Uranyl(VI) Interaction with 2-Phosphonobutane-1,2,4-Tricarboxylic Acid (PBTC): A Spectroscopic and Computational Study over a Wide pH Range.

To investigate the extraction of uranium(VI) in HCl media by Aliquat® 336 in 1:99 (v:v) 1-decanol:n-dodecane mixture, our objective is to identify the complexe(s) in the organic phase by time-resolved laser-induced luminescence spectroscopy (TRLS). The extraction mechanism is supposed to involve the formation of [ U O 2 C l 4 2 − ⋅ ( R 4 N + ) 2 ] $[U{O_2}Cl_4^{2 - } \cdot {({R_4}{N^ + })_2}]$ in the organic phase. The occurrence of such a species leads to the presence of the UO 2 Cl 4 2 − ${\rm{U}}{{\rm{O}}_2}{\rm{Cl}}_4^{2 - }$ species in the organic solution, which luminescence shows particular features. The luminescence spectra and decay time evolutions are obtained in the organic phase as a function of HCl concentration in the aqueous phase (0.5–6 M). The extraction of UO 2 Cl 4 2 − ${\rm{U}}{{\rm{O}}_2}{\rm{Cl}}_4^{2 - }$ is confirmed by the particular spectrum of uranium(VI) in the organic phase, and the typical splitting of the luminescence bands, due to the crystal field effect, is clearly evidenced. The stoichiometry is verified using luminescence intensity variation as a function of the activity of Cl−, and extraction constants are calculated both using the specific interaction theory and Pitzer model. A decomposition of the spectrum of the extracted complex in the organic phase is also proposed. The decay time variation as a function of temperature allows estimating the activation energy of the luminescence process of the extracted complex.

U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions – Spectroscopic investigations of retention mechanisms

The electroendosmotic behavior of IsoGel and Agarose IEF was determined in a series of various wide and narrow pH range electrofocusing experiments in which glucose served as marker substance.In IsoGel its liquid flow caused towards the anode in all wide and narrow pH range electrofocusing. The strength of segmetal liquid flow was proportional to voltage distribution across the gel. The pH gradients obtained in IsoGel when using same wide pH range ampholyte has markedly low pH values than that of Agerose IEF at acidic region.In Agarose IEF its liquid fow behavior differed in wide and narrow pH range electrofocusing. In the case of wide pH range electrofocusing its liquid flow reversed towards the anode at pH 5.5∼6 region in the foucsed gels. The other hand, in narrow pH range electrofocusing the direction of liquid flow was differed with pH range of ampholyte. In higher pH range than Amopholine 5-7 its liquid flow coused towards the cathode and in lower pH range than Ampholine 4-6 reversed towards the anode. The direction and the streght of liquid flow in narrow pH range Agarose IEF depends on the pH distribution in the focused gel. The pH curves obtained in Agarose IEF when using same narrow pH range Ampholyte were slightly higher than that of IsoGel.

Complexation by small organic ligands controls the bioavailability of contaminants and influences their mobility in the geosphere. We have studied the interactions of Cm3+, as a representative of the trivalent actinides, and Eu3+, as an inactive homologue, with glucuronic acid (GlcA) a simple sugar acid. Time-resolved laser-induced luminescence spectroscopy (TRLFS) shows that complexation at pH 5.0 occurs only at high ligand to metal ratios in the form of 1:1 complexes with standard formation constants log β0 = 1.84 ± 0.22 for Eu3+ and log β0 = 2.39 ± 0.19 for Cm3+. A combination of NMR, QMMM, and TRLFS reveals the structure of the complex to be a half-sandwich structure wherein the ligand binds through its carboxylic group, the ring oxygen, and a hydroxyl group in addition to five to six water molecules. Surprisingly, Y3+, which was used as a diamagnetic reference in NMR, prefers a different coordination geometry with bonding through at least two hydroxyl groups on the opposite side of a distorted GlcA molecule. QMMM simulations indicate that the differences in stability among Cm, Eu, and Y are related to ring strain induced by smaller cations. At higher pH a stronger complex was detected, most likely due to deprotonation of a coordinating OH group.

Deficiency of sulfur (S) is becoming widespread in the rainfed systems of India, and there is increasing need for diagnosing the deficiency. Calcium chloride and Ca phosphate are commonly used for extracting available S in soils. Because of cost and the ease of availability locally, we prefer using Ca chloride as an extractant over Ca phosphate, for extracting available S. However, there is paucity of data on the comparative evaluation of the two extractants to extract available S, especially in soils having a wide range in natural pH (from acidic to alkaline range). It is recognized that soil pH plays a dominant role in the adsorption–desorption and extractability of sulfate‐S in soils. We compared the extraction of S by Ca chloride and Ca phosphate in 86 Indian soils having a wide range in pH (4.5 to 10.6). Sulfur in the extracts was determined by ICP‐AES. Considering all the 86 soil samples tested, there was an excellent agreement between the values of extractable S determined by using the two extractants (r = 0.96, p < 0.001). However, the correlation coefficient (r) between the values of extractable S by the two reagents, although highly significant, varied among the groups of soil samples according to the range in soil pH. The highest correlation coefficient (r = 0.99, p < 0.0001, n = 17) was found for soils with pH in the alkaline range (8.5–10.6), and the lowest correlation coefficient (r = 0.71, p < 0.0001, n = 58) was obtained with a set of soil samples with pH in the acidic range (4.5–6.5). For soil samples having pH in the near‐neutral range (6.7–7.3), an excellent agreement was observed (r = 0.93, p < 0.0001, n =11) between the extractable‐S values obtained by the two extractants. While Ca phosphate extracted higher amount of S compared to Ca chloride in soil samples with pH in the acidic range, the two extractants were equally effective for soil samples with pH in the neutral or alkaline range. Our results suggest that for most of the soils in the semiarid tropical regions, which have pH in the neutral to alkaline range, Ca chloride can replace Ca phosphate as an extractant for removing available S in such soils.

The potential of gluconate, a common cement additive, to mobilize lanthanides (used as analogues of actinides) from cement is investigated. For this purpose, complex formation of trivalent lanthanides, Ln(III), (Ln: La, Sm, Eu, Gd, Lu) with gluconate (GLU) was studied applying time-resolved laser-induced luminescence spectroscopy (TRLFS) in combination with parallel factor analysis (PARAFAC), capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS), nuclear magnetic resonance (NMR) spectroscopy, and density functional (DF) calculations. Up to circumneutral conditions, binary complexes form with Ln(III):GLU stoichiometric ratios of 1:1-1:4 depending only on the Ln:GLU ratio, regardless of the concentration regime (micromolar to millimolar). Coordination facilitates via the carboxyl group (C1) and the adjacent hydroxyl group (at C2) forming a five-membered ring chelation motif, with a probable participation of the C3 hydroxyl group. Beyond circumneutral pH, with the exact onset depending on the specific lanthanide, a fundamental change in speciation takes place. Speciation then becomes more complex upon coexistence and interconversion of several (isomeric) complexes concluded to involve one or more deprotonated GLU hydroxyl groups not necessarily participating in coordination.

The formation constants of CaUO2(CO3)32- and Ca2UO2(CO3)3(aq) were determined in NaCl medium at ionic strengths between 0.1 and 1 mol kgw-1 using time-resolved laser-induced luminescence spectroscopy (TRLS). Spectroluminescence titration of UO2(CO3)34- complex by Ca2+ were conducted at atmospheric CO2(g) and varying pH values in order to eliminate the eventual precipitation of both schoepite (UO3 : 2H2O) and calcite (CaCO3) in aqueous solutions. To identify the stoichiometry of calcium, the slope analyses corrected by the Ringböm coefficient for UO2(CO3)34- relative to pH and CO2(g)-instead of typical expression relative to UO22+ and CO32--was applied in this work. Satisfactory linear fits assessed the conditional stepwise formation constants in the range of ionic strength employed in this work, the values of which are in good agreement with literature data at comparable ionic strengths. Extrapolations to infinite dilution were realized in the framework of the specific ion interaction theory (SIT), also providing the evaluation of the specific ion interaction coefficients. The cumulative stability constants at infinite dilution was determined to be log10 β°(CaUO2(CO3)32-) = 27.20 ± 0.04 and log10 β°(Ca2UO2(CO3)3(aq)) = 30.49 ± 0.05, which are in good agreement with extrapolation proposed elsewhere in literature using a different extrapolation framework. The specific ion interaction coefficients were found to be ε(CaUO2(CO3)32-,Na+) = (0.29 ± 0.11) and ε(Ca2UO2(CO3)3(aq),NaCl) = (0.66 ± 0.12) kgw mol-1. Integration of alkali metals into the ternary species may explain these positive and relatively large interaction coefficients. Implications on the speciation of uranium in clay groundwaters, representative of radioactive waste repositories, and in seawater are discussed.

A porous layer open-tubular capillary column with immobilized pH gradient (PLOT-IPG) for isoelectric focusing of amino acids and proteins

The stability constants of ternary calcium uranyl tricarbonate complexes, CaUO2(CO3)32- and Ca2UO2(CO3)3(aq), were determined in NaClO4 medium at various ionic strengths using time-resolved laser-induced luminescence spectroscopy (TRLS) - also known as time-resolved laser-induced fluorescence spectroscopy (TRLFS). As in a previous study, the potential precipitation of schoepite (UO3·2H2O) and calcite (CaCO3) was avoided via titration of the triscarbonatouranyl complex with Ca2+ at varying pH values. The Ringböm coefficients relative to UO2(CO3)34- were individually evaluated under test sample conditions. Steadily enhanced luminescence intensity and increased decay-times were representative of complexation processes. The stoichiometry of calcium was quantified by slope analysis, and its measured intensity was corrected by using the corresponding Ringböm coefficient. The conditional formation constants, i.e. log10 Kn.1.3, were then assessed after rounding off the slope values to their nearest integers. Cumulative formation constants at infinite dilution log10 β°n.1.3, and specific ion interaction parameters ε were determined based on the experimental origin and slope values, respectively, over the range of 0.1-2.46 mol kgw-1 NaClO4 using the specific ion interaction theory (SIT) approach. The cumulative stability constants are log10 β°(CaUO2(CO3)32-) = 27.26 ± 0.04 and log10 β°(Ca2UO2(CO3)3(aq)) = 30.53 ± 0.06. The specific ion interaction coefficients are estimated to be ε(CaUO2(CO3)32-,Na+) = (0.02 ± 0.04) kgw mol-1 and ε(Ca2UO2(CO3)3(aq),NaClO4) = (0.18 ± 0.07) kgw mol-1. These latter values are different from the ones that were previously obtained in NaCl, and underlying causes are discussed from different aspects. This work provides valuable information to address the interaction effects between Ca-UO2-CO3 species and 1 : 1 type electrolytes. It is suggested that the affinity of the cation in a background electrolyte with CanUO2(CO3)3(4-2n)- (n = {1;2}) has to be taken into consideration at high ionic strengths, especially for globally non-charged species.

Process analytical technologies in food industry - challenges and benefits: A status report and recommendations.

BACKGROUNDImmobilization of more than one peroxidase on the same support is an ideal technology for application because such a multi‐enzyme catalytic system may show high activity over a very wide optimal range of pH, temperature and H2O2 concentration. In this work, chloroperoxidase (CPO) and horseradish peroxidase (HRP) were co‐immobilized on ZnO nanowires/macroporous SiO2 composite support through an in situ cross‐linking method. An anionic bi‐epoxy cross‐linker was used by adsorption on the surface of ZnO nanowires before cross‐linking.RESULTSThe cross‐linking was carried out under suitable conditions: pH 6.5, reaction temperature 15°C and reaction time 15 h. Using a 1/1 mixture of CPO and HRP resulted in a co‐immobilized enzyme with loading 79.6 mgCPO g‐1support and 52.8 mgHRP g‐1support, and total specific activity up to 15.7 U per mgsupport. The co‐immobilized enzyme also showed good stability after 60 days of storage, and excellent reusability over 20 repeat uses.CONCLUSIONSFor the decolorization of azo dyes the co‐immobilized CPO (60%)/HRP (40%) exhibited high catalytic activity over very wide ranges of pH, temperature and H2O2 concentration. Using this robust biocatalyst, complete decolorizations of azo dyes have been realized within 3 h of reaction. © 2017 Society of Chemical Industry

The stability constants of complexes formed between iron (III) and fulvic acid extracted from organic manures and wastes such as urban domestic sewage sludge, farmyard manure, poultry manure and sulfitation pressmud were investigated by the potentiometric titration method in an ionic medium of 0.1 M KNO3 at 25±1 °C. A modification of the Katchalsky's model was employed for the estimation of stability constants. The displacement of the titration curves due to presence of Fe3+ in FA solutions formed the basis of calculations. The weak acidic property of fulvic acids due to carboxyl groups resulted in buffering over a wide range of pH; fulvic acids were completely neutralized in the pH range of 7.00–8.85. Apparent dissociation constants (pKAPP) of weakly acidic carboxyl groups were a direct function of degree of dissociation (αL) in the mid-range of titration curves but were non-linear at high and low αL values. The stability constants for formation of Fe–FA complexes (log βFe) calculated from the titration data were in the range of 5.64–7.55, depending upon αL and electrostatic properties of fulvic acids. The relatively high stability constants of Fe–FA complexes in comparison to those with other competing cations suggest that the Fe–FA complexes are relatively stable in a soil environment.

Characterization and solubility measurement of synthetic uranophane and sklodowskite under oxic groundwater conditions

Luminescence lifetime of lanthanide(III) ions in aqueous solution containing azide ion

Determination of Formation Constants and Specific Ion Interaction Coefficients for Mg/Ca-UO₂-CO₃ Complexes in NaCl Solution by Time-Resolved Laser-Induced Luminescence Spectroscopy.