PubMed Health⌕ Search

Biomedical subjects

Masaki Takata

Publications and source records attributed to Masaki Takata.

At least 19 recordsLinked to original sources
PubMed2006

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.

Journal Article↗
PubMed2006

Stable top-up operation at SPring-8.

Top-up operation allows SPring-8 to provide highly stable X-ray beams with arbitrary filling patterns. The implementation of top-up operation is described, with a focus on the simultaneous achievement of stability of stored current, beam orbit, purity of an isolated single bunch, and beam injection efficiency. Stored-current fluctuations have been routinely reduced to a level of 10(-3). Stored-beam oscillation on frequent beam injection, which was originally regarded as the most serious problem, has been successfully suppressed to a sufficiently low level that it never perturbs imaging experiments. Current impurities in nominally empty buckets have been reduced to a level of 10(-9) over more than one week of operation, making possible the measurement of time-resolved spectra using high-current bunches. Finally, excellent injection efficiency, higher than 80%, is routinely obtained, even for small undulator gaps, which is critical for preventing radiation damage to insertion-device magnets and to reduce leakage radiation. The process of achieving highly stabilized top-up operation at SPring-8 and its utility for user experiments are described.

Electrons↗
PubMed2006

Single structure widely distributed in a GeTe-Sb2Te3 pseudobinary system: a rock salt structure is retained by intrinsically containing an enormous number of vacancies within its crystal.

GeTe(1-x)-Sb2Te3(x) sputtered amorphous film was crystallized into a simple NaCl-type structure through instantaneous laser irradiation over a wide composition range from x = 0 to at least 2/3. When the ratio of Sb2Te3 increases, a vacancy is generated at every Na site for two Sb atoms. The fraction of vacancies, v(x), changes according to x/(1 + 2x), and the cubic root unit cell volume varies with a strong correlation to v(x). Through these created vacancies, valence electrons provided by adjacent Ge/Sb and Te atoms remain constant regardless of the composition, ensuring that these electrons occupy predominantly the bonding molecular orbitals. This results in crystal chemical stability, with the closed shell p-p bondings in the valence electrons arranging the crystal's atomic configuration into an NaCl-type structure.

Journal Article↗
PubMed2005

Structure basis for antitumor effect of aplyronine a.

Aplyronine A, isolated from the sea hare Aplysia kurodai, possesses an exceedingly potent antitumor effect in vivo and it is one of the promising candidates as an anticancer drug. This macrolide is known to depolymerize F-actin and inhibit the polymerization of actin by forming a 1:1 complex with monomeric actin. The first complex structure of actin-aplyronine A was determined via a synchrotron X-ray analysis at a 1.45 A resolution. As expected, aplyronine A binds to a hydrophobic cleft composed of subdomains 1 and 3 of actin by intercalating its aliphatic tail part into the actin molecule as do the other reported F-actin depolymerizing agents. Unexpectedly, this complex structure shows the specific structural features around the trimethylserine moiety, revealed as an important moiety of aplyronine A for cytotoxicity against HeLa cells. Combining this result and our previous one, the moiety should strongly relate to the specific biological activity of aplyronine A; i.e. a potent antitumor effect.

Actins↗
PubMed2005

Formation and characterization of crystalline molecular arrays of gas molecules in a 1-dimensional ultramicropore of a porous copper coordination polymer.

Molecules and atoms confined in a nanospace may have properties distinctly different from those of the bulk fluid, owing to the formation of a specific molecular array characteristic of nanospace. In situ synchrotron powder X-ray diffraction measurements have been used to observe confined guest molecules such as N2, O2, Ar, and CH4 in the well-regulated ultramicropore of a copper coordination polymer, 1 ([Cu2(pzdc)2pyz]: pzdc = 2,3-pyrazinedicarboxylate and pyz = pyrazine). The obtained crystal structures indicate that guest molecules are confined in a linear fashion to form crystalline-like regular ordered arrays, in contrast to the situation in the gas and liquid state, even at temperatures above the boiling point, and the ordered arrays are characteristic of the kind of gas molecule and the geometrical and potential properties of the ultramicropore of 1.

Journal Article↗
PubMed2005

Low-spin state structure of [Fe(chloroethyltetrazole)6](BF4)2 obtained from synchrotron powder diffraction data.

The complex [Fe(teec)6](BF4)2 (teec = chloroethyltetrazole) shows a two-step complete spin-crossover transition in the temperature range 300-90 K. Time-resolved synchrotron powder diffraction experiments have been carried out in this temperature range, and crystal structure models have been obtained from the powder patterns by using the parallel tempering technique. Of these models, the low-spin state structure at 90 K has been refined completely with Rietveld refinement. Its structural characteristics are discussed in relation to the high-spin state model and other spin-crossover compounds. The complex shows a remarkable anisotropic unit-cell parameter contraction that is dependent on the applied cooling rate. In addition, the possible important implications for the interpretation of spin-crossover behavior in terms of structural changes are discussed.

Journal Article↗
PubMed2005

Highly controlled acetylene accommodation in a metal-organic microporous material.

Metal-organic microporous materials (MOMs) have attracted wide scientific attention owing to their unusual structure and properties, as well as commercial interest due to their potential applications in storage, separation and heterogeneous catalysis. One of the advantages of MOMs compared to other microporous materials, such as activated carbons, is their ability to exhibit a variety of pore surface properties such as hydrophilicity and chirality, as a result of the controlled incorporation of organic functional groups into the pore walls. This capability means that the pore surfaces of MOMs could be designed to adsorb specific molecules; but few design strategies for the adsorption of small molecules have been established so far. Here we report high levels of selective sorption of acetylene molecules as compared to a very similar molecule, carbon dioxide, onto the functionalized surface of a MOM. The acetylene molecules are held at a periodic distance from one another by hydrogen bonding between two non-coordinated oxygen atoms in the nanoscale pore wall of the MOM and the two hydrogen atoms of the acetylene molecule. This permits the stable storage of acetylene at a density 200 times the safe compression limit of free acetylene at room temperature.

Journal Article↗
PubMed2004

Guest shape-responsive fitting of porous coordination polymer with shrinkable framework.

In situ synchrotron X-ray powder diffraction patterns of porous coordination polymers [[Cu(2)(pzdc)(2)(bpy)].G] have been measured (pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4'-bipyridine) (where G = H(2)O for CPL-2 superset H(2)()O, G = benzene for CPL-2 superset benzene, and G = void for the apohost). The structures of apohost and CPL-2 superset benzene were determined from Rietveld analysis. Adsorption of benzene in the channels induced a remarkable contraction in the crystal (b axis; 6.8%, volume; 4.9%), although the channels were occupied by the benzene molecules. This crystal transformation provides a new pore structure that is well suited for benzene molecules, and we denote it as a "shape-responsive fitting" transformation. This type of pore gives rise to a new guideline: frameworks can be composed of flexible motifs that are linked via strong bond and/or stiff motifs that are connected via weaker bonds.

Journal Article↗
PubMed2004

1-D cobalt(II) spin transition compound with strong interchain interaction: [Co(pyterpy)Cl(2)].X.

Cobalt(II) compounds [Co(pyterpy)Cl(2)].MeOH (1.(MeOH)) and [Co(pyterpy)Cl(2)].2H(2)O (1.(2H(2)O)) were synthesized. The compound 1.(MeOH) forms the quasi 3-D networks by making pi-pi stacking between the 1-D chains. The methanol molecules from 1.(MeOH) can be removed by heating, and substituted by absorption of water molecules. The MeOH molecules in 1.(MeOH) are removed by heating at 410 K, and they are substituted by water molecules to form 1.(2H(2)O). 1.(2H(2)O) exhibits a S = (3)/(2) (HS) left arrow over right arrow S = (1)/(2) (LS) spin transition with a thermal hysteresis. We have succeeded in constructing a guest dependent 1-D spin-crossover cobalt(II) compound.

Journal Article↗