Vibrational Circular Dichroism and Theoretical Study of the Conformational Equilibrium in (−)‐S‐Nicotine

We report an extensive study of the molecular and electronic structure of (?)‐S‐nicotine, to deduce the phenomenon that controls its conformational equilibrium and to solve its solution‐state conformer population. Density functional theory, ab initio, and molecular mechanics calculations were used together with vibrational circular dichroism (VCD) and Fourier transform infrared spectroscopies. Calculations and experiments in solution show that the structure and the conformational energy profile of (?)‐S‐nicotine are not strongly dependent on the medium, thus suggesting that the conformational equilibrium is dominated by hyperconjugative interactions rather than repulsive electronic effects. The analysis of the first recorded VCD spectra of (?)‐S‐nicotine confirmed the presence of two main conformers at room temperature. Our results provide further evidence of the hypersensitivity of vibrational optical activity spectroscopies to the three‐dimensional structure of chiral samples and prove their suitability for the elucidation of solution‐state conformer distribution.     

Commercial Origanum compactum Benth. and Cinnamomum zeylanicum Blume essential oils against natural mycoflora in Valencia rice

Chemical composition of commercial Origanum compactum and Cinnamomum zeylanicum essential oils and the antifungal activity against pathogenic fungi isolated from Mediterranean rice grains have been investigated. Sixty-one compounds accounting for more than 99.5% of the total essential oil were identified by using gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). Carvacrol (43.26%), thymol (21.64%) and their biogenetic precursors p-cymene (13.95%) and γ-terpinene (11.28%) were the main compounds in oregano essential oil, while the phenylpropanoids, eugenol (62.75%), eugenol acetate (16.36%) and (E)-cinnamyl acetate (6.65%) were found in cinnamon essential oil. Both essential oils at 300 μg/mL showed antifungal activity against all tested strains. O. compactum essential oil showed the best antifungal activity towards Fusarium species and Bipolaris oryzae with a total inhibition of the mycelial growth. In inoculated rice grains at lower doses (100 and 200 μg/mL) significantly reduced the fungal infection, so O. compactum essential oil could be used as ecofriendly preservative for field and stored Valencia rice.     

Strained Ruthenium Complexes Bearing Tridentate Guanidine-Derived Ligands

The dimer [{(η⁶-p-cymene)RuCl}₂(μ-Cl)₂] (cymene=MeC₆H₄ⁱPr) reacts with N,N′-bis(p-tolyl)-N′′-(2-pyridinylmethyl)guanidine ( H₂L1 ) and N,N′-bis(p-tolyl)-N′′-(2-diphenylphosphanoethyl)guanidine ( H₂L2 ), in the presence of NaSbF₆, giving rise to chlorido compounds of formula [(η⁶-p-cymene)RuCl( H₂L )][SbF₆] ( H₂L = H₂L1 ( 1 ), H₂L2 ( 2 )) in which the guanidine ligand adopts a κ² chelate coordination mode. The related ligand (S)-N,N′-bis(p-tolyl)-N′′-(1-isopropyl, 2-diphenylphosphano ethyl)guanidine ( H₂L3 ) affords mixtures of the corresponding chlorido compound [(η⁶-p-cymene)RuCl( H₂L3 )][SbF₆] ( 3 ) together with the complexes [(η⁶-p-cymene)RuCl₂( H₃L3 )][SbF₆] ( 4 ) and [(η⁶-p-cymene)Ru(κ³N,N′,P- HL3 )][SbF₆] ( 10 ) which contain phosphano-guanidinium and phosphano-guanidinate ions acting as monodentate and tridentate ligand, respectively. Compounds 1 , 2 and mixture of 3 / 4 / 10 react with AgSbF₆ rendering the cationic aqua-complexes [(η⁶-p-cymene)Ru( H₂L )(OH₂)][SbF₆]₂ ( H₂L = H₂L1 ( 5 ), H₂L2 ( 6 ), H₂L3 ( 7 )). These aqua-complexes exhibit a temperature-dependent fluxional process in solution. Experimental NMR studies and DFT theoretical calculations on complex 6 suggest that the process involves the exchange between two rotamers around one of the C−N guanidine bonds. Treatment of 5 – 7 with NaHCO₃ renders the complexes [(η⁶-p-cymene)Ru(κ³N,N′,N′′- HL1 )][SbF₆] ( 8 ) and [(η⁶-p-cymene)Ru(κ³N,N′,P- HL )][SbF₆] ( HL = HL2 ( 9 ), HL3 ( 10 )), respectively, in which the HL ligand adopts a fac κ³ coordination mode. The new complexes have been characterized by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1 , 2 , 5 , 9 and 10 , by X-ray diffractometric methods.     

UEGO, an Abstract Clustering Technique for Multimodal Global Optimization

In this paper, UEGO, a new general technique for accelerating and/or parallelizing existing search methods is suggested. The skeleton of the algorithm is a parallel hill climber. The separate hill climbers work in restricted search regions (or clusters) of the search space. The volume of the clusters decreases as the search proceeds which results in a cooling effect similar to simulated annealing. Besides this, UEGO can be effectively parallelized; the communication between the clusters is minimal. The purpose of this communication is to ensure that one hill is explored only by one hill climber. UEGO makes periodic attempts to find new hills to climb. Empirical results are also presented which include an analysis of the effects of the user-given parameters and a comparison with a hill climber and a GA.     

Spectrometric-based techniques for metal-binding protein assessment in clinical,environmental, and food samples

Metalloproteins and metal–protein complexes play key roles in all organisms. For example, certain metalloproteins are involved in metal homeostasis and detoxification, or oxidative stress protection; whereas, metals serve as essential cofactors in a large number of metal–protein complexes. Advances in analytical instrumentation as well as informatics have allowed a complete characterization/assessment of both metalloproteins and metal–protein complexes. In some cases, the identification of the protein is a key factor for understanding its physiological function, such as when assessing protein corona in nanoparticles–protein assemblies. On other occasions, the identification of the binding sites in the peptide chain and conformational changes as a consequence of the metal–protein interaction, as well as the lability of this interaction, can explain the role of these metal-based biomolecules in living organisms. This article attempts to critically review the current state-of-the-art of the available analytical techniques for characterizing metalloproteins and metal–protein complexes. Methods for assessing the structure, characterization of the metal-binding sites, as well as the class of proteins involved in some metal (metallic nanoparticle)-binding proteins are discussed. Recent developments when assessing metalloproteins and metal–protein complexes in the clinical, environmental, and food fields, and pioneering research regarding nanoparticle–protein characterization, are also reviewed.     

Effect of Ultrasound-Assisted Extraction of Carotenoids from Papaya (Carica papaya L. cv. Sweet Mary) Using Vegetable Oils

By-products from fruits and are of great interest for their potential use in the food industry due to their high content of bioactive compounds. Herein, we examined the ultrasound-assisted extraction (UAE) of carotenoid and carotenoid esters from papaya pulp and peel using soybean oil and sunflower oil as alternative green solvents. Response surface methodology (RSM) was established to optimize the UAE process. Three independent variables, ultrasonic amplitude (20–60%), time (10–60 min), and co-solvent percentage (ethanol) (5–20%, v/v), were applied. The highest total carotenoid content in the UAE extracts was obtained from papaya pulp extracts (58.7 ± 1.6 and 56.0 ± 1.5 μg carotenoids/g oil) using soybean oil and sunflower oil, respectively (60% amplitude/ 10 min/ 20% ethanol). On the other hand, the highest carotenoid content (52.0 ± 0.9 μg carotenoids/g oil) was obtained from papaya peel using soybean oil applying the UAE process (20% amplitude/ 77 min/ 20% ethanol); a minor content of 39.3 ± 0.5 μg carotenoids/g oil was obtained from papaya peel using sunflower oil at 60% amplitude/ 60 min/ 5% ethanol. Lycopene was the most abundant carotenoid among all individual carotenoids observed in papaya oil extracts, obtaining the highest yields of this carotenoid when papaya pulp and peel were extracted using soybean oil (94% and 81%, respectively) and sunflower oil (95% and 82%, respectively). Great extraction of xanthophyll esters was detected using 20% of ethanol in the vegetable oil extraction solvent (v/v). High correlations (>0.85) was obtained between total carotenoid content and color determination in the UAE oil extracts. UAE vegetable oil extracts enriched with carotenoids from papaya by-products could be useful to formulate new food ingredients based on emulsions with interesting potential health benefits.