Rapid detection strategies for the ultra-level chemosensing of uranyl ions.

A simple and reliable colorimetric probe N,N'-bis-(4-diethylamino-2-hydroxybenzylidene)-1,10-phenanthroline-2,9-carbohydrazide (L) has been synthesised by reacting 4-(diethylamino)salicylaldehyde with 1,10-phenanthroline-2,9-dicarbohydrazide. The sensing ability of L was studied by its interactions with various f-block metal ions and other selected metal ions from s- and d-block by colorimetry, UV-visible spectrophotometry, and smartphone integrated red-green-blue (RGB) model in DMSO : H2O (7 : 3, v/v). The pale-yellow colour of L turns to wine-red upon interaction with uranyl ions (UO22+) and yellow-orange in the presence of Th4+, Zr4+, Fe3+, and Lu3+ ions. Other tested metal ions did not show any colour change of L. This color change offered a simple, quick, and consistent method for the selective and sensitive visual detection of trace levels of UO22+ ions without any need for sophisticated instruments. Sensor L exhibits two absorption bands at 358 and 389 nm due to ligand-to-ligand charge transfer (LLCT). Upon interaction of L with UO22+ and Th4+ ions, absorption bands are exhibited at 480 nm and 422 nm, respectively, due to ligand-to-metal charge transfer (LMCT). The UV-vis spectral studies indicated the formation of a 1 : 2 ligand-to-metal complex between L and UO22+ with an estimated association constant of 1.0 × 104 M-2. Using L, the concentration of UO22+ can be detected as low as 73 nM and 150 nM by spectrophotometry and RGB methods, respectively, without any interference from other tested ions with an RSD < 5% (n = 3). The binding mechanism was studied by 1H NMR titration, ESI mass, and FT-IR spectral analysis and was well supported by theoretical results. Overall, sensor L demonstrates promising analytical applicability for the detection of UO22+ ions in a semi-aqueous medium.

Post synthetically modified IRMOF-3 for efficient recovery and selective sensing of U(vi) from aqueous medium.

A simple and efficient route to develop various novel functionalized MOF materials for rapid and excellent recovery of U(vi) from aqueous medium, along with selective sensing has been demonstrated in the present study. In this connection, a set of four distinct post synthetically modified (PSM) iso-reticular metal organic frameworks were synthesized from IRMOF-3 namely, IRMOF-PC (2-pyridine carboxaldehyde), IRMOF-GA (glutaric anhydride), IRMOF-SMA (sulfamic acid), and IRMOF-DPC (diphenylphosphonic chloride) for the recovery and sensing of U(vi) from aqueous medium. The MOFs were characterized by Fourier transform infrared spectroscopy (FTIR), powder XRD, BET surface area analysis, thermogravimetric analysis (TGA), NMR (13C, 1H and 31P), Scanning Electron Microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Among all MOFs, post synthetically modified IRMOF-SMA showed enhanced thermal stability of about 420 °C. The MOFs were investigated for U(vi) sorption studies using a batch technique. All the MOFs exhibit excellent sorption capacity towards U(vi) (>90%) and maximum uptake was observed at pH 6. Sorption capacity of MOFs have the following order; IRMOF-3-DPC (300 mg U g-1) > IRMOF-SMA (292 mg U g-1) > IRMOF-PC (289 mg U g-1) > IRMOF-GA (280 mg U g-1) > IRMOF-3 (273 mg U g-1). IRMOF-DPC shows rapid sorption of uranium within 5 min with excellent uptake of U(vi) (>99%). The desorption of U(vi) was examined with different eluents and 0.01 M HNO3 was found to be most effective. The fluorescence sensing studies of U(vi) via IRMOF-3 and its PSM MOFs revealed high sensitivity and selectivity towards U(vi) over other competing rare earth metal ions (La3+, Ce4+, Sm3+, Nd3+, Gd3+, and Eu3+), wherein IRMOF-GA displayed an impressive detection limit of 0.36 mg L-1 for U(vi).

Assorted functionality-appended UiO-66-NH2 for highly efficient uranium(vi) sorption at acidic/neutral/basic pH.

A series of functionalized metal organic frameworks (MOFs) were synthesized by the post-synthetic modification (PSM) of Zr(iv)-containing UiO-66-NH2 MOFs using covalent grafting with various functional groups utilizing pendant -NH2 moieties. The tethering of amide (with/without pendant carboxylic acid), iminopyridine, phoshinic amide and sulphur-containing functionalities produced a library of eight different UiO-66-NH2 derivatives. The functionalized MOFs were characterized by FT-IR spectroscopy, NMR, PXRD, TGA, SEM-EDX and BET surface area analysis. Uranyl ion extraction with the functionalized MOFs was investigated in acidic/neutral/basic conditions (pH 1 to 9). This work presents a comprehensive study of different functionalized MOFs to investigate the effects of various analytical parameters, including pH, contact time, and desorption process. The MOFs as solid phase extractants (SPEs) provide a direct comparison of the sorption efficiencies of different functional groups on a common solid support. A phosphorous-functionalized material, UiO-66-PO-Ph, with enhanced thermal stability (∼500 °C) exhibits the best sorption capacity (∼96%) in an acidic medium (pH 3). The parent MOF UiO-66-NH2 (92%) and iminopyridine-functionalized UiO-66-IMP (90%) showed excellent sorption in neutral conditions (pH 7). Amide-containing MOFs UiO-66-AM1 (40%), UiO-66-AMMal (31%) and UiO-66-AMGlu (70%), sulfur-based MOFs UiO-66-SMA (65%) and UiO-66-SSA (27%), and phosphorous-functionalized UiO-66-PO-OPh (50%) displayed maximum sorption in basic conditions (pH 8). The kinetics studies revealed rapid uranium sorption in about 2 h due to the effective binding of uranyl ions with the anchored functional groups of MOFs; quantitative elution of uranyl ions from the MOF framework was carried out with 0.1/0.01 M HNO3. The MOFs also exhibit moderate recyclability for uranium sorption and can be regenerated by an acidic solution. The functionalized MOFs alter the stability in acidic/basic media; thus, UiO-66-NH2 is a versatile MOF material employed as an SPE for the extraction of radionuclides from aqueous media. This work also provides a platform for the development of new functionalized MOF materials for the efficient sorption of uranium as well as moderate recyclability for its removal, and the potential applications include the removal of uranium from aqueous waste streams.

Strong influence of weak hydrogen bonding on actinide-phosphonate complexation: accurate predictions from DFT followed by experimental validation.

Among the varied classes of weak hydrogen bond, the CHO type is one of immense interest as it governs the finer structures of biological and chemical molecules, hence determining their functionalities. In the present work, this weak hydrogen bond has been shown to strongly influence the complexation behaviour of uranyl nitrate [UO2(NO3)2] with diamyl-H-phosphonate (DAHP) and its branched isomer disecamyl-H-phosphonate (DsAHP). The structures of the bare ligands and complexes have been optimized by density functional theory (DFT) calculations. Surprisingly, despite having the same chemical composition the branched UO2(NO3)2·2DsAHP complex shows a remarkably higher stability (by ∼14 kcal mol-1) compared to the UO2(NO3)2·2DAHP complex. Careful inspection of the optimized structures reveals the existence of multiple CHO hydrogen-bonding interactions between the nitrate oxygens or U[double bond, length as m-dash]O oxygens and the α-hydrogens in the alkyl chains of the ligands. Comparatively stronger such bonds are found in the UO2(NO3)2·2DsAHP complex. The binding free energies associated with the complexes are computed and favoured superior binding energetics for the more stable UO2(NO3)2·2DsAHP complex. Calculations involving diisoamyl-H-phosphonate (DiAHP) and its complexes have also been performed. Theoretical predictions are experimentally tested by carrying out the extraction of U(vi) from nitric acid media using these ligands. DAHP, DsAHP and DiAHP are synthesised, characterised by NMR and evaluated for their physicochemical properties viz. viscosity, density and aqueous solubility. It was experimentally discovered that indeed DsAHP complexation with uranyl nitrate is more favoured. H-phosphonates are generically classified as acidic extractants owing to the formation of an enol tautomer at lower acidities, hence complexing the metal ion by proton exchange. Our experiments interestingly reveal a neutral ligand characteristic for DsAHP alone which is generically an acidic extractant. Furthermore, the enol tautomer of H-phosphonates that governs their extraction profiles at low acidities is also explored by DFT and the anomalous pH dependent complexation trend of DsAHP could be successfully explained. The extractions of Pu(iv) and Th(iv) have also been carried out in addition to U(vi). Solvent extraction behaviour of Am(iii) was also studied with all three ligands; the positive binding energies computed for the Am(iii) complexation corroborate with our experimental results on the poor extraction of Am(iii).

Highly selective CHEF-type chemosensor for lutetium (III) recognition in semi-aqueous media.

A simple phosphoryl quinolone (L) based sensor has been synthesized for the selective recognition of Lu3+ by spectrofluorimetric method. In methanol-water (1:1, v/v), the ligand L exhibits a weak emission peak at 400 nm upon excitation at 280 nm. Upon interaction with various f-metal and other selected metals from s, p, and d-block elements, the fluorescence of L is selectively enhanced in the presence of Lu3+ due to the chelation enhanced fluorescence (CHEF) effects. The quantum yield (φ) of L (φ = 0.063) is enhanced to φ = 0.118 upon chelation with Lu3+ ion. From the titration experiment, the limit of detection (LOD) of sensor L to recognize Lu3+ is estimated down to 24.2 nM, which is much lower than the WHO guidelines (76 µM) in drinking water. The formation of host-guest complexation between L and Lu3+ in 2:1 binding stoichiometry is studied by Job's method and the binding constant is estimated by band fit analysis (logKf = 5.1). Further, the coordination behaviour between L and Lu3+ is well supported by FT-IR, 1H NMR, 13C NMR, 31P NMR, ESI mass spectral data and the theoretical results.

Development of the Smartphone-Assisted Colorimetric Detection of Thorium by Using New Schiff's Base and Its Applications to Real Time Samples.

In this paper, a new Th4+ ion-selective chromogenic sensor (L) was developed by reacting 1,10-phenanthroline-2,9-dicarbohydrazide with 2-hydroxy naphthaldehyde. The sensing ability of L toward Th4+ was investigated in solution and paper strips loaded with L using spectrophotometric and colorimetric methods. The selective interaction of L was examined with various f-metal ions and other selected metal ions from s-block and d-block elements. Results show that by the colorimetric method in solution-phase dimethyl sulfoxide/H2O (7:3, v/v) and paper strip methods, the naked-eye detectable color change of L occurred from colorless solution to yellow-orange and pale yellow colour upon interacting with Th4+ and Al3+, respectively, whereas other metal ions did not interfere. The ligand L exhibits two absorbance bands at 320 and 375 nm because of ligand-to-ligand charge transfer. Upon interaction with Th4+, L undergoes red shift of both absorption bands and the formation of a new UV-vis band at 335 and 440 nm. The UV-visible spectral studies indicate the formation of a 1:1 host-guest complex between L and Th4+ with an association constant of 4.7 × 103 M-1. The limit of quantification and limit of detection of L for the analysis of Th4+ are found to be 167 and 50 nM, respectively. The visually detectable color change of L has been well integrated with a smartphone RGB color value to make it an analytical signal for real-time analysis of Th4+ with the detection limit down to 116 nM. Besides, L was applied for the analysis of Th4+ content present in various real water samples, monazite, and lantern mantle samples by spectrophotometry and RGB color values. The binding mode of L with Th4+ is investigated by 1H NMR, electrospray ionization-mass, and theoretical studies.

Evaluation of polybenzimidazole-based polymers for the removal of uranium, thorium and palladium from aqueous medium.

Four types of polybenzimidazole (PBI)-based polymers (m-PBI, p-PBI, pyridine-based m-PBI and alkylated m-PBI) have been prepared and characterized. Extraction behaviour of heavy metal ions, viz. U(VI), Th(IV) and Pd(II), with these polymers was investigated. Distribution ratios for the extraction of these metal ions were measured as a function of nitric acid concentration. Extraction data reveal that, in general, p-PBI exhibits a higher distribution ratio for U(VI), Th(IV) and Pd(II) compared with the other polymeric resins evaluated in the present study. Column chromatography experiments were carried out with a solution of U(VI), Th(IV) and Pd(II) in dilute nitric acid media using columns packed with m- and p-PBI polymeric material for understanding the sorption and elution behaviour. The p-PBI-based resin has shown higher palladium sorption capacity (1.8 mmol g-1). The studies also established that p-PBI resin is a potential candidate material for the recovery of U(VI) and Th(IV) (capacity 0.22 mmol g-1 and 0.13 mmol g-1) from an aqueous stream, e.g. mine water samples.

Dynamically modified C18 silica monolithic column for the rapid determinations of lead, cadmium and mercury ions by reversed-phase high-performance liquid chromatography.

In this article, a new reversed-phase high-performance liquid chromatography (RP-HPLC) method for the rapid, selective and sequential separation of toxic heavy metal ions namely, Pb2+, Hg2+, and Cd2+ is reported. For this RP-HPLC method, a C18 silica monolith column (Chromolith RP-18e, 100 × 4.6 mm) has been surface modified using a laboratory-synthesized amphiphilic organic ligand namely, 1,5-dioctanoyl-1,5-diphenylcarbazide (DODPC), which acts an ion-selective receptor, for the separation of the target analytes. The eluted metal ions were subjected to post-column derivatization reaction with 4-(2-pyridylazo) resorcinol (PAR) prior to their detection using a UV-vis detector (at 520 nm). The post-column reagent (PAR; 4.7 × 10-4 M; pH 9.0; 1.5 mL/min) was mixed with the column eluate through an ingeniously designed T-connector. An ultra-fast separation of Pb2+, Cd2+, and Hg2+ ions with a retention time of 1.67, 1.88 and 3.62 min, respectively was achieved, using 0.0526 mmol of DODPC coated C18 monolithic column along with tartaric acid solution (1.0 × 10-2 M; pH 4.0; 1.0 mL/min), as the isocratic eluent (mobile phase). The chromatographic parameters such as linearity, accuracy, recovery, limits of detection and quantification were validated to achieve superior analytical results. The influence of various analytical parameters such as nature of mobile phase and its concentration, solution pH, flow rate, post-column reagent and its concentration were studied and optimized. The studies revealed a lower detection limits of 0.075, 0.090 and 0.120 µg/L, and a quantification limits of 0.225, 0.270 and 0.450 µg/L, for Pb2+, Cd2+ and Hg2+ ions, respectively. A linear signal response in the concentration range of 0.05-50.0 µg/mL, was observed for the target metal ions, with an average r2 value of 0.9994. The method was selective for the target metal ions, with excellent data reliability and reproducibility that accounts for an average recovery value of 99.76%, with a relative standard deviation of ≤1.83%.

Remarkable structural effects on the complexation of actinides with H-phosphonates: a combined experimental and quantum chemical study.

The structural effects of the carbon chain on the extraction of actinides by organo-phosphorus extractants have been examined experimentally and by computation. Branched butyl H-phosphonates and their linear chain isomer, n-butyl H-phosphonate (DBHP), were synthesised and characterised using IR, NMR and GC-MS techniques. Their physical properties viz. viscosity, density and aqueous solubility have been examined. DBHP, Di-iso-butyl H phosphonate (DiBHP) and Di-sec-butyl H phosphonate (DsBHP) were employed for the extraction of uranium and americium ions from nitric acid. 233U (α-tracer) and 241Am (γ-tracer) were employed as representative isotopes for the extraction of U and Am, respectively, and their distribution ratios (D) were obtained as a function of nitric acid concentration (0.01-8 M). Branching of the alkyl chain at the secondary carbon atom showed unexpected neutral extractant behaviour for DsBHP which is generally classified as an acidic extractant. The acid-dependent dual extraction mechanisms for the H-phosphonates have been examined both experimentally and through quantum chemical calculations. This dramatic effect can be partly attributed to the hindrance in the formation of the enol tautomer through the strengthening of the P[double bond, length as m-dash]OH hydrogen bonding in the DsBHP extractant. Density functional theory (DFT) based calculations were carried out to understand the complexation behaviour of actinides with the two extractants. Possible structures and binding affinities of actinides with H-phosphonates have been deduced from electronic structure calculations. Finally, the trends in distribution ratios were additionally explored and correlated with experimental observations for both metal ions.

Complexation Behavior of the Tri-n-butyl Phosphate Ligand with Pu(IV) and Zr(IV): A Computational Study.

Tri-n-butyl phosphate (TBP), used as the extractant in nuclear fuel reprocessing, shows superior extraction abilities for Pu(IV) over a large number of fission products including Zr(IV). We have applied density functional theory (DFT) calculations to explain this selectivity by investigating differences in electronic structures of Pu(NO3)4·2TBP and Zr(NO3)4·2TBP complexes. On the basis of our quantum chemical calculations, we have established the lowest energy electronic states for both complexes; the quintet is the ground state for the former, whereas the latter exists in the singlet spin state. The calculated structural parameters for the optimized geometry of the plutonium complex are in agreement with the experimental results. Atoms in Molecules analysis revealed a considerable amount of ionic character to M-O{TBP} and M-O{NO3} bonds. Additionally, we have also investigated the extraction behavior of TBP for metal nitrates and have estimated the extraction energies to be -73.1 and -57.6 kcal/mol for Pu(IV) and Zr(IV), respectively. The large extraction energy of Pu(IV) system is in agreement with the observed selectivity in the extraction of Pu.

Design and adaptation of a novel supercritical extraction facility for operation in a glove box for recovery of radioactive elements.

The design and development of a novel supercritical extraction experimental facility adapted for safe operation in a glove box for the recovery of radioactive elements from waste is described. The apparatus incorporates a high pressure extraction vessel, reciprocating pumps for delivering supercritical fluid and reagent, a back pressure regulator, and a collection chamber. All these components of the system have been specially designed for glove box adaptation and made modular to facilitate their replacement. Confinement of these materials must be ensured in a glove box to protect the operator and prevent contamination to the work area. Since handling of radioactive materials under high pressure (30 MPa) and temperature (up to 333 K) is involved in this process, the apparatus needs elaborate safety features in the design of the equipment, as well as modification of a standard glove box to accommodate the system. As a special safety feature to contain accidental leakage of carbon dioxide from the extraction vessel, a safety vessel has been specially designed and placed inside the glove box. The extraction vessel was enclosed in the safety vessel. The safety vessel was also incorporated with pressure sensing and controlling device.

Retention studies on uranium, thorium and lanthanides with amide modified reverse phase support and its applications.

The retention behaviour of uranium and thorium was investigated on modified reverse phase supports using 3-oxo-pentanedioicacid bis-[bis-(2-ethyl-hexyl)-amide (OPAEHA), 3-oxo-pentanedioicacid bis diisobutyl amide (OPAIBA) and bis-2-ethylhexyl succinamic acid (BEHSA). alpha-Hydroxy isobutyric acid (alpha-HIBA) was employed as the complexing reagent for elution. Elution profiles of uranium and thorium were studied as a function of the modifier concentration, mobile phase composition and its pH. Based on these investigations, a novel high performance liquid chromatography (HPLC) based separation technique was developed using BEHSA modified support for the isolation and quantitative determination of lanthanides as a group in uranium matrix. Hundreds of samples obtained from pyrochemical reprocessing of molten salts containing lanthanides in uranium matrix (e.g. 1:20,000) were separated and determined within 7 min using the coated support. The advantage of the present HPLC technique lies in the simultaneous separation and assay of total lanthanides and uranium whereas other analytical methods necessitate the separation of uranium matrix prior to lanthanide assay.

High performance liquid chromatographic studies on lanthanides, uranium and thorium on amide modified reversed phase supports.

The retention behavior of uranium, thorium and lanthanides has been investigated with amide modified reversed phase C(18) supports using alpha-hydroxy isobutyric acid (alpha-HIBA) as the mobile phase. Four structurally different amide moieties namely, 4-hydroxy-N,N-dihexyl butyramide (4HHBA), 4-hydroxy-N,N-di-2-ethylhexylhexanamide (4HEHHA), bis(N,N,N',N'-2-ethylhexyl)malonamide (B2EHM) and N-methyl-tris(dihexylcarbamoyl-3-methoxy)pivolamide (MTDCMPA) have been synthesized and studied. Among the various amide coated columns, the supports modified with 4HHBA, B2EHM and MTDCMPA exhibit an interesting retention for uranium and thorium, which is different from 4HEHHA modified support. The retention time for uranium and thorium increases with increasing amide concentration for 4HHBA, B2EHM and MTDCMPA supports, while the same decreases with increasing 4HEHHA content. However, the separation factor for uranium and thorium is greater on a 4HEHHA support, compared to an unmodified C(18) column, reflecting the amide's preferential complexation of uranium over thorium. Columns modified with 4HHBA, B2EHM and MTDCMPA exhibit relatively higher retentions for lanthanides. However, MTDCMPA modified support shows a different elution profile for lanthanides compared to 4HHBA, and B2EHM modified columns. Individual separations of heavier lanthanides, i.e., from gadolinium to lutetium also have been achieved using 4HHBA and B2EHM modified supports. The influence of modifier content, mobile phase concentration and its pH on the retention of metal ions has also been studied. Based on these investigations, an efficient high performance liquid chromatographic method (HPLC) has been developed for the rapid separation of uranium from thorium as well as for the individual separation of heavier lanthanides.

QSPR modeling for solubility of fullerene (C(60)) in organic solvents.

Solubility of fullerene C(60) in 75 organic solvents was examined to develop quantitative structure-solubility relationships. Topological indices and polarizability parameter computed from refractive index were used to form the regression models. The models suggested for individual data sets such as alkanes, alkyl halides, alcohols, cycloalkanes, alkylbenzenes, and aryl halides have good predictive ability and are better than the models for the combined groups. Inclusion of an indicator parameter which is a combination of atom contributions and contributions of substituents' position in benzenes improved the predictive ability significantly.

Hypertension and virilization caused by a unique desoxycorticosterone- and androgen-secreting adrenal adenoma.

We describe a rare androgen and desoxycorticosterone (DOC)-secreting adrenal tumor in a non-Cushingoid 14 year-old Haitian girl with secondary amenorrhea, hypertension and virilization. Her steroid pattern simulated an 11 beta-hydroxylation defect with notable elevation of adrenal androgens, 11-desoxycortisol (S), DOC, 17 alpha-hydroxyprogesterone and pregnenelone. Exogenous ACTH stimulated steroidogenesis. A CAT scan unfortunately failed to delineate an adrenal mass. Dexamethasone (DEX) was administered, therefore, which partially suppressed androgen levels, reduced DOC and S by 80% and 82% respectively, and normalized blood pressure. Nevertheless, the response to glucocorticoid was incomplete and an MRI was obtained, which revealed a right adrenal tumor. Post surgery, the patient promptly resumed menses and became normotensive. This case illustrates that ACTH and DEX cannot reliably differentiate tumor from hyperplasia, whereas the simultaneous increase of delta 4 and delta 5 steroids, present here, may favor a tumor. This case also allows speculation that the hypersecretion of DOC may result from inhibition of 11 beta-hydroxylase activity by excess androgens. The importance of appropriate imaging for diagnosis is underscored.