  The dynamics and structural characteristics of polymethacrylic acid bound
rhodamine-123 (PMAAR123) and its interpolymer complex with
poly(vinylpyrrolidone) were investigated using single molecular fluorescence
studies. The time resolved fluorescence anisotropy decay of PMAA-R123 at
different pH exhibits an associated anisotropy decay behavior characteristic of
two different environments experienced by the fluorophore and decays with one
shorter and another longer lifetime components. The anisotropy decay retains
normal bi-exponential behavior under neutral pH. Fluorescence correlation
spectroscopic investigation reveals that the attached fluorophore undergoes
hydrolysis under basic condition which results in the release of the
fluorophore from the polymer backbone. Shrinkage in the hydrodynamic radius of
PMAA is observed on addition of the complementary polymer PVP which is
attributed to the formation compact solubilized nanoparticle like aggregates.
The size of particle further decreases on the addition of NaCl. The detailed
results show that these complexes have potential for use as drug-delivery
system under physiological conditions.
