Reversible Dual Fluorescence-Lifetime Imaging of Mitochondrial GSH and Microviscosity: Real-Time Evaluation of Ferroptosis Status.

Ferroptosis, as a new form of regulated cell death, is implicated in various physiological and pathological processes. Developing a single probe for an independent analysis of multiple analytes related to ferroptosis can provide more accurate information and simplify the detection procedures, but it faces great challenges. In this work, we develop a fluorescent probe for the simultaneous detection of GSH through ratiometric fluorescence response and microviscosity via a fluorescence lifetime model. Based on the reversible Michael addition reaction between GSH and unsaturated C═C bond, the probe responds reversibly to GSH with a ratiometric fluorescence variation and a fast response time (t1/2 = 4.7 s). At the same time, the probe is sensitive to environmental viscosity by changing its fluorescence lifetimes. The probe was applied to monitor the drug-induced ferroptosis process through both the classical Xc-/GSH/GPX4- and DHODH-mediated defense mechanisms. We hope that the probe will provide a useful molecular tool for the real-time live-cell imaging of GSH dynamics, which is benefit to unveiling related physiological and pathological processes.

The Photodynamic Agent Designed by Involvement of Hydrogen Atom Transfer for Enhancing Photodynamic Therapy.

Although Type-I photodynamic therapy has attracted increasingly growing interest due to its reduced dependence on oxygen, the design of effective Type-I photosensitizers remains a challenge. In this work, we report a design strategy for Type-I photosensitizers by the involvement of hydrogen atom transfer (HAT). As a proof of concept, a HAT-involved Type-I PS, which simultaneously generates superoxide and carbon-centered radicals under light-irradiation, was synthesized. This photosensitizer is comprised of a fluorene-substituted BODIPY unit as an electron acceptor covalently linked with a triphenylamine moiety as an electron donor. Under light-irradiation, photo-induced intramolecular electron transfer occurs to generate the BODIPY anion radical and triphenylamine cation radical. The former transfers electrons to oxygen to generate O2-•, while the latter loses a proton to produce a benzyl carbon-centered radical which is well characterized. The resulting carbon-centered radicals efficiently oxidize NADH by HAT reaction. This photosensitizer demonstrates remarkable photocytotoxicity even under hypoxic conditions, along with outstanding in vivo antitumor efficacy in mouse models bearing HeLa tumors. This work offers a novel strategy for the design of Type-I photosensitizers by involvement of HAT.

Photo-Induced Disproportionation-Mediated Photodynamic Therapy: Simultaneous Oxidation of Tetrahydrobiopterin and Generation of Superoxide Radicals.

We herein present an approach of photo-induced disproportionation for preparation of Type-I photodynamic agents. As a proof of concept, BODIPY-based photosensitizers were rationally designed and prepared. The photo-induced intermolecular electron transfer between homotypic chromophores leads to the disproportionation reaction, resulting in the formation of charged intermediates, cationic and anionic radicals. The cationic radicals efficiently oxidize the cellularimportant coenzyme, tetrahydrobiopterin (BH4 ), and the anionic radicals transfer electrons to oxygen to produce superoxide radicals (O2 - ⋅). One of our Type-I photodynamic agents not only self-assembles in water but also effectively targets the endoplasmic reticulum. It displayed excellent photocytotoxicity even in highly hypoxic environments (2 % O2 ), with a half-maximal inhibitory concentration (IC50 ) of 0.96 µM, and demonstrated outstanding antitumor efficacy in murine models bearing HeLa tumors.

Spontaneous Symmetry Breaking of Achiral Molecules Leading to the Formation of Homochiral Superstructures that Exhibit Mechanoluminescence.

Chirality, with its intrinsic symmetry-breaking feature, is frequently utilized in the creation of acentric crystalline functional materials that exhibit intriguing optoelectronic properties. On the other hand, the development of chiral crystals from achiral molecules offers a solution that bypasses the need for enantiopure motifs, presenting a promising alternative and thereby expanding the possibilities of the self-assembly toolkit. Nevertheless, the rational design of achiral molecules that prefer spontaneous symmetry breaking during crystallization has so far been obscure. In this study, we present a series of six achiral molecules, demonstrating that when these conformationally flexible molecules adopt a cis-conformation and engage in multiple non-covalent interactions along a helical path, they collectively self-assemble into chiral superstructures consisting of single-handed supramolecular columns. When these homochiral supramolecular columns align in parallel, they form polar crystals that exhibit intense luminescence upon grinding or scraping. We therefore demonstrate our molecular design strategy could significantly increase the likelihood of symmetry breaking in achiral molecular synthons during self-assembly, offering a facile access to novel chiral crystalline materials with unique optoelectronic properties.

Intense Circularly Polarized Luminescence Induced by Chiral Supramolecular Assembly: The Importance of Intermolecular Electronic Coupling.

Herein we report on circularly polarized luminescence (CPL) emission originating from supramolecular chirality of organic microcrystals with a |glum| value up to 0.11. The microcrystals were prepared from highly emissive difluoroboron ß-diketonate (BF2dbk) dyes R-1 or S-1 with chiral binaphthol (BINOL) skeletons. R-1 and S-1 exhibit undetectable CPL signals in solution but manifest intense CPL emission in their chiral microcrystals. The chiral superstructures induced by BINOL skeletons were confirmed by single-crystal XRD analysis. Spectral analysis and theoretical calculations indicate that intermolecular electronic coupling, mediated by the asymmetric stacking in the chiral superstructures, effectively alters excited-state electronic structures and facilitates electron transitions perpendicular to BF2bdk planes. The coupling increases cosθµ,m from 0.05 (monomer) to 0.86 (tetramer) and triggers intense optical activity of BF2bdk. The results demonstrate that optical activity of chromophores within assemblies can be regulated by both orientation and extent of intermolecular electronic couplings.

Supramolecular Photosensitizer Enables Oxygen-Independent Generation of Hydroxyl Radicals for Photodynamic Therapy.

The highly oxygen-dependent nature of photodynamic therapy (PDT) limits its therapeutic efficacy against hypoxic solid tumors in clinics, which is an urgent problem to be solved. Herein, we develop an oxygen-independent supramolecular photodynamic agent that produces hydroxyl radical (•OH) by oxidizing water in the presence of intracellularly abundant pyruvic acid under oxygen-free conditions. A fluorene-substituted BODIPY was designed as the electron donor and coassembled with perylene diimide as the electron acceptor to form the quadruple hydrogen-bonded supramolecular photodynamic agent. Detailed mechanism studies reveal that intermolecular electron transfer and charge separation upon light irradiation result in an efficient generation of radical ion pairs. Under oxygen-free conditions, the cationic radicals directly oxidize water to generate highly cytotoxic •OH, and the anionic radicals transfer electrons to pyruvic acid, realizing the catalytic cycle. Thus, this photodynamic agent exhibited superb photocytotoxicity even under severe hypoxic environments and excellent in vivo antitumor efficacy on HeLa-bearing mouse models. This work provides a strategy for constructing oxygen-independent photodynamic agents, which opens up an avenue for effective PDT against hypoxic tumors.

Comparison of in vitro starch digestibility and structure of matcha-fortified starch vermicelli from different botanical sources.

BACKGROUND: In a study to explore the utilization of polyphenols in complex digestive systems, starch-based vermicelli was employed as the carrier and matcha (MT) was used as the source of polyphenols. Four percent MT was extruded with A-, B-, and C-type starch of rice, sweet potato, and mung bean to prepared starch vermicelli rice starch vermicelli (RSV), sweet potato starch vermicelli (SPSV), and mung bean starch vermicelli (MBSV), respectively. The multi-scale structure of starch, the digestive kinetics of starch, and the bioaccessibility of polyphenols during in vitro digestion were monitored. RESULTS: Matcha did not change the crystal configuration of vermicelli, but increased the relative crystallinity of RSV. Vermicelli with MT possessed a more uniform structure, and the polydispersity index decreased from 3.85-4.89 to 2.56-3.69. However, these structural changes made only a limited contribution to delaying digestion. The detection of polyphenols during digestion revealed that the release of most polyphenols was accomplished in the first 20 min of digestion. The release amount was in the order RSV + MT > MBSV + MT > SPSV + MT, and reached 4.81-5.45 mg GAE g-1 . Correspondingly, the activity of digestive enzyme decreased in the order RSV + MT < MBSV + MT < SPSV + MT. Consequently, MT significantly (P < 0.05) reduced the digestive rate of vermicelli, and the rapidly digested starch and predicted glycemic index of RSV + MT decreased from 71.28% to 56.31% and from 74.68 to 62.86, respectively. The released polyphenols were also the main source of the strong antioxidant capacity of vermicelli with MT. CONCLUSIONS: These results provided a theoretical basis for using polyphenols to pursue healthy starch-based food. © 2023 Society of Chemical Industry.

Circularly Polarized Laser Emission from Homochiral Superstructures based on Achiral Molecules with Conformal Flexibility.

Without external chiral intervention, it is a challenge to form homochirality from achiral molecules with conformational flexibility. We here report on a rational strategy that uses multivalent noncovalent interactions to clamp the molecular conformations of achiral D-A molecules. These interactions overcome the otherwise dominant dipole-dipole interactions and thus disfavor their symmetric antiparallel stacking. It in turn facilitates parallel packing, leading to spontaneous symmetry breaking during crystallization and thus the formation of homochiral conglomerates. When this emergent homochirality is coupled with optical gain characteristics of the molecules, the homochiral crystals are explored as excellent circularly polarized micro-lasers with low lasing threshold (16.4 µJ cm-2 ) and high dissymmetry factor glum (0.9). This study therefore provides a facile design strategy for supramolecular chiral materials and active laser ones without the necessity of intrinsic chiral element.

Visualizing the Underlying Signaling Pathway Related to Nitric Oxide and Glutathione in Cardiovascular Disease Therapy by a Sequentially Activated Fluorescent Probe.

Clarifying the signaling pathway associated with nitric oxide (NO) and glutathione (GSH) in cardiovascular disease therapy is important for understanding its physiological and pathological processes but is challenging due to the lack of efficient analytical techniques. Herein, we report a BODIPY-based fluorescent probe for recognition of NO and GSH in sequence with high sensitivity and selectivity. The probe exhibits turn-on fluorescence triggered by NO, followed by red-shifted emission in the presence of GSH. The sequentially activated mechanism allows the visualization of NO-induced GSH upregulation in drug-treated endothelial cells and zebrafish for the first time, revealing a signal pathway during the therapy. We hope that it can be used as a convenient and efficient tool for the study of the interplay between NO and GSH and for the screening of effective drugs for cardiovascular disease therapy.

BODIPY-Based Photodynamic Agents for Exclusively Generating Superoxide Radical over Singlet Oxygen.

Developing Type-I photosensitizers is considered as an efficient approach to overcome the deficiency of traditional photodynamic therapy (PDT) for hypoxic tumors. However, it remains a challenge to design photosensitizers for generating reactive oxygen species by the Type-I process. Herein, we report a series of α,ß-linked BODIPY dimers and a trimer that exclusively generate superoxide radical (O2-. ) by the Type-I process upon light irradiation. The triplet formation originates from an effective excited-state relaxation from the initially populated singlet (S1 ) to triplet (T1 ) states via an intermediate triplet (T2 ) state. The low reduction potential and ultralong lifetime of the T1 state facilitate the efficient generation of O2-. by inter-molecular charge transfer to molecular oxygen. The energy gap of T1 -S0 is smaller than that between 3 O2 and 1 O2 thereby precluding the generation of singlet oxygen by the Type-II process. The trimer exhibits superior PDT performance under the hypoxic environment.

Fluorescent Probe for Simultaneous Discrimination of GSH, Cys, and SO2 Derivatives.

Biothiols and SO2 derivatives, as essential reactive sulfur species (RSS), play vital roles in various physiological processes and have a close network of generation and metabolic pathways among them. To clarify their complex correlations, fluorescent probes to simultaneously detect GSH, Cys, and SO2 derivatives are highly desirable. Herein, we develop the first fluorescent probe (BO-HEM) to simultaneously discriminate GSH, Cys, and SO2 derivatives. The fluorescent probe is designed by integration of hemicyanine and BODIPY fluorophores through an ether bond. The ether bond of the probe is rapidly replaced by thiolates through nucleophilic aromatic substitution (SNAr) to generate hemicyanine with NIR fluorescence and sulfur-BODIPY. The amino groups of Cys but not GSH then further replace the thiolate to form amino-BODIPY. As for SO32-, nucleophilic addition to the double bond of BO-HEM generates adduct O-BODIPY with green fluorescence. To further improve the sensing performance, the nanoprobe with increased reactivity and biocompatibility is constructed by encapsulation of BO-HEM into the polymeric micelle. More importantly, by taking advantage of the hydrophilicity of the reaction products, the spectral discrimination was further enhanced to avoid signal interference. The nanoprobe is applied to discriminate biothiols and SO2 derivatives in living cells through three-color fluorescence imaging.

Time-Dependent Afterglow Color in a Single-Component Organic Molecular Crystal.

An organic crystal of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (pCBP) exhibits time-dependent afterglow color from blue to orange over 1 s. Both experimental and computational data confirm that the color evolution results from well-separated, long-persistent thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) with different but comparable decay rates. TADF is enabled by a small S1 -T1 energy gap of 0.7 kcal mol-1 . The good separation of TADF and RTP is due to a 11.8 kcal mol-1 difference in the S0 energies of the S1 and T1 structures, indicating that apart from the excited-state properties, tuning the ground state is also important for luminescence properties. This afterglow color evolution of pCBP allows its applications in anticounterfeiting and data encryption with high security levels.

BODIPY-Based Fluorescent Probe for Dual-Channel Detection of Nitric Oxide and Glutathione: Visualization of Cross-Talk in Living Cells.

Nitric oxide (NO) and glutathione (GSH) have interplaying roles in oxidant-antioxidant balance. In this work, we developed the first example of a single fluorescent probe that displayed a turn-on fluorescence response toward NO and GSH from dual emission channels. The probe was synthesized by introducing 4-amino-3-(methylamino)-phenol to a BODIPY scaffold. Specifically, the NO-mediated transformation of diamine into a triazole triggered the fluorescence in the green channel, and the GSH-induced SNAr substitution reaction led to the red-shifted emission in the red channel. The probe was successfully applied to detect the exogenous and endogenous NO and GSH in macrophage cells. More importantly, the probe revealed that NO induced by interferon-γ (IFN-γ), lipopolysaccharide (LPS), and l-arginine (l-Arg) could also elicit the augmentation of intracellular GSH. We anticipate the probe would hold great potential for investigating the redox balance in biological processes.

Synthesis of N,O,B-Chelated Dipyrromethenes through an Unexpected Intramolecular Cyclisation: Enhanced Near-Infrared Emission in the Aggregate/Solid State.

The first example of the synthesis of mono-N,O-B-chelated dipyrromethene (BODIPY) derivatives through an unexpected intramolecular nucleophilic displacement of the fluorine by alkenols in the presence of boron trifluoride as Lewis acid is reported. The chlorine in the indacene core allowed for further structural modifications through nucleophilic substitutions or palladium-catalysed coupling reactions to afford new fluorophores with tuneable photophysical properties. Their expanded conjugation structure resulted in distinct red-shifted absorption and emission spectra in organic solutions. Furthermore, the twisted steric hindrance of the benzene substitution patterns suppressed aggregation-induced quenching, leading to an enhanced NIR emission in the aggregate/solid state, which was rarely observed for BODIPY dyes. Nanoparticles of the fluorophores formed by the assembly with the polymeric surfactant F127 were successfully used for bioimaging of living cells and for tumour-targeted imaging in a tumour-bearing mouse model.

A mitochondria-targeting fluorescent probe for the selective detection of glutathione in living cells.

We report a fluorescent probe for the selective detection of mitochondrial glutathione (GSH). The probe, containing triphenylphosphine as a mitochondrial targeting group, exhibited ratiometric and selective detection of GSH over Cys/Hcy. The probe was used for imaging mitochondrial GSH in living HeLa cells.

A Phosphorescent Platinum(II) Bipyridyl Supramolecular Polymer Based on Quadruple Hydrogen Bonds.

A platinum(II) bipyridyl complex bearing bis-ureidopyrimidinone (Pt-bisUPy) has been designed and its self-assembling behavior has been thoroughly investigated by 1 H NMR, DOSY NMR, Ubbelohde viscometry analysis, UV/Vis, and emission spectroscopies. Pt-bisUPy underwent concentration-dependent ring-chain polymerization in apolar solvents. Hydrogen-bonding interactions play an important role during the formation of the supramolecular polymers. Hydrogen-bonded supramolecular polymers were transformed to nanoparticles in water through the miniemulsion method. These nanoparticles showed strong π-π excimeric emission. Metal-metal-to-ligand charge transfer (MMLCT) from Pt-Pt interactions was not significant in the emission spectrum. The phosphorescence of the nanoparticle persisted even under aerobic conditions. The triplet state of these phosphorescent nanomaterials were long-lived and possessed moderate emission quantum yields. Furthermore, the low toxicity of these materials promises a place for them in in vitro and in vivo bioimaging.

Design strategies of fluorescent probes for selective detection among biothiols.

Simple thiol derivatives, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play key roles in biological processes, and the fluorescent probes to detect such thiols in vivo selectively with high sensitivity and fast response times are critical for understanding their numerous functions. However, the similar structures and reactivities of these thiols pose considerable challenges to the development of such probes. This review focuses on various strategies for the design of fluorescent probes for the selective detection of biothiols. We classify the fluorescent probes for discrimination among biothiols according to reaction types between the probes and thiols such as cyclization with aldehydes, conjugate addition-cyclization with acrylates, native chemical ligation, and aromatic substitution-rearrangement.

Light-Harvesting Systems Based on Organic Nanocrystals To Mimic Chlorosomes.

We report the first highly efficient artificial light-harvesting systems based on nanocrystals of difluoroboron chromophores to mimic the chlorosomes, one of the most efficient light-harvesting systems found in green photosynthetic bacteria. Uniform nanocrystals with controlled donor/acceptor ratios were prepared by simple coassembly of the donors and acceptors in water. The light-harvesting system funneled the excitation energy collected by a thousand donor chromophores to a single acceptor. The well-defined spatial organization of individual chromophores in the nanocrystals enabled an energy transfer efficiency of 95 %, even at a donor/acceptor ratio as high as 1000:1, and a significant fluorescence of the acceptor was observed up to donor/acceptor ratios of 200 000:1.

Convenient synthesis of functionalized bis-ureidopyrimidinones based on thiol-yne reaction.

The preparation of functionalized bis-ureidopyrimidinones (Bis-UPy) through the thiol-yne reaction is described. Various Bis-UPys with different functional groups were synthesized by using the readily available functionalized alkynes and UPy-thiol to affirm the simplicity and versatility of the methodology.