Primary photochemical processes in aromatic molecules. Part 6.—The absorption spectra and acidity constants of phenoxyl radicals

Land, Edward J.; Porter, Gerald B.; Strachan, E.

doi:10.1039/tf9615701885

Cited by 225 publications

(122 citation statements)

References 1 publication

Supporting

Mentioning

107

Contrasting

Order By: Relevance

“…Recently, difference spectra of tyrosine radicals from pulse radiolysis experiments have been presented (57). These spectra were largely shifted (up to 40 nm) to red wavelengths when compared to other in vitro spectra in a large body of literature (58,61,69,70) and to Y Z in PSII (see Figure 3), and the extinction coefficients in the UV in ref 57 were smaller, about 50-75% of the values obtained for the oxidation of tyrosine in vitro (58,61,69,70) and in PSII (see ref 57 and references therein). Furthermore, the contribution of the reduced state to the oxidized-minus-reduced spectra seemed to be much higher than in other in Vitro and in vivo spectra (see above).…”

Section: Raw Absorption Difference Spectra and Their Deconvolutionmentioning

confidence: 99%

See 1 more Smart Citation

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

1998

View full text Add to dashboard Cite

In oxygen-evolving photosystem II (PSII), a tyrosine residue, D1Tyr161 (Y Z ), serves as the intermediate electron carrier between the catalytic Mn cluster and the photochemically active chlorophyll moiety P 680 . A more direct catalytic role of Y Z , as a hydrogen abstractor from bound water, has been postulated. That Y Z ox appears as a neutral (i.e. deprotonated) radical, Y Z • , in EPR studies is compatible with this notion. Data based on electrochromic absorption transients, however, are conflicting because they indicate that the phenolic proton remains on or near to Y Z ox . In Mn-depleted PSII the electron transfer between Y Z and P 680 + can be almost as fast as in oxygen-evolving material, however, only at alkaline pH. With an apparent pK of about 7 the fast reaction is suppressed and converted into an about 100-fold slower one which dominates at acid pH. In the present work we investigated the optical difference spectra attributable to the transition Y Z f Y Z ox as function of the pH. We scanned the UV and VIS range and used Mn-depleted PSII core particles and also oxygen-evolving ones. Comparing these spectra with published in vitro and in vivo spectra of phenolic compounds, we arrived at the following conclusions: In oxygen-evolving PSII Y Z resembles a hydrogen-bonded tyrosinate, Y Z (-) ‚‚‚H (+) ‚B. The phenolic proton is shifted toward a base B already in the reduced state and even more so in the oxidized state. The retention of the phenolic proton in a hydrogen-bonded network gives rise to a positive net charge in the immediate vicinity of the neutral radical Y Z • . It may be favorable both for the very rapid reduction by Y Z of P 680 + and for electron (not hydrogen) abstraction by Y Z • from the Mn-water cluster.Photosystem II (PSII) 1 produces molecular oxygen from water. It is located in photosynthetic membranes of plants and cyanobacteria. The inner core of PSII is a heterodimer of the D1D2 subunits which show homology with the L and M subunits of the purple bacterial RC (1). The primary electron donor of PSII, P 680 , is located close to the lumenal side of the membrane. The absorption of a quantum of light drives the charge separation between P 680 and the quinone acceptor at the stromal side (2). The very high redox potential of P 680 + drives water oxidation. It is a four-stepped process with at least four increasingly oxidized, metastable states S 0 to S 3 , plus a transient state S 4 that decays in milliseconds into S 0 under release of O 2 . P 680 + is reduced (in nanoseconds) by a redox-active tyrosine residue, Y Z (D1Tyr161 (3, 4)). Y Z ox is, in turn, reduced in microseconds by the oxygenevolving complex (OEC). The structure and exact location of the OEC is still ill-defined. It is formed by four manganese atoms (5, 6), possibly another redox cofactor, X (7-9), plus at least one Cl -ion (10) and one Ca 2+ (11, 12) ion. These cofactors serve various functions during water oxidation: The Mn cluster stores at least two of the oxidizing equivalents (namely on transitions S ...

show abstract

Section: Raw Absorption Difference Spectra and Their Deconvolutionmentioning

confidence: 99%

“…The reasons for these discrepancies are still unknown. We preferred to use the more consistent set of spectra from the elder literature (58,61,69,70) for our simulations.…”

Section: Raw Absorption Difference Spectra and Their Deconvolutionmentioning

confidence: 99%

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

1998

View full text Add to dashboard Cite

show abstract

“…159,160) Radical cations of phenol derivatives, which are precursors of phenoxy radicals in many cases, had been more elusive than phenoxy radicals. 158,[161][162][163][164][165][166][167][168] The absorption maxima of radical cations of phenol and p-cresol are at 440 and 430 nm, respectively. 169) The radiation chemistry of the model compounds for protected PHS such as methoxybenzene (anisole), methoxytoluene, and dimethoxybenzene has also been intensively investigated using pulse radiolysis, [170][171][172][173] photolysis, 174,175) chemical oxidation, [176][177][178] and electrochemical methods.…”

Section: Aromatic Polymersmentioning

confidence: 99%

“…Phenoxy radicals, which are stable decomposition intermediates of phenols, were first observed in the 1950s. 157) Land et al reported that phenoxy radicals are very weak bases 158) and show a characteristic absorption band. 159,160) The absorption maxima of phenoxy radicals of phenol and p-cresol in water are at 400 and 405 nm, respectively.…”

Section: Aromatic Polymersmentioning

confidence: 99%

Radiation Chemistry in Chemically Amplified Resists

Kozawa

Tagawa

2010

Jpn. J. Appl. Phys.

336

319

View full text Add to dashboard Cite

Historically, in the mass production of semiconductor devices, exposure tools have been repeatedly replaced with those with a shorter wavelength to meet the resolution requirements projected in the International Technology Roadmap for Semiconductors issued by the Semiconductor Industry Association. After ArF immersion lithography, extreme ultraviolet (EUV; 92.5 eV) radiation is expected to be used as an exposure tool for the mass production at or below the 22 nm technology node. If realized, 92.5 eV EUV will be the first ionizing radiation used for the mass production of semiconductor devices. In EUV lithography, chemically amplified resists, which have been the standard resists for mass production since the use of KrF lithography, will be used to meet the sensitivity requirement. Above the ionization energy of resist materials, the fundamental science of imaging, however, changes from photochemistry to radiation chemistry. In this paper, we review the radiation chemistry of materials related to chemically amplified resists. The imaging mechanisms from energy deposition to proton migration in resist materials are discussed.

show abstract

“…Only with 4,4′-biphenol was a transient species with an absorption maximum at 400 nm observed. We used flash photoysis to achieve the one-electron oxidation of 4,4′-biphenol: Phenols are known to photolyse by ejecting a photoelectron (10). Figure 2 shows the flash photolysis of 4,4′-biphenol: Within nanoseconds of the flash, a product that absorbs strongly at 400 nm is formed.…”

Section: Resultsmentioning

confidence: 99%