The formation of paramagnetic species on
catalyst surfaces at room temperature through the interaction of polynuclear
aromatics in solid, liquid, or solute form with hydrated platinum oxide (PtO2,2H2O) is reported. The results
are attributed to the formation of charge-transfer complexes, where the
transferred electrons couple weakly, forming essentially a "diradicaloid" complex with a low-lying, thermally
populated, triplet state. The effect of solvent, particle size, oxygen, water
of crystallization, and temperature on the generation and stability of these
e.s.r. active species has been investigated. The possible importance of these
paramagnetic species in catalytic self-activation and hydrogen exchange
reactions has been discussed. The following Group VIII transition metal oxides
gave no e.s.r. spectra under relatively severe reaction conditions such as 1 hr
at 120�: PdO; Ru02,2H20;
RuO2; Rh2O3;
IrO2,2H2O; ReO2;
and NiO.
Surface Immobilization of pH-Responsive Polymer Brushes on Mesoporous Silica Nanoparticles by Enzyme Mimetic Catalytic ATRP for Controlled Cargo Release
