title: Conformational heterogeneity of methyl 4-hydroxycinnamate: a gas-phase UV-IR spectroscopic study.
abstract: UV excitation and IR absorption spectroscopy on jet-cooled molecules is used to study the conformational heterogeneity of methyl 4-hydroxycinnamate, a model chromophore of the Photoactive Yellow Protein (PYP), and to determine the spectroscopic properties of the various conformers. UV-UV depletion spectroscopy identifies four different species with distinct electronic excitation spectra. Quantum chemical calculations argue that these species are associated with different conformers involving the s-cis/s-trans configuration of the ester with respect to the propenyl C-C single bond and the syn/anti orientation of the phenolic OH group. IR-UV hole-burning spectroscopy is used to record their IR absorption spectra in the fingerprint region. Comparison with IR absorption spectra predicted by quantum chemical calculations provides vibrational markers for each of the conformers, on the basis of which each of the species observed with UV-UV depletion spectroscopy is assigned. Although both DFT and wave function methods reproduce experimental frequencies, we find that calculations at the MP2 level are necessary to obtain agreement with experimentally observed intensities. To elucidate the role of the environment, we compare the IR spectra of the isolated conformers with IR spectra of methyl 4-hydroxycinnamate-water clusters, and with IR spectra of methyl 4-hydroxycinnamate in solution.
authors.affiliation: Van't Hoff Institute for Molecular Sciences, Faculty of Science, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
authors.forename: Eric M M
authors.initials: EM
authors.lastname: Tan
authors.forename: Saeed
authors.initials: S
authors.lastname: Amirjalayer
authors.forename: Szymon
authors.initials: S
authors.lastname: Smolarek
authors.forename: Alexander
authors.initials: A
authors.lastname: Vdovin
authors.forename: Anouk M
authors.initials: AM
authors.lastname: Rijs
authors.forename: Wybren J
authors.initials: WJ
authors.lastname: Buma
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002934:Cinnamates / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D020607:Halorhodospira halophila / Q000378:metabolism; D007536:Isomerism; D008968:Molecular Conformation; D020283:Photoreceptors, Microbial / Q000737:chemistry / Q000378:metabolism; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D002934:Cinnamates; D005740:Gases; D020283:Photoreceptors, Microbial; C478851:methyl-p-coumarate; C050162:photoactive yellow protein, Bacteria; D014867:Water