Microcrystalline cellulose structure

The purpose of this study is only intended to illustrate and evaluate the decision tree approach for CSP prediction using as attributes the 166 molecular keys publicly available in ISIS. This assay was carried out a CHIRBASE file of 3000 molecular structures corresponding to a list of samples resolved with an a value superior to 1.8. For each solute, we have picked in CHIRBASE the traded CSP providing the highest enantioselectivity. This procedure leads to a total selection of 18 CSPs commercially available under the following names Chiralpak AD [28], Chiral-AGP [40], Chiralpak AS [28], Resolvosil BSA-7 [41], Chiral-CBH [40], CTA-I (microcrystalline cellulose triacetate) [42], Chirobiotic T [43], Crownpak CR(-i-) [28], Cyclobond I [43], DNB-Leucine covalent [29], DNB-Phenylglycine covalent [29], Chiralcel OB [28], Chiralcel OD [28], Chiralcel OJ [28], Chiralpak OT(-i-) [28], Ultron-ES-OVM [44], Whelk-0 1 [29], (/ ,/ )-(3-Gem 1 [29]. 

Both inorganic and organic sorbent materials are suitable for apphcation in partition PLC. The relevant material in this connection is cellulose. Celluloses are natural products with the universal chemical formula (CgHioOj),. These native celluloses have a fibrous structure and they need to be groimd and purified before use in PLC. Besides native cellulose, microcrystalline cellulose can also be used in partition PLC. In this case the cellulose has been recrystaUized and is rod-shaped. The specific surface area of celluloses is in the range of about 2 m /g. 

The first practical CSP derived from polysaccharides is cellulose triacetate (21, Figure 3.10) prepared by Hesse and Hagel in 1973.94,95 Since this derivative was prepared by the heterogeneous acetylation of native microcrystalline cellulose (Avicel) in benzene, it has been postulated that its structure is closely related to that of native cellulose (form I). This has been called microcrystalline cellulose triacetate (CTA-I). CTA-I shows characteristic chiral... 

In an attempt to separate the domains from the cores, we used limited degradation with several proteases. CBH I (65 kda) and CBH II (58 kda) under native conditions could only be cleaved successfully with papain (15). The cores (56 and 45 kda) and terminal peptides (11 and 13 kda) were isolated by affinity chromatography (15,16) and the scission points were determined unequivocally. The effect on the activity of these enzymes was quite remarkable (Fig. 7). The cores remained perfectly active towards soluble substrates such as those described above. They exhibited, however, a considerably decreased activity towards native (microcrystalline) cellulose. These effects could be attributed to the loss of the terminal peptides, which were recognized as binding domains, whose role is to raise the relative concentration of the intact enzymes on the cellulose surface. This aspect is discussed further below. The tertiary structures of the intact CBH I and its core in solution were examined by small angle X-ray scattering (SAXS) analysis (17,18). The molecular parameters derived for the core (Rj = 2.09 mm, Dmax = 6.5 nm) and for the intact CBH I (R = 4.27 nm, Dmax = 18 nm) indicated very different shapes for both enzymes. Models constructed on the basis of these SAXS measurements showed a tadpole structure for the intact enzyme and an isotropic ellipsoid for the core (Fig. 8). The extended, flexible tail part of the tadpole should thus be identified with the C-terminal peptide of CBH I. 

Atypical Spherazole CR system is a tablet that consists of a sandwiched structure as shown in Figure 22.14. Such a system was prepared by the following procedures The water-insoluble drug itraconazole is layered onto microcrystalline cellulose with Eudragit E100 as a binder to form... 

Badawy SF, Gray DB, Hussain MA. 2006. A study of the effect of wet granulation on microcrystalline cellulose particle structure and performance. Pharm. Res. 23(3) 634-640. 

In natural cellulose, the microcrystals are packed tightly in the fiber direction in a compact structure resembling bundles of wooden match sticks placed side by side. Unhinging the interconnecting chains by acid treatment does not destroy this structure. However, the unhinged crystals are now free to be dispersed by mechanical disintegration.. . . We immediately set out to explore this new avenue, developing uses for colloidal dispersions of microcrystalline celluloses, known commercially as Avicel. 

Johansson B, Wikberg M, Ek R, et al. Compression behavior and crunpactability of microcrystalline cellulose pellets in relationship to their pore structure and mechanical properties. Int J Pharm 1995 117 57-73. 

Nilsson M, Mihranyan A, Valizadeh S, et al. Mesopore structure of microcrystalline cellulose tablets characterized by nitrogen adsorption and SEM the influence on water-induced ionic conduction. J Phys Chem B 2006 110 15776-15781. 

Colloidal, aqueous dispersions of microcrystalline cellulose can be prepared by boiling cotton linters for 15 minutes with 2.5 N hydrochloric acid, followed by subjecting the resulting (level-off D.P.) cellulose to vigorous mechanical agitation. The microcrystals ( Avicel ), which are thereby freed from their fibrous packed structure, have been put to a variety of uses in the production of food gels and structural materials. ... 

Figure 4. Electron micrographs of crystals of cellulose prepared at 90 C after shadowing with W/Ta. 4A from Avicel (DP 120) cellulose solution the structure consists of rod-like elements together with granular aggregates (arrows). Insert corresponding X-ray diagram. from microcrystalline cellulose (DP 34)solution. Insert corresponding electron diffraction diagram.

In all these studies, microcrystalline cellulose was used as the solid powdered substrate. The structural formula of cellulose is presented in Figure 18. 

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