Interpolyelectrolyte reactions in solutions of polycarboxybetaines

The utility of different polycarboxybetaines (PCB) as positively charged components of polyelectrolyte complexes was elucidated by potentiometry, turbidimetry, and fluorescence spectroscopy. PCB practically did not quench the fluorescence of either pyrenyl-tagged poly(methacrylic acid) or ethidium bromide intercalated in DNA. This indicates small, if any, interaction of PCB with the above polyanions due to formation of stable ion pairs between carboxylic and quaternary amino groups positioned in each repeated unit of PCB chains. Potentiometric titration curves of PCB solutions practically coincided with the curve of distilled water in the studied pH range 2-11. Addition of sodium poly(styrenesulfonate) (PSS) did not result in phase separation or noticeable change of the titration curve of PCB at pH > 7, whereas at pH < 7 phase separation occurred and the titration curve of the mixture significantly changed, being in close proximity with the curve of poly(acrylic acid). The pH value corresponding to the cloud point decreased gradually with the increase in PSS content, invariably of PSS molecular weight in the studied region M-w = 4000- 100 000. These findings suggest that sulfonate groups of PSS are not able to compete with carboxylate groups of PCB for binding with the amino groups in neutral and alkaline media, whereas the competitive binding becomes pronounced at pH < 7. The revealed ability of PCB to interact efficiently with PSS forming polyelectrolyte complex with pH-controlled solubility can be important for development of bioseparation techniques.