THERMAL INDUCED HOMOLYTIC SCISSIONS OF LIGNIN INTERUNITARY BONDS IN THE HARDWOOD LIGNIN SOLUTION. AN ESR STUDY COMBINED WITH A SPIN TRAPPING METHOD

An electron spin resonance (ESR) method combined with a spin trapping reagent was successfully applied to trap and characterize unstable free radicals which were generated by heat-treatment of the dimethylsulfoxide (DMSO) solution of a hardwood, Japanese beech (Fagus crenata) lignin. It was found, consequently, that two unstable secondary carbon radicals, ～ CH? in the solution were created and the resulting radicals were trapped as the stable nitroxide spin adducts when the DMSO solution was heat-treated in the presence of a spin trapping reagent: 2,4,6-tri-tert-butylnitrosobenzene (BNB) at ca. 91°C. This means that so-called alkyl phenyl ether bonds, ～ CH-O- phenyl, known as important lignin interunitary bonds were homolytically scissoned by the heat-treatment of the lignin solution. Further the detailed analysis of the observed ESR spectrum revealed that two positions of alkyl phenyl ether bonds, i.e., β-O-4 and/or α-O-4 bonds as the interunitary linkages in the lignin are homolytically scissioned, although the phenoxy radical, Ph-O ? as the counter radical of the secondary carbon radicals was not trapped by the BNB spin trap. This suggests that fairly large steric hindrances operate between the syringyl with two methoxy moieties at the ortho positions and/or guaiacyl moieties with a methoxy moiety at the ortho position, and the BNB molecule bearing two bulky ortho tert-butyl groups in the phenyl ring.     

Thermally induced homolytic scissions of interunitary bonds in a softwood lignin solution: A spin‐trapping study

Unstable chemical species, that is, radicals generated by the thermal treatment of a dimethyl sulfoxide (DMSO) solution of the lignin of a softwood, Yezo spruce (Picea jezoensis Carr.), were studied in detail with an electron spin resonance (ESR) method combined with a spin‐trapping technique. An unstable secondary carbon radical (～CH ·) in the solution was trapped as a stable nitroxide spin adduct [R? (N? O ·)? CH～ (R = tert‐butyl benzene)] when the DMSO solution was heat‐treated in the presence of a spin‐trapping reagent [2,4,6‐tri‐tert‐butylnitrosobenzene (BNB)] at about 40°C. This meant that alkyl phenyl ether bonds (～CH? O‐phenyl), known as interunitary lignin bonds, were homolytically scissioned by the thermal treatment in the lignin solution. A detailed analysis of the ESR spectrum revealed that three kinds of radicals—primary (～CH₂ ·), secondary (～CH ·), and tertiary (～C ·) carbon radicals—were trapped as stable spin adducts at about 60°C, although the phenoxy radical (Ph? O ·) was not trapped by the BNB spin trap as the counter radical of the secondary carbon radical. This suggested that a fairly large steric hindrance existed between the so‐called guaiacoxy radical with a methoxy group in the ortho position and the BNB molecule bearing two butyl groups as bulky moieties in the ortho positions. However, the phenoxy radicals in the lignin solution were stable up to about 60°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2136–2141, 2004     

Synthesis and characterization of polyurethane–chitosan interpenetrating polymer networks

A polyurethane–chitosan (PU–CH) coating was synthesized from castor-oil-based PU prepolymer and highly deacetylated and depolymerized chitosan. The films cast with the coating were used for the characterization. X-ray photoelectron spectroscopy, a surface-sensitive technique, indicated the chemical bonding between the chitosan and PU prepolymer as well as the enrichment of chitosan on the surface of the film PU–CH. Electron spin resonance (ESR) spectroscopy using the nitroxyl radical 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (4-hydroxy-TEMPO) as a reporter group was used to study the chain mobility in the film PU–CH. It was observed that T_50G of the probe and the first glass transition temperature (T_g1) of the film PU–CH were 10 and 18°C higher than those in the PU film, respectively, and the activation energy (27.0 kJ mol⁻¹) of tumbling for the probe covalently bonded with PU–CH was 12.8 kJ mol⁻¹ higher than that of the probe with the film PU. It suggests that the molecular motion in the PU–CH was restricted by grafted and crosslinked interpenetrating polymer networks (IPNs). The results of the differential thermal analysis and thermogravimetric analysis proved that the thermostability of the film PU–CH was significantly higher than that of the film PU, and the T_g1 value is in good agreement with that calculated from ESR. It could be concluded that the IPNs resulted from the chitosan grafting and crosslinking with PU exist in the film PU–CH. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1321–1329, 1998     

利用ESR技术研究α—蒎烯β—蒎烯光敏氧化反应机理

本文主要利用电子顺磁共振自旋捕获技术研究９,１０－二氰基蒽敏化α－蒎烯,β－蒎烯光氧化反应,提供了在乙腈中α－蒎烯和β－蒎烯的光氧化反应过程中存在超氧负离子基和单重 氧的直接证据;在四氯化碳溶剂中只捕获到＾１Ｏ２;在正己烷中没有捕获到Ｏ＾－２或＾１Ｏ２．ＥＳＲ实验结果进一步证明在乙腈中光敏氧化反应的＾１Ｏ２可能来自Ｏ＾－２和反应底物α－β,蒎烯正离子自由基之间的电荷复合。     

Spin trapping of propagating radicals with 2,4,6-tri-tert-butyl-1-nitrosobenzene in radical polymerization initiated with di-tert-butyl hyponitrite

To examine the polar effect on spin trapping with 2,4,6-tri-tert-butyl-1-nitrosobenzene (BNB), propagating radicals from monomers were allowed to react with BNB to provide anilino radicals and nitroxides of which the amounts were determined by ESR spectroscopy. The proportion of the anilino radical increased with an increase in the steric congestion and electron donating character of the radical. Poly(vinyl ether) radicals exclusively gave the respective anilino radicals. Poly(vinyl ester) radicals yielded large amounts (>50%) of the anilino radicals, although the nitroxides were the main products (>85%) from the poly(alkyl acrylate) radicals. The polymer radicals of methyl methacrylate and ethyl itaconate only yielded the anilino radicals. The polymer radicals from ethyl -chloroacrylate and acrylonitrile reacted preferentially with the respective monomers leading to polymer formation, and the ESR spectra of the adducts were not observed.     

Carbon radicals generated by solid polymers: Electron spin resonance spectroscopy for detection of species in water

Radicals generated in plastic medical devices (solid phase) by γ-rays or electron-beam irradiation during sterilization are known to cause oxidation of protein drugs, resulting in a loss or reduction in drug efficacy. The generation of radical species in water by the radical species in solid polymers has not been proved. Using electron spin resonance (ESR) spectroscopy, we confirm the generation of new radicals in water by γ-ray irradiated cyclic olefin polymers (COP). ESR measurements are obtained using 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) as a spin probe and 5-(2,2-dimethyl-1,3-propoxycyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO) as a spin trap, in which the irradiated COP was immersed. The ESR signals indicate the TEMPOL radicals decline over time, suggesting the generation of new radicals. Conversely, the characteristic ESR signals of the adduct formed by the reaction between CYPMPO and the hydroxyl radical are observed. Thus, hydroxyl radicals are generated because of the migration of the radicals from COP to water. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48604.     

Bulk polymerization of methyl methacrylate initiated by high intensity ultrasonic irradiation and ESR study

High‐intensity ultrasound was used to initiate the bulk polymerization of methyl methacrylate. The polymerization rate varied with the sonication time, the intensity of the ultrasound, and the initiator concentration of poly (methyl methacrylate) in the monomer. Electron spin resonance (ESR) spectra, obtained by the spin trapping technique, testified that free radicals were produced during the sonication process, and the concentration of radicals also changed with the sonication condition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1731–1735, 2002     

Spatially resolved degradation in heterophasic polymers by ESR imaging and FTIR: The case of propylene-ethylene copolymers

Heterophasic propylene-ethylene copolymers (HPEC) containing bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (Tinuvin 770) as a hindered amine stabilizer (HAS) were thermally aged at 393 and 433 K. Two types of HPEC were examined, containing 25% and 10% ethylene (E), respectively, as ethylene/propylene rubber (EPR). Electron spin resonance (ESR) spectra of nitroxide radicals in HPEC were studied in the temperature range 100–433 K; the nitroxides were derived from the HAS and are termed HAS-NO. The results were compared with ESR spectra of the same radicals obtained first by oxidation of Tinuvin 770 and then were doped in HPEC and related homopolymers, polyethylene (PE) and polypropylene (PP); these nitroxides are termed “spin probes.” ESR spectra indicated that HAS-NO and the spin probes reside in a range of amorphous sites differing in their dynamic properties. The relative population of the sites was explained by assuming that the crystalline domains exert a restraining effect on chains located in vicinal amorphous domains. Spatial and temporal effects of the aging process were studied by ESR and ESR imaging (ESRI) of HAS-derived nitroxide radicals, and by FTIR of films prepared by compression molding. 1D ESRI enabled the visualization of an outer region of thickness ≈100 μm that contained a lower amount of nitroxides, and is believed to result from the loss of the stabilizer by diffusion (“blooming”) and possibly also in chemical reactions during aging. Two-dimensional spectral-spatial ESRI indicated the presence of nitroxide radicals in two amorphous sites, fast and slow; the corresponding relative intensity varied with sample depth. Both ESRI and FTIR experiments suggested a faster degradation rate in HPEC containing 25% E, as compared to 10% E; moreover, a larger Tinuvin 770 content in the polymers led to less efficient stabilization. FTIR spectra indicated increased ordering of polypropylene segments in HPEC during aging at 433 K.     

In situ detection of hindered amine stabilizer consumption in polymer through oxidation by indirect electron spin resonance

The stabilization mechanisms of hindered amine stabilizers (HAS) involve various oxidation products of the piperidine structure. Thus, we propose a novel method, based on electron spin resonance (ESR) spectroscopy, to check in situ the consumption of the total piperidyl species (intact HAS and all of its byproducts) in polypropylene (PP) films through photooxidation. First, the concentration of nitroxyl radicals produced upon irradiation in stabilized PP has been measured by direct ESR analysis. Then, the changes of concentration of the overall stabilizing species have been detected by indirect ESR, after conversion of the overall HAS derivatives into nitroxyl-free radicals by exposure of photooxidized PP to peracetic acid vapor at room temperature. Results were compared with those obtained by the conventional Fourier transform infrared method in the particular case of [2,2,6,6-tetramethyl piperidinyl]sebacate, and the reliability of both techniques was discussed. Thus, we assume that indirect ESR experiments consist of a easy, accurate, and very sensitive method to monitor the time evolution of a low-molecular weight HAS–NH concentration in PP upon photooxidation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1107–1114, 1998     

酞花菁及金属酞菁化物紫外光解的ESR研究

在较强的紫外辐射作用下,即使较为稳定的酞菁化合物也可能发生光解。水文用自旋捕捉与ESR技术相结合的方法检出了在光解中生成的氮中心自由基。     

Fragmentation of Fluorinated Model Compounds Exposed to Oxygen Radicals: Spin Trapping ESR Experiments and Implications for the Behaviour of Proton Exchange Membranes Used in Fuel Cells

Low‐molecular weight model compounds (MCs) for Nafion membranes used in fuel cells were exposed at 300 K to ^·OH radicals produced by UV irradiation of aqueous H₂O₂ solutions. The MCs contained fluorinated and partially fluorinated groups terminated by sulphonic or carboxylic acid groups. The fragmentation process in the MCs was studied by spin trapping electron spin resonance (ESR) methods, using 5,5‐dimethylpyrroline‐N‐oxide (DMPO), N‐tert‐butyl‐α‐phenylnitrone (PBN) and 2‐methyl‐2‐nitrosopropane (MNP) as the spin traps. The objective of these experiments was to assess the effect of the type of ionic groups (sulphonic or carboxylic) and of fluorine substitution on the spin adducts detected. DMPO experiments led to the detection of spin adducts of ^·OH and of carbon‐centred radicals (CCRs), and allowed the determination of the ^·OH attack site on the ionic and/or on the protiated or fluorinated groups. CCR adducts were also detected when using PBN as a spin trap; a key point in the interpretation of the PBN results was, however, the realisation that MNP is formed during PBN exposure to UV irradiation and oxygen or other oxidants such as H₂O₂. Experiments with MNP as the spin trap were the most informative in terms of structural details for adducts obtained from each MC. The results allowed the identification of CCRs present as adducts, based on large hyperfine splittings (hfs) from, and the number of, interacting ¹⁹F nuclei; in addition, oxygen‐centred radicals (OCRs) as MNP adducts were also identified, with much lower hfs from ¹⁹F nuclei. Taken together, the results deduced by spin trapping suggest that both sulphonic acid and acetic acid groups can be attacked by ^·OH radicals and confirm two possible degradation mechanisms in Nafion membranes: initiated at the backbone and at the side chain.     

苯甲醛及对溴苯甲醛光解初级过程自由基的ESR研究

苯甲醛的光解与其在放置过程中的自氧化引发机理密切相关,因此确定光解过程的主要中间产物有重要意义。自氧化的全过程比较复杂,但单纯的光解本身显然相对简单一些。本文用自旋捕捉-ESR技术研究了苯甲醛及与其相类似的对溴苯甲醛在紫外和可见光作用下生成的活泼中间体,并讨论了在本文实验条件下的光解初级过程。 苯甲醛为色谱纯样品,对溴苯甲醛和二苯酮经两次重结晶提纯,溶剂苯经重蒸馏后     

有机锡化合物光解活泼自由基的ESR研究

本文用自旋捕捉技术与ESR相结合的方法,研究了六种有机锡化合物的光解反应历程。结果表明:有机锡化合物紫外光照时,碳—锡键发生均裂,产生碳中心和锡中心自由基。其中碳中心自由基易被捕捉剂α-苯基-N-特丁基氮氧化物(PBN)或2,3,5,6-四甲基亚硝基苯(ND)所捕获;而锡中心自由基可与菲醌形成稳定的环状加合物。由于环状加合物中配体的不同,产生的空间效应也不同,从而导致加合物中的未偶电子云密度发生变化,给出相异的ESR信号。     

Über die Reaktion von Chloranil mit Cyanidionen – eine ESR-Studie

On the Reaction of Chloranil with Cyanide Ions – an ESR Study The reaction of chloranil 1 with cyanide ions in acetonitrile and methanol solutions has been studied. The ESR Spectra revealed the formation of semiquinone anion radicals 7,8 , and 9 . The latter has been found as its protonated form in methanol only. In addition, both 1 and 2,3-dicyano-5,6-dichloro-1,4-benzoquinone 4 gave tetracyanoethylene anion radicals 6 upon reaction with cyanide ions in acetonitrile. Using ¹³C-labelled cyanide 6 was shown to originate from the fragmentation of the cyanide addition product to 4 . Using the spin trapping technique it was found that no cyanyl free radicals are formed during the thermal reaction of either 1 or 4 with cyanide ions.     

乙酸钠、草酸钠、酒石酸钾在三氧化钨-水体系中光生自由基的研究

当分散在溶液中的TiO_2、znO、CdS、WO_3等多相体系受到光照时,固态的半导体物质吸收光子后会产生电子-空穴对,它们在半导体界面上与周围介质反应,可能以各种方式进行电荷转移而形成不同的活泼中间体,引起人们对发生在半导体粉末上的光化学过程的关注。     

Biopolymer films to control fusarium dry rot and their application to preserve potato tubers

Films were cast using sodium alginate (NaAlg), high molecular weight (HMW) chitosan, and low molecular weight (LMW) chitosan as film forming biopolymers. Fludioxonil (Fl) at 1% concentration was used as fungicide. Thermal stability, mechanical, and water sorption properties of the films were examined. The effects of films on the Fusarium solani colony radial growth were evaluated in vitro and in potato tubers. Results showed that chitosan films were more thermally stable and less hydrophilic than alginate films. Addition of fluodioxonil to the films significantly reduced the film strength and increased the elongation at break as well as the film stiffness. In vitro studies showed that when fludioxonil was added to the formulation, NaAlg and Chitosan‐LMW films had significantly higher antifungal activity (Fungistatic index = 56%) than Chitosan‐HMW films (Fungistatic index = 50%). In vivo studies showed that Chitosan‐LMW‐1%Fl films delay the mycelial growth of F. solani in tubers kept at 25 °C for 2 weeks. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44017.     

氧化锌分散体光反应产生的自由基中间体

溶液中光诱导的电子转移反应已进行了大量的研究。而半导体粉末在水相或非水溶剂中的光化学研究也与自俱增。这种光化学与成像体系、太阳能转换以及光催化或污物的光降解有关。因此,越来越引起人们的重视。 Harbour和Hair用自旋捕捉技术研究了在ZnO-H_2O的分散体系中光合成过氧化氢,并检测到羟基自由基。他们认为氧化锌可能通过水的氧化将O_2还原成H_2O_2,从而使太阳能转换成化学能。人们自然会想到ZnO在其它溶剂中是否-也能观察到溶剂光氧化     

Investigation of oxygen diffusion into contact lenses using electron spin resonance spectroscopy

Oxygen permeability is the most important parameter of contact lenses, as lack of oxygen causes corneal edema and threatens the vision of the patient. This study was unique in that it used an electron spin resonance (ESR) technique to determine the oxygen diffusion coefficient (D) of contact lenses. Although there are many methods and techniques for investigating oxygen diffusion into contact lenses, ESR was used for the first time in this study. The ESR technique is based on the scavenging of radicals produced in lenses by oxygen. As a contact lens is not a paramagnetic substance, it cannot give an ESR spectrum. But it does produce an ESR spectrum after γ irradiation. When a vacuum‐irradiated contact lens is exposed to air, the radicals trapped in the lens are transformed into peroxide radicals by the addition of molecular oxygen to the free radicals, and the ESR spectrum begins to change with time. This effect can be used as a tool to measure oxygen uptake in irradiated contact lenses. The oxygen diffusion coefficient of a contact lens was determined from changes in ESR signal intensity varying with time. The diffusion coefficients of oxygen for a contact lens were determined for rapid decay [(1.5 + 0.4) × 10^?8 cm²/s] and slow decay [(1.3 + 0.3) × 10^?9 cm²/s] in this study. These values are in agreement with the D values given in the literature for polymeric materials used for contact lenses. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2937–2941, 2006     

Radicals generated in autoxidized methyl linoleate by light irradiation

The structure of free radicals generated in the autoxidation of methyl linoleate (ML) was studied by the spin trapping technique using deuterated nitrosodurene, (CD₃)₄C₆HNO, as the spin trap. The secondary alkyl radicals were trapped after irradiation of ML with UV light. The formation rate of secondary alkyl radicals increased upon shortening the wavelength of irradiation light and was closely correlated with the peroxide value of autoxidized ML when a UV light longer than 250 nm was employed. When hydroperoxides separated from autoxidized ML were added to ML, the relationship between the formation rate of secondary alkyl radicals and the amounts of added hydroperoxides was nearly linear. These results suggest that secondary alkyl radicals are generated by proton abstraction of the active radicals, such as RO and HO, which are produced by the photolysis of hydroperoxides with UV light. The spin trapping technique can be applied to the study of lipid oxidation and/or photolysis of autoxidized lipid.