Kinetics cellulose

In Escherichia coli. Salmonella typhimurium and Aerobacter aerogenes two soluble multi-activity enzymes or enzyme complexes function in the utilisation of chorismate (14) for L-phenyl-alanine and L-tyrosine synthesis An enzyme or enzyme complex (P-protein) containing chorismate mutase and prephenate dehydratase activities has been isolated and partially purified from Escherichia coli. Salmonella typhimurium and Aerobacter aerogenes. The enzyme complex catalyses the transformation of chorismate (14) to phenylpyruvate (32) and both enzymic activities are retained in physical association after chromatography on DEAE cellulose. Kinetic analysis indicated that in isolated enzyme systems direct synthesis of phenylpyruvate (32) from chorismate (14) does not occur. Prephenate (31) once formed dissociates from the enzyme surface and accumulates in the reaction medium. After a lag period it is converted to phenylpyruvate (32). Schmit, Artz and Zalkin also obtained evidence to show that functionally distinct sites (catalytic and regulatory) exist on the P-protein from Salmonella typhimurium for chorismate mutase and prephenate dehydratase activities. The P-protein was obtained from Escherichia coli K-12 by Davidson, Blackburn and Dopheide who showed that it existed in solution mainly as a dimer of similar (and probably identical) sub-units of... 

Seshadri V, Westmoreland PR. Concerted reactions and mechanism of glucose pyrolysis and implications for cellulose kinetics. J Phys Chem A. 2012 116 11997— 12013. 

Another important aspects of solubilization are the physical state of the dissolved polymer as well as the thermo-chemistry and kinetics of the dissolution reaction. It is known that a clear cellulose solution is a necessary, but not sufficient condition for the success of derivatization. The reason is that the polymer may be present as an aggregate, as will be discussed below. Additionally, dissolution of activated cellulose requires less time at low temperature, e.g., 2 h at 40 °C, and more than 8 h at 70 °C [106]. These aspects will be commented on below. 

Bode, H-J, The Use of Liquid Polyacrylamide in Electrophoresis III. Properties of Liquid Polyacrylamide in the Presence of Cellulose Acetate, Analytical Biochemistry 92, 99, 1979. Bowman, CN Peppas, NA, A Kinetic Gelation Method for the Simulation of Free-Radical Polymerizations, Chemical Engineering Science 47, 1411, 1992. 

The isoenzymes can be separated by electrophoresis on cellulose acetate, and Roberts, et al ( ) have described a method whereby the separated isoenzymes are eluted and then assayed kinetically. 

L Westman, T Lindstrom. Swelling and mechanical properties of cellulose hydrogels. IV. Kinetics of swelling in liquid water. J Appl Polym Sci 26 2561-2572, 1981. 

Thermogravimetric analysis (TGA) measures cellulose pyrolytic mass loss rates and activation parameters. The technique is relatively simple, straightforward and fast, but it does have disadvantages. One disadvantage is that determination of the kinetic rate constants from TGA data is dependent on the interpretation/analysis technique used. Another disadvantage of TGA is that the rate of mass loss is probably not equivalent to the cellulose pyrolysis rate. 

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

Thermogravimetric analysis (TGA) has often been used to determine pyrolysis rates and activation energies (Ea). The technique is relatively fast, simple and convenient, and many experimental variables can be quickly examined. However for cellulose, as with most polymers, the kinetics of mass loss can be extremely complex (8 ) and isothermal experiments are often needed to separate and identify temperature effects (9. Also, the rate of mass loss should not be assumed to be related to the pyrolysis kinetic rate ( 6 ) since multiple competing reactions which result in different mass losses occur. Finally, kinetic rate values obtained from TGA can be dependent on the technique used to analyze the data. 

Researchers in previous studies generally used lst-order kinetics to describe cellulose pyrolysis, but rarely have they examined 2nd-order kinetics. Thus, discussion of our results for untreated samples will concentrate on lst-order rate constants so that our results can be directly compared with results from prior studies. A true reaction order of cellulose pyrolysis based on TGA data is essentially meaningless, however, since mass loss involves complex competing multiple reactions (2,4,8). In addition, reaction order was calculated on a dimensionless mass value rather than on the correct but uncalculable molar concentration term. 

Cellulose pyrolysis kinetics, as measured by isothermal TGA mass loss, were statistically best fit using 1st- or 2nd-order for the untreated (control) samples and 2nd-order for the cellulose samples treated with three additives. Activation parameters obtained from the TGA data of the untreated samples suggest that the reaction mechanism proceeded through an ordered transition state. Sample crystallinity affected the rate constants, activation parameters, and char yields of the untreated cellulose samples. Various additives had different effects on the mass loss. For example, phosphoric acid and aluminum chloride probably increased the rate of dehydration, while boric acid may have inhibited levoglucosan... 

In a study of the pectinesterase from bananas,64,85,102 three pectinesterase fractions were obtained after respective extraction with water, 150 mM sodium chloride, and 150 mM sodium chloride of pH 7.5. The fractions obtained were further purified by fractional salting-out with ammonium sulfate, and chromatography on columns of DEAE- and CM-cellulose. A 50-fold purification was achieved, and the individual, purified fractions were characterized with respect to different effects of cations, inhibition by sucrose, and reaction kinetics. 

In the purification of pectinesterase from the fruits of Citrus nat-sudaidai,61 fractional salting-out with ammonium sulfate was followed by chromatography on a column of DEAE-cellulose and by separation of the active fraction on Sephadex G-100. A preparation (purified solution) having a specific activity 460-fold greater than that of the original extract was obtained. Its homogeneity was checked by disc electrophoresis, and its amino acid content was determined and fundamental, kinetic data were obtained. 

The kinetics of homogeneous reaction of several reactive dyes of the vinylsulphone type with methyl-a-D-glucoside (7.9), selected as a soluble model for cellulose, were studied in aqueous dioxan solution. The relative reactivities of the various hydroxy groups in the model compound were compared by n.m.r. spectroscopy and the reaction products were separated by a t.l.c. double-scanning method [38]. The only sites of reaction with the vinylsulphone system were the hydroxy groups located at the C4 and C6 positions [39,40]. 

The kinetics of alkaline hydrolysis of a series of eleven vinylsulphone reactive dyes fixed on cellulose have been investigated at 50 °C and pH 11. Bimodal hydrolytic behaviour was observed under these conditions, the reaction rates being rapid at first but becoming slower as the concentration of fixed dye remaining gradually decreased. These results were attributed to differences in the degree of accessibility of the sites of reaction of the dyes within the fibre structure [87]. 

Figure 6.16 Reconformation of adsorbed cationic polyacrylamide (MW 4 x 106) on cellulose fibres as shown by the kinetics of adsorption and adsorption stoichiometry (measured by counter ion release).

Simmons, G.M., Lee, W.H. Kinetics of gas formation from cellulose and wood pyrolysis, in Fundamentals of Thermochemical Biomass Conversion, Overend, R.P. et al. (Eds.), Elsevier Applied Science, London, pp. 385—395, (1985). 

Miller, R. S. and Bellan, J. (1997) A generalized biomass pyrolysis model based on superimposed cellulose, hemicellulose and lignin kinetics. Comb. Sci. and Techn., 126, 97-137. 

Stability and Performance of Bound En me. The stability of the IME was determined by two methods. One measurement of bound activity was obtained using traditional cellulose hydrolysis experiments (described below). In the other method, direct kinetic parameter measurements were obtained using a recirculating differential (RDR) reactor system following the method of Ford et al. (46). 

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