Amphiphilic Copolymers Capable of Concomitant Release of HNO and Small Molecule Organics

Nitroxyl donating and visualization with a coumarin-based fluorescence probe

Nitroxyl (HNO), the single-electron reduction product of nitric oxide (NO), has attracted great interest in the treatment of congestive heart failure in clinical trials. In this paper, we describe the first coumarin-based compound N-hydroxy-2-oxo-2H-chromene-6-sulfonamide (CD1) as a dualfunctional HNO donor, which can release both an HNO signaling molecule and a fluorescent reporter. Under physiological conditions (pH 7.4 and 37 °C), the CD1 HNO donor can readily decompose with a half-life of ∼90 min. The corresponding stoichiometry HNO from the CD1 donor was confirmed using both Vitamin B12 and phosphine compound traps. In addition to HNO releasing, specifically, the degradation product 2-oxo-2H-chromene-6-sulfinate (CS1) was generated as a fluorescent marker during the decomposition. Therefore, the HNO amount released in situ can be accurately monitored through fluorescence generation. As compared to the CD1 donor, the fluorescence intensity increased by about 4.9-fold. The concentration limit of detection of HNO releasing was determined to be ∼0.13 μM according to the fluorescence generation of CS1 at physiological conditions. Moreover, the bioimaging of the CD1 donor was demonstrated in the cell culture of HeLa cells, where the intracellular fluorescence signals were observed, inferring the site of HNO release. Finally, we anticipate that this novel coumarin-based CD1 donor opens a new platform for exploring the biology of HNO.

Synthesis and nitroxyl (HNO) donating properties of benzoxadiazole-based Piloty's acids

Developing functional nitroxyl (HNO) donors play a significant role in the further exploration of endogenous HNO in biochemistry and pharmacology. In this work, two novel Piloty's acids (SBD-D1 and SBD-D2) were proposed by incorporating benzoxadiazole-based fluorophores, in order to achieve the dual-function of releasing both HNO and a fluorophore in situ. Under physiological conditions, both SBD-D1 and SBD-D2 efficiently donated HNO (t_1/2 = 10.96 and 8.18 min, respectively). The stoichiometric generation of HNO was determined by both vitamin B₁₂ and phosphine compound traps. Interestingly, due to the different substitution groups on the aromatic ring, SBD-D1 with the chlorine showed no fluorescence emission, but SBD-D2 was strongly fluorescent due to the presence of the dimethylamine group. Specifically, the fluorescent signal would decrease during the release process of HNO. Moreover, theoretical calculations were performed to understand the emission difference. A strong radiation derived from benzoxadiazole with dimethylamine group due to the large transition dipole moment (∼4.3 Debye), while the presence of intramolecular charge transfer process in the donor with chlorine group caused a small transition dipole moment (<0.1 Debye). Finally, these studies would contribute to the future design and application of novel functional HNO donors for the exploration of HNO biochemistry and pharmacology.

Dual Polymerizations: Untapped Potential for Biomaterials

Block copolymers with unique architectures and those that can self-assemble into supramolecular structures are used in medicine as biomaterial scaffolds and delivery vehicles for cells, therapeutics, and imaging agents. To date, much of the work relies on controlling polymer behavior by varying the monomer side chains to add functionality and tune hydrophobicity. Although varying the side chains is an efficient strategy to control polymer behavior, changing the polymer backbone can also be a powerful approach to modulate polymer self-assembly, rigidity, reactivity, and biodegradability for biomedical applications. There are many developments in the syntheses of polymers with segmented backbones, but these developments are not widely adopted as strategies to address the unique constraints and requirements of polymers for biomedical applications. This review highlights dual polymerization strategies for the synthesis of backbone-segmented block copolymers to facilitate their adoption for biomedical applications.