Laser Fluorescence Spectroscopy Research Articles

An atomic beam of titanium for ultracold atom experiments.

We generate an atomic beam of titanium (Ti) using a "Ti-ball" Ti-sublimation pump, which is a common getter pump used in ultrahigh vacuum systems. We show that the sublimated atomic beam can be optically pumped into the metastable 3d3(4F)4sa5F5 state, which is the lower energy level in a cycling optical transition that can be used for laser cooling. We measure the atomic density and transverse and longitudinal velocity distributions of the beam through laser fluorescence spectroscopy. We find a metastable atomic flux density of 4.3(2) × 109s-1cm-2 with a mean forward velocity of 773(8) m/s at 2.55cm directly downstream of the center of the Ti-ball. Owing to the details of optical pumping, the beam is highly collimated along the transverse axis parallel to the optical pumping beam and the flux density falls off as 1/r. We discuss how this source can be used to load atoms into a magneto-optical trap.

Cm(III) speciation in the presence of citrate from neutral to hyperalkaline conditions and the effect of calcium

We investigated the binary Cm-citrate system using time-resolved laser fluorescence spectroscopy (TRLFS), parallel factor analysis (PARAFAC), and quantum chemical calculations. Evidence collectively suggests the stepwise coordination and deprotonation of citrate alcohol groups in Cm-cit complexes with two bound citrate moieties upon increasing pH, which is supported by a bathochromic shift in emission spectra, an observed increase in lifetime measurements, and lower energy minima for citrate alcohol involvement versus hydrolysis of the Cm-citrate species. Our PARAFAC results agree with a 3-component model for the Cm-citrate system and offer pure component decompositions, yielding fraction species across the studied pH range that have a correlated slope = 1 as a function of pH. For the first time, evidence of ternary Ca-Cm-citrate complexes was revealed by TRLFS with increasing calcium concentration at fixed pHm. The formation of these ternary complexes was substantiated with density functional theory (DFT) calculations on simple model systems of the complexes. Shared citrate carboxylate groups between calcium and curium were proposed for all three ternary Ca-Cm-cit complexes based on DFT-determined Ca–O and Cm–O distances. Moreover, we found that the ternary complex with both alcohol groups deprotonated is most stable when it shares both two carboxylate and two alcohol groups between Ca and Cm. The presence of shared functional groups highlights the enhanced stability of these ternary complexes. Additional work is warranted to further constrain the stoichiometry, stability constants and dependence on ionic strength of these complexes for purposes of thermodynamic modeling of repository settings.

6-(6-Methyl-1,2,4,5-Tetrazine-3-yl)-2,2'-Bipyridine: A N-Donor Ligand for the Separation of Lanthanides(III) and Actinides(III).

Here, we report the synthesis of the 6-(6-methyl-1,2,4,5-tetrazine-3-yl)-2,2'-bipyridine (MTB) ligand that has been developed for lanthanide/actinide separation. A multimethod study of the complexation of MTB with trivalent actinide and lanthanide ions is presented. Single-crystal X-ray diffraction measurements reveal the formation of [Ce(MTB)2(NO3)3], [Pr(MTB)(NO3)3H2O], and [Ln(MTB)(NO3)3MeCN] (Ln = Nd, Sm, Eu, Gd). In addition, the complexation of Cm(III) with MTB in solution was studied by time-resolved laser fluorescence spectroscopy. The results show the formation of [Cm(MTB)1-3]3+ complexes, which occur in two different isomers. Quantum chemical calculations reveal an energy difference between these isomers of 12 kJ mol-1, clarifying the initial observations made by time-resolved laser fluorescence spectroscopy (TRLFS). Furthermore, quantum theory of atoms in molecules (QTAIM) analysis of the Cm(III) and Ln(III) complexes was performed, indicating a stronger covalent contribution in the Cm-N interaction compared to the respective Ln-N interaction. These findings align well with extraction data showing a preferred extraction of Am and Cm over lanthanides (e.g., max. SFAm/Eu = 8.3) at nitric acid concentrations <0.1 mol L-1 HNO3.

Trivalent lanthanide sorption onto illite in the presence of carbonate: A study combining thermodynamic sorption modeling, time-resolved laser fluorescence spectroscopy, and parallel factor analysis

Formation of aqueous actinide complexes with dissolved inorganic carbon (DIC) in groundwater decreases the sorption of actinides onto clay minerals in a geological disposal environment. Hence, the effect of DIC on actinide sorption must be evaluated quantitatively. In this study, batch sorption experiments using Eu(III) and Sm(III) as the chemical analogs of trivalent actinides were performed to assess their sorption behavior onto illite in the presence of DIC. In the studied pH region between 8.4 and 11, the sorption was significantly lower in the presence of DIC, with the largest effect being observed at pH 9–10. The effect increased with increasing DIC from 10 to 50 mM. A thermodynamic sorption model (TSM) was used to evaluate the results of batch sorption experiments. The experimental results can only be predicted when ternary-surface complexes with carbonate ions are considered. Moreover, information on the chemical forms of sorbed Eu on illite was obtained via time-resolved laser fluorescence spectroscopy (TRLFS) measurements. Parallel factor analysis of TRLFS data indicated the presence of two chemical species of Eu. These chemical species exhibited pH dependence, which is consistent with that of the surface species predicted using the TSM. In the presence of DIC, the dominant chemical species showed a long fluorescence lifetime and was inferred to coordinate with carbonate ions, supporting the validity of the TSM.

Uptake of Cm (III) and Eu (III) by C–S–H phases under saline conditions in presence of EDTA: A batch sorption and TRLFS study

Eu (III) and Cm (III) uptake by calcium silicate hydrate phases (C–S–H) was investigated in presence of EDTA in NaCl and CaCl2 solutions. Different experimental parameters, i.e., ionic strength (0.1 m ≤ I'm ≤ 5.05 m), ligand concentration (10−5 m ≤ [EDTA] ≤ 10−2 m), calcium-to-silicon ratio (0.6 ≤ C/S ≤ 1.3) and sorption time (7 d ≤ t ≤ 365 d) were varied in the frame of batch sorption experiments and Time Resolved Laser Fluorescence spectroscopy (TRLFS) measurements. No effect of EDTA on the retention of Eu(III)/Cm(III) by C–S–H phases in NaCl or CaCl2 systems was observed at ligand concentrations ≤ 10−3 M. In NaCl solutions with [EDTA] = 10−2 M and C/S < 1.3, low retention (log Rd = 2–3, with Rd in L∙kg−1) of Eu(III) was detected after 7 d of sorption time, while strong retention (log Rd = 5–6) was observed after 50 d. This behaviour was explained by the initial stabilization of Eu(III)/Cm(III) in the aqueous phase due to the formation of two aqueous Eu(III)/Cm(III)-(OH)n-EDTA complexes, followed by the slow incorporation of Eu(III)/Cm(III) into the C–S–H structure. In CaCl2 solutions for all C/S ratios, as well as in NaCl solutions for C/S ∼ 1.3, the presence of [EDTA] = 10−2 M led to a significant decrease of the uptake (log Rd = 2–3) after 7 and 50 d of contact time. This effect was explained by the formation of stable aqueous Ca–Eu(III)/Cm(III)-EDTA complexes triggered by the presence of moderate to high Ca concentrations. No evident effect caused by increased ionic strength conditions could be confirmed in our sorption experiments.Results obtained in batch sorption experiments are underpinned by TRLFS data, with the observation of three main aqueous species, tentatively defined as Cm(OH)(EDTA)2-, Cm(OH)x (EDTA)-(x+1) and Ca–Cm(III)-EDTA, as well as a fourth species corresponding to Cm(III) incorporated in the CaO-layer of the C–S–H phases. In spite of the thermodynamic stability of the CaEDTA2− complex, which reduces the concentration of free EDTA, the formation of ternary Ca–Eu(III)/Cm(III)-EDTA complexes is expected to result in a significant impact of EDTA on the uptake of An (III)/Ln (III) by cement at high ligand concentrations. The assumption that Ca outcompetes actinides for the complexation with EDTA in cementitious systems may need to be revisited under these conditions.

2,6-Bis(5-(tert-butyl)-1H-pyrazol-3-yl)pyridine: Effects of the Peripheral Aliphatic Side Chain on the Coordination of Actinides(III) and Lanthanides(III).

To improve our understanding of the interaction mechanism in trivalent lanthanide and actinide complexes, studies with structurally different hard and soft donor ligands are of great interest. For that reason, the coordination chemistry of An(III) and Ln(III) with 2,6-bis(5-(tert-butyl)-1H-pyrazol-3-yl)pyridine (C4-BPP) has been explored. Time-resolved laser fluorescence spectroscopy (TRLFS) studies have revealed the formation of [Cm(C4-BPP)n]3+ (n = 1-3) (log β1' = 7.2 ± 0.4, log β2' = 10.1 ± 0.5, and log β3' = 11.8 ± 0.6) and [Eu(C4-BPP)m]3+ (m = 1-2) (log β1' = 4.9 ± 0.2 and log β2' = 8.0 ± 0.4). The absence of the [Eu(C4-BPP)3]3+ complex shows a more favorable complexation of Cm(III) over that of Eu(III). Additionally, complementary NMR measurements have been conducted to examine the M(III)-N bond in Ln(III) and Am(III) C4-BPP complexes. 15N NMR data have revealed notable differences in the chemical shifts of the coordinating nitrogen atoms between the Am(III) and Ln(III) complexes. In the Am(III) complex, the coordinating nitrogen atoms have shown a shift by 260 ppm, indicating a higher fraction of covalent bonding in the Am(III)-N bond compared with the Ln(III)-N bond. This observation aligns excellently with the differences in the stability constants obtained from TRLFS studies.

Natural and synthetic plagioclases: Surface charge characterization and sorption of trivalent lanthanides (Eu) and actinides (Am, Cm)

The environmental fate of radiotoxic actinides may be controlled by their interactions with feldspars. Here, the sorption of trivalent minor actinides (Am, Cm) and their rare earth analog Eu onto synthetic pure Ca-feldspar (anorthite) and natural plagioclases of different Ca contents is investigated, covering ranges of [M3+] (52 nM–10 μM), solid-liquid ratios (1–3 g/L), pH (3–9), and ionic strengths (0.01–0.1 M NaCl) under both ambient and CO2-free conditions. As a first step to understand the uptake behavior of the heavy metals, the hitherto unknown surface charge and (de-)protonation reaction of Ca-feldspars is characterized. The zeta potential shows an unusual increase and charge reversal between pH 4 and 7 , which becomes more pronounced with increasing amounts of Ca in the crystal lattice and is likely connected to adsorption and/or surface precipitation of dissolved Al3+. Streaming potential measurements yield (de)protonation constants for anorthite surface sites of log K- = −6.94 ± 0.38 and log K+ = +6.84 ± 0.38. Batch sorption data shows strong immobilization of M3+ by plagioclases at mildly acidic and basic pH. Time-resolved laser fluorescence spectroscopy using Cm indicates the formation of an inner-sphere complex and its two hydrolyzed forms. The complex reactivity of dissolved Al3+ at the plagioclase-water interface severely complicated the development of a surface complexation model, emphasizing the need for additional research in this area. Our study highlights the importance of molecular-level studies to understand surface reactions and uncover unknown processes, which may have significant impact on the transport of (radiotoxic) contaminants in the geosphere.

U(VI) sorption on illite in the presence of carbonate studied by cryogenic time-resolved laser fluorescence spectroscopy and parallel factor analysis

Identification of sorption species of uranium (U) on clay minerals by spectroscopic techniques would consolidate the reliability of predicted sorption models. However, it is still challenging, especially, under complex environmental conditions, where the surface loading is low, and quenching elements for spectroscopic analyses hamper the application. In light of this, the sorption of U(VI) on illite at different pH and dissolved inorganic carbon (DIC) levels was investigated by using batch experiments, surface complexation modeling, and cryogenic time-resolved laser fluorescence spectroscopy (cryo-TRLFS) combined with parallel factor analysis (PARAFAC). The inhibiting effect of DIC on U(VI) sorption was revealed by the macroscopic batch experimental results. However, there was still sorption of U(VI) on illite even at a high DIC (19 mM), validating certain retention capacities of illitic clay minerals for U(VI) even from pore waters with high DIC. An updated 2-site protolysis non-electrostatic surface complexation and cation exchange model considering the formation of two uranyl-carbonate sorption complexes was able to reproduce the experimental results well. Based on the PARAFAC analysis on the cryo-TRLFS spectra, there was clear correspondence in the variation trend of the derived components with the sorption species from the modeling results, validating the formation of ternary uranyl-carbonate sorption species. The results imply that ternary uranyl-carbonate sorption species need particular consideration in the modeling of U(VI) sorption on clay minerals at high DIC levels. Identifying the sorption species adds more credibility to the predictive sorption model, which provides more confidence in the safety assessment of deep geological disposal. In addition, these results help better understand the fate of uranium during transport in geological disposal-related environments.

Thermodynamics of the Eu(III)-Mg-SO4-H2O and Eu(III)-Na-SO4-H2O systems. Part II: spectroscopy experiments, complexation and Pitzer/SIT models.

A time-resolved laser fluorescence spectroscopy (TRLFS) study was carried out to investigate the Eu(III)-SO4 complexation at room temperature over a wide range of Na2SO4 concentrations (0-2 mol kg-1). Spectroscopic observations confirm the step-wise formation of the aqueous complexes Eu(SO4)+, Eu(SO4)2- and Eu(SO4)33- over the investigated Na2SO4 concentrations. Combining TRLFS data obtained in this study and solubility data reported in Part I of this work for the Eu2(SO4)3-Na2SO4-H2O and Eu2(SO4)3-MgSO4-H2O systems, thermodynamic and activity models were derived based on the SIT and Pitzer formalisms. A combination of the geochemical calculation codes PhreeqC (SIT), PhreeSCALE (Pitzer) and the parameter estimation code PEST was used to determine the solubility products of Eu2(SO4)3·8H2O(cr) and Na2Eu2(SO4)4·2H2O(cr), stability constants of the Eu(III)-SO4 complexes (β0i), and the specific binary and ternary interaction parameters (εij, β(0)ij, β(1)ij, Cϕij, θik, Ψijk) for both activity models. The thermodynamic constants determined in this work are discussed with reference to values available in the literature.

Spectroscopic characterization of europium binding to a calmodulin-EF4 hand peptide-polymer conjugate.

The emergence of biological ligand as an alternative to chemical ligands enables a sustainable lanthanide extraction route. In this study, a peptide originating from the loop of domain 4 calmodulin (EF4) was synthesized and the interaction with europium ions was monitored using time resolved laser fluorescence spectroscopy (TRLFS). Despite being retracted from its full protein structure, the twelve amino acids of calmodulin-EF4 showed binding to europium. Europium-peptide complex formation was evident by an increase in decay time from 110 to 187 μs. The spectra of europium bound to peptide can be easily distinguished from the free europium ion as the 5D0 → 7F2 peak intensifies. When europium bound to the peptide-polymer conjugate, the decay time was further increased to 259 μs. This suggests that lanthanide binding can be enhanced by immobilizing the short peptide into a polymer matrix. The europium-peptide/conjugate bond was reversible, triggered by pH, promoting peptide reusability. Due to the fact that the study was conducted exclusively in water, it suggests minimal use of chemicals is possible while maintaining peptide affinity. This makes the calmodulin-EF4 peptide an ideal candidate as biological ligand. This study lays the groundwork for developing a peptide-based filter material for lanthanide separation.

Sampling volume assessment for wearable multimodal optical diagnostic device.

The process and results of numerical Monte Carlo simulation of optical radiation propagation in laser Doppler flowmetry (LDF) and fluorescence spectroscopy (FS) channels of a wearable diagnostic multimodal device are described in this paper. To achieve the goal, a multilayer skin model with different parameters of blood and melanin content and different distances between sources and radiation receivers was designed. The changes in the sampling (diagnostic) volume depending on the anatomical features of the biological tissues, as well as on the technical parameters of the device were shown. Depending on the scattering media optical properties and the source-detector configuration of the device, the diagnostic volume can range from 2 to 7 mm3 . The obtained results allow the formation of specialized medical and technical requirements for wearable multimodal devices implementing LDF and FS channels.

Red- and Near-Infrared-Excited Autofluorescence as a Marker for Acute Oxidative Stress in Skin Exposed to Cigarette Smoke Ex Vivo and In Vivo.

Air pollution is increasing worldwide and skin is exposed to high levels of pollution daily, causing oxidative stress and other negative consequences. The methods used to determine oxidative stress in the skin are invasive and non-invasive label-free in vivo methods, which are severely limited. Here, a non-invasive and label-free method to determine the effect of cigarette smoke (CS) exposure on skin ex vivo (porcine) and in vivo (human) was established. The method is based on the measurement of significant CS-exposure-induced enhancement in red- and near-infrared (NIR)-excited autofluorescence (AF) intensities in the skin. To understand the origin of red- and NIR-excited skin AF, the skin was exposed to several doses of CS in a smoking chamber. UVA irradiation was used as a positive control of oxidative stress in the skin. The skin was measured with confocal Raman microspectroscopy before CS exposure, immediately after CS exposure, and after skin cleaning. CS exposure significantly increased the intensity of red- and NIR-excited skin AF in a dose-dependent manner in the epidermis, as confirmed by laser scanning microscopy AF imaging and fluorescence spectroscopy measurements. UVA irradiation enhanced the intensity of AF, but to a lower extent than CS exposure. We concluded that the increase in red- and NIR-excited AF intensities of the skin after CS exposure could clearly be related to the induction of oxidative stress in skin, where skin surface lipids are mainly oxidized.

Wearable Devices for Multimodal Optical Diagnostics of Microcirculatory-Tissue Systems: Application Experience in the Clinic and Space

This work demonstrates some results of the successful experience of using wearable devices for multimodal optical diagnostics of microcirculatory-tissue systems both in clinical practice and in the conditions of a Space experiment. The multimodal approach based on simultaneously applying a minimum of 2 optical diagnostic methods, for example, laser Doppler flowmetry and fluorescence spectroscopy, allows analysing of blood flow and metabolic processes in biological tissue more systematically. Combining several wearable devices into a distributed diagnostic system allows placing them simultaneously on symmetrical parts of the body (such as opposite limbs) thus providing a possibility to study the symmetry of the measured signals. The obtained data on the state of the microcirculatory-tissue systems of the human body recorded with wearable multimodal devices make it possible to assess the relationship and dynamics of oxygen delivery and utilization by tissues more comprehensively and reliably in a variety of diagnostic tasks.

The Effect of Photobiostimulation by Light Waves in the Blue Range of the Spectrum on Microcirculation Parameters and the Activity of Oxidative Homeostasis Enzymes in the Skin

The study employs laser doppler flowmetry and laser fluorescence spectroscopy to reveal the changes in microcirculation and activity of coenzymes of oxidative metabolism in the finger skin under the influence of photobiostimulation by monochrome incoherent low-intensity electromagnetic radiation with a wavelength of 470 nm. Photobiostimulation with light waves in the blue range has contributed to an increase in hemomicrocirculation during and 15 min after the termination of exposure, while the indicator lymph outflow, on the contrary, decreased during the irradiation period and recovered after its termination. The dynamics of changes within the parameters of blood microcirculation, the lymph flow in microvessels and the indicators of oxidative metabolism showed that the skin microcirculation system is an important acceptor of the photobiostimulating effect of light in the blue range of the spectrum. Photobiostimulation triggers the mechanism of activation of hemomicrocirculation by reducing myogenic vasomotion, thereby increasing the conductivity of cardiogenic biorhythm in the vessels of the microcirculatory bed. With an increase in the level of hemomicrocirculation, photobiostimulation is directly associated with the activation of tissue oxidative metabolism.

Uranium(VI) Sorption onto Hardened Cement Paste under High Saline and Alkaline Conditions

Evaluation of the mobility behaviour of radionuclides under highly saline and alkaline conditions is a major concern for the performance assessment of radioactive waste disposal. The aim of this study was to determine the effect of up to 2.8 mol/kgsolution content of NaNO3, on the solubility and the retention of U(VI) at 22 °C onto a hardened cement paste (HCP) prepared from ordinary Portland cement (CEM I). To avoid the interference of the high salt concentration and ionic strength, and because of the expected low solubility of uranium under such alkaline conditions, time-resolved laser fluorescence spectroscopy (TRLFS) was selected to accurately measure U(VI) concentration in solution using the standard addition method in 85% H3PO4. This allows both limiting the dilution and matrix effects and determining the resulting [U(VI)] in solution with acceptable precision for the distribution factor (Rd) in both sorption and desorption experiments. The operational solubility limit measured at high ionic strength lowered by a factor of three compared to the reference cementitious condition, and its Rd values decreased by a factor ca. four. The sorption of U(VI) appears to be reversible under these conditions.

Laser fluorescence spectroscopy in surgical treatment of intramedullary tumors: experience of the Burdenko Neurosurgery Center

To analyze efficacy of fluorescence navigation technique and laser fluorescence spectroscopy in surgical treatment of various spinal cord tumors. There were more than 1000 patients with intramedullary spinal cord tumors between 2001 and 2022. Intraoperative fluorescence navigation with laser spectroscopy was used in 47 cases. All patients underwent examination before and after surgery. We analyzed somatic, neurological and functional status (McCormick scale). MRI of the spinal cord and intraoperative fluorescence spectroscopy (OPMI Pentero 900 microscope with a fluorescent module, Carl Zeiss, Germany) were performed. To induce visible fluorescence, we used 5-ALA-Alasens (NIOPIK, Russia). Laser spectroscopy was carried out on a LESA-01-BIOSPEC analyzer (Biospec JSC, Russia). Morphological analysis of intramedullary spinal cord tumors was carried out in the laboratory of neuromorphology of the Burdenko Neurosurgery Center. In our sample, fluorescence navigation and laser fluorescence spectroscopy were used only in surgical treatment of intramedullary tumors. Laser fluorescence spectroscopy was valuable to identify fragments of intramedullary ependymoma and astrocytoma in 86% of cases, visual fluorescence - only in 81% of cases. Advisability of this technique for low-grade astrocytomas is unclear and requires further study. Visual fluorescence combined with laser spectroscopy is a promising method for intraoperative imaging of tumor remnants. This approach can improve safety, quality and results of surgical treatment.

The place of laser fluorescence spectroscopy, doppler flowmetry and ultrasound in the diagnosis and assessment of treatment efficacy for plaque scleroderma

According to modern ideas, a reasonable choice of an effective method of treating plaque scleroderma is based on the diagnosis of the pathological process prevailing in the tissues (inflammation-sclerosis). Therefore, an urgent problem of a personalized approach to dermatosis therapy is the possibility of an objective assessment of the prevailing process using non-invasive diagnostic methods. The article presents a clinical case of widespread plaque scleroderma in a 66-year-old patient, demonstrating the possibility of using laser fluorescence spectroscopy and laser Doppler flowmetry to determine the degree of activity of the focus and determine the leading pathological process.&#x0D; We selected three pathological skin foci localized in the abdomen and characterizing three clinical stages of the disease (inflammation, induration, sclerosis). The analysis of fluorescence and laser Doppler flowmetry data showed that in areas clinically defined as inflammation, there is an increase in the average values of the indices of tissue content of porphyrins, lipofuscin and microcirculation index compared with intact skin, while the intensity of collagen fluorescence does not differ significantly. In the induration zone, along with an increase in the fluorescence indices of lipofuscin and porphyrins, there is an increase in the average values of collagen fluorescence indices at effective registration waves. The data obtained by us indicate an active inflammatory process in these foci and the process of fibrosis in the induration zone. In the sclerosis zone, there is an increase in the average values of collagen fluorescence indices compared with intact skin, and the fluorescence of optical markers of inflammation (lipofuscin and porphyrins) do not differ significantly in comparison with the control intact skin. When analyzing the fluorescence spectra and laser Doppler flowmetry data after treatment, we found that in the zones of induration and inflammation, the average values of the fluorescence indices of porphyrins, lipofuscin, collagen and microcirculation index are reduced relative to the initial values (before treatment), but remain higher in comparison with intact skin. The data obtained may indicate that active inflammation in these foci persists at the time of the study. In the study of the focus of sclerosis, the obtained autofluorescence and microcirculation data in dynamics do not differ significantly from the initial values. The data for laser Doppler flowmetry and laser fluorescence spectroscopy are consistent with ultrasound examination of the skin.&#x0D; In our study, the potential possibility of using laser fluorescence spectroscopy and laser Doppler flowmetry methods to establish the degree of activity of the focus, determine the leading pathological process, as well as to evaluate the effectiveness of therapy was demonstrated for the first time.

Thermodynamic Study of Am(III)-Isosaccharinate Complexation at Various Temperatures Implicating a Stepwise Reduction in Binding Denticity.

Isosaccharinic acid, a major final product of cellulose degradation under highly alkaline cement porewater conditions, is known to increase the mobility of actinides via strong complex formation. In this study, the formation of Am(III) complexes with α-d-isosaccharinate (ISA) was studied in terms of thermodynamics and coordination structures by combining spectrophotometry, time-resolved laser fluorescence spectroscopy (TRLFS), and density functional theory (DFT) calculations. The formation constants of the Am(III)-ISA complexes were determined by absorption spectroscopy at temperatures in the range of 15-70 °C. The measured reaction enthalpy and entropy changes indicate that the formation of a 1:1 Am(III)-ISA complex is driven by an increase in entropy. By contrast, the 1:2 complex formation is exothermic with a much less increase in entropy. DFT calculations predict that C2- and C4-hydroxyl groups, along with the carboxyl group, participate in the tridentate chelate binding of the primary ISA. The thermodynamic, TRLFS, and DFT results collectively suggest the tridentate binding of the primary ISA to Am(III) via a carboxylate and C2- and C4-hydroxyl groups in the protonated state and reduced dentate binding of the secondary ISA, such as bidentate binding, forming a four-membered ring structure via the carboxylate group.

Insights into the Complexation Mechanism of a Promising Lipophilic PyTri Ligand for Actinide Partitioning from Spent Nuclear Fuel.

The challenging issue of spent nuclear fuel (SNF) management is being tackled by developing advanced technologies that point to reduce environmental footprint, long-term radiotoxicity, volumes and residual heat of the final waste, and to increase the proliferation resistance. The advanced recycling strategy provides several promising processes for a safer reprocessing of SNF. Advanced hydrometallurgical processes can extract minor actinides directly from Plutonium and Uranium Reduction Extraction raffinate by using selective hydrophilic and lipophilic ligands. This research is focused on a recently developed N-heterocyclic selective lipophilic ligand for actinides separation to be exploited in advanced Selective ActiNide EXtraction (SANEX)-like processes: 2,6-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)pyridine (PyTri-Ethyl-Hexyl-PTEH). The formation and stability of metal-ligand complexes have been investigated by different techniques. Preliminary studies carried out by electrospray ionization mass spectrometry (ESI-MS) analysis enabled to qualitatively explore the PTEH complexes with La(III) and Eu(III) ions as representatives of lanthanides. Time-resolved laser fluorescence spectroscopy (TRLFS) experiments have been carried out to determine the ligand stability constants with Cm(III) and Eu(III) and to better investigate the ligand complexes involved in the extraction process. The contribution of a 1:3 M/L complex, barely identified by ESI-MS analyses, was confirmed as the dominant species by TRLFS experiments. To shed light on ligand selectivity toward actinides over lanthanides, NMR investigations have been performed on PTEH complexes with Lu(III) and Am(III) ions, thereby showing significant differences in chemical shifts of the coordinating nitrogen atoms providing proof of a different bond nature between actinides and lanthanides. These scientific achievements encourage consideration of this PyTri ligand for a potential large-scale implementation.

Complexation and Extraction Studies of Trivalent Actinides and Lanthanides with Water-Soluble and CHON-Compatible Ligands for the Selective Extraction of Americium.

Novel hydrophilic ligands to selectively separate Am(III) are synthesized: 3,3'-([2,2'-bipyridine]-6,6'-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PrOH-BPTD) and 3,3'-([2,2'-bipyridine]-6,6'-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(ethan-1-ol) (EtOH-BPTD). The complexation of An(III) and Ln(III) with PrOH- and EtOH-BPTD is studied by time-resolved laser fluorescence spectroscopy. [ML2]3+ is found for both Cm(III) and Eu(III), while [ML]3+ is only formed with Cm(III). Stability constants show a preferential coordination of Cm(III) over Eu(III) with PrOH-BPTD being the stronger ligand. The distribution of Am(III), Cm(III), and Ln(III) between an organic phase containing the extracting agent N,N,N',N'-tetra-n-octyl-3-oxapentanediamide (TODGA) and aqueous phases containing PrOH-BPTD is studied as a function of time and temperature as well as the TODGA, BPTD, and HNO3 concentrations. A system composed of 0.2 mol/L TODGA and 0.04 mol/L PrOH-BPTD in 0.33-0.39 mol/L HNO3 allows for selective Am(III) back-extraction into the aqueous phase while keeping Cm(III) and Ln(III) in the organic phase, marking PrOH-BPTD as an excellent complexant for an optimized AmSel process (Am(III) selective extraction).