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Gas-phase Photochemistry of the Photoactive Yellow Protein Chromophore Trans-P-Coumaric Acid

Gas-phase Photochemistry of the Photoactive Yellow Protein Chromophore Trans-P-Coumaric Acid

Wendy L Ryan, David J Gordon, Donald H Levy

J Am Chem Soc. 2002 May 29;124(21):6194-201.

PMID: 12022854

Abstract:

The photoisomerization of trans-p-coumaric acid (trans-CA) triggers a photocycle in photoactive yellow protein that ultimately mediates a phototactic response to blue light in certain purple bacteria. We have used fluorescence excitation and dispersed emission methods in a supersonic jet to investigate the nature of the electronic excited states involved in the initial photoexcitation and subsequent photoisomerization of trans-CA. We observed three distinct regions in the fluorescence excitation spectrum of trans-CA. Region I is characterized by sharp features that upon excitation exhibit trans-CA S(1) emission. In region II, features increase in width and decrease in intensity with increasing excitation energy. Upon excitation, we observed dual emission from the S(1) state of trans-CA and what may be the S(1) state of cis-CA. The onset of dual emission corresponds to an isomerization barrier of about 3.4 kcal/mol. Finally, the extremely broad absorption feature in region III is excitation to the S(2) electronic excited state and excitation results in trans-CA S(1) emission. Furthermore, we collected CA from the molecular beam after laser excitation in each of the three regions as further evidence of the photoisomerization process. The relative amounts of trans- and cis-CA in the collected molecules were measured with high-pressure liquid chromatography. Although trans-CA was excited in all three regions, a significant cis-CA peak appeared only in region II, though a small cis peak was observed in region III.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP501984-A	trans-p-Coumaric acid		501-98-4	Price

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