Water-Assisted Concerted Proton-Electron Transfer at Co(II)-Aquo Sites in Polyoxotungstates With Photogenerated RuIII (bpy)33+ Oxidant.

The cobalt substituted polyoxotungstate [Co6 (H2 O)2 (α-B-PW9 O34 )2 (PW6 O26 )]17- (Co6) displays fast electron transfer (ET) kinetics to photogenerated RuIII (bpy)33+ , 4 to 5 orders of magnitude faster than the corresponding ET observed for cobalt oxide nanoparticles. Mechanistic evidence has been acquired indicating that: (i) the one-electron oxidation of Co6 involves Co(II) aquo or Co(II) hydroxo groups (abbreviated as Co6(II)-OH2 and Co6(II)-OH, respectively, whose speciation in aqueous solution is associated to a pKa of 7.6), and generates a Co(III)-OH moiety (Co6(III)-OH), as proven by transient absorption spectroscopy; (ii) at pH>pKa , the Co6(II)-OH→RuIII (bpy)33+ ET occurs via bimolecular kinetics, with a rate constant k close to the diffusion limit and dependent on the ionic strength of the medium, consistent with reaction between charged species; (iii) at pH

Multiple Functions Integrated inside a Single Molecule for Amplification of Photodynamic Therapy Activity.

Nitric oxide (NO) can play both prosurvival and prodeath roles in photodynamic therapy (PDT). The generation efficiency of peroxynitrite anions (ONOO-), by NO and superoxide anions (O2•-), significantly influenced the outcome. Reports indicated that such efficiency is closely related to the distance between NO and O2•-. Thus, in this manuscript, l-arginine (Arg) ethyl ester-modified zinc phthalocyanine (Arg-ZnPc) was designed and synthesized as a photosensitizer (PS) and NO donor. Post light irradiation, the guanido of Arg-ZnPc can be effectively oxidized by the generated reactive oxygen species (ROS) in the PDT process to release NO. Such a strategy could ensure O2•- and NO generation in the same place at the same time to guarantee effective ONOO- formation. In addition, NO has other multiple synergistic cancer treatment functions, including tumor tissue vasodilatation for drug extravasation promotion, P-glycoprotein (P-gp) downregulation for drug efflux inhibition, and glutathione depletion for cancer cell endogenous antioxidant defense destruction. In vitro and in vivo results indicated that the effective ONOO- formation and multiple functions of Arg-ZnPc could synergistically enhance its PDT activity and ensure satisfactory cancer treatment outcome.

Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using 'Ene'-Reductases with Photoredox Catalysts.

Flavin-dependent 'ene'-reductases (EREDs) are highly selective catalysts for the asymmetric reduction of activated alkenes. This function is, however, limited to enones, enoates, and nitroalkenes using the native hydride transfer mechanism. Here we demonstrate that EREDs can reduce vinyl pyridines when irradiated with visible light in the presence of a photoredox catalyst. Experimental evidence suggests the reaction proceeds via a radical mechanism where the vinyl pyridine is reduced to the corresponding neutral benzylic radical in solution. DFT calculations reveal this radical to be "dynamically stable", suggesting it is sufficiently long-lived to diffuse into the enzyme active site for stereoselective hydrogen atom transfer. This reduction mechanism is distinct from the native one, highlighting the opportunity to expand the synthetic capabilities of existing enzyme platforms by exploiting new mechanistic models.

Oxidative stress generated by irradiation of a zinc(II) phthalocyanine induces a dual apoptotic and necrotic response in melanoma cells.

Melanoma is an aggressive form of skin carcinoma, highly resistant to traditional therapies. Photodynamic therapy (PDT) is a non-invasive therapeutic procedure that can exert a selective cytotoxic activity toward malignant cells. In this work we evaluated the effect of a cationic zinc(II) phthalocyanine (Pc13) as photosensitizer on a panel of melanoma cells. Incubation with Pc13 and irradiation induced a concentration and light dose-dependent phototoxicity. In order to study the mechanism underlying Pc13-related cell death and to compare the effect of different doses of PDT, the most sensitive melanoma B16F0 cells were employed. By confocal imaging we showed that Pc13 targeted lysosomes and mitochondria. After irradiation, a marked increase in intracellular reactive oxygen species was observed and a complete protection from Pc13 phototoxicity was reached in the presence of the antioxidant trolox. Acridine orange/ethidium bromide staining showed morphological changes indicative of both apoptosis and necrosis. Biochemical hallmarks of apoptosis, including a significant decrease in the expression levels of Bcl-2, Bcl-xL and Bid and mitochondrial membrane permeabilization, were observed at short times post irradiation. The consequent release of cytochrome c to cytosol and caspase-3 activation led to PARP-1 cleavage and DNA fragmentation. Simultaneously, a dose dependent increase of lactate dehydrogenase in the extracellular compartment of treated cells revealed plasma membrane damage characteristic of necrosis. Taken together, these results indicate that a dual apoptotic and necrotic response is triggered by Pc13 PDT-induced oxidative stress, suggesting that combined mechanisms of cell death could result in a potent alternative for melanoma treatment.

Light-Responsive Metal-Organic Framework as an Oxidase Mimic for Cellular Glutathione Detection.

Nanomaterials with enzyme-like characteristics (nanozymes) have been developed to mimic enzymes because of their low cost, high stability, and large-scale production. By using light as an external stimulation, one can modulate nanozymes' catalytic activities with controlled spatial and temporal precision. A few inorganic photoactive materials have been investigated to construct light-responsive oxidase-like nanozymes. However, these materials suffered from limited absorbance of visible light. To address this challenge, herein we have developed a photosensitized metal-organic framework (PSMOF) by using a derivative of Ru(bpy)32+ with stronger visible-light absorption as a PS linker. The PSMOF exhibited excellent oxidase-like activity, which could be modulated by switching light on and off. Moreover, the PSMOF was used to detect glutathione levels in both normal and cancer cells with good selectivity and high sensitivity. This study not only provides a smart strategy to modulate nanozymes' activities but also broadens the sensing applications of nanozymes.

Biometals as conformational modulators of α-synuclein photochemical crosslinking.

Metal dyshomeostasis has long been linked to Parkinson's disease (PD), and the amyloidogenic protein α-synuclein (αS) is universally recognized as a key player in PD pathology. Structural consequences upon coordination of copper and iron to αS have gained attention due to significant dyshomeostasis of both metals in the PD brain. Protein-metal association can navigate protein folding in distinctive pathways based on the identity of the bio-metal in question. In this work, we employed photo-chemical crosslinking of unmodified proteins (PICUP) to evaluate these potential metal ion-induced structural alterations in the folding dynamics of N-terminally acetylated αS (NAcαS) following metal coordination. Through fluorescence analysis and immunoblotting analyses following photoirradiation, we discovered that coordination of iron obstructs copper-promoted crosslinking. The absence of intra-molecular crosslinking upon iron association further supports its C-terminal coordination site and suggests a potential role for iron in mitigating nearby post-translational modification of tyrosine residues. Decreased fluorescence emission upon synergistic coordination of both copper and iron highlighted that although copper acts as a conformational promotor of NAcαS crosslinking, iron inhibits analogous conformational changes within the protein. The metal coordination preferences of NAcαS suggest that both competitive binding sites as well as dual metal coordination contribute to the changes in folding dynamics, unveiling unique structural orientations for NAcαS that have a direct and measureable influence on photoinitiated dityrosine crosslinks. Moreover, our findings have physiological implications in that iron overload, as is associated with PD-insulted brain tissue, may serve as a conformational block of copper-promoted protein oxidation.

Nanoelectrode-emitter spectral overlap amplifies surface enhanced electrogenerated chemiluminescence.

Electrogenerated chemiluminescence (ECL) is a promising technique for low concentration molecular detection. To improve the detection limit, plasmonic nanoparticles have been proposed as signal boosting antennas to amplify ECL. Previous ensemble studies have hinted that spectral overlap between the nanoparticle antenna and the ECL emitter may play a role in signal enhancement. Ensemble spectroscopy, however, cannot resolve heterogeneities arising from colloidal nanoparticle size and shape distributions, leading to an incomplete picture of the impact of spectral overlap. Here, we isolate the effect of nanoparticle-emitter spectral overlap for a model ECL system, coreaction of tris(2,2'-bipyridyl)dichlororuthenium(ii) hexahydrate and tripropylamine, at the single-particle level while minimizing other factors influencing ECL intensities. We found a 10-fold enhancement of ECL among 952 gold nanoparticles. This signal enhancement is attributed exclusively to spectral overlap between the nanoparticle and the emitter. Our study provides new mechanistic insight into plasmonic enhancement of ECL, creating opportunities for low concentration ECL sensing.

Cryodesiccation-driven crystallization preparation approach for zinc(II)-phthalocyanine nanodots in cancer photodynamic therapy and photoacoustic imaging.

Multifunctional nanodots represent an emerging platform for overcoming the delivery challenges of poorly water-soluble drugs for use in the diagnosis and treatment of cancer. The authors describe the preparation of nanocrystallites composed of the water-insoluble photosensitizer zinc(II)-phthalocyanine in the form of nanodots by applying a cryodesiccation-driven crystallization approach. Modification of the surface of the nanodots with Pluronic F127 and folic acid endows them with excellent water solubility and stealth properties in blood. Under near-infrared (NIR) photoexcitation at 808 nm, the nanodots are shown to produce singlet oxygen, which is widely used in photodynamic therapy of cancer. The nanodots exhibit strong NIR absorbance at 808 nm and can be used as a non-toxic contrast agent for photoacoustic imaging of tissue. Graphical abstract Schematic presentation of the preparation of ZnPcNDs by droplet-confined/cryodesiccation-driven crystallization.

Highly Ordered and Field-Free 3D DNA Nanostructure: The Next Generation of DNA Nanomachine for Rapid Single-Step Sensing.

Herein, by directly using Watson-Crick base pairing, a highly ordered and field-free three-dimensional (3D) DNA nanostructure is self-assembled by azobenzene (azo)-functionalized DNA nippers in a few minutes, which was applied as a 3D DNA nanomachine with an improved movement efficiency compared to traditional Au-based 3D nanomachines due to the organized and high local concentration of nippers on homogeneous DNA nanostructure. Once microRNA (miRNA) interacts with the 3D nanomachine, the nippers "open" to hybridize with the miRNA. Impressively, photoisomerization of the azo group induces dehybridization/hybridization of the nippers and miRNA under irradiation at different wavelengths, which easily solves one main technical challenge of DNA nanotechnology and biosensing: reversible locomotion in one step within 10 min. As a proof of concept, the described 3D machine is successfully applied in the rapid single-step detection of a biomarker, which gives impetus to the design of new generations of mechanical devices beyond the traditional ones with ultimate applications in sensing analysis and diagnostic technologies.

Photoinduced Intermolecular Electron Transfer Mediated by the Colloidal Tyrosyl Bolaamphiphile Assembly.

The self-assembly of tyrosyl bolaamphiphiles is exploited to create a colloidal protein-like host matrix, upon which sacrificial electron-donor molecules associate to create a photosystem II (PSII) mimetic electron-relay system. This system harnesses the tyrosine phenol groups abundant on the surface of the assemblies to mediate photoinduced intermolecular electron transfer. Compared with the l-tyrosine molecules, the tyrosyl bolaamphiphile assembly facilitates electron transfer from the sacrificial electron donor to the oxidized photosensitizer. The enhanced electron relay is likely to be driven by the host function of the assembly associated with the sacrificial electron donor and by the suppression of the oxidative cross-linking of phenoxyl radicals. The tyrosyl bolaamphiphile assembly is advantageous in the construction of a PSII mimetic system with a protein-like nature and displaying biochemical functions.

Photosensitization of CuI - the role of visible light induced CuI→ CuII transition in photocatalytic degradation of organic pollutants and inactivation of microorganisms.

Bare and photosensitized copper iodides were tested in photocatalysed degradation of an organic dye (Acid Red 1) and inactivation of fungi (Saccharomyces cerevisiae). CuI, with the band gap energy slightly lower than that of TiO2, appeared to be highly efficient in these processes. Sensitization of copper iodide was achieved by surface modification with [Cu(SCN)2(phen)2]. The photosensitization mechanism encompasses a metal to metal charge transfer, CuI→ CuII. The applied photosensitizer binds to CuI through thiocyanate ligands resulting in the formation of an active CuII/CuI hybrid photocatalyst ([CuII(SCN)2(phen)2]@CuII). Its absorption edge is red shifted towards a lower energy when compared with bare CuI, resulting in enhanced visible light induced photocatalytic activity. The studied materials appeared to be photoactive in current generation, degradation of organic compounds and inactivation of fungi.

Insights on the relaxation of liposomes encapsulating paramagnetic Ln-based complexes.

PURPOSE: To describe and quantify the different relaxation mechanisms operating in suspensions of liposomes that encapsulate paramagnetic lanthanide(III) complexes. THEORY AND METHODS: The transverse relaxation rate of lanthanide-loaded liposomes receives contribution from the exchange between intraliposomal and bulk water protons, and from magnetic susceptibility effects. Phospholipids vesicles encapsulating different Ln(III)-HPDO3A complexes (Ln = Eu, Gd, or Dy) were prepared using the conventional thin film rehydration method. Relaxation times (T1 , T2 , and T2*) were measured at 14 Tesla (T) and 25 °C. The effect of compartmentalization of the paramagnetic agent inside the liposomal cavity was evaluated by means of an IRON-modified MRI sequence. RESULTS: NMR measurements demonstrated that Curie spin relaxation is the dominant contribution (> 90%) to the observed transverse relaxation rate of paramagnetic liposomes. This was further confirmed by MRI that showed the ability of the liposome entrapped lanthanide complexes to generate IRON-MRI positive contrast in a size dependent manner. CONCLUSION: The Curie spin relaxation mechanism is by far the principal mechanism involved in the T2 shortening of the water protons in suspension of paramagnetic liposomes at 14T. The access to IRON contrast extends the potential of such nanosystems as MRI contrast agents.

Dynamic entangled framework based on an iridium-organic unit showing reversible luminescence turn-on sensing.

A new entangled metal-organic framework shows reversible structural dynamics and luminescence changing in response to the loss of guest H2O molecules. Furthermore, an intense and sensitive luminescence turn-on sensing was observed by the naked eye for 1 upon detection of the volatile organic solvent molecule CH3CN, accompanied by reversible structural transformation.

Synergistic cytotoxicity and DNA strand breaks in cells and plasmid DNA exposed to uranyl acetate and ultraviolet radiation.

Depleted uranium (DU) has a chemical toxicity that is independent of its radioactivity. The purpose of this study was to explore the photoactivation of uranyl ion by ultraviolet (UV) radiation as a chemical mechanism of uranium genotoxicity. The ability of UVB (302 nm) and UVA (368 nm) radiation to photoactivate uranyl ion to produce single strand breaks was measured in pBR322 plasmid DNA, and the presence of adducts and apurinic/apyrimidinic sites that could be converted to single strand breaks by heat and piperidine was analyzed. Results showed that DNA lesions in plasmid DNA exposed to UVB- or UVA-activated DU were only slightly heat reactive, but were piperidine sensitive. The cytotoxicity of UVB-activated uranyl ion was measured in repair-proficient and repair-deficient Chinese hamster ovary cells and human keratinocyte HaCaT cells. The cytotoxicity of co-exposures of uranyl ion and UVB radiation was dependent on the order of exposure and was greater than co-exposures of arsenite and UVB radiation. Uranyl ion and UVB radiation were synergistically cytotoxic in cells, and cells exposed to photoactivated DU required different DNA repair pathways than cells exposed to non-photoactivated DU. This study contributes to our understanding of the DNA lesions formed by DU, as well as their repair. Results suggest that excitation of uranyl ion by UV radiation can provide a pathway for uranyl ion to be chemically genotoxic in populations with dermal exposures to uranium and UV radiation, which would make skin an overlooked target organ for uranium exposures.

Resistance of lung cancer cells grown as multicellular tumour spheroids to zinc sulfophthalocyanine photosensitization.

Photodynamic therapy (PDT) is phototherapeutic modality used in the treatment of neoplastic and non-neoplastic diseases. The photochemical interaction of light, photosensitizer (PS) and molecular oxygen produces singlet oxygen which induces cell death. Zinc sulfophthalocyanine (ZnPcSmix) has been shown to be effective in A549 monolayers, multicellular tumor spheroids (MCTSs) (250 µm) and not on MCTSs with a size of 500 µm. A549 cells used in this study were grown as MCTSs to a size of 500 µm in order to determine their susceptibility to PDT. ZnPcSmix distribution in MCTSs and nuclear morphology was determined using a fluorescent microscope. Changes in cellular responses were evaluated using cell morphology, viability, proliferation, cytotoxicity, cell death analysis and mitochondrial membrane potential. Untreated MCTSs, showed no changes in cellular morphology, proliferation, cytotoxicity and nuclear morphology. Photoactivated ZnPcSmix also showed no changes in cellular morphology and nuclear morphology. However, photoactivated ZnPcSmix resulted in a significant dose dependant decrease in viability and proliferation as well as an increase in cell membrane damage in MCTSs over time. ZnPcSmix photosensitization induces apoptotic cell death in MCTSs with a size of 500 µm and more resistantance when compared to monolayer cells and MCTSs with a size of 250 µm.

Photoinduced electron transfer reactions of ruthenium(II)-complexes containing amino acid with quinones.

With the aim of mimicking, at basic level the photoinduced electron transfer process in the reaction center of photosystem II, ruthenium(II)-polypyridyl complexes, carrying amino acids were synthesized and studied their photoinduced electron transfer reactions with quinones by steady state and time resolved measurements. The reaction of quinones with excited state of ruthenium(II)-complexes, I-V in acetonitrile has been studied by luminescence quenching technique and the rate constant, k(q), values are close to the diffusion controlled rate. The detection of the semiquinone anion radical in this system using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. The semiclassical theory of electron transfer has been successfully applied to the photoluminescence quenching of Ru(II)-complexes with quinones.

Biodistribution of meglumine antimoniate in healthy and Leishmania (Leishmania) infantum chagasi-infected BALB/c mice.

Pentavalent antimonials such as meglumine antimoniate (MA) are the primary treatments for leishmaniasis, a complex disease caused by protozoan parasites of the genus Leishmania . Despite over 70 years of clinical use, their mechanisms of action, toxicity and pharmacokinetics have not been fully elucidated. Radiotracer studies performed on animals have the potential to play a major role in pharmaceutical development. The aims of this study were to prepare an antimony radiotracer by neutron irradiation of MA and to determine the biodistribution of MA in healthy and Leishmania (Leishmania) infantum chagasi-infected mice. MA (Glucantime®) was neutron irradiated inside the IEA-R1 nuclear reactor, producing two radioisotopes, ¹²²Sb and ¹²4Sb, with high radionuclidic purity and good specific activity. This irradiated compound presented anti-leishmanial activity similar to that of non-irradiated MA in both in vitro and in vivo evaluations. In the biodistribution studies, healthy mice showed higher uptake of antimony in the liver than infected mice and elimination occurred primarily through biliary excretion, with a small proportion of the drug excreted by the kidneys. The serum kinetic curve was bi-exponential, with two compartments: the central compartment and another compartment associated with drug excretion. Radiotracers, which can be easily produced by neutron irradiation, were demonstrated to be an interesting tool for answering several questions regarding antimonial pharmacokinetics and chemotherapy.

Photochemical hydrogen evolution from cobalt microperoxidase-11.

A photochemical system utilizing the semisynthetic biomolecular catalyst acetylated cobalt microperoxidase-11 (CoMP11-Ac) along with [Ru(bpy)3]2+ as a photosensitizer and ascorbic acid as an electron donor is shown to generate hydrogen from water in a visible light-driven reaction. The reductive quenching pathway facilitated by photoexcited [Ru(bpy)3]2+ overcomes the high overpotential observed for CoMP11-Ac in electrocatalysis, yielding turnover numbers ranging from 606 to 2390 (2 µM - 0.1 µM CoMP11-Ac). The longevity of CoMP11-Ac in the photochemical system, sustaining catalysis for over 20 h, is in contrast to its previously reported behavior in an electrochemical system where catalysis slows after 15 min. Proton reduction turnover number and rate are highest at a neutral pH, a rare feature among cobalt catalysts in similar photochemical systems, which typically function best under acidic conditions. Incorporating biomolecular components into the design of catalysts for photochemical systems may address the need for hydrogen generation from neutral-pH water sources.

Energy funnelling within multichromophore architectures monitored with subnanometre resolution.

The funnelling of energy within multichromophoric assemblies is at the heart of the efficient conversion of solar energy by plants. The detailed mechanisms of this process are still actively debated as they rely on complex interactions between a large number of chromophores and their environment. Here we used luminescence induced by scanning tunnelling microscopy to probe model multichromophoric structures assembled on a surface. Mimicking strategies developed by photosynthetic systems, individual molecules were used as ancillary, passive or blocking elements to promote and direct resonant energy transfer between distant donor and acceptor units. As it relies on organic chromophores as the elementary components, this approach constitutes a powerful model to address fundamental physical processes at play in natural light-harvesting complexes.

Survey of X-ray induced Cherenkov excited fluorophores with potential for human use.

X-ray induced molecular luminescence (XML) is a phenomenon that can be utilized for clinical, deep-tissue functional imaging of tailored molecular probes. In this study, a survey of common or clinically approved fluorophores was carried out for their megavoltage X-ray induced excitation and emission characteristics. We find that direct scintillation effects and Cherenkov generation are two possible ways to cause these molecules' excitation. To distinguish the contributions of each excitation mechanism, we exploited the dependency of Cherenkov radiation yield on X-ray energy. The probes were irradiated by constant dose of 6 MV and 18 MV X-ray radiation, and their relative emission intensities and spectra were quantified for each X-ray energy pair. From the ratios of XML, yield for 6 MV and 18 MV irradiation we found that the Cherenkov radiation dominated as an excitation mechanism, except for aluminum phthalocyanine, which exhibited substantial scintillation. The highest emission yields were detected from fluorescein, proflavin and aluminum phthalocyanine, in that order. XML yield was found to be affected by the emission quantum yield, overlap of the fluorescence excitation and Cherenkov emission spectra, scintillation yield. Considering all these factors and XML emission spectrum respective to tissue optical window, aluminum phthalocyanine offers the best XML yield for deep tissue use, while fluorescein and proflavine are most useful for subcutaneous or superficial use.