Conformational behaviour of biologically active ferulic acid derivatives

Spectroscopic and theoretical investigations of phenolic acids in white wines

Model solutions of white wines containing phenolic acids have been investigated by means of UV-vis, laser induced fluorescence and Raman spectroscopic techniques. In order to interpret the spectra, density functional theory calculations of phenolic acids have been performed. This work demonstrates that only hydroxynamic acids are in resonance with a laser excitation line with 325nm wavelength and are therefore at the origin of the strong enhancement of the Raman light scattering. Real white wines also display such resonance Raman scattering so that their content in hydroxycinnamic acids may be quite precisely determined. The analysis of the Raman spectrum of a real dry white wine reveals qualitatively the preponderance in its composition of p-coumaric and caftaric acids.

A theoretical antioxidant pharmacophore for natural hydroxycinnamic acids

The structure-activity relationship analysis has been performed for trans- and cis-hydroxycinnamic acids, to determine their theoretical antioxidant pharmacophore. Based on the detailed conformational studies, the most stable rotamers have been selected. We have analyzed the descriptors of four antioxidant mechanisms important in free radical scavenging: hydrogen atom transfer, sequential proton loss electron transfer, single electron transfer - proton transfer and transition metal chelation, based on the B3LYP/6-311++G(2d,2p) calculations in vacuum and polar media. The results explain the activity difference between cinnamic acid and its derivatives. The descending order of antioxidant potential is as follows: caffeic > sinapinic ~ ferulic > p-coumaric > o-coumaric > m-coumaric ~ phenol. The results have shown that transisomers indicate higher reactivity than cis- and may be considered as good antioxidants. It has been determined that the highest antioxidant ability is related to the hydroxyl group in para position, supported by planar structure and stability of radical forms. π-Type delocalization of unpaired electron on aromatic ring, double bond and para O-atom is the key to radical stabilization. The ortho-dihydroxy substitution in benzene ring positively influences the ability to neutralize free radicals and makes caffeic acid the antioxidant pharmacophore of hydroxycinnamic acids.

An inelastic neutron scattering study of dietary phenolic acids

The conformational preferences and hydrogen-bonding motifs of several potential chemopreventive hydroxycinnamic derivatives were determined by inelastic neutron scattering spectroscopy. The aim is to understand their recognized beneficial activity and establish reliable structure-activity relationships for these types of dietary phytochemicals. A series of phenolic acids with different hydroxyl/methoxyl ring substitution patterns were studied: trans-cinnamic, p-coumaric, m-coumaric, trans-caffeic and ferulic acids. Their INS spectra were completely assigned by theoretical calculations performed at the Density Functional Theory level, for the isolated molecule, dimeric centrosymmetric species and the solid (using plane-wave expansion approaches). Access to the low energy vibrational region of the spectra enabled the identification of particular modes associated with intermolecular hydrogen-bonding interactions, which are the determinants of the main conformational preferences and antioxidant capacity of these systems.

Energetics and structural properties, in the gas phase, of trans-hydroxycinnamic acids

We have studied the energetics and structural properties of trans-cinnamic acid (CA), o-, m-, and p-coumaric acids (2-, 3-, and 4-hydroxycinnamic acids), caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), iso-ferulic acid (3-hydroxy-4-methoxycinnamic acid), and sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid). The experimental values of Δ(f)H(m)°(g), determined (in kJ·mol(-1)) for CA (-229.8 ± 1.9), p-coumaric acid (-408.0 ± 4.4), caffeic acid (-580.0 ± 5.9), and ferulic acid (-566.4 ± 5.7), allowed us to derive Δ(f)H(m)°(g) of o-coumaric acid (-405.6 ± 4.4), m-coumaric acid (-406.4 ± 4.4), iso-ferulic acid (-565.2 ± 5.7), and sinapic acid (-698.8 ± 4.1). From these values and by use of isodesmic/homodesmotic reactions, we studied the energetic effects of π-donor substituents (-OH and -OCH(3)) in cinnamic acid derivatives and in the respective benzene analogues. Our results indicate that the interaction between -OCH(3) and/or -OH groups in hydroxycinnamic acids takes place without significant influence of the propenoic fragment.

Characterization of antioxidant olive oil biophenols by spectroscopic methods

BACKGROUND

Olive oil contains numerous phenolic components with well-recognized health-beneficial activity. The major phenolic compounds present in olives and virgin olive oil-hydroxytyrosol, oleuropein and the oleuropein aglycones 3,4-DHPEA-EA and 3,4-DHPEA-EDA-as well as some of their metabolites were studied in the present work, regarding their main structural preferences. Vibrational spectroscopy (Raman) coupled to theoretical methods were used, aiming at fully characterizing the systems and therefore enabling their quick and reliable identification in food samples.

RESULTS

The raman data, assisted by the theoretical simulations, allowed us to obtain the main geometrical and spectroscopic features of the olive oil constituents under study, which determine their known antioxidant and chemoprotective properties. In fact, it was verified that the spectra comprise distinctive bands for each compound, allowing their ready detection and differentiation.

CONCLUSION

This is the first reported study on the structural behaviour of olive oil phenolic compounds, and it established Raman spectroscopy as a rapid, non-destructive and reliable analytical technique for identifying these bioactive components in dietary extracts. It can surpass other analytical methods currently used, once it allows the concomitant identification of several olive oil components in a particular sample.

Feruloyl dioleoylglycerol antioxidant capacity in phospholipid vesicles

Ferulic acid and its esters are known to be effective antioxidants. Feruloyl dioleoylglycerol was assessed for its ability to serve as an antioxidant in model membrane phospholipid vesicles. The molecule was incorporated into single-lamellar vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine at 1 and 5 mol fractions. Employing a lipid peroxidation inhibition assay, feruloyl dioleoylglycerol was demonstrated to express an oxidation protection ratio relative to Trolox of 0.94 and 0.74 at the 1% and 5% incorporation levels, respectively. The impact of feruloyl dioleoylglycerol incorporation on vesicle integrity was examined by determining calcein-cobalt complex leakage rates. Vesicle leakage was not influenced at 22 or 37 degrees C with 5% feruloyl dioleoylglycerol incorporation in comparison to that of vesicles lacking feruloyl dioleoylglycerol. Resonance energy transfer analysis showed that the closest approach distance between feruloyl dioleoylglycerol and 1,2-dioleoyl-sn-glycero-3-phospho-L-serine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) was approximately 31 A, which indicated that feruloyl dioleoylglycerol was thoroughly distributed throughout the bilayer plane. Conformational analysis determined that feruloyl dioleoylglycerol has a splayed conformation in which its feruloyl moiety is not closely contacted by its oleoyl groups. Feruloyl dioleoylglycerol integrates into the bilayer with its feruloyl moiety oriented close to the hydrophilic/lipophilic interface and its oleoyl groups extended deeply in the membrane. These findings indicate that feruloyl dioleoylglycerol expresses antioxidant activity by intercepting aqueous-phase free radicals as they penetrate the bilayer.