Towards Understanding Photodegradation Pathways in Lignins: The Role of Intramolecular Hydrogen Bonding in Excited States
| Autor: | Vasilios G. Stavros, Jacob C. Dean, Michael N. R. Ashfold, Michael Staniforth, Tolga N. V. Karsili, Jamie D. Young, Timothy S. Zwier, Federico Mazzoni, Gareth M. Roberts |
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| Rok vydání: | 2015 |
| Předmět: |
DYNAMICS
VIBRATIONAL WAVE-PACKETS Hydrogen bond Syringol MASS-SPECTROMETRY Photoionization IONIZATION SPECTROSCOPY Chromophore BIOMOLECULES chemistry.chemical_compound chemistry PHENOL Excited state Intramolecular force FLUOROPHENOL Physical chemistry PHOTOELECTRON BIOSYNTHESIS General Materials Science Guaiacol Physical and Theoretical Chemistry Ground state METHOXYPHENOL |
| Zdroj: | Young, J D, Staniforth, M, Dean, J C, Roberts, G M, Mazzoni, F, Karsili, T N V, Ashfold, M N R, Zwier, T S & Stavros, V G 2014, ' Towards Understanding Photodegradation Pathways in Lignins : The Role of Intramolecular Hydrogen Bonding in Excited States ', Journal of Physical Chemistry Letters, vol. 5, no. 12, pp. 2138-2143 . https://doi.org/10.1021/jz500895w |
| ISSN: | 1948-7185 |
| Popis: | The photoinduced dynamics of the lignin building blocks syringol, guaiacol, and phenol were studied using time-resolved ion yield spectroscopy and velocity map ion imaging. Following irradiation of syringol and guaiacol with a broad-band femtosecond ultraviolet laser pulse, a coherent superposition of out-of-plane OH torsion and/or OMe torsion/flapping motions is created in the first excited (1)pi pi* (S-1) state, resulting in a vibrational wavepacket, which is probed by virtue of a dramatic nonplanar -> planar geometry change upon photoionization from S-1 to the ground state of the cation (D-0). Any similar quantum beat pattern is absent in phenol. In syringol, the nonplanar geometry in S-1 is pronounced enough to reduce the degree of intramolecular H bonding (between OH and OMe groups), enabling H atom elimination from the OH group. For guaiacol, H bonding is preserved after excitation, despite the nonplanar geometry in S-1, and prevents O-H bond fission. This behavior affects the propensities for forming undesired phenoxyl radical sites in these three lignin chromophores and provides important insight into their relative "photostabilities" within the larger biopolymer. |
| Databáze: | OpenAIRE |
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