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Abstract

The paper describes molecular dynamics (MD) simulations on the crystal structures of the Ibeta and II phases of cellulose. Structural proposals for each of these were made in the 1970s on the basis of X-ray diffraction data. However, due to the limited resolution of these data some controversies remained and details on hydrogen bonding could not be directly obtained. In contrast to structure factor amplitudes in X-ray diffraction, energies, as obtained from MD simulations, are very sensitive to the positions of the hydroxyl hydrogen atoms. Therefore the latter technique is very suitable for obtaining such structural details. MD simulations of the Ibeta phase clearly shows preference for one of the two possible models in which the chains are packed in a parallel orientation. Only the parallel-down mode (in the definition of Gardner and Blackwell (1974) J Biopolym 13: 1975-2001) presents a stable structure. The hydrogen bonding consists of two intramolecular hydrogen bonds parallel to the glycosidic linkage for both chains, and two intralayer hydrogen bonds. The layers are packed hydrophobically. All hydroxymethyl group are positioned in the tg conformation. For the cellulose II form it was found that, in contrast to what seemed to emerge from the X-ray fibre diffraction data, both independent chains had the gt conformation. This idea already existed because of elastic moduli calculations and 13C-solid state NMR data. Recently, the structure of cellotetraose was determined. There appear to be a striking similarity between the structure obtained from the MD simulations and this cellotetraose structure in terms of packing of the two independent molecules, the hydrogen bonding network and the conformations of the hydroxymethyl group, which were also gt for both molecules. The structure forms a 3D hydrogen bonded network, and the contribution from electrostatics to the packing is more pronounced than in case of the Ibeta structure. In contrast to what is expected, in view of the irreversible transition of the cellulose I to II form, the energies of the Ibeta form is found to be lower than that of II by 1 kcal mol(-1) per cellobiose.

Thermal decomposition of mercerized linter cellulose and its acetates obtained from a homogeneous reaction

“…The flask was immersed in an oil bath, the pressure was reduced (2 mm Hg) and the oil bath temperature was heated from room temperature to 110 °C at 3 °C/min. The oil bath temperature was externally controlled (FE50RP controller, Flyever, The cellulose I chains has a higher mobility, when swelled by NaOH, allowing them to rotate about their axes, producing the antiparallel structure, characteristic of cellulose II [19] . This change is due to the fact that the hydroxymethyl group (-CH 2 OH) can assumes different conformations, generating two different packing structures of cellulose chains in a microcrystal.…”

“…The parallel chain structure, characteristic of cellulose I, occurs when the -adjacent chains have the CH 2 OH groups in the same conformation. The antiparallel structure, characteristic of cellulose II, occurs when the adjacent chains have the -CH 2 OH groups in different positions [11,19] .…”

“…In cellulose I (untreated linters), whose chains are orientated in parallel, the -CH 2 OH groups of adjacent chains have the same conformation, while in cellulose II (mercerized linters), the adjacent chains have these groups in different positions (antiparallel structure) [11,[18][19][20][21] . Despite the lower crystallinity of mercerized linters, due to the different -CH 2 OH group orientations in cellulose II, the hydrogen bonds among their chains are stronger than those of the cellulose I chains (untreated linters), which results in cellulose II being a more stable structure compared to cellulose I.…”

Effects of Supplementary Alkali after Alkaline Peroxide Treatment on the Properties of Bleached Kraft Pine Fluff Pulp

“…This indicated that the crystalline type of the fiber tended to vary from cellulose I structure to cellulose II structure when it was treated using the two-step chemical treatment. According to studies by Kroon-Batenburg and Kroon (1997) and Zugenmaier (2001), the crystalline type of the cellulose II structure was rather active, and its crystallites' sizes were rather larger than those of cellulose I structure, which meant accessibility to a solvent for the fiber was superior with a cellulose II structure. As a result, the absorbability of the fluff pulp fiber was increased when using a two-step chemical treatment.…”

Detergent-Compatible Purified Endoglucanase from the Agro-Industrial Residue by Trichoderma harzianum under Solid State Fermentation

“…The formation of cellulose fibers constitutes approximately 30 entities of cellulose molecules in each subunit assembled to produce large units known as microfibrils. Ultimately, these micro-fibrils assemble to make long cellulose fibers (Koyama et al 1997;Kroon-Batenburg and Kroon 1997).…”