Photoactive Ruthenium Nitrosyls: Effects of Light and Potential Application as NO Donors

In recent years, various exogenous nitric oxide (NO) donors have been synthesized to modulate NO concentrations in cellular environments and control physiological processes that are regulated by NO. Transition metal complexes of NO (metal nitrosyls) are one such class of NO donors. Since complexes of ruthenium are in general more stable, a variety of ruthenium nitrosyls have been isolated and studied in detail in terms of their NO donating capacities. A large number of {Ru–NO}⁶ type of nitrosyls release NO upon exposure to UV light. Several research groups have studied their photochemistry to evaluate their potential as NO donors under the control of light. In general, the nitrosyls with non-porphyrin ligands (such as amines, Schiff bases, thiolates and ligands with carboxamide groups) readily release NO upon illumination and generate Ru(III) photoproducts. In contrast, NO photorelease from ruthenium nitrosyls derived from porphyrins remains limited due to rapid recombination. In some cases, the {Ru–NO}⁶ nitrosyls are photochemically converted to nitrite species (especially in water at neutral pH) while a few afford Ru(II) photoproducts. UV irradiation of selected ruthenium nitrosyls in the solid state results in NO linkage isomerism. To date, notable progress has been made in the area of nitrosyl-polymer hybrids that could be used for site-specific delivery of NO. Various strategies have also been developed to make these nitrosyls release NO under the influence of visible and/or near IR light. Although some ruthenium nitrosyls are stable under physiological conditions and are capable to NO delivery to proteins such as myoglobin and cytochrome c oxidase, so far success has been limited in using these nitrosyls as light-activated NO donors in cellular and tissue models. In this review, the effects of light on ruthenium nitrosyls derived from a wide variety of ligands (reported so far) have been summarized and their utility as NO donors have been discussed.     

Determination of N-NO Bond Heterolysis and Homolysis Energies of Nitrosoureas and Nitrosothioureas

There is currently great interest in the chemistry of nitric oxide (NO) following many important discoveries showing that NO is involved in a range of human physiological processes.¹ Among ocean of researches in this area, some attention has been paid on the release of NO from aromatic N-nitrosoureas,not only from the point of view of their potential therapeutical use as alternative NO-releasing drugs,² but also with regard to their possible involvement in vivo as potential NO-storage and transport vehicles.³ Thus, the cytoxicity mediated by NO is expected to be potent in aromatic N-nitrosoureas having NO-releasing ability. For NO-donor compounds, homolytic cleavage energy of N-NO bond (ΔHhomo) is considered a good measure of their NO-releasing ability. Here, we provide a method to derive the ΔHhomo data and present some results showing structure influence on the N-NO bond strengthes for several series of disubstituted ureas and thioureas.     

Determination of N-NO bond dissociation energies of N-methyl-N-nitrosobenzenesulfonamides in acetonitrile and application in the mechanism analyses on NO transfer

The heterolytic and homolytic N-NO bond dissociation energies of seven substituted N-methyl-N-nitrosobenzenesulfonamides (abbreviated as G-MNBS, G = p-OCH(3), p-CH(3), p-H, p-Cl, p-Br, 2,5-2Cl, m-NO(2)) in acetonitrile solution were evaluated for the first time by using titration calorimetry and relative thermodynamic cycles according to Hess' law. The results show that the energetic scales of the heterolytic and homolytic N-NO bond dissociation energies of G-MNBS in acetonitrile solution cover the ranges from 44.3 to 49.5 and from 33.0 to 34.9 kcal/mol for the neutral G-MNBS, respectively, which indicates that N-methyl-N-nitrosobenzenesulfonamides are much easier to release a NO radical (NO(*)) than to release a NO cation (NO(+)). The estimation of the heterolytic and homolytic (N-NO)(-)(*) bond dissociation energies of the seven G-MNBS radical anions in acetonitrile solution gives the energetic ranges of -15.8 to -12.9 and -3.1 to 1.8 kcal/mol for the (N-NO)(-)(*) bond homolysis and heterolysis, respectively, which means that G-MNBS radical anions are very unstable at room temperature and able to spontaneously or easily release a NO radical or NO anion (NO(-)), but releasing a NO radical is easier than releasing NO anion. These determined N-NO bond dissociation energies of G-MNBS and their radical anions have been successfully used in the mechanism analyses of NO transfer from G-MNBS to 3,6-dibromocarbazole and the reactions of NO with the substituted N-methyl-benzenesulfonamide nitranions (G-MBSN(-)) in acetonitrile solution.     

Direct Photocatalysis for Organic Synthesis by Using Plasmonic‐Metal Nanoparticles Irradiated with Visible Light

Recent advances in direct‐use plasmonic‐metal nanoparticles (NPs) as photocatalysts to drive organic synthesis reactions under visible‐light irradiation have attracted great interest. Plasmonic‐metal NPs are characterized by their strong interaction with visible light through excitation of the localized surface plasmon resonance (LSPR). Herein, we review recent developments in direct photocatalysis using plasmonic‐metal NPs and their applications. We focus on the role played by the LSPR of the metal NPs in catalyzing organic transformations and, more broadly, the role that light irradiation plays in catalyzing the reactions. Through this, the reaction mechanisms that these light‐excited energetic electrons promote will be highlighted. This review will be of particular interest to researchers who are designing and fabricating new plasmonic‐metal NP photocatalysts by identifying important reaction mechanisms that occur through light irradiation.     

Structural features of aliphatic N-nitrosamines of 7-azabicyclo[2.2.1]heptanes that facilitate N-NO bond cleavage

N-Nitrosamines can be considered as potential nitric oxide (NO)/nitrosonium ion (NO(+)) donors. However, the relation of the structures of N-nitrosamines, in particular of aliphatic N-nitrosamines, to the characteristics of release of NO or NO(+) remains unclear. Here we show that aliphatic N-nitrosoamines of 7-azabicyclo[2.2.1]heptanes can undergo heterolytic N-NO bond cleavage. On the basis of the observation of reduced rotational barriers of the N-NO bonds in solution and nitrogen-pyramidal structures of the N-nitroso group in the solid state, we postulate that N-NO bond cleavage of N-nitrosamines is enhanced by a reduction of the resonance in the N-NO group. Computational studies suggest that these structural features of the N-nitrosamines of 7-azabicyclo[2.2.1]heptane are derived from angle strain imposed on the CNC angles.     

Tuning the reduction power of supported gold nanoparticle photocatalysts for selective reductions by manipulating the wavelength of visible light irradiation

Gold nanoparticles supported on CeO(2) were found to be efficient photocatalysts for three selective reductions of organic compounds at ambient temperatures, under irradiation of visible light; their reduction ability can be tuned by manipulating the irradiation wavelength.     

N-亚硝基吲哚系列化合物及其自由基负离子在乙腈介质中N—NO键断裂能的测定

利用滴定量热技术并结合适当的热力学循环测定了乙腈溶液中7个取代的N-亚硝基吲哚化合物中N—NO键的异裂能和均裂能, 能量范围分别为206.1~246.2 kJ/mol和119.1~124.6 kJ/mol. 表明N-亚硝基吲哚均裂释放NO自由基(NO·)比异裂释放NO正离子(NO+)要容易得多, 通过热力学循环得到的相应自由基负离子中N—NO键的异裂能和均裂能的能量范围分别为25.5~34.4和5.0~40.5 kJ/mol, 表明所研究化合物的自由基负离子在室温下很不稳定.     

Paramagnetic centers of photocatalysts based on nitrogen-doped titanium dioxide

Titanium dioxide doped with nitrogen (N-TiO₂) was studied by electron paramagnetic resonance spectroscopy. Two types of paramagnetic centers were observed: N^· and NO. The concentration of these centers depends significantly on temperature and irradiation with visible and UV light. It was established that the energy levels corresponding to the N^· and NO centers are, respectively, 2.3 and 2.0 eV below the N-TiO₂ conduction band. These centers are involved in the photooxidation of organic compounds on the N-TiO₂ surface.     

Organic dye-based photoinitiating systems for visible-light-induced photopolymerization

Even though many organic dyes have been reported as photoinitiators/photosensitizers for free radical polymerization in the literature, the design and development of novel photoinitiating systems based on organic dyes adaptable for visible light irradiation, for example, 405 nm LED and sunlight still remains challenging. Recently, major achievements in the development of high-performance photoinitiating systems based on organic dyes as light-harvesting compounds and their uses as photoinitiators for photopolymerization under visible-light irradiation have clearly emerged, giving rise to abundant literature. In this review, an overview of the recently synthesized chromophores belonging to various families of organic dyes and used as photoinitiators of polymerization during the 2018–2021 period are presented and classified. Recent works have resulted in the development of new chromophores exhibiting remarkable visible light absorption properties and excellent photoinitiation abilities upon irradiation with LEDs and/or sunlight in free radical photopolymerization processes. These developments notably indicate that sunlight has the advantages of being a cheap, unlimited, broad emission spectrum, and energy-saving light source capable to be an efficient substitute to artificial light sources. The newly developed dye-based photoinitiating systems designed to initiate visible-light-induced photopolymerization processes are likely to expand the scope of application of photopolymerization in modern sciences and technologies.     

Mechanistic studies of the photocatalytic oxidation of trichloroethylene with visible-light-driven N-doped TiO2 photocatalysts

Visible-light-driven TiO2 photocatalysts doped with nitrogen have been prepared as powders and thin films in a cylindrical tubular furnace under a stream of ammonia gas. The photocatalysts thus obtained were found to have a band-gap energy of 2.95 eV. Electron spin resonance (ESR) under irradiation with visible light (lambda > or = 430 nm) afforded the increase in intensity in the visible-light region. The concentration of trapped holes was about fourfold higher than that of trapped electrons. Nitrogen-doped TiO2 has been used to investigate mechanistically the photocatalytic oxidation of trichloroethylene (TCE) under irradiation with visible light (lambda > or = 420 nm). Cl and O radicals, which contribute significantly to the generation of dichloroacetyl chloride (DCAC) in the photocatalytic oxidation of TCE under UV irradiation, were found to be deactivated under irradiation with visible light. As the main by-product, only phosgene was detected in the photocatalytic oxidation of TCE under irradiation with visible light. Thus, the reaction mechanism of TCE photooxidation under irradiation with visible light clearly differs markedly from that under UV irradiation. Based on the results of the present study, we propose a new reaction mechanism and adsorbed species for the photocatalytic oxidation of TCE under irradiation with visible light. The energy band for TiO2 by doping with nitrogen may involve an isolated band above the valence band.     

Heterolytic and Homolytic N-NO Bond Dissociation Energies of N-Nitroso-benzenesulfonylmethylamines in Acetonitrile

Great interests have been accumulated in recent years in the chemistry and biochemistry of nitric oxide (NO) since the remarkable discoveries of its key roles in a wide range of human physiological processes. To elucidate the mechanistic details of NO migration from its donor to its acceptor, it is necessary to determine the Y-NO bind energy that registers the thermodynamic driving force for NO release and capture. In this paper the heterolytic and homolytic N-NO bond dissociation energies [ i. e., △Hhet(N-NO) and △Hhomo(N-NO)] for ten N-nitroso-p-substituted-benzensulfonyl methylamines in acetonitrile are offered, which were obtained from titration calorimetry and thermodynamic cycles, respectively (Scheme 1).     

Pristine simple oxides as visible light driven photocatalysts: highly efficient decomposition of organic compounds over platinum-loaded tungsten oxide

Tungsten oxide loaded with nanoparticulate platinum is demonstrated to exhibit high activity for the decomposition of organic compounds both in liquid and gas phases; the activity was almost comparable to that of TiO2 under UV light irradiation and much higher than that of nitrogen-doped TiO2 under visible irradiation.     

Visible-Light-Induced Catalytic Selective Halogenation with Photocatalyst

Halide moieties are essential structures of compounds in organic chemistry due to their popularity and wide applications in many fields such as natural compounds, agrochemicals, and pharmaceuticals. Thus, many methods have been developed to introduce halides into various organic molecules. Recently, visible-light-driven reactions have emerged as useful methods of organic synthesis. Particularly, halogenation strategies using visible light have significantly improved the reaction efficiency and reduced toxicity, as well as promoted reactions under mild conditions. In this review, we have summarized recent studies in visible-light-mediated halogenation (chlorination, bromination, and iodination) with photocatalysts.     

钴前驱体对掺杂TiO2微结构和可见光催化性能的影响

In order to develop photoactive cobalt-doped TiO2 for the degradation of organic pollutants using visible light irradiation, the effects of cobalt precursor on TiO2 microstructure were investigated. Three cobaltprecursors, i.e. CoCl2, Co(NO3)2 and CoSO4 with two doping levels (nominally 1% and 10%), and two annealing temperatures (400 and 800 ℃) were adopted to prepare the doped titania through the sol-gel method. The powder samples were characterized with XRD, SEM, BET surface area analysis and UV-Vis absorption spectroscopy, and their photocatalytic activities were evaluated by the degradation of aniline under visible light irradiation. The results showed that the distribution of titania phases, particle size,morphology, surface area and the optical absorption of the catalysts were greatly dependent on the cobalt precursors. Samples prepared from Co(NO3)2, especially for those doped at 1% and calcined at 400 ℃,showed the highest photocatalytic activity towards the degradation of aniline, and the possible reasons are discussed briefly.     

A Host–Guest Supramolecular Complex with Photoregulated Delivery of Nitric Oxide and Fluorescence Imaging Capacity in Cancer Cells

Herein we report the design, preparation, and properties of a supramolecular system based on a tailored nitric oxide (NO) photodonor and a rhodamine‐labeled β‐cyclodextrin conjugate. The combination of spectroscopic and photochemical experiments shows the absence of significant interchromophoric interactions between the host and the guest in the excited states. As a result, the complex is able to release NO under the exclusive control of visible light, as unambiguously demonstrated by direct detection of this transient species through an amperometric technique, and exhibits the typical red fluorescence of the rhodamine appendage. The supramolecular complex effectively internalizes in HeLa cancer cells as proven by fluorescence microscopy, shows a satisfactory biocompatibility in the dark, and induces about 50 % of cell mortality upon irradiation with visible light. The convergence of all these properties in one single complex makes the present host–guest ensemble an appealing candidate for further delevopment of photoactivatable nanoscaled systems addressed to photostimulated NO‐based therapy.     

Synthesis, property characterization and photocatalytic activity of the novel composite polymer polyaniline/Bi2SnTiO7

A novel polyaniline/Bi(2)SnTiO(7 )composite polymer was synthesized by chemical oxidation in-situ polymerization method and sol-gel method for the first time. The structural properties of novel polyaniline/Bi(2)SnTiO(7) have been characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray spectrometry. The lattice parameter of Bi(2)SnTiO(7) was found to be a = 10.52582(8) ?. The photocatalytic degradation of methylene blue was realized under visible light irradiation with the novel polyaniline/Bi(2)SnTiO(7) as catalyst. The results showed that novel polyaniline/Bi(2)SnTiO(7 )possessed higher catalytic activity compared with Bi(2)InTaO(7) or pure TiO(2) or N-doped TiO(2) for photocatalytic degradation of methylene blue under visible light irradiation. The photocatalytic degradation of methylene blue with the novel polyaniline/Bi(2)SnTiO(7) or N-doped TiO(2) as catalyst followed first-order reaction kinetics, and the first-order rate constant was 0.01504 or 0.00333 min(-1). After visible light irradiation for 220 minutes with novel polyaniline/Bi(2)SnTiO(7 )as catalyst, complete removal and mineralization of methylene blue was observed. The reduction of the total organic carbon, the formation of inorganic products, SO(4)2- and NO(3-), and the evolution of CO(2) revealed the continuous mineralization of methylene blue during the photocatalytic process. The possible photocatalytic degradation pathway of methylene blue was obtained under visible light irradiation.     

Ion engineering techniques for the preparation of the highly effective TiO<Subscript>2</Subscript> photocatalysts operating under visible light irradiation

The successful application of ion engineering techniques for the development of TiO₂ photocatalysts operating under visible and/or solar light irradiations has been summarized in this review article. First, we have physically doped various transition metal ions within a TiO₂ lattice on an atomic level by using an advanced metal ion implantation method. The metal ion implanted TiO₂ could efficiently work as a photocatalyst under visible light irradiation. Some field tests under solar light irradiation clearly revealed that the Cr or V ions implanted TiO₂ samples showed 2–3 times higher photocatalytic reactivity than the un-implanted TiO₂. Second, we have developed the visible light responsive TiO₂ thin film photocatalyst by a single process using an RF-magnetron sputtering (RF-MS) deposition method. The vis-type TiO₂ thin films showed high photocatalytic reactivity for various reactions such as reduction of NOx, degradation of organic compounds, and splitting of H₂O under visible and/or solar light irradiations.     

Thermal and photochemical oxidation of self-assembled monolayers on alumina particles exposed to nitrogen dioxide

Alumina is an important component of airborne dust particles as well as of building materials and soils found in the tropospheric boundary layer. While the uptake and reactions of oxides of nitrogen and their photochemistry on alumina have been reported in the past, little is known about the chemistry when organics are also present. Fourier transform infrared (FTIR) spectroscopy at ～23 °C was used to study reactions of NO(2) on γ-Al(2)O(3) particles that had been derivatized using 7-octenyltrichlorosilane to form a self-assembled monolayer (SAM). For comparison, the reactions with untreated γ-Al(2)O(3) were also studied. In both cases, the particles were exposed to water vapor prior to NO(2) to provide adsorbed water for reaction. As expected, surface-bound HONO, NO(2)(-), and NO(3)(-) were formed. Surprisingly, oxidation of the organic by surface-bound nitrogen oxides was observed in the dark, forming organo-nitrogen products identified as nitronates (R(2)C[double bond, length as m-dash]NO(2)(-)). Oxidation was more rapid under irradiation (λ > 290 nm) and formed organic nitrates and carbonyl compounds and/or peroxy nitrates in addition to the products observed in the dark. Mass spectrometry of the gas phase during irradiation revealed the production of NO, CO(2), and CO. These studies provide evidence for oxidation of organic compounds on particles and boundary layer surfaces that are exposed to air containing oxides of nitrogen, as well as new pathways for the formation of nitrogen-containing compounds on these surfaces.     

Comparative study of the dark and light-induced toxicity of lipofuscin granules from human retinal pigment epithelium and their chromophore A2E on the cardiolipin liposome model

The damaging effect of lipofuscin granules from the human retinal pigment epithelium and fluorophore A2E was studied on models of calcein- and ascorbate-loaded cardiolipin liposomes and outer segments of the bovine eye photoreceptor cells in dark and under visible light irradiation. In dark fluorophore A2E induces the release of calcein from calcein-loaded liposomes and reduces the lifetime of the artificial bilayer lipid membrane prepared from dioleyl phosphatidilcholine. A similar detergent-like action A2E exhibits towards ascorbate-loaded liposomes, significantly accelerating the release of ascorbate in dark. In the presence of A2E, irradiation with the full visible light (390?C700 nm) stimulates both the release of ascorbate from liposomes and accelerates the destruction of the bilayer lipid membrane. Retinal pigment epithelium lipofuscin granules also accelerate the release of ascorbate from ascorbate-loaded liposomes under visible light irradiation; the blue light (457.9 nm) was twice as more efficient as the green light (514.5 nm). The preliminary irradiation of A2E with the visible light decreases its detergent-like action on the cardiolipin liposomal membranes under the dark conditions and the photosensitizing effect on the lipid peroxidation of the outer segments of photoreceptor cells. Unlike A2E, the visible light irradiation of a suspension of lipofuscin granules under similar conditions does not noticeably decrease their sensitizing activity towards lipid peroxidation. It is assumed that the phototoxicity of retinal pigment epithelium lipofuscin granules is related not only to A2E in their composition, but depends mainly on the content of other photosensitizers (chromophores) in the granules.     

水热合成Bi2WO6/SC光催化剂及其光催化脱硝性能研究

以活性半焦(SC)为载体,采用水热法合成新型可见光催化剂Bi₂WO₆ /SC, 利用SEM、BET、XRD、FT-IR和紫外可见漫反射(UV-vis)光谱等系列手段对所制备的样品进行了表征,并以可见光(λ＞ 400 nm)为光源,模拟烟气中的NO为氧化脱除对象,进行光催化活性测试。 结果表明,通过水热法合成的Bi₂WO₆具有微米花形状,且光响应波长已扩展到400 nm以上的可见光区, Bi₂WO₆/SC光催化脱硝剂性能最好,反应4 h后脱硝率仍高于70%。