Formation and geminate quenching of singlet oxygen in purple bacterial reaction center

The phosphorescence of singlet oxygen (1X*) photosensitized by the carotenoidless reaction center (RC) of Rhodobacter sphaeroides R26.1 has been investigated, using H2O and D2O as the suspending media. To enhance (under neutral conditions) the triplet quantum yield of the special pair P870 (P) by th...

Full description

Bibliographic Details
Main Authors:	Arellano, Juan B., Yousef, Yaser A., Melo, Thor Bernt, Mohamad, Samsun Baharin, Cogdell, Richard J., Naqvi, K. Razi
Format:	Article
Language:	English
Published:	Elsevier 2007
Subjects:	QC Physics
Online Access:	http://irep.iium.edu.my/12191/ http://irep.iium.edu.my/12191/ http://irep.iium.edu.my/12191/ http://irep.iium.edu.my/12191/1/Arellano-Samsun.pdf

id	iium-12191
recordtype	eprints
spelling	iium-121912012-05-31T02:56:32Z http://irep.iium.edu.my/12191/ Formation and geminate quenching of singlet oxygen in purple bacterial reaction center Arellano, Juan B. Yousef, Yaser A. Melo, Thor Bernt Mohamad, Samsun Baharin Cogdell, Richard J. Naqvi, K. Razi QC Physics The phosphorescence of singlet oxygen (1X) photosensitized by the carotenoidless reaction center (RC) of Rhodobacter sphaeroides R26.1 has been investigated, using H2O and D2O as the suspending media. To enhance (under neutral conditions) the triplet quantum yield of the special pair P870 (P) by the radical pair mechanism, the quinone acceptor QA was removed by means of a chemical treatment. The phosphorescence signal fits the functional form P0[exp (�t/s) � exp(�t/f)], regardless of whether 1X is sensitized by P� or M� (where the dagger denotes triplet excitation and M is a water-soluble molecule). The time constant f was identified with the decay time of 1X; when P� is the sensitizer, one finds fð1Þ P ¼ 3:3 � 0:3 ls, and fð2Þ P ¼ 34 � 3 ls, where the superscripts 1 and 2 refer to H2O and D2O, respectively; the corresponding values for sensitization by M� (in the absence of RC) are fð1Þ M ¼ 3:7 � 0:4 ls, and fð2Þ M ¼ 75 � 5 ls. The addition of RC’s to the solution of M in D2O reveals that the RC is a quencher of 1X; however, for equal concentrations of the RC, fð2Þ P < fð2Þ M , showing that 1X* is deactivated, after its entry into the suspending medium, mainly by the solvent or the same RC which acts as the sensitizer. The values of sP are similar in both solvents, ca. 2 ls, but this time constant does not figure in the disappearance of P�, which follows a bi-exponential course, a1exp(�t/s1) + a2exp(�t/s2). The time constants s1 and s2 (72 ± 5 ls and 12 ± 1 ls, respectively) as well as the factor a2 are insensitive to the oxygen content, and quenching of P� is manifested only through a threefold reduction in the magnitude of a1; these data imply the absence of dynamic quenching and heterogeneity of the RC. The mean lifetime of 1X* inside the protein matrix is identified with sP, and the absence of a prompt component in the phosphorescence signal rationalized by proposing that the radiative decay of 1X* within the RC is much slower than that in an aqueous environment. Elsevier 2007-05-25 Article PeerReviewed application/pdf en http://irep.iium.edu.my/12191/1/Arellano-Samsun.pdf Arellano, Juan B. and Yousef, Yaser A. and Melo, Thor Bernt and Mohamad, Samsun Baharin and Cogdell, Richard J. and Naqvi, K. Razi (2007) Formation and geminate quenching of singlet oxygen in purple bacterial reaction center. Journal of Photochemistry and Photobiology B: Biology, 87 (2). pp. 105-112. ISSN 1011-1344 (P), 1873-2682 (O) http://www.sciencedirect.com/science/article/pii/S1011134407000401 10.1016/j.jphotobiol.2007.03.004
repository_type	Digital Repository
institution_category	Local University
institution	International Islamic University Malaysia
building	IIUM Repository
collection	Online Access
language	English
topic	QC Physics
spellingShingle	QC Physics Arellano, Juan B. Yousef, Yaser A. Melo, Thor Bernt Mohamad, Samsun Baharin Cogdell, Richard J. Naqvi, K. Razi Formation and geminate quenching of singlet oxygen in purple bacterial reaction center
description	The phosphorescence of singlet oxygen (1X) photosensitized by the carotenoidless reaction center (RC) of Rhodobacter sphaeroides R26.1 has been investigated, using H2O and D2O as the suspending media. To enhance (under neutral conditions) the triplet quantum yield of the special pair P870 (P) by the radical pair mechanism, the quinone acceptor QA was removed by means of a chemical treatment. The phosphorescence signal fits the functional form P0[exp (�t/s) � exp(�t/f)], regardless of whether 1X is sensitized by P� or M� (where the dagger denotes triplet excitation and M is a water-soluble molecule). The time constant f was identified with the decay time of 1X; when P� is the sensitizer, one finds fð1Þ P ¼ 3:3 � 0:3 ls, and fð2Þ P ¼ 34 � 3 ls, where the superscripts 1 and 2 refer to H2O and D2O, respectively; the corresponding values for sensitization by M� (in the absence of RC) are fð1Þ M ¼ 3:7 � 0:4 ls, and fð2Þ M ¼ 75 � 5 ls. The addition of RC’s to the solution of M in D2O reveals that the RC is a quencher of 1X; however, for equal concentrations of the RC, fð2Þ P < fð2Þ M , showing that 1X* is deactivated, after its entry into the suspending medium, mainly by the solvent or the same RC which acts as the sensitizer. The values of sP are similar in both solvents, ca. 2 ls, but this time constant does not figure in the disappearance of P�, which follows a bi-exponential course, a1exp(�t/s1) + a2exp(�t/s2). The time constants s1 and s2 (72 ± 5 ls and 12 ± 1 ls, respectively) as well as the factor a2 are insensitive to the oxygen content, and quenching of P� is manifested only through a threefold reduction in the magnitude of a1; these data imply the absence of dynamic quenching and heterogeneity of the RC. The mean lifetime of 1X* inside the protein matrix is identified with sP, and the absence of a prompt component in the phosphorescence signal rationalized by proposing that the radiative decay of 1X* within the RC is much slower than that in an aqueous environment.
format	Article
author	Arellano, Juan B. Yousef, Yaser A. Melo, Thor Bernt Mohamad, Samsun Baharin Cogdell, Richard J. Naqvi, K. Razi
author_facet	Arellano, Juan B. Yousef, Yaser A. Melo, Thor Bernt Mohamad, Samsun Baharin Cogdell, Richard J. Naqvi, K. Razi
author_sort	Arellano, Juan B.
title	Formation and geminate quenching of singlet oxygen in purple bacterial reaction center
title_short	Formation and geminate quenching of singlet oxygen in purple bacterial reaction center
title_full	Formation and geminate quenching of singlet oxygen in purple bacterial reaction center
title_fullStr	Formation and geminate quenching of singlet oxygen in purple bacterial reaction center
title_full_unstemmed	Formation and geminate quenching of singlet oxygen in purple bacterial reaction center
title_sort	formation and geminate quenching of singlet oxygen in purple bacterial reaction center
publisher	Elsevier
publishDate	2007
url	http://irep.iium.edu.my/12191/ http://irep.iium.edu.my/12191/ http://irep.iium.edu.my/12191/ http://irep.iium.edu.my/12191/1/Arellano-Samsun.pdf
first_indexed	2023-09-18T20:21:26Z
last_indexed	2023-09-18T20:21:26Z
_version_	1777408132986699776

Formation and geminate quenching of singlet oxygen in purple bacterial reaction center

Similar Items