A revised structure and hydrogen-bonding system in cellulose II from a neutron fiber diffraction analysis
A revised structure and hydrogen-bonding system in cellulose II from a neutron fiber diffraction analysis
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DOI：
10.1021/ja9916254
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发表时间：
1999-11-03
影响因子：
15
通讯作者：
Chanzy, H
中科院分区：
文献类型：
--
作者：
Langan, P;Nishiyama, Y;Chanzy, H
用中子衍射数据修正了纤维素Ⅱ的晶体结构、分子结构和氢键体系，所用的中子衍射数据从两种高度结晶的丝光亚麻纤维样品中获得，其分辨率可达1.2埃。一种样品在NaOH/H_2O中丝光，另一种样品在NaOD/D_2O中丝光，对应于不稳定的羟甲基部分分别被氢化和氘代。傅立叶差分图计算，其中中子差幅与从两个修订的纤维素II，A和B '的X射线模型计算的相位相结合。通过使用LALS方法对Kolpak和Blackwell的X射线数据集进行细化，确定了修订的定相模型（8）。(37)模型A和B'都有两个以P2（1）空间群组织的反平行链和晶胞参数：a = 8.01埃; B = 9.04埃，c = 10.36埃，γ = 117.1度。(15)模型A具有两条链的等效骨架构象，但羟甲基部分的构象不同：起始链为gt，中心链为fg。基于纤维四糖的最新晶体结构的模型B '（21-23）对于两个链具有不同的构象，但对于羟甲基部分具有几乎相等的构象。仅根据X线数据，无法区分模型A和模型B'。根据中子傅里叶差分图，确定了每个模型可能的不稳定氢原子位置，并使用LALS进行了细化。我们能够淘汰模型A而采用模型B '。为模型B'确定的氢键方案与先前基于纤维四糖的晶体结构、（21-23）纤维素II的MD模拟、（25）以及在早期X射线纤维衍射研究中确定的纤维素II结构中的任何潜在氢键网络的提议显著不同。（7，8）给出并讨论了参与这种键合的不稳定氢原子的精确定位以及它们的供体和受体特性。这项研究首次提供了纤维素II中所有原子的坐标。
The crystal and molecular structure and hydrogen bonding system in cellulose II have been revised using new neutron diffraction data extending to 1.2 Angstrom resolution collected from two highly crystalline fiber samples of mercerized flax, Mercerization was achieved in NaOH/H2O for one sample and in NaOD/D2O for the other, corresponding to the labile hydroxymethyl moieties being hydrogenated and deuterated, respectively. Fourier difference maps were calculated in which neutron difference amplitudes were combined with phases calculated from two revised X-ray models of cellulose II, A and B'. The revised phasing models were determined by refinement against the X-ray data set of Kolpak and Blackwell,(8) using the LALS methadology.(37) Both models A and B' have two antiparallel chains organized in a P2(1) space group and unit cell parameters: a = 8.01 Angstrom; b = 9.04 Angstrom, c = 10.36 Angstrom, and gamma = 117.1 degrees.(15) Model A has equivalent backbone conformations for both chains but different conformations for the hydroxymethyl moieties: gt for the origin chain and fg for the center chain. Model B', based on the recent crystal structures of cellotetraose,(21-23) has different conformations for the two chains but nearly equivalent conformations for the hydroxymethyl moieties. On the basis of the X-ray data alone, model A and model B' could not be differentiated. From the neutron Fourier difference maps, possible labile hydrogen atom positions were identified for each model and refined using LALS. We were able to eliminate model A in favor of model B'. The hydrogen-bonding scheme identified for model B' is significantly different from previous proposals based on the crystal structures of cellotetraose,(21-23) MD simulations of cellulose II,(25),and any potential hydrogen-bonding network in the structure of cellulose II determined in earlier X-ray fiber diffraction studies.(7,8) The exact localization of the labile hydrogen atoms involved in this bonding, together with their donor and acceptor characteristics, is presented and discussed. This study provides, for the first time, the coordinates of all of the atoms in cellulose II.