A dissipative particle dynamics simulation of controlled loading and responsive release of theranostic agents from reversible crosslinked triblock copolymer vesicles.

To control the transport stability and release efficiency of loaded theranostic drugs in triblock copolymer carriers, the reversible crosslinking ability is of great significance. A molecular level exploration of such a function is needed to extend existing stabilizing and responsive dissociation mechanisms of carriers. Here, dissipative particle dynamics simulations were used to first demonstrate the formation of triblock copolymer vesicular carriers. Chemical crosslinking was used to strengthen the structural stability of the vesicle shell to avoid drug leakage. Reversible decrosslinking along with dissociation of the vesicle and release of loaded drugs were then explored. The structural, energetic and dynamical properties of the system were discussed at the molecular level. The regulation mechanism of drug release patterns was revealed by systematically exploring the effect of intra and intermolecular repulsive interactions. The results indicate that the chemical crosslinking of copolymers enhanced the compactness of the vesicle shell with a strengthened microstructure, increased binding energy, and limited chain migration, thus achieving more stable delivery of drugs. In terms of drug release, we clarified how the pairwise interactions of beads in the solution system affect the responsive dissociation of the vesicle and associated release patterns (speed and amount) of drugs. More efficient delivery and smart release of theranostic drugs are achieved using such reversible crosslinked triblock copolymer vesicles.

Electrocatalytic oxygen reduction by a Co/Co3O4@N-doped carbon composite material derived from the pyrolysis of ZIF-67/poplar flowers.

Catalysts used for the oxygen reduction reaction (ORR) are crucial to fuel cells. However, the development of novel catalysts possessing high activity at a low cost is very challenging. Recently, extensive research has indicated that nitrogen-doped carbon materials, which include nonprecious metals as well as metal-based oxides, can be used as excellent candidates for the ORR. Here, Co/Co3O4@N-doped carbon (NC) with a low cost and highly stable performance is utilized as an ORR electrocatalyst through the pyrolysis of an easily prepared physical mixture containing a cobalt-based zeolite imidazolate framework (ZIF-67 precursor) and biomass materials from poplar flowers. Compared with the pure ZIF-derived counterpart (Co@NC) and PL-bio-C, the as-synthesized electrocatalysts show significantly enhanced ORR activities. The essential roles of doped atoms (ZIF-67 precursor) in improving the ORR activities are discussed. Depending mainly on the formation of Co-Co3O4 active sites and abundant nitrogen-containing groups, the resulting Co/Co3O4@NC catalyst exhibits good electroactivity (onset and half-wave potentials: E onset = 0.94 V and E 1/2 = 0.85 V, respectively, and a small Tafel slope of 90 mV dec-1) compared to Co@NC and PL-bio-C and follows the 4-electron pathway with good stability and methanol resistance. The results of this study provide a reference for exploring cobalt-based N-doped biomass carbon for energy conversion and storage applications.