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40 巻 , 5 号
選択された号の論文の9件中1~9を表示しています
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  • 神山 崇
    40 巻 (1998) 5 号 p. 301-307
    公開日: 2010/09/30
    ジャーナル フリー
    入門講座「結晶学の原点を読む」の第2回目は, リートベルト法です.粉末回折法で構造を決定する非常に有力な手段であるリートベルト法は, 現在非常に多くの利用者がおり, 結晶学の分野では欠かせない解析法となっています.この方法の原理は非常に簡単であり, 測定された粉末回折の強度データのパターンと構造モデルから計算された強度のパターンが一致するように最小自乗法でパラメーターを求めるだけです.このように簡単な原理からなっているにもかかわらず, 計算機のプログラムは非常に複雑で多岐に渡っており, 使用している方々のほとんどにとってそのプログラムの中身はまったくブラックボックスであり, かつ出力された結果に対する吟味もどのようにしたら良いかあまりわからず使っている感があります.また, リートベルト自身によるさまざまな物質への適用例は施設報告が多く手に入りにくいものです.そのような中には, 現在の単結晶の実験からみて明らかに間違った結果を出している例も見られます.これも, 当時の技術力と言うよりは, 相転移のような微妙な構造変化の問題を取扱う時, リートベルト法は非常に注意が必要であると言う今日的な問題です.これら, 粉末回折でのリートベルト法の有利な点や適用範囲は何か, また, リートベルト自身がどのような問題点や注意点がこの方法にあると考えていたのかを原著論文で見ることは大変意義があると言えます.今回は, J. Appl. Cryst.に投稿されたリートベルト法の原点とも言える論文を易しく解説していただきます.
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  • 塩野 正明
    40 巻 (1998) 5 号 p. 308-315
    公開日: 2010/09/30
    ジャーナル フリー
    Recent development of crystal structure determination methods enables us to produce ab initio solution for protein crystals. Some such methods are based on reciprocal space direct methods and some of them employs real space density modification methods. One of most successful methods called Shake & Bake is a hybrid of reciprocal and real space methods. This article introduces recently developed methods which have been successfully applied to protein crystals.
    Although many methods described here require atomic resolution data, it is getting possible to collect high resolution data for standard protein crystals with development of data collection technique at low temperature and strong synchrotron X-ray source such as Spring-8.
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  • 保坂 晴美, 田中 勲
    40 巻 (1998) 5 号 p. 316-321
    公開日: 2010/09/30
    ジャーナル フリー
    The structure of ribosomal protein S7 from Bacillus stearothermophilus has been solved at 2.5 Å resolution by multiwavelength anomalous diffraction method using selenomethionyl-substituted proteins. The molecule consists of a helical hydrophobic core domain and a β-ribbon arm extending from the hydrophobic core. The helical core domain is composed of a pair of entangled helix-turn-helix motifs; the fold of the core is similar to that of a DNA architectural factor. Highly conserved basic and aromatic residues are clustered on one face of the S7 molecule and create a 16S rRNA contact surface. The molecular structure of S7, together with the results of previous cross-linking experiments, suggests how this ribosomal protein binds to the 3' major domain of 16S rRNA and mediates the folding of 16S rRNA to create the ribosome decoding center.
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  • 北所 健悟, 三木 邦夫
    40 巻 (1998) 5 号 p. 322-328
    公開日: 2010/09/30
    ジャーナル フリー
    The crystal structure of 8-HDF type photolyase from Anacystis nidulans showed the similarity of the backbone structure with MTHF type E. coli photolyase but completely different binding site of the light-harvesting cofactor. This is a first example that homologous primary and tertiary structures in closely related proteins recognize two different types of cofactors at different binding-sites. The structure and function of photolyase and its cofactor recoginition are reviewed and discussed.
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  • 大庭 卓也
    40 巻 (1998) 5 号 p. 329-334
    公開日: 2010/09/30
    ジャーナル フリー
    The AuCd is one of the typical alloys which show martensitic transformation. There are two distinct martensites called γ2' and ζ2' phases appearing proximate to the composition of Au52.5Cd47.5 and Au50Cd50, respectively. The crystal structure of ζ2' martensite was solved and it was described to be a superposition of transverse waves whose poralization is ‹110› and wave vector is ‹110›. The phonon dispersion relations were observed for Au52.5Cd47.5 and Au50.5Cd49.5 overcoming the difficulty of strong absorption of neutron with an isotope 114Cd. The phonon softening behaviors were observed in addition to the peculiar behavior on Au52.5Cd47.5.
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  • 上江洲 由晃
    40 巻 (1998) 5 号 p. 335-340
    公開日: 2010/09/30
    ジャーナル フリー
    The optical second harmonic generation can be applied to the observation of ferroic domains. In particular, ferroelectric 180° domain structures were successfully observed using a nonlinear microscope termed SHG microscope. The principle utilizes the phase difference of the second harmonic waves produced in domains with opposite polarizations and the interference effect was utilized to make the intensity contrast. Other applications to the J-aagre-gate in monomolecular films and antiferromagnetic domain structure are also possible using the SHG microscope.
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  • 沖津 康平, 上ヱ地 義徳, 小口 拓世, 圓山 裕, 長谷川 祐司, 雨宮 慶幸
    40 巻 (1998) 5 号 p. 341-354
    公開日: 2010/09/30
    ジャーナル フリー
    A new type of energy-tunable X-ray polarimeter has been developed by introducing a Hirano-Ishikawa-Kikuta's transmission-type X-ray phase retarder into an X-ray polarimeter consisting of Hart-Rodrigues' polarizer and analyzer. By using the new type of polarimeter, simultaneous detections of X-ray linear birefringence and dichroism, and simultaneous detections of X-ray linear triple refraction and trichroism, have been made for the first time. The Kramers-Kronig relation has been confirmed in the absolute scale of dielectric constant between linear birefringence and dichroism (and between linear triple refraction and trichroism), which correspond to the real and imaginary parts of dielectric anisotropy, respectively. Phase shift due to the birefringence (or the triple refraction) has been measured with a precision of 2π 110, 000, which is limited mainly by photon-counting statistics.
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  • 新村 信雄
    40 巻 (1998) 5 号 p. 355-356
    公開日: 2010/09/30
    ジャーナル フリー
  • 熊沢 紳太郎, 保坂 晴美, 沖津 康平, 北所 健悟
    40 巻 (1998) 5 号 p. 357-359
    公開日: 2010/09/30
    ジャーナル フリー
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