Conformational changes of aliphatic ionenes in water-salt solutions as a factor controlling stability of their complexes with calf thymus DNA

Fractions of symmetrical XX-ionenes (X = 3, 6 and 10) with degrees of polymerization DP = 30-250 and nonsymmetrical 2,Y-ionenes (Y = 4, 6, 8, and 10), DP = 4-30, were used as positively charged partners of calf thymus DNA in polyelectrolyte complexes (PEC). The determined values of salt concentration, C*(salt), corresponding to the complete dissociation of PEC increased with the lengthening of ionenes of both families. CLINIC for PEC formed by relatively short 2,Y-ionenes of the same DP increased markedly with Y decrease. However the impact of this factor was substantially diminished upon lengthening of the 2,Y-ionenes. For the long-chained X,X-ionenes a more than 3-fold increase in X resulted only in moderate decrease in C*(NaCl). These finding suggest that the effective charge density of different ionenes releasing from PEC at relatively high C*(salt) becomes comparable owing to their pronounced compaction. This assumption was supported by the results of treatment of the experimental data using the developed model of PEC dissociation in water-salt media, which established the conformations of the releasing chains as slightly more swollen than theta-coil for 3,3-ionenes, theta-coil for 6,6-ionenes, and close to globule for 10,10-ionenes. The findings appear to be of particular interest to gain a better insight into the mechanism of DNA interaction with positively charged counterpart in vivo and in vitro.