Trace analysis of uranium ore concentrates using laser ablation inductively coupled plasma mass spectrometry for nuclear forensics

Journal of Radioanalytical and Nuclear Chemistry - We present a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method for trace-element analysis of uranium ore concentrates...     

Standardized basis sets for high-level-correlated relativistic calculations of atomic and molecular electric properties in the spin-averaged Douglas-Kroll (no-pair) approximation I. Groups Ib and IIb

Summary The technique developed earlier for the generation of the so-called first-order polarized basis sets for accurate non-relativistic calculations of molecular electric properties is used to obtain similar basis sets suitable for calculations in the Douglas-Kroll no-pair approximation. The corresponding (relativistic) basis sets are devised for atoms of the Groups Ib and IIb of the periodic table and tested in calculations of atomic polarizabilities and dipole moments of the coinage metal hydrides. Excellent performance of these basis sets has been found in the case of molecular calculations.     

Lamellar-to-cubic phase change in phospholipid bilayer systems incorporated with block copolymers: DMPC and PEO-PPO-PEO (P85)

We have used small-angle X-ray scattering and calorimetric methods to investigate the temperature-dependent phase behavior of ternary systems of phospholipid (DMPC), amphiphilic PEO-PPO-PEO block copolymer (Pluronics P85), and water. It is shown that a relatively small amount of block copolymers ( approximately 3 wt %) results in a lamellar-to-cubic phase transition. Still, both the bilayer-characteristic main transition, associated with chain melting, and the pretransition, associated with in-plane modulations, are preserved for copolymer concentrations up to 50-70 wt %, indicating the preservation of a bilayer type of lipid organization also within the cubic phase. The main transition splits up into two transitions upon the addition of copolymers, one resembling the high cooperativity of the main transition and one broad transition which may reflect complex formation with the copolymers. Parallel studies incorporating poly(ethylene glycol) into the DMPC multilamellar vesicles do not give analogous structural changes. It is concluded that the major effect on the molecular scale of adding PEO-PPO-PEO block copolymers is not only due to the hydration of the membrane but also due to the incorporation of the PPO block into the bilayer structure.     

Electric properties of hydrogen iodide: Reexamination of correlation and relativistic effects

The electric dipole moment and the static dipole polarizability of the hydrogen iodide molecule were studied using sophisticated correlated and relativistic methods. Both scalar and spin–orbit relativistic effects were carefully accounted for. We conclude that the large differences between the theoretical and experimental dipole moment, the dipole moment derivative and the polarizability cannot be reconciled by improved account of electron correlation and relativistic effects. The most striking difference between theory and experiment is observed for the polarizability anisotropy. We believe that experimental data, namely the experimental dipole moment (the most recent value is 0.176 au as compared to our best theoretical estimate, 0.154±0.003 au), the parallel polarizability (44.4 and 38.47±0.05 au) and the anisotropy (11.4 and 2.33±0.05 au) must be inaccurate. Experimental and theoretical perpendicular polarizability components (33.0 and 36.14±0.05 au,) and the mean polarizability (36.8 and 36.92±0.05 au) agree better. Our vibrationally corrected relativistic CCSD(T) results represent the most sophisticated predictions of electric properties of HI obtained so far.Contribution to the Björn Roos Honorary Issue     

New Insight into the Water‐Soluble Chlorophyll‐Binding Protein from Lepidium virginicum

This study describes new recombinant water‐soluble chlorophyll (Chl)‐binding proteins (WSCP) from Lepidium virginicum (LvWSCP). This complex binds four Chls (i.e. two dimers of Chls) per protein tetramer. We show that absorption, emission, hole‐burned (HB) spectra and the shape of the zero‐phonon hole (ZPH) action spectrum are consistent with the presence of uncorrelated excitation energy transfer between two Chl dimers. Thus, there is no need to include slow protein relaxation within the lowest excited state (as suggested in a previous analysis of cauliflower WSCP [Schmitt, F.‐J. et al. (2008) J. Phys. Chem. B, 112, 13951; Pieper, J. et al. (2011) J. Phys. Chem. B, 115, 4053]) in order to explain the large shift observed between the maxima of the ZPH action and emission spectra. Experimental evidence is provided which shows that electron exchange between lowest energy Chls and the protein may occur, i.e. electrons can be trapped at low temperature by nearby aromatic amino acids. The latter explains the shape of nonresonant HB spectra (i.e. the absence of antihole), demonstrating that the hole‐burning process in LvWSCP is largely photochemical in nature, though a small contribution from nonphotochemical hole burning (in resonant holes) is also observed.     

FragNet,a Contrastive Learning-Based Transformer Model for Clustering,Interpreting, Visualizing,and Navigating Chemical Space

The question of molecular similarity is core in cheminformatics and is usually assessed via a pairwise comparison based on vectors of properties or molecular fingerprints. We recently exploited variational autoencoders to embed 6M molecules in a chemical space, such that their (Euclidean) distance within the latent space so formed could be assessed within the framework of the entire molecular set. However, the standard objective function used did not seek to manipulate the latent space so as to cluster the molecules based on any perceived similarity. Using a set of some 160,000 molecules of biological relevance, we here bring together three modern elements of deep learning to create a novel and disentangled latent space, viz transformers, contrastive learning, and an embedded autoencoder. The effective dimensionality of the latent space was varied such that clear separation of individual types of molecules could be observed within individual dimensions of the latent space. The capacity of the network was such that many dimensions were not populated at all. As before, we assessed the utility of the representation by comparing clozapine with its near neighbors, and we also did the same for various antibiotics related to flucloxacillin. Transformers, especially when as here coupled with contrastive learning, effectively provide one-shot learning and lead to a successful and disentangled representation of molecular latent spaces that at once uses the entire training set in their construction while allowing “similar” molecules to cluster together in an effective and interpretable way.     

A weak pulsed magnetic field affects adenine nucleotide oscillations, and related parameters in aggregating Dictyostelium discoideum amoebae

A model eukaryotic cell system was used to explore the effect of a weak pulsed magnetic field (PMF) on time-varying physiological parameters. Dictyostelium discoideum cells (V12 strain) were exposed to a pulsed magnetic field (PMF) of flux density 0.4 mT, generated via air-cored coils in trains of 2 ms pulses gated at 20 ms. This signal is similar to those used to treat non-uniting fractures. Samples were taken over periods of 20 min from harvested suspensions of amoebae during early aggregation phase, extracted and derivatised for HPLC fluorescent assay of adenine nucleotides. Analysis of variance showed a significant athermal damping effect (P < 0.002, n = 22) of the PMF on natural adenine nucleotide oscillations and some consistent changes in phase relationships. The technique of nonlinear dielectric spectroscopy (NLDS) revealed a distinctive effect of PMF, caffeine and EGTA in modulating the cellular harmonic response to an applied weak signal. Light scattering studies also showed altered frequency response of cells to PMF, EGTA and caffeine. PMF caused a significant reduction of caffeine induced cell contraction (P < 0.0006, n = 19 by paired t-test) as shown by Malvern particle size analyser, suggesting that intracellular calcium may be involved in mediating the effect of the PMF.     

Multifunctional nanoprobes for pathogen-selective capture and detection

The synthesis of magnetic and fluorescent particles is described. The particles are biofunctionalized by binding pathogen-specific proteins to the particles via interactions between His-tags of proteins and zinc of the quantum dots. Detection of Salmonella and Staphylococcus aureus (S. aureus) by these particles is demonstrated.     

Polarizabilities of confined two-electron systems: the 2-electron quantum dot,the hydrogen anion,the helium atom and the lithium cation

The static dipole polarizabilities of two-electron systems confined by a spherical harmonic-oscillator potential?ω?have been calculated by the coupled-cluster CCSD method. The combined effect of the confining potential?ω?and the central electrostatic field on the polarizabilities of the quantum dot, and the confined systems, H^?, He and Li⁺, respectively, have been investigated. The polarizabilities of the quantum dot can be calculated analytically. The polarizability?α?of the 2-electron quantum dot for ω?=?0.01 is calculated to be 19?996?au, in perfect agreement with the exact value, 20?000?au. Already medium confinement, ω?=?1.0, reduces?α?to 2.00?au. The decrease of the polarizability is smaller for H^? (α?=?216.1?au for ω?=?0.0 and 0.985 au for ω?=?1.0), and much smaller for He and Li⁺ (1.3819 and 0.3813?au for He for ω?=?0.0 and ω?=?1.0, respectively, and 0.1921 and 0.128?au for Li⁺). The theoretical polarizabilities for unconfined (ω?=?0.0) H^?, He and the Li⁺ cation are in very good agreement with the best published theoretical and/or experimental data. Our final polarizability for H^?, 216.0±0.5?au, appears to be one of the most accurate values published so far. The optimization procedures of basis sets applicable to calculations of polarizabilities of systems confined by a spherical harmonic-oscillator potential are presented.