Solid-State and Solution-State Coordination Chemistry of Lanthanide(III) Complexes with α-Hydroxyisobutyric Acid

Thorium Complexation with Aliphatic and Aromatic Hydroxycarboxylates: A Combined Experimental and Theoretical Study

Hydroxycarboxylic acids, viz., α-hydroxyisobutyric acid (HIBA) and mandelic acid (MA), have been widely employed as eluents for inner transition metal separation studies. Both extractants have identical functional groups (OH and COOH) with different side-chains. Despite their similarities in binding motifs, they show different retention behaviors for thorium and uranium in liquid chromatography. To understand the mechanism behind the trend, a detailed study on the aqueous phase interaction of thorium with both extractants is carried out by speciation, spectroscopy, and density functional theory-based calculations. Potentiometric titration experiments are carried out to reveal the stability and species formed. Electrospray ionization mass spectrometry is performed to identify the formation of different species by Th with both HIBA and MA. It is seen that for Th-HIBA and Th-MA, the dominating species are ML3 and ML4, respectively. A similar pattern observed in potentiometric speciation analysis supports the tendency of Th to form higher stoichiometric species with MA than with HIBA. The difference in the dominating species thus helps in explaining the reversal in the retention behavior of uranium and thorium in the reverse-phase liquid chromatographic separation. The results obtained are corroborated with extended X-ray absorption fine structure spectroscopic measurements and density functional theory (DFT) calculations.

Enhanced Tb(III) fluorescence on gelatin-coated silver nanoparticles in dopamine detection

A composite fluorescent nanoprobe based on metal enhanced fluorescence (MEF) effect of gelatin-coated silver nanoparticles (AgNPs@gel) was developed for selective and sensitive detection of dopamine (DA). The characteristic fluorescence of Tb(III) was using as the detection signal and AgNPs@gel served as substrates of the MEF. Gelatin with rich amine and carboxylic groups was used not only as a co-ligand of Tb(III) complex, but also as a bridging substance and a spacing material for improving the MEF of AgNPs@gel on the intrinsic luminescent intensity of Tb(III). Under the optimal conditions, the increment of the fluorescence intensity (measured at 307/544 nm as excitation/emission wavelength) of the system increased linearly with the concentration of DA in the range of 0.80-100 nM (R² = 0.9937) and 100-1000 nM (R² = 0.9978). The fluorescent probe greatly improved Tb(III) luminescence, which paved the way for sensitive detection with a low detection limit of 0.54 nM. It also showed good selectivity among other neurotransmitters. This work was successfully applied to the determination of DA in human serum samples with recoveries ranging from 99.8 to 102.2%. We believe that the Tb(III)-DA-AgNPs@gel composite fluorescent probe can be developed as a new approach for DA detection.

The first amorphous and crystalline yttrium lactate: synthesis and structural features

The synthesis and crystal structure of the first molecular yttrium lactate complex, Y(Lac)₃(H₂O)₂, is reported, where the coordination sphere of yttrium is saturated with lactate ligands and water molecules, resulting in a neutral moiety. In Y(Lac)₃(H₂O)₂, hydrogen bonding between α-hydroxy groups and water molecules allows for the formation of 2D layers. A subtle variation in synthetic conditions, i.e. a slight increase in pH (5.5 instead of 4.5) promoted the formation of a semi-amorphous fibrous material with a presumed chemical composition of Y₄(OH)₅(C₃H₅O₃)₇·6H₂O. The flattened fibres in this material are responsible for its good flexibility and foldability.

The synthesis and crystal structure of the first molecular yttrium lactate complex, Y(Lac)₃(H₂O)₂, is reported, where the coordination sphere of yttrium is saturated with lactate ligands and water molecules, resulting in a neutral moiety.

Preconcentration mechanism of trivalent lanthanum on eQCM electrodes in the presence of α-hydroxy isobutyric acid

Electroprecipitation can be used to preconcentrate lanthanum on carbon electrode surfaces. The use of complexing ligands is expected to improve the electroprecipitation of lanthanum by protecting La ions in solution from the alkaline region near the electrode surface. However, the electroprecipitation mechanism of La in the presence of a complexing ligand is not known. The goal of this work is to 1) determine the effect of the complexing ligand, α-hydroxy isobutyric acid (HIBA), on the electroprecipitation of La onto the gold electrodes, and 2) identify the changes in the mechanism of accumulation when preconcentrating in the presence of HIBA. We used an electrochemical quartz crystal microbalance (eQCM) and needle type pH microelectrodes to determine pH near the electrode surface in combination with cyclic voltammetry to understand the electroprecipitation mechanism. We used the bi-dentate ligand HIBA as a ligand and found that lanthanum electroprecipitation is hindered in the presence of HIBA. The presence of HIBA also delayed the onset of film formation during a cyclic voltammetric experiment by ~100 mV compared to experiments performed without HIBA. The shift in onset potential is attributed to the buffering action of HIBA (pK_a = 3.7) since the shift is not present in subsequent scans. The precipitated film was characterized by scanning electron microscopy, X-ray photoelectron spectrometry, and Auger nanoprobe spectrometry. While we found that La(OH)₃ was the predominant chemical state of the film on electrodes in the absence of HIBA, La₂O₃ was found for films created in the presence of HIBA. Our finding demonstrates that La(OH)₃ can be electrodeposited at room temperature.

A specific fluorescent nanoprobe for dopamine based on the synergistic action of citrate and gold nanoparticles on Tb(III) luminescence

A nanoprobe was developed for the fluorometric determination of the neurotransmitter dopamine (DA). It is based on the synergistic enhancement action of citrate and gold nanoparticles (AuNPs) on the luminescence of Tb(III). AuNPs serve as substrates of surface enhanced fluorescence (SEF). Citrate, in turn, acts as a spacer for the SEF effect, a co-ligand of Tb(III) complex, and a recognizing component for DA. The synergistic action of citrate and AuNPs significantly increases the intrinsic green fluorescence of Tb(III) (best measured at excitation/emission peaks of 300/547 nm). Under the optimum conditions, the fluorescence intensity increases linearly in the 3.0 to 200 nM DA concentration ranging (with an R² value of 0.9959), and the limit of detection (at S/N = 3) is 0.84 nM. The nanoprobe shows good selectivity for DA among other interfering neurotransmitters, some amino acids and ions. The method was applied to the detection of DA in human serum samples where it gave recoveries ranging from 100.5 to 102.9%. Graphical abstract Schematic of a Tb(III) composite fluorescent nanoprobe for the sensitive determination of dopamine (DA). Citrate and gold nanoparticles (AuNPs) synergistically enhance the fluorescence of Tb(III)-DA.

Complications in complexation kinetics for lanthanides with DTPA using dye probe molecules in aqueous solution

Dye probe molecules were used to investigate lanthanide complexation and verify the viability of the ligand displacement methodology for measuring DTPA complexation rate constants. Results showed that dye probes underestimate the rate constants.

A highly selective and sensitive fluorescent nanosensor for dopamine based on formate bridged Tb(iii) complex and silver nanoparticles

The proposed fluorescent nanosensor can distinguish DA from EP.

Americium(iii) and europium(iii) complex formation with lactate at elevated temperatures studied by spectroscopy and quantum chemical calculations

Spectroscopic techniques (NMR and ATR FT-IR) in combination with calculations (DFT) show that the hydroxyl group of the lactate is deprotonated under complex formation with Eu(iii).

Syntheses, structures and properties of 5-azotetrazolyl salicylic acid and its dilanthanide complexes

Two hydrated 5-azotetrazolyl salicylic acids (H₃ASA) and five H₃ASA based dinuclear Ln³⁺ complexes have been synthesized and characterized by single crystal X-ray diffraction analysis.