Building photoswitchable 3,4'-AMPB peptides: Probing chemical ligation methods with reducible azobenzene thioesters

Small-Molecule-based Supramolecular Plastics Mediated by Liquid-Liquid Phase Separation

Plastics are one of the most widely used polymeric materials. However, they are often undegradable and non-recyclable due to the very stable covalent bonds of macromolecules, causing environmental pollution and health problems. Here, we report that liquid-liquid phase separation (LLPS) could drive the formation of robust, stable, and sustainable plastics using small molecules. The LLPS process could sequester and concentrate solutes, strengthen the non-covalent association between molecules and produce a bulk material whose property was highly related to the encapsulated water amounts. It was a robust plastic with a remarkable Young's modulus of 139.5 MPa when the water content was low while became adhesive and could instantly self-heal with more absorbed water. Finally, responsiveness enabled the material to be highly recyclable. This work allowed us to understand the LLPS at the molecular level and demonstrated that LLPS is a promising approach to exploring eco-friendly supramolecular plastics that are potential substitutes for conventional polymers.

Recent Advances in Application of Azobenzenes Grafted on Mesoporous Silica Nanoparticles in Controlled Drug Delivery Systems Using Light as External Stimulus

Hybrid materials based on Mesoporous Silica Nanoparticles (MSN) have attracted plentiful attention due to the versatility of their chemistry, and the field of Drug Delivery Systems (DDS) is not an exception. MSN present desirable biocompatibility, high surface area values, and a well-studied surface reactivity for tailoring a vast diversity of chemical moieties. Particularly important for DDS applications is the use of external stimuli for drug release. In this context, light is an exceptional alternative due to its high degree of spatiotemporal precision and non-invasive character, and a large number of promising DDS based on photoswitchable properties of azobenzenes have been recently reported. This review covers the recent advances in design of DDS using light as an external stimulus mostly based on literature published within last years with an emphasis on usually overlooked underlying chemistry, photophysical properties, and supramolecular complexation of azobenzenes.

Light controllable catalytic activity of Au clusters decorated with photochromic molecules

By ab initio calculations, we show that when decorated with a photochromic molecule, the catalytic activity of an Au nanocluster can be reversibly controlled by light. The combination of a photochromic thiol-pentacarbonyl azobenzene (TPA) molecule and an Au₈ cluster is chosen as a model catalyst. The TPA molecule has two configurations (trans and cis) that can be reversibly converted to each other upon photo-excitation. Our calculations show that when the TPA takes the trans configuration, the combined system (trans-Au₈) is an excellent catalyst for CO oxidation. The reaction barrier of the catalyzed CO oxidation is less than 0.4 eV. While, the reaction barrier of CO oxidation catalyzed by cis-Au₈ is very high (>2.7 eV), indicating that the catalyst is inactive. These results pave the way for a new class of light controllable nanoscale catalysts.

Multiresponsive Azobenzene End-Cap for Self-Immolative Polymers

Azobenzene was introduced as a new multiresponsive end-cap for self-immolative polymers. Using small-molecule model compounds, it was demonstrated that reducing agents including hydrazine and dithiothreitol could reduce the azobenzene to the corresponding hydrazobenzene, resulting in a 1,6-elimination reaction with the potential to initiate the depolymerization of self-immolative polycarbamates. An activated azobenzene derivative was then prepared, allowing for its incorporation as an end-cap for polycarbamates based on alternating N,N'-dimethylethylene diamine and 4-hydroxybenzyl alcohol. Upon treatment with hydrazine, depolymerization proceeded. To demonstrate the versatility of this end-cap, the chemistry was also applied to polycarbamates based on 4-aminobenzyl alcohol. In addition to allowing triggered depolymerization, the azobenzene end-cap also provides a visual signal upon triggering owing to the strong visible absorption of the azobenzene, which shifts to the UV range upon reduction. Furthermore, azobenzene is capable of undergoing trans-cis isomerization in response to UV light, providing multiple functions in a single end-cap.