Significance of water quality and radiation wavelength for UV photolysis of PhCs in simulated mixed solutions

Ultraviolet (UV) photolysis of sixteen pharmaceutical compounds (PhCs) in mixed solutions with four types of water and two sets of UV radiation was investigated. UVC (254 nm) photolysis was ineffective at eliminating a large number of PhCs while a big number of them were refractory. However, vacuum UV (VUV: 185 nm + 254 nm) photolysis in the same experimental conditions eliminated the PhCs almost completely. The eliminations in ultrapure water (UPW), tap water (TW) and Neya River water (NRW) and their organic/inorganic contents were inversely correlated, which was more evident in VUV photolysis. Natural organic matter (NOM) in NRW did not have an impact in indirect photolysis, but effluent organic matter (EfOM) in secondary-treated effluent (NWTPE) enhanced indirect photolysis, which was more evident in VUV photolysis underlining the point that radiation wavelength/intensity can be a limiting factor in organic-rich waters. Moreover, VUV photolysis was far superior (90% mineralization) to UVC photolysis (10% mineralization) for PhCs mineralization. The greatly enhanced elimination and mineralization efficiencies observed for VUV photolysis were attributed to accelerated direct photolysis with 185 nm wavelength and indirect photolysis involving ^·OH. The results demonstrated efficacy of VUV photolysis in wastewater treatment and its potential use as a tertiary treatment.      

Photochemical reactions of organomercury compounds in organic solvents

The quantum yields of photolysis of organomercury compounds in different organic solvents have been measured. It was shown that the quantum yields of photolysis of nitro derivatives of mercury compounds and the symmetric (methylnaphtyl)mercury compound are equal to unity. The photolysis of halo derivatives of benzylmercury proceeds with lower quantum yields as compared with photolysis of analogous dibenzylmercury derivatives. The quantum yields of photolysis of organomercury compounds are almost independent of the solvent.     

THE PHOTOLYSIS OF TRYPTOPHAN WITH 337.1 nm LASER RADIATION

Abstract— Aqueous solutions of L-tryptophan were photolyzed by exposure to 337.1 nm radiation from a pulsed nitrogen laser. These data were compared with results for the 290 nm conventional-source photolysis of tryptophan. The progress of photolysis was monitored by fluorescence analysis of tryptophan. UV absorption spectroscopy, HPLC, TLC, and proton NMR spectroscopy. The loss of Trp was observed to be first order for 290 nm photolysis but of mixed order for 337.1 nm photolysis. Five photolysis products were detected by TLC analysis, including: N-formylkynurenine. kynurenine, tryptamine (detected after 290 nm photolysis but not 337.1 nm photolysis) and two unknown products. The tryptophan-containing peptides N-acetyl-tryptophanamide (NATA) and tryptophylglycine (Trp-Gly) were also observed to photolyze upon 337.1 nm laser radiation demonstrating that this phenomenon is not restricted to free tryptophan monomer.
Since Trp is not ordinarily thought to absorb U V radiation at wavelengths as long as 337.1 nm. a number of experiments were performed in an effort to determine the mechanism of photolysis at this wavelength. Evidence is presented which indicates that the 337.1 nm laser photolysis of Trp does not result from two photon absorption, dielectric breakdown, or other laser-specific processes. Instead. it is concluded that this photolysis results either from a very weak absorption tail extending to 337.1 nm in tryptophan itself or from a reaction involving an impurity sensitizer which absorbs the 337.1 nm radiation. The sensitizing impurity. if present, could not. however, be removed by preparative HPLC and could not be detected by TLC or fluorescence analysis.     

玫瑰红作用下γ-六氯环己烷在冰相中的光敏化降解

考察了在玫瑰红(RB)存在下γ-六氯环己烷(γ-HCH)在冰中的光降解.结果表明,光敏剂RB通过其激发态[RB]~*及其产生的~1O_2~*加速了γ-HCH的光降解,RB浓度是影响光降解率最显著的因素;γ-HCH在较低初始浓度下的光敏化降解更快;无机盐离子的种类和浓度可以改变冰表面上类液层(LLL)的比例从而影响γ-HCH的光解.通过分析γ-HCH光降解产物提出了RB存在时冰中γ-HCH的光降解作用机理.     

Trimethyl acetate on TiO2(110): preparation and anaerobic photolysis

The preparation and anaerobic ultraviolet photolysis of trimethyl acetate (TMA) on rutile TiO(2)(110) have been examined with an emphasis on reaction paths. Substrates for photolysis were prepared by dosing trimethyl acetic acid at 100, 300, and 550 K. The chemistry was characterized by mass spectrometry during dosing and by H(2)O adsorption and temperature programmed desorption (TPD) after dosing. Using TPD after photolysis and mass spectrometry during photolysis, the products ejected and retained during photolysis were sought. The photolysis results are interpreted using the following mechanistic model. Photons with energies exceeding 3 eV create electron-hole pairs in the substrate. With probabilities of 10(-5) or lower, the holes initiate TMA chemistry by extracting an electron from the pi orbital of the carboxylate moiety. The accompanying electrons are trapped at the surface and inhibit subsequent events of this chemistry. The electron-deficient intermediate, TMA, decarboxylates to form CO(2) and either chemisorbed tert-butyl (-C(CH(3))(3)) or physisorbed i-butene. For photolysis at 100 or 200 K, the -C(CH(3))(3) accumulates and there is a slow photon-driven secondary reaction that, with a source of H, hydrogenates adsorbed tert-butyl to physisorbed i-butane. For photolysis at 300 K, -C(CH(3))(3) thermally reacts to form and desorb i-butene and i-butane during photolysis.     

Photochemical aging of α-pinene secondary organic aerosol: effects of OH radical sources and photolysis

This study addresses photochemical aging of secondary organic aerosol (SOA) produced from α-pinene ozonolysis. The SOA is aged via hydroxyl radical (OH) reactions with first-generation vapors and UV photolysis. OH radicals are created through tetramethylethylene ozonolysis, HOOH photolysis, or HONO photolysis, sources that vary in OH concentration and the presence or absence of UV illumination. Aging strongly influences observed SOA mass concentrations, but the behavior is complex. In the dark or with high concentrations of OH, vapors are functionalized, lowering their volatility, resulting in an increase in OA by a factor of 2-3. However, with lower concentrations of OH under UV illumination SOA mass concentrations decrease over time. We attribute this decrease to evaporation driven by photolysis of the highly functionalized second-generation products. The photolysis rates are rapid, a few percent of the NO(2) photolysis frequency, and can thus be highly competitive with other aging mechanisms in the atmosphere.     

二烷基(4-羟基苯基)硫鎓盐的电荷转移络合物及其敏化光降解

二烷基(4-羟基苯基)硫鎓盐作为一类新型的光引发剂由于其合成方法简便以及具较宽的光谱范围(可延伸至300nm)。因而近年来颇受重视。由于该引发剂在光照激发后生成了共振一稳定的内鎓盐(Ylide)结构和质子酸。     

Kinetics and mechanism of the photolysis of CF<Subscript>2</Subscript>ClBr exposed to light with a wavelength of 253.7 nm

CF₂ClBr mixed with oxygen was photolyzed using a low pressure mercury lamp, and the kinetics of photolysis was studied. The absorption spectra of the starting material and products of photolysis were recorded in the wavelength range from 200 to 900 nm on an Agilent 8453 spectrophotometer. The concentrations of the main photolysis products at different irradiation times were calculated by the mathematical processing of the absorption spectra. The scheme of CF₂ClBr photolysis was suggested, the model calculations according to this scheme were performed, and the results of simulation were compared with experimental data.     

On-line photo-derivatization with flow injection and liquid chromatography-atmospheric pressure electrospray mass spectrometry for the identification of indoles

The application of on-line photochemistry with flow injection (FI) and liquid chromatography (LC) in conjunction with atmospheric pressure electrospray mass spectrometry (LC-APESI-MS) for the identification of similar indole derivatives is reported here. The photo-transformation of the indole compounds is strongly affected by the substituent groups on the aromatic and heterocyclic rings. Upon photolysis for 2.5 min, the mass spectrum of tryptamine (Try) which has no OH substituent on the aromatic ring does not differ greatly from that obtained without photolysis. However, after photolysis of serotonin (Ser) which has one OH group on C5 of the aromatic ring, the mass spectrum indicates the formation of dimers and higher molecular weight ions. The fragmentation pattern of 5-hydroxytryptophol (Phol) without photolysis resembles that of Ser with a base peak of m/z 160. Upon photolysis using MeOH-H₂O (10/90), Phol is found to form a base peak at m/z 375 (100%) and a major peak at m/z 214 (66%) in addition to other ions with lower abundance. Melatonin (Mel) and tryptophan (Phan) upon photolysis are found to form high molecular weight ions with a relative low abundance. The mass spectrum of indole-3-acetic acid (Inaa) with on-line photolysis also shows different ions that are not formed without photolysis.     

Rules governing the formation of photolysis products in the lead azide-copper(I) oxide system

It was found that, along with a decrease in the rate of photolysis and photocurrent in the region of lead azide intrinsic absorption, the addition of copper(I) oxide broadened the range of spectral sensitivity, and preliminary treatment of the PbN₆(Ab)-Cu₂O system with light (λ = 365 nm) increased the rate of photolysis. The rate constants for photolysis were estimated. An analysis of the results of current-voltage characteristic, contact potential difference, and contact photo-electromotive force measurements was used to construct a diagram of energy zones and suggest a model of the photolysis of the PbN₆(Ab)-Cu₂O system including stages of the generation, recombination, and redistribution of nonequilibrium carriers in a contact field, formation of microheterogeneous PbN₆(Ab)-Pb (photolysis product) systems, and formation of final photolysis products.     

Ozone initiated oxidation of long chained n -alkanes in the presence of activated charcoal or silica gel

Photolysis behavior of acetamiprid in different kinds of surfactant solutions were investigated. The results showed that acetamiprid was prone to photolysis when exposed to the irradiation of a mercury lamp, and the photolysis kinetics fit in well with the first-order kinetic equation. Surfactants did not participate in the acetamiprid’s photolysis process directly, whereas they all had obvious inhibiting effects on it.     

The Rules Governing the Formation of Silver Azide Photolysis Products

Irradiation of silver azide at λ = 365 nm (I > 1 × 10¹⁵ quantum cm^?2 s^?1) in a vacuum (1 × 10^?5 Pa) leads to an increase in the rate of photolysis and photoinduced current and the appearance of a new long-wave region of spectral sensitivity. The photolysis products, silver metal and gaseous nitrogen, are formed in a stoichiometric ratio on the surface of silver azide. The rate constants for silver azide photolysis were determined. Measurements of contact potential difference, current—voltage characteristics, photoelectromotive force, and photocurrent showed that AgN₃(A₁)—Ag (photolysis product) microheterogeneous systems were formed in silver azide photolysis. The limiting stage of silver azide photolysis is the diffusion of interstitial silver cations to the (T_nAg_m)⁰ neutral center.     

Photolysis of polycyclic aromatic hydrocarbons on water and ice surfaces

Laser-induced fluorescence detection was used to measure photolysis rates of anthracene and naphthalene at the air-ice interface, and the kinetics were compared to those observed in water solution and at the air-water interface. Direct photolysis proceeds much more quickly at the air-ice interface than at the air-water interface, whereas indirect photolysis due to the presence of nitrate or hydrogen peroxide appears to be suppressed at the ice surface with respect to the liquid water surface. Both naphthalene and anthracene self-associate readily on the ice surface, but not on the water surface. The increase in photolysis rates observed on ice surfaces is not due to this self-association, however. The wavelength dependence of the photolysis indicates that it is due to absorption by the PAH. No dependence of the rate on temperature is seen, either at the liquid water surface or at the ice surface. Molecular oxygen appears to play a complex role in the photolytic loss mechanism, increasing or decreasing the photolysis rate depending on its concentration.     

EVALUATING THE STABILITY AND REACTIVITY OF A LIGHT-SENSITIVE PROBE BY ENZYME ANALYSIS

Abstract— Enzymes can provide well defined functional targets for determining the availability and reaction characteristics of light sensitive probes. Trypsin and chymotrypsin are inhibited by flash photolysis with a photoprobe, 4-fluoro-3-nitrophenylazide (FNPA). Inhibition is competitive in the dark, and non-competitive (irreversible) following photolysis of the FNPA enzyme solution. Photoinactivation is dependent upon the concentration of FNPA, the flash rate, and the time of photolysis. The enzymes can be protected from photolytic inactivation with FNPA if photolysis is carried out in the presence of 2,4-dinitrophenol or 4-fluoro-3-nitroaniline which compete with FNPA for binding sites. The photo-probe is effective over a wide pH range (i.e. pH 2–11), and provides a sensitive tool for probing conformational and charge adjustments which increase or decrease the affinity of the binding site. Chymotrypsinogen was also sensitive to photolysis, indicating that FNPA binding sites are present in the zymogen structure.     

ON THE MECHANISMS OF PHOTOLYSIS OF COMPOUNDS I AND II OF HORSERADISH PEROXIDASE AT 77 K*

Abstract—When Compounds I and II of horseradish peroxidase in glycerol/water glasses at 77 K were irradiated with the light of a mercury lamp, some changes in optical spectra as well as the development of strong EPR signals of a free-radical type were detected. In case of photolysis of Compound I the light of wavelengths around 400 nm was the most effective, while only short wavelength (≥ 280 nm) light affected Compound II. The results of experiments with thawing and freezing the product of photolysis of Compound I (called Intermediate Y) provide further evidence for the suggestion that the ferric state of the heme iron is generated in the course of the photolysis. The quantum yields of the photolysis of Compound I at different wavelengths of irradiating light were obtained and mechanisms of the photolysis of Compounds I and II are proposed.     

Effect of crystallinity and flexibility on the photodegradation of polyurethanes

Using fluorescence spectroscopy and gel content measurement, the photolysis of simple polyurethanes based on methylene 4,4′-diphenyldiisocyanate (MDI) is shown to depend on both the flexibility and crystallinity of the polymer. Polyurethane films based on MDI and 1,12-dodecanediol (MDI-12) can be either annealed or quenched to yield a semicrystalline (as measured by DSC and X-ray diffraction) or amorphous film, respectively. In the case of the quenched (amorphous) film, photolysis yields an ortho photo-Fries product whereas the annealed (semicrystalline) film does not. Similarly, for a given photolysis time the annealed film generates a lower extent of crosslinked gel. In addition, photolysis of amorphous polyurethane films derived from MDI and ethylene oxide oligomers shows that for relatively inflexible polymers with only three ethylene oxide segments, little or no ortho photo-Fries rearrangement products are generated upon photolysis. In contrast, photolysis of more flexible polyurethane films with approximately 13 ethylene oxide linkages yields the ortho photo-Fries product. Apparently, for aromatic diisocyanate based polyurethanes, the extent and mechanism of degradation is directly dependent on the crystallinity and main-chain flexibility of the polymer.     

铁－芳烃络合物光引发剂的吸收光谱研究

铁－芳烃络合物光引发剂的吸收光谱研究陈旭东，黄新华陈用烈，梁兆熙（西南师范大学化学系重庆，６３０７１５）（中山大学高分子研究所广州）关键词铁－芳烃络合物，光引发剂，吸收光谱，光解铁－芳烃络合物作为环氧化物阳离子聚合光引发剂已引起人们关注［１，２］．我...     

Study of spectral and kinetic characteristics of products of photolysis of a trifunctional compound with light of different wavelengths

Spectral and kinetic characteristics of intermediate products of photolysis of a novel phototrifunctional compound (PTC), whose molecule combines spironaphthoxazine, hydroxyazomethine, and azobenzene fragments, have been studied by microsecond flash photolysis with UV and visible light in toluene and methanol solutions. Three products of PTC photolysis have been detected. It has been found that the efficiency of the photoprocesses substantially depends on the solvent and the wavelength of excitation light.     

Formation of stable radicals upon the photolysis of perfluoro-2,4-dimethyl-3-ethyl-2-pentene

Conclusions The photolysis of liquid perfluoro-2,4-dimethyl-3-ethyl-2-pentene gives perfluoroallyl and perfluoroalkyl radicals with anomalously long lifetime in the liquid at room temperature. The accumulation and decomposition of perfluoroallyl radicals occurs in the initial stage of the photolysis. Accumulation of perfluoroalkyl radicals occurs upon more prolonged photolysis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2359–2361, October, 1986.     

Photolysis of 2,6-dimethyl-3,5-dicarboethoxy- 1,4-dihydropyridine-4-carboxylic acid

The photolysis of 2,6-dimethyl-3,5-dicarboethoxy-1,4-dihydropyridine-4-carboxylic acid 1 gives with a pyrex filter pyridine 2 and glycol 3. At low concentration, aldehyde 4 accumulates. The photochemical dimerization of this aldehyde gives glycol 3 in methanol or ethanol. The aldehydic hydrogen in aldehyde 4 is replaced by deuterium on performing the photolysis of acid 1 in MeOD as is the case for the photolysis of 2,6-dimethyl-3,5-diacetyl-1,4-dihydropyridine. A concerted mechanism for the decarboxylation of acid 1 to aldehyde 4 is possible. When the photolysis of 1 is performed in quartz, another reaction occurs leading to 1,2-dihydropyridine 8.