Catalytic single-chain polymeric nanoparticles atwork: from ensemble towards single-particlekinetics

摘要

Folding a single polymer chain around catalytically active sites to construct catalytic single chain polymericnanoparticles (SCPNs) is a novel approach to mimic the activity and selectivity of enzymes. In order to relatethe efficiency of SCPNs to their three-dimensional structure, a better understanding of their catalyticactivity at an individual level, rather than at an ensemble level, is highly desirable. In this work, we presentthe design and preparation of catalytic SCPNs and a family of fluorogenic substrates, their characterizationat the ensemble level as well as our progress towards analyzing individual SCPNs with single-moleculefluorescence microscopy (SMFM). Firstly, organocopper-based SCPNs together with rhodamine-basedfluorogenic substrates were designed and synthesized. The SCPNs catalyze the carbamate cleavage reactionof mono-protected rhodamines, with the dimethylpropargyloxycarbonyl protecting group beingcleaved most efficiently. A systematic study focusing on the conditions during catalysis revealed that the ligandacceleration effect as well as the accumulation of substrates and catalytically active sites in SCPNssignificantly promote their catalytic performance. Secondly, a streptavidin–biotin based strategy was developedto immobilize the catalytic SCPNs on the surface of glass coverslips. Fluorescence correlationspectroscopy experiments confirmed that the SCPNs remained catalytically active after surface immobilization.Finally, single-SCPN activity measurements were performed. The results qualitatively indicated thatfluorescent product molecules were formed as a result of the catalytic reaction and that individual fluorescentproduct molecules could be detected. So far, no evidence for strongly different behaviors has beenobserved when comparing individual SCPNs.