过渡金属络合物猝灭单重态氧能力的研究

研究了多种不同过渡金属络合物对单重态氧的猝灭问题。结果表明过渡金属络合物猝灭单重态氧的能力主要和络合物分子的几何构型有关。能形成平面四方形结构的络合物由于中心金属原子易于和¹O₂分子相接近因而具有强的猝灭¹O₂的能力,反之形成四面体形结构的络合物则猝灭能力减弱。     

竹红菌素自敏光氧化反应机制的研究

本文对竹红菌素自敏光氧化反应的机制作了较详细的研究,竹红菌素通过自敏光氧化反应生成不稳定的过氧化物,它可以放出¹O₂回到母体化合物,也可以转化为稳定的氧化产物,我们用活泼的单重态氧的接受体捕获到了体系中放出的¹O₂,用吸收光谱的变化证明过氧化物回到了母体化合物。文中还用猝灭实验证实此自敏光氧化反应除涉及¹O₂机制外,还有其它机制起着作用。     

受阻胺光稳定剂GW-540作用机理的研究

本文用抗张强度、ESR、IR、氧吸收测定方法,以及亚甲基蓝敏化光氧化方法研究了新型受阻胺光稳定剂——三(1,2,2,6,6-五甲基-4-哌啶)亚磷酸酯(GW-540)的作用机理。实验结果表明,GW-540具有较好的光稳定效能,它能在光稳定作用过程中产生稳定的氮氧自由基(>NO^·),也能分解大分子氢过氧化物及猝灭单线态氧。它的光稳定作用可能与其同时具有分解氢过氧化物,清除游离基,猝灭单线态氧等多功能的自协同作用有关。     

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。     

丙烯-马来酸哌啶酯共聚物的合成与表征

<正> 以2,2,6,6-四甲基哌啶为母体的衍生物作为受阻胺光稳定剂,其效率约为镍-螯合物光稳定剂的2—6倍,已引起人们的注意,但是小分子受阻胺易于挥发,从而使其光稳定作用较差。为了克服上述缺点,使受阻胺稳定剂高分子化是近年来展的趋势,本文合成了含有“丙烯”单元的高分子受阻胺光稳定剂——丙烯-马来酸哌啶酯共聚物,力求改进它与丙烯的相容性,提高光稳定效率,本文还对共聚物进行表征。     

苯乙烯-甲基丙烯酸四甲基哌啶醇酯共聚物对聚丙烯的光照接枝研究

<正> 苯乙烯-甲基丙烯酸四甲基哌啶醇酯共聚物具有下列结构: 是高效的大分子受阻胺光稳定剂(我国商品名称为PDS)。关于它的高防护效率的原因和光防护机理研究尚少。吴世康等研究了单线态氧发生剂亚甲基蓝存在下的PDS-苯-甲醇体系的光氧化,发现PDS氮氧稳定自由基对芘的荧光猝灭还不如小分子的四甲基     

磺化酞菁类染料光敏氧化胆固醇及L-半胱氨酸的反应

本文合成了磺化酞菁、磺化酞菁镓和磺化酞菁铝,研究了它们光敏氧化胆固醇及L-半胱氨酸的反应。染料的聚集态和溶液的pH值对反应速率有不同程度的影响。D₂O加速反应而NaN₃猝灭反应的结果表明,光敏氧化反应主要通过Ⅱ型(涉及¹O₂)机制进行。     

α-甲氧基萘的电子转移光氧化反应

近年来芳烃和杂环化合物的电子转移光氧化反应受到日益的注意^[1-5]。电子转移光氧化反应不仅可应用于很多对¹O₂为惰性的烯烃和芳烃^[1-7],而且对某些¹O₂活性化合物,也可给出与¹O₂反应不同的产物。     

高分子金属卟啉敏化剂的合成及其产生单线态氧的能力

本工作用氯甲基化的苯乙烯系的树脂和四-(对-氨基苯)卟啉及其Mg²⁺、Cd²⁺、Ni²⁺、Cu²⁺的络合物,合成了一组高分子的金属卟啉敏化剂。并用9,10-二甲基蒽作为¹O₂受体,测定了它们光敏化产生¹O₂的相对能力,分别为1.0、1.56、0.73、0.25、0.21。表明高分子卟啉镁具有较强的敏化能力,是一种良好的敏化剂,其他三种过渡金属元素,特别是具有顺磁性的Ni和Cu,对卟啉光敏化能力起了明显的抑制作用。     

高分子受阻胺对顺1,4-聚丁二烯溶液光敏降解过程的稳定作用

本文研究了高分子受阻胺光稳定剂苯乙烯4-(甲基丙烯酸)-2,2,6,6-四甲基哌啶醇酯共聚物在用罗丹明6G光敏氧化降解顺1,4-聚丁二烯过程中的稳定作用。它具有淬灭单线态氧、分解过氧化氢以及捕获大分子自由基的能力,对其光稳定机理也进行了初步的讨论。     

TWO NEW METHODS OF ACTINOMETRY FOR EPR-MEASUREMENTS

Abstract— Two methods to perform actinometry in an EPR-cavity are described. One method is based on the observation that photoproduced anion radicals of hematoporphyrin react with the stable free radical 2,2,6,6-tetramethyl-4-piperidone-N-oxyl to eliminate the spin. The other method is based on the dye sensitized photoproduction of nitroxyl radicals resulting from the reaction of singlet oxygen with sterically hindered amines.     

Photostabilizing activity of tertiary hindered amines

The influence of the N-alkyl group of tertiary hindered amines on the photostabilization of polymers was studied. The photostabilizing effects of the tertiary amine derivatives of 4-benzoyloxy-2,2,6,6-tetramethylpiperidine ( 1a ) in polypropylene were compared. All tertiary amine derivatives having α-H to hindered N showed higher effectiveness than 1a . Model liquid phase photoxidations were carried out by irradiating (UV-lamp) the solutions of tertiary hindered amines containing tert-butyl hydroperoxide as a photoinitiator. The tertiary hindered amines were oxidized more easily than corresponding parent hindered amine and converted to the parent amine, which was identified as its salt, resulting from the carboxylic acid produced from the N-alkyl group by oxidation. The thermal reaction of the tertiary hindered amines with tert-butyl hydroperoxide was also studied in the liquid phase. The tertiary hindered amines decomposed tert-butyl hydroperoxide more rapidly than the parent secondary hindered amine, and generated the parent amine. It was also found that the photostabilizing effects of tertiary hindered amines for polyolefins were higher than that of the parent secondary hindered amine.     

Chemically induced dynamic electron polarization generated through the interaction between singlet molecular oxygen and nitroxide radicals

An absorptive chemically induced dynamic electron polarization (CIDEP) was generated by the quenching of singlet oxygen by nitroxide radicals (TEMPO derivatives). The spin polarization decay time of the nitroxide (measured by time-resolved EPR) correlates with the lifetime of singlet oxygen (measured by singlet oxygen phosphorescence spectroscopy). In addition, a deuterium isotope effect on the spin polarization decay time was observed, a signature of singlet oxygen involvement. With use of isotope labeled nitroxides (15N, 14N), the relative spin polarization efficiencies of TEMPO, 4-oxo-TEMPO, and 4-hydroxy-TEMPO by singlet oxygen were determined. The relative spin polarization efficiencies (per quenching event) decrease in the order 4-hydroxy-TEMPO > TEMPO > 4-oxo-TEMPO, whereas an opposite trend was observed for the total quenching rate constants of singlet oxygen by the nitroxides where the order is 4-hydroxy-TEMPO < TEMPO < 4-oxo-TEMPO.     

Functionalized ZrP nanosheet with free‐radical quenching capability and its synergism in intumescent flame‐retardant polypropylene

The combination of catalyzing carbonization and free‐radical quenching mechanism is proposed to be a promising strategy for the preparation of high‐efficiency flame‐retardant polypropylene (PP). Herein, a novel functionalized zirconium phosphate (RQZrP) nanosheet with free‐radical quenching capability was fabricated by decorating macromolecular N‐alkoxy hindered amine (MNOR) onto the surface of ZrP. It was combined with an intumescent flame retardant (IFR) to flame‐retard PP. The results showed that there was a good synergism between RQZrP and IFR, which effectively improved the fire safety of PP. When the content of RQZrP was 2 wt% and IFR was 23 wt%, the limiting oxygen index (LOI) of PP increased from 19.0% to 33.0%, and it achieved a UL‐94 V‐0 rating. Meanwhile, the peak heat release rate (PHRR), total heat release (THR), carbon monoxide production (COP), and carbon dioxide production (CO₂P) were significantly decreased. It revealed that nitroxyl radicals generated by RQZrP could capture alkyl radicals and peroxy radicals that produced during the degradation and combustion of PP. Meanwhile, RQZrP acted as a solid acid that catalyzed PP chains rapidly cross‐linking to form char on its surface, and it also played as a supporting skeleton to enhance the strength and compactness of the char layer, thus effectively preventing the transmission of heat, oxygen, and combustible gases.     

Formation of polymer-bonded nitroxyl radicals in the UV stabilization of polypropylene by a bifunctional hindered amine light stabilizer

The formation of polymer-bonded stabilizer derivatives during photooxidation of isotactic polypropylene, which contains the hindered amine light stabilizer bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate and the corresponding bisnitroxyl radical, was investigated. The photooxidized polypropylene films that contain these additives were studied by ESR, IR, and nitrogen analysis before and after exhaustive solvent extraction of the photooxidized films. ESR showed that under the conditions in use a maximum of 20% of the nitroxyl radicals formed from the hindered amine was bonded to the polymer chain. Regeneration of nitroxyl radicals from the polymer-bonded stabilizer derivatives under photooxidative conditions indicated that the stabilizer was bonded to the polymer chain by O-alkyl-substituted hydroxylamine linkages >N? O? PP.     

ON THE PRODUCTION OF NITROXIDE RADICALS BY SINGLET OXYGEN REACTION: AN EPR STUDY

Abstract— The production of free radicals by reaction of 2,2,6,6-tetramethyl-4-piperidinol with singlet oxygen was studied by EPR spectroscopy. The rate constant of the amine was found to be equal to 8 ×10⁵ M ^-1s^-1 in ethanol and to 4 × 10⁷M^-1s^-1 in phosphate buffer (pH 8). Competition experiments were performed with singlet oxygen quenchers such as NaN₃, DABCO and the quenching rate constants were found to be consistent with the literature values. The EPR method proved to be a valuable technique to study the reaction of singlet O₂ with the sterically hindered amine without any interfering effect.     

ON THE MECHANISM OF QUENCHING OF SINGLET OXYGEN BY AMINES-III. EVIDENCE FOR A CHARGE-TRANSFER-LIKE COMPLEX

Abstract— A series of amines were found to quench singlet oxygen in the order tertiary > secondary > primary, with a reasonable correlation between the log of their rate constant of quenching and their ionization potential. In addition, a Hammett rho plot gave a rho value of - 1.39 for the quenching of singlet oxygen by a series of substituted N, N-dimethylanilines, in good agreement with the results obtained by a different method. It was found that some of the amines (anilines) quenched the triplet state of the dye-sensitizer (Rose Bengal) used for the production of singlet oxygen. Corrections in the results were made in the calculations of rates of quenching of singlet oxygen to allow for the triplet-state quenching. No extensive quenching of the singlet state of the dye was observed at the concentrations of the amines necessary for singlet-oxygen quenching. In one case (N, N, N', N'-tetramethylphenylenediamine) there was no observable chemical reaction between singlet oxygen and the amine. It was concluded that singlet oxygen undergoes physical quenching by the amines via partial charge-transfer intermediates.     

THE QUENCHING OF SINGLET OXYGEN BY AMINO ACIDS AND PROTEINS

Abstract— The physical quenching of singlet molecular oxygen (¹Δ_g) by amino acids and proteins in D₂O solution has been measured by their inhibition of the rate of singlet oxygen oxidation of the bilirubin anion. Steady-state singlet oxygen concentrations are produced by irradiating the oxygenated solution with the 1–06 μm output of a Nd-YAG laser, which absorbs directly in the electronic transition ¹Δ_g+ 1 v →³Σ_g^-. The rate of quenching by most of the proteins studied is approximated by the sum of the quenching rates of their amino acids histidine, tryptophan and methionine, which implies that these amino acids in the protein structure are all about equally accessible to the singlet oxygen. The quenching constants differ from those obtained by the ruby-laser methylene-blue-photosensitized method of generating singlet oxygen, or from the results of steady-state methylene-blue-photosensitized oxidation, where singlet oxygen is assumed to be the main reactive species. The singlet oxygen quenching rates in D₂O, pD 8, are (10⁷ℒ mol^-1 s^-1): alanine 0–2, methionine 3, tryptophan 9, histidine 17, carbonic anhydrase 85, lysozyme 150, superoxide dismutase 260, aposuperoxide dismutase 250.     

Photostabilization of commercial polypropylene by hindered piperidine compounds: An ESR and luminescence study

The photostabilization of commercial polypropylene by a hindered piperidine stabilizer, bis [2,2,6,6-tetramethyl-4-piperidinyl] sebacate (I) and by a model N-oxy radical compound, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxy (II) is examined using ESR and luminescence spectroscopy. ESR spectroscopy shows that I operates through the formation of a stable nitroxyl radical in the polymer. On the other hand, II disappears rapidly during the early stages of photo-oxidation but continues to act as an effective stabilizer. A low steady-state equilibrium concentration of nitroxyl radicals is believed to be responsible for the high photostabilizing efficiency of I. Both compounds also inhibit the photolysis of the luminescent α,β-unsaturated impurity groups present in the polymer; possible mechanisms are discussed.