Exclusive and Switchable Superoxide Radical Generation by O2-Capture-Based Electron Transfer and Supramolecular Assembly.

Type-I photosensitizers (PSs) can generate free radical anions with a broad diffusion range and powerful damage effect, rendering them highly desirable in various areas. However, it still remains a recognized challenge to develop pure Type-I PSs due to the inefficiency in producing oxygen radical anions through the collision of PSs with nearby substrates. In addition, regulating the generation of oxygen radical anions is also of great importance toward the control of photosensitizer (PS) activities on demand. Herein, a piperazine-based cationic Type-I PS (PPE-DPI) that exhibits efficient intersystem crossing and subsequently captures oxygen molecules through binding O2 to the lone pair of nitrogen in piperazine is reported. The close spatial vicinity between O2 and PPE-DPI strongly promotes the electron transfer reaction, ensuring the exclusive superoxide radical (O2 •-) generation via Type-I process. Particularly, PPE-DPI with cationic pyridine groups is able to associate with cucurbit[7]uril (CB[7]) through host-guest interactions. Thus, supramolecular assembly and disassembly are easily utilized to realize switchable O2 •- generation. This switchable Type-I PS is successfully employed in photodynamic antibacterial control.

Stereoisomeric engineering of aggregation-induced emission photosensitizers towards fungal killing.

Fungal infection poses and increased risk to human health. Photodynamic therapy (PDT) as an alternative antifungal approach garners much interest due to its minimal side effects and negligible antifungal drug resistance. Herein, we develop stereoisomeric photosensitizers ((Z)- and (E)-TPE-EPy) by harnessing different spatial configurations of one molecule. They possess aggregation-induced emission characteristics and ROS, viz. 1O2 and O2-• generation capabilities that enable image-guided PDT. Also, the cationization of the photosensitizers realizes the targeting of fungal mitochondria for antifungal PDT killing. Particularly, stereoisomeric engineering assisted by supramolecular assembly leads to enhanced fluorescence intensity and ROS generation efficiency of the stereoisomers due to the excited state energy flow from nonradiative decay to the fluorescence pathway and intersystem (ISC) process. As a result, the supramolecular assemblies based on (Z)- and (E)-TPE-EPy show dramatically lowered dark toxicity without sacrificing their significant phototoxicity in the photodynamic antifungal experiments. This study is a demonstration of stereoisomeric engineering of aggregation-induced emission photosensitizers based on (Z)- and (E)-configurations.

Free Energy Prediction of Ion-Induced Nucleation of Aqueous Aerosols.

Ion-induced nucleation (IIN) is thought to be an important nucleation pathway of atmospheric aerosols. We present a combined polarizable molecular dynamics (MD) simulation and the classic ion-induced nucleation theory (IINT) approach to predict the free energy profiles of the ion-induced nucleation of aqueous aerosols in a qualitative or semiquantitative way. The dependence of both cluster structure and thermodynamic properties on cluster sizes and ion species is also systemically studied. It is confirmed the ions can significantly enhance the cluster stability, and thereby increase the nucleation rate. The ability of the common atmospheric ions to enhance the nucleation rate follows the order SO42- > H3O+ > NH4+ > NO3-, coinciding with the order of their solvation free energies. Therefore, the solvation energy can be employed as a rough index for evaluating the INN ability. Overall, the consistency between the present predictions and previous experimental and theoretical observations demonstrates the combination of MD simulation and the IINT appears to be a promising approach for exploring the IIN process and understanding the microscopic mechanism of atmospheric-related ions.