A Heteromeric Carboxylic Acid Based Single-Crystalline Crosslinked Organic Framework.

The development of large pore single-crystalline covalently linked organic frameworks is critical in revealing the detailed structure-property relationship with substrates. One emergent approach is to photo-crosslink hydrogen-bonded molecular crystals. Introducing complementary hydrogen-bonded carboxylic acid building blocks is promising to construct large pore networks, but these molecules often form interpenetrated networks or non-porous solids. Herein, we introduced heteromeric carboxylic acid dimers to construct a non-interpenetrated molecular crystal. Crosslinking this crystal precursor with dithiols afforded a large pore single-crystalline hydrogen-bonded crosslinked organic framework HC OF-101. X-ray diffraction analysis revealed HC OF-101 as an interlayer connected hexagonal network, which possesses flexible linkages and large porous channels to host a hydrazone photoswitch. Multicycle Z/E-isomerization of the hydrazone took place reversibly within HC OF-101, showcasing the potential use of HC OF-101 for optical information storage.

Structure Property Analysis of the Solution and Solid-State Properties of Bistable Photochromic Hydrazones.

The development of new photochromic compounds and the optimization of their photophysical and switching properties are prerequisites for accessing new functions and opportunities that are not possible with currently available systems. To this end we recently developed a new bistable hydrazone switch that undergoes efficient photoswitching and emission ON/OFF toggling in both solution and solid-state. Here, we present a systematic structure-property analysis using a family of hydrazones and show how their properties, including activation wavelengths, photostationary states (PSSs), photoisomerization quantum yields, thermal half-lives (τ1/2), and solution/solid-state fluorescence characteristics vary as a function of electron donating (EDG) and/or withdrawing (EWG) substituents. These studies resulted in the red-shifting of the absorption profiles of the Z and E isomers of the switches, while maintaining excellent PSSs in almost all of the compounds. The introduction of para-NMe2 and/or para-NO2 groups improved the photoisomerization quantum yields, and the extremely long thermal half-lives (tens to thousands of years) were maintained in most cases, even in a push-pull system, which can be activated solely with visible light. Hydrazones bearing EDGs at the stator phenyl group are an exception and show up to 6 orders of magnitude acceleration in τ1/2 (i.e., days) because of a change in the isomerization mechanism. Moreover, we discovered that a para-NMe2 group is required to have reasonable fluorescence quantum yields in solution and that rigidification enhances the emission in the solid-state. Finally, X-ray crystallography analysis showed that the switching process is more efficient in the solid-state when the hydrazone is loosely packed.

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone.

In this work we apply a combination of steady state and time resolved luminescence and absorption spectroscopies to investigate the excited-state dynamics of a recently developed molecular photoswitch, belonging to the hydrazone family. The outstanding properties of this molecule, involving fluorescence toggling, bistability, high isomerization quantum yield and non-negligible two-photon absorption cross section, make it very promising for numerous applications. Here we show that the light induced Z/E isomerization occurs on a fast <1 ps timescale in both toluene and acetonitrile, while the excited state lifetime of the Z-form depends on solvent polarity, suggesting a partial charge transfer nature of its low lying excited state. Time-resolved luminescence measurements evidence the presence of a main emission component in the 500-520 nm spectral range, attributed to the Z-isomer, and a very short living blue-shifted emission, attributed to the E-isomer. Finally, transient absorption measurements performed upon far-red excitation are employed as an alternative method to determine the two-photon absorption cross-section of the molecule.

Building Strain with Large Macrocycles and Using It To Tune the Thermal Half-Lives of Hydrazone Photochromes.

Strain has been used as a tool to modulate the reactivity (e.g., mechanochemistry) and thermal isomerization kinetics of photochromic compounds. Macrocyclization is used to build-up strain in such systems, and in general the reactivity and rates increase with the decrease in macrocycle size. To ascertain the effect of strain on recently reported bistable hydrazone photoswitches, we incorporated them into macrocycles having varying aliphatic linker lengths (C3-C7), and studied their switching behavior, and effect of macrocycle size on the thermal isomerization rate. Surprisingly, while the systems with C3-C5 linkers behave as expected (i.e., the rate is faster with smaller linkers), the isomerization rate in the systems with larger aliphatic linkers (C6-C8) is enhanced up to 4 orders of magnitude. NMR spectroscopy, X-ray crystallography and DFT calculations were used to elucidate this unexpected behavior, which on the basis of our analyses results from the buildup of Pitzer (torsional), Prelog (transannular) and Baeyer (large angle) strain in the longer linkers.

Solution and Solid-State Emission Toggling of a Photochromic Hydrazone.

The proliferation of light-activated switches in recent years has enabled their use in a broad range of applications encompassing an array of research fields and disciplines. All current systems, however, have limitations (e.g., from complicated synthesis to incompatibility in biologically relevant media and lack of switching in the solid-state) that can stifle their real-life application. Here we report on a system that packs most, if not all, the desired, targeted and sought-after traits from photochromic compounds (bistability, switching in various media ranging from serum to solid-state, while exhibiting ON/OFF fluorescence emission switching, and two-photon assisted near-infrared light toggling) in an easily accessible structure.

Eight new cycloartane triterpenoids from Beesia calthifolia with hepatoprotective effects against D-galactosamine induced L02 cell damage.

Fourteen 20,24-epoxy-cycloartane triterpenoids, including eight new ones (1-8), were isolated from 95% ethanol extract of the rhizomes of Beesia calthifolia. Their structures were determined by spectroscopic and chemical methods, especially 2D NMR and HRMS techniques. Among them, four new compounds (1-4) possess carbonyl groups at C-16, which were rarely found in cycloartane triterpenoids from this genus. Relative configuration at C-12 in beesioside III (9) and its aglycone (10) was revised to be 12α-OH rather than the reported 12ß-OH. Some of the compounds showed potential hepatoprotective activities against human hepatic L02 cell damage induced by d-galactosamine.

A molecular anion pump.

Pumping ions against a concentration gradient through protein-based transporters is a cornerstone of numerous biological processes. Mimicking this function by using artificial receptors remains a daunting challenge, mainly because of the difficulties in balancing between the requirement for high binding affinities and precise and on-demand ion capture and release properties. We report a trimeric hydrazone photoswitch-based receptor that converts light energy into work by actively transporting chloride anion against a gradient through a dichloromethane liquid membrane, functioning as a molecular pump. The system manifests ease of synthesis, bistability, excellent photoswitching properties, and superb ON-OFF binding properties (difference of up to six orders of magnitude).

Use of pyridazinediones for tuneable and reversible covalent cysteine modification applied to peptides, proteins and hydrogels.

Reversible cysteine modification has been found to be a useful tool for a plethora of applications such as selective enzymatic inhibition, activity-based protein profiling and/or cargo release from a protein or a material. However, only a limited number of reagents display reliable dynamic/reversible thiol modification and, in most cases, many of these reagents suffer from issues of stability, a lack of modularity and/or poor rate tunability. In this work, we demonstrate the potential of pyridazinediones as novel reversible and tuneable covalent cysteine modifiers. We show that the electrophilicity of pyridazinediones correlates to the rates of the Michael addition and retro-Michael deconjugation reactions, demonstrating that pyridazinediones provide an enticing platform for readily tuneable and reversible thiol addition/release. We explore the regioselectivity of the novel reaction and unveil the reason for the fundamental increased reactivity of aryl bearing pyridazinediones by using DFT calculations and corroborating findings with SCXRD. We also applied this fundamental discovery to making more rapid disulfide rebridging agents in related work. We finally provide the groundwork for potential applications in various areas with exemplification using readily functionalised "clickable" pyridazinediones on clinically relevant cysteine and disulfide conjugated proteins, as well as on a hydrogel material.

A biomimetic nanodrug self-assembled from small molecules for enhanced ferroptosis therapy.

Ferroptosis drugs often induce oxidative damage or block antioxidant defense due to the key mechanism of ferroptosis involved in cancer treatment, regulating the intracellular redox balance. However, these ferroptosis drugs are unstable during systemic circulation, and they lack tumor-targeting capability. Herein, we developed a stimuli-responsive and cell membrane-coated nanodrug for the simultaneous delivery of two ferroptosis drugs, an iron-chelating drug as a ROS inducer and sorafenib as an antioxidase inhibitor. The coating of the cancer cell membrane over the nanodrug can enhance the tumor-targeting capability and improve the stability in the blood circulation. In addition, the nanodrug exhibits sensitive drug release profiles in response to glutathione (GSH) and reactive oxygen species (ROS) in tumor microenvironments due to the dynamic diselenide bonds. The released iron-chelating drug and sorafenib not only produce hydroxyl radicals (˙OH) to induce ferroptosis, but also inhibit the expression of GPX4 to mitigate the ferroptosis resistance. Excitingly, the systemic administration of this biomimetic nanodrug displays superior antitumor and anti-metastatic effects in tumor-bearing mice. Our findings provide a promising therapeutic strategy for the co-delivery of ferroptosis inducers and antioxidase inhibitors to strengthen the therapeutic efficacy of ferroptosis.

A small-molecule self-assembled nanodrug for combination therapy of photothermal-differentiation-chemotherapy of breast cancer stem cells.

The combination therapy with different treatment modalities has been widely applied in the clinical applications of cancer treatment. However, it stills a considerable challenge to achieve co-delivery of different drugs because of distinct drug encapsulation mechanisms, low drug loading, and high excipient-related toxicity. Cancer stem cells (CSCs) are closely related to tumor metastasis and recurrence due to high chemoresistance. Herein, we report a stimuli-responsive and tumor-targeted small-molecule self-assembled nanodrug for the combination therapy against CSCs and normal cancer cells. The hydrophobic differentiation-inducing agent (all-trans retinoic acid, ATRA) and hydrophilic anticancer drug (irinotecan, IRI) constitute this amphiphilic nanodrug, which could self-assemble into stable nanoparticles and encapsulate the photothermal agent IR825. Upon cellular uptake, this nanodrug display good release profiles in response to acid and esterase microenvironments by ester linkage. The released drugs not only increase chemotherapy sensitivity by the differentiation of CSCs into non-CSCs, but also exhibit superior cytotoxicity in cancer cells. In addition, IR825 within this nanodrug enables in vivo fluorescence/photoacoustic (PA) imaging allowing for tracking drug distribution. Moreover, the DSPE-PEG-RGD-functionalized nanodrug displayed high tumor accumulation and good biocompatibility, enabling efficient inhibition of tumor growth and tumor metastasis in tumor-bearing mice.

Controlled Polymerization of Norbornene Cycloparaphenylenes Expands Carbon Nanomaterials Design Space.

Carbon-based materials-such as graphene nanoribbons, fullerenes, and carbon nanotubes-elicit significant excitement due to their wide-ranging properties and many possible applications. However, the lack of methods for precise synthesis, functionalization, and assembly of complex carbon materials has hindered efforts to define structure-property relationships and develop new carbon materials with unique properties. To overcome this challenge, we employed a combination of bottom-up organic synthesis and controlled polymer synthesis. We designed norbornene-functionalized cycloparaphenylenes (CPPs), a family of macrocycles that map onto armchair carbon nanotubes of varying diameters. Through ring-opening metathesis polymerization, we accessed homopolymers as well as block and statistical copolymers constructed from "carbon nanohoops" with a high degree of structural control. These soluble, sp2-carbon-dense polymers exhibit tunable fluorescence emission and supramolecular responses based on composition and sequence. This work represents an important advance toward bridging the gap between small molecules and functional carbon-based materials.

Planarization-Induced Activation Wavelength Red-Shift and Thermal Half-Life Acceleration in Hydrazone Photoswitches.

The optimization and modulation of the properties of photochromic compounds, such as their activation wavelengths and thermal relaxation half-lives (τ1/2), are essential for their adaptation in various applications. In this work, we studied the effect of co-planarization of the rotary fragment of two photochromic hydrazones with the core of the molecule on their switching properties. The Z and E isomers of both compounds exhibit red-shifted absorption bands relative to their twisted versions, allowing for their photoswitching using longer wavelengths of light. Additionally, the thermal half-lives of both hydrazones are drastically shortened from hundreds of years to days.

Visualizing intracellular particles and precise control of drug release using an emissive hydrazone photochrome.

The spatiotemporal control over the structure of nanoparticles while monitoring their localization in tumor cells can improve the precision of controlled drug release, thus enhancing the efficiency of drug delivery. Here, we report on a photochromic nanoparticle system (LSNP), assembled from fluorescent bistable hydrazone photoswitch-modified amphiphilic copolymers. The intrinsic emission of the hydrazone switch allows for the visualization of particle uptake, as well as their intracellular distribution. The Z → E photoswitching of the hydrazone switch within the nanoparticle leads to the expansion of the nanoparticles (i.e., drug release) accompanied by emission quenching, the degree of which can function as an internal indicator for the amount of drug released. The bistability of the switch enables the kinetic trapping of particles of different sizes as a function of irradiation time, and allows for the exhibition of light-dependent cell cytotoxicity in MDA-MB-231 cells using LSNP loaded with doxorubicin.

White-light emission from a structurally simple hydrazone.

Two hydrazones featuring a unique excitation wavelength-dependent dual fluorescence emission have been developed. The mixing extent of the two emission bands can be modulated by tuning the excitation wavelength, resulting in multicolor and even white light emission from structurally simple hydrazones.

Five new cycloartane triterpenoids from Beesia calthifolia.

Phytochemical study on rhizomes of Beesia calthifolia resulted in the isolation of five new (1-5) and three known (6-8) cycloartane triterpenoids possessing a hemiketal or ketal group at C-24 from the EtOAc fraction of 95% ethanol extract. Their structures were determined by spectroscopic and chemical methods, especially HRMS and 2D NMR techniques. Compounds 3 and 4 showed potential hepatoprotective activities against D-galactosamine induced human hepatic L02 cell damage.