Thermodynamically Stable,Photoreversible Pharmacology in Neurons with One‐ and Two‐Photon Excitation

Photoswitchable bioprobes enable bidirectional control of cell physiology with different wavelengths of light. Many current photoswitches use cytotoxic UV light and are limited by the need for constant illumination owing to thermal relaxation in the dark. Now a photoswitchable tetrafluoroazobenzene(4FAB)‐based ion channel antagonist has been developed that can be efficiently isomerized in two separate optical channels with visible light. Importantly, the metastable cis configuration showed very high stability in the dark over the course of days at room temperature. In neurons, the 4FAB antagonist reversibly blocks voltage‐gated ion channels with violet and green light. Furthermore, photoswitching could also be achieved with two‐photon excitation yielding high spatial resolution. 4FAB probes have the potential to enable long‐term biological studies where both ON and OFF states can be maintained in the absence of irradiation.     

Tunable Water‐Soluble Supramolecular Polymers by Visible‐Light‐Regulated Host–Guest Interactions

The development of artificial self‐assembling systems with dynamic photo‐regulation features in aqueous solutions has drawn great attention owing to the potential applications in fabricating elaborate biological materials. Here we demonstrate the fabrication of water‐soluble cucurbit[8]uril (CB[8])‐mediated supramolecular polymers by connecting the fluorinated azobenzene (FAB) containing monomers through host‐enhanced heteroternary π–π stacking interactions. Benefiting from the unique visible‐light‐induced E→Z photoisomerization of the FAB photochromophores, the encapsulation behaviors between the CB[8] macrocycle and the monomers could be regulated upon visible light irradiation, resulting in the depolymerization of such CB[8]‐mediated supramolecular polymers.     

Remote Regulation of Membrane Channel Activity by Site‐Specific Localization of Lanthanide‐Doped Upconversion Nanocrystals

The spatiotemporal regulation of light‐gated ion channels is a powerful tool to study physiological pathways and develop personalized theranostic modalities. So far, most existing light‐gated channels are limited by their action spectra in the ultraviolet (UV) or visible region. Simple and innovative strategies for the specific attachment of photoswitches on the cell surface without modifying or genetically encoding channel structures, and more importantly, that enable the remote activation of ion‐channel functions within near‐infrared (NIR) spectral window in living systems, remain a challenging concern. Herein, metabolic glycan biosynthesis is used to achieve site‐specific covalent attachment of near‐infrared‐light‐mediated lanthanide‐doped upconversion nanocrystals (UCNs) to the cell surface through copper‐free click cyclization. Upon irradiation with 808 nm light, the converted emission at 480 nm could activate a light‐gated ion channel, channelrhodopsins‐2 (ChR2), and thus remotely control the cation influx. This unique strategy provides valuable insights on the specific regulation membrane‐associated activities in vivo.     

Dissociation mechanisms and implication for the presence of multiple conformations for peptide ions with arginine at the C‐terminus: time‐resolved photodissociation study

Time‐resolved photodissociation (PD) patterns of singly protonated peptides with arginine at the C‐terminus (C‐arg peptide ions) have been used to classify the dissociation channels into two categories, i.e. high‐energy channels generating v, w and x and low‐energy ones generating b, y and z. x + 1 formed by C_α? CO cleavage seems to be the intermediate ion in high‐energy channels just as a + 1 is for N‐arg peptide ions. Difference in time‐resolved pattern indicates that the two sets of channels, high‐ and low‐energy ones, are not in direct competition. Noncompetitive dissociation is also indicated by the observation of anomalous effect of matrix used in matrix‐assisted laser desorption ionization, a cooler matrix generating more high‐energy product ions both in spontaneous dissociation and in PD. Results from detailed investigation suggest that the two sets of channels start from two (or more) different conformations. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient Gating of Ion Transport in Three‐Dimensional Metal–Organic Framework Sub‐Nanochannels with Confined Light‐Responsive Azobenzene Molecules

1D nanochannels modified with responsive molecules are fabricated to replicate gating functionalities of biological ion channels, but gating effects are usually weak because small molecular gates cannot efficiently block the large channels in the closed states. Now, 3D metal–organic framework (MOF) sub‐nanochannels (SNCs) confined with azobenzene (AZO) molecules achieve efficient light‐gating functionalities. The 3D MOFSNCs consisting of a MOF UiO66 with ca. 9–12 Å cavities connected by ca. 6 Å triangular windows work as angstrom‐scale ion channels, while confined AZO within the MOF cavities function as light‐driven molecular gates to efficiently regulate the ion flux. The AZO‐MOFSNCs show good cyclic gating performance and high on–off ratios up to 17.8, an order of magnitude higher than ratios observed in conventional 1D AZO‐modified nanochannels (1.3–1.5). This work provides a strategy to develop highly efficient switchable ion channels based on 3D porous MOFs and small responsive molecules.     

Make them Blink: Probes for Super‐Resolution Microscopy

In recent years, a number of approaches have emerged that enable far‐field fluorescence imaging beyond the diffraction limit of light, namely super‐resolution microscopy. These techniques are beginning to profoundly alter our abilities to look at biological structures and dynamics and are bound to spread into conventional biological laboratories. Nowadays these approaches can be divided into two categories, one based on targeted switching and readout, and the other based on stochastic switching and readout of the fluorescence information. The main prerequisite for a successful implementation of both categories is the ability to prepare the fluorescent emitters in two distinct states, a bright and a dark state. Herein, we provide an overview of recent developments in super‐resolution microscopy techniques and outline the special requirements for the fluorescent probes used. In combination with the advances in understanding the photophysics and photochemistry of single fluorophores, we demonstrate how essentially any single‐molecule compatible fluorophore can be used for super‐resolution microscopy. We present examples for super‐resolution microscopy with standard organic fluorophores, discuss factors that influence resolution and present approaches for calibration samples for super‐resolution microscopes including AFM‐based single‐molecule assembly and DNA origami.     

Cytotoxicity of All‐Trans‐Retinal Increases Upon Photodegradation†

All‐trans‐retinal (AtRal) can accumulate in the retina as a result of excessive exposure to light. The purpose of this study was to compare cytotoxicity of AtRal and photodegraded AtRal (dAtRal) on cultured human retinal pigment epithelial cells in dark and upon exposure to visible light. AtRal was degraded by exposure to visible light. Cytotoxicity was monitored by imaging of cell morphology, propidium iodide staining of cells with permeable plasma membrane and measurements of reductive activity of cells. Generation of singlet oxygen photosensitized by AtRal and dAtRal was monitored by time‐resolved measurements of characteristic singlet oxygen phosphorescence. Photodegradation of AtRal resulted in a decrease in absorption of visible light and accumulation of the degradation products with absorption maximum at ～330 nm. Toxicity of dAtRal was concentration‐dependent and was greater during irradiation with visible light than in dark. DAtRal was more cytotoxic than AtRal both in dark and during exposure to visible light. Photochemical properties of dAtRal indicate that it may be responsible for the maximum in the action spectra of retinal photodamage recorded in animals. In conclusion, photodegradation products of AtRal may impose a significant threat to the retina and therefore their roles in retinal pathology need to be explored.     

Photocatalytic Self‐Doped SnO2−x Nanocrystals Drive Visible‐Light‐Responsive Color Switching

Visible‐light‐responsive reversible color‐switching systems are attractive to many applications because visible light has superior penetration and causes far less damage to organic molecules than UV. Herein, we report that self‐doping of SnO_2−x nanocrystals with Sn²⁺ red‐shifts their absorption to the visible region and simultaneously produces oxygen vacancies, which can effectively scavenge photogenerated holes and thus enable the color switching of redox dyes using visible light. Wavelength‐selective switching can also be achieved by coupling the photocatalytic activity of the SnO_2−x NCs with the color‐switching kinetics of different redox dyes. The fast light response enables the further fabrication of a solid film that can be repeatedly written on using a visible laser pen or projection printing through a photomask. This discovery represents a big step forward towards practical applications, especially in areas in which safety issues and photodamage by UV light are of concern.     

Nondoped Deep‐Blue Organic Light‐Emitting Diodes with Color Stability and Very Low Efficiency Roll‐Off: Solution‐Processable Small‐Molecule Fluorophores by Phosphine Oxide Linkage

A series of solution‐processable small molecules PO1 – PO4 were designed and synthesized by linking N‐phenylnaphthalen‐1‐amine groups to a phenyl phosphine oxide core through a π‐conjugated bridge, and their thermal, photophysical, and electrochemical properties were investigated. The phosphine oxide linkage can disrupt the conjugation and allows the molecular system to be extended to enable solution processability and high glass transition temperatures (159–181 °C) while preserving the deep‐blue emission. The noncoplanar molecular structures resulting from the trigonal‐pyramidal configuration of the phosphine oxide can suppress intermolecular interactions, and thus these compounds exhibit strong deep‐blue emission both in solution and the solid state with high photoluminescent quantum yield (PLQY) of 0.88–0.99 in dilute toluene solution. Solution‐processed nondoped organic light‐emitting diodes featuring PO4 as emitter achieve a maximum current efficiency of 2.36 cd A^?1 with CIE coordinates of (0.15, 0.11) that are very close to the NTSC blue standard. Noticeably, all devices based on these small‐molecular fluorescent emitters show striking deep‐blue electroluminescent color stability and extremely low efficiency roll‐off.     

Theoretical study of one‐carbon unit transfer between methyl‐AICA and N1‐methyl‐N1‐acryloyl‐formamide

The mechanism of one‐carbon unit transfer between 1‐methyl‐5‐amino‐4‐carboxamide imidazole (M‐AICA) and N¹‐methyl‐N¹‐acryloyl‐formamide (the model molecule of 10‐f‐H4F) is investigated by the Hartree–Fock and DFT methods, respectively, at the 6‐31G* basis level. There are two different channels for the proton transfer, resulting in two reaction pathways with different properties. The results indicate that both channels can complete the reaction, but path a is slightly favored due to its lower active energy barrier. Furthermore, the influence of 4‐carboxamindde in M‐AICA is also discussed. This group can stabilize the reactant and intermediates, and reduce the active energy barrier through the intermolecular hydrogen bond. The intermolecular hydrogen bond results in an enlarged conjugation system and makes the transition states more stable. Our results are in agreement with experiments. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Tetrakis(diethyl‐phosphonat)‐, Tetrakis(ethyl‐phenylphosphinat)‐ und Tetrakis(diphenylphosphin‐oxid)‐substituierte Phthalocyanine

Tetrakis(diethyl phosphonate), Tetrakis(ethyl phenylphosphinate)‐, and Tetrakis(diphenylphosphine oxide)‐Substituted Phthalocyanines The title compounds 7, 9 , and 11 are obtained by tetramerization of diethyl (3,4‐dicyanophenyl)phosphonate ( 5 ), ethyl (3,4‐dicyanophenyl)phenylphosphinate ( 8 ), and 4‐(diphenylphosphinyl)benzene‐1,2‐dicarbonitrile ( 10 ). The ³¹P‐NMR spectra of the phthalocyanines 7, 9 , and 11 and of their metal complexes present five to eight signals confirming the formation of four constitutional isomers with the expected C_4h, D_2h, C_2v, and C_s symmetry. In the FAB‐MS of the Zn, Cu, and Ni complexes of 7 and 9 , the peaks of dimeric phthalocyanines are observed. By gel‐permeation chromatography, the monomeric complex [Ni( 7 )] and a dimer [Ni( 7 )]₂ can be separated. These dimers differ from the known phthalocyanine dimers, i.e., possibly the P(O)(OEt)₂ and P(O)(Ph)(OEt) substituents in 7 and 9 are involved in complexation. The free phosphonic acid complex [Zn( 12 )] and [Cu( 12 )] are H₂O‐soluble. In the FAB‐MS of [Zn( 12 )], only the peaks of the dimer are present; the ESI‐MS confirms the existence of the dimer and the metal‐free dimer. In the UV/VIS spectrum of [Zn( 12 )], the hypsochromic shift characteristic for the known type of dimers from 660–700 nm to 620–640 nm is observed. As in the FAB‐MS of [Zn( 12 )], the free phosphinic acid complex [Zn( 13 )] shows only the monomer, an ESI‐MS cannot be obtained for solubility problems. The UV/VIS spectrum of [Zn( 13 )] demonstrates the existence of the monomer as well as of the dimer.     

Metal Complexes Supported on Solid Matrices for Visible‐Light‐Driven Molecular Transformations

Hybridization of visible‐light‐responsive metal complexes with solid matrices offers an attractive route for practical catalyst design of nanostructured photocatalysts that are operationally simple and can attain unprecedented reactions owing to synergistic effects. This Minireview highlights the precise architectures of hybrid photocatalysts that enable efficient and selective photochemical molecular transformations, including selective oxidation by O₂ and H₂ evolution from water. Several techniques for the immobilization of metal complexes are discussed, including encapsulation within zeolite cavities, anchoring within mesoporous channels, incorporation within the macroreticular space of ion‐exchange resins, intercalation within the interlayer spaces of layered materials, and anchoring onto the plasmonic colloidal Ag nanoparticles. The relationships between photoluminescence characteristics and photocatalytic activities of these hybrid materials are also discussed.     

两类三组份反应产物：1,3-恶嗪及嘧啶-2-酮类化合物的质谱学行为研究

电喷雾质谱被应用于分辨2-氨基-1,3-恶嗪及六氢化-4-苯基-吡喃[2,3-d]嘧啶-2-酮的杂环结构。两类化合物均为三组份反应的产物,且其杂环的结构很难用NMR判断。实验首次系统研究了两类化合物的质谱学行为（包括氘代实验和高分辨质谱研究）,发现前者在CID实验中丢失CH2N2和HCNO,而后者为直接丢失尿素。这些特征丢失为该类衍生物的结构判断,尤其是高通量的合成产物分析提供了重要的依据。     

Masked Rhodamine Dyes of Five Principal Colors Revealed by Photolysis of a 2‐Diazo‐1‐Indanone Caging Group: Synthesis,Photophysics, and Light Microscopy Applications

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as “hidden” markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2‐diazo‐1‐indanone group can be irreversibly photoactivated, either by irradiation with UV‐ or violet light (one‐photon process), or by exposure to intense red light (λ～750 nm; two‐photon mode). All dyes possess a very small 2‐diazoketone caging group incorporated into the 2‐diazo‐1‐indanone residue with a quaternary carbon atom (C‐3) and a spiro‐9H‐xanthene fragment. Initially they are non‐colored (pale yellow), non‐fluorescent, and absorb at λ=330–350 nm (molar extinction coefficient (ε)≈10⁴ M^?1 cm^?1) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range (λ=511–633 and 525–653 nm, respectively). The unmasked dyes are highly colored and fluorescent (ε= 3–8×10⁴ M^?1 cm^?1 and fluorescence quantum yields (?)=40–85 % in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water‐soluble caged red‐emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino‐reactive N‐hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375–420 nm light or intense red light (λ=775 nm). Protein conjugates with optimal degrees of labeling (3–6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions (?=20–38 %). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10–40 % of the non‐fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a “dark” non‐emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super‐resolution optical microscopy is exemplified.     

Additive‐Free Green Light‐Induced Ligation Using BODIPY Triggers

Photochemical ligation is important in biomaterials engineering for spatiotemporal control of biochemical processes. Such reactions however generally require activation by high energy UV or short wavelength blue light, which can limit their use as a consequence of the potential of these high energy light sources to damage living cells. Herein, we present an additive‐free, biocompatible, chemical ligation triggered by mild visible light. BODIPY dyes with a pendant thioether attached at the meso‐position undergo photolysis of the [C?S] bond under green light (λ=530 nm) excitation, producing an ion pair intermediate that can react specifically with a propiolate group. The utility of this photochemical ligation in materials science is demonstrated by the fabrication of hydrogels with specific architectures, photo‐immobilization of biomacromolecules, and live cell encapsulation within a hydrogel scaffold.     

Synthesis ofN1‐3‐{(4‐Substituted aryl‐3‐chloro‐2‐oxo‐azetidine)‐iminocarbamyl}‐propyl‐6‐nitroindazole Derivatives and Their Biological Significance

Synthesis ofN¹‐3‐{(4‐substitute daryl‐3‐chloro‐2‐oxo‐azetidine)‐iminocarbamyl}‐propyl‐6‐nitroindazole 4a – 4s was conducted by a conventional method. All the compounds were synthesized and characterized by IR, ¹H NMR, ¹³C NMR, FAB‐Mass techniques and chemical methods. All the final synthesized compounds were evaluated for their antimicrobial activity and antitubercular activity with MIC values against some selected microorganisms.     

Insight into Ion Transfer through the Sub‐Nanometer Channels in Zeolitic Imidazolate Frameworks

A crack‐free sub‐nanometer composite structure for the study of ion transfer was constructed by in situ growth of ZIF‐90 [Zn(ICA)₂, ICA=Imidazole‐2‐carboxaldehyde] on the tip of a glass nanopipette. The potential‐driven ion transfer through the sub‐nanometer channels in ZIF‐90 is strongly influenced by the pH of the solution. A rectification ratio over 500 is observed in 1 m KCl solution under alkaline conditions (pH 11.58), which is the highest value reported under such a high salt concentration. Fluorescence experiments show the super‐high rectification ratio under alkaline conditions results from the strong electrostatic interaction between ions and the sub‐nanometer channels of ZIF‐90. In addition to providing a general pathway for further study of mass‐transfer process through sub‐nanometer channels, the approach enable all kinds of metal–organic frameworks (MOFs) to be used as ionic permselectivity materials in nanopore‐based analysis.     

Efficient Excitation‐Energy Transfer in Ion‐Based Organic Nanoparticles with Versatile Tunability of the Fluorescence Colours

Organic nanoparticles consisting of 3,3′‐diethylthiacyanine (TC) and ethidium (ETD) dyes are synthesized by ion‐association between the cationic dye mixture (10 % ETD doping) and the tetrakis(4‐fluorophenyl)borate (TFPB) anion, in the presence of a neutral stabilizing polymer, in aqueous solution. Doping with ETD makes the particle size smaller than without doping. Size tuning can also be conducted by varying the molar ratio (ρ) of the loaded anion to the cationic dyes. The fluorescence spectrum of TC shows good overlap with the absorption of ETD in the 450–600 nm wavelength region, so efficient excitation‐energy transfer from TC (donor) to ETD (acceptor) is observed, yielding organic nanoparticles whose fluorescence colours are tunable. Upon ETD doping, the emission colour changes significantly from greenish‐blue to reddish or whitish. This change is mainly dependent on ρ. For the doped nanoparticle sample with ρ=1, the intensity of fluorescence ascribed to ETD is ～150‐fold higher than that from pure ETD nanoparticles (efficient antenna effect). Non‐radiative Förster resonance‐energy transfer (FRET) is the dominant mechanism for the ETD fluorescence enhancement. The organic nanoparticles of a binary dye system fabricated by the ion‐association method act as efficient light‐harvesting antennae, which are capable of transferring light energy to the dopant acceptors in very close proximity to the donors, and can have multi‐wavelength emission colours with high fluorescence quantum yields.     

Photosensory Functions of Channelrhodopsins in Native Algal Cells†

Photomotility responses in flagellate alga are mediated by two types of sensory rhodopsins (A and B). Upon photoexcitation they trigger a cascade of transmembrane currents which provide sensory transduction of light stimuli. Both types of algal sensory rhodopsins demonstrate light‐gated ion channel activities when heterologously expressed in animal cells, and therefore they have been given the alternative names channelrhodopsin 1 and 2. In recent publications their channel activity has been assumed to initiate the transduction chain in the native algal cells. Here we present data showing that: (1) the modes of action of both types of sensory rhodopsins are different in native cells such as Chlamydomonas reinhardtii than in heterologous expression systems, and also differ between the two types of rhodopsins; (2) the primary function of Type B sensory rhodopsin (channelrhodopsin‐2) is biochemical activation of secondary Ca²⁺‐channels with evidence for amplification and a diffusible messenger, sufficient for mediating phototaxis and photophobic responses; (3) Type A sensory rhodopsin (channelrhodopsin‐1) mediates avoidance responses by direct channel activity under high light intensities and exhibits low‐efficiency amplification. These dual functions of algal sensory rhodopsins enable the highly sophisticated photobehavior of algal cells.