A Nucleic Acid Dependent Chemical Photocatalysis in Live Human Cells

Only two nucleic acid directed chemical reactions that are compatible with live cells have been reported to date. Neither of these processes generate toxic species from nontoxic starting materials. Reactions of the latter type could be applied as gene‐specific drugs, for example, in the treatment of cancer. We report here the first example of a chemical reaction that generates a cytotoxic drug from a nontoxic prodrug in the presence of a specific endogeneous ribonucleic acid in live mammalian cells. In this case, the prodrug is triplet oxygen and the drug is singlet oxygen. The key component of this reaction is an inert molecule (InP–2′‐OMe‐RNA/Q–2′‐OMe‐RNA; P: photosensitizer; Q: quencher), which becomes an active photosensitizer (InP–2′‐OMe‐RNA) in the presence of single‐stranded nucleic acid targets. Upon irradiation with red light, the photosensitizer produces over 6000 equivalents of toxic singlet oxygen per nucleic acid target. This reaction is highly sequence specific. To detect the generation of singlet oxygen in live cells, we prepared a membrane‐permeable and water‐soluble fluorescent scavenger, a derivative of 2,5‐diphenylisobenzofurane. The scavenger decomposes upon reaction with singlet oxygen and this is manifested in a decrease in the fluorescence intensity. This effect can be conveniently monitored by flow cytometry.     

Sensitizer-controlled photochemical reactivity via upconversion of red light

By combining the energy input from two red photons, chemical reactions that would normally require blue or ultraviolet irradiation become accessible. Key advantages of this biphotonic excitation strategy are that red light usually penetrates deeper into complex reaction mixtures and causes less photo-damage than direct illumination in the blue or ultraviolet. Here, we demonstrate that the primary light-absorber of a dual photocatalytic system comprised of a transition metal-based photosensitizer and an organic co-catalyst can completely alter the reaction outcome. Photochemical reductions are achieved with a copper(i) complex in the presence of a sacrificial electron donor, whereas oxidative substrate activation occurs with an osmium(ii) photosensitizer. Based on time-resolved laser spectroscopy, this changeover in photochemical reactivity is due to different underlying biphotonic mechanisms. Following triplet energy transfer from the osmium(ii) photosensitizer to 9,10-dicyanoanthracene (DCA) and subsequent triplet–triplet annihilation upconversion, the fluorescent singlet excited state of DCA triggers oxidative substrate activation, which initiates the cis to trans isomerization of an olefin, a [2 + 2] cycloaddition, an aryl ether to ester rearrangement, and a Newman–Kwart rearrangement. This oxidative substrate activation stands in contrast to the reactivity with a copper(i) photosensitizer, where photoinduced electron transfer generates the DCA radical anion, which upon further excitation triggers reductive dehalogenations and detosylations. Our study provides the proof-of-concept for controlling the outcome of a red-light driven biphotonic reaction by altering the photosensitizer, and this seems relevant in the greater context of tailoring photochemical reactivities.

Triplet–triplet annihilation upconversion enables oxidative activation of substrates that would normally require blue or green light irradiation. Photocatalysis experiments are complemented by in-depth laser spectroscopic investigations.     

Photocatalytic generation of hydrogen from water using a platinum(II) terpyridyl acetylide chromophore

The cationic complex [Pt(tolylterpyridine)(phenylacetylide)]+ has been used as a photosensitizer for the reduction of aqueous protons in the presence of a sacrificial electron donor to make H2. In this system, triethanolamine (TEOA) acts as the sacrificial reducing agent, methyl viologen (MV2+) serves as an electron transfer agent, and colloidal Pt stabilized by polyacrylate functions as the catalyst for H2 generation. The Pt(II) chromophore undergoes both oxidative and reductive quenching, but H2 is only seen when both TEOA and MV2+ are present. Irradiation of the reaction solution for 10 h with lambda > 410 nm leads to 85 turnovers and an overall yield of 34% based on TEOA. While H2 evolution is maximized for the system at pH 7, it is also seen at pH 5 and 9, in contrast with earlier reports using Ru(bpy)32+ as the photosensitizer. This is the first time that a Pt diimine or terpyridyl complex has been used as the photosensitizer for H2 generation from aqueous protons.     

Synthesis of a Polymer-bound Sensitizer and its Application in the Photoisomerization of trans-Vitamin D_3 to cis-Vitamin D_3

The photochemistry of the vitamin D family and their precursors has been the subject of extensive studies for many years1-4. Most of the studies focus on the photoisomer- ization of 7-dehydrocholesterol and that of tachysterol to previtamin D3, which is of commercial importance in the synthesis of vitamin D34, 5. Recently the cis/trans isomerization of vitamin D analogs (Scheme 1) draws attention because of its importance in the synthesis of hydroxylated vitamin D metabolites6. However, o…     

Sunlight-driven synthesis of γ-diketones via oxidative coupling of enamines with silyl enol ethers catalyzed by [Ru(bpy)3]2+

A photosensitizer [Ru(bpy)(3)](2+) catalyzes oxidative coupling reaction of enamines with silyl enol ethers under visible light irradiation by a Xe lamp or sunlight to produce γ-diketones. A 2e-oxidation process involved in this reaction is achieved by a combination of the photoexcited [Ru(bpy)(3)](2+) species and duroquinone, a 2e-acceptor.     

Study of photopolymer. XVII. Synthesis of novel photosensitive polymers with pendant photosensitive group and photosensitizer groups

Novel photosensitive polymers with pendant photosensitive group, such as cinnamic ester, and photosensitizer groups, such as N-carbamoyl-p-nitroaniline and N-carbamoly-4-nitro-1-naphthylamine, were synthesized from radical copolymerizations of (2-cinnamoyloxy)ethylmethacrylate with photosensitizer monomers, such as p-nitrophenylmethacrylamide and 4-nitro-1-na-phthylmethacrylamide, by using asobisisobutyronitrile (AIBN) in benzene and from the copolymerizations of (2-hydroxy)ethylmethacrylate or (2-hydroxy)ethylacrylate with photosensitizer monomers by using AIBN in DMF. This procedure was followed by condensation reactions of the copolymers with cinnamoyl chloride with pyridine as HCL acceptor in the same reaction flask. The photoreactivities of the polymers obtained were influenced by the concentration of photosensitive group and photosensitizer groups and their ratio in the polymer matrix. In addition, the photosensitivity of cinnamic ester groups attached to a soft polymer segment was higher than that of cinnamic ester group attached to a hard polymer segment when these polymers had the same pendant N-carbamoyl-p-nitroaniline group as photosensitizer. Furthermore, the spacer length between the polymer chain and photosensitizer group was important for increasing the photoreactivity of the photosensitive group in the polymers with pendant cinnamic ester and N-carbamoyl-p-nitroaniline groups.     

The influence of sodium dodecyl sulfate/benzyl alcohol/H2O system on the photoisomerization of trans-stilbene

Photoisomerization of trans-stilbene (TS) was investigated in sodium dodecyl sulfate (SDS)/benzyl alcohol (BA)/H(2)O systems in order to establish the relationship between the reaction yields and the compositions and structures of molecular organized assemblies. The results show that, in SDS/BA/H(2)O systems with the structures of oil in water microemulsions, bicontinuous microemulsions, and hexagonal liquid crystals, the reaction yields are much larger than those in benzyl alcohol, both with and without the photosensitizer 9,10-anthracenedicarbonitrile. However, SDS/BA/H(2)O water in oil microemulsion and lamellar liquid crystal can obviously catalyze the photoisomerization of TS only when the photosensitizer is not present. The yield is increased with the increase in H(2)O content or with the decrease in BA content.     

Synthesis and photoactivity of pH-responsive amphiphilic block polymer photosensitizer bonded zinc phthalocyanine

A zinc tetraaminophthalocyanine derivative, zinc tetra(methacryloyl moiety)aminophthalocyanine (MeZnAPc) (with a double bond) was synthesized by the reaction between zinc tetraaminophthalocyanine (ZnTAPc) and methacryloyl chloride. Atom transfer radical polymerization (ATRP) was employed as the polymerization technique to obtain a novel pH-responsive polymeric photosensitizer (PEG110-b-P(DPAn-co-MeZnAPcm)) by copolymerizing of methoxypolyethylene glycols (MPEG) (as reducing agent), 2-(isopropylamino)ethyl methacrylate (DPA) and MeZnAPc. This photosensitizer was characterized by UV-vis spectroscopy, FTIR, H NMR, etc. The results indicated that the photosensitizer presented the well pH-responsive be 1 havior around the pH range 6.0-6.5 and the high photoactivity to 1,3-diphenylisobenzofuran (DPBF). The result of photocatalysis oxidation of L-tryptophan (L-Try) suggested that zinc phthalocyanine could present high photoactivity due to its dispersivity at pH 5.5 without formation of micelles, and its photoactivity decreased dramatically at pH 7.4 due to wrapping ZnTAPc into the micelles. Therefore, the novel pH-responsive polymeric photosensitizer has better application prospects in the field of photodynamic therapy.     

Synthesis of Silica-anchored Sensitizer and its Application in the Preparation of Previtamin D3 from Tachysterol

A silica gel-anchored photosensitizer was synthesized with anthracene as sensitizer moiety. The photoisomerization of tachysterol to previtamin D3 was carried out with this heterogeneous photosensitizer in ethanol. The experiment results demonstrate that this solid phase photosensitizer is efficient for the photoisomerization and can be simply separated from the reaction mixture by filtration.     

Versatile photosensitization system for 1O2-mediated oxidation of alkenes based on nafion-supported platinum(II) terpyridyl acetylide complex

[structure: see text] Platinum(II) terpyridyl acetylide complex (1) was incorporated into Nafion membranes as a photosensitizer, and the Nafion was immersed in an aqueous or organic solution of 7-dehydrocholesterol, alpha-pinene, or cyclopentadiene. This photosensitizer system can generate singlet oxygen ((1)O(2)) in high quantum yield to oxidize the alkenes in the solution outside the Nafion and can be easily removed from the reaction vessel at the end of the photooxidation.     

New pyridinium based ionic dyes for the hydrogen evolution reaction

The presented work comprised the synthesis and characterization of new ionic organic dyes as potential photosensitizer (PS) in the photocatalytic H₂ evolution reaction. The presented dyes are consisting of donor-π-acceptor (D-π-A) structures that are commonly used for organic dyes for organic solar cells. The acceptor is based on a cationic pyridinium moiety. Furthermore, a complex was synthesized, in which a D-π-A photosensitizer is linked as ligand to cobaloxime. The latter is a common proton reduction catalyst. The attached ligand enabled a fast intramolecular electron transfer to the cobalt center. The resulted complex showed high stability and potential in the homogeneous photocatalytic H₂ evolution reaction. Finally, one ionic dye showed a high activity when combined with TiO₂ and Pt in a heterogeneous hydrogen evolution reactions with a TOF of up to 407 h^?1.     

A molecular light-driven water oxidation catalyst

Two mononuclear Ru(II) complexes, [Ru(ttbt)(pynap)(I)]I and [Ru(tpy)(Mepy)(2)(I)]I (tpy = 2,2';6,2"-terpyridine; ttbt = 4,4',4"-tri-tert-butyltpy; pynap = 2-(pyrid-2'-yl)-1,8-naphthyridine; and Mepy = 4-methylpyridine), are effective catalysts for the oxidation of water. This oxidation can be driven by a blue (λ(max) = 472 nm) LED light source using [Ru(bpy)(3)]Cl(2) (bpy = 2,2'-bipyridine) as the photosensitizer. Sodium persulfate acts as a sacrificial electron acceptor to oxidize the photosensitizer that in turn drives the catalysis. The presence of all four components, light, photosensitizer, sodium persulfate, and catalyst, are required for water oxidation. A dyad assembly has been prepared using a pyrazine-based linker to join a photosensitizer and catalyst moiety. Irradiation of this intramolecular system with blue light produces oxygen with a higher turnover number than the analogous intermolecular component system under the same conditions.     

Photosensitization reaction-induced acute electrophysiological cell response of rat myocardial cells in short loading periods of talaporfin sodium or porfimer sodium

Electrophysiological responses of rat myocardial cells to exogenous photosensitization reactions for a short period of incubation with two photosensitizers, talaporfin sodium or porfimer sodium, were measured in a subsecond time scale. The loading period of the photosensitizer when the photosensitizer might not be taken up by the cells was selected as 15min, which was determined by the fluorescence microscopic observation. We measured the intracellular Ca(2+) concentration ([Ca(2+) ](in) ) by using a fluorescent Ca(2+) indicator, Fluo-4 AM, under a high-speed confocal laser microscope to evaluate the acute electrophysiological cell response to the photosensitization reaction. The measured temporal change in Fluo-4 fluorescence intensity indicated that the response to the photosensitization reaction might be divided into two phases in both photosensitizers. The first phase is acute response: disappearance of Ca(2+) oscillation when irradiation starts, which might be caused by ion channel dysfunction. The second phase is slow response: [Ca(2+) ](in) elevation indicating influx of Ca(2+) due to the concentration gradient. The continuous Ca(2+) influx followed by changes in cell morphology suggested micropore formation on the surface of the cell membrane, resulting in necrotic cell death.     

Cross-dehydrogenative Coupling of N-Aryl Tetrahydroisoquinolines Catalyzed by an Anthraquinone-containing Polymeric Photosensitizer

This work reports the photocatalytic application of an anthraquinone-containing polymeric photosensitizer (AQ-PHEMA) in the visible light-induced cross - dehydrogenative-coupling of N-aryl tetrahydroisoquinolines with several nucleophiles, including nitromethane, 1-methyl-2-alkyl ketone and dialkyl (aryl) phosphine oxide. The results revealed that the reaction could be catalyzed by AQ-PHEMA efficiently to afford a series of 1-substituted-2-aryl-1,2,3,4-tetrahydroisoquinolines in good to excellent yields with nice substrate tolerance under aerobic conditions at room temperature. The practical application potential was also showcased by a gram-scale synthesis. More importantly, the utilization of AQ-PHEMA as a heterogeneous photosensitizer also showed nice recyclability and reusability of the catalyst, whereas AQ-PHEMA can be easily separated and reused for at least 8 times without significant loss of photocatalytic activity.     

Intracellular Modulation of Excited‐State Dynamics in a Chromophore Dyad: Differential Enhancement of Photocytotoxicity Targeting Cancer Cells

The photosensitized generation of reactive oxygen species, and particularly of singlet oxygen [O₂(a¹Δ_g)], is the essence of photodynamic action exploited in photodynamic therapy. The ability to switch singlet oxygen generation on/off would be highly valuable, especially when it is linked to a cancer‐related cellular parameter. Building on recent findings related to intersystem crossing efficiency, we designed a dimeric BODIPY dye with reduced symmetry, which is ineffective as a photosensitizer unless it is activated by a reaction with intracellular glutathione (GSH). The reaction alters the properties of both the ground and excited states, consequently enabling the efficient generation of singlet oxygen. Remarkably, the designed photosensitizer can discriminate between different concentrations of GSH in normal and cancer cells and thus remains inefficient as a photosensitizer inside a normal cell while being transformed into a lethal singlet oxygen source in cancer cells. This is the first demonstration of such a difference in the intracellular activity of a photosensitizer.     

Phototoxic process after rapid photosensitive membrane damage of 5,5"-bis(aminomethyl)-2,2':5',2"-terthiophene dihydrochloride

We report a new aspect of rapid (<30 s) light-induced cell membrane damage photosensitized by 5,5"-bis(aminomethyl)-2,2':5',2"-terthiophene dihydrochloride (BAT), which is a water-soluble alpha-terthienyl analogue, using a high-power laser (light intensity 1.6 W cm(-2)). In this paper, we will discuss the relationship between the exposure time of the cells to the photosensitizer and the phototoxic process. Three toxic processes can be identified: first, a non-light-mediated toxicity dependent on BAT-cell incubation; second, a phototoxicity independent of BAT exposure time when the BAT concentration is in the 2-10-microM range; third, a phototoxicity dependent on BAT exposure time when BAT concentration becomes 20 microM. The cytotoxicity decreases when alpha-tocopherol, an antioxidant, is added to a cell membrane. This pattern of phototoxicity is the typical of a phospholipid peroxidation chain reaction and oxidative damage of membrane proteins triggered by a reactive oxygen species generated by a triplet state of BAT. The BAT exposure time is clearly correlated with the partition of the photosensitizer in the cell membrane and inside the cell.     

Direct Arylation of N‐Heteroarenes with Aryldiazonium Salts by Photoredox Catalysis in Water

A highly effective visible light‐promoted “radical‐type” coupling of N‐heteroarenes with aryldiazonium salts in water has been developed. The reaction proceeds at room temperature with [Ru(bpy)₃]Cl₂ ? 6 H₂O as a photosensitizer and a commercial household light bulb as a light source. Pyridine and a variety of substituted pyridines are effective substrates under these reaction conditions, and only monosubstituted products are formed with different regioselectivities. Using aqueous formic acid as solvent, an array of xanthenes, thiazole, pyrazine, and pyridazine are compatible with this new arylation approach. The broad substrate scope, mild reaction conditions, and use of water as reaction solvent make this procedure a practical and environmentally friendly method for the synthesis of compounds containing aryl‐heteroaryl motifs.     

Environmental Effects on Cellular Photosensitization: Correlation of Phototoxicity Mechanism with Transient Absorption Spectroscopy Measurements

Abstract— Little is directly known about the influence of the local environment experienced by a photosensitizer in a biological system on its photophysics and photochemistry. In this paper, we have addressed this issue by correlating mechanistic studies using laser flash photolysis with cellular phototoxicity data, obtained under the same experimental conditions. In particular, we have focused on the interaction between local concentrations of photosensitizer (deuteroporphyrin) and oxygen in determining the mechanism of phototoxicity in L1210 cells. In cells, as well as in models such as liposomes and red blood cell ghosts, hypochromicity and a reduction in fluorescence and intersystem crossing yields are observed on increasing the photosensitizer concentration between 0.5 and 20 μM, which illustrates the onset of a self-association. In aerated cellular preparations, the phototoxicity is predominantly type II (singlet oxygen) for all concentrations studied but an oxygen-independent mechanism occurs at the higher concentrations in deaerated samples. These observations are readily explained by consideration of triplet state kinetics as a function of oxygen and photosensitizer concentrations in cells. The rate constant for quenching of the photosensitizer triplet state by oxygen in cells was measured as 6.6 × 10⁸ M^?1 s^?1 and by photosensitizer ground state as -10⁶M^?1s^?1 (in terms of local concentration). The latter reaction gave rise to a long-lived species that is presumably responsible for the oxygen-independent phototoxicity observed at the higher photosensitizer concentrations used. This self-quenching of the triplet state is postulated to arise from electron transfer resulting in radical ion formation. Under conditions where no self-quenching contributes, the phototoxicity measured as a function of oxygen concentration correlates well with a model based on the determined kinetic parameters, thus, unambiguously proving the intermediacy of singlet oxygen. These effects should be borne in mind when interpreting phototoxicity mechanisms from in vitro cell studies. The excellent correlation achieved between laser flash photolysis data and measured phototoxicity gives credence to the direct use of photophysical techniques to elucidate photochemical mechanisms in biological media.     

Research advances in the use of tetrapyrrolic photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising new treatment modality for several diseases, most notably cancer. In PDT, light, O2, and a photosensitizing drug are combined to produce a selective therapeutic effect. Lately, there has been active research on new photosensitizer candidates, because the most commonly used porphyrin photosensitizers are far from ideal with respect to PDT. Finding a suitable photosensitizer is crucial in improving the efficacy of PDT. Recent synthetic activity has created such a great number of potential photosensitizers for PDT that it is difficult to decide which ones are suitable for which pathological conditions, such as various cancer species. To facilitate the choice of photosensitizer, this review presents a thorough survey of the photophysical and chemical properties of the developed tetrapyrrolic photosensitizers. Special attention is paid to the singlet-oxygen yield (PhiDelta) of each photosensitizer, because it is one of the most important photodynamic parameters in PDT. Also, in the survey, emphasis is placed on those photosensitizers that can easily be prepared by partial syntheses starting from the abundant natural precursors, protoheme and the chlorophylls. Such emphasis is justified by economical and environmental reasons. Several of the most promising photosensitizer candidates are chlorins or bacteriochlorins. Consequently, chlorophyll-related chlorins, whose PhiDelta have been determined, are discussed in detail as potential photosensitizers for PDT. Finally, PDT is briefly discussed as a treatment modality, including its clinical aspects, light sources, targeting of the photosensitizer, and opportunities.     

Photochemical dechlorination of DDT catalyzed by a hydrophobic vitamin B12 and a photosensitizer under irradiation with visible light

Dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) was catalyzed by a hydrophobic vitamin B(12), heptamethyl cobyrinate perchlorate, with a visible light irradiation system containing a [Ru(ii)(bpy)(3)]Cl(2) photosensitizer, and the hydrophobic vitamin B(12) showed high catalytic efficiency and stability during the reaction.