Development of new photocatalytic water splitting into H2 and O2 using two different semiconductor photocatalysts and a shuttle redox mediator IO3-/I-

A new type of photocatalytic reaction that splits water into H2 and O2 was designed using a two-step photoexcitation system composed of an iodate/iodide (IO3-/I-) shuttle redox mediator and two different photocatalysts, one for H2 evolution and the other for O2 evolution. Photocatalytic oxidation of water to O2 and reduction of IO3- to I- selectively proceeded with good efficiencies over TiO2-rutile and Pt-WO3 photocatalysts under UV and visible light irradiations, respectively. The O2 evolution selectively proceeded even in the presence of a considerable amount of I- in the solutions, although the oxidation of water is thermodynamically less favorable than oxidation of I-. Both the adsorption property of IO3- anions and the oxidation property of the photocatalysts are doubtless responsible for the selective oxidation of water. On the other hand, photocatalytic reduction of water to H2 and oxidation of I- to IO3- proceeded over Pt-TiO2-anatase and Pt-SrTiO3:Cr/Ta (codoped with Cr and Ta) photocatalysts under UV and visible light, respectively. The combination of two different photocatalysts results in a stoichiometric evolution of H2 and O2 via the redox cycle of IO3- and I-. The photocatalytic water splitting under visible light irradiation (lambda > 420 nm) was demonstrated by using the Pt-SrTiO3:Cr/Ta, Pt-WO3, and IO3-/I- shuttle redox mediator.     

Analysis of a photosensitive lesion induced by sunlamp UV greater than 315 nm exposure of 254-nm-irradiated human cells

Normal human skin fibroblasts were exposed to 0-10 J m-2 of 254 nm UV, incubated 0-16 h and then treated with 0-150 kJ m-2 of sunlamp UV greater than 315 nm. For each treatment, the cells were subjected to alkaline elution in order to measure the yield of single strand breaks (ssb) produced. It was found that treatment of 254-nm-irradiated cells with sunlamp UV greater than 315 nm resulted in the production of a higher level of ssb than that produced by separate exposures. Hence, lesions are produced by the 254 nm irradiation that are photolyzed through exposure to sunlamp UV greater than 315 nm. Approximately 50% of these lesions are removed following a 2-4 h incubation of the 254-nm-irradiated cells and nearly complete removal is achieved by 16 h. In addition, the profiles for elutions performed at pH 12.8 with cells exposed to the combined treatment were indicative of the presence of alkali labile sites. The repair kinetics of this lesion and alkaline lability of the photolysis product suggest that this photosensitive lesion may represent pyrimidine(6-4)pyrimidone photoproducts. Hence, this approach may represent a relatively simple and sensitive assay for the measurement of this DNA damage.     

Photocatalytic overall water splitting under visible light by TaON and WO3 with an IO3-/I- shuttle redox mediator

Photocatalytic water splitting into H2 and O2 under visible-light irradiation (lambda > 420 nm) is demonstrated using the oxynitride Pt-TaON for H2 evolution and a Pt-WO3 catalyst for O2 evolution in an IO3-/I- shuttle redox-mediated system.     

Speciation of iodide, iodine, and iodate in environmental matrixes by inductively coupled plasma atomic emission spectrometry using in situ chemical manipulation

Dissolved iodine, iodide, and iodate are determined in environmental matrixes by in situ chemical manipulation and inductively coupled plasma atomic emission spectrometry (ICPAES). The method uses equipment commonly available to most laboratories involved in environmental inorganic analysis. Total dissolved iodine, iodide, and iodate are determined by ICPAES using iodine vapor generation. Total iodine is determined directly by ICPAES after filtration. Total dissolved iodide (I-) is oxidized in situ to iodine by the addition of sodium nitrite in sulfuric acid in a simplified continuous flow manifold. Iodate is determined by prereduction at the instrument before analysis by the in situ oxidation ICPAES procedure. A standard nebulizer produces the gas-liquid separation of the total iodine, which is then quantified by ICPAES at 206.16 nm. The instrument detection limit for the iodine analysis was 0.04 microgram/mL. Recoveries from seawater, saltwater, and freshwater standard reference materials ranged from 85 to 118% and averaged 98%. For samples containing both iodine and iodide, the total is determined with in situ oxidation, iodine is determined without the oxidizing reagents, and iodine is calculated from the difference. For samples containing all 3 species, pre-reduction is used and the iodine and iodide concentrations are subtracted for quantitation of iodate. The analysis is selective for these 3 species (I-, I2, and IO3). A group of 20-30 samples may be analyzed and quantitated for all 3 individual, commonly occurring iodide species in less than 1 h. The procedure is considerably faster than any other reported techniques. This method is especially well-suited to the analysis of small environmental samples.     

Stoichiometric water splitting into H2 and O2 using a mixture of two different photocatalysts and an IO3-/I- shuttle redox mediator under visible light irradiation

The stoichiometric splitting of water into H2 and O2 (H2/O2 = 2) under visible light irradiation (lambda > 420 nm) took place for the first time using a mixture of Pt-WO3 and Pt-SrTiO3 (Cr-Ta-doped) photocatalysts and an IO3-/I- shuttle redox mediator.     

DNA-PROTEIN CROSSLINKING IN NORMAL HUMAN SKIN FIBROBLASTS EXPOSED TO SOLAR ULTRAVIOLET WAVELENGTHS

Three normal human skin fibroblast cell lines were exposed to the simulated solar UV radiation produced by a fluorescent sunlamp under conditions in which the wavelength components shorter than either 295, 305 or 315 nm were excluded. The level of DNA-protein crosslinks (DPC) was then measured in those cells using the alkaline elution technique either immediately after irradiation or following a 24 h incubation. In each case, cells were exposed to fluences that induce similar levels of DPC. For cells exposed to 10 kJ m(-2) of sunlamp UV > 295 nm, the level of DPC exhibited a 2-5-fold increase following incubation. In contrast, 40-100% of the DPC were removed upon incubation of cells irradiated with either 100 kJ m(-2) of sunlamp UV > 305 nm or 150 kJ m(-2) of sunlamp UV > 315 nm. A major difference between the effects induced by these wavelength regions is that, in addition to DPC, a very high level of pyrimidine dimers is also produced by sunlamp UV > 295 nm, whereas much lower dimer yields result from treatment with either sunlamp UV > 305 nm or sunlamp UV > 315 nm. A potential role for type II DNA topoisomerase in the formation of these DPC resulting from either the change in conformational structure caused by the presence of a high level of dimers or an involvement of this enzyme in dimer excision repair is discussed.     

Radioanalytical studies of iodine behaviour in the environment

The behaviour of iodine in the environment is of interest both in relation to radioecology and human nutrition. Radiochemical techniques were used to evaluate various aspects of the behaviour of iodine in the environment. The natural iodine content of plant, water and soil samples collected from three sites was determined using preconcentration neutron activation analysis (PNAA). The effect of initial chemical speciation on the distribution of iodine between various soils, sediments and waters was evaluated using I-131 tracer. Iodide was found to adsorb more extensively than iodate, although for most of the solid/water systems examined, a substantial portion of the iodate was slowly reduced to iodide. Experiments involving gamma irradiation suggest that much of the sorption of iodide and reduction of iodate involved microbial processes. Distribution coefficients measured using I-131 were comparable with values based on the natural I-127 content.     

Synthesis and characterization of f-element iodate architectures with variable dimensionality, alpha- and beta-Am(IO3)3

Two americium(III) iodates, beta-Am(IO3)3 (I) and alpha-Am(IO3)3 (II), have been prepared from the aqueous reactions of Am(III) with KIO(4) at 180 degrees C and have been characterized by single-crystal X-ray diffraction, diffuse reflectance, and Raman spectroscopy. The alpha-form is consistent with the known structure type I of anhydrous lanthanide iodates. It consists of a three-dimensional network of pyramidal iodate groups bridging [AmO8] polyhedra where each of the americium ions are coordinated to eight iodate ligands. The beta-form reveals a novel architecture that is unknown within the f-element iodate series. beta-Am(IO3)3 exhibits a two-dimensional layered structure with nine-coordinate Am(III) atoms. Three crystallographically unique pyramidal iodate anions link the Am atoms into corrugated sheets that interact with one another through intermolecular IO3-...IO3- interactions forming dimeric I2O10 units. One of these anions utilizes all three O atoms to simultaneously bridge three Am atoms. The other two iodate ligands bridge only two Am atoms and have one terminal O atom. In contrast to alpha-Am(IO3)3, where the [IO3] ligands are solely corner-sharing with [AmO8] polyhedra, a complex arrangement of corner- and edge-sharing mu2- and mu3-[IO3] pyramids can be found in beta-Am(IO3)3. Crystallographic data: I, monoclinic, space group P2(1)/n, a = 8.871(3) A, b = 5.933(2) A, c = 15.315(4) A, beta = 96.948(4) degrees , V = 800.1(4) A(3), Z = 4; II, monoclinic, space group P2(1)/c, a = 7.243(2) A, b = 8.538(3) A, c = 13.513(5) A, beta = 100.123(6) degrees , V = 822.7(5) A(3), Z = 4.     

Structural polarity induced by cooperative hydrogen bonding and lone-pair alignment in the molecular uranyl iodate Na2[UO2(IO3)4(H2O)

Na2[UO2(IO3)4(H2O)] has been synthesized under mild hydrothermal conditions. Its structure consists of Na+ cations and [UO2(IO3)4(H2O)](2-) anions. The [UO2(IO3)4(H2O)](2-) anions are formed from the coordination of a nearly linear uranyl, UO2(2+), cation by four monodentate IO(3-) anions and a coordinating water molecule to yield a pentagonal bipyramidal environment around the uranium center. The water molecules form intermolecular hydrogen bonds with the terminal oxo atoms of neighboring [UO2(IO3)4(H2O)](2-) anions to yield one-dimensional chains that extend down the b axis. There are two crystallographically unique iodate anions in the structure of Na2[UO2(IO3)4(H2O)]. One of these anions is aligned so that the lone-pair of electrons is also directed along the b axis. The overall structure is therefore polar, owing to the cooperative alignment of both the hydrogen bonds and the lone-pair of electrons on iodate. The polarity of the monoclinic space group C2 (a = 11.3810(12) A, b = 8.0547(8) A, c = 7.6515(8) A, beta = 90.102(2) degrees , Z = 2, T = 193 K) found for this compound is consistent with the structure. Second-harmonic generation of 532 nm light from a 1064 nm laser source yields a response of approximately 16x alpha-SiO2.     

SUNLIGHT-INDUCED PYRIMIDINE DIMERS IN HUMAN SKIN FIBROBLASTS IN COMPARISON WITH DIMERIZATION AFTER ARTIFICIAL UV-IRRADIATION

Abstract— We compared artificial UV-sources such as germicidal- or sun-lamps with summer noon sunlight in Switzerland for selective efficiency in the induction of pyrimidine dimers in the DNA of human cells. In our studies we determined cytosine-thymine (C-T) as well as thymine-thymine dimer densities (T-T) by high pressure liquid chromatography in cultures of xeroderma pigmentosum cells of group A. Using far-UV light from a germicidal lamp, we found a rate of formation per Jirr² for C-T and T-T of 0.0019% and 0.0024%, respectively, of the total thymine radioactivity in hydrolysates of [³H]thymidine labeled cells. After irradiation with an unfiltered sunlamp we measured a rate of formation of 0.0005% per Jm-² both for C-T and T-T, based on the sunlamp emission of 297 ±4 nm wavelength. Utilization of Kodacel- or Mylar-filters lowered the rate of dimerization by a factor of 2 and 60, respectively. One hour of irradiation with noon summer sunlight induced 0.038 ±0.012% C-T and 0.036 ±0.011% T-T. This extent of dimer production is equivalent to 15 Jm^-2 of far-UV exposure at 254 nm.     

THE PHOTOCHEMISTRY OF p-AMINOBENZOIC ACID

We have studied the photoreactions occurring when p-aminobenzoic acid (PABA), a component of some sunscreens, is irradiated in aqueous solution. These studies were carried out in the presence and absence of oxygen, using light of lambda = 254 nm as well as light of wavelengths greater than 290 nm. In deoxygenated solution between pH 7.5 and 11.0, we found two photoproducts that were identified as 4-(4'-aminophenyl)aminobenzoic acid (I) and 4-(2'-amino-5'-carboxyphenyl)aminobenzoic acid (V); we used 1H and 13C NMR, electron impact mass spectrometry and synthesis by an independent route to identify each of these compounds. Rapid discoloration of the photolyzed sample was observed when PABA was irradiated in aerated solution. Although a number of products were detected under these conditions, the three most abundant stable compounds have been isolated and identified as 4-amino-3-hydroxybenzoic acid, 4-aminophenol and 4-(4'-hydroxyphenyl)aminobenzoic acid (IV). The latter compound was shown to result from rapid photo-induced oxidation of I in the presence of oxygen. Even in the presence of trace amounts of oxygen, the yield of I was significantly reduced in favor of IV. Studies of the thermal oxidation of I, coupled with evidence gathered from studies of the photochemistry of incompletely deoxygenated PABA solutions, indicate that 4-(2,5-cyclohexadien-4-one)iminobenzoic acid (III) is an intermediate on the pathway between I and IV. Qualitatively, we found that the photochemical reactions resulting from irradiation of PABA solutions with lambda = 254 nm light and light with lambda greater than 290 nm were the same. The quantum yields for formation of I and V are highly pH dependent, both being less than 10(-4) at pH 7 and rising steadily to values greater than 10(-3) at pH 11. The detailed pH dependence suggests that the deprotonated PABA radical cation may be an important intermediate entering into the reactions forming I and IV.     

Flow-injection spectrophotometric determination of periodate and iodate by their reaction with pyrogallol red in acidic media

A simple and efficient flow-injection method was used with good results to determine periodate and iodate in water. The method is based on the reaction of periodate or iodate with pyrogallol red in sulfuric acid media. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of pyrogallol red at 470 nm. The chemical and FIA variables were established using the univariate and simplex optimization methods. The calibration curve was linear over the concentration ranges of 0.8-73.0 and 2.0-100.0 microM for IO4- and IO3-, respectively. The detection limits were 0.7 and 1.0 microM for IO4- and IO3-, respectively. The sample throughput was 20 +/- 5 h(-1). The influence of potential interfering ions in the determination of the anions was tested. The relative standard deviations for 4.20 and 5.73 microM periodate and iodate were 1.8 and 2.2%, respectively.     

Photoreactivity of UV-b damage in bacteriophage phi X174 DNA

Abstract— The fraction of biological damage in isolated single-strand and double-strand forms of bac-teriophage DNA resulting from pyrimidine dimers following exposure to germicidal UV (254 nm) and UV-B (280-320. nm) radiation has been compared. Radiation from a Westinghouse FS-40 sunlamp filtered through a cellulose acetate sheet was used as the UV-B radiation source. Biological damage from pyrimidine dimers was determined by measuring the survival of the viral DNA with and without photoreactivation, an enzymatic process specific for repair of pyrimidine dimers. The same fraction of biological damage in the single strand and double–strand forms of φX174 DNA is repairable by photo-reactivation following exposures to germicidal UV and UV-B radiation.     

A sensitive colorimetric method for the micro determination of iodine in marine water

More than 70% of the earth surface is covered by water bodies. Marine pollution is associated with the discharge of oils, petroleum products, sewage agricultural wastes, pesticides, heavy metals, waste substances and dumping of radioactive waters in sea. This in turn results in hazards to human health, hindrance to aquatic organisms and impairment of quality for use of sea water. Sea water is reported to contain iodine but the concentration varies according to the location and depth. Here a simple and sensitive method is described for the determination of iodine using leucocrystal violet as a reagent in different samples of sea water. The method is based on the oxidation of iodine to iodate with bromine water and the liberation of free iodine from the iodate by addition of potassium iodide in acedic medium. This iodine selectively oxidises leucocrystal violet to form the crystal violet dye. Beer's law is obeyed over the concentration range of 0.04-0.36 ppm of iodine at lambda(max) 592 nm. The dye was further extracted in chloroform. The extracting system obeys Beer's law in the range of 0.008-0.08 ppm at lambda(max) 588 nm.     

USE OF METABOLIC INHIBITORS TO INVESTIGATE THE EXCISION REPAIR OF PYRIMIDINE DIMERS AND NON-DIMER DNA DAMAGES INDUCED IN HUMAN AND ICR 2A FROG CELLS BY SOLAR ULTRAVIOLET RADIATION

Abstract— ICR 2A frog and normal human skin fibroblasts were exposed to either 5 J/m² of 254 nm UV or 50 kJ/m² of the Mylar-filtered solar UV wavelengths produced by a fluorescent sunlamp. Following these approximately equitoxic treatments, cells were incubated in medium containing the DNA synthesis inhibitors hydroxyurea (HU) and 1–β-D-arabinofuranosyl cytosine (ara C) for 0–20 min (human fibroblasts) or 0–4 h (frog cells) to accumulate DNA breaks resulting from enzymatic incision during excision repair. It was found that breaks were formed in human cells at about a 200-f-old higher rate compared with the ICR 2A cells indicating a relatively low capacity for excision repair in the frog cells. In addition, the rate of DNA break formation in solar UV-irradiated cells was only one-third of the level detected in 254 nm-irradiated cells. This result is consistent with the conclusion that the pathway(s) involved in the repair of solar UV-induced DNA damages differs from the repair of lesions produced in cells exposed to 254 nm UV.     

Matrix reactivity of Al and Ga atoms (M) in the presence of silane: generation and characterization of the eta2-coordinated complex M.SiH4, the insertion product HMSiH3, and the MI species MSiH3 in a solid argon matrix

Matrix isolation experiments give evidence for the formation of the loosely bonded metal-silane complex M.SiH(4) by the spontaneous reaction of Al or Ga atoms (M) with silane in a solid Ar matrix at 12 K; however, Ga(2) appears to insert spontaneously into an Si--H bond to form HGaGaSiH(3), probably with the structure HGa(micro-SiH(3))Ga. In M.SiH(4) the metal atom is eta(2)-coordinated by the silane, resulting in a species with C(2v) symmetry. The complex has a distinctive photochemistry: it can be converted on photolysis at lambda approximately 410 or approximately 254 nm to its tautomer, HMSiH(3), which also has a doublet ground electronic state and from which it can be regenerated with lambda approximately 580 nm radiation. Broadband UV-visible photolysis (lambda=200-800 nm) results in decomposition of HMSiH(3), the univalent species MSiH(3) being the only detectable product. The experimental data collected for several silane isotopomers (SiH(4), SiD(4), and SiD(3)H) and different reagent concentrations, together with the results of sophisticated quantum chemical calculations, are used to explore in detail the properties of the detected species and the reaction pathways compassing their formation.     

Potassium Iodide as a Chemical Actinometer for 254 nm Radiation: Use of lodate as an Electron Scavenger

Abstract— A solution of 0.6 M iodide and 0.1 M iodate in 0.01 M borate buffer (pH 9.25) can be used as a chemical actinometer to measure the incident fluence from a low-pressure mercury lamp that puts out more than 85% of its energy at 254 nm. The actinometric solution is optically opaque to light below 290 nm and is optically transparent to wavelengths greater than 330 nm. Hence, the solution absorbs all of the germicidal wavelengths but little if any of the ambient light normally present in the laboratory. Iodate acts as an electron scavenger and prevents the back reaction of the free electron with the iodine atom following UV excitation of KI. Irradiation results in the linear formation of triiodide, which is quantitated by measuring its absorbance at 352 nm. The quantum yield for this system is approximately 0.75 0.03 at 20.7A_oC or approximately three times greater than that obtained previously using nitrous oxide as an electron scavenger. A model is proposed to account for this difference. A precise expression to account for the concentration and temperature dependence of the quantum yield is given by pH = 0.75(1 + 0.23[C - 0.577])(1 + 0.02[T - 20.7]) where C is the concentration of iodide and T is the temperature. The concentration of iodide can be obtained from the absorbance at 300 nm prior to irradiation using 1.061 MJ cm⁻¹ as the molar extinction coefficient. This actinometric system meets the quality criteria established by the International Union of Pure and Applied Chemistry with the caveat that it is designed to measure only germicidal radiation (i.e. wavelengths less than 290 nm).     

Structural and spectroscopic trends in actinyl iodates of uranium,neptunium, and plutonium

Two neptunyl(VI) iodates, NpO(2)(IO(3))(2)(H(2)O) (1) and NpO(2)(IO(3))(2).H(2)O (2), have been prepared from the aqueous reactions of Np(V) in HCl with KIO(4) or H(5)IO(6) at 180 degrees C and have been characterized by single crystal X-ray diffraction and Raman spectroscopy. Both compounds consist of two-dimensional arrangements of pentagonal bipyramidal [NpO(7)] polyhedra with axial neptunyl, NpO(2)(2+), dioxocations. In 1, the neptunium centers are bound in the equatorial plane by four bridging iodate anions and one terminal water molecule. The iodate anions link the [NpO(7)] units into corrugated sheets that interact with one another through intermolecular IO(3)(-)...IO(3)(-) interactions as also observed in UO(2)(IO(3))(2)(H(2)O). Compound 2 is isostructural with the recently reported PuO(2)(IO(3))(2).H(2)O, where oxygen atoms from bridging iodate anions occupy the five equatorial sites around the neptunyl moieties. The iodate anions occur as both mu(2)- and mu(3)-units and link the neptunyl polyhedra into sheets. Both types of iodate anions have their stereochemically active lone-pair of electrons aligned on one side of each layer creating a polar structure. Raman spectra of 1, UO(2)(IO(3))(2)(H(2)O), and PuO(2)(IO(3))(2).H(2)O show a sequential shift of the nu(1)(AnO(2)(2+)) stretch to lower wavenumber as the atomic number of the actinide is increased. Crystallographic data: 1, orthorhombic, space group Pcan, a = 7.684(2) A, b = 8.450(2) A, c = 12.493(3) A, Z = 4; 2, orthorhombic, space group Pna2(1), a = 7.314(1) A, b = 11.631(2) A, c = 9.449(2) A, Z = 4.     

Fluorescence response of a 4-trifluoroacetylaminophthalimide to iodide ions upon 254 nm irradiation in MeCN

The title trifluoroacetylaminophthalimide derivative produced a violet fluorescence (lambdaFLmax 392 nm) in MeCN, and it displayed a green emission (lambdaFLmax 506 nm) after irradiation at 254 nm in the presence of iodide ions. The corresponding amidate ion of the trifluoroacetamide was identified as the green fluorescence emitter. The deprotonation reaction may be caused by proton-abstracting solvated electrons generated by a photochemical charge--transfer-to-solvent process from I(-) to MeCN.     

Determination of the solubility product of Ba(IO(3))(2) by flow injection with amperometric detection

The solubility of Ba(IO(3))(2) has been determined in solutions containing a supporting electrolyte (KCl) to maintain the ionic strength in the 0-0.5 M range. The approach envisaged was based in the amperometric determination of iodine (or triiodide) generated in the reaction involving iodate in equilibrium in the saturated solutions and iodide contained in the solution carrier using a flow injection procedure, the electrode potential being maintained at +0.2 V in a wall-jet cell. The effect of the supporting electrolyte on the solubility of barium iodate was demonstrated and a good approximation of the value for the thermodynamic solubility constant of the precipitate was found by an appropriate correction of the solubility data using mean activity coefficients of barium iodate. The mean activity coefficients were estimated at each ionic strength by using the Debye-Hückel equation and the corrected solubility constant determined at 27 degrees C was found to be 2.7x10(-9) mol(3) l(-3).