ABSTRACT
Macromolecular scaffolds are rapidly emerging in catalysis owing to the ability to control catalyst placement at precise locations. This spatial proximity allows for enhanced catalyst activity that may not be observed using small molecules. Herein, we describe a triphenylpyrylium (TPT)-based visible-light active single-chain polymer nanoparticle (SCNP) that facilitates the radical cation [4 + 2]-cycloaddition. We find that the catalytic activity is highly dependent on the styrylarene comonomer used, wherein it can act as a redox mediator under confinement, increasing the catalytic turnover (TON) by up to 30 times in comparison to free TPT in solution. Mechanistic studies indicate that TPT excited states are quenched by the acene, with the resultant radical cation formed from naphthalene-based SCNPs able to proceed in oxidizing the dienophile in the elementary step of the reaction, while leading to near quantitative yields of the cycloadduct. The TPT-SCNP demonstrates enhanced photocatalyst efficiency compared to molecular TPT, and is able to be recycled and reused in three iterations of the reaction prior to decreased performance from photobleaching. Our results overall suggest that the confined nature of the SCNP and spatial proximity of acene-based pendants enforces their participation as cocatalytic redox mediators that impart enhanced photoredox catalysis under confinement.
ABSTRACT
PURPOSE: The use of stent-grafts has proved to be safe and effective treatment for complicated aortic dissections but usually requires surgical cutdown to accommodate large-profile devices. Preliminary results of the use of a low-profile design that allows percutaneous access are presented. MATERIALS AND METHODS: Fifteen patients with aortic dissection were treated with use of a low-profile stent-graft. Dissection types included Stanford type A (n = 6) and type B (n = 9). The procedures were performed with use of Perclose devices to achieve hemostasis. The stent-graft device was composed of Gianturco stents connected with longitudinal wire struts covered with radially expanded polytetrafluoroethylene. The delivery sheath sizes were 14-20 F. RESULTS: In 87% of patients (13 of 15), the entry tear was excluded completely. Successful femoral closures were achieved in 93% of patients (14 of 15) with use of the suture-mediated devices. In 7% of patients (one of 15), surgical closure of the femoral arteries was required. The rate of pseudoaneurysm occurrence was 7% (one of 15). Hospitalization ranged from 1 to 30 days with a mean duration of 6.5 days. The 30-day mortality rate was 27% (four of 15). In the remaining 11 patients, entry tear sites were excluded and, on follow-up CT examinations, there was thrombosis and retraction of the false lumen and enlargement of the true lumen. CONCLUSION: Preliminary results of the use of a low-profile stent-graft device to treat aortic dissections show that, in most patients, it can be used with a suture-mediated device without surgical exposure of the common femoral artery.
