A conformational study of hydroxylated isoflavones by vibrational spectroscopy coupled with DFT calculations

Abstract

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Vibrational analysis of α-cyanohydroxycinnamic acid

“…However, the aromatic rings deformation modes only give rise to strong IR bands and are generally undetectable in the Raman spectra since the corresponding in-plane modes are more Raman active [50]. The peaks observed are the weakest for the CA sample (Fig.…”

Raman microspectroscopy for probing the impact of a dietary antioxidant on human breast cancer cells

“…pH, temperature, ionic strength or exposure to drugs). 22,27,28 Following previous studies by the authors on dietary polyphenolic compounds -both regarding their structural and conformational preferences 17,[29][30][31][32][33][34][35][36][37][38][39][40] and their chemopreventive and/or chemotherapeutic properties towards several cancer cells -the present work reports the effect of daidzein on the biochemical profile of two human breast cancer cell lines: MCF-7 (estrogendependent, ER + ) and MDA-MB-231 (estrogen-independent, ER -). The results thus obtained are expected to help establishing an accurate balance between DAID´s antioxidant and prooxidant capacities, aiming at a prospective use against breast cancer: either as a chemopreventive agent (sole or in combination with other flavones) or as an adjuvant in chemotherapy (coupled with conventional drugs such as tamoxifen, paclitaxel, docetaxel, methotrexate, gemcitabine or doxorubicin 41,42 and cisplatin.…”

Addressing Facts and Gaps in the Phenolics Chemistry of Winery By-Products

“…For instance, in different crystallization procedures, the same compound can display distinct conformations in the solid state, which is due to this kind of H-bond interaction, formed during the crystallization, and occur within the crystal lattice [ 124 , 125 , 126 ]. Moreover, those interactions occurring at the intra-molecular level can lead to the formation of additional cyclic structures, mainly in the case of flavonoids, for instance, the enolic –OH group in the position C-3 in flavones forms a relatively weak hydrogen bond with the neighbouring carbonyl group ( Figure 2 III), which increases planarity, and thus electronic delocalization, consequently increasing their ability to accomodate one unpaired electron with minimal fuss, thus facilitating the liberation of an H atom [ 126 , 127 , 128 , 129 ]. Furthermore, this effect is exacerbated when the C-3 position is occupied by a carboxylic group, with the spatial proximity between the H atom and the C4=O leading to a strong H-bond type interaction, and forming a rather stable 6-atom ring, as observed in the case of a 5-OH ( Figure 2 IV,V), which is reflected in the anomalous high pka presented by such a compound of ca.…”

“…As a consequence of the contribution of this kind of interactions to enhance molecular stability, its occurrence, which is preferred respecting non-bonded conformations [ 129 ], can also contribute to the retention of the H-atom. For instance, concerning the flavonoids, 7-hydroxyflavone and chrysin (5,7-hydroxyflavone), the –OH group in position 5, in the latter, is blocked by the H-bond interaction with the neighbouring carbonyl ( Figure 3 ), while these compounds display equivalent antioxidant activity, therefore, it can be elated that the functional moiety is the –OH in position 7 [ 125 , 132 ].…”

“…In fact, quercetin, a very-well known antioxidant flavonoid, from which several derivatives are found in distinct winery industry residues ( Figure 3 ; Table 3 ) presents most of the aforementioned structural features, thus, representing a good model to summarise all the distinct dynamics that may occur simultaneously concerning this kind of polyphenols, due to the intricate interplay between non-covalent interactions in this molecule. In this sense, the reactivity of the 7-OH is reduced respecting the same OH group in 7-hydroxyflavone, due to the remote H-bond effect exerted by the 5-OH, besides other groups [ 125 , 129 ]. On the other hand, the 3-OH in quercetin is expected to be more reactive than in 3-hydroxyflavone, since in quercetin the carbonyl group is also involved in a H-bond from the 5-OH ( Figure 3 IV), thus representing a relatively weaker HBA group, respecting the former compound [ 95 , 125 , 132 ].…”