J Fluoresc (2011) 21:1897–1906
1905
The 3.7±0.3 kcal/mol activation energy of trans-
resveratrol photoisomerization into the cis-form calculated
through the Arrhenius plot shown in Fig. 7, is comparable
with the value of 3.4 kcal/mol reported by Sumitani et al.
and that at pH 1 50% of cis-form was isomerized to the
trans-resveratrol. Whereas there is a growing confidence
that trans-resveratrol is non-toxic, very little is known
about the pharmacology of cis-resveratrol. The results
presented in this paper can become an important component
in analyzing and securing that resveratrol containing
pharmaceuticals contains only the trans isomer.
[
45] for the photoisomerization energy of trans-stilbene in
hexane. According to Wiemers at al. [36], trans-4-
stilbenemethanol has a photoisomerization Arrhenius
activation energy (exc. 298 nm) of 5.7 kcal/mol in ethanol,
7
.9 kcal/mol in propanol and 5.2 kcal/mol in hexane.
According to Garner et al. [37], the activation energy of
photoisomerization (exc. 436 nm) of trans-4-nitro-4′-
dimethylaminostilbene in toluene is 10.5 kcal/mol. Steiner
et al. [38] showed that the activation energy for cis-trans
thermal isomerization of 4-nitro-4′-methoxystilbene is
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0
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acid buffer conditions is stable at pH 7, less stable at pH 3