97 0

Site-dependent effects of methylation on the electronic spectra of jet-cooled methylated xanthine compounds

Title
Site-dependent effects of methylation on the electronic spectra of jet-cooled methylated xanthine compounds
Author
김두리
Keywords
EXCITED-STATE DYNAMICS; INTERNAL-ROTATION; SUBSTITUTED TOLUENES; AROMATIC-MOLECULES; DNA METHYLATION; SPECTROSCOPY; CAFFEINE; CATIONS; HYPERCONJUGATION; PHOTOIONIZATION
Issue Date
2017-07
Publisher
ROYAL SOC CHEMISTRY
Citation
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, v. 19, no. 33, page. 22375-22384
Abstract
We obtained the electronic spectra of various methylated xanthine compounds including caffeine in a supersonic jet by resonant two-photon ionization spectroscopy. The methyl group in the tested methylated xanthine compounds has a distinct, site-dependent effect on the electronic spectrum. Methylation at the N3 position causes a significant red shift of the pi pi* state, whereas methylation at the N1 position has only minimal effects on the electronic spectrum. The notably broad spectra of theobromine and caffeine result from methyl substitution at the N7 position, which causes a large displacement between the potential energy surfaces of the S-0 and S-1 states, and a strong vibronic coupling. We also investigated the internal rotation of the methyl group and its effect on the electronic spectrum of the methylated xanthine compounds. We found that the barrier height for the torsional motion in the ground state is significantly affected by a carbonyl or methyl group that lies close to the methyl group of interest. In contrast, the torsional barrier in the excited state is governed by the hyperconjugation interaction in the lowest unoccupied molecular orbital. The agreement between the experimental and simulated spectra of torsional vibronic bands suggested that the low frequency torsional vibrations arising from the tunneling splitting and the coupling between the torsional and molecular motions give theobromine and theophylline the multiplet nature of their origin bands. This study provides a new level of understanding for the methyl substitution effects on the electronically excited states of xanthine compounds, which may very well be applicable to many other methyl substituted biomolecules including DNAs and proteins.
URI
https://pubs.rsc.org/en/content/articlelanding/2017/CP/C7CP03380J#!divAbstracthttps://repository.hanyang.ac.kr/handle/20.500.11754/114853
ISSN
1463-9076; 1463-9084
DOI
10.1039/c7cp03380j
Appears in Collections:
COLLEGE OF NATURAL SCIENCES[S](자연과학대학) > CHEMISTRY(화학과) > Articles
Files in This Item:
There are no files associated with this item.
Export
RIS (EndNote)
XLS (Excel)
XML


qrcode

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

BROWSE