title: Activation energy of light induced isomerization of resveratrol.
abstract: 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.
authors.affiliation: NanoBiotechnology Group, Department of Physics and Nanotechnology, Aalborg University, Skjernvej 4A, Aalborg, Denmark.
authors.forename: Teresa Sofia
authors.initials: TS
authors.lastname: Figueiras
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Neves-Petersen
authors.forename: Steffen B
authors.initials: SB
authors.lastname: Petersen
mesh_terms: D005453:Fluorescence; D007700:Kinetics; D015394:Molecular Structure; D000077185:Resveratrol; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D013267:Stilbenes / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D013267:Stilbenes; D000077185:Resveratrol