Internal mobility, cellulose

The freedom to vary < ) and i so extensively—even if exaggerated here owing to the absence of other molecules—renders cellulose fragments such as an octamer, surprisingly flexible. Cellulose is generally considered to be a stiff molecule, but at least single-molecule simulations in vacuum at 400 K show it to have considerable internal mobility. The range of conformations that result from this mobility are quite apparent when the molecular shape is... 

The extensibility of the swollen objects depends on the conditions of preparation and on the degree of swelling, but lies in the order of magnitude of 100% (for the air-dry filaments, which contain about 15% water, the extensibility is usu Jly smaller and below 100%). Fully dried filaments cannot be extended at all, they are hard and brittle as glass and can be pulveris ed in a mortar. The presence of water is essential in order to make a cellulose gel deformable. Dry cellulose is comparable with rubber cooled to temperatures far below 2 ero, say — 100°. In both cases the cohesion between the chains is so considerable that there is no more question of an internal mobility, which is essential in order to render large deformations possible,... 

A full interpretation of the relationships between direct or vat dye structure and substantivity for cellulose must take into account the contribution of multilayer adsorption of dye molecules within the pore structure of the fibre [71]. The great difference in substantivity between Cl Direct Red 28 (3.66) and the monoazo acid dye (3.67) that is the half-size analogue of this symmetrical disazo dye may be interpreted in terms of their relative tendencies to form multilayers within the fibre pores as a result of dye-dye aggregation. Saturation adsorption values of these two dyes on viscose fibres at pH 9 and 50 °C corresponded to monolayer coverage areas of approximately 90 and 11 m2/g of internal surface respectively [72]. In view of the smaller molecular area and greater mobility of the half-size acid dye, higher uptake than the direct dye would be anticipated if there were only a limited area of internal surface available for true monolayer adsorption. 

A mixture of proteins is separated on a column with a stationary phase of carboxymethylated cellulose. The internal diameter of the column is 0.75 cm and its length is 20 cm. The dead volume is 3 ml. The flow rate of the mobile phase is 1 ml/min. The pH of the mobile phase is adjusted to 4.8. Three peaks appear upon the chromatogram corresponding to the elution volumes V, V2 and V2 at 12 ml, 18 ml and 34 ml respectively. 

The substrate, 4-(6-methoxy-2-benzoxazolyl)acetophenone, the R and S enantiomers of the product, 4-(6-methoxy-2-benzoxazolyl)phenethyl alcohol, and the internal standard, 3-acetyl-7-(dimethylamino)coumarin, were separated by chromatography on a cellulose-based chiral column (Chiracel OD from Daicel). The mobile phase was a 93 7 mixture (v/v) of n-hexane and 2-propanol, which was used at ambient temperature and a flow rate of 1.2 mL/ min. Detection of the enantiomeric alcohols and the internal standard was by fluorescence, with excitation and emission wavelengths of 315 and 375 nm, respectively. 

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