Ultraviolet photolytic vapor generation from particulate ensembles for detection of malathion residues in aerosols

A method to selectively generate vapor signatures from malathion entrained within matrices of surface-impacted aerosol particles has been demonstrated. The method uses ultraviolet radiation (172 or 222 nm) from a continuous wave discharge lamp to photodissociate malathion molecules collected within and on surface-impacted particles, followed by detection via ion mobility spectrometry (IMS). Since surface heating does not occur, only those molecules whose photofragments exhibit high vapor pressure are introduced into the IMS instrument and then only those exhibiting high proton affinity are subsequently detected. This process produces less signal clutter than in pyrolysis-IMS, where the background aerosol is pyrolyzed along with the sample. Quantities of malathion as small as 50 ng could be detected when the malathion was entrained on a clean surface, and as small as 100 ng when co-entrained on a surface with much larger quantities of background aerosols such as diesel soot, road dust, Bacillus globigii, albumin, and cotton lint. This sensitivity indicates that, when combined with a particle collector as an effective pre-concentrator, detection of malathion aerosol concentrations of <0.01 mg/m³ will be possible. Since malathion can be viewed as a model compound, this technique is also extendable to the detection of organophosphate war chemicals.     

Determination of liposome permeability of ionizable carbamates of zidovudine by steady state fluorescence spectroscopy

In the present paper the relative permeabilities of AZT-Pyp and AZT-Ethy across a phospholipid bilayer were estimated by the means of fluorescence spectroscopy.

The center of spectral mass of both non-encapsulated AZT-derivatives (AZT-der) emission spectra increased as a function of the illumination time inside the spectrofluorimeter cell. This phenomenon was even more evident when drugs were incubated under an UV mercury lamp, suggesting its photolytic origin. AZT-der were protected from photolysis inside liposomes and decomposed upon irradiation when they were free in the aqueous phase. The time-dependent decrease in the fluorescence intensity at a constant wavelength was fitted to a two-exponential equation and the values of rate constants for permeability and photolysis were calculated. It was concluded that AZT-Pyp but not AZT-Ethy diffused across the bilayer. This behavior correlated with the molecular volumes of AZT-Pyp (379.6 Å³) and AZT-Ethy (450.5 Å³), determined from the minimum energy conformations but not with previously reported log P values. These results reinforce the concept that not only lipophilicity but also membrane structure and AZT-der molecular size had a critical influence in passive diffusion across bilayers and may help in future refinements of other AZT-der molecular design.     

Photoinduced iron-cyclopentadienyl (Fe-Cp) bond cleavage reactions and photocontrolled polymerizations of strained [1]ferrocenophanes

Although extensive previous studies have shown that strained [1]ferrocenophanes predominantly undergo ring-opening chemistry at the bridging atom E-cyclopentadienyl (E-Cp) bond, recent reports have highlighted that reactivity at the Fe-Cp bond can also occur, especially on photoactivation. We provide an overview of recent results from our group and those of other researchers. In addition, the development of photocontrolled living polymerizations of sila[1]ferrocenophanes using Fe-Cp bond cleavage chemistry is described.     

Photolysis of thin films of cypermethrin using in situ FTIR monitoring: Products, rates and quantum yields

Cypermethrin is a synthetic pyrethroid insecticide commonly used both indoors and outdoors. Following its application, cypermethrin residues are exposed to atmospheric oxidants, such as ozone and OH radicals, as well as to solar radiation. The current work focuses on the photochemical degradation of cypermethrin under 254 nm, 310 nm, and solar radiation; including kinetic analysis, quantum yields, and identification of volatile and non-volatile products. The investigation was done using a combined FTIR set-up for parallel analysis of condensed and gas phases. Complementary GC–MS analysis was conducted on the pesticide’s residues. Quantum yields of 0.41 and 0.25 were obtained under 254 and 310 nm, respectively. These values are in agreement with outdoor studies and are higher than the known yields for aqueous solution. The values obtained under all tested conditions suggest that photodegradation of adsorbed cypermethrin is a major outdoor degradation pathway. Oxygen presence was found to increase degradation rate and quantum yield.The identified photoproducts include 3-phenoxybenzaldehyde, 3-phenoxybenzoic acid, acetonitrile (m-phenoxyphenyl), and cypermethrin isomers on the surface and formic acid, CO₂ and CO in the gas phase. The condensed phase products are more polar than the parent molecule, suggesting that they may be susceptible to a greater leaching rate in soils.     

在ADC(2)水平上通过从头算非绝热动力学方法模拟硝酸甲酯的光解

在ADC(2)水平上通过轨线面跳跃方法模拟了硝酸甲酯的非绝热动力学. 结果证实该体系存在快速的非绝热动力学过程,导致了体系回到电子基态. 当动力学从S₁和S₂电子态开始时,光解产物是CH₃O+NO₂,这个发现与实验研究的结果以及更高精度的XMS-CASPT2水平上模拟出的结果一致. 在ADC(2)水平上,当动力学从S₃态开始时,光解产物依然是CH₃O+NO₂. 该研究表明：ADC(2)方法可用于研究硝酸甲酯在长波下的光解机理,然而无法用于理解其在短波段下的光解动力学. 本文为在ADC(2)水平上处理类似化合物的光诱导过程提供了有价值的信息.     

Molecular many-body dissociation: Data reduction strategies in translational spectroscopy

Advanced time- and position-sensitive multi-hit detectors allow to study molecular breakup processes into two, three, and more massive fragments by translational spectroscopy. We discuss the feasibility to perform kinematically complete final state analysis of complex molecular dissociation processes using such detectors. We have developed new algorithms to determine - for an arbitrary number of fragments - the fragment momentum vectors in the center-of-mass frame from the measured positions and arrival time differences. These algorithms can easily be implemented to perform online data reduction in coincidence experiments. We have tested the new data reduction strategies in an experimental study and in Monte-Carlo simulations of realistic experimental conditions. We show that the new algorithms can discriminate between two-, three-, and four-body decay of a four-atomic molecule and can uniquely determine the momentum vectors of all fragments. For two-body decay, we find that the accuracy of the new algorithm is superior to the frequently used approximate formula introduced by DeBruijn and Los. We demonstrate this improvement in the evaluation of experimental data for the decay of laser-excited triatomic hydrogen H₃ 3s (N=1,K=0) into H + H₂(v,J) fragment pairs. Received 12 April 2000     

Photolysis of oxygen saturated ethers in the presence of Sn(Ⅱ) or Cu(Ⅱ) salts

Photolysis of diethyl ether-oxygen charge transfer complex in the presence of Sn(Ⅱ)or Cu(Ⅱ)salts gave higher yields of the oxidation products,ethyl acetate,acetaldehyde,ethanol,ethyl formate and methanol compared with those without the salts.In addition,the photolysis of an oxygen saturated te-trahydrofuran(THF)or dibutyl ether solution gave y-butyro-lactone or butanol and butyl butyrate as major products with small amounts of undetermined compounds,respectively.Their yields were also affected by the addition of Cu(Ⅱ)or Sn(Ⅱ)salts.     

荧光分析法研究环糊精对溶解态蒽光降解的影响

以快速、简便和有效的荧光分析法研究了 5种环糊精 (cyclodextrins,CDs)对溶解态蒽在水溶液中光降解的影响。发现 5种 CDs都能够促进蒽在水溶液中的光降解过程 ,促进作用的能力的顺序为 :HPCD(hydroxypropyl- β- CD) >DMCD(heptakis(2 ,6 - di- o- methyl) - β- CD) >β- CD>γ- CD>α- CD。这是因为蒽进入 CDs空腔后 ,抑制了蒽三重态的自猝灭过程以及延长了单重态的寿命 ,这使三重态氧猝灭蒽的激发态的几率增加 ,生成的单重态的氧的量增加。探讨了 CDs空腔大小及空间位阻对蒽光降解的影响。     

在ADC(2)水平上通过从头算非绝热动力学方法模拟硝酸甲酯的光解（英文）

在ADC(2)水平上通过轨线面跳跃方法模拟了硝酸甲酯的非绝热动力学.结果证实该体系存在快速的非绝热动力学过程,导致了体系回到电子基态.当动力学从S₁和S₂电子态开始时,光解产物是CH₃O+NO₂,这个发现与实验研究的结果以及更高精度的XMS-CASPT2水平上模拟出的结果一致.在ADC(2)水平上,当动力学从S₃态开始时,光解产物依然是CH₃O+NO₂.该研究表明:ADC(2)方法可用于研究硝酸甲酯在长波下的光解机理,然而无法用于理解其在短波段下的光解动力学.本文为在ADC(2)水平上处理类似化合物的光诱导过程提供了有价值的信息.     

Photodegradation of Decabromo Diphenyl Ether Flame Retardant in Poly (Acrylonitrile Butadiene Styrene) (ABS)

Abstract

Decabromodiphenylether (DBDE) is a brominated flame retardant which belongs to the group of polybromodiphenylethers (PBDEs) often used as a fire resistant additive in various well known polymeric systems like polystyrene, poly(acrylonitrile-butadiene-styrene) (ABS), polypropylene, etc. This compound can be considered as a persistent organic pollutant and presents certain risks for the environment owing to the fact that it is bioaccumulable and not biodegradable. A detailed investigation, described here, was carried out on the effect of ultraviolet/visible radiation on DBDE in ABS with the aim to study the photolytic reactions of this molecule in the solid state, in order to improve the economic and ecological treatment of brominated plastic waste from waste electrical and electronic equipment (WEEE). This study presents new aspects of the photochemical degradation of DBDE/ABS systems in the solid state. The photodegradation of DBDE in ABS was followed by Fourier transform infrared spectroscopy (FTIR) as well as by thermogravimetrical analysis (TGA). Good agreement was obtained for the results of both analytical methods in terms of the overall photolysis of DBDE.