正性远紫外抗蚀剂 Ⅱ.聚苯乙烯砜的荧光光谱研究

利用荧光光谱研究了聚苯乙烯砜正性远紫外抗蚀剂薄膜和溶液的光氧化反应。发现聚苯乙烯砜的荧光随光照时间的延长而逐步减少。这一现象和在未辐照的聚苯乙烯砜中加入微量的芳香氢过氧化物或羰基化合物时的情况相同。这表明:聚苯乙烯砜经光照后荧光的淬灭和体系光氧化过程中产生了氢过氧化物或羰基化合物有关。这一方法适宜于对高聚物光氧化初始阶段的研究。     

二氢吡喃光敏氧化反应的研究

本文研究了二氢吡喃的氰基蒽(9,10-二氰基蒽、9-氰基蒽)敏化光氧化反应。在几种不同溶剂(乙腈、二氯甲烷、苯、四氯化碳)中,其敏化光氧化反应所生成的产物、产物分布及溶剂同位素效应与典型单线态氧的氧化反应相同。荧光淬灭、激基复合物的生成和自由能的变化支持了电子转移反应机理。我们认为,反应首先经过敏化剂的激发单线态与反应底物之间的电子转移反应,尔后在反应过程中生成了活性中间体单线态氧1O2。     

菜籽油热氧化过程中荧光光谱特征的变化研究

为探讨菜籽油热氧化过程中荧光光谱特征的变化规律,采用平行因子分析方法结合二维相关技术解析菜籽油的三维同步荧光光谱,并与油脂氧化化学指标进行相关分析。结果表明:菜籽油具有叶绿素a的荧光特征(Δλ=10 nm,λex=674 nm)和叶绿素b的荧光特征(Δλ=60 nm,λex=620 nm);热氧化过程中,产生了(Δλ=60 nm,λex=448 nm)的特征同步荧光峰。双因子的平行因子分析表明:Δλ为10和60 nm的同步荧光光谱分别为第一、第二主要成分,分别对应叶绿素a和油脂氧化产物的荧光特征;随着热氧化时间的延长,叶绿素a的同步荧光强度降低,而油脂氧化产物的同步荧光强度逐渐升高。二维相关分析表明,叶绿素a热氧化速度、叶绿素b热氧化速度、油脂氧化产物生成速度依次降低。代表叶绿素氧化程度的SFI674和代表油脂氧化产物产量的SFI448与油脂氧化化学指标具有良好的相关性。因此,同步荧光光谱可作为衡量食用油热氧化劣变的指标。     

聚丙烯膜光氧化过程中表层光氧化产物的X-射线光电子能谱(XPS)的研究

本文用X-射线光电子能谱(XPS)研究了聚丙烯膜表层的光氧化产物,得出几种主要氧化产物的相对含量随氧化时间变化的规律并将其与缸外光谱所测结果及文献报道的相比较,证明膜表层光氧化和膜整体光氧化规律有所不同。根据实验结果提出了反应机理。     

一系列单硅烷-寡聚噻吩共聚高分子膜中电荷载流子及其迁移率的研究

研究了一系列由单硅烷和寡聚噻吩组成的共聚高分子膜在较宽掺杂电位范围内的光谱电化学变化规律. 用PSnT表示这一系列共聚高分子, 其中n表示高分子链上寡聚噻吩单元中噻吩环的个数, n分别为5, 7, 8, 10和14. 结果表明在一定的掺杂电位范围内这些PSnT膜可以可逆地电致变色. PSnT膜的光谱电化学和循环伏安研究均表明在电化学掺杂过程中PSnT膜中的寡聚噻吩单元可被两步氧化. 第一步氧化生成极子, 极子可二聚形成p-dimers, 两者之间存在着平衡. 而第二步氧化生成双极子. 双极子不能稳定存在于PS5T和PS7T膜中, 但可稳定存在于其它具有更长寡聚噻吩单元的PSnT膜中. 结合PSnT膜在不同电位下的表观迁移率数据讨论了膜中各种载流子对表观迁移率的影响. 表明当掺杂电位低于两步氧化过程的平均电位Emean时, 膜中表观迁移率的增加主要是由于p-dimers的形成及数量增加所引起的. 随着寡聚噻吩共轭长度(n)的增加, p-dimers更易形成, 因此PSnT膜中载流子的表观迁移率在更低的掺杂电位下开始增加并具有更大的增幅.     

阳离子交换法制备稳定的近红外区核/壳型PbS/CdS量子点

硫化铅量子点(PbS QDs)的光氧化稳定性差是其应用于太阳能电池等领域的主要限制因素之一. 采用阳离子交换法在合成的PbS量子点表面包裹一层具有更稳定、更大禁带宽度的硫化镉(CdS)壳层, 制备出稳定的核/壳型PbS/CdS量子点; 同时, 研究了反应温度和反应时间对阳离子交换过程的影响规律. 通过透射电子显微镜和高分辨透射电子显微镜(TEM/HRTEM)、X射线衍射仪(XRD)、吸收光谱和荧光光谱考察了所制备PbS/CdS量子点的结构、光学特性和光氧化稳定性．结果表明: 阳离子交换过程中, 离子交换反应程度有限、仅发生在量子点的表面层, 但极薄的CdS壳层已能有效钝化PbS量子点的表面缺陷、显著提高其光氧化稳定性.     

碱性介质中甲醇氧化红外光谱电化学循环伏吸研究

本文利用红外光谱电化学循环伏吸法,对碱性体系下甲醇在Pt电极上的氧化过程的中间产物进行分析和研究。结果表明,碱性体系中,CH3OH在Pt电极上具有较好的电化学活性,存在和在酸性体系中不同的反应机理。利用现场红外差谱对氧化过程的产物进行分析,对生成的产物进行指认,并未发现毒化中间产物COL的生成。运用红外光谱电化学循环伏吸及导数伏吸法,对生成的中间体的生成过程进行分析和指认,结果表明:CH3OH的氧化中间产物为HCOO-,在碱性体系下,会继续转化为CO2,CO32-和HCO3-。     

煅烧气氛对LuGd_2Ga_3Al_2O_(12):Ce~(3+)荧光粉的发光性质影响

在O_2, 2%H_2+98%Ar气氛下,通过高温固相法制备了LuGd_2Ga_3Al_2O_(12):0.5%Ce~(3+)(原子分数)荧光粉试样。利用荧光光谱、荧光衰减曲线和热释光谱研究了气氛对试样发光性质的影响。结果表明:O_2气氛下煅烧有助于抑制氧空位的生成,缩短荧光寿命,而还原气氛下煅烧及热处理有利于Ce~(4+)还原成Ce~(3+)离子,并相应生成氧空位;还原性气氛较氧化性气氛下煅烧所得的试样发光强度更强、荧光寿命也更长,并出现了明显的余辉现象。     

母核结构对三碳菁染料光氧化过程的影响

本文研究三种不同母核结构的三碳菁染料在乙醇溶剂中的光氧化反应,实验中采用了近红外区光谱能量分布平稳的光源,得出了母核结构对染料的光氧化稳定的影响,其影响次序:叮恶唑>硒唑>噻唑。同时本文还利用β值的测定,算出染料光氧化过程中敏化产生的单重态氧的浓度以及二者反应的速率常数。     

苯乙烯-4-(甲基丙烯酸)2,2,6,6-四甲基哌啶醇酯共聚物光稳定能力的初步评价

<正> 2,2,6,6四甲基哌啶类受阻胺化合物是一类新型的光稳定剂。由于它们都有较低的离子化电位,因此有着较强的猝灭单线态氧的能力。在猝灭单线态氧的过程中哌啶基可氧化生成稳定的氮氧自由基,这种稳定自由基可以再进一步在高分子光稳定中起到作用。它能清除高分子降解或氧化过程中产生的能引起高分子进一步降解的活性自由基,以及通过其它途径起到稳定作用。     

Studies on the photooxidation mechanism of polymers. I. Photolysis and photooxidation of polystyrene

A new mechanism has been proposed for the photooxidation of polystyrene as film and in benzene. The initial stage of the photooxidative degradation may involve reactions of singlet oxygen with polystyrene molecules. Singlet oxygen may be formed in the reaction between excited benzene ring in polystyrene molecule and molecular oxygen. The addition of singlet oxygen quenchers such as 1,3-cyclohexadiene or β-carotene reduces the rate of polymer degradation in benzene solution. The mechanisms of the photolysis of polystyrene as film and in benzene solution, in vacuo and in the presence of oxygen, are discussed and interpretations proposed. The pronounced yellowing of polystyrene during the photooxidation process is interpreted as a reaction involving benzene ring-opening photooxidation in polystyrene molecule. These results were obtained by comparing ultraviolet and infrared spectra in experiments of photooxidation of pure liquid benzene and polystyrene film.     

Effect of photooxidation of polystyrene on its dielectric properties. II. Use of dielectric loss measurements to study photooxidation

Dielectric loss measurements have been applied to study the short-wave (λ = 254 nm) and long-wave (λ > 300 nm) photooxidation of polystyrene which had been prepared using both free radical and anionic initiator. The high-frequency loss peak, attributable to carbonyl products of oxidation is a sensitive monitor of the rate of oxidation, the sensitivity being greater than that of manometric measurements. The data are specific to carbonyl compounds and the technique is particularly suitable for studying the surfaces, on which most of the above photooxidation occurs with polystyrene. Effects of radiation intensity and oxygen pressure were also studied. The measurements have permitted a more detailed study of the long-wave photooxidation process than has previously been undertaken, and the results emphasize differential reactivities of radically and anionically prepared polymers. Results are interpreted in terms of initiation by both impurities and charge-transfer complexes.     

Chain and photochain mechanisms of photooxidation of polymers

The mechanisms of photooxidation of the popular commercial polymers polystyrene (PS), polyethylene (PE), and an ethylene-carbon monoxide copolymer (polyketone, PK) differing in the polymer chain structure and the nature and concentration of chromophore groups are considered. In the case of the formation of photosensitive intermediates in polystyrene, taken as an example, the photochain oxidation mechanism was revealed and thoroughly studied, according to which the polymer “burns” into complete oxidation products (CO₂, H₂O) with a degree of conversion of ≥50% and a kinetic-chain length of l = 10³–10⁴ units. The hydroperoxide mechanism plays a minor role in the photooxidation of PS, it is a short-chain process (as in the case of thermal oxidation, l ∼ 10) and does not exceed 1.5% of the total amount of absorbed oxygen. Carbonyl groups, as weak photoinitiators, induce in PE and PK the conventional radical chain mechanism of photooxidation with degenerate branching of kinetic chains on hydroperoxide groups and other oxidations products.     

Antioxidants and stabilizers—LXXV. Effect of 2,6-ditert.-butyl-4-methylphenol on the photooxidation of high-impact polystyrene

High impact polystyrene (HIPS) was used in an investigation of the stabilizing effect of 2,6-ditert.-butyl-4-methylphenol (I, BHT) in photooxidation. Changes in the polymer due to photooxidation were examined by reflexion spectroscopy in the u.v. and visible ranges, and by i.r. spectroscopy. It was shown that BHT, 3,5,3′,5′-tetratert.-butylstilbenequinone (II) and 2,6-ditert.-butyl-1,4-benzo-quinone (III), which are important products of the transformation of BHT, possess specific stabilizing properties. Using DSC, it was demonstrated that I-III interfere with the photooxidative process mainly because of their antioxidative properties. In the overall mechanism of action of I in the stabilization of HIPS, the predominant role is played by its major transformation product i.e. quinone II.     

PHOTOCHEMICAL MODIFICATIONS OF lac REPRESSOR: EFFECT OF EFFECTORS BINDING ON TRYPTOPHAN PHOTOOXIDATION

Abstract— UV irradiation of lac repressor modifies the fluorescence of the protein and its binding to the inducer and to the operator. It has been previously shown that the total loss of fluorescence is due to photooxidation of, on average, one of the two tryptophyl residues of each protomer. The present work explains this observation by showing that N-formylkynurenine formed at one site is responsible for the quenching of fluorescence of the other tryptophan via an energy transfer process. Consequently, no photoreaction occurs for the second tryptophyl residue. Photodamage of the two tryptophyl residues (in position 201 and 220) of each protomer were assayed by spectrofluorometric titration in the pH range from 8.5 to 5. For repressor alone, both residues are equally photodamaged. In the presence of the inducer isopropyl-β-D-thio-galactoside, IPTGt, residue 220 is completely protected, and tryptophan 201 is slightly more exposed to photooxidation. In the presence of antiinducer, residue 220 is only partially protected. Our results are discussed in terms of conformational changes triggered by the two types of ligands.     

The influence of amphiphilic polymers on the photocatalytic activity of water-soluble porphyrin photosensitizers

The influence of amphiphilic polymers polyvinylpyrrolidone, poly(ethylene oxide), poly(vinyl alcohol), and pluronic F127 (propylene oxide-ethylene oxide triblock copolymer) on the catalytic activity of a number of water-soluble metal-free porphyrin photosensitizers was studied in the reaction of tryptophan photooxidation in aqueous solution. The introduction of the specified polymers was found to enhance the activity of carbon-substituted tetrafluorophenylporpyrin, photoditazine, and dimegin. It was ascertained that introduction of polyvinylpyrrolidone had the strongest effect on the increase in the photooxidation process rate; the change in the activity of porphyrins was 30–70%. The introduction of poly(ethylene oxide), poly(vinyl alcohol), and pluronic F127 was shown to enhance the rate of the process by 10–40%. It was concluded that this polymer effect was connected with the dissociation of aggregates, in which form porphyrin molecules were present in aqueous solutions, as indicated by an increase in fluorescence intensity of porphyrins. The introduction of polymers resulted in a bathochromic shift of the fluorescence bands for all porphyrins, which accounted for the formation of complexes of porphyrin sensitizers with the polymers.     

Photooxidation of polystyrene by O2 and N2O

Strips of polystyrene held in a flowing O₂ or N₂O atmosphere have been exposed to 240-600 nm radiation. The extent of photooxidation has been followed by x-ray photoelectron spectroscopy (XPS). Although N₂O is a more reactive gas than O₂, it produces a less oxidized polymer surface. This surprising observation can be correlated to the photochemistry occurring at the gas/polystyrene interface. © 1992 John Wiley & Sons, Inc.     

Photooxidized products of recombinant alpha A-crystallin and W9F mutant

Human lenses contain many photosensitizers that absorb light at wavelengths above 300 nm, most notably UVA light (320-400 nm). Kynurenine (Kyn) and 3-hydroxykynurenine (HK), two of the best-known photosensitizers in the human lens, may play a significant role in photooxidation-related changes in lens proteins, such as conformational change and aggregation. In vitro irradiation experiments with proteins indicate that the Trp residue (with maximal absorption at 295 nm) is more susceptible to photooxidation by UVB light (280-320 nm) than by UVA light, but most UVB light below 300 nm is screened by the cornea and little reaches the lens, especially the nuclear region where nuclear color develops. Therefore, if photooxidation is an important contributor to nuclear color or nuclear cataract, it must arise from a photosensitized reaction. In the present study, we use recombinant alpha A- and its Trp-deficient mutant W9F as models to study the effects of UVA irradiation in the presence of HK or Kyn and of UVB (300 nm) irradiation on alpha-crystallins. alpha A-crystallin showed a large decrease in Trp fluorescence and a large increase in non-Trp (blue) fluorescence after the HK-sensitized or 300 nm photooxidation. For the W9F mutant, a smaller decrease in protein fluorescence (lambda ex at 280 nm) and a smaller increase in blue fluorescence than for the wild-type alpha A-crystallin were observed. A decrease in the near-UV CD was also observed for both photooxidized alpha A and the W9F mutant. The effect of Kyn sensitization is smaller than that of HK sensitization. A study of chaperone-like activity indicated that only 300 nm photooxidized alpha A and the W9F mutant increased the ability to protect insulin from dithiothreitol-induced aggregation. Thus, sensitized photooxidation can occur in amino acids other than Trp by UVA in the presence of HK or Kyn with effects similar to, albeit smaller than, those of direct UVB (300 nm) photooxidation.     

A Molecular Rotor that Measures Dynamic Changes of Lipid Bilayer Viscosity Caused by Oxidative Stress

Oxidation of cellular structures is typically an undesirable process that can be a hallmark of certain diseases. On the other hand, photooxidation is a necessary step of photodynamic therapy (PDT), a cancer treatment causing cell death upon light irradiation. Here, the effect of photooxidation on the microscopic viscosity of model lipid bilayers constructed of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine has been studied. A molecular rotor has been employed that displays a viscosity‐dependent fluorescence lifetime as a quantitative probe of the bilayer's viscosity. Thus, spatially‐resolved viscosity maps of lipid photooxidation in giant unilamellar vesicles (GUVs) were obtained, testing the effect of the positioning of the oxidant relative to the rotor in the bilayer. It was found that PDT has a strong impact on viscoelastic properties of lipid bilayers, which ‘travels’ through the bilayer to areas that have not been irradiated directly. A dramatic difference in viscoelastic properties of oxidized GUVs by Type I (electron transfer) and Type II (singlet oxygen‐based) photosensitisers was also detected.