Theoretical Investigation on the Selective Hydroxyl Radical–Induced Decolorization of Methylene-Blue-Dyed Polymer Films

On the basis of decolorization caused by reaction active oxygen species (AOSs) with methylene blue (MB), our group recently developed colorimetric indicators for hydroxyl radical (OH radical) embedding MB in polymer thin films made water-soluble pullulan or sodium alginate. In present work, to elucidate reason selective induced OH compared other AOSs, such as ozone (O3) and hydrogen peroxide (H2O2), density-functional-theory calculations were performed at B3LYP/6-31G(d) level these AOSs its complexes alginate model molecules. A frontier orbital analysis revealed that π tends delocalize on whole molecule upon complexing alginate, while energy is lower than lowest unoccupied molecular levels O3 H2O2 but higher singly occupied radical. The results support observation only radical, strongest oxidant, can react matrices. MB-dyed due not steric hindrance matrix also perturbation through interaction