Near-IR-Triggered, Remote-Controlled Release of Metal Ions: A Novel Strategy for Caged Ions

Elaborating the Fluorescence Regulation and Quenching Mechanism of Sulfur-for-Oxygen Replacement for Fluorophores

Thio-caged fluorophores can be effectively desulfurized into their oxygenated derivatives through visible light, thereby restoring the strong emission of fluorophores, and are applied in the field of live cell super-resolution imaging. Herein, we theoretically investigated the reasons for the low fluorescence quantum yields of a series of thio-caged fluorophores and the underlying reasons for the differences in fluorescence quantum yields of their oxygenated derivatives. The calculation results show that the S atom on the thiocarbonyl group is more likely to excite n electrons to form the nπ* state, which reduces the energy of the nπ* state and leads to fluorescence quenching. In contrast, the O atom on the carbonyl group is more likely to excite π electrons to form ππ* state, which is the main reason for restoring the strong emission of fluorophore. Meanwhile, the calculation results show that the difference of fluorescence intensity caused by oxygenated derivatives is determined by the number of the carbonyl group, which affects the vibronic coupling between ππ* and nπ* states and thereby leads to fluorescence quenching. These results can effectively reveal the fluorescence quenching mechanism of thio-caged fluorophores and the luminescence mechanism of their oxygenated derivatives, and provide correct and guiding design strategies for the development of new thio-caged fluorophores.

Efficiency of Functional Group Caging with Second-Generation Green- and Red-Light-Labile BODIPY Photoremovable Protecting Groups

BODIPY-based photocages release substrates by excitation with wavelengths in the visible to near-IR regions. The recent development of more efficient BODIPY photocages spurred us to evaluate the scope and efficiency of these second-generation boron-methylated green-light and red-light-absorbing BODIPY photocages. Here, we show that these more photosensitive photocages release amine, alcohol, phenol, phosphate, halides, and carboxylic acid derivatives with much higher quantum yields than first-generation BODIPY photocages and excellent chemical yields. Chemical yields are near-quantitative for the release of all functional groups except the photorelease of amines, which react with concomitantly photogenerated singlet oxygen. In these cases, high chemical yields for photoreleased amines are restored by irradiation under an inert atmosphere. The photorelease quantum yield has a weak relationship with the leaving group pK_a of the green-absorbing BODIPY photocages but little relationship with the red-absorbing derivatives, suggesting that factors other than leaving group quality impact the quantum yield. For the photorelease of alcohols, in all cases a carbonate linker (that loses CO₂ upon photorelease) significantly increases both the quantum yield and the chemical yield compared to those for direct photorelease via the ether.

Dual-Ligand Near-Infrared Luminescent Lanthanide-Based Metal-Organic Framework Coupled with In Vivo Microdialysis for Highly Sensitive Ratiometric Detection of Zn2+ in a Mouse Model of Alzheimer's Disease

Zinc, which is the second most abundant trace element in the human central nervous system, is closely associated with Alzheimer's disease (AD). However, attempts to develop highly sensitive and selective sensing systems for Zn²⁺ in the brain have not been successful. Here, we used a one-step solvothermal method to design and prepare a metal-organic framework (MOF) containing the dual ligands, terephthalic acid (H₂BDC) and 2,2':6',2″-terpyridine (TPY), with Eu³⁺ as a metal node. This MOF is denoted as Eu-MOF/BDC-TPY. Adjustment of the size and morphology of Eu-MOF/BDC-TPY allowed the dual ligands to produce multiple luminescence peaks, which could be interpreted via ratiometric fluorescence to detect Zn²⁺ using the ratio of Eu³⁺-based emission, as the internal reference, and ligand-based emission, as the indicator. Thus, Eu-MOF/BDC-TPY not only displayed higher selectivity than other metal cations but also offered a highly accurate, sensitive, wide linear, color change-based technique for detecting Zn²⁺ at concentrations ranging from 1 nM to 2 μM, with a low limit of detection (0.08 nM). Moreover, Eu-MOF/BDC-TPY maintained structural stability and displayed a fluorescence intensity of at least 95.4% following storage in water for 6 months. More importantly, Eu-MOF/BDC-TPY sensed the presence of Zn²⁺ markedly rapidly (within 5 s), which was very useful in practical application. Furthermore, the results of our ratiometric luminescent method-based analysis of Zn²⁺ in AD mouse brains were consistent with those obtained using inductively coupled plasma mass spectrometry.

Dynamics of Excitons in Conjugated Molecules and Organic Semiconductor Systems

The exciton, an excited electron-hole pair bound by Coulomb attraction, plays a key role in photophysics of organic molecules and drives practically important phenomena such as photoinduced mechanical motions of a molecule, photochemical conversions, energy transfer, generation of free charge carriers, etc. Its behavior in extended π-conjugated molecules and disordered organic films is very different and very rich compared with exciton behavior in inorganic semiconductor crystals. Due to the high degree of variability of organic systems themselves, the exciton not only exerts changes on molecules that carry it but undergoes its own changes during all phases of its lifetime, that is, birth, conversion and transport, and decay. The goal of this review is to give a systematic and comprehensive view on exciton behavior in π-conjugated molecules and molecular assemblies at all phases of exciton evolution with emphasis on rates typical for this dynamic picture and various consequences of the above dynamics. To uncover the rich variety of exciton behavior, details of exciton formation, exciton transport, exciton energy conversion, direct and reverse intersystem crossing, and radiative and nonradiative decay are considered in different systems, where these processes lead to or are influenced by static and dynamic disorder, charge distribution symmetry breaking, photoinduced reactions, electron and proton transfer, structural rearrangements, exciton coupling with vibrations and intermediate particles, and exciton dissociation and annihilation as well.

BODIPY-Based Polymers of Intrinsic Microporosity for the Photocatalytic Detoxification of a Chemical Threat

Effective heterogeneous photocatalysts capable of detoxifying chemical threats in practical settings must exhibit outstanding device integrity. We report a copolymerization that yields robust, porous, processible, chromophoric BODIPY (BDP; boron-dipyrromethene)-containing polymers of intrinsic microporosity (BDP-PIMs). Installation of a pentafluorophenyl at the meso position of a BDP produced reactive monomer that when combined with 5,5,6,6-tetrahydroxy-3,3,3,3-tetramethyl-1,1-spirobisindane (TTSBI) and tetrafluoroterephthalonitrile (TFTPN) yields PIM-1. Postsynthetic modification of these polymers yields Br-BDP-PIM-1a and -1b─polymers containing bromine at the 2,6-positions. Remarkably, the brominated polymers display porosity and processability features similar to those of H-BDP-PIMs. Gas adsorption reveals molecular-scale porosity and Brunette-Emmet-Teller surface areas as high as 680 m² g^-1. Electronic absorption spectra reveal charge-transfer (CT) bands centered at 660 nm, while bands arising from local excitations, LE, of BDP and TFTPN units are at 530 and 430 nm, respectively. Fluorescence spectra of the polymers reveal a Förster resonance energy-transfer (FRET) pathway to BDP units when TFTPN units are excited at 430 nm; weak phosphorescence at room temperature indicates a singlet-to-triplet intersystem crossing. The low-lying triplet state is well positioned energetically to sensitize the conversion of ground-state (triplet) molecular oxygen to electronically excited singlet oxygen. Photosensitization capabilities of these polymers toward singlet-oxygen-driven detoxification of a sulfur-mustard simulant 2-chloroethyl ethyl sulfide (CEES) have been examined. While excitation of CT and LE_BDP bands yields weak catalytic activity (t_1/2 > 15 min), excitation to higher energy states of TFTPN induces significant increases in photoactivity (t_1/2 ≅ 5 min). The increase is attributable to (i) enhanced light collection, (ii) FRET between TFTPN and BDP, (iii) the presence of heavy atoms (bromine) having large spin-orbit coupling energies that can facilitate intersystem crossing from donor-acceptor CT-, FRET-, or LE-generated BDP singlet states to BDP-related triplet states, and (iv) polymer triplet excited-state sensitization of the formation of CEES-reactive, singlet oxygen.

Oxime as a general photocage for the design of visible light photo-activatable fluorophores

Photoactivatable fluorophores have been widely used for tracking molecular and cellular dynamics with subdiffraction resolution. In this work, we have prepared a series of photoactivatable probes using the oxime moiety as a new class of photolabile caging group in which the photoactivation process is mediated by a highly efficient photodeoximation reaction. Incorporation of the oxime caging group into fluorophores results in loss of fluorescence. Upon light irradiation in the presence of air, the oxime-caged fluorophores are oxidized to their carbonyl derivatives, restoring strong fluorophore fluorescence. To demonstrate the utility of these oxime-caged fluorophores, we have created probes that target different organelles for live-cell confocal imaging. We also carried out photoactivated localization microscopy (PALM) imaging under physiological conditions using low-power light activation in the absence of cytotoxic additives. Our studies show that oximes represent a new class of visible-light photocages that can be widely used for cellular imaging, sensing, and photo-controlled molecular release.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

C=C Bond Oxidative Cleavage of BODIPY Photocages by Visible Light

Photocages for protection and the controlled release of bioactive compounds have been widely investigated. However, the vast majority of these photocages employ the cleavage of single bonds and high-energy ultraviolet light. The construction of a photoactivation system that uses visible light to cleave unsaturated bonds still remains a challenge. Herein, we report a regioselective oxidative cleavage of C=C bonds from a boron-dipyrrolemethene (BODIPY)-based photocage by illumination at 630 nm, resulting in a free aldehyde and a thiol fluorescent probe. This strategy was demonstrated in live HeLa cells, and the generated α-formyl-BODIPY allowed real-time monitoring of aldehyde release in the cells. In particular, it is shown that a mannose-functionalized photocage can target HepG2 cells.

Efficient Far-Red/Near-IR Absorbing BODIPY Photocages by Blocking Unproductive Conical Intersections

Photocages are light-sensitive chemical protecting groups that give investigators control over activation of biomolecules using targeted light irradiation. A compelling application of far-red/near-IR absorbing photocages is their potential for deep tissue activation of biomolecules and phototherapeutics. Toward this goal, we recently reported BODIPY photocages that absorb near-IR light. However, these photocages have reduced photorelease efficiencies compared to shorter-wavelength absorbing photocages, which has hindered their application. Because photochemistry is a zero-sum competition of rates, improvement of the quantum yield of a photoreaction can be achieved either by making the desired photoreaction more efficient or by hobbling competitive decay channels. This latter strategy of inhibiting unproductive decay channels was pursued to improve the release efficiency of long-wavelength absorbing BODIPY photocages by synthesizing structures that block access to unproductive singlet internal conversion conical intersections, which have recently been located for simple BODIPY structures from excited state dynamic simulations. This strategy led to the synthesis of new conformationally restrained boron-methylated BODIPY photocages that absorb light strongly around 700 nm. In the best case, a photocage was identified with an extinction coefficient of 124000 M^-1 cm^-1, a quantum yield of photorelease of 3.8%, and an overall quantum efficiency of 4650 M^-1 cm^-1 at 680 nm. This derivative has a quantum efficiency that is 50-fold higher than the best known BODIPY photocages absorbing >600 nm, validating the effectiveness of a strategy for designing efficient photoreactions by thwarting competitive excited state decay channels. Furthermore, 1,7-diaryl substitutions were found to improve the quantum yields of photorelease by excited state participation and blocking ion pair recombination by internal nucleophilic trapping. No cellular toxicity (trypan blue exclusion) was observed at 20 μM, and photoactivation was demonstrated in HeLa cells using red light.

Self-Amplified Photodynamic Therapy through the 1 O2 -Mediated Internalization of Photosensitizers from a Ppa-Bearing Block Copolymer

Nanocarriers are employed to deliver photosensitizers for photodynamic therapy (PDT) through the enhanced penetration and retention effect, but disadvantages including the premature leakage and non-selective release of photosensitizers still exist. Herein, we report a 1 O2 -responsive block copolymer (POEGMA-b-P(MAA-co-VSPpaMA) to enhance PDT via the controllable release of photosensitizers. Once nanoparticles formed by the block copolymer have accumulated in a tumor and have been taken up by cancer cells, pyropheophorbide a (Ppa) could be controllably released by singlet oxygen (1 O2 ) generated by light irradiation, enhancing the photosensitization. This was demonstrated by confocal laser scanning microscopy and in vivo fluorescence imaging. The 1 O2 -responsiveness of POEGMA-b-P(MAA-co-VSPpaMA) block copolymer enabled the realization of self-amplified photodynamic therapy by the regulation of Ppa release using NIR illumination. This may provide a new insight into the design of precise PDT.

Near Infrared-Triggered Liposome Cages for Rapid, Localized Small Molecule Delivery

Photolabile chelating cages or protecting groups need complex chemical syntheses and require UV, visible, or two-photon NIR light to trigger release. Different cages have different solubilities, reaction rates,  and energies required for triggering. Here we show that liposomes containing calcium, adenosine triphosphate, or carboxyfluorescein are tethered to plasmon-resonant hollow gold nanoshells (HGN) tuned to absorb light from 650-950 nm. Picosecond pulses of near infrared (NIR) light provided by a two-photon microscope, or by a stand-alone laser during flow through microfluidic channels, trigger contents release with spatial and temporal control. NIR light adsorption heats the HGN, inducing vapor nanobubbles that rupture the liposome, releasing cargo within milliseconds. Any water-soluble molecule can be released at essentially the same rate from the liposome-HGN. By using liposomes of different composition, or HGN of different sizes or shapes with different nanobubble threshold fluences, or irradiating on or off resonance, two different cargoes can be released simultaneously, one before the other, or in a desired ratio. Calcium release from liposome-HGN can be spatially patterned to crosslink alginate gels and trap living cells. Liposome-HGN provide stable, biocompatible isolation of the bioactive compound from its surroundings with minimal interactions with the local environment.

Single-Atom Fluorescence Switch: A General Approach toward Visible-Light-Activated Dyes for Biological Imaging

Photoactivatable fluorophores afford powerful molecular tools to improve the spatial and temporal resolution of subcellular structures and dynamics. By performing a single sulfur-for-oxygen atom replacement within common fluorophores, we have developed a facile and general strategy to obtain photoactivatable fluorogenic dyes across a broad spectral range. Thiocarbonyl substitution within fluorophores results in significant loss of fluorescence via a photoinduced electron transfer-quenching mechanism as suggested by theoretical calculations. Significantly, upon exposure to air and visible light residing in their absorption regime (365-630 nm), thio-caged fluorophores can be efficiently desulfurized to their oxo derivatives, thus restoring strong emission of the fluorophores. The effective photoactivation makes thio-caged fluorophores promising candidates for super-resolution imaging, which was realized by photoactivated localization microscopy (PALM) with low-power activation light under physiological conditions in the absence of cytotoxic additives (e.g., thiols, oxygen scavengers), a feature superior to traditional PALM probes. The versatility of this thio-caging strategy was further demonstrated by multicolor super-resolution imaging of lipid droplets and proteins of interest.

Simultaneous dual-colour tracking lipid droplets and lysosomes dynamics using a fluorescent probe

After entering a cell, most small molecule fluorescent probes are dispersed in the cytoplasm before they then accumulate in a specific organelle or subcellular zone. Molecules that can enter two or more organelles with high selectivity are all but unknown. In this work, we report a naphthalimide-based fluorescent probe, NIM-7, that allows lipid droplets and lysosomes to be labelled simultaneously and with high specificity. These subcellular entities can then be visualized readily through yellow and red fluorescence, using different excitation and detection channels. NIM-7 allows 3D imaging and quantitative visualizing of lipid droplets and lysosomes. It is also able to track simultaneously the movement of lipid droplets and lysosomes in real-time. We also report here that NIM-7 can be used to image both different cell lines and zebrafish embryos.

Near-Infrared Photoactivatable Nitric Oxide Donors with Integrated Photoacoustic Monitoring

Photoacoustic (PA) tomography is a noninvasive technology that utilizes near-infrared (NIR) excitation and ultrasonic detection to image biological tissue at centimeter depths. While several activatable small-molecule PA sensors have been developed for various analytes, the use of PA molecules for deep-tissue analyte delivery and monitoring remains an underexplored area of research. Herein, we describe the synthesis, characterization, and in vivo validation of photoNOD-1 and photoNOD-2, the first organic, NIR-photocontrolled nitric oxide (NO) donors that incorporate a PA readout of analyte release. These molecules consist of an aza-BODIPY dye appended with an aryl N-nitrosamine NO-donating moiety. The photoNODs exhibit chemostability to various biological stimuli, including redox-active metals and CYP450 enzymes, and demonstrate negligible cytotoxicity in the absence of irradiation. Upon single-photon NIR irradiation, photoNOD-1 and photoNOD-2 release NO as well as rNOD-1 or rNOD-2, PA-active products that enable ratiometric monitoring of NO release. Our in vitro studies show that, upon irradiation, photoNOD-1 and photoNOD-2 exhibit 46.6-fold and 21.5-fold ratiometric turn-ons, respectively. Moreover, unlike existing NIR NO donors, the photoNODs do not require encapsulation or multiphoton activation for use in live animals. In this study, we use PA tomography to monitor the local, irradiation-dependent release of NO from photoNOD-1 and photoNOD-2 in mice after subcutaneous treatment. In addition, we use a murine model for breast cancer to show that photoNOD-1 can selectively affect tumor growth rates in the presence of NIR light stimulation following systemic administration.

Family of BODIPY Photocages Cleaved by Single Photons of Visible/Near-Infrared Light

Photocages are light-sensitive chemical protecting groups that provide external control over when, where, and how much of a biological substrate is activated in cells using targeted light irradiation. Regrettably, most popular photocages (e.g., o-nitrobenzyl groups) absorb cell-damaging ultraviolet wavelengths. A challenge with achieving longer wavelength bond-breaking photochemistry is that long-wavelength-absorbing chromophores have shorter excited-state lifetimes and diminished excited-state energies. However, here we report the synthesis of a family of BODIPY-derived photocages with tunable absorptions across the visible/near-infrared that release chemical cargo under irradiation. Derivatives with appended styryl groups feature absorptions above 700 nm, yielding photocages cleaved with the highest known wavelengths of light via a direct single-photon-release mechanism. Photorelease with red light is demonstrated in living HeLa cells, Drosophila S2 cells, and bovine GM07373 cells upon ∼5 min irradiation. No cytotoxicity is observed at 20 μM photocage concentration using the trypan blue exclusion assay. Improved B-alkylated derivatives feature improved quantum efficiencies of photorelease ∼20-fold larger, on par with the popular o-nitrobenzyl photocages (εΦ = 50-100 M^-1 cm^-1), but absorbing red/near-IR light in the biological window instead of UV light.

Optochemical Control of Biological Processes in Cells and Animals

Biological processes are naturally regulated with high spatial and temporal control, as is perhaps most evident in metazoan embryogenesis. Chemical tools have been extensively utilized in cell and developmental biology to investigate cellular processes, and conditional control methods have expanded applications of these technologies toward resolving complex biological questions. Light represents an excellent external trigger since it can be controlled with very high spatial and temporal precision. To this end, several optically regulated tools have been developed and applied to living systems. In this review we discuss recent developments of optochemical tools, including small molecules, peptides, proteins, and nucleic acids that can be irreversibly or reversibly controlled through light irradiation, with a focus on applications in cells and animals.

Detoxification of a Sulfur Mustard Simulant Using a BODIPY-Functionalized Zirconium-Based Metal-Organic Framework

Effective detoxification of chemical warfare agents is a global necessity. As a powerful photosensitizer, a halogenated BODIPY ligand is postsynthetically appended to the Zr₆ nodes of the metal-organic framework (MOF), NU-1000, to enhance singlet oxygen generation from the MOF. The BODIPY/MOF material is then used as a heterogeneous photocatalyst to produce singlet oxygen under green LED irradiation. The singlet oxygen selectively detoxifies the sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES), to the less toxic sulfoxide derivative (2-chloroethyl ethyl sulfoxide, CEESO) with a half-life of approximately 2 min.

Peptide Receptor-Targeted Fluorescent Probe: Visualization and Discrimination between Chronic and Acute Ulcerative Colitis

The inflammatory activity of ulcerative colitis plays an important role in the medical treatment. However, accurate and real-time monitoring of the colitis activity with noninvasive bioimaging method is still challenging, especially in distinguishing between chronic and acute colitis. As a good receptor, the oligopeptide transporter (PepT1) is overexpressed in the colonic epithelial cells of chronic ulcerative colitis, which can deliver tripeptide KPV (Lys-Pro-Val, the C-terminal sequence of α-MSH) into cytosol in the intestine. Herein, we report a PepT1 peptide receptor-targeted fluorescent probe, dicyanomethylene-4H-pyran (DCM)-KPV, with the strategy of conjugating the KPV into the DCM chromophore. The diagnostic fluorescent probe bestows a specific receptor-targeted interaction with PepT1 through the KPV moiety, possessing several beneficial characteristics, such as efficient long emission, low photobleaching, negligible cytotoxicity, and high cytocompatibility in living cells. We build the overexpressed PepT1 on the cytomembrane of ulcerative colitis model Caco-2 cell as the efficient receptor to accumulate the targeted tripeptide KPV in the cytoplasm and nucleus. With the co-localization of DCM-KPV and the DNA-specific fluorophore, DAPI, the specifically long emission from chromophore DCM and efficient receptor-targeted peptide KPV, the fluorescent probe of DCM-KPV makes a breakthrough to the direct noninvasive observation of the accumulation in colon inflammation regions via intestinal mucosa, even successfully distinguishing the chronic, acute ulcerative colitis and normal groups. Compared with the traditional unenhanced magnetic resonance imaging and hematoxylin and eosin (H&E) staining, we make full use of exploiting the specific target-receptor interaction between the tripeptide unit, KPV, and the oligopeptide transporter, PepT1, for sensing selectivity. The desirable diagnostic ability of DCM-KPV can guarantee the real-time tracking and visualization of the role of intracellular KPV on ulcerative colitis, which provides an alternative to replace the time-consuming and tissue sampling-invasive H&E staining diagnosis.

Smart Nanostructures for Cargo Delivery: Uncaging and Activating by Light

Nanotechnology has begun to play a remarkable role in various fields of science and technology. In biomedical applications, nanoparticles have opened new horizons, especially for biosensing, targeted delivery of therapeutics, and so forth. Among drug delivery systems (DDSs), smart nanocarriers that respond to specific stimuli in their environment represent a growing field. Nanoplatforms that can be activated by an external application of light can be used for a wide variety of photoactivated therapies, especially light-triggered DDSs, relying on photoisomerization, photo-cross-linking/un-cross-linking, photoreduction, and so forth. In addition, light activation has potential in photodynamic therapy, photothermal therapy, radiotherapy, protected delivery of bioactive moieties, anticancer drug delivery systems, and theranostics (i.e., real-time monitoring and tracking combined with a therapeutic action to different diseases sites and organs). Combinations of these approaches can lead to enhanced and synergistic therapies, employing light as a trigger or for activation. Nonlinear light absorption mechanisms such as two-photon absorption and photon upconversion have been employed in the design of light-responsive DDSs. The integration of a light stimulus into dual/multiresponsive nanocarriers can provide spatiotemporal controlled delivery and release of therapeutic agents, targeted and controlled nanosystems, combined delivery of two or more agents, their on-demand release under specific conditions, and so forth. Overall, light-activated nanomedicines and DDSs are expected to provide more effective therapies against serious diseases such as cancers, inflammation, infections, and cardiovascular disease with reduced side effects and will open new doors toward the treatment of patients worldwide.

Red emission fluorescent probes for visualization of monoamine oxidase in living cells

Here we report two novel red emission fluorescent probes for the highly sensitive and selective detection of monoamine oxidase (MAO) with large Stokes shift (227 nm). Both of the probes possess solid state fluorescence and can accomplish the identification of MAO on test papers. The probe MAO-Red-1 exhibited a detection limit down to 1.2 μg mL⁻¹ towards MAO-B. Moreover, the cleavage product was unequivocally conformedby HPLC and LCMS and the result was in accordance with the proposed oxidative deamination mechanism. The excellent photostability of MAO-Red-1 was proved both in vitro and in vivo through fluorescent kinetic experiment and laser exposure experiment of confocal microscopy, respectively. Intracellular experiments also confirmed the low cytotoxity and exceptional cell imaging abilities of MAO-Red-1. It was validated both in HeLa and HepG2 cells that MAO-Red-1 was capable of reporting MAO activity through the variation of fluorescence intensity.

Rewiring Multidomain Protein Switches: Transforming a Fluorescent Zn(2+) Sensor into a Light-Responsive Zn(2+) Binding Protein

Protein-based sensors and switches provide attractive tools for the real-time monitoring and control of molecular processes in complex biological environments. Fluorescent sensor proteins have been developed for a wide variety of small molecules, but the construction of genetically encoded light-responsive ligand binding proteins remains mostly unexplored. Here we present a generic approach to reengineer a previously developed FRET-based Zn(2+) sensor into a light-activatable Zn(2+) binding protein using a design strategy based on mutually exclusive domain interactions. These so-called VividZn proteins consist of two light-responsive Vivid domains that homodimerize upon illumination with blue light, thus preventing the binding of Zn(2+) between two Zn(2+) binding domains, Atox1 and WD4. Following optimization of the linker between WD4 and the N-terminus of one of the Vivid domains, VividZn variants were obtained that show a 9- to 55-fold decrease in Zn(2+) affinity upon illumination, which is fully reversible following dark adaptation. The Zn(2+) affinities of the switch could be rationally tuned between 1 pM and 2 nM by systematic variation of linker length and mutation of one of the Zn(2+) binding residues. Similarly, introduction of mutations in the Vivid domains allowed tuning of the switching kinetics between 10 min and 7 h. Low expression levels in mammalian cells precluded the demonstration of light-induced perturbation of cytosolic Zn(2+) levels. Nonetheless, our results firmly establish the use of intramolecular Vivid dimerization as an attractive light-sensitive input module to rationally engineer light-responsive protein switches based on mutually exclusive domain interactions.

4-Trifluoromethyl-p-quinols as dielectrophiles: three-component, double nucleophilic addition/aromatization reactions

In recent years, numerous methods have emerged for the synthesis of trifluoromethylated arenes based on the late-stage introduction of a trifluoromethyl group onto an aryl ring. In sharp comparison, the synthesis of trifluoromethylated arenes based on the pre-introduction of a trifluoromethyl group onto an "aromatic to be" carbon has rarely been addressed. It has been found that 4-trifluoromethyl-p-quinol silyl ethers, the readily available and relatively stable compounds, can act as dielectrophiles to be applied to multi-component reactions for the synthesis of various trifluoromethylated arenes. Catalyzed by In(OTf)3, 4-trifluoromethyl-p-quinol silyl ethers react with C-, N-, and S-nucleophiles, respectively, in a regiospecific 1,2-addition manner to generate the corresponding highly reactive electrophilic intermediates. Further reaction of the in-situ generated electrophiles with a C-nucleophile followed by spontaneous aromatization enables the construction of functionalized trifluoromethyl arenes. This three-component, double nucleophilic addition/aromatization reaction based on the pre-introduction of a trifluoromethyl group onto an "aromatic to be" carbon provides a divergent strategy for the synthesis of trifluoromethylated arenes under mild reaction conditions in a single operation.

Morphology-Tailoring of a Red AIEgen from Microsized Rods to Nanospheres for Tumor-Targeted Bioimaging

Efficient morphology modulation of a red AIEgen from pristine microsized rods to nanospheres is achieved via encapsula ting QM-2 (quinolinemalononitrile-2) into hybrid micelles. This novel reagent shows great potential in tumor-targeted bioimaging because of its monodispersion in aqueous systems, the uniform diameter of ≈30 nm, enhanced fluorescence brightness with a large Stokes shift of 190 nm, and strongly increased biocompatibility and photostability.

Efficient Red Light Photo-Uncaging of Active Molecules in Water Upon Assembly into Nanoparticles

We introduce a means of efficiently photo-uncaging active compounds from amino-1,4-benzoquinone in aqueous environments. Aqueous photochemistry of this photocage with one-photon red light is typically not efficient unless the photocaged molecules are allowed to assemble into nanoparticles. A variety of biologically active molecules were functionalized with the photocage and subsequently formulated into water-dispersible nanoparticles. Red light irradiation through various mammalian tissues achieved efficient photo-uncaging. Co-encapsulation of NIR fluorescent dyes and subsequent photomodulation provides a NIR fluorescent tool to assess both particle location and successful photorelease.

Selective photosensitization through an AND logic response: optimization of the pH and glutathione response of activatable photosensitizers

A series of pH and GSH responsive photosensitizers were designed and synthesized. pKa values were optimized by adjusting the inductive contribution of substituents to reach a pH range (6.0-7.4) relevant to the tumour microenvironment. pH-Activatable behaviour and redox mediated release of the quencher from the PS by GSH allow the construction of an AND logic operator for selective photodynamic action in aqueous solutions.