Inaccessible fibril surfaces

The formation of fibril aggregates leads to a situation where some fibril surfaces are in direct contact. At such contact zones, intermolecular bonds may not develop to the same state found in the crystal lattice of cellulose I. Hence, die contact zone is some kind of geometrical discontinui. The polyglucan chains at such contact zones may possess a characteristic behavior and are herein referred to as inaccessible fibril surfaces (IS) (11). There are other situations diat may lead to the formation of inaccessible fibril surfeces, three such situations are discussed below. 

Direct association of hemicelluloses to accessible fibril surfece present at die fibril aggregate boundary transform accessible fibril surfece to inaccessible fibril surface with the accompanying change in behavior of the affected polyglucan chains. 

In a sense, accessible fibril surfeces and inaccessible fibril surfaces are both geometrical discontinuities compared to the ciystal lattice of cellulose I. The polyglucan chains at both kinds of surfeces may exist in conformations distinct... 

The Gain-of-Interaction model of fibril formation (Elam et al, 2003) proposes that a conformational change in a limited region of the native protein exposes a normally inaccessible interaction surface that drives fibril formation. In these models, the bulk of the protein retains its native... 

Figure 2. Features of the SFAM. A diagrammatic picture showing haw the SFAM models a cross-section through a fibril aggregate (16fibrils surrounded by water). White squares are cross-sections through the individual cellulose I fibrils, gray color represents water. Polyglucan chains (not shown explicitly) are perpendicular to the plane cf the pcper. Annotations within the figure show some example positions of the different cellulose forms, C= crystalline cellulose, PC=para-crystalline cellulose, AS accessible fibril surface, 11 inaccessible...

An important feature of cellulose is its crystalline structure [180], which shows highly ordered crystalline domains interspersed by amorphous regions [177]. The high-crystallinity of cellulose fibrils renders the internal surface of the biopolymer inaccessible to hydrolyzing enzymes, as well as water. 

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