Dilute solution properties of some polycarboxybetaines with antibacterial activity

The dilute solution properties of polymeric quaternary ammonium betaines derived from poly(N-vinylimidazole) PNVI and containing either a methylene (B1), ethylene (B2), or propylene (B3) betaine group, respectively, were analyzed. A PNVI blank was also tested. The weight-average molecular weight \( {{\overline{M}}_{\text{w}}} \), second virial coefficient A ₂, radius of gyration R _g, and hydrodynamic radius R _h of unfractionated probes were determined by MALLS (multiangle laser light scattering) and WALLS (wide-angle laser light scattering) measurements. All of these parameters varied with the type of solvent: pure water, an aqueous solution of 0.5 M NaCl, or an alcohol. These solution properties were useful for predicting the interactions of the polycarboxybetaines (acting as antimicrobial agents) with the components of the bacterial cell wall. Some of the polycarboxybetaines exhibited antimicrobial activities, as shown by the Kirby–Bauer diffusion method. A concentration of about 20 mg mL⁻¹ for B1 or B3 in an aqueous solution of 0.5 M NaCl is sufficient to inhibit the growth of Escherichia coli.