Structure Factors and Charge Density Description of Aluminum: A Quantum Crystallographic Study.

Static structure factors and charge density for metallic aluminum were investigated by periodic calculations using atom-centered Gaussian-type basis sets with the Perdew-Burke-Ernzerhof (PBE) functional implemented in the CRYSTAL14 package and X-ray constrained wave function (XCW) fitting. The effects of additional diffuse d and f basis functions on structure factors were compared with synchrotron powder X-ray diffraction and quantitative convergent electron beam diffraction data. Changes in structure factors from an independent atom model at 022, 113, and 222 reflections introduced d and f basis functions similar to those of the experimental data. The XCW fitting was applied to different sizes of aluminum clusters. The charge density features for a 50-atom cluster clearly demonstrated electron accumulation at tetrahedral sites and electron depletion at octahedral sites. The resolution dependence of the XCW study suggests that structure factors of the five lowest resolution reflections with 0.1% accuracy were indispensable for determining the detailed bonding description in the case of metallic aluminum.

Hemozoin produced by mammals confers heme tolerance.

Free heme is cytotoxic as exemplified by hemolytic diseases and genetic deficiencies in heme recycling and detoxifying pathways. Thus, intracellular accumulation of heme has not been observed in mammalian cells to date. Here we show that mice deficient for the heme transporter SLC48A1 (also known as HRG1) accumulate over ten-fold excess heme in reticuloendothelial macrophage lysosomes that are 10 to 100 times larger than normal. Macrophages tolerate these high concentrations of heme by crystallizing them into hemozoin, which heretofore has only been found in blood-feeding organisms. SLC48A1 deficiency results in impaired erythroid maturation and an inability to systemically respond to iron deficiency. Complete heme tolerance requires a fully-operational heme degradation pathway as haplo insufficiency of HMOX1 combined with SLC48A1 inactivation causes perinatal lethality demonstrating synthetic lethal interactions between heme transport and degradation. Our studies establish the formation of hemozoin by mammals as a previously unsuspected heme tolerance pathway.

Specialized cells, known as red blood cells, are responsible for transporting oxygen to various organs in the body. Each red blood cell contains over a billion molecules of heme which make up the iron containing portion of the hemoglobin protein that binds and transports oxygen. When red blood cells reach the end of their life, they are degraded, and the heme and iron inside them is recycled to produce new red blood cells. Heme, however, is highly toxic to cells, and can cause severe tissue damage if not properly removed. Scavenger cells called macrophages perform this recycling role in the spleen, liver and bone marrow. Collectively, macrophages can process around five million red blood cells every second or about 100 trillion heme molecules. But, it is unclear how they are able to handle such enormous volumes. Macrophages isolated from human and mice have been shown to transport heme from damaged red blood cells using a protein called HRG1. To investigate the role HRG1 plays in heme-iron recycling, Pek et al. used a gene editing tool known an CRISPR/Cas9 to remove the gene for HRG1 from the macrophages of mice. If HRG1 is a major part of this process, removing the gene should result in a build-up of toxic heme and eventual death of the mouse. But, rather than dying of heme-iron overload as expected, these mutant mice managed to survive. Pek et al. found that despite being unable to recycle heme, these mice were still able to make new red blood cells as long as they had a diet that was rich in iron. However, the darkening color of the spleen, bone marrow, and liver in these HRG1 deficient mice indicated that these mice were still accumulating high levels of heme. Further experiments revealed that these mice protected themselves from toxicity by converting the excess heme into crystals called hemozoin. This method of detoxification is commonly seen in blood-feeding parasites, and this is the first time it has been observed in a mammal. These crystals invite new questions about how mammals recycle heme and what happens when this process goes wrong. The next step is to ask whether humans also start to make hemozoin if the gene for HRG1 is faulty. If so, this could open a new avenue of exploration into treatments for red blood cell diseases like anemia and iron overload.

Tightly binding valence electron in aluminum observed through X-ray charge density study.

Accurate and high reciprocal resolution experimental structure factors of aluminum were determined from a synchrotron powder X-ray diffraction data measured at 30 K with sin θ/λ < 2.31 Å-1. The structure factors have small deviations from independent atom model in sin θ/λ < 0.83 Å-1. Theoretical structure factors were prepared using density functional theoretical calculations by full potential linearized augmented plane wave method. The deviation between experimental and theoretical data was also observed at around sin θ/λ ≈ 0.4 Å-1. The charge density was determined by an extended Hansen-Coppens multipole modeling using experimental and theoretical structure factors. Charge density maxima at tetrahedral site were observed in both experimental and theoretical deformation density. The charge-density difference peaks indicating directional bonding formation were observed in the difference density between experiment and theory. The present study reveals tight binding like character of valence electron of aluminum. The fact will provide a crucial information for development of high-performance aluminum alloy.

Structural Basis for Polymer Packing and Solvation Properties of the Organogermanium Crystalline Polymer Propagermanium and Its Derivatives.

Of organogermanium compounds known to have an immunostimulatory action, propagermanium [PGe; 3-oxygermylpropionic acid polymer, (C3 H5 GeO3.5 )n] is the only one used as a pharmaceutical agent, to treat the hepatitis B virus in Japan. However, because of lack of information about its structure, PGe has been confused with a polymeric solid, repagermanium (RGe, Ge-132, poly-trans-[(2-carboxyethyl) germasesquioxane], (C18 H30 Ge6 O21 )n), which has the same essential formula as PGe. To clarify this issue, the structure of PGe was analyzed using X-ray diffraction (XRD). PGe has a polymeric ladder-shaped structure of a concatenated eight-membered ring composed of Ge-O bonds, which is clearly distinguished from the infinite sheet structure in RGe. Moreover, we observed temperature or moisture-dependent transformations among these compounds using powder XRD. For instance, PGe was easily dissolved in water, and transformed to RGe by exposure to water vapor, but transformed into another straight-chain structure when exposed to aqueous solution. As a result of these findings, PGe was indicated to have labile polymer packing against RGe. These characteristics of PGe may affect pharmaceutical properties such as respective stability and solubility, which indicate its unique impact on physiological activity.

Solid-state ligand-driven light-induced spin change at ambient temperatures in bis(dipyrazolylstyrylpyridine)iron(II) complexes.

We previously reported that an Fe(II) complex ligated by two (Z)-2,6-di(1H-pyrazol-1-yl)-4-styrylpyridine ligands (Z-H) presented a solid state ligand-driven light-induced spin change (LD-LISC) upon one-way Z-to-E photoisomerization, although modulation of the magnetism was trivial at ambient temperatures (Chem. Commun.2011, 47, 6846). Here, we report the synthesis of new derivatives of Z-H, Z-CN and Z-NO(2), in which electron-withdrawing cyano and nitro substituents are introduced at the 4-position of the styryl group to attain a more profound photomagnetism at ambient temperatures. Z-CN and Z-NO(2) undergo quantitative one-way Z-to-E photochromism upon excitation of the charge transfer band both in acetonitrile and in the solid state, similar to the behavior observed for Z-H. In solution, these substituents stabilized the low-spin (LS) states of Z-CN and Z-NO(2), and the behavior was quantitatively analyzed according to the Evans equation. The photomagnetic properties in the solid state, on the other hand, cannot be explained in terms of the substituent effect alone. Z-CN displayed photomagnetic properties almost identical to those of Z-H. Z-CN preferred the high-spin (HS) state at all temperatures tested, whereas photoirradiated Z-CN yielded a lower χ(M)T at ambient temperatures. The behavior of Z-NO(2) was counterintuitive, and the material displayed surprising photomagnetic properties in the solid state. Z-NO(2) occupied the LS state at low temperatures and underwent thermal spin crossover (SCO) with a T(1/2) of about 270 K. The photoirradiated Z-NO(2) displayed a higher value of χ(M)T and the modulation of χ(M)T exceeded that of Z-H or Z-CN. Z-NO(2)·acetone, in which acetone molecules were incorporated into the crystal lattice, further stabilized the LS state (T(1/2) > 300 K), thereby promoting large modulations of the χ(M)T values (87% at 273 K and 64% at 300 K) upon Z-to-E photoisomerization. Single crystal X-ray structure analysis revealed that structural factors played a vital role in the photomagnetic properties in the solid state. Z-H and Z-CN favored intermolecular π-π stacking among the ligand molecules. The coordination sphere around the Fe(II) nucleus was distorted, which stabilized the HS state. In contrast, Z-NO(2)·acetone was liberated from such intermolecular π-π stacking and coordination distortion, resulting in the stabilization of the LS state.

High-resolution analysis of (Sc3C2)@ C80 metallofullerene by third generation synchrotron radiation X-ray powder diffraction.

The X-ray structure of Sc(3)C(82) is redetermined by the MEM/Rietveld method by using synchrotron radiation powder data at SPring-8, where the C(2) encapsulated structure available to discuss the Sc-Sc interatomic distances has been determined. The encapsulated three scandium atoms form a triangle shape. A spherical charge distribution originating from the C(2) molecule is located at the center of the triangle. Interatomic distances between Sc and Sc are 3.61(3) A in the triangle. The distance between Sc and the center of the C(2) molecule is 2.07(1) A.