title: Direct Evidence of an Excited-State Triplet Species upon Photoactivation of the Chlorophyll Precursor Protochlorophyllide.
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.
authors.affiliation: School of Chemistry and the Photon Science Institute, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.|Manchester Institute of Biotechnology, University of Manchester , 131 Princess Street, Manchester M1 7DN, United Kingdom.
authors.forename: Guillem
authors.initials: G
authors.lastname: Brandariz-de-Pedro
authors.affiliation: Manchester Institute of Biotechnology, University of Manchester , 131 Princess Street, Manchester M1 7DN, United Kingdom.
authors.forename: Derren J
authors.initials: DJ
authors.lastname: Heyes
authors.affiliation: Manchester Institute of Biotechnology, University of Manchester , 131 Princess Street, Manchester M1 7DN, United Kingdom.
authors.forename: Samantha J O
authors.initials: SJ
authors.lastname: Hardman
authors.affiliation: Manchester Institute of Biotechnology, University of Manchester , 131 Princess Street, Manchester M1 7DN, United Kingdom.
authors.forename: Muralidharan
authors.initials: M
authors.lastname: Shanmugam
authors.affiliation: School of Chemistry and the Photon Science Institute, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.|Manchester Institute of Biotechnology, University of Manchester , 131 Princess Street, Manchester M1 7DN, United Kingdom.
authors.forename: Alex R
authors.initials: AR
authors.lastname: Jones
authors.affiliation: Institute of Physical Chemistry, Albert-Ludwigs-Universität Freiburg , 79104 Freiburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
authors.affiliation: Institute of Physical Chemistry, Albert-Ludwigs-Universität Freiburg , 79104 Freiburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Nohr
authors.affiliation: Manchester Institute of Biotechnology, University of Manchester , 131 Princess Street, Manchester M1 7DN, United Kingdom.
authors.forename: Nigel S
authors.initials: NS
authors.lastname: Scrutton
authors.affiliation: School of Chemistry and the Photon Science Institute, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.
authors.forename: Alistair J
authors.identifier: http://orcid.org/0000-0002-4437-9791
authors.initials: AJ
authors.lastname: Fielding
mesh_terms: D002384:Catalysis; D002734:Chlorophyll; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism*; D010777:Photochemistry; D011521:Protochlorophyllide / Q000737:chemistry / Q000378:metabolism*; D012997:Solvents; D013057:Spectrum Analysis
chemical_list: D012997:Solvents; D002734:Chlorophyll; D011521:Protochlorophyllide; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase