While maleic acid, the cis isomer, is a synthetic organic compound, its trans isomer, fumaric acid, is an organic acid widely found in nature (Felthhouse et al.
In the laboratory, the conversion of cis isomer into trans isomer (Pasto et al, 1992) is performed by treating maleic acid with aqueous bromine under uv light, and in industry it is produced by catalytic isomerization with mineral acids (Vogel, 1980).
We can see that the cis isomer
is almost fully consumed irrespective of the distance from the air surface, whereas the trans isomer only cures near the surface.
NPG, the [alpha]-proton of the cis isomer is found at 2.
However, cis/trans isomerization that can occur during the synthetic process of 1,4-CHDA, which is originally 70 to 79% cis isomer, (18) had been found to lead to a thermodynamic equilibrium mixture of 35% cis and 65% trans, (19) or a mixture of 55% cis and 45% trans isomers, depending upon the method of synthesis.
Regular amino acids form secondary amides, in which the trans isomer is considerably more stable than the cis isomer
(Figure 3), resulting in a linear chain.
In all cases, the chemical shift of the C-1 methine proton of the cis isomer
is more deshielded (larger ppm value) than the methine proton of the trans isomer.
12]MDI, the difference in molecule linearity between the cis isomer
and the trans isomer is not very obvious, as shown in figure 1.
o] (a low value is preferable) and the percentage of cis isomer
(which should be high).
Of the studies that differentiated between 9- and 13-cis isomers
of [beta]-carotene, some identified 9-cis (10% of alltrans-[beta]-carotene) [38, 39] and some 13-cis (5% of total [beta]-carotene) [37, 40] as the main cis isomer
of [beta]-carotene in plasma.
The ratio of cis and trans configurations in commercial products is also an important determinant of pyrethroid toxicity in mammals, with cis isomers
generally being more potent.
Another highlight of the present method is the ability to differentiate between the trans and cis isomers
of resveratrol-4'-O-glucuronide, resveratrol-3-O-glucuronide, resveratrol-4'-sulfate, and resveratrol-3-sulfate.