Conformational Heterogeneity of Methyl 4-Hydroxycinnamate: A Gas-Phase UV鈥揑R Spectroscopic Study

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• 作者：Eric M. M. Tan ; Saeed Amirjalayer ; Szymon Smolarek ; Alexander Vdovin ; Anouk M. Rijs ; Wybren J. Buma
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：May 2, 2013
• 年：2013
• 卷：117
• 期：17
• 页码：4798-4805
• 全文大小：431K
• 年卷期：v.117,no.17(May 2, 2013)
• ISSN：1520-5207

文摘

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鈥揢V 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鈥揅 single bond and the syn/anti orientation of the phenolic OH group. IR鈥揢V 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鈥揢V 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鈥搘ater clusters, and with IR spectra of methyl 4-hydroxycinnamate in solution.