Structural studies of bacterial cellulose through the solid-phase nitration and acetylation by CP/MAS 13C NMR spectroscopy
Structural studies of bacterial cellulose through the solid-phase nitration and acetylation by CP/MAS 13C NMR spectroscopy
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DOI：
10.1007/s10570-005-9034-z
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发表时间：
2006-01
期刊：
影响因子：
5.7
通讯作者：
Hiroyuki Yamamoto;F. Horii;A. Hirai
中科院分区：
文献类型：
--
作者：
Hiroyuki Yamamoto;F. Horii;A. Hirai
细菌纤维素的固相硝化和乙酰化过程中已主要通过CP/MAS 13 C NMR光谱研究，以澄清这些反应的特点，包括在微纤维的无序组分的表征。细菌和Valoniacellulose样品的CP/MAS ~（13）C NMR谱随硝化过程发生明显变化，与以前报道的棉短绒的情况相似，葡萄糖残基中OH基团的相对反应活性按O（6）H>O（2）H>O（3）H的顺序降低。此外，硝化速率和硝化方式在很大程度上取决于反应介质中硝酸的浓度。在稀释和中等浓度下，O（6）H基团的结晶和无序的组件进行硝化在几乎相同的速率，这表明这两个组件几乎随机分布在每个微纤维的整个区域。硝酸优先渗透到每个微纤维中也发生在硝化之前，在中等浓度下，导致无序组分的摩尔分数增加。相反，所有OH基团在较高浓度下都非常迅速地发生硝化，尽管O（3）H基团的硝化在一定程度上是平稳的。在固相乙酰化中，没有区域选择性的反应性之间观察到的三种OH基团，这可能是由于在每个微纤维中的乙酰化和非乙酰化区域之间的一个非常薄的层中进行的特征反应。在该固相乙酰化中也证实了无序组分在微纤丝的整个区域中的几乎随机分布。在此基础上，对固相反应机理和微纤结构进行了讨论。
The solid-phase nitration and acetylation processes of bacterial cellulose have been investigated mainly by CP/MAS13C NMR spectroscopy to clarify the features of these reactions in relation to the characterization of the disordered component included in the microfibrils. CP/MAS13C NMR spectra of bacterial andValoniacellulose samples are markedly changed as the nitration progresses, in a similar way to the case of cotton linters previously reported; and the relative reactivity of the OH groups in the glucose residues is found to decrease in the order of O(6)H>O(2)H>O(3)H. Moreover, the nitration rate and mode greatly depend on the concentration of nitric acid in the reaction media. At dilute and medium concentrations, the O(6)H groups in the crystalline and disordered components are subjected to nitration at nearly the same rate, indicating that these two components are distributed almost at random in the entire region of each microfibril. The preferential penetration of nitric acid into each microfibril also occurs prior to nitration at the medium concentration, resulting in an increase in the mole fraction of the disordered component. In contrast, all OH groups undergo nitration very rapidly at the higher concentration, although nitration levels off to a certain extent for O(3)H groups. In solid-phase acetylation, no regio-selective reactivity is observed among the three kinds of OH groups, which may be due to the characteristic reaction that proceeds in a very thin layer between the acetylated and nonacetylated regions in each microfibril. The almost random distribution of the disordered component in the entire region of the microfibrils is also confirmed in this solid-phase acetylation. On the basis of these results, the mechanism of the solid-phase reactions and the microfibril structure are discussed.