Meyer-Misch cell

Fig. 7.—Schematic Diagram Showing the Interrelationship of Base-plane Packing for Three Unit cells of Native Cellulose. (The one in heaviest outline is the Meyer-Misch cell. The cell proposed for Valonia cellulose is twice as large in the base-plane dimensions. The third cell, having a angle of 93°14 is another proposal. )...

Fig. 3. —Diagrammatic Representation of Stacks of Cellulose Chains and Their Possible Aggregation.94 [Each cellulose chain is ribbon-like and approximately oval in cross-section (labeled) the view is down the ribbon. Note that the stacks are labeled as sheets in the drawing, after the original authors, b = fiber and chain axis, which is perpendicular to the plane of this diagram and therefore not shown a and c are the other edges of the Meyer-Misch cell.]...

The unit cell of cellulose from Chaetomorpha melagonium is monoclinic, with a = 16.43 A (1.643 nm), b(fiber axis) = 10.33 A (1.033 nm), c = 15.70 A (1.570 nm), and /3 = 96.97°. In base-plane projection, each of the Meyer-Misch subcells that make up the super-lattice are identical. All equatorial reflections can be indexed by using a one-chain unit-cell, meaning that every single chain has... 

Neutron diffraction studies of cellulose I (cotton crystallites) showed that the a andc dimensions (b is the fiber axis) of the conventional unit-cell should be doubled. The dimensions deduced are a = 1.678 nm, b (fiber axis) = 1.03 nm, c = 1.588 nm, and /3 = 82°. These are the same as the values proposed by Honjo and Watanabe,33 except that the b dimension is less than the value of 1.058 nm proposed by them. It was found that, in the region of 101, 101, and 002 reflections, there are a number of additional reflections that cannot be indexed by using the Meyer-Misch unit cell, but they can be indexed as 102, 102, 211, 211, 203, 203, 121, and 121 by using the larger cell. 

Electron-diffraction measurements on cellulose microfibrils from Valonia show that the reciprocal-lattice points can be indexed, not by a Meyer-Misch unit cell, but by a unit cell having a and c periods twice as long. - This finding has been confirmed, and it is suggested that, although bacterial cellulose probably has the same unit cell, other native celluloses might differ. 

The refinement (2) proceeded in the same way as for the x-ray work, except that o and S q were refined as additional variables. We assumed that the scattering was kinematic. The cross sectional dimensions of the microfibrils are 200xl0C)X and our previous work on synthetic polymer single crystals showed that the kinematic approximation was adequate for such small crystallites. Intensity measurement presented considerable difficulty in that multiple film exposures could not be obtained. Sequential exposures of the same area of the specimen led to problems of beam damage, and patterns from different areas were not comparable due to differences in the preferred orientation. As a result, only the 28 strongest non-meridional intensities could be measured. These were all for reflections which could be indexed by the Meyer and Misch unit cell, and thus the two chain unit cell was used for the refinement. 

Monoclinic unit cell of cellulose I according to the model by Meyer and Misch [37], which shows the antiparallel orientation of adjacent chains (left) and the hydrogen-bonding network of two adjacent cellulose chains forming a sheet-like structure according to Gardner and Blackwell [38]... 

Fig. 75. Unit cell of cellulose I according to Meyer and Mark [21], Mark and Misch [22].

Cellulose I is natural cellulose as found in cotton, wood, and Valonia. Although the Meyer and Misch structure (unit-cell dimensions a = 8.35,... 

Other workers (19-20) have interpreted these differences in the NMR spectra and other data in alternative ways. They believe that celluloses I and II have the same skeletal conformation but are packed in different lattices. In this theory, the differences within the cellulose I family are derived from the size of the unit cells. Valonia contains a larger 8 chain unit cell, whereas ramie contains a mixture of the 8 chain unit cell and the smaller Meyer and Misch unit cell. Therefore the interpretation of the NMR spectra remains controversial. 

Studies on highly crystalline algal cellulose led to a reopening of the question of the unit cell and space group proposed by Meyer and Misch. In particular, electron diffraction studies, made at low temperature on Valonia cellulose, produced results that were incompatible with both fire unit-cell dimensions and the space-group symmetry proposed previously. The results, confirmed by independent studies, contradicted the two-fold symmetry of the ehain, and suggested that Valonia cellulose had the space group Pi and a triclinic unit cell. " ... 

Another class of polymers that occupied 165 pages in the book and many years of effort by Meyer and his collaborators is the celluloses. The detailed X-ray crystallography that resolved the local and mesoscopic structure of cellulose and its micelles is presented in detail. His chief collaborators included Herman Mark, J.R. Katz, Michael Polanyi, L. Misch and G. von Susich. A detailed model of the unit cell of native cellulose is given in Fig. 3.13. 

Cellulose is the most plentiful natural polymer on earth. Studies of structure of cellulose goes back as early as 1839 well before the development of X-ray diffraction. After the coming of X-ray diffraction in the years following 1912, extensive X-ray diffraction studies of cellulose were reported. Various researchers have proposed models of the crystal structure dating from the 1920s. Sponsler and Dore [115] proposed a unit cell as early as 1926. Different crystal structures were proposed by Meyer and Mark [ 116] in 1928 and by Meyer and Misch [ 117] in 1937. Meyer and Misch [117] reported a new crystallographic model of cellulose that is monoclinic, a = 8.35 A, b = 10.38 A, c = 7.95 A, p = 84°. Cellulose today is considered to be polymorphic and to have a (triclinic) and p (monocHnic) forms. 

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