Interaction of water-soluble collagen with poly(acrylic acid)

Interactions between poly(acrylic acid) labeled with pyrene (PAA–Py) and succinylated calfskin collagen (type I) (SCSC) were studied by fluorescence spectroscopy. PAA–Py exhibits a strong emission from pyrene monomer (intensity, IM) when it exists in an extended conformation. It exhibits another broad emission from pyrene excimer (intensity, IE) when it adopts a collapsed globule conformation. At pH 3, a value that is lower than the isoelectric point of SCSC, the ratio IE/IM value decreased cooperatively with increasing concentration of SCSC at constant PAA–Py concentration, under salt-free condition. On the other hand, this effect was not observed in the presence of 0.1 NaCl. At pH 7, a value higher than the isoelectric point of SCSC, the ratio IE/IM was not affected by the presence of SCSC in the absence and presence of salt. From electrophoretic light scattering experiments, it was found that at pH 3 PAA–Py was negatively charged, while SCSC had a positive charge. Thus it is strongly suggested that the two polymers interact by electrostatic attraction at low pH where they are oppositely charged, and that PAA–Py adopts an extended conformation in the complex formed with SCSC. Similar interactions are believed to occur between dentinal collagen and the polycarboxylate component of glass-ionomer cements.