The metal selectivity of a short peptide maquette imitating the high-affinity metal-binding site of E. coli HypB

A seven-residue peptide based on the high-affinity metal-binding site of E. coli HypB maintains the nickel-binding activity of the full-length protein. The ability of the peptide to bind transition metals other than nickel was explored, and is discussed in the context of the function of HypB in hydrogenase biosynthesis.     

Thermodynamics of black plane solution

We obtain a new phantom black plane solution in $4$ 4 D of the Einstein–Maxwell theory coupled with a cosmological constant. We analyse their basic properties, as well as its causal structure, and obtain the extensive and intensive thermodynamic variables, as well as the specific heat and the first law. Through the specific heat and the so-called geometric methods, we analyse in detail their thermodynamic properties, the extreme and phase transition limits, as well as the local and global stabilities of the system. The normal case is shown with an extreme limit and the phantom one with a phase transition only for null mass, which is physically inaccessible. The systems present local and global stabilities for certain values of the entropy density with respect to the electric charge, for the canonical and grand canonical ensembles.     

XGobi: Interactive Dynamic Data Visualization in the X Window System

Abstract

XGobi is a data visualization system with state-of-the-art interactive and dynamic methods for the manipulation of views of data. It implements 2-D displays of projections of points and lines in high-dimensional spaces, as well as parallel coordinate displays and textual views thereof. Projection tools include dotplots of single variables, plots of pairs of variables, 3-D data rotations, various grand tours, and interactive projection pursuit. Views of the data can be reshaped. Points can be labeled and brushed with glyphs and colors. Lines can be edited and colored. Several XGobi processes can be run simultaneously and linked for labeling, brushing, and sharing of projections. Missing data are accommodated and their patterns can be examined; multiple imputations can be given to XGobi for rapid visual diagnostics. XGobi includes an extensive online help facility. XGobi can be integrated in other software systems, as has been done for the data analysis language S, the geographic information system (GIS) Arc View?, and the interactive multidimensional scaling program XGvis. XGobi is implemented in the X Window System? for portability as well as the ability to run across a network.     

Using the K5Connected Cognition Diagram to analyze teachers’ communication and understanding of regions in three-dimensional space

This paper reports on a study that introduces and applies the K₅Connected Cognition Diagram as a lens to explore video data showing teachers’ interactions related to the partitioning of regions by axes in a three-dimensional geometric space. The study considers “semiotic bundles” ( Arzarello, 2006), introduces “semiotic connections,” and discusses the fundamental role each plays in developing individual understanding and communication with peers. While all teachers solved the problem posed, many failed to make or verbalize connections between the types of semiotic resources introduced during their discussions.     

Structural, magnetic, and thermal characteristics of the phase transitions in Gd5GaxGe4−x magnetocaloric materials

Temperature-dependent, single crystal and powder X-ray diffraction studies as well as magnetization, and heat capacity measurements were carried out on two phases of the Gd₅Ga_xGe_4−x system: for x=0.7 and 1.0. Gd₅Ga_0.7Ge_3.3 shows three structure types as a function of temperature: (i) from 165 K to room temperature, the orthorhombic Sm₅Ge₄-type structure exists; (ii) below 150 K, it transforms to a orthorhombic Gd₅Si₄-type structure; and (iii) a monoclinic Gd₅Si₂Ge₂-type component is observed for the intermediate temperature range of 150 K≤T≤165 K. This is the first time that all these three structure types have been observed for the same composition. For Gd₅Ga_1.0Ge_3.0, the room temperature phase belongs to the orthorhombic Pu₅Rh₄-type structure with interslab contacts between main group atoms of 2.837(4) Å. Upon heating above 523 K, it transforms to a Gd₅Si₄-type structure with this distance decreasing to 2.521(7) Å before decomposing above 573 K.     

Long-lived dipolar molecules and Feshbach molecules in a 3D optical lattice

We have realized long-lived ground-state polar molecules in a 3D optical lattice, with a lifetime of up to 25 s, which is limited only by off-resonant scattering of the trapping light. Starting from a 2D optical lattice, we observe that the lifetime increases dramatically as a small lattice potential is added along the tube-shaped lattice traps. The 3D optical lattice also dramatically increases the lifetime for weakly bound Feshbach molecules. For a pure gas of Feshbach molecules, we observe a lifetime of greater than 20 s in a 3D optical lattice; this represents a 100-fold improvement over previous results. This lifetime is also limited by off-resonant scattering, the rate of which is related to the size of the Feshbach molecule. Individually trapped Feshbach molecules in the 3D lattice can be converted to pairs of K and Rb atoms and back with nearly 100% efficiency.     

Bimanes 28: Extraction of sulfur from fluorescent models for biological thiols

Sulfur extraction from the tripeptide thiol, glutathione (α-glu-cys-gly) ( 1 ) via reaction with syn-(1-bromo-ethyl, methyl)bimane ( 2 ) yields glutathione slfide and the thiabridged bimane, μ(S)-syn-(methylmethylene, methyl)bimane ( 3 ) [1]. The reaction with 2 has been extended to dithiols as models for important biological thiols such as reduced trypanothione. The fluorescent dithiols were derived through reductive cleavage with triphenylphosphine (tetrahydrofuan, Hcl−Kbr solution, pH 1.5) of the dithiatriclic bimane esters, μ(O₂C(CH₂)SS(CH₂)_nCO₂)-syn-(CH₂,CH₃)B, n = 1, 2, 3, prepared from syn-(bromomethyl, methyl)bimane ( 4 ) and the corresponding dithiadicarboxylic acids. Sulfur extraction led to 3 and the cyclic sulfide derived from the dithiol in moderate yields. The dithiols, dithiothreitol and dithioerythritol, also yielded moderate amounts of 3 . Sterically hindered thiols (e.g., those in hemoglobin) gave 3 in lower yields. Treatment of human red blood cells and red cells membranes (hemoglobin-free ghosts) with 2 gave rise to some 3 . A side product in some reactions was the oxabridged bimane, μ(O)-syn-(methylmethylene, methyl)bimane.     

Customising excitation properties of polycyclic aromatic hydrocarbons by rational positional heteroatom doping: the peri-xanthenoxanthene (PXX) case

In this paper we tackle the challenge of gaining control of the photophysical properties of PAHs through a site-specific N-doping within the structural aromatic framework. By developing a simple predictive tool that identifies C(sp²)-positions that if substituted with a heteroatom would tailor the changes in the absorption and emission spectral envelopes, we predict optimal substitutional patterns for the model peri-xanthenoxanthene (PXX) PAH. Specifically, TDDFT calculations of the electron density difference between the S₁ excited state and S₀ ground state of PXX allowed us to identify the subtleties in the role of sites i.e., electron donating or withdrawing character on excitation. The replacement of two C(sp²)-atoms with two N-atoms, in either electron donating or withdrawing positions, shifts the electronic transitions either to low or high energy, respectively. This consequently shifts the PXX absorption spectral envelop bathochromically or hypsochromically, as demonstrated by steady-state absorption spectroscopic measurements. Within the series of synthesised N-doped PXX, we tune the optical band gap within an interval of ∼0.4 eV, in full agreement with the theoretical predictions. Relatedly, measurements show the more blueshifted the absorption/emission energies, the greater the fluorescence quantum yield value (from ∼45% to ∼75%). On the other hand, electrochemical investigations suggested that the N-pattern has a limited influence on the redox properties. Lastly, depending on the N-pattern, different supramolecular organisations could be obtained at the solid-state, with the 1,7-pattern PXX molecule forming multi-layered, graphene-like, supramolecular sheets through a combination of weak H-bonding and π–π stacking interactions. Supramolecular striped patterned sheets could also be formed with the 3,9- and 4,10-congeners when co-crystallized with a halogen-bond donor molecule.

In this paper we tackle the challenge of gaining control of the photophysical properties of PAHs through a site-specific N-doping within the structural aromatic framework.     

Copper‐64‐Alloyed Gold Nanoparticles for Cancer Imaging: Improved Radiolabel Stability and Diagnostic Accuracy

Gold nanoparticles, especially positron‐emitter‐ labeled gold nanostructures, have gained steadily increasing attention in biomedical applications. Of the radionuclides used for nanoparticle positron emission tomography imaging, radiometals such as ⁶⁴Cu have been widely employed. Currently, radiolabeling through macrocyclic chelators is the most commonly used strategy. However, the radiolabel stability may be a limiting factor for further translational research. We report the integration of ⁶⁴Cu into the structures of gold nanoparticles. With this approach, the specific radioactivity of the alloyed gold nanoparticles could be freely and precisely controlled by the addition of the precursor ⁶⁴CuCl₂ to afford sensitive detection. The direct incorporation of ⁶⁴Cu into the lattice of the gold nanoparticle structure ensured the radiolabel stability for accurate localization in vivo. The superior pharmacokinetic and positron emission tomography imaging capabilities demonstrate high passive tumor targeting and contrast ratios in a mouse breast cancer model, as well as the great potential of this unique alloyed nanostructure for preclinical and translational imaging.