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Direct Evidence of an Excited-State Triplet Species upon Photoactivation of the Chlorophyll Precursor Protochlorophyllide

Brandariz-de-Pedro, G, Heyes, DJ, Hardman, SJO, Shanmugam, M, Jones, AR, Weber, S, Nohr, D, Scrutton, NS and Fielding, AJ (2017) Direct Evidence of an Excited-State Triplet Species upon Photoactivation of the Chlorophyll Precursor Protochlorophyllide. Journal of Physical Chemistry Letters, 8 (6). pp. 1219-1223. ISSN 1948-7185

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Abstract

The chlorophyll precursor protochlorophyllide (Pchlide), which is the substrate for the light-driven enzyme protochlorophyllide oxidoreductase, has unique excited-state properties that facilitate photocatalysis. Previous time-resolved spectroscopy measurements have implied that a long-lived triplet state is formed during the excited-state relaxation of Pchlide, although direct evidence of its existence is still lacking. Here we use time-resolved electron paramagnetic resonance (EPR) in combination with time-resolved absorption measurements at a range of temperatures (10–290 K), solvents, and oxygen concentrations to provide a detailed characterization of the triplet state of Pchlide. The triplet decays in a biphasic, oxygen-dependent manner, while the first reported EPR signature of a Pchlide triplet displays both emissive and absorptive features and an antisymmetric spectrum similar to other porphyrin triplet states. This work demonstrates that the Pchlide triplet is accessible to various cryogenic spectroscopic probes over a range of time scales and paves the way for understanding its potential role in catalysis.

Item Type: Article
Uncontrolled Keywords: 03 Chemical Sciences, 02 Physical Sciences
Subjects: Q Science > QD Chemistry
Q Science > QH Natural history > QH301 Biology
Divisions: Pharmacy & Biomolecular Sciences
Publisher: American Chemical Society
Related URLs:
Date Deposited: 23 Jan 2019 09:13
Last Modified: 23 Jan 2019 22:02
DOI or Identification number: 10.1021/acs.jpclett.7b00200
URI: http://researchonline.ljmu.ac.uk/id/eprint/9994

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