UV Irradiation Of Aqueous Solutions Research Articles

Photo‐induced polymerization of methyl methacrylate/cyclodextrin complex in aqueous solution

AbstractPolymerization of hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) complex of methyl methacrylate (MMA) (MMA/HP‐β‐CD) was carried out under UV irradiation in aqueous solution with Irgacure 2959 (4‐(2‐hydroxyethoxy)phenyl‐(2‐hydroxy‐2‐propyl)ketone) as a photoinitiator at room temperature. The effects of some principal factors, including UV irradiation intensity, initiator concentration, and the ratio of HP‐β‐CD to MMA, on the polymerization were investigated in detail. Compared to the corresponding thermal polymerization, photo‐induced polymerization of the MMA/HP‐β‐CD complex could be accomplished at a higher speed; the polymerization conversion in photo‐induced polymerization reached 94% within 30 min, while it was only 62% for the thermal polymerization of 16 hr at 70°C. The number‐average molecular weight (Mn) and polymerization conversion decreased with the increase in UV intensity and initiator concentration. The resulting PMMA precipitated spontaneously from the solution during polymerization in the absence of any precipitator. About 95 wt% of the HP‐β‐CD remained in the solution after polymerization and the reusability of the residual HP‐β‐CD was experimentally demonstrated. Copyright © 2008 John Wiley & Sons, Ltd.

Photo-Control of Adhesion Properties by Detachment of the Outermost Layer in Layer-by-Layer Assembled Multilayer Films of Preyssler-Type Polyoxometalate and Polyethyleneimine

The ability to generate small-scale structures and assemble functional substances in the fields of micro electronics and optoelectronics continues to support advances in information technology. Here we present a novel type of “layer-by-layer” assembled films, whose surface properties can be controlled by UV irradiation in aqueous solution. We have designed a photochromic multilayer film of Preyssler-type polyoxometalate (NaP5W30) and polyethyleneimine (PEI) by using the layer-by-layer method. We found that the outermost PEI layer could be detached by UV irradiation in aqueous solution, and that this process could then cause inversion of the zeta potential. Furthermore, we achieved reversible-control of the surface properties first by UV irradiation, which induced the detachment of the outermost PEI layer, and by subsequent dipping into a PEI solution, which attached a new PEI layer. Finally, we successfully prepared photopatterned films with highly site-selective adsorption abilities by image-wise UV expo...

Products of photolysis of cadmium thiosulfate aqueous solutions

On the basis of X-ray diffraction and chemical analysis data, it was found that cadmium sulfide exhibiting the ‘size effect’ is formed during the UV irradiation of aqueous solutions of cadmium thiosulfate. Sulfate ions and hydrogen ions accumulate in the aqueous solution. It was shown that the yield of cadmium sulfide is affected by the concentration of thiosulfate ions in the solution. The overall equation of photolysis of cadmium thiosulfates is proposed.

Chlorobenzene Degradation Assisted by TiO2 under UV Irradiation in Aqueous Solutions

AbstractWe report the photocatalytic degradation of chlorobenzene (CB) in suspended TiO

Preparation of lead sulfide nanoparticles in the photolysis of aqueous solutions of lead thiosulfate complex

It was found from spectroscopic and microscopic data that lead sulfide nanoparticles are formed during the UV irradiation of aqueous solutions of lead thiosulfate complex. The yield and the size of the lead sulfide nanoparticles depend on the concentration of solution and the lead to thiosulfate ion ratio in the solution.

Novel triblock copolymers synthesized via radical telomerization of N-isopropylacrylamide in the presence of polypseudorotaxanes made from thiolated PEG and α-CDs

A protocol for the preparation of novel triblock copolymers comprising a polyrotaxane center block and outer blocks of poly(N-isopropylacrylamide) (PNIPAAm) as bulky stoppers was developed, in which N-isopropylacrylamide was allowed to telomerize in the presence of polypseudorotaxanes made from the self-assembly of thiol end-capped PEG with a varying amount of α-CDs under UV irradiation in aqueous solution. The molecular structure of the resulting copolymers was characterized in detail by 1H NMR, FTIR, XRD, TG and DSC analyses. It was demonstrated that the PNIPAAm blocks are successfully attached to the two terminals of the polypseudorotaxanes and each block having the minimum 7 NIPAAm units seems long and bulky enough to efficiently impede the dethreading of α-CDs from the PEG axle to give rise to the triblock polyrotaxane-containing copolymers.

On the Generation of Free Radical Species from Quantum Dots

Radical discoveries? Semiconductor quantum dots (QDs) produce free radicals upon UV irradiation in aqueous solution. While CdS QDs generate superoxide and hydroxyl radicals, only the latter are produced from CdSe QDs. In contrast, CdSe/ZnS core/shell QDs, often applied in biolabeling applications, do not generate radicals.

Automated solid-phase extraction and high-performance liquid chromatographic determination of nitrosamines using post-column photolysis and tris(2,2′-bipyridyl) ruthenium(III) chemiluminescence

A sensitive and selective post-column detection system for nitrosamines is described. The principle upon which the detector works is that UV irradiation of aqueous solutions of nitrosamines leads to cleavage of the N NO bond. The amine generated is subsequent detected by chemiluminescence using tris(2,2′-bipyridyl) ruthenium(III), which is on-line generated by photo-oxidation of the ruthenium(II) complex in the presence of peroxydisulfate. Factors affecting the photochemical and chemiluminescent reactions were optimized to minimise their contribution to the total band-broadening. This detection system was tested for N-nitrosodimethylamine, N-nitroso-diethylamine, N-nitrosomorpholine, N-nitrosopiperidine and N-nitrosopyrrolidine, which were separated on an ODS column by isocratic reversed-phase chromatography with acetonitrile–water containing 5 mM acetate buffer at pH 4.0. A linear relationship between analyte concentration and peak area was obtained within the range 0.13–500 μg l −1 with correlation coefficients greater than 0.9995 and detection limits of between 0.03 and 0.76 μg l −1. Intra- and inter-day precision values of about 1.2% RSD ( n = 11) and 2.5% RSD ( n = 10), respectively, were obtained. The sensitivity may increase from 9 to 280 times with respect to UV detection, depending on the nitrosamine in question. An automated solid-phase extraction (SPE) system was used in conjunction with HPLC to determine nitrosamine residues in waters. Detection limits within the range 0.10–3.0 ng l −1 were achieved for only 250 ml of sample.

Photochemical alkylation of inorganic arsenic : Part 1. Identification of volatile arsenic species

Volatile arsenic species generated by UV irradiation of aqueous solutions of arsenite in low molecular weight (LMW) carboxylic acid media (formic, acetic, propionic and butyric) were identified using ICP-TOF-MS and GC-MS. Cryogenic trapping-GC-MS reveals that inorganic arsenite can be alkylated to yield AsH3 in the presence of formic acid, trimethylarsine in acetic acid, triethylarsine in propionic acid and tripropylarsine in butyric acid solutions. Mixed ligand arsenic species such as methylarsine, dimethylarsine, dimethylethylarsine and diethylmethylarsine are also formed when a mixture of acids is used. Using 0.05 mg l−1 As(III) as the test solution in 3.1 M acetic acid, a methylation efficiency of approximately 75% was achieved.

Fabrication of Light-Leakage Type Photocatalytic Fiber Bundle for Photodegradation of Basic Dye

Light-leakage type photocatalytic fibers coated with a titanium oxide layer were fabricated to decontaminate aqueous waste solution. The titanium oxide layer was prepared by a sol-gel process using titanium tetra-butoxide and salt catalyst, and characterized by SEM and EDX analyses. The titanium oxide layer was sufficiently dense and stable against long term UV-irradiation in aqueous solutions. The fibers were bundled into a tube of about 3 mm in diameter, constituting a tubular reactor that promotes photocatalytic degradation of basic dyes by a single pass process.

Photochemical Reduction of Cytochrome c by a 1,4,5,8‐Naphthalenediimide Radical Anion¶

AbstractSteady‐state UV irradiation of aqueous solutions containing cytochrome c (cyt c) and N,N′‐bis(2‐phosphonoethyl)‐1,4,5,8‐naphthalenediimide (BPNDI), a water‐soluble aromatic imide, resulted in the reduction of the heme iron from the Fe(III) to the Fe(II) oxidation state. The reaction kinetics were followed by the increase of the ferrocytochrome c absorbance band at 549 nm. The rate of the photochemical reaction was pH dependent, reaching its maximum values over the pH range 4–7. Addition of electrolyte (NaCl) at pH 5 resulted in a decrease in the reaction rate, as expected for reactions between oppositely charged species. Flash photolysis studies revealed that the actual reductant in the reaction was a photogenerated BPNDI radical anion, which transferred an electron to the cyt c heme iron. The participation of imide radicals in the process was confirmed by the ready reduction of cyt c by BPNDI radicals chemically generated with sodium dithionite.

Photochemical Reduction of Cytochrome c by a 1,4,5,8-Naphthalenediimide Radical Anion ¶

Steady-state UV irradiation of aqueous solutions containing cytochrome c (cyt c) and N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (BPNDI), a water-soluble aromatic imide, resulted in the reduction of the heme iron from the Fe(III) to the Fe(II) oxidation state. The reaction kinetics were followed by the increase of the ferrocytochrome c absorbance band at 549 nm. The rate of the photochemical reaction was pH dependent, reaching its maximum values over the pH range 4-7. Addition of electrolyte (NaCl) at pH 5 resulted in a decrease in the reaction rate, as expected for reactions between oppositely charged species. Flash photolysis studies revealed that the actual reductant in the reaction was a photogenerated BPNDI radical anion, which transferred an electron to the cyt c heme iron. The participation of imide radicals in the process was confirmed by the ready reduction of cyt c by BPNDI radicals chemically generated with sodium dithionite.

Photochemical transformations of tetrabromobisphenol A and related phenols in water

A method was developed for studies of the phototransformation at UV irradiation of aqueous solutions of tetrabromobisphenol A (TBBPA), tribromobisphenol A (TriBBPA), tetrachlorobisphenol A (TCBPA), 2,4-dichlorophenol at various pHs as well as 2-chlorophenol, 2-bromophenol, 3,4-dichlorophenol and bisphenol A at pH 11. The absorbance spectra of the compounds and the emission spectra of the light-source were determined and used to calculate disappearance quantum yields of the photochemical reactions that were taking place. No major differences between the disappearance quantum yields of TBBPA and TCBPA were observed at pH 10, while the disappearance quantum yield of TriBBPA was approximately two times higher. The rate of decomposition of TBBPA was six times higher at pH 8 than at pH 6. Identification of the degradation products of TBBPA and TriBBPA, by GC–MS analysis and by comparison to synthesised reference compounds, indicated that TBBPA and TriBBPA decompose via different mechanisms. Three isopropylphenol derivatives; 4-isopropyl-2,6-dibromophenol, 4-isopropylene-2,6-dibromophenol and 4-(2-hydroxyisopropyl)-2,6-dibromophenol, were identified as major degradation products of TBBPA while the major degradation product of TriBBPA was tentatively identified as 2-(2,4-cyclopentadienyl)-2-(3,5-dibromo-4-hydroxyphenyl)propane.

The pH-Dependent Primary Photoreactions of Ochratoxin A

Steady-state and time-resolved spectroscopies are used to elucidate the primary photoprocesses following the excitation of ochratoxin A (OTA), its dechlorinated derivative ochratoxin B (OTB), and O-methyl ether of OTA (MOA). The excited-state dynamics of OTA and OTB depend on the protonation of the isocoumarin moiety. Fluorescence spectra of the protonated forms reveal anomalously large Stokes shifts that are attributed to the enol tautomer formed via an intramolecular excited-state proton transfer. No evidence for “normal” emission of the keto form of OTA and OTB is found even in aqueous solutions. MOA, which lacks a proton on the phenol moiety and exists, therefore, only in the keto form, exhibits weak fluorescence with a substantially smaller Stokes shift. The deprotonated species show relatively strong emission typical for phenolate anions. OTA decomposes slowly upon UV irradiation in aqueous solutions. The photoreaction quantum yield varies significantly with solution pH and O2 concentration. The hig...

Photochemistry of 4-Thiothymine Derivatives in the Presence of N-9-Substituted-Adenine Derivatives: Formation of N-6-Formamidopyrimidines.

UV irradiation of aqueous solutions containing either 4-thiothymin-1-ylacetic acid (1b) and adenosine (2a), 4-thiothymidine (1a) and adenin-9-ylacetic acid (2b), or 1b and 2b led to 4,5-diamino-6-formamidopyrimidine (N-6-Fapy-Ade) derivatives as observed after irradiation of a mixture of 1a and 2a (J. Am. Chem. Soc. 1996, 118, 8142-8143). These new observations demonstrate that the replacement of one or both nucleoside sugar residues by a carboxymethyl group does not affect the regioselective course of the photochemical reaction. The thermal decomposition of 3a that resulted from irradiation of 1a in the presence of 2a, was examined along with its behavior under mild alkaline conditions. Finally, irradiation of N-3-methyl-4-thiothymidine (6a) in the presence of adenosine gave the N-3-methylcytidine derivative 7.

Vacuum UV photolysis of aqueous solutions of nitrate. Effect of organic matter II. Methanol

Vacuum UV irradiation of aqueous solutions containing NO 3 − and methanol results in the simultaneous mineralization of methanol and depletion of NO 3 −, yielding NO 2 − and NH 4 +. Moreover, the depletion rates of NO 3 − are two to three orders of magnitude faster in the presence of methanol than in corresponding experiments with pure nitrate solutions. A possible mechanism is discussed in which the reactions of NO 2 . and NO . with the radicals formed during methanol oxidation are proposed to be mainly responsible for the overall behaviour observed. The reactions between these intermediates and No . seem to follow reduction pathways leading to NH 4 + formation, whereas a one-electron reduction yielding N 2O is observed in the absence of organic material. The formation of CNO − as an intermediate product is a clear indication that reactions between nitrogen-containing ions, carbon-centered radicals and/or methanol and its oxidation products occur. The present results are in complete agreement with previously reported data concerning the enhanced reduction of NO 3 − in the presence of phenol, thus suggesting that the behaviour observed may probably be generalized to most organic substrates.

Synthesis, characterization and applications of azo-containing photodestructible surfactants

Photodestructible surfactants, sodium 4-(2-cyano-2-undecylazo)benzoate and a series of sodium 4alkylphenylazosulfonates, have been synthesized and were shown to be surface active in solution, each exhibiting a distinct critical micelle concentration (CMC). UV irradiation of aqueous solutions of the alkylazobenzoate led to a distinct increase in surface tension, but even after complete photolysis significant surface activity remained, indicating a substantial amount of cage recombination after nitrogen evolution. UV irradiation of sodium 4-dodecylazosulfonate caused a photoscission reaction, completely destroying its surface active properties. In the case of azosulfonates with shorter alkyl chains, however, some residual surface activity remained after complete removal of the azo linkage, indicating that secondary surfactants were formed by the photolysis. The 4-alkylphenylazosulfonates were able to solubilize an oil-soluble dye in water to produce isotropic coloured solutions. Photoirradiation of these solutions led to complete loss of colour, presumably as a result of microprecipitation of the dye. The azosulfonate surfactants also readily emulsified vinyl monomers, such as styrene, in water. Attempts to achieve emulsion polymerization led to only low conversion of monomer, most likely owing to side reactions between initiating radicals and the azo linkage of the surfactant, leading in turn to disruption of the micelle.

THE VACUUM ULTRAVIOLET PHOTOCHEMISTRY OF NUCLEOTIDES

Abstract— Photodestruction of nucleotides by vacuum UV (λ < 200 nm) and near UV radiation in thin films has been studied; the products were analyzed by thin‐layer chromatography. Vacuum UV photolysis leads to the rupture of the N‐glycosidic bond with liberation of bases, the quantum yield of the process being about 2 × 10‐4 for guanosine‐5'‐monophosphate. No bases have been found among the products of near UV photolysis.Vacuum UV irradiation of aqueous solutions of adenosine‐5'‐monophosphate and guanosine‐5'‐monophosphate produces, along with bases, some other fluorescent substances. The identity of photoproducts of vacuum UV photolysis with those of γ‐radiolysis is established. The mechanism of photochemical conversion is discussed.