Cargando…

Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine

Flavin chromophores play key roles in a wide range of photoactive proteins, but key questions exist in relation to their fundamental spectroscopic and photochemical properties. In this work, we report the first gas-phase spectroscopy study of protonated alloxazine (AL∙H(+)), a model flavin chromopho...

Descripción completa

Detalles Bibliográficos
Autores principales: Matthews, Edward, Cercola, Rosaria, Dessent, Caroline E. H.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6222404/
https://www.ncbi.nlm.nih.gov/pubmed/30110962
http://dx.doi.org/10.3390/molecules23082036
_version_ 1783369199292252160
author Matthews, Edward
Cercola, Rosaria
Dessent, Caroline E. H.
author_facet Matthews, Edward
Cercola, Rosaria
Dessent, Caroline E. H.
author_sort Matthews, Edward
collection PubMed
description Flavin chromophores play key roles in a wide range of photoactive proteins, but key questions exist in relation to their fundamental spectroscopic and photochemical properties. In this work, we report the first gas-phase spectroscopy study of protonated alloxazine (AL∙H(+)), a model flavin chromophore. Laser photodissociation is employed across a wide range (2.34–5.64 eV) to obtain the electronic spectrum and characterize the photofragmentation pathways. By comparison to TDDFT quantum chemical calculations, the spectrum is assigned to two AL∙H(+) protomers; an N5 (dominant) and O4 (minor) form. The protomers have distinctly different spectral profiles in the region above 4.8 eV due to the presence of a strong electronic transition for the O4 protomer corresponding to an electron-density shift from the benzene to uracil moiety. AL∙H(+) photoexcitation leads to fragmentation via loss of HCN and HNCO (along with small molecules such as CO(2) and H(2)O), but the photofragmentation patterns differ dramatically from those observed upon collision excitation of the ground electronic state. This reveals that fragmentation is occurring during the excited state lifetime. Finally, our results show that the N5 protomer is associated primarily with HNCO loss while the O4 protomer is associated with HCN loss, indicating that the ring-opening dynamics are dependent on the location of protonation in the ground-state molecule.
format Online
Article
Text
id pubmed-6222404
institution National Center for Biotechnology Information
language English
publishDate 2018
publisher MDPI
record_format MEDLINE/PubMed
spelling pubmed-62224042018-11-13 Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine Matthews, Edward Cercola, Rosaria Dessent, Caroline E. H. Molecules Article Flavin chromophores play key roles in a wide range of photoactive proteins, but key questions exist in relation to their fundamental spectroscopic and photochemical properties. In this work, we report the first gas-phase spectroscopy study of protonated alloxazine (AL∙H(+)), a model flavin chromophore. Laser photodissociation is employed across a wide range (2.34–5.64 eV) to obtain the electronic spectrum and characterize the photofragmentation pathways. By comparison to TDDFT quantum chemical calculations, the spectrum is assigned to two AL∙H(+) protomers; an N5 (dominant) and O4 (minor) form. The protomers have distinctly different spectral profiles in the region above 4.8 eV due to the presence of a strong electronic transition for the O4 protomer corresponding to an electron-density shift from the benzene to uracil moiety. AL∙H(+) photoexcitation leads to fragmentation via loss of HCN and HNCO (along with small molecules such as CO(2) and H(2)O), but the photofragmentation patterns differ dramatically from those observed upon collision excitation of the ground electronic state. This reveals that fragmentation is occurring during the excited state lifetime. Finally, our results show that the N5 protomer is associated primarily with HNCO loss while the O4 protomer is associated with HCN loss, indicating that the ring-opening dynamics are dependent on the location of protonation in the ground-state molecule. MDPI 2018-08-14 /pmc/articles/PMC6222404/ /pubmed/30110962 http://dx.doi.org/10.3390/molecules23082036 Text en © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Matthews, Edward
Cercola, Rosaria
Dessent, Caroline E. H.
Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine
title Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine
title_full Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine
title_fullStr Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine
title_full_unstemmed Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine
title_short Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine
title_sort protomer-dependent electronic spectroscopy and photochemistry of the model flavin chromophore alloxazine
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6222404/
https://www.ncbi.nlm.nih.gov/pubmed/30110962
http://dx.doi.org/10.3390/molecules23082036
work_keys_str_mv AT matthewsedward protomerdependentelectronicspectroscopyandphotochemistryofthemodelflavinchromophorealloxazine
AT cercolarosaria protomerdependentelectronicspectroscopyandphotochemistryofthemodelflavinchromophorealloxazine
AT dessentcarolineeh protomerdependentelectronicspectroscopyandphotochemistryofthemodelflavinchromophorealloxazine