Malabsorption of bile acids at the end part of the small intestine causes bile acid diarrhea in human body. The aim of this study is to investigate the possibility of using nonionic triblock copolymers based on poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) instead of present sequestrants in the treatment of this disease. The influence of a bile salt, sodium glycodeoxycholate (NaGDC), on the association behavior in water of three copolymers with different block lengths of PEO and PPO (EO19-PO29-EO19 = P65, EO20-PO69-EO20 = P123 and EO100-PO65-EO100 = F127) has been studied by means of light, X-ray and neutron scattering in combination with differential scanning calorimetry. In water, above a critical micelle concentration and a critical micelle temperature, the block copolymers form spherical micelles with a PPO core and a PEO corona (7-10 nm in hydrodynamic radius). Furthermore, for micelles of P123, a sphere-to-rod transition at the elevated temperatures has been reported [1]. The size of the NaGDC micelle is 1.6 nm [2]. In mixed NaGDC/copolymer solutions, at low bile salt concentrations, copolymer-rich mixed complexes are formed that become increasingly charged as the concentration of bile salt increases. The electrostatic interaction between the complexes is evidenced in the scattering experiments. At high bile salt concentrations, as the disintegration of the block copolymer micelle begins, bile-salt-rich mixed complexes coexist with the polymer-rich complexes. In addition, the shape change of the P123 micelle is prohibited by addition of the bile salt.
[1] Löf, D., Niemiec, A., Schillén, K., Loh, W., Olofsson, G., J. Phys. Chem. B 2007, 111, 5911-5920.
[2] Galantini, L., Giglio, E. , Leonelli, A., Pavel, N. V., J. Phys. Chem. B 2004, 108, 3078-3085.
Karin.Schillen@fkem1.lu.se
