THE MOLECULAR WEIGHT DISTRIBUTIONS OF BACTERIAL CELLULOSE AS A FUNCTION OF SYNTHESIS TIME.

摘要

The kinetics of the biosynthesis of isolatable bacterial cellulose produced by the organism Acetobacter xylinum was investigated by monitoring the yield, the number-average molecular weight and the weight-average molecular weight as functions of synthesis duration. The simultaneous measurement of all three parameters made it possible to observe the increase in the number of polymers as well as their relative degree of elongation at any given time. The experimental objective of this study was to test the hypothesis whether or not cellulose polymers are stochastically polymerized from monomeric or polymeric cellulose precursors that are not directly connected to a synthesizing enzyme. A theoretical Poisson polymerization function was utilized as an appropriate model to calculate, as functions of time and precursor molecular weight, the yield and the average molecular weights that would be expected from a random polymerization. Theoretical results were then compared with equivalent experimental results.;The experimental results demonstrated that the rate of increase in the number of cellulose molecules, the rate of cellulose-mass accumulation, and the relative rate of cellulose-chain elongation are described by approximate first-order kinetics characteristic of bacteria in their logarithmic growth phase. A Poisson polymerization function predicts that these rates will also be first-order, but, the interrelationship between the rate constants for each experimental variable indicated that a stochastic mechanism does not occur. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI;The molecular weight averages were obtained from the gel permeation chromatography (GPC) chromatograms of the bacterial cellulose tricarbanilate derivatives. In order to ensure accurate molecular weight determination, a dispersionally-correct universal calibration was developed to account for the large differences between the instrumental spreading coefficients for the polystyrene calibration standards and the tricarbanilates. Because bacterial cellulose normally resists derivatization, it was also necessary to utilize an accessibilization procedure prior to derivatization in order to open its microfibrillar structure for complete tricarbanilation. The procedure entailed: initial preparation of a methylol derivative, regeneration in warm sodium sulfite, repeated washings with water, and, finally, freeze-drying to yield the substantially modified but undegraded cellulose.