Synergistic Strategies in Aminocatalysis

Synergistic catalysis offers the unique possibility of simultaneous activation of both the nucleophile and the electrophile in a reaction. A requirement for this strategy is the stability of the active species towards the reaction conditions and the two concerted catalytic cycles. Since the beginning of the century, aminocatalysis has been established as a platform for the stereoselective activation of carbonyl compounds through HOMO-raising or LUMO-lowering. The burgeoning era of aminocatalysis has been driven by a deep understanding of these activation and stereoinduction modes, thanks to the introduction of versatile and privileged chiral amines. The aim of this review is to cover recent developments in synergistic strategies involving aminocatalysis in combination with organo-, metal-, photo-, and electro-catalysis, focusing on the evolution of privileged aminocatalysts architectures.     

Glycidol syntheses and valorizations: Boosting the glycerol biorefinery

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1H-NMR Profiling Shows as Specific Constituents Strongly Affect the International EVOO Blends Characteristics: The Case of the Italian Oil

Considering the growing number of extra virgin olive oil (EVOO) producers in the world, knowing the influence of olive oils with different geographical origins on the characteristics of the final blend becomes an interesting goal. The present work is focused on commercial organic EVOO blends obtained by mixing multiple oils from different geographical origins. These blends have been studied by ¹H-NMR spectroscopy supported by multivariate statistical analysis. Specific characteristics of commercial organic EVOO blends originated by mixing oils from Italy, Tunisia, Portugal, Spain, and Greece were found to be associated with the increasing content of the Italian component. A linear progression of the metabolic profile defined characteristics for the analysed samples—up to a plateau level—was found in relation to the content of the main constituent of the Italian oil, the monocultivar Coratina. The Italian constituent percentage appears to be correlated with the fatty acids (oleic) and the polyphenols (tyrosol, hydroxytyrosol, and derivatives) content as major and minor components respectively. These results, which highlight important economic aspects, also show the utility of ¹H-NMR associated with chemometric analysis as a powerful tool in this field. Mixing oils of different national origins, to obtain blends with specific characteristics, could be profitably controlled by this methodology.     

Review of aminopolycarboxylic acids–based metal complexes application to water and wastewater treatment by (photo-)Fenton process at neutral pH

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Theoretical study on Pd dimer and trimer interaction with the hydrogen molecule

The H₂ interaction with the Pd dimer and trimer were studied using multiconfigurational self-consistent field (MC-SCF) calculations with the relativistic effective core potential (RECP); the correlation energy correction was included in the extended multireference configuration interaction (MRCI), variational and perturbative to second order. Here, we considered the Pd₂ first six states: ³Σ⁺_u, ¹Σ⁺_g, ³Π_g, ³Δ_xy, ¹Σ⁺_u, and ³Σ⁺_g. For them, the four geometrical approaches included were the side-on H₂ toward Pd₂, for the hydrogen molecule in and out the Pd dimer plane; the perpendicular end-on H₂ toward Pd₂; and the perpendicular end-on Pd₂ to H₂. The Pd₂ ground state is ³Σ⁺_u, which only captures H₂ in the C_2v end-on approach, softly relaxing the H(SINGLE BOND)H bond. The closed-shell ¹Σ⁺_g captures the H₂ molecule in all the approaches considered: The side-on approach of this state presents deep wells and relaxes the H(SINGLE BOND)H bond, and the end-on approach captures H₂ with a relatively longer H(SINGLE BOND)H distance and also a deep well. The ³Π_g state was the only one which did not capture H₂. For the triangular Pd₃ clusters, H₂ was approached in the C_2v symmetry in and out of the Pd₃ plane. In the triangular case, H₂ was absorbed in both spin states, with deep wells and relaxing the H(SINGLE BOND)H distance. The linear Pd₃ singlet and triplet states capture outside of the Pd₃ and break the H(SINGLE BOND)H bond. © 1997 John Wiley & Sons, Inc.     

Pomegranate By-Products as Natural Preservative to Prolong the Shelf Life of Breaded Cod Stick

This work evaluated the efficacy of pomegranate byproducts, specifically peel powder, as valid preservatives for food quality. Ready-to-cook cod sticks breaded with pomegranate peel powder were prepared. Shelf-life tests were conducted on breaded cod sticks during refrigerated storage (17 days) at 4 °C, monitoring the pH, microbiological and sensory quality. In addition, the nutritional quality of both the breaded and control samples was assessed. The results highlighted that active samples showed higher phenol and flavonoid content and higher antioxidant activity compared to the control fish, suggesting that pomegranate peel powder was responsible for a significant increase in cod stick nutritional quality. Furthermore, the cod stick active breading led to a delay in microbial growth without affecting the sensory properties; rather, it helped slow down the sensory attribute decline during the refrigerated storage. The data suggest that using pomegranate byproducts in breaded cod stick was effective in prolonging its shelf life, as well as improving its nutritional quality. Therefore, pomegranate peel powder can be considered as a potential resource as natural food preservative.     

Monitoring of the Pre-Equilibrium Step in the Alkyne Hydration Reaction Catalyzed by Au(III) Complexes: A Computational Study Based on Experimental Evidences

The coordination ability of the [(ppy)Au(IPr)]²⁺ fragment [ppy = 2-phenylpyridine, IPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene] towards different anionic and neutral X ligands (X = Cl⁻, BF₄⁻, OTf⁻, H₂O, 2-butyne, 3-hexyne) commonly involved in the crucial pre-equilibrium step of the alkyne hydration reaction is computationally investigated to shed light on unexpected experimental observations on its catalytic activity. Experiment reveals that BF₄⁻ and OTf⁻ have very similar coordination ability towards [(ppy)Au(IPr)]²⁺ and slightly less than water, whereas the alkyne complex could not be observed in solution at least at the NMR sensitivity. Due to the steric hindrance/dispersion interaction balance between X and IPr, the [(ppy)Au(IPr)]²⁺ fragment is computationally found to be much less selective than a model [(ppy)Au(NHC)]²⁺ (NHC = 1,3-dimethylimidazol-2-ylidene) fragment towards the different ligands, in particular OTf⁻ and BF₄⁻, in agreement with experiment. Effect of the ancillary ligand substitution demonstrates that the coordination ability of Au(III) is quantitatively strongly affected by the nature of the ligands (even more than the net charge of the complex) and that all the investigated gold fragments coordinate to alkynes more strongly than H₂O. Remarkably, a stabilization of the water-coordinating species with respect to the alkyne-coordinating one can only be achieved within a microsolvation model, which reconciles theory with experiment. All the results reported here suggest that both the Au(III) fragment coordination ability and its proper computational modelling in the experimental conditions are fundamental issues for the design of efficient catalysts.     

Density and Sound Velocity Studies of Aqueous Solutions of Tetradecyltrimethylammonium Nitrate at Different Temperatures

The density and ultrasound velocity of aqueous solutions of tetradecyltrimethylammonium nitrate were measured in the temperature range of 15 to 35°C in 5°C intervals. The concentration range covered the premicellar and micellar regimes. By assuming a pseudophase separation model for the micellar system, we applied the densitometric data to estimate the apparent molar volumes and the apparent thermal expansibility coefficients of the surfactant in monomeric and micellar forms. Ultrasound velocity and density data enabled us to estimate the isentropic compressibility of the surfactant in both forms. The results are compared with relevant literature data for alkyltrimethylammonium bromides.     

An insight into the aromaticity of fullerene anions: experimental evidence for diamagnetic ring currents in the five-membered rings of C(60)(6-) and C(70)(6-)

Reduction of the two "closed" [6,6] methanofullerenes, [6,6]C(61)H(2) (1) and [6,6]C(71)H(2) (5), to the corresponding hexaanions with lithium metal causes the bridgehead-bridgehead bonds to open, at least partially, and this change gives rise to diamagnetic ring currents in the resulting homoconjugated six-membered rings (6-MRs). These new ring currents shield the overlying hydrogen atoms on the methylene bridge and induce upfield shifts of 1.60 and 0.11 ppm in their (1)H NMR resonances, respectively. Analogous reduction of the already "open" [5,6]methanofullerenes, [5,6]C(61)H(2) (2) and [5,6]C(71)H(2) (3 and 4), only slightly enhances the shielding of the hydrogen atoms over the homoconjugated 6-MRs (upfield shifts of 0.13, 0.68, and 0.14 ppm, respectively) but leads to exceptionally strong diamagnetic ring currents in the homoconjugated five- membered rings (5-MRs), as evidenced by dramatic shielding of the hydrogen atoms situated over them (upfield shift of 5.01, 6.78, and 1.63 ppm, respectively). The strongest shielding is seen for the hydrogen atom sitting over the 5-MR at the pole of C(71)H(2)(6)(-) (delta = -0.255 ppm) indicating that the excess charge density is concentrated at the poles.