Accessibility cellulose

Grafting presents a means of modifying the cellulose molecule through the creation of branches of synthetic polymers, which impart to the cellulose certain desirable properties without destroying the properties of cellulose. The polymerization of vinyl monomers may be initiated by free radicals or by certain ions. Depending on the monomer, one or the other type of initiation may be preferred. The grafting process depends on the reactivity of the monomer used, the type of initiation, and cellulose accessibility [1,2]. 

Processes need to be developed to expose LHC for effective penetration of chemicals that promote separation of LHC or which render cellulose accessible by swelling. These processes can have many objectives (1) to get at cellulose (2) to remove hemicellulose from the reaction site before cellulose hydrolysis (3) to remove lignin from the site and (4) to bring penetrating or hydrolysis agents into effective contact with cellulose. 

Kelsey, R. G. and F. Shafizadeh, "Enhancement of Cellulose Accessibility and Enzymatic Hydrolysis by Simultaneous Wet Milling," Biotechnol. Bioeng. 22 (1980) 1025-1036. 

Another variant of this method has been used by Howell2 for estimating the surface of cellulose accessible to coloured salt such as cobalt chloride. Filter paper is soaked in solutions of different concentrations, and dried the amount of coloured salt on the total surface is thus known, the volume of solution taken up being observed. On examining the absorption spectrum of the now coloured cellulose it is found that, for the first portions of salt deposited, the intensity of the colour increases almost linearly up to a certain critical amount deposited and only slowly thereafter assuming that this critical amount is a layer one molecule thick on the surface, the available surface was found to be about 85 times the apparent surface, as measured microscopically. 

Figure 14. Relationship between the initial rate of reaction and the surface area of cellulose accessible to molecules of different sizes...

Methyl Cellulose, http //en.wikipedia.org/wiki/Methyl cellulose (accessed March 2013). 

Meng, X. and Ragauskas, A.J. (2014) Recent advances in understanding the role of cellulose accessibility in enzymatic hydrolysis of lignocellulosic... 

The removal of lignin not only increases cellulose accessibility but also enhances cellulase availability. Lignin and its complexes physically and chemically resist enzymatic attack, and condensed lignin also has the ability to adsorb protein from aqueous solutions (50). Thus, it appears that lignin removal not only opens up more space for enzymes but also reduces non-specific enzyme adsorption, improving the efficacy of hydrolysis (41, 51,52,53,54). 

The ( >PAsc - Avicel difference varied among cellulases, indicating differential cellulose accessibility of these cellulases, even when they were close structural/functional analogs. For instance, T. reesei CBH-I had a < i on PASC 3 times larger than that on Avicel, but H. insolens CBH-I had a i > on PASC 26 times larger dian that on Avicel. 

Jeoh T, Ishizawa Cl, Davis ME, Himmel ME, Adney WS, Johnson DK. (2007). Cellulase digestibility of pretreated biomass is limited by cellulose accessibility. Biotechnol Bioeng, 98(1), 112-122. 

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