The fleeting existence of the classical vinyl cation structure

Using a hyperbolic function type-potential and Schrödinger’s equation transformed into a hypergeometric differential equation along with the results presented from an ab-initio CASSCF(10,11)/cc-pVTZ calculation we show that the potential well of the classical vinyl cation minimum is incapable of supporting a zero point vibrational motion for the protons. Furthermore, as opposed to the previously found transition state linking the classical and bridged vinyl cations, we suggest that it becomes a transition state for the interconversion or tautomerization of the bridged vinyl cation.</p

Contribution of Flavonoids to the Overall Radical Scavenging Activity of Olive (<i>Olea europaea</i> L.) Leaf Polar Extracts

The contribution of flavonoids to the overall radical scavenging activity of olive leaf polar extracts, known to be good sources of oleuropein related compounds, was examined. Off line and on line HPLC-DPPH• assays were employed, whereas flavonoid content was estimated colorimetrically. Individual flavonoid composition was first assessed by RP-HPLC coupled with diode array and fluorescence detectors and verified by LC−MS detection system. Olive leaf was found a robust source of flavonoids regardless sampling parameters (olive cultivar, leaf age or sampling date). Total flavonoids accounted for the 13−27% of the total radical scavenging activity assessed using the on line protocol. Luteolin 7-O-glucoside was one of the dominant scavengers (8−25%). Taking into consideration frequency of appearance the contribution of luteolin (3−13%) was considered important, too. Our findings support that olive leaf, except for oleuropein and related compounds, is also a stable source of bioactive flavonoids

Unprecedented Ultra-High-Resolution Hydroxy Group ¹H NMR Spectroscopic Analysis of Plant Extracts

A general method is demonstrated for obtaining ultra-high resolution in the phenolic hydroxy group ¹H NMR spectroscopic region, in DMSO-<i>d</i>₆ solution, with the addition of picric acid. Line-width reduction by a factor of over 100 was observed, which resulted in line-widths ranging from 1.6 to 0.6 Hz. This unprecedented resolution, in combination with the shielding sensitivity of the hydroxy group absorptions to substituent effects at least up to 11 bonds distant and the application of 2D ¹H–¹³C HMBC techniques, allows the unequivocal structure analysis of natural products with phenolic hydroxy groups in complex plant extracts

Rapid and Direct Low Micromolar NMR Method for the Simultaneous Detection of Hydrogen Peroxide and Phenolics in Plant Extracts

A rapid and direct low micromolar ¹H NMR method for the simultaneous identification and quantification of hydrogen peroxide and phenolic compounds in plant extracts was developed. The method is based on the highly deshielded ¹H NMR signal of H₂O₂ at ∼10.30 ppm in DMSO-<i>d</i>₆ and the combined use of picric acid and low temperature, near the freezing point of the solution, in order to achieve the minimum proton exchange rate. Line widths of H₂O₂ below 3.8 Hz were obtained for several Greek oregano extracts which resulted in a detection limit of 0.7 μmol L^–1. Application of an array of NMR experiments, including 2D ¹H–¹³C HMBC, spiking of the samples with H₂O₂, and variable temperature experiments, resulted in the unequivocal assignment of H₂O₂ precluding any confusion with interferences from intrinsic phenolics in the extract

Understanding Zinc(II) Chelation with Quercetin and Luteolin: A Combined NMR and Theoretical Study

The Zn­(II) chelation with natural flavonoids, quercetin and luteolin, was investigated by the use of NMR spectroscopy and various levels of ab initio calculations. Very sharp phenolic OH 1H resonances in DMSO-d6 were observed for both free and complexed quercetin which allowed (i) the unequivocal assignment with the combined use of 1H–13C HSQC and HMBC experiments and (ii) the determination of complexation sites which were found to be the CO-4 carbonyl oxygen and the deprotonated C-5 OH group of quercetin and CO-4 carbonyl oxygen and the deprotonated C-5 OH group of luteolin. DOSY experiments allowed the determination of the effective molecular weight of the Zn–quercetin complex which was shown to be mainly 1:1. DFT calculations of the 1:1 complex in the gas phase demonstrated that the C-3 O– and CO-4 sites are favored for quercetin at both GGA and LDA approximations and the C-5 O– and CO-4 groups of luteolin at the LDA approximation. Quantum chemical calculations were also performed by means of the conductor polarizable model in DMSO by employing various functionals. The energetically favored Zn chelation sites of the 1:1 complex were found to be either the C-3 O– and CO-4 or C-5 O– and CO-4 sites, depending on the functional used, for quercetin and the C-5 O– and CO-4 sites for luteolin

Selective One-Dimensional Total Correlation Spectroscopy Nuclear Magnetic Resonance Experiments for a Rapid Identification of Minor Components in the Lipid Fraction of Milk and Dairy Products: Toward Spin Chromatography?

We report a rapid, direct, and unequivocal spin-chromatographic separation and identification of minor components in the lipid fraction of milk and common dairy products with the use of selective one-dimensional (1D) total correlation spectroscopy (TOCSY) nuclear magnetic resonance (NMR) experiments. The method allows for the complete backbone spin-coupling network to be elucidated even in strongly overlapped regions and in the presence of major components from 4 × 10² to 3 × 10³ stronger NMR signal intensities. The proposed spin-chromatography method does not require any derivatization steps for the lipid fraction, is selective with excellent resolution, is sensitive with quantitation capability, and compares favorably to two-dimensional (2D) TOCSY and gas chromatography–mass spectrometry (GC–MS) methods of analysis. The results of the present study demonstrated that the 1D TOCSY NMR spin-chromatography method can become a procedure of primary interest in food analysis and generally in complex mixture analysis

Complexes of Zn²⁺, Cd²⁺, and Hg²⁺ with 2-(α-Hydroxybenzyl)thiamine Monophosphate Chloride

The binding sites of Zn2+, Cd2+, and Hg2+ in complexes with 2-(α-hydroxybenzyl)thiamine monophosphate chloride, (LH)+Cl-, have been investigated in the solid state [2-(α-hydroxybenzyl)thiamin monophosphate chloride monoprotonated at the phosphate group and protonated at N1‘ is denoted as (LH)+Cl-; therefore, the ligand monoprotonated at the phosphate group and deprotonated at N1‘ is L]. Complexes of formulae MLCl2, M(LH)Cl3, and (MCl4)2-(LH)2+ (M = Zn2+, Cd2+, and Hg2+) were isolated in aqueous and methanolic solutions, depending on pH. The crystal structure of the complex of formula HgL2Cl2 was solved, together with that of the free ligand (LH)+Cl-, by X-ray crystallography. HgL2Cl2 crystallizes in C2/c, with a = 32.968(6) Å, b = 7.477(2) Å, c = 21.471(4) Å, β = 118.19(1)°, V = 4665(2) Å3, and Z = 4. (LH)+Cl- crystallizes in Cc, with a = 10.951(3) Å, b = 17.579(4) Å, c = 13.373(3) Å, β = 105.36(2)°, V = 2482.4(10) Å3, and Z = 4. Mercury(II) binds to the N(1‘) of the pyrimidine ring. Both ligands are in the S conformation [ΦT = −98.1(9)° and ΦP = 176.1(10)° for HgL2Cl2 and ΦT = 104.1(5)° and ΦP = 171.9(6)° for (LH)+Cl-]. 31P and 13C NMR spectra, together with vibrational spectra (IR/Raman), are used to deduce the binding sites of the metal and the protonation states of the ligand at various pH values. It is found that solid-state 31P NMR spectroscopy is particularly useful in characterizing these complexes as the 31P shielding tensors are sensitive to the state of the phosphate group. On the other hand, the 31P NMR spectra indicate that direct bonding between Zn2+ and Cd2+ to the phosphate can occur under certain preparation conditions. Solid-state 13C NMR and vibrational (IR/Raman) spectroscopic results are also in agreement with the other techniques

Deconvoluting the Dual Antiplatelet Activity of a Plant Extract

A thorough evaluation of the antiplatelet activity profile of hexane olive leaf extract in human platelets indicated a potent activity accomplished through a two axis inhibition of platelet activation triggered both by ADP and thrombin. To delineate the extract components responsible for this dual activity, an NMR based method was established to determine and quantify the triterpenoid content leading to the characterization of uvaol, erythrodiol, and oleanolic acid. The antiplatelet profile of the total extract and of the 3 determined triterpenoids was evaluated against in vitro platelet aggregation induced by several platelet agonists as also on PAC-1 binding and P-selectin membrane expression both in healthy volunteers and in platelets from patients with an acute coronary syndrome receiving dual antiplatelet therapy with aspirin and ticagrelor. The extract was identified to inhibit ADP-induced platelet activation due to its erythrodiol content and TRAP-induced platelet activation due to the activity of uvaol and oleanolic acid

Design and Synthesis of a Potent Cyclic Analogue of the Myelin Basic Protein Epitope MBP_72-85: Importance of the Ala⁸¹ Carboxyl Group and of a Cyclic Conformation for Induction of Experimental Allergic Encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP), such as guinea pig sequence MBP72-85. Two linear and one cyclic analogues based on MBP72-85 have been synthesized and evaluated for EAE induction in Lewis rats. The linear peptide Gln-Lys-Ser-Gln-Arg-Ser-Gln-Asp-Glu-Asn-Pro-Val (1) was found to induce EAE, while substitution of the Asp residue at position 8 with Ala resulted in an analogue (2) which suppressed the induction of EAE by its parent peptide. Nuclear magnetic resonance studies of analogue 1 in dimethyl sulfoxide (DMSO) using TOCSY/ROESY techniques revealed a head-to-tail intramolecular interaction (ROE connectivity between βVal12-γGln1), indicating a pseudocyclic conformation for the immunogenic peptide 1. A conformational model was developed using NMR constraints and molecular dynamics. Based on this model, a novel amide-linked cyclic analogue has been designed and synthesized by connecting the side-chain amino and carboxyl groups of Lys and Glu at positions 2 and 9, respectively, of linear analogue 1. The cyclic analogue (3) had similar activity to the linear peptide 1, and the EAE effects induced by cyclic analogue 3 were completely suppressed by co-injection with the Ala81-substituted analogue 2 in Lewis rats. The similar potencies of analogues 1 and 3 support the proposed cyclic comformation suggested for analogue 1 from NMR studies and computer modeling and provides the basis for designing more potent molecules with improved properties such as increased resistance to degradation. The present findings suggest that a cyclic conformation for the MBP72-85 epitope positions the carboxyl group of Asp81 correctly and presumably other side groups of the peptide such as Arg78 in a manner which enables functional binding of the trimolecular complex MHC−peptide−T cell receptor resulting in EAE

Direct Binding of Bcl‑2 Family Proteins by Quercetin Triggers Its Pro-Apoptotic Activity

Bcl-2 family proteins are important regulators of apoptosis and its antiapoptotic members, which are overexpressed in many types of cancer, are of high prognostic significance, establishing them as attractive therapeutic targets. Quercetin, a natural flavonoid, has drawn much attention because it exerts anticancer effects, while sparing normal cells. A multidisciplinary approach has been employed herein, in an effort to reveal its mode of action including dose–response antiproliferative activity and induced apoptosis effect, biochemical and physicochemical assays, and computational calculations. It may be concluded that, quercetin binds directly to the BH3 domain of Bcl-2 and Bcl-xL proteins, thereby inhibiting their activity and promoting cancer cell apoptosis