate solutions was investigated. Solubility measurements of NaEu(CO3)2·5H2O(s) were performed at 23 ± 1 °C under fixed [Na+], by using NaClO4. In 3 mol l−1 Na+ aqueous solutions, the limiting complex Eu(CO3)33− was identified in the range 0.01 < [CO32−] < 2 mol l−1; experimental solubilities were modelled with the equilibrium: NaEu(CO3)2·5H2O(s) + CO32− ⇌ Na+ + Eu(CO3)33− + 5H2O, and the logarithm of the corresponding equilibrium constant was found to be logKs,3 = −4.2 ± 0.2. To interpret the measurements at different [Na+], the activity coefficients of the species were calculated with the SIT formula. Time-resolved laser-induced fluorescence spectroscopy was used to verify the presence of a single complex of Eu(III) in aqueous solutions. From fluorescence lifetime measurements in 1 mol l−1 Na2CO3 solutions in H2O–D2O mixtures, it was determined that about two water molecules remained in the first coordination sphere of Eu(CO3)33−. From a critical review of literature data and sensitivity analysis, it was concluded that solubility results should be more reliable than solvent extraction and spectroscopic results in determining the stoichiometry of limiting carbonate complexes. Tricarbonate complexes of most M3+ f-elements appeared to be the limiting stable species in Na+ aqueous solutions, except for Ce(III), for which a tetracarbonate complex was indeed observed. Interestingly, supporting electrolytes based on K+ can favour tetracarbonate complexes at high ionic strength. Available values of thermodynamic constants related to various ionic media are compared on the basis of the SIT formula.

Luminescence Study on the Inner‐Sphere Hydration Number of Lanthanide(III) Ions in Neutral Organo‐Phosphorus Complexes

Time‐resolved laser‐induced fluorescence spectroscopy (TRLFS) was employed to determine the inner‐sphere (i.e., first coordination sphere) hydration number (N H2O) of lanthanide(III) ions (Ln = Sm, Eu, Tb, and Dy) in the TRPO‐dodecane/HNO3 (or HNO3–NaNO3) system under various conditions. In addition, the N H2O of Ln(III) in extracted complexes with octyl(phenyl)‐N,N‐diisobutylcarbamoylmethyl phosphine oxide (CMPO), dihexyl‐N,N‐diethylcarbamoylmethyl phosphonate (CMP), trioctyl phosphine oxide (TOPO), and tributyl phosphate (TBP) were also determined. The results show that there is no water molecule in the first coordination sphere of Ln(III) complexes, except for Sm(III) and Dy(III) in CMP complexes.

Speciation study on complex formation of uranium(VI) with phosphate and fluoride at high temperatures and pressures by time-resolved laser-induced fluorescence spectroscopy

Summary The complex formation of U(VI) with phosphate and with fluoride has been studied at elevated temperatures (20–150 °C) and pressures (0.1–40 MPa) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Emission spectra and lifetimes of 5×10–5 M uranium(VI) in 0.5 M NaClO4 solutions in the presence and absence of ligand ions were measured as a function of the pH, ligand concentration, temperature and pressure. The emission intensities and lifetimes of uranium(VI) decreased rapidly with increasing temperature. In contrast, a pressure effect on the fluorescence properties was quite small. The fluorescence decay curves could be resolved into several fluorescent species. The temperature dependence of the lifetimes followed the Arrhenius law, and the activation energies were estimated for the phosphate and fluoride complexes. These results were compared with speciation calculations at several temperatures obtained by using the DQUANT equation and thermodynamic data in the literature. From these comparisons, each component of the fluorescence was identified as a complexed species or a free uranyl ion at several temperatures, indicating that the Arrhenius plot of fluorescence lifetime is an effective method for in-situ speciation of uranyl complexation at elevated temperatures.

Uranyl Precipitation byPseudomonas aeruginosavia Controlled Polyphosphate Metabolism

The polyphosphate kinase gene from Pseudomonas aeruginosa was overexpressed in its native host, resulting in the accumulation of 100 times the polyphosphate seen with control strains. Degradation of this polyphosphate was induced by carbon starvation conditions, resulting in phosphate release into the medium. The mechanism of polyphosphate degradation is not clearly understood, but it appears to be associated with glycogen degradation. Upon suspension of the cells in 1 mM uranyl nitrate, nearly all polyphosphate that had accumulated was degraded within 48 h, resulting in the removal of nearly 80% of the uranyl ion and >95% of lesser-concentrated solutions. Electron microscopy, energy-dispersive X-ray spectroscopy, and time-resolved laser-induced fluorescence spectroscopy (TRLFS) suggest that this removal was due to the precipitation of uranyl phosphate at the cell membrane. TRLFS also indicated that uranyl was initially sorbed to the cell as uranyl hydroxide and was then precipitated as uranyl phosphate as phosphate was released from the cell. Lethal doses of radiation did not halt phosphate secretion from polyphosphate-filled cells under carbon starvation conditions.

Sorption behavior of europium(III) and curium(III) on the cell surfaces of microorganisms

SummaryWe investigated the association of europium(III) and curium(III) with the microorganismsChlorella vulgaris,Bacillus subtilis,Pseudomonas fluorescens,Halomonassp.,Halobacterium salinarum, andHalobacterium halobium. We determined the kinetics and distribution coefficients (Kd) for Eu(III) and Cm(III) sorption at pH 3-5 by batch experiments, and evaluated the number of water molecules in the inner-sphere (NH₂O) and the degree of strength of ligand field (RE/M) for Eu(III) by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Exudates fromC. vulgaris,Halomonassp., andH. halobiumhad an affinity for Eu(III) and Cm(III). The logKdof Eu(III) and Cm(III) showed that their sorption was not fully due to the exchange with three protons on the functional groups on cell surfaces. The halophilic microorganisms (Halomonassp.,Halobacterium salinarum,H. halobium) showed almost no pH dependence in logKd, indicating that an exchange with Na+on the functional groups was involved in their sorption. The Δ NH₂O(=9-NH₂O) for Eu(III) onC. vulgariswas 1-3, while that for the other microorganisms was over 3, demonstrating that the coordination of Eu(III) withC. vulgariswas predominantly an outer-spherical process. TheRE/Mfor Eu(III) on halophilic microorganisms was 2.5-5, while that for non-halophilic ones was 1-2.5. This finding suggests that the coordination environment of Eu(III) on the halophilic microorganisms is more complicated than that on the other three non-halophilic ones.

Luminescence properties of tetravalent uranium in aqueous solution

Summary The luminescence spectra of U4+ in aqueous solutions were observed in the UV-VIS region at ambient and liquid nitrogen temperatures. The excitation spectrum indicates that the luminescence is arising from the deexcitation of a 5f electron at the 1 S 0 level and no other emissions of U4+ in aqueous solutions were detected for other f–f transitions. All the luminescence peaks were assigned to the transitions from 1 S 0 to lower 5f levels. To estimate the luminescence lifetime, luminescence decay curves were measured using time-resolved laser-induced fluorescence spectroscopy. At room temperature, the decay curve indicated that the lifetime was shorter than 20 ns. On the other hand, the frozen sample of U4+ in aqueous solution at liquid nitrogen temperature showed the same emission spectrum as at room temperature and its lifetime was 149 ns in H2O system and 198 ns in D2O system. The longer lifetime at liquid nitrogen temperature made it possible to measure the spectrum of U4+ at the concentration as low as 10-6 M. The difference in the anion species (ClO4 -, Cl-, SO4 2-) affected the structure of the emission spectrum to some extent.

Fluorescence characteristics of complex formation of europium(III)-salicylate

Summary The complexation of salicylate with Eu3+ was studied by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS) using ultra-short pulses at a concentration of sodium salicylate of 1.00×10-4 M. Ionic media was kept constant at 0.1M NaClO4. pH was adjusted to 4.00. The concentration of Eu3+ was varied from 1.98×10-3 M to 1.31×10-2 M. From the fluorescence lifetime analysis of the salicylate, we confirmed that a dynamic quenching process did not take place, while static quenching proceeded under the experimental conditions. The Stern Volmer plots indicated only the formation of a 1:1 complex, and the stability constant was assigned to be logβ 1,1= 2.08±0.02. This agrees with reported values, which have been determined by other techniques. This result shows that the studies on complex formation can be safely investigated quantitatively by means of TRLFS from not only the luminescence of Eu3+ but the fluorescence of salicylate.

Spectroscopic Characterization of the Uranium Carbonate Andersonite Na2Ca[UO2(CO3)3]·6H2O

The uranium carbonate andersonite Na2Ca[UO2(CO3)3] x 6H2O was synthesized and identified with classical analytical and spectroscopic methods. The classical methods applied were powder X-ray diffraction (XRD), nitric acid digestion, and scanning electron microcopy combined with energy-dispersive spectroscopy (SEM/EDS). To characterize andersonite spectroscopically, time-resolved laser-induced fluorescence spectroscopy (TRLFS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) were used. Natural and synthetic andersonite samples were characterized with the nondestructive TRLFS by six fluorescence emission bands at 470.6, 486.1, 505.4, 526.7, 549.6, and 573.9 nm. In addition, andersonite was characterized by FT-IR measurements by the appearance of the asymmetric stretching vibration of the uranyl cation [v3(UO2(2+))] at 902 cm(-1) with a shoulder at 913 cm(-1). XPS measurements verified the composition of the synthetic andersonite sample. The measured intensity ratios of the XPS lines agree with the stoichiometry of Na2Ca[UO2(CO3)3] x 6H2O. The XPS features of the inner valence molecular orbitals are characteristic of the [UO2(CO3)3]4- structural moiety. These spectroscopic methods can be used to identify in a fingerprinting procedure secondary U(VI) phases in mixtures with other phases or as thin coatings on mineral and rock surfaces.

An EXAFS and TRLFS investigation on uranium(VI) sorption to pristine and leached albite surfaces

Uranium(VI) was sorbed to freshly ground and leached albite in batch and flow-through systems in the pH range 5.0–6.4. The uranium(VI) surface complexes were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The EXAFS analysis of uranium(VI) sorbed on albite at pH 5.8 and 5 × 10 −6 M U(VI) showed one silicon atom at a U Si distance of 3.09 Å, which is indicative of the formation of an inner-sphere, mononuclear, bidentate uranium(VI) surface complex, Si(O) 2 UO 2, on the silicate tetrahedra of albite. Two additional uranium(VI) sorption complexes were detected by TRLFS at higher initial aqueous U(VI) concentrations. However, the structure of these surface complexes could not be derived from EXAFS, since the measured EXAFS spectra represent the average of two surface complex structures. In order to simulate U(VI) sorption onto weathered feldspar surfaces, albite was leached with 0.01 M HClO 4, resulting in surface material similar to amorphous silica gel. EXAFS showed that the equatorial oxygen shell of uranium(VI) sorbed on this material at pH 5.0 and 5.8 was split in two distances of 2.23 and 2.44 Å. This indicates the formation of an inner-sphere surface complex.

Spectroscopic characterization of alkaline earth uranyl carbonates

A series of alkaline uranyl carbonates, M[UO 2(CO 3) 3]· nH 2O ( M=Mg 2, Ca 2, Sr 2, Ba 2, Na 2Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). The molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba 2[UO 2(CO 3) 3]·6H 2O was obtained for the first time. The EXAFS analysis showed that this compound consists of (UO 2)(CO 3) 3 clusters similar to the other alkaline earth uranyl carbonates. The average U–Ba distance is 3.90±0.02 Å.Fluorescence wavelengths and life times were measured using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The U–O bond distances determined by EXAFS, TRLFS, XPS, and Raman spectroscopy agree within the experimental uncertainties. The spectroscopic signatures observed could be useful for identifying uranyl carbonate species adsorbed on mineral surfaces.