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Determination of the primary charge separation rate in Photosystem II reaction centers at 15 K (1989)

Wasielewski, Michael R. ; Johnson, Douglas G. ; Govindjee ; [et al.]

Springer

Photosynthesis research 22 (1989), S. 89-99

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ISSN: 1573-5079

Keywords: electron transfer ; picosecond spectroscopy ; PS II reaction centers

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We have measured the rate constant for the formation of the oxidized chlorophyll a electron donor (P680+) and the reduced electron acceptor pheophytin a − (Pheo a −) following excitation of isolated Photosystem II reaction centers (PS II RC) at 15 K. This PS II RC complex consists of D1, D2, and cytochrome b-559 proteins and was prepared by a procedure which stabilizes the protein complex. Transient absorption difference spectra were measured from 450–840 nm as a function of time with 500fs resolution following 610 nm laser excitation. The formation of P680+-Pheo a − is indicated by the appearance of a band due to P680+ at 820 nm and corresponding absorbance changes at 490, 515 and 546 nm due to the formation of Pheo a −. The appearance of the 490 nm and 820 nm bands is monoexponenital with τ=1.4±0.2 ps. Treatment of the PS II RC with sodium dithionite and methyl viologen followed by exposure to laser excitation results in accumulation of Pheo a −. Laser excitation of these prereduced RCs at 15 K results in formation of a transient absorption spectrum assigned to 1*P680. We observe wavelength-dependent kinetics for the recovery of the transient bleach of the Qy absorption bands of the pigments in both untreated and pre-reduced PS II RCs at 15K. This result is attributed to an energy transfer process within the PS II RC at low temperature that is not connected with charge separation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00114769

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Photorefractive liquid crystalsWe gratefully acknowledge support from the Office of Computational and Technological Programs, Division of Advanced Energy Projects, U. S. Department of Energy, under contract W-31-109-ENG-38. (1996)

Wiederrecht, Gary P. ; Yoon, Beth A. ; Wasielewski, Michael R.

Weinheim : Wiley-Blackwell

Advanced Materials 8 (1996), S. 535-539

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ISSN: 0935-9648

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Photorefractive liquid crystals represent the newest class of photorefractive materials. The low electric fields required for reorienting liquid crystals, combined with their high birefringence, results in the observation of photorefractivity with very low optical intensities and low applied fields. Photoinducing efficient charge transport over macroscopic distances is the primary hurdle for producing the space-charge field required for photorefractivity.

Additional Material: 3 Ill.