ИСТИНА

Ion-exchange properties and swelling capacity of cell walls from thalii red seaweeds were investigated by the potentiometric method. The thalli of Phyllophora crispa (Hudson) P.S. Dixon collected at northeastern part of Black sea (capes Maliy and Bolshoy Utrish) and peninsula the Crimea in July 2008-2009. Thalii examples were collected at a depth of 4.5 and 8 meters with using underwater equipment. The ion-exchange capacity and the swelling coefficient of the red alga cell walls ware estimated at various pH values (from 2 to 12) and at constant ionic strength of a solution (10 mM NaCl). To analyse the polysigmoid titration curves, the Gregor’s equation was employed. It was shown that the Gregor’s model fits well the experimental data. The total amount of the cation exchange and the anion exchange groups were determined in the cell walls. The amount of the functional group of each type was estimated, and the corresponding values of pKa were calculated. It was found that there are 2 cation-exchange groups and one anion exchange group (amine group) in red algae cell wall. It can be assumed that ionogenic groups with pKa ~ 5 are carboxyl groups of uronic acid, and ionogenic groups with pKa ~ 7.5 are carboxyl groups of proteins. It was shown that the swelling of the cell walls does not change with pH. The results reveal that the ion-exchange properties of the cell wall strongly depend on growth depth. This work is supported by the Russian Foundation of Fundamental Research (Grant No. 08-04-01398-а).