Cellulose
observed in simulations of cellulose I b (Bergenstra˚hle et al. 2007; Matthews et al. 2011). The intermolecular H-bonds at high temperature were more dynamic and less regular than the relatively stable pattern at room temperature, but remarkably, the intramolecular H-bond O3H3 O5 was found to persist even at 500 K. The regularity of the interchain H-bond arrange- ments in native cellulose suggests that H-bonds have an organizing role in creating the fibril structures. That would not be unique to cellulose since hydrogen bonds define some of the most important structures known to molecular biology: the secondary structure in proteins (Pauling and Corey 1951; Pauling et al. 1951), and the Fig. 2 H-bonding system in two cellulose allomorphs, cellulose Ib and cellulose II. Based on the location of the heavy atoms, several patterns are possible. The figure depicts the one for Ib that is lowest in energy based on simulations, denoted
formation of base-pairs in DNA (Watson and Crick 1953). Yet, it has been argued that even for the structure of DNA, hydrophobic interactions have a strong contributing and perhaps dominant role (Lind- man et al. 2021). Hydrophobic interactions are, however, not specific. This means that even if they constitute a strong thermodynamic driving force to compact moieties together to minimize the total amount of non-polar (‘‘hydrophobic’’) surface area that is exposed to water, hydrophobicity does not, for the same reason, concern the interactions between those molecular surfaces. To create crystalline order, additional interactions that are specific to the type of atoms involved are needed, such as ionic interaction, pattern A. For cellulose II, the sole difference between the patterns is whether OH2 and OH6 act as donor or acceptor, respectively. The orientation of the hydroxymethyl groups is highlighted, denoted tg in cellulose Ib, and gt in cellulose II
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