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  • 1
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spontaneous hydrolysis of p-nitrobenzyl cellulose xanthate (CelXNB) with a degree of substitution (DS) in the range 2-9 was studied in 10% aqueous ethanol at pH 10, and was followed spectrophotometrically by the appearance of p-nitro-α-toluenethiol, in a continuous-flow system where the reactor was shaken. CelXNB was characterized by solid-state 13C NMR spectra. The reaction occurs through two parallel processes due to two xanthate ester groups with different reactivities. The fast hydrolysis was ascribed to the reaction of the C-2 + C-3 isomers, whereas the slow hydrolysis was due to the C-6 isomer. The percentage of the latter is much higher than C-2 + C-3. The solvent isotope effect of the fast hydrolysis (k′H2O/)k′H2D 11 was 2·22 ± 0·16 and the proton inventory indicated that there is only one proton transfer involved in the transition state, where a second water (or a neighbouring OH group) acts as a general base. The entropy of activation of the fast hydrolysis was only 3·3 ± 0·8 e.u., suggesting that the water molecules involved are highly oriented with respect to the coordinates required to reach the transition state. It is proposed that they form part of the three-dimensional hydrogen-bonded ice-like structure that involves the cellulose matrix.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: P-Nitrobenzyl cellulose xanthate (CelXNB) was obtained with a degree of substitution (DS) in the range 0.5-3. The first order rate constant for hydrolysis of CelXNB at 25°C, extrapolated to zero buffer concentration, is hydroxide ion catalysed, whereas the water-catalyed path is about 2000 times faster than that observed for p-nitrobenzyl ethylxanthate (EXNB), probably owing to the highly ordered cybotactic region of cellulose. Aminolysis of CelXNB produces the corresponding thioncarbamate ester; for simple alkylamines, the second-order rate constants are similar to those obtained for EXNB. The secod-order rate constants are similar to those obtained for EXNB. The second-order rate constants at pH 11 for immobilization of bacterial α-amylase and bovine serum albumin were 13.4 and 112 1 mol-1 s-1, respectively, unexpectedly high values when compared with simple alkylamines, even considering the concentration of external reactive groups of the proteins. CelXNB with low DS should release 1 mol of p-nitro-α-toluenethiol for every mole of protein that becomes immobilized. The net weight increase of the cellulose matrix allows the calculation of the absolute molecular weight of the protein. Preliminary results support this assumption.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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