Self-Immolative Phthalate Esters Sensitive to Hydrogen Peroxide and Light

In Situ Formation of Polymeric Nanoassemblies Using an Efficient Reversible Click Reaction

Polymer-drug conjugates are promising as strategies for drug delivery, because of their high drug loading capacity and low premature release profile. However, the preparation of these conjugates is often tedious. In this paper, we report an efficient method for polymer-drug conjugates using an ultrafast and reversible click reaction in a post-polymerization functionalization strategy. The reaction is based on the rapid condensation of boronic acid functionalities with salicylhydroxamates. The polymer, bearing the latter functionality, has been designed such that the reaction with boronic acid bearing drugs induces an in situ self-assembly of the conjugates to form well-defined nanostructures. We show that this method is not only applicable for molecules with an intrinsic boronic acid group, but also for the other molecules that can be linked to aryl boronic acids through a self-immolative linker. The linker has been designed to cause traceless release of the attached drug molecules, the efficiency of which has been demonstrated through intracellular delivery.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Secondary structure-induced aggregation by hydrogen peroxide: a stimuli-triggered open/close implementation by recombination

The fabrication of reactive aggregation nanomaterials through assemblies in a facile and cost-effective manner is much desired but remains to be well explored. Here we show that exquisite and ultra-long (>2 μm) hybrid polymer nanorods (NRs) can be formed by a simple self-assembly of a phenylboronic acid modified genistein crosslinker (Ge-di(HMPBA-pin)) and d-α-tocopheryl polyethylene glycol 1000 (TPGS). The obtained NRs exhibit quantitative and sensitive colorimetric detection of H₂O₂ with a remarkable detection limit for different stromal materials. More significantly, the presence of H₂O₂ triggers a distinct morphological transformation of the polymer NR assembly into the secondary structure of micelles via the oxidative deboronation of boronate moieties in HMPBA-pin-SA. It spontaneously induces the aggregation of metal nanoparticles (Au NPs), metal nanorods (Au NRs), quantum dots (MoS₂ QDs), metal ions (Cu²⁺), protein (ferritin) and tetraphenylethene (TPE) molecules, giving rise to a dramatic stimuli-triggered open/close switchable complexation and apparent colorimetric transitions in vitro. This study, for the first time, showcases the fascinating advantages of such unprecedented secondary structure-induced aggregation and uncovers the immense potential to design a plethora of other sensing systems by virtue of the alternate trigger-specific, sacrifice-aggregated building moieties.

Designing Smart Polymer Conjugates for Controlled Release of Payloads

Incorporating labile bonds inside polymer backbone and side chains yields interesting polymer materials that are responsive to change of environmental stimuli. Drugs can be conjugated to various polymers through different conjugation linkages and spacers. One of the key factors influencing the release profile of conjugated drugs is the hydrolytic stability of the conjugated linkage. Generally, the hydrolysis of acid-labile linkages, including acetal, imine, hydrazone, and to some extent β-thiopropionate, are relatively fast and the conjugated drug can be completely released in the range of several hours to a few days. The cleavage of ester linkages are usually slow, which is beneficial for continuous and prolonged release. Another key structural factor is the water solubility of polymer-drug conjugates. Generally, the release rate from highly water-soluble prodrugs is fast. In prodrugs with large hydrophobic segments, the hydrophobic drugs are usually located in the hydrophobic core of micelles and nanoparticles, which limits the access to the water, hence lowering significantly the hydrolysis rate. Finally, self-immolative polymers are also an intriguing new class of materials. New synthetic pathways are needed to overcome the fact that much of the small molecules produced upon degradation are not active molecules useful for biomedical applications.