Activation Energy of Light Induced Isomerization of Resveratrol

• Published in: Journal of fluorescence 2011-09, Vol.21 (5), p.1897-1906
• Main Authors: Figueiras, Teresa Sofia, Neves-Petersen, Maria Teresa, Petersen, Steffen B.
• Format: Article
• Language: English
• Subjects: Activation energy; Analytical Chemistry; Biochemistry; Biological and Medical Physics; Biomedical and Life Sciences; Biomedicine; Biophysics; Biotechnology; Blue shift; Excitation; Excitation spectra; Fluorescence; Isomerization; Isomers; Kinetics; Molecular Structure; Original Paper; Spectra; Spectrometry, Fluorescence; Stereoisomerism; Stilbenes - chemistry; Temperature; Time Factors; Ultraviolet Rays
• ISSN: 1053-0509; 1573-4994
• DOI: 10.1007/s10895-011-0886-3

Isomerization of trans -stilbenes is known to be induced by light. The two isomers have distinct absorption, fluorescence excitation and emission spectra. Resveratrol, 3,4′,5-trihydroxystilbene, is a member of the stilbene family. The interest of the scientific community in resveratrol has increased over the last years due to its biomedical properties. Whereas there is a growing confidence that trans -resveratrol is non-toxic, very little is known about the pharmacology of cis -resveratrol. Of this very reason there is considerable interest in knowing the energetics of the trans-cis conversion. Cis -resveratrol is characterized by a large fluorescence quantum yield when compared to trans -resveratrol. In the present paper we report a detailed analysis of the spectral changes induced in trans -resveratrol upon 260 nm excitation for different time periods. Spectral changes have been monitored with UV-visible absorption and steady-state fluorescence spectroscopy at pH 4 at 20, 25, 30, 35, 40, 45 and 50 °C. Continuous 260 nm excitation induces a blue shift in the absorption and fluorescence excitation spectra of resveratrol and a 14 nm blue shift in its fluorescence emission. The photoisomerization yield is reported as a function of 260 nm excitation time. 330 min continuous excitation led to ~60% isomerization yield. The kinetics of trans-cis isomerization has been monitored following the increase in fluorescence quantum yield upon continuous 260 nm excitation of trans -resveratrol. The study was carried out at the above mentioned temperatures in order to obtain the Arrhenius activation energy of photoisomerization. Activation energy and pre-exponential factor were 3.7 ± 0.3 kcal.mol −1 and 10.6 ± 1.6 s −1 , respectively. The activation energy is comparable with previously reported values for the photoisomerization of other stilbenes.