Theoretical characterization of the chemical bonds of some three-membered ring compounds through QTAIM theory

Structural Chemistry - In this paper, we investigate the nature of the carbonyl and the intraring C–C, C–N, C–O, N–N, O–O and N–O bonds of cyclopropanone and the...     

Iron Oxide Nanoparticles Labeled with an Excited‐State Intramolecular Proton Transfer Dye

Excited‐state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica‐coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.     

Efficiency of the refocused 31P-29Si MAS-J-INEPT NMR experiment for the characterization of silicophosphate crystalline phases and amorphous gels

One- and two-dimensional refocused MAS-J-INEPT NMR experiments in the solid state (through-bond polarization transfer) involving the highly abundant 31P spin and the rare 29Si spin are described for the crystalline silicophosphate phase Si5O(PO4)6 and complex mixtures of SiP2O7 polymorphs. The evaluation of the 2JP-O-Si coupling constants for all 29Si sites is obtained by the careful analysis of the INEPT build-up curves under fast MAS. The results are in agreement with the crystallographic data, taking into account the various J coupling paths. The efficiency of the experiment is demonstrated by its application to more complex systems such as silicophosphate amorphous gels (obtained by the sol-gel process).     

Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry of monoterpenoids as a powerful tool for grape origin traceability

The establishment of the monoterpenoid profile of Vitis vinifera L. cv. 'Fern?o-Pires' white grape was achieved by headspace solid-phase microextraction coupled with comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-ToF-MS). The plot of the first dimension versus the second dimension retention times using the m/z 93, 121, and 136 was used. The grapes were found to contain 56 monoterpenoids identified by GCxGC-ToF-MS. From these, 20 were reported for the first time in grapes. According to their chemical structure, the compounds were organized in different groups: monoterpene hydrocarbons and monoterpene oxygen-containing compounds, this later divided in oxides, alcohols (monoterpenols and monoterpendiols), aldehydes, esters, and ketones. A database composed by the retention indices of monoterpenoids calculated in the bi-dimensional column set was created, representing a developmental step in monoterpenoid analysis using a GCxGC system. Remarkable results were also obtained in terms of compound classification based on the organized structure of the peaks of structurally related compounds in the GCxGC contour plot. This information represents a valuable approach for future studies, as the ordered-structure principle can considerably help the establishment of the composition of samples. This study proposes a methodology and provides data that can be applied to determine the monoterpenoid profile of grapes, and its extension to the analysis of musts, and wines. As monoterpenoids are secondary metabolites whose synthesis is encoded by variety-related genes, the terpenoid profile may be used as a way to trace its varietal origin.     

Adsorption of the fusogenic peptide B18 onto solid surfaces: insights into the mechanism of peptide assembly

The adsorption and assembly of B18 peptide on various solid surfaces were studied by reflectometry techniques and atomic force microscopy. B18 is the minimal membrane binding and fusogenic motif of the sea urchin protein bindin, which mediates the fertilization process. Silicon substrates were modified to obtain hydrophilic charged surfaces (oxide layer and polyelectrolyte multilayers) and hydrophobic surfaces (octadecyltrichlorosilane). B18 does not adsorb on hydrophilic positively charged surfaces, which was attributed to electrostatic repulsion since the peptide is positively charged. In contrast, the peptide irreversibly adsorbs on negatively charged hydrophilic as well as on hydrophobic surfaces. B18 showed higher affinity for hydrophobic surfaces than for hydrophilic negatively charged surfaces, which must be due to the presence of hydrophobic side chains at both ends of the molecule. Atomic force microscopy provided the indication that lateral diffusion on the surface affects the adsorption process of B18 on hydrophobic surfaces. The adsorption of the peptide on negatively charged surfaces was characterized by the formation of globular clusters.     

The degree of the bicanonical map of a surface with

In this note it is shown that, given a smooth minimal complex surface of general type with , , for which the bicanonical map is a morphism, the degree of is not 3. This completes our earlier results, showing that if is a minimal surface of general type with , such that is free, then the bicanonical map of can have degree 1, 2 or 4.

     

Solvent Mixture Optimization in the Extraction of Bioactive Compounds and Antioxidant Activities from Garlic (Allium sativum L.)

Garlic is a health promoter that has important bioactive compounds. The bioactive extraction is an important step in the analysis of constituents present in plant preparations. The purpose of this study is to optimize the extraction with the best proportion of solvents to obtain total phenolic compounds (TPC) and thiosulfinates (TS) from dried garlic powder, and evaluate the antioxidant activities of the optimized extracts. A statistical mixture simplex axial design was used to evaluate the effect of solvents (water, ethanol, and acetone), as well as mixtures of these solvents, after two ultrasound extraction cycles of 15 min. Results showed that solvent mixtures with a high portion of water and pure water were efficient for TPC and TS recovery through this extraction procedure. According to the regression model computed, the most significant solvent mixtures to obtain high TPC and TS recovery from dried garlic powder are, respectively, the binary mixture with 75% water and 25% acetone and pure water. These optimized extracts presented oxygen radical absorbance capacity. Pure water was better for total antioxidant capacity, and the binary mixture of water–acetone (75:25) was better for DPPH scavenging activity. These optimized extracts can be used for industrial and research applications.     

Catalytic Transfer Hydrogenation and Acid Reactions of Furfural and 5-(Hydroxymethyl)furfural over Hf-TUD-1 Type Catalysts

Heterogeneous catalysis, which has served well the petrochemical industry, may valuably contribute towards a bio-based economy by sustainably enabling selective reactions to renewable chemicals. Carbohydrate-containing matter may be obtained from various widespread sources and selectively converted to furanic platform chemicals: furfural (Fur) and 5-(hydroxymethyl)furfural (Hmf). Valuable bioproducts may be obtained from these aldehydes via catalytic transfer hydrogenation (CTH) using alcohols as H-donors under relatively moderate reaction conditions. Hafnium-containing TUD-1 type catalysts were the first of ordered mesoporous silicates explored for the conversion of Fur and Hmf via CTH/alcohol strategies. The materials promoted CTH and acid reactions leading to the furanic ethers. The bioproducts spectrum was broader for the reaction of Fur than of Hmf. A Fur reaction mechanism based on literature data was discussed and supported by kinetic modelling. The influence of the Hf loading and reaction conditions (catalyst load, type of alcohol H-donor, temperature, initial substrate concentration) on the reaction kinetics was studied. The reaction conditions were optimized to maximize the yields of 2-(alkoxymethyl)furan ethers formed from Fur; up to 63% yield was reached at 88% Fur conversion, 4 h/150 °C, using Hf-TUD-1(75), which was a stable catalyst. The Hf-TUD-1(x) catalysts promoted the selective conversion of Hmf to bis(2-alkoxymethyl)furan; e.g., 96% selectivity at 98% Hmf conversion, 3 h/170 °C for Hf-TUD-1(50).     

Magnetic coupling between Gd and Pr ions and magnetocaloric effect in Gd0.5Pr0.5Al2 compound

In this work, we report the theoretical and experimental investigations on the magnetic and magnetocaloric properties for Gd_0.5Pr_0.5Al₂ compound in different magnetic fields. The magnetization features indicate that Gd_0.5Pr_0.5Al₂ is ferrimagnetic at low temperatures. We also present data from X-ray magnetic circular dichroism (XMCD) experiments for this compound, with which we have confirmed that the magnetic moments of the Pr ions are antiparallel to the magnetic moments of the Gd ions. The magnetocaloric parameters, ΔT_S and ΔS_T, were obtained from calorimetric data and both curves present normal and inverse magnetocaloric effect. A theoretical model for ferrimagnetic coupling, including the crystalline electrical field anisotropy, was used to describe the ΔT_S and ΔS_T experimental results.     

Liquid–liquid miscibility and volumetric properties of aqueous solutions of ionic liquids as a function of temperature

The volumetric properties of seven {water + ionic liquid} binary mixtures have been studied as a function of temperature from (293 to 343) K. The phase behaviour of the systems was first investigated using a nephelometric method and excess molar volumes were calculated from densities measured using an Anton Paar densimeter and fitted using a Redlich–Kister type equation. Two ionic liquids fully miscible with water (1-butyl-3-methylimidazolium tetrafluoroborate ([C₁C₄Im][BF₄]) and 1-ethyl-3-methylimidazolium ethylsulfate ([C₁C₂Im][EtSO₄])) and five ionic liquids only partially miscible with water (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₁C₂Im][NTf₂]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₁C₄Im][NTf₂]), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₁C₄Im][PF₆]), 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C₁C₄Pyrro][NTf₂]), and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N₄₁₁₁][NTf₂])) were chosen. Small excess volumes (less than 0.5 cm³ · mol^?1 at 298 K) are obtained compared with the molar volumes of the pure components (less than 0.3% of the molar volume of the pure ionic liquid). For all the considered systems, except for {[C₁C₂Im][EtSO₄] + water}, positive excess molar volumes were calculated. Finally, an increase of the non-ideality character is observed for all the systems as temperature increases.