Langmuir and Langmuir-Blodgett films of bilirubin

The surface pressure-area isotherms of bilirubin (H2B R) monolayers at an a ir-water interface on subphases with different pH values and on subphases c ontaining metal ions such as Ca2+, Mg2+, Cu2+, Ni2+, Zn2+ and Pb2+ ion were investigated. H2BR can form expanded and stable monolayer on neutral and a cidic subphases, while it can hardly form monolayer on basic subphases. The acid-base equilibrium of H2BR was discussed at the air-water interface. Th e association-dissociation of H2BR with H+ ions in the interfacial region w as very different from that in the bulk solution. Some information regardin g the packing density and degree of ionization of the head group under diff erent experimental conditions were obtained. The formation of H2BR-metal co mplexes leads to changes in the shape of isotherms of H2BR and changes in U V-visible absorption spectra of the monolayer assemblies. In XPS spectra ne w XPS peaks assigned to the metal ions containing subphases appeared. Low-a ngle X-ray diffraction indicates that a Y-type LB films were formed with bi layer spacing of ca. 2.50 nm.