Interdonato lemon from Nizza di Sicilia (Italy): chemical composition of hexane extract of lemon peel and histochemical investigation

Considering that the determination of authenticity and of the geographical origin of food is a very challenging issue, in this study we studied by means of histological and histochemical analyses the famous Sicilian lemon known as ‘Interdonato Lemon of Messina PGI’. Since the protected geographical indication Interdonato lemon of Messina possesses high organoleptic properties, the composition of the hexane extract of lemon peel was determined by HRGC and HRGC–MS analyses and compared with that of lemon of different cultivars. The results obtained are informative of the oil’s quality and explain the variation of the lemon essential oil composition. Given the fundamental economic implications of any fraud, the aim of this study was to determine a fingerprint able to evaluate the authentication of the geographic origin in such way to prevent frauds in national and international markets.     

The Effect of Blood Contained in the Samples on the Metabolomic Profile of Mouse Brain Tissue: A Study by NMR Spectroscopy

(1) Recently, metabolic profiling of the tissue in the native state or extracts of its metabolites has become increasingly important in the field of metabolomics. An important factor, in this case, is the presence of blood in a tissue sample, which can potentially lead to a change in the concentration of tissue metabolites and, as a result, distortion of experimental data and their interpretation. (2) In this paper, the metabolomic profiling based on NMR spectroscopy was performed to determine the effect of blood contained in the studied samples of brain tissue on their metabolomic profile. We used 13 male laboratory CD-1^® IGS mice for this study. The animals were divided into two groups. The first group of animals (n = 7) was subjected to the perfusion procedure, and the second group of animals (n = 6) was not perfused. The brain tissues of the animals were homogenized, and the metabolite fraction was extracted with a water/methanol/chloroform solution. Samples were studied by high-frequency ¹H-NMR spectroscopy with subsequent statistical data analysis. The group comparison was performed with the use of the Student’s test. We identified 36 metabolites in the brain tissue with the use of NMR spectroscopy. (3) For the major set of studied metabolites, no significant differences were found in the brain tissue metabolite concentrations in the native state and after the blood removal procedure. (4) Thus, it was shown that the presence of blood does not have a significant effect on the metabolomic profile of the brain in animals without pathologies.     

Revealing the configuration and crystal packing of organic compounds by solid-state NMR spectroscopy: methoxycarbonylurea, a case study

The molecular configuration and intermolecular arrangement of polycrystalline methoxycarbonylurea (MCU) has been studied by a combination of chemical editing, rotational echo double resonance (REDOR) spectroscopy and ab initio calculations. From the multispin IS(n) REDOR experiments several dipolar couplings were determined and converted into distance constraints. Intra- and intermolecular dipolar couplings were distinguished by isotope dilution. The configuration of the MCU molecule can be determined from three torsion angles Psi1, Psi2, and Psi3. Ab initio calculations showed that these angles are either 0 degrees or 180 degrees (Z or E). From the REDOR experiments, the E configuration was found for Psi1 and Psi2 and the Z configuration for Psi3. Thus the configuration of MCU in the solid state was determined to be EEZ. Distance constraints for the intermolecular arrangement of MCU were obtained by performing REDOR experiments on 13C15N2 MCU with different degrees of isotope dilution and on a cocrystallized 1:1 mixture of 13C(urea) MCU and 15N(amide) MCU. By combining these distance constraints with molecular modeling, three different possible packing motifs for MCU molecules were found. The molecules in these motifs are arranged as linear chains with methoxy groups at the borders of the chains. All the intermolecular hydrogen bond donors and acceptors in the interior of the chain are saturated.     

The prediction of the absolute stereochemistry of primary and secondary 1,2-diols by 1H NMR spectroscopy: principles and applications

The absolute configuration of 1,2-diols formed by a primary and a secondary (chiral) hydroxyl group can be deduced by comparison of the 1H NMR spectra of the corresponding (R)- and bis-(S)-MPA esters (MPA = methoxyphenylacetic acid). This method involves the use of the chemical shifts of substituents L1/L2 attached to the secondary (chiral) carbon, and of the hydrogen atom linked to the chiral center (C alpha-H) as diagnostic signals. Theoretical (AM1, HF, and B3 LYP calculations) and experimental data (dynamic and low-temperature NMR spectroscopy, studies on deuterated derivatives, constant coupling analysis, circular dichroism (CD) spectra, and NMR studies with a number of diols of known absolute configuration) prove that the signs of the delta delta(RS) obtained for those signals correlate with the absolute configuration of the diol. A graphical model for the reliable assignment of the absolute configuration of a 1,2-diol by comparison of the NMR spectra of its bis-(R)- and bis-(S)-MPA esters is presented.     

Revealing the Fine Details of Functionalized Silica Surfaces by Solid‐State NMR and Adsorption Isotherm Measurements: The Case of Fluorinated Stationary Phases for Liquid Chromatography

The structural and chromatographic characterization of two novel fluorinated mesoporous materials prepared by covalent reaction of 3‐(pentafluorophenyl)propyldimethylchlorosilane and perfluorohexylethyltrichlorosilane with 2.5 μm fully porous silica particles is reported. The adsorbents were characterized by solid state ²⁹Si, ¹³C, and ¹⁹F NMR spectroscopy, low‐temperature nitrogen adsorption, elemental analysis (C and F), and various chromatographic measurements, including the determination of adsorption isotherms. The structure and abundance of the different organic surface species, as well as the different silanol types, were determined. In particular, the degree of so‐called horizontal polymerization, that is, Si‐O‐Si bridging parallel to the silica surface due to the reaction, under “quasi‐dry” conditions, of trifunctional silanizing agents with the silica surface was quantified. Significant agreement was found between the information provided by solid‐state NMR, elemental analysis, and excess isotherms regarding the amount of surface residual silanol groups, on the one hand, and the degree of surface functionalization, on the other. Finally, the kinetic performance of the fluorinated materials as separation media for applications in near‐ultrahigh‐performance liquid chromatography was evaluated. At reduced velocities of about 5.5 (ca. 600 bar backpressure at room temperature) with 3 mm diameter columns and toluene as test compound, reduced plate heights on the order of 2 were obtained on columns of both adsorbents.     

The application of (199)Hg NMR and (199m)Hg perturbed angular correlation (PAC) spectroscopy to define the biological chemistry of Hg(II): a case study with designed two- and three-stranded coiled coils

The use of de novo designed peptides is a powerful strategy to elucidate Hg(II)-protein interactions and to gain insight into the chemistry of Hg(II) in biological systems. Cysteine derivatives of the designed alpha-helical peptides of the TRI family [Ac-G-(L(a)K(b)A(c)L(d)E(e)E(f)K(g))(4)-G-NH(2)] bind Hg(II) at high pH values and at peptide/Hg(II) ratios of 3:1 with an unusual trigonal thiolate coordination mode. The resulting Hg(II) complexes are good water-soluble models for Hg(II) binding to the protein MerR. We have carried out a parallel study using (199)Hg NMR and (199m)Hg perturbed angular correlation (PAC) spectroscopy to characterize the distinct species that are generated under different pH conditions and peptide TRI L9C/Hg(II) ratios. These studies prove for the first time the formation of [Hg{(TRI L9C)(2)-(TRI L9C-H)}], a dithiolate-Hg(II) complex in the hydrophobic interior of the three-stranded coiled coil (TRI L9C)(3). (199)Hg NMR and (199m)Hg PAC data demonstrate that this dithiolate-Hg(II) complex is different from the dithiolate [Hg(TRI L9C)(2)], and that the presence of third alpha-helix, containing a protonated cysteine, breaks the symmetry of the coordination environment present in the complex [Hg(TRI L9C)(2)]. As the pH is raised, the deprotonation of this third cysteine generates the trigonal thiolate-Hg(II) complex Hg(TRI L9C)(3)(-) on a timescale that is slower than the NMR timescale (0.01-10 ms). The formation of the species [Hg{(TRI L9C)(2)(TRI L9C-H)}] is the result of a compromise between the high affinity of Hg(II) to form dithiolate complexes and the preference of the peptide to form a three-stranded coiled coil.     

The investigation on the NH reactivity of pentacoordinate spirophosphoranes by H/D exchange and NMR experiments

Different pentacoordinate spirophosphoranes were investigated by H/D exchange and NMR tracking experiments. The H/D exchanged site of spirophosphoranes was confirmed to be the NH bond instead of the PH bond according to the integration of the signal changes in proton-decoupled, proton-coupled ³¹P NMR and ¹H NMR tracking experiments. The reactivity of NH bond at the spiroring of spirophosphoranes was explored by the rate constant of H/D exchange of different spirophosphoranes. The results demonstrated that the reactivity of NH bond of spirophosphoranes was influenced by steric hindrance and the species of substituent at phosphorus atom, and the electronic effect of the substituent was the main effect factor on the reactivity of the NH bond. The strong electron-withdrawing group at phosphorus resulted in more reactive NH bond of spirophosphoranes. These results are beneficial to further understand and explore the characteristics of pentacoordinate spirophosphoranes.