The interaction of photo-excited chlorophyll
 a
 with duroquinone,
 α
 -tocopherylquinone and vitamin K
 1

Kelly, John M.; Porter, George

doi:10.1098/rspa.1970.0181

Cited by 46 publications

(12 citation statements)

References 12 publications

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“…We have some reservations as to the correctness of the assignment of their rapidly decaying ESR signal as the Chl+ Qbiradical, and thus do not choose to use their value for the rate of disappearance in our calculations. In view of lack of other sources of information, we took the literature value for the rate constant for the reaction Chl+ + Q-, which is (3.0 i 1.0) X 109 liter mol-sec- (10,7,12). We normalized this value to an apparent quinone concentration in which the distance between the quinone and the chlorophyll would be 6 i, and multiplied the result by a steric factor that accounts for only one semiquinone radical per Chl+.…”

Section: Discussionmentioning

confidence: 99%

“…The photosensitized oxidation of chlorophyll by different oxidizing agents is being investigated in several laboratories (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), in order to provide guidelines for understanding the primary steps in photosynthesis. Among the various oxidants, the reaction of chlorophyll with various quinones is of special interest.…”

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confidence: 99%

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Photooxidation of Chlorophyll b by Quinones Studied by Chemically-Induced Dynamic Nuclear Polarization

Tomkiewicz

Klein

1973

Proc. Natl. Acad. Sci. U.S.A.

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The photooxidation of chlorophyll b by 1,4-benzoquinone and 2,6-dimethyl-1,4-benzoquinone was investigated by the technique of chemically-induced dynamic nuclear polarization. Polarization of the proton magnetic resonance lines of the quinone was detected. A mechanism for the photooxidation was postulated that invokes the reaction of the quinone with the excited singlet state of the chlorophyll to form a radical pair. This mechanism, together with a theoretical model and parameters taken from the literature, yields a theoretical proton magnetic resonance spectrum for the polarized quinone that agrees well with that observed experimentally.The photosensitized oxidation of chlorophyll by different oxidizing agents is being investigated in several laboratories (1-17), in order to provide guidelines for understanding the primary steps in photosynthesis. Among the various oxidants, the reaction of chlorophyll with various quinones is of special interest. It is well established that this reaction proceeds through free-radical intermediates, but the mechanistic details are still controversial (16). There are conflicting data on the nature of the excited states of chlorophyll with which the quinones react. The main sources of information about the nature of the precursors involved were obtained from flash photolysis, electron spin resonance (ESR), and fluorescence studies with 3-carotene as a competing quencher of the excited states. It was assumed that P-carotene reacts only with the triplet state of the excited chlorophyll. Addition of quinone reduced the concentration of the excited triplet of the chlorophyll, but not its lifetime (13,14), suggesting that the quinone reacts with a precursor of the chlorophyll triplet.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Photooxidation of Chlorophyll b by Quinones Studied by Chemically-Induced Dynamic Nuclear Polarization

Tomkiewicz

Klein

1973

Proc. Natl. Acad. Sci. U.S.A.

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“…The tensile coupon for the fragmentation test consists of a single filament embedded in the matrix and parallel to the axis of tension. The fiber is broken into successively shorter lengths as a tensile load is a p plied to the specimen, and the ultimate fragment length, I,, can be used to compute the average interfacial shear strength 7 (9,14,15). The evaluation of 7 requires the value of the fiber tensile strength at I , which is very short (0.3 to 1 mm).…”

Section: Introductionmentioning

confidence: 99%

The adhesion of elastomer‐coated glass fibers to an epoxy matrix. Part I: The effect of the surface treatments on the tensile strength of the glass fibers

Ahlstrom

Gérard

1995

Polymer Composites

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E‐glass fibers were subjected to various surface treatments to study the interfacial adhesion with an epoxy matrix by means of the fragmentation test. The glass fibers considered were both untreated and treated with γ‐aminopropyltriethoxysilane (γ‐APS). In addition, glass fibers were coated with a thin layer of a crosslinkable elastomer including (or not) a silane coupling agent. To evaluate the effect of the coating process, the glass fibers were also passed through the pure solvent (washed fibers). The tensile strength of glass fibers at short length (near the critical length, lc, for the fragmentation test) cannot be measured directly, thus, extrapolation techniques were used. The Weibull statistics technique was applied and accurately described the tensile strength data of the tensile strength at various fiber gauge lengths for the different surface treatments. Nevertheless, the Weibull parameter, m, changes with the gauge length, and therefore, the extrapolation value at lc depends on the method. The tensile strength of the silane‐treated glass fibers is higher than for the untreated fibers, in agreement with reported data. This effect could be attributed to the protection against water provided by the silane sizing. The coating process does not induce any damage of the glass fibers since the washed fibers display mechanical properties close to those obtained for the untreated fibers. An additional effect is observed for the elastomer‐coated fibers which present the highest tensile strength. This effect could be attributed to an improved protection and/or elimination of the weakest filaments in the glass strand during the treatment.

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“…Various methods have been employed to determine, both quantitatively and qualitatively, the mechanical strength of fiber-reinforced composites. Fiber pull-out (29,30), transverse tensile strength (20), longitudinal compressive strength (3 1). and in-plane shear strength (20) are the ones most commonly employed.…”

Section: Introductionmentioning

confidence: 99%

“…and in-plane shear strength (20) are the ones most commonly employed. Models have been proposed to predict the mechanical response of composites (20,(29)(30)(31)(32)(33), based on the volume fraction and orientation of the fibers. Takayanagi and Katayose studied the dynamic mechanical properties of surface-modified Kevlar fiber-reinforced ionomers (33).…”

Section: Introductionmentioning

confidence: 99%

Interfacial adhesion between ionic copolymers and high‐modulus surface‐treated carbon fibers

1989

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High‐modulus carbon‐fiber‐reinforced thermoplastic composites typically fail at the interface due to poor adhesion between fiber and matrix. To increase interfacial strength, the research described herein focuses on modifying the fiber surface (via high‐temperature acid treatment or zinc electrolysis) to facilitate chemical functional groups on the fiber that might increase fiber‐matrix inter‐actions. The thermoplastic matrix materials used in this study were random copolymers of ethylene and methacrylic acid in which the carboxyl groups in the methacrylic acid segments were neutralized with either sodium or zinc counterions. Mechanical tests were performed to determine the macroscopic effects of fiber pretreatment on the ultimate mechanical properties of the composites. Fabrication was designed such that fiber‐matrix separation provides the dominant contribution to mechanical gracture. Composites containing fibers treated with nitric acid, or a mixture of nitric and sulfuric acids exhibit a 20 to 25 percent increase in transverse (tensile) fracture stress relative to composites fabricated with as‐received fibers. Scanning electron microscopy of the fiber‐matrix interface at fracture allows one to “zoom‐in” and obtain qualitative details related to adhesion. Fracture surface micrographs of the above‐mentioned acid‐treated fiber‐reinforced composites reveal an increase in the amount of matrix material that adhered to the fiber surface relative to the appearance of the fracture surface of composites fabricated with as‐received fibers. The presence of acid functionality in the matrix, rather than the divalent nature of the zinc counterions, produces the largest relative enhancement of transverse (tensile) fracture stress in the above‐mentioned composites containing surface‐treated carbon fibers.

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The interaction of photo-excited chlorophyll a with duroquinone, α -tocopherylquinone and vitamin K ₁

Cited by 46 publications

References 12 publications

Photooxidation of Chlorophyll b by Quinones Studied by Chemically-Induced Dynamic Nuclear Polarization

Photooxidation of Chlorophyll b by Quinones Studied by Chemically-Induced Dynamic Nuclear Polarization

The adhesion of elastomer‐coated glass fibers to an epoxy matrix. Part I: The effect of the surface treatments on the tensile strength of the glass fibers

Interfacial adhesion between ionic copolymers and high‐modulus surface‐treated carbon fibers

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The interaction of photo-excited chlorophyll a with duroquinone, α -tocopherylquinone and vitamin K 1

Cited by 46 publications

References 12 publications

Photooxidation of Chlorophyll b by Quinones Studied by Chemically-Induced Dynamic Nuclear Polarization

Photooxidation of Chlorophyll b by Quinones Studied by Chemically-Induced Dynamic Nuclear Polarization

The adhesion of elastomer‐coated glass fibers to an epoxy matrix. Part I: The effect of the surface treatments on the tensile strength of the glass fibers

Interfacial adhesion between ionic copolymers and high‐modulus surface‐treated carbon fibers

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Product

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The interaction of photo-excited chlorophyll a with duroquinone, α -tocopherylquinone and vitamin K ₁