Allowing for polymer polydispersion as a necessary condition for determination of aqueous pore diameters in cell walls and membranes using polymers

A method of allowing for polydispersion of polyethylene glycol (PEG) prepar ations was developed for the use of these preparations for the osmometrical evaluation of pore diameters with aqueous pores of Chara corallina cell wa lls as an example. The mass share of polyethylene glycol preparation fracti ons gamma(p) penetrating through the pores was determined using cellular << shadows>>, fragments of internodal cell walls tied up at the ends and fille d with a 25% solution of nonpenetrating PEG 6000. When immersed into water, such <<shadow>> acquired a turgor (hydrostatic) pressure close to the cell ular pressure and persistent over long time. The determination of gamma(p) for polyethylene glycols with different average molecular weights (M) over bar(w) was performed from the degree of pressure restoration after water wa s replaced by a 5-10% polymer solution. The kinetics of pressure changes wa s recorded using a mechanotronic dynamometer, which measures, in the quasi- isometric mode, the force necessary for partial compression of the <<shadow >> in its small fragment. By utilizing the dependence of the overall share of fractions with molecular weights M-i < M-k on M-k (data of [1]), we foun d that gamma(p), for these polyethylene glycols corresponds to the threshol d value of M-k = 800-1100 D (hydrodynamic radius of molecules r(h) = 0.85-1 .05 nm). Thus, the effective diameter of the pores in the cell wall of Char a does not exceed 2.1 nm. It was shown that the smoothness of the sigmoid s hape of the dependence of ionic channel conductivity on the (M) over bar(w) value of the polymer in the media is largely due to the polydispersion of polymer preparations, particularly, to the reduction in the share of fracti ons penetrating the channel as (M) over bar(w) is increased, The method nor mally used to estimate pore diameters in ionic channels which ignores the d ispersion of polymer preparations, results in overestimated values.