Sub-picosecond oscillatory phenomena in silica glasses

Hong, Qiang; Durrant, James R.; Hastings, Gary; Porter, George; Klug, David R.

doi:10.1016/0009-2614(93)85262-m

Cited by 18 publications

(11 citation statements)

References 6 publications

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“…2 shows the same data up to 16 ps only. The ultrafast oscillations around t = 0 are due to an interaction of the pump and probe pulses with the buffer/cell system, and have been observed before by Hong et al [41]. This signal is roughly linear with pump energy, and as such it cannot be removed by going to lower pump energies.…”

Section: Kinetics At 544 Nm With 200 Nj Pump Pulsessupporting

confidence: 59%

Wavelength and intensity dependent primary photochemistry of isolated Photosystem II reaction centers at 5°C

Greenfield¹,

Seibert²,

Wasielewski³

1996

Chemical Physics

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The long wavelength absorption band of the isolated Photosystem II reaction center was directly excited at five wavelengths between 655 and 689 nm to study the effects of excitation wavelength and intensity on both excitation energy transfer and charge separation processes. Subpicosecond transient absorption measurements were made monitoring principally the bleach of the pheophytin a Qx band at 544 nm. At all pump wavelengths, the kinetics require three exponentials (1-3, 10-25 and 50-100 ps) to be fit properly. The pump energy was varied by a factor of twenty-five (40-1000 nJ), with no apparent effect on either the rates or the amplitude ratios of the three components, although clear evidence of nonlinear behavior was observed at the higher excitation energies. The dependence of both the rates and amplitude ratios of the three components upon pump wavelength will be discussed in terms of excitation energy transfer occurring on a 30 ps timescale. Selective excitation into the short and long-wavelength sides of the composite Qy band give identical transient spectra at 500 ps, indicating near-unity efficiency of excitation energy transfer. At 1 ps, the spectra are quite different, calling into question the extent of ultrafast ( ~ 100 fs) excitation energy transfer. The time after the excitation pulse at which the transient crosses A A = 0 was found to be a highly sensitive measure of both the excitation energy and the identity of the pigment pool that had been excited.

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Section: Kinetics At 544 Nm With 200 Nj Pump Pulsessupporting

confidence: 59%

Wavelength and intensity dependent primary photochemistry of isolated Photosystem II reaction centers at 5°C

Greenfield¹,

Seibert²,

Wasielewski³

1996

Chemical Physics

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“…5). Lifetime fits were made 300-400 fs after t ϭ 0 because of an interaction between the pump and probe pulses and the buffer͞cell system (37,45,61). When pumped at 687 nm ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Functional asymmetry of photosystem II D1 and D2 peripheral chlorophyll mutants of Chlamydomonas reinhardtii

Wang

Gosztola

Ruffle

et al. 2002

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

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The peripheral accessory chlorophylls (Chls) of the photosystem II (PSII) reaction center (RC) are coordinated by a pair of symmetryrelated histidine residues (D1-H118 and D2-H117). These Chls participate in energy transfer from the proximal antennae complexes (CP43 and CP47) to the RC core chromophores. In addition, one or both of the peripheral Chls are redox-active and participate in a low-quantum-yield electron transfer cycle around PSII. We demonstrate that conservative mutations of the D2-H117 residue result in decreased Chl fluorescence quenching efficiency attributed to reduced accumulation of the peripheral accessory Chl cation, Chl Z ؉ . In contrast, identical symmetry-related mutations at residue D1-H118 had no effect on A mong the photosynthetic organisms, there are two different, quinone-type photosynthetic reaction centers (RCs): the oxygenic type present in chloroplasts and cyanobacteria (photosystem II, PSII) and the nonoxygenic type (bacterial reaction center, BRC) as typified by that in purple-sulfur photosynthetic bacteria (for reviews, see refs. 1 and 2). In 1984, the crystal structure of the Rhodopseudomonas viridis BRC was determined at 3-Å resolution by Deisenhofer et al. (3). It soon was recognized that the L and M polypeptides of the BRC had substantial amino acid sequence similarity with the PSII D1 and D2 proteins, respectively. Early models of the D1 and D2 proteinfolding topologies indicated that the PSII D1 and D2 polypeptides were structurally analogous to the L and M subunits (3-8). These models of the PSII RC polypeptides and their associated cofactors were verified by electron and x-ray diffraction of twoand three-dimensional PSII crystals (9-12). Recently, a 3.8-Å resolution structure of the oxygen-evolving PSII complex from Synechecoccus elongatus was determined (13).The PSII RC has six chlorophylls (Chls), two pheophytins (Pheos), two quinones, and one cytochrome b 559 (Cyt b 559 ) heme (8, 13). Significantly, the PSII RC has two additional Chls, relative to the BRC. Site-directed mutagenesis and spectroscopic studies demonstrated that the additional pair of Chls present in PSII is coordinated by a pair of conserved and C 2 symmetryrelated histidine residues (D1-H118 and D2-H117, Chlamydomonas reinhardtii nomenclature) (14-20). Unlike the four Chls and two Pheos involved in primary charge separation, the additional pair of Chls present in the PSII RC is located on the periphery of D1 and D2 polypeptides.Biophysical evidence for the involvement of the peripheral Chls in energy transfer first was obtained from analysis of P680 oxidation kinetics by Schelvis et al. (14). They observed a Ϸ30-ps P680 oxidation lifetime component, which they attributed to energy transfer from a Chl monomer to P680. Based on a Förster mechanism (21) for energy transfer, they calculated that the distance between the peripheral Chl and P680 was 30 Å, a distance confirmed by the recent PSII crystal structure. A similar distance relationship also was predicted on the basis of Chl fluorescence decay kine...

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“…For probing pulses in the visible and near-IR ranges, a frequency selection of the continuum output is carried out by In the experiments the bidistilled deionized water, pH 6.8, was used; the sample thickness is 1 mm. In order to minimize the nonlinear effects, 30,31 thin (1 mm) cell windows made from calcium fluoride (CaF 2 ) are applied, giving an important improvement compared to fused silica. During the measurements the water cell is continuously moved in the plane perpendicular to the pump beam, avoiding undesirable thermal effects.…”

Section: Methodsmentioning

confidence: 99%

Primary Photochemical Processes in Water

1996

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The primary photochemical processes which occur in neat water after 282 nm high-intensity excitation via a two-photon mechanism were studied. Using probe pulses in UV, visible, and near-IR spectral ranges, the absorption process itself and the time evolution of the generated electrons and other photoproducts in the 0.1-80 ps scale were investigated. Different to previous femtosecond laser studies of water a quantitative analysis of the absorption process and yields of primary photoproducts was carried out. The two-photon absorption coefficient of liquid water for femtosecond pulses at 282 nm was measured to be ) (1.9 ( 0.5) × 10 -12 m/W, while the quantum yield of the hydrated electron at the same wavelength was determined to be Φ (e aq -) ) 0.11 ( 0.03. The results of the electron solvation and geminate recombination dynamics at 282 nm (excitation energy E 2hν ) 8.8 eV) are in accordance with the findings of other groups for different excitation wavelengths. The numerical simulations of our data suggest that the energy threshold for H 2 O + ion formation is above 8.8 eV. IntroductionAmong all the solvents, water occupies an extraordinary position. Being the natural environment of such important biological molecules as nucleic acids and peptides, water is present in almost any living organism. Therefore, a detailed understanding of charge-transfer reactions initiated in water by light absorption and of light absorption processes in water itself is necessary for a proper description of photochemical experiments performed in water solution. It is well-known that at low intensities of light (below 10 11 W/m 2 ) the water is transparent for UV light with λ > 190 nm; i.e., the linear and nonlinear absorption is negligible. However, with intense UV light at λ > 190 nm, it is possible to excite a water molecule via a two-photon absorption (TPA) mechanism 1 and initiate its chemical decomposition. It was shown in 1980 that under highintensity picosecond UV excitation with λ ) 266 nm the water molecule undergoes two-photon absorption 2,3 with subsequent dissociation and ionization 4In the first experiments 2-4 the total two-photon energy value was E total ) 9.3 eV, and the ionization threshold for liquid water was determined to be E ion ) 6.5 ( 0.5 eV, 4 consistent with earlier estimates of water ionization potential of 6.5 ( 0.1 5 and 6.0-6.5 eV. 6 An updated value E ion ) 6.36-6.41 eV follows from recent experiments. 7,8 The dissociation energy for neat water is reported to be E dis ) 6.41-6.71 eV. 9 The development of high-intensity femtosecond laser systems made it possible to investigate the dynamics of primary photochemical reactions in water. Using the common pump and probe techniques with two-photon excitation in the UV and probing in the visible and near-IR ranges, the electron trapping and solvation as well as geminate recombination were studied by many experimental groups with time resolution up to 20 fs. In many of these investigations a colliding pulse mode-locked dye laser with second harmonic generation (SH...

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Sub-picosecond oscillatory phenomena in silica glasses

Cited by 18 publications

References 6 publications

Wavelength and intensity dependent primary photochemistry of isolated Photosystem II reaction centers at 5°C

Wavelength and intensity dependent primary photochemistry of isolated Photosystem II reaction centers at 5°C

Functional asymmetry of photosystem II D1 and D2 peripheral chlorophyll mutants of Chlamydomonas reinhardtii

Primary Photochemical Processes in Water

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