Packing Analysis of Carbohydrates and Polysaccharides. 6. Molecular and Crystal Structure of Regenerated Cellulose II
Packing Analysis of Carbohydrates and Polysaccharides. 6. Molecular and Crystal Structure of Regenerated Cellulose II
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DOI：
10.1021/ma60053a027
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发表时间：
1976-09
期刊：
影响因子：
5.5
通讯作者：
A. Stipanovic;A. Sarko
中科院分区：
文献类型：
--
作者：
A. Stipanovic;A. Sarko
采用立体化学填充细化和x射线衍射分析相结合的方法对再生纤维素II （Fortisan）的晶体结构进行了解析。该结构基于反平行链填料和广泛的氢键网络的双链单元胞。后者将两个方向的链连接成薄片，并进一步通过薄片间的氢键连接成三维稳定的结构。氢键是由单位细胞的两个链上的0(6)羟甲基的不相等旋转而达到最大的。利用填充能量最小化和氢键最大化的标准，通过填充分析预测的最可能的结构在所有细节上都与x射线分析确定的结构相同。x射线衍射图中弱奇序子午线的存在可能是由于羟基的旋转无序所致。最终结构的R指数为0.15，表明采用这种结构精化方法可以获得可靠度。纤维素，高等植物的主要结构成分，已知至少以四种多态形式结晶，通常被称为纤维素I， II， III和IV。在这四种形式中，纤维素I和II是工业上最常用的两种形式。因此，对其晶体结构的兴趣几十年来一直很高，但直到最近才确定了天然纤维素I多晶型的晶体结构。这些研究中最有趣的发现是，生物合成纤维素结晶具有平行链极性。
The crystal structure of regenerated cellulose II (Fortisan) has been solved by a combined stereochemi-cal packing refinement and x-ray diffraction analysis. The structure is based on a two-chain unit cell with antiparallel chain packing and an extensive hydrogen bond network. Thelatter links the chains in two directions into sheets and further by intersheet hydrogen bonds into a three-dimensionally stabilized structure. The hydrogen bonding is maxi-mized by unequal rotationsof the 0 (6) hydroxymethyl groups in the two chains of the unit cell. The most probable structure predicted by packing analysis, using thecriteria of minimization of packing energy and maximization of hydrogen bonding, is identical in all details with thestructure refined by x-ray analysis. The presence of weak odd-order meridionals in the x-ray diffraction diagram may be due to rotational disorder of the hydroxymethyl groups. The R index for the final structure is 0.15, which indicates the reliability that can be obtained with this method of structure refinement.Cellulose, the major structural component of higher plants, is known to crystallize in at least four polymorphic forms, commonly known as celluloses I, II, III, and IV. 1 Of the four, celluloses I and II are the two industrially most utilized forms. As such, interest in their crystal structures has re-mained high for many decades but it was only recently that the crystal structure of the native cellulose I polymorph was determined. 2’3 The most interesting finding of these studies was that the biosynthetic cellulose crystallizes with parallel chain polarity.