Trans-p-Coumaric acid

Theoretically, trans-p-coumaric acid can produce 12 isomers depending on whether head-to-tail (4,4 -dihydroxytruxillic acid) or head-to-head (4,4 -dihydroxytruxinic acid) dimerizations occur with syn or anti and with cis or trans ring junctions (37). Mass spectrometric analysis of the tetra-TMSi derivatives showed that head-to-tail dimers split symmetrically on electron impact, whereas head-to-head dimers fragment asymmetrically (Figures 2 and 3) (33,35,38,39). Thus the tetra-TMSi derivative of 4,4 -dihydroxytruxillic acid has a mass spectrum similar to that of the bis-TMSi derivative of p-coumaric acid (33). 

It therefore seems probable that, in the cell walls of the growing plant, dimerization of p-coumaric and ferulic acid units linked to arabinoxylan occurs under the influence of sunlight. Earlier work (34) showed that trans-p-coumaric acid converts readily in sunlight to 4,4 -dihydroxytruxillic acid. It has recently been shown (40) that FA-FA and PCA-FA type cyclodimers can be obtained in low yield (less than 10%) by irradiating mixtures of the... 

The Photoactive Yellow Protein (PYP) is the blue-light photoreceptor that presumably mediates negative phototaxis of the purple bacterium Halorhodospira halophila [1]. Its chromophore is the deprotonated trans-p-coumaric acid covalently linked, via a thioester bond, to the unique cystein residue of the protein. Like for rhodopsins, the trans to cis isomerization of the chromophore was shown to be the first overall step of the PYP photocycle, but the reaction path that leads to the formation of the cis isomer is not clear yet (for review see [2]). From time-resolved spectroscopy measurements on native PYP in solution, it came out that the excited-state deactivation involves a series of fast events on the subpicosecond and picosecond timescales correlated to the chromophore reconfiguration [3-7]. On the other hand, chromophore H-bonding to the nearest amino acids was shown to play a key role in the trans excited state decay kinetics [3,8]. In an attempt to evaluate further the role of the mesoscopic environment in the photophysics of PYP, we made a comparative study of the native and denatured PYP. The excited-state relaxation path and kinetics were monitored by subpicosecond time-resolved absorption and gain spectroscopy. 

Figure 5.17 Application of the window diagram method for optimizing the pH in RPLC. Solutes S = scopoletin, U = umbelliferone, TF = trans-ferulic acid, TC = trans-p-coumaric acid, CF = cis-feruiic acid and CC = cis-p-coumaric acid, (a) retention surfaces, (b) window diagram. Figure taken from ref. (552J. Reprinted with permission.

Figure S.21 Resulting chromatogram at the optimum conditions predicted by figure S.20. pH = S.8 concentration of n-octylamine = 3.2 mM. ODS column mobile phase methanol-water (20/80) with 0.010 M acetate buffer. Solutes E = phenylethylamine, P = phenylalanine, V = vanillic acid, C = trans caffeic acid, M = trans p-coumaric acid, F = trans ferulic acid, A = phenylacetic acid, H = hydrocinnamic acid and N = trans cinnamic acid. Figure taken from ref. [559]. Reprinted with permission. 

The degradation of plant cell walls requires fra/is-p-coumaroyl esterase, an important enzyme in the digestion of forages and dietary fiber. The trans-p-coumaric acid released by enzymatic hydrolysis was assayed by reversed-phase HPLC. 

The trans-a- and rrans-/3-anomers of the substrate, 0-[5-0-(trans-p-coumaroyl)-a-L-arabinofuranosyl] -(1 —> 3)- 0-/3- D-xylopyranosyl-( 1—> 4)-d-xylopyranose, were separated from each other and from the product, trans-p-coumaric acid, by chromatography on a Resolve C)8 column (3.9 mm X 150 mm). The mobile phase consisted of a 10 mM NaOH solution titrated to pH 3.0 with formic acid. Methanol was added to this solution to give a final concentration of 21% (v/v). The flow rate was 2 mL/min. The absorbance of the elute was monitored at 313 nm. 

Cinnamate 4-hydroxylases catalyze the hydroxylation of frans-cinnamic acid into trans-p-coumaric acid. The ability to monitor this enzyme activity in Jerusalem artichoke allowed isolation of the P450 enzyme CYP73A1 using conventional chromatography and generation of specific antibodies . ... 

Fig. 1. Changes in the absorption spectra caused by 15 min of irradiation with UV light at 25 C of (A) an aqueous extract of the hypocotyls of dark-grown gherkin seedlings, (B) the upper part of the hypo-ootyl of a dark-grown seedling, and (C) a solution of trans-p-coumaric acid (10 M) in water. Spectra...

Simple phenolic compounds include (1) the phenylpropanoids, trans-cinnamic acid, p-coumaric acid and their derivatives (2) the phenylpropanoid lactones called coumarins (Fig. 3.4) and (3) benzoic acid derivatives in which two carbons have been cleaved from the three carbon side chain (Fig. 3.2). More complex molecules are elaborated by additions to these basic carbon skeletons. For example, the addition of quinic acid to caffeic acid produces chlorogenic acid, which accumulates in cut lettuce and contributes to tissue browning (Fig. 3.5). 

Price, W.P., Jr., and Deming, S.N. (1979), Optimized Separation of Scopoletin and Umbelliferone and cis-trans Isomers of Ferulic and p-Coumaric Acids by Reverse-Phase High-Performance Liquid Chromatography, Anal. Chim. Acta, 108, 227-231. 

The amounts of the trans isomers of p-coumaric and ferulic acids were approximately ten times those of the corresponding cis isomers dehydrodiferulic acid occurred mainly as the trans, trans isomer. A major difference between cell walls of temperate (e.g., ryegrass, wheat) and sub-tropical (e.g., maize, Coastal bermudagrass) graminaceous plants is that the latter group contain comparatively large amounts of frans-p-coumaric acid... 

Figure 6.8 UV spectra of standard chlorogenic acid (a) trans-cinnamic acid (b) cafFeic acid (c) p-coumaric acid (d) and femlic acid (e). The spectra of peaks 1 (chlorogenic acid) (f), peak 2 (chlorogenic acid isomer) (g), and peak 3 (caffeic acid) (h) were determined with HPLC fractions isolated from extracts of Superior potato peel.

The Photoactive Yellow Protein (PYP) is thought to be the photoreceptor responsible for the negative phototaxis of the bacterium Halorhodospira halophila [1]. Its chromophore, the deprotonated 4-hydroxycinnamic (or p-coumaric) acid, is covalently linked to the side chain of the Cys69 residue by a thioester bond. Trans-cis photoisomerization of the chromophore was proved to occur during the early steps of the PYP photocycle. Nevertheless, the reaction pathway leading to the cis isomer is still discussed (for a review, see ref. [2]). Time-resolved spectroscopy showed that it involves subpicosecond and picosecond components [3-7], some of which could correspond to a flipping motion of the chromophore carbonyl group [8,9]. 

Most HPLC applications used for phenolic analysis simply allow the room temperature to determine the operating temperature of the column, but elevated temperatures of between 30°C and 40°C are often applied for phenolics and derivatives in apples (14), carrots (15), apple juice (6,13), bilberry juice (16), and for cis-trans isomers of caffeic and p-coumaric acids in wines (17). Generally, a change in temperature has only a minor effect on band spacing in reversed-phase HPLC and has essentially no effect in normal-phase separations. Thermostatic control of the column temperature is generally recommended to provide reproducible retention. 

An HPLC method using a 90-min binary gradient with (a) acidified water, pH 2.4, and (b) acetonitrile on an Adsorbosphere C]8, 3-/zl cartridge (Alltech) was also developed for pheno-lics in barley (127). Seven phenolic compounds, including vanillic acid, p-coumaric acid, ferulic acid, and their derivatives, were separated by HPLC after alkaline hydrolysis in order to evaluate the role of bound phenolic acids in their antioxidant activity in beer. In this method, cis and trans isomers of p-coumaric and ferulic acids are quantified by HPLC, although cls-p-coumaric acid was not well separated from its trans isomer in this analysis. 

Hydroxycinnamic acids possess a C6-C3 skeleton and formally belong to the group of phenylpropanoids. The different compounds present in wine are mainly derived from the hydroxycinnamic acids caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid (Fig. 9C.2). These derivatives can be present in cis- and trans-configured forms, while the trans forms are more stable and therefore more prevalent. In wine HCA are present in low amounts in their free form, while the depside forms, i.e. esters of l-(-i-)-tartaric acid, are predominant. The ubiquitous chlorogenic acids, esters of HCA and quinic acid, cannot be found in wine but are replaced by the tartaric acid esters instead (Ong and Nagel 1978 Singleton et al. 1978 Somers etal. 1987). 

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