Evaluation of DGT techniques for measuring inorganic uranium species in natural waters: Interferences,deployment time and speciation

Three adsorbents (Chelex-100, manganese dioxide [MnO₂] and Metsorb), used as binding layers with the diffusive gradient in thin film (DGT) technique, were evaluated for the measurement of inorganic uranium species in synthetic and natural waters. Uranium (U) was found to be quantitatively accumulated in solution (10–100 μg L⁻¹) by all three adsorbents (uptake efficiencies of 80–99%) with elution efficiencies of 80% (Chelex-100), 84% (MnO₂) and 83% (Metsorb). Consistent uptake occurred over pH (5–9), with only MnO₂ affected by pH < 5, and ionic strength (0.001–1 mol L⁻¹ NaNO₃) ranges typical of natural waters, including seawater. DGT validation experiments (5 days) gave linear mass uptake over time (R² ≥ 0.97) for all three adsorbents in low ionic strength solution (0.01 M NaNO₃). Validation experiments in artificial sea water gave linear mass uptake for Metsorb (R² ≥ 0.9954) up to 12 h and MnO₂ (R² ≥ 0.9259) up to 24 h. Chelex-100 demonstrated no linear mass uptake in artificial sea water after 8 h. Possible interferences were investigated with SO₄²⁻ (0.02–200 mg L⁻¹) having little affect on any of the three DGT binding layers. PO₄³⁻ additions (5 μg L⁻¹–5 mg L⁻¹) interfered by forming anionic uranyl phosphate complexes that Chelex-100 was unable to accumulate, or by directly competing with the uranyl species for binding sites, as with MnO₂ and the Metsorb. HCO₃⁻ (0.1–500 mg L⁻¹) additions formed anionic species which interfered with the performance of the Chelex-100 and the MnO₂, and the Ca²⁺ (0.1–500 mg L⁻¹) had the affect of forming labile calcium uranyl species which aided uptake of U by all three resins. DGT field deployments in sea water (Southampton Water, UK) gave a linear mass uptake of U over time with Metsorb and MnO₂ (4 days). Field deployments in fresh water (River Lambourn, UK) gave linear uptake for up to 7 and 4 days for Metsorb and MnO₂ respectively. Field deployment of the Metsorb-DGT samplers with various diffusive layer thicknesses (0.015–0.175 cm) allowed accurate measurements of the diffusive boundary layer (DBL) and allowed DBL corrected concentrations to be determined. This DBL-corrected U concentration was half that determined when the effect of the DBL was not considered. The ability of the DGT devices to measure U isotopic ratios with no isotopic fractionation was shown by all three resins, thereby proving the usefulness of the technique for environmental monitoring purposes.     

Informed Molecular Design of Conjugated Oligoelectrolytes To Increase Cell Affinity and Antimicrobial Activity

Membrane‐intercalating conjugated oligoelectrolytes (COEs) are emerging as potential alternatives to conventional, yet increasingly ineffective, antibiotics. Three readily accessible COEs, belonging to an unreported series containing a stilbene core, namely D4 , D6 , and D8 , were designed and synthesized so that the hydrophobicity increases with increasing side‐chain length. Decreased aqueous solubility correlates with increased uptake by E. coli. The minimum inhibitory concentration (MIC) of D8 is 4 μg mL^?1 against both E. coli and E. faecalis, with an effective uptake of 72 %. In contrast, the MIC value of the shortest COE, D4 , is 128 μg mL^?1 owing to the low cellular uptake of 3 %. These findings demonstrate the application of rational design to generate efficacious antimicrobial COEs that have potential as low‐cost antimicrobial agents.     

How ion properties determine the stability of a lipase enzyme in ionic liquids: a molecular dynamics study

The influence of eight different ionic liquid (IL) solvents on the stability of the lipase Candida antarctica lipase B (CAL-B) is investigated with molecular dynamics (MD) simulations. Considered ILs contain cations that are based either on imidazolium or guanidinium as well as nitrate, tetrafluoroborate or hexafluorophosphate anions. Partial unfolding of CAL-B is observed during high-temperature MD simulations and related changes of CAL-B regarding its radius of gyration, surface area, secondary structure, amount of solvent close to the backbone and interaction strength with the ILs are evaluated. CAL-B stability is influenced primarily by anions in the order NO(3)(-)? BF(4)(-) < PF(6)(-) of increasing stability, which agrees with experiments. Cations influence protein stability less than anions but still substantially. Long decyl side chains, polar methoxy groups and guanidinium-based cations destabilize CAL-B more than short methyl groups, other non-polar groups and imidazolium-based cations, respectively. Two distinct causes for CAL-B destabilization are identified: a destabilization of the protein surface is facilitated mostly by strong Coulomb interactions of CAL-B with anions that exhibit a localized charge and strong polarization as well as with polar cation groups. Surface instability is characterized by an unraveling of α-helices and an increase of surface area, radius of gyration and protein-IL total interaction strength of CAL-B, all of which describe a destabilization of the folded protein state. On the other hand, a destabilization of the protein core is facilitated when direct core-IL interactions are feasible. This is the case when long alkyl chains are involved or when particularly hydrophobic ILs induce major conformational changes that enable ILs direct access to the protein core. This core instability is characterized by a disintegration of β-sheets, diffusion of ions into CAL-B and increasing protein-IL van der Waals interactions. This process describes a stabilization of the unfolded protein state. Both of these processes reduce the folding free energy and thus destabilize CAL-B. The results of this work clarify the impact of ions on CAL-B stabilization. An extrapolation of the observed trends enables proposing novel ILs in which protein stability could be enhanced further.     

A convenient one-pot synthesis of o-phenylene bis(diphenylphosphine)

The reaction between $\text{o}$-difluorobenzene and sodium diphenylphosphide in liquid ammonia provides a convenient synthesis of the title compound.     

Long-range nuclear spin–spin coupling between selenium-77 and phosphorus-31 in biphosphorus compounds

The coupling constants ⁿJ(⁷⁷Se³¹P), n = 1–4, have been measured in the proton-decoupled ³¹P NMR spectra of a range of diphosphorus selenides and diselenides. ³¹P–{¹H, ³¹P} and ³¹P–{¹H, ⁷⁷Se} triple resonance experiments have been used to establish the signs of the coupling constants, and it is found that both the magnitudes and signs depend upon the stereochemical relationship of the coupled nuclei.     

Lineshape effects in atomic absorption spectroscopy

Deviations from Beer's Law caused by the relative lineshape functions of source and absorber in atomic absorption experiments are considered. The validity of using a modified form of the law incorporating a correction factor γ, which is particularly convenient in time-resolved atomic absorption experiments, to account for these deviations, has been critically examined for a wide range of source and absorber lineshapes using numerical evaluation of the transmission integrals involved. It is concluded that there is, in general, no theoretical justification for the use of such a γ factor, except in the case of large source linewidth/absorber linewidth ratios when the line broadening in the absorber involves a significant homogeneous (Lorentzian) contribution. The use of empirically determined γ factors, much different from unity to analyse experimental data, should be viewed with suspicion unless direct evidence is presented to show that under the experimental conditions γ happens to be constant or slowly varying.     

Regioselective Suzuki coupling of benzofuran or benzothiophene boronic acids and dibromo substituted naphthalenes: synthesis of a potent inhibitor of plasminogen activator inhibitor-1

An efficient route to the biologically active naphthyl benzofuran derivative is described. The synthesis highlights a regioselective Suzuki coupling of a benzofuran and a dibromo substituted naphthalene. The scope of regioselective Suzuki coupling has been investigated.     

Production of electronically excited iodine atoms I(5p52P12) by collisional release in molecular I2

The appearance rate of 1^* (5p⁵²P_{$\text{1}\text{2}$}) following laser photolysis of molecular I₂ 1.2 kT below the dissociation limit o the I₂ (B³ Π_ou+) state has been monitored by time-resolved atomic absorption as a function of I₂ pressure. Data were also taken with N₂ as an added gas. The results confirm the production of I^* from the B state by a collisional process and reveal an additional process by which I^* continues to appear for several hundred nanoseconds after the laser pulse even at N₂ pressures as high as 750 torr.     

Synthesis and structural characterisation of a novel phosphine-borane-stabilised dicarbanion and an unusual bis(phosphine-borane)

The reaction between the phosphine-borane-substituted alkene [Pr(n)(2)P(BH(3))](Me(3)Si)C[double bond]CH(2) and elemental lithium in THF yields the complex [(pmdeta)Li[Pr(n)(2)P(BH(3))](Me(3)Si)CCH(2)](2)(2b) after recrystallisation; an X-ray crystallographic study of 2b reveals that the lithium is bound to the BH(3) hydrogens of the ligand, with no Li-C(carbanion) contact.     

Fractal Morphology and Breakage of DLCA and RLCA Aggregates

Latex aggregates, formed in 1 M McIlvaine buffer solution and 0.2 M NaCl solution, have been characterized in terms of aggregate size distribution and fractal morphology. This was achieved using three sizing techniques (image analysis, laser scattering, and electrical sensing) in which size distributions and fractal properties of the aggregates were measured. Estimates of fractal dimensions were made using the two-slope method based on dimensional analysis and the small-angle light scattering method. Aggregate suspensions were prepared using both water and a mixture of heavy water/ water as the solvent. The latter essentially eliminated sedimentation, which was observed after one day of aggregation when water alone was used as a solvent. Latex aggregates formed by diffusion-limited colloid aggregation (DLCA) and reaction-limited colloid aggregation (RLCA) had fractal dimensions close to 1.8 and 2.1, respectively. As observed through image analysis, DLCA aggregates possessed a loose tenuous structure, whereas RLCA aggregates were more compact. Disruption of both DLCA and RLCA aggregates has been investigated in laminar flow and turbulent capillary flow. The shear forces introduced by a laminar shear device with a shear rate up to 1711 s(-1) were unable to bring about aggregate breakup; shearing facilitates aggregate growth in the case of DLCA. However, latex aggregates were significantly disrupted after passage through a turbulent capillary tube at 95209 s(-1). Copyright 2000 Academic Press.