Gas phase absorption studies of photoactive yellow protein chromophore derivatives.
Photoabsorption spectra of deprotonated trans p-coumaric acid and two of its methyl substituted derivatives have been studied in gas phase both experimentally and theoretically. We have focused on the spectroscopic effect of the location of the two possible deprotonation sites on the trans p-coumaric acid which originate to either a phenoxide or a carboxylate. Surprisingly, the three chromophores were found to have the same absorption maximum at 430 nm, in spite of having different deprotonation positions. However, the absorption of the chromophore in polar solution is substantially different for the distinct deprotonation locations. We also report on the time scales and pathways of relaxation after photoexcitation for the three photoactive yellow protein chromophore derivatives. As a result of these experiments, we could detect the phenoxide isomer within the deprotonated trans p-coumaric acid in gas phase; however, the occurrence of the carboxylate is uncertain. Several computational methods were used simultaneously to provide insights and assistance in the interpretation of our experimental results. The calculated excitation energies S(0)-S(1) are in good agreement with experiment for those systems having a negative charge on a phenoxide moiety. Although our augmented multiconfigurational quasidegenerate perturbation theory calculations agree with experiment in the description of the absorption spectrum of anions with a carboxylate functional group, there are some puzzling disagreements between experiment and some calculational methods in the description of these systems.
Rocha-Rinza
Toms
T
Lundbeck Foundation Center for Theoretical Chemistry, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark.
Christiansen
Ove
O
Rajput
Jyoti
J
Gopalan
Aravind
A
Rahbek
Dennis B
DB
Andersen
Lars H
LH
Bochenkova
Anastasia V
AV
Granovsky
Alexander A
AA
Bravaya
Ksenia B
KB
Nemukhin
Alexander V
AV
Christiansen
Kasper Lincke
KL
Nielsen
Mogens Brøndsted
MB
D001426:Bacterial Proteins / Q000737:chemistry*; D003373:Coumaric Acids / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D055668:Photochemical Processes; D020283:Photoreceptors, Microbial / Q000737:chemistry*; D011422:Propionates; D011789:Quantum Theory; D013057:Spectrum Analysis
D001426:Bacterial Proteins; D003373:Coumaric Acids; D005740:Gases; D020283:Photoreceptors, Microbial; D011422:Propionates; C050162:photoactive yellow protein, Bacteria; C495469:p-coumaric acid