Effect of polyethylenimine, a cell permeabilizer, on the photosensitized destruction of algae by methylene blue and nuclear fast red

The present study reports the effect a cell permeabilizer, polyethylenimine (PEI) has on the photodynamic effect of methylene blue (MB) and nuclear fast red (NFR) in the presence of hydrogen peroxide (H2O2). The photosensitized destruction of the algae Chlorella vulgaris under irradiation with visible light is examined. The photodynamic effect was investigated under aerobic and anaerobic conditions. The presence of a permeabilizer during the photosensitized destruction of C. vulgaris does not enhance the activity of the MB, MB/H2O2 system or the NFR, NFR/H2O2 system under aerobic conditions. However under anaerobic conditions we have determined that when a cell permeabilizer was added to the MB/H202 system, the photosensitized destruction of C. vulgaris proceeded via a combination of Type I and Type II mechanisms. The presence of PEI enforces MB/H2O2 to be active toward the destruction of C. vulgaris whether oxygen is present or absent. Under aerobic and anaerobic conditions the activity of NFR was suppressed in the presence of PEI as a result of electrostatic interactions between the photosensitizer and the cell permeabilizer. The decrease in fluorescence recorded is indicative of destruction of the chlorophyll a pigment.     

Ag@AgBr光催化剂的制备及其可见光催化降解亚甲基蓝反应性能

采用沉积-沉淀及光还原法制备了Ag@AgBr等离子体光催化剂,利用X射线衍射、扫描电镜和紫外-可见漫反射光谱对其进行了表征,并考察了该等离子体光催化剂在可见光(λ420nm)下的催化性能,探讨了催化剂用量、pH值、亚甲基蓝初始浓度、H2O2添加量、循环使用及捕获剂对Ag@AgBr催化性能的影响.结果表明,当亚甲基蓝的初始浓度为10mg/L,催化剂用量为1g/L,pH=9.8时,光照12min后,亚甲基蓝的降解率高达96%,且样品经5次循环使用后活性基本保持不变;而少量H2O2的添加对光催化活性影响不大,过量的H2O2会降低光催化活性;乙二胺四乙酸捕获空穴后比异丙醇捕获·OH后的光催化活性降得更低.同时,对Ag@AgBr等离子体光催化剂可见光降解亚甲基蓝的催化机理进行了分析.     

Mechanism of photoinduced superhydrophilicity on the TiO2 photocatalyst surface

The physicochemical properties of the H(2)O molecules adsorbed on TiO(2) surfaces during UV light irradiation were fully investigated by near-infrared (NIR) absorption spectroscopy. It was found that the H(2)O molecules adsorbed on the TiO(2) surfaces desorb during UV light irradiation by the heating effect of the light source. Since the amount of the H(2)O adsorbed on the TiO(2) surfaces decreased, the distribution of the hydrogen bonds within the H(2)O molecules decreased, resulting in a decrease in the surface tension of the H(2)O clusters. The decrease in the surface tension of H(2)O under UV light irradiation was found to be one of the most important driving forces in which the H(2)O clusters on the TiO(2) surface spread out thermodynamically, forming H(2)O thin layers. The partial elimination of the hydrocarbons from the TiO(2) surface by the photocatalytic complete oxidation was seen to be the other important factor, providing free spaces on the surface where the H(2)O clusters could spill over and spread out to form the thin H(2)O layers. Moreover, the temperature changes of the TiO(2) powder samples during UV light irradiation were found to show a good correspondence with the changes in the contact angle of the H(2)O droplets on the TiO(2) thin film surfaces. Especially the time scale for the hydrophilic conversion on the TiO(2) surfaces under UV light irradiation was in good agreement with the decrease in the amount of H(2)O molecules adsorbed on the TiO(2) surfaces but not the amount of the hydrocarbons eliminated by the photocatalytic oxidation reactions, showing that the adsorption and desorption of H(2)O molecules are generally quite sensitive to the temperature changes of solid surfaces.     

CO Preferential oxidation promoted by UV irradiation in the presence of H2 over Au/TiO2

The catalytic oxidation of CO was performed over Au/TiO(2) under UV irradiation in the presence of H(2) in different reaction systems. It was found that the introduction of H(2) enhanced the CO thermocatalytic oxidation in a CO pre-introduced system (CO/O(2)vs. CO/H(2)/O(2)), but suppressed that in an O(2) pre-introduced (O(2)/CO vs. O(2)/H(2)/CO) system. Although the CO oxidation in both CO/H(2)/O(2) and O(2)/H(2)/CO systems could be remarkably enhanced under UV irradiation, the oxidation of H(2) was suppressed under UV irradiation. It was proposed that the dissociative chemisorption H ([triple bond]Ti-H) at surface oxygen vacancy sites of TiO(2) could act as both the electron-acceptors for the photogeneration electrons and the electron-donors for the chemisorbed O(2) at TiO(2), and thus enhance the CO oxidation during the coinstantaneous process of thermocatalysis and photocatalysis. The suppression of H(2) thermocatalytic oxidation under UV irradiation might be ascribed to the electron transfer effect, i.e., the dissociative chemisorption H on Au (Au-H) could be desorbed at the H(2) molecule via accepting the photogenerated electrons from TiO(2).     

Effects of bulk impurity concentration on the reactivity of metal surface: sticking of hydrogen molecules and atoms to polycrystalline Nb containing oxygen

Nonmetallic impurities segregated onto metal surfaces are able to drastically decrease the chemical reactivity of metals. In the present paper, effects of bulk impurities on the reactivity of metallic surfaces were investigated in a wide temperature range on an example of the sticking of hydrogen molecules and atoms to Nb [polycrystalline, with mainly (100)] containing solute oxygen. At all the investigated surface temperatures, T(S) (300-1400 K), we found the bulk oxygen concentration C(O) to have a strong effect on the integral probability, alpha(H(2) ), of dissociative sticking of H(2) molecules followed by hydrogen solution in the metal lattice: alpha(H(2) ) monotonically decreased by orders of magnitude with increasing C(O) from 0.03 to 1.5 at. %. The sticking coefficient alpha(H(2) ) was found to depend on T(S) but not on the gas temperature. The effect of C(O) on alpha(H(2) ) is explained by the presence of oxygen-free sites (holes in coverage) serving as active centers of the surface reaction in the oxygen monolayer upon Nb. In contrast to H(2) molecules, H atoms were found to stick to, and be dissolved in, oxygen-covered Nb with a probability comparable to 1, depending neither on C(O) nor on T(S). This proves that, unlike H(2) molecules, H atoms do stick to be dissolved mainly through regular surface sites covered by oxygen and not through the holes in coverage.     

Biolocalisation and photochemical properties of two novel macrocyclic photosensitisers: a spectroscopic study

Biolocalisation and photochemical properties of novel macrocyclic photosensitisers, guanidiniocarbonyl-substituted tetraphenylporphyrin (1) and sugar-substituted sapphyrin (2) were investigated by spectroscopic methods. Both photosensitisers absorb in far visible region and showed good tumour localisation. Photosensitiser 2 demonstrated significantly larger absolute and relative to normal tissue (T/N) amount in tumour (330 microg g(-1) wet tissue, T/N=19.0) than photosensitiser 1 did (13 microg g(-1) wet tissue, T/N=2.1). According to iodometric and uric acid assays, compound 1 produced large amount of 1O2 (phidelta=0.60-0.68), while compound 2 showed non-significant 1O2 production (phidelta=0.04). The electronic spectroscopic study confirms that only photosensitiser 1 is able to mediate photooxidation of model compounds (BSA, poly(Trp), Tyr, Trp, and GMP) after light irradiation. Pour photochemical activity of compound 2 was explained by its self-aggregation. Raman spectroscopic study indicated that monomerised photosensitiser 2 effectively damaged BSA and calf thymus DNA after light excitation at the conditions of high excess of these macromolecules.     

Photochemical properties of a potential photosensitiser indocyanine green in vitro

The present study investigates the photochemical properties of a potential photosensitiser, indocyanine green (ICG), in an in vitro HeLa cell system. Cell proliferation was studied after a combined effect of ICG, at a concentration range of 24-94 microM, and therapeutic laser irradiation at several different energy densities. In addition, ICG cytotoxicity was evaluated in HeLa cells and V79 Chinese hamster by the MTT assay. Phototoxicity was evaluated at 1, 24, and 48 h after irradiation. No phototoxic effect was detected 1h after irradiation. The maximum phototoxic effect of ICG on HeLa cells was detected for an ICG concentration of 94 microM, a laser output of 360 mW, and an energy density of 99 J/cm(2) at 24h after irradiation. Potentiation of the ICG phototoxic effect was achieved by adding 20 microM H(2)O(2), which was a non-toxic concentration for HeLa cells in this experimental design. At 48 h after laser irradiation a statistically significant difference was found between the toxicity of ICG plus peroxide, as compared to ICG alone. The addition of H(2)O(2) at a concentration of 20 microM caused a significant increase in phototoxicity of ICG for HeLa cells. Our results confirm that ICG could be a perspective agent for use in photodynamic therapy and that its phototoxic effect can be potentiated by addition of an oxidative agent.     

Photocatalytic intercalated material based on HLaNb_2O_7 as host and Cd_(0.8)Zn_(0.2)S as guest

A novel photocatalytic material (Pt,Cd0.8Zn0.2S)/HLaNb2O7 was fabricated by successive intercalation and exchange reactions. The (Pt,Cd0.8Zn0.2S)/HLaNb2O7 possessed a gallery height less than 0.5 nm and showed a broad absorption with wavelength over 370―500 nm. Using (Pt,Cd0.8Zn0.2S)/HLaNb2O7 as catalyst, the photocatalytic H2 evolution was more than 160 cm3·h-1·g-1 in the presence of Na2S as a sacrificial agent under irradiation with wavelength more than 290 nm from a 100-W mercury lamp. Furthermore, the catalyst showed photocatalytic activity even under visible light irradiation.     

Binding, aggregation and photochemical properties of methylene blue in mitochondrial suspensions

Methylene Blue (MB) has well-established photochemical properties and has been used in a variety of photochemical applications including photodynamic therapy. Despite the fact that most of MB's cytotoxic effects in cells are attributed to mitochondrial damage, the interactions of this dye with mitochondria and the consequent effects on photochemical properties have not yet been fully determined. We monitored MB binding, aggregation and its ability to release singlet oxygen (1O2) on irradiation when interacting with mitochondrial suspensions. MB actively binds to mitochondria and enters the matrix in a manner stimulated by the mitochondrial proton potential and by the increase in mitochondrial concentrations. The greater accumulation of MB in mitochondria with elevated proton potentials or those treated with high concentrations of MB results in the formation of MB dimers, previously shown to be less effective generators of 1O2. Accumulation of MB within mitochondria with high membrane potentials also results in the reduction of MB to the photochemically inactive leuco-MB. Indeed, irradiation of mitochondria with high proton potentials in the presence of MB results in the generation of approximately half the quantity of 1O2 compared with 1O2 generated in mitochondria with low proton potentials. These differences in photochemical properties should influence the cytotoxic effects of photodynamic treatment in the presence of MB.     

Fe物种改性海胆状Nb2O5光催化降解类吩噻嗪染料

我们在合成海胆状Nb2O5纳米球光催化剂的基础上,向体系中直接引入Fe3+离子,制备了Fe物种修饰的Nb2O5纳米球。对产物进行了X射线粉末衍射(XRD)、傅里叶变换红外光谱(FT-IR)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、N2吸附-脱附测试、紫外可见吸收谱(UV-Vis)和光致发光谱(PL)表征。结果表明,引入Fe3+后,Nb2O5纳米球的微观形貌和晶型结构没有发生显著变化,但其比表面积有所增加,原位复合的Fe物种以低结晶度的Fe2O3和Fe(Ⅱ)NbxOy物种分布在Nb2O5纳米球表面。相比于单一海胆状Nb2O5,Fe物种修饰的Nb2O5催化剂表现出了良好的光催化活性,能高效且选择性地降解类吩噻嗪染料亚甲基蓝(MB)和甲苯胺蓝(TB),原因为:(1) Fe物种可以对类吩噻嗪染料分子中的N和S形成配位吸附;(2) Fe物种与Nb2O5导带匹配,可以有效分离其光生电子,提高空穴的氧化能力;(3) Fenton反应在快速消耗光生电子的同时产生大量·OH用于染料的氧化。     

Adsorption factor and photocatalytic degradation of dye-constituent aromatics on the surface of TiO2 in the presence of phosphate anions

The photocatalytic degradation for some kinds of dye-constituent aromatics with TiO₂ in the presence of phosphate anions in aqueous dispersion was investigated under both visible light (λ>480 nm) and UV irradiation. The influences of phosphate anion upon the degradation of organics under these different conditions was revealed by the measurement of point of zero ξ-potential (P _ZC) of TiO₂, UV-VIS spectra, HPLC and LC-MS. The adsorption and photodegradation of some organics, which adsorb on the surface of TiO₂ by a dominating group bearing a positive charge, was enhanced, while that of others, which adsorb on the surface of TiO₂ by a dominating group bearing negative charge, was depressed by the presence of phosphate anions under UV irradiation at the experimental conditions (pH 4.3). It was confirmed that better adsorption of organics on the surface of TiO₂ had an advantage in their photocatalytic degradation under UV irradiation. On the other hand, although the adsorption of rhodamine B (RhB) and methylene Blue (MB) markedly increased, their degradation under visible light irradiation was depressed in the presence of phosphate anions. It is suggested that phosphate anion greatly blocked the electron transfer from excited RhB and MB molecules as RhB and MB molecules predominantly adsorbed on the surface of TiO₂ through the electrostatic interaction with surface adsorbed phosphate anions.     

Adsorption of sulfur dioxide on hematite and goethite particle surfaces

The adsorption of sulfur dioxide (SO(2)) on iron oxide particle surfaces at 296 K has been investigated using X-ray photoelectron spectroscopy (XPS). A custom-designed XPS ultra-high vacuum chamber was coupled to an environmental reaction chamber so that the effects of adsorbed water and molecular oxygen on the reaction of SO(2) with iron oxide surfaces could be followed at atmospherically relevant pressures. In the absence of H(2)O and O(2), exposure of hematite (alpha-Fe(2)O(3)) and goethite (alpha-FeOOH) to SO(2) resulted predominantly in the formation of adsorbed sulfite (SO(3)(2-)), although evidence for adsorbed sulfate (SO(4)(2-)) was also found. At saturation, the coverage of adsorbed sulfur species was the same on both alpha-Fe(2)O(3) and alpha-FeOOH as determined from the S2p : Fe2p ratio. Equivalent saturation coverages and product ratios of sulfite to sulfate were observed on these oxide surfaces in the presence of water vapor at pressures between 6 and 18 Torr, corresponding to 28 to 85% relative humidity (RH), suggesting that water had no effect on the adsorption of SO(2). In contrast, molecular oxygen substantially influenced the interactions of SO(2) with iron oxide surfaces, albeit to a much larger extent on alpha-Fe(2)O(3) relative to alpha-FeOOH. For alpha-Fe(2)O(3), adsorption of SO(2) in the presence of molecular oxygen resulted in the quantitative formation of SO(4)(2-) with no detectable SO(3)(2-). Furthermore, molecular oxygen significantly enhanced the extent of SO(2) uptake on alpha-Fe(2)O(3), as indicated by the greater than two-fold increase in the S2p : Fe2p ratio. Although SO(2) uptake is still enhanced on alpha-Fe(2)O(3) in the presence of molecular oxygen and water, the enhancement factor decreases with increasing RH. In the case of alpha-FeOOH, there is an increase in the amount of SO(4)(2-) in the presence of molecular oxygen, however, the predominant surface species remained SO(3)(2-) and there is no enhancement in SO(2) uptake as measured by the S2p : Fe2p ratio. A mechanism involving molecular oxygen activation on oxygen vacancy sites is proposed as a possible explanation for the non-photochemical oxidation of sulfur dioxide on iron oxide surfaces. The concentration of these sites depends on the exact environmental conditions of RH.     

On the formation of ozone in oxygen-rich solar system ices via ionizing radiation

The irradiation of pure molecular oxygen (O(2)) and carbon dioxide (CO(2)) ices with 5 keV H(+) and He(+) ions was investigated experimentally to simulate the chemical processing of oxygen rich planetary and interstellar surfaces by exposure to galactic cosmic ray (GCR), solar wind, and magnetospheric particles. Deposited at 12 K under ultra-high vacuum conditions (UHV), the irradiated condensates were monitored on-line and in situ in the solid-state by Fourier transform infrared spectroscopy (FTIR), revealing the formation of ozone (O(3)) in irradiated oxygen ice; and ozone, carbon monoxide (CO), and cyclic carbon trioxide (c-CO(3)) in irradiated carbon dioxide. In addition to these irradiation products, evolution of gas-phase molecular hydrogen (H(2)), atomic helium (He) and molecular oxygen (O(2)) were identified in the subliming oxygen and carbon dioxide condensates by quadrupole mass spectrometry (QMS). Temporal abundances of the oxygen and carbon dioxide precursors and the observed molecular products were compiled over the irradiation period to develop reaction schemes unfolding in the ices. These reactions were observed to be dependent on the generation of atomic oxygen (O) by the homolytic dissociation of molecular oxygen induced by electronic, S(e), and nuclear, S(n), interaction with the impinging ions. In addition, the destruction of the ozone and carbon trioxide products back to the molecular oxygen and carbon dioxide precursors was promoted over an extended period of ion bombardment. Finally, destruction and formation yields were calculated and compared between irradiation sources (including 5 keV electrons) which showed a surprising correlation between the molecular yields (～10(-3)-10(-4) molecules eV(-1)) created by H(+) and He(+) impacts. However, energy transfer by isoenergetic, fast electrons typically generated ten times more product molecules per electron volt (～10(-2)-10(-3) molecules eV(-1)) than exposure to the ions. Implications of these findings to Solar System chemistry are also discussed.     

Properties of ternary insulating systems: the electronic structure of MgSO4.H2O

Structural and electronic properties of (100)-oriented MgSO(4) and MgSO(4).H(2)O surfaces and the adsorption of water on the latter were investigated theoretically with a combination of ab initio and semiempirical methods. Ab initio electronic structure calculations were based on a density functional theory (DFT)-Hartree-Fock (HF) hybrid approach. The semiempirical method MSINDO was used for the determination of the local adsorption geometry of the water molecule. With the hybrid method good agreement was obtained with the experimental band gap of 7.4 eV determined with electron energy loss spectroscopy of polycrystalline MgSO(4).H(2)O samples under ultrahigh vacuum conditions. The valence bands of the (100) surfaces of both MgSO(4) and MgSO(4).H(2)O are formed mainly by the O2p levels, whereas the S2p states contribute to the lower part of the conduction band. The preferred adsorption site of water at MgSO(4).H(2)O (100) is above a surface Mg atom. The water molecule is stabilized by two additional hydrogen bonds with surface atoms. Only small differences between the electronic structure of MgSO(4).H(2)O and MgSO(4) were observed. Also, the molecular adsorption of water on the MgSO(4).H(2)O surface leads to only small shifts of the electronic energy levels.     

Light-induced aggregation of colloidal gold nanoparticles capped by thymine derivatives

The colloid stability of thymine-coated gold nanoparticles under light irradiation as a function of particle size, surface charge, and exposure time was investigated in alkaline, aqueous solutions as well as in a 0.5 vol % of DMF in H(2)O mixture. With increasing exposure to light irradiation at 280 nm, more and more particles coagulated. Light-induced aggregation of colloidal gold nanoparticles was attributed to reorientation of thymine terminal groups tethered on gold particle surfaces. A smaller particle size and negatively charged surface reduced the rate of photodimerization or even inhibited the photoreaction. UV-vis and FTIR spectroscopy confirmed the photodimerization of terminal thymine molecules under 280 nm light irradiation. The reaction kinetics of thymine photodimerization appears to be a combination of first-order reactions, each having different rates, reflecting the inhomogeneity and high curvature of the gold nanoparticle surfaces.     

Reactions of early lanthanide metal atoms (Nd, Sm, Eu) with water molecules. A matrix isolation infrared spectroscopic and theoretical study

The reactions of early lanthanide metal atoms Nd, Sm, and Eu with water molecules have been investigated using matrix isolation infrared spectroscopy and density functional calculations. The reaction intermediates and products were identified on the basis of isotopic labeled experiments and density functional frequency calculations. The ground state metal atoms react with water to form the M(H2O) and M(H2O)(2) complexes spontaneously on annealing (M = Nd, Sm, Eu). The M(H2O) complexes isomerize to the inserted HMOH molecules under red light irradiation, which further decompose to give the metal monoxides upon UV light irradiation. The Nd(H2O)(2) complex decomposes to form the trivalent HNd(OH)(2) molecule, while the Sm(H2O)(2) and Eu(H2O)(2) complexes rearrange to the divalent Sm(OH)(2) and Eu(OH)(2) molecules under red light irradiation.     

Towards new molecular photocatalysts for CO2 reduction: photo-induced electron transfer versus CO dissociation within [Os(NN)(CO)2Cl2] Complexes

Optical excitation in the visible region of trans-(Cl)-[Os(bpy)(CO)(2)Cl(2)] (bpy=2,2'-bipyridine; C1) and trans-(Cl)-[Os(dmbpy)(CO)(2)Cl(2)] (dmbpy=4,4'-dimethyl 2,2'-bipyridine; C2) is known to induce the common CO dissociation reaction. However, the quantum yield of the reactions is less than 0.15, although C1 and C2 display pronounced photoluminescence in the visible region at room temperature with a lifetime of few tens of nanoseconds. Taking into account the characteristics of their emitting state, we have investigated the capability of C1 and C2 to act as a photosensitiser in redox reactions in different solvents (MeCN, PrCN and DMF). The efficient oxidation and reduction of both complexes under continuous irradiation in the presence of a sacrificial electron acceptor or donor is reported here. The photo-induced transformations and the nature of the resulting compounds were analysed by UV/Vis and IR spectroscopies and cyclic voltammetry. Photo-induced oxidation of C1 and C2 leads to the corresponding monocarbonyl oxidised species, whereas photo-induced reduction under argon leads mainly to the formation of the corresponding Os-bonded molecular wires P1 and P2 after exchange of two electrons associated with the loss of two chloro ligands. The chemical yield of the latter reaction (around 65%) becomes quantitative by adding [Ru(bpy)(3)](2+) as an external redox photosensitiser. This behaviour has been used to photocatalyse the two electron, two proton conversion of CO(2) to CO. Turnover numbers (TON) of 11.5 and 19.5 have been obtained respectively for C1 and C2 after 4.5 h of irradiation under CO(2) in DMF with triethanolamine as the electron donor. TON can be slightly increased by adding [Ru(bpy)(3)](2+) to the solution.     

Synthesis and photocatalytic activity of single-crystalline hollow rh-In2O3 nanocrystals

We report here for the first time the hollow, metastable, single-crystal, rhombohedral In(2)O(3) (rh-In(2)O(3)) nanocrystals synthesized by annealing solvothermally prepared InOOH solid nanocrystals under ambient pressure at 400 °C, through a mechanism of the Kirkendall effect, in which pore formation is attributed to the difference in diffusion rates of anions (OH(-) and O(2-)) in a diffusion couple. The InOOH solid nanocrystals were prepared via a controlled hydrolysis solvothermal route by using In(NO(3))(3)·4.5H(2)O as a starting material and glycerol-ethanol as a mixed solvent. The glycerol-ethanol mixed solvent plays a key role on the formation of the intermediate InOOH, thus the final product of rh-In(2)O(3). The as-synthesized In(2)O(3) nanocrystals present excellent photocatalytic degradation of rhodamine B (RhB) and methylene blue (MB) dyes, which present ～92% degradation of RhB or MB after 4 or 3 h reaction in the presence of the as-synthesized In(2)O(3) nanocrystals, respectively.     

Singlet oxygen reacts with 2',7'-dichlorodihydrofluorescein and contributes to the formation of 2',7'-dichlorofluorescein

Abstract There are controversial reports in the literature concerning the reactivity of singlet oxygen ((1)O(2)) with the redox probe 2',7'-dichlorodihydrofluorescein (DCFH). By carefully preparing solutions in which (1)O(2) is quantitatively generated in the presence of DCFH, we were able to show that the formation rate of the fluorescent molecule derived from DCFH oxidation, which is 2',7'-dichlorofluorescein (DCF), increases in D(2)O and decreases in sodium azide, proving the direct role of (1)O(2) in this process. We have also prepared solutions in which either (1)O(2) or dication (MB(*2+)) and semi-reduced (MB(*)) radicals of the sensitizer and subsequently super-oxide radical (O(2)(*-)) are generated. The absence of any effect of SOD and catalase ruled out the DCFH oxidation by O(2)(*-), indicating that both (1)O(2) and MB(*2+) react with DCFH. Although the formation of DCF was 1 order of magnitude larger in the presence of MB(*2+) than in the presence of (1)O(2), considering the rate of spontaneous decays of these species in aqueous solution, we were able to conclude that the reactivity of (1)O(2) with DCFH is actually larger than that of MB(*2+). We conclude that DCFH can continue to be used as a probe to monitor general redox misbalance induced in biologic systems by oxidizing radicals and (1)O(2).     

Effective increasing of optical absorption and energy conversion efficiency of anatase TiO2 nanocrystals by hydrogenation

Disorder-engineered nanophase anatase TiO(2) through hydrogenation has been demonstrated to exhibit substantial solar-driven photocatalytic activities [X. Chen, L. Liu, P. Y. Yu, S. S. Mao, Science, 2011, 331, 746], while the detailed image of the disorder is unclear, and the role of the hydrogenation as well as the mechanism of high photoactivity is still ambiguous. Based on first-principles calculations, we find by taking into account the synergic effect of Ti-H and O-H bonds that hydrogen atoms can be chemically absorbed both on Ti(5c) and O(2c) atoms for (101), (001), and (100) surfaces, while previous studies predicted that chemical absorption of H on both Ti(5c) and O(2c) only takes place on the (001) surface due to overlooking the synergic effect. The hydrogenation induces obvious lattice distortions on (101) and (100) surfaces of nanoparticles enhancing the intraband coupling within the valence band, while the (001) surface is not largely affected. Different from the previous understanding that the lattice disorder accounts for the induced mid-gap states while the hydrogen only stabilizes the lattice disorders by passivating their dangling bonds, we find that the adatoms not only induce the lattice disorders but also interact strongly with the Ti 3d and O 2p states, resulting in a considerable contribution to the mid-gap states. The optical absorption is dramatically red shifted due to the mid-gap states and the photogenerated electron-hole separation is substantially promoted as a result of electron-hole flow between different facets of hydrogenated nanoparticles, which may account for the exceptional high energy conversion efficiency under solar irradiation. Even more interestingly, we find that hydrogenation reverses the redox behavior of different surfaces of nanoparticles, which provides new hints that one can tune the photoexcited electron-hole flow between different surfaces of nanoparticles in accordance to one's request by appropriate chemical surface treatment. We believe that band-offset-engineering between different facets of nanocrystals can be an effective way to facilitate energy conversion efficiency and should be applicable to other nanophase materials.