Synthesis and Structural Characterization of a Novel Cyclotetraphosphate

The crystal structure of (2-NH₂-5-ClC₅H₄N)₄P₄O₁₂.6H₂O was determined by X-ray diffraction on a single crystal. This compound crystallizes in an orthorhombic unit cell Pccn with the parameters a = 25,387(7) Å, b = 15,756(6) Å, c = 9,750(5) Å, V = 3900(2) ų, Z = 4, and D _x = 1,605 g.cm^?3. Crystal structure has been determined and refined to R = 0,036, using 7678 independent reflexions. This structure can be described as inorganic layers stacked along a-direction and held together through N-H… O hydrogen bonds, originating from the organic cations, giving rise to three-dimensional H-bonded assemblies. In addition, in this structure there is electrostatic, van der Waal forces and Cl… Cl interaction so as to increase the cohesion of 3D-network. Chemical preparation and characterization by RX diffraction, IR absorption, and thermal analysis are described.     

Lewis acid-catalyzed Csp3–H functionalization of methyl azaarenes with α-trifluoromethyl carbonyl compounds

A Lewis acid promoted Csp³–H bond functionalization of methyl azaarenes with α-trifluoromethylated carbonyl compounds is described. Catalytic amounts of Yb(OTf)₃ provided a straightforward access to the corresponding trifluoromethylated alcohols in excellent yields up to 94% under mild reaction conditions.     

A Pyrimidopyrimidine Janus‐AT Nucleoside with Improved Base‐Pairing Properties to both A and T within a DNA Duplex: The Stabilizing Effect of a Second Endocyclic Ring Nitrogen

Janus bases are heterocyclic nucleic acid base analogs that present two different faces able to simultaneously hydrogen bond to nucleosides that form Watson–Crick base pairs. The synthesis of a Janus‐AT nucleotide analogue, ^N J_AT , that has an additional endocyclic ring nitrogen and is thus more capable of efficiently discriminating T/A over G/C bases when base‐pairing in a standard duplex‐DNA context is described. Conversion to a phosphoramidite ultimately afforded incorporation into an oligonucleotide. In contrast to the first generation of carbocyclic Janus heterocycles, it remains in its unprotonated state at physiological pH and, therefore, forms very stable Watson–Crick base pairs with either A or T bases. Biophysical and computational methods indicate that ^N J_AT is an improved candidate for sequence‐specific genome targeting.     

SYNTHESIS OF TRIFLUOROMETHYL-IMINES BY SOLID ACID/SUPERACID CATALYZED MICROWAVE ASSISTED APPROACH

A new solid acid/superacid catalyzed microwave assisted synthesis of trifluoromethyl-imines is described. Various α,α,α-trifluoromethylketones react readily with primary amines to produce the corresponding imines. Two different strategies have been employed; one is the application of microwave irradiation coupled with solvent-free solid acid catalysis. The other method, for highly deactivated substrates includes the use of a pressure vessel at 175 °C temperature, with solid superacid catalysis. Using the solid acid K-10 montmorillonite or the superacidic perfluorinated resinsulfonic acid Nafion-H, a wide variety of trifluoromethylated imines have been synthesized using the above methods. The products have been isolated in good to excellent yields and high selectivities. This new environmentally friendly synthetic methodology provides significantly higher yields than traditional methods during relatively short reaction times for the preparation of the target compounds.     

Desymmetrised pentaporphyrinic gears mounted on metallo-organic anchors

Mastering intermolecular gearing is crucial for the emergence of complex functional nanoscale machineries. However, achieving correlated motion within trains of molecular gears remains highly challenging, due to the multiple degrees of freedom of each cogwheel. In this context, we designed and synthesised a series of star-shaped organometallic molecular gears incorporating a hydrotris(indazolyl)borate anchor to prevent diffusion on the surface, a central ruthenium atom as a fixed rotation axis, and an azimuthal pentaporphyrinic cyclopentadienyl cogwheel specifically labelled to monitor its motion by non-time-resolved Scanning Tunneling Microscopy (STM). Desymmetrisation of the cogwheels was first achieved sterically, i.e. by introducing one tooth longer than the other four. For optimal mechanical interactions, chemical labelling was also investigated as a preferential way to induce local contrast in STM images, and the electronic properties of one single paddle were modulated by varying the porphyrinic scaffold or the nature of the central metal. To reach such a structural diversity, our modular synthetic approach relied on sequential cross-coupling reactions on a penta(p-halogenophenyl)cyclopentadienyl ruthenium(ii) key building block, bearing a single pre-activated p-iodophenyl group. Chemoselective Sonogashira or more challenging Suzuki–Miyaura reactions allowed the controlled introduction of the tagged porphyrinic tooth, and the subsequent four-fold cross-couplings yielded the prototypes of pentaporphyrinic molecular gears for on-surface studies, incorporating desymmetrised cogwheels over 5 nm in diameter.

Star-shaped cogwheel prototypes incorporating one sterically- or chemically-labelled porphyrinic paddle were designed and synthesised with the aim of achieving intermolecular gearing on surfaces.     

New analogs of temporin-LK1 as inhibitors of multidrug-resistant (MDR) bacterial pathogens

The peptide temporin-LK1 (1) was obtained from the skin secretion of frog Limnonectes kuhlii (Ranidae). It is a unique antimicrobial peptide with 17 residues, including four L-phenylalanines and single glycine. Mass spectrometry and Edmand degradation were used for the determination of sequence of amino acids in temporin-LK 1 (1), and confirmed by cDNA cloning. We report here the synthesis and structural studies of temporin-LK1 (1) and its analogs 2–4. Peptides 2–4 were prepared by substitution of achiral glycine residue of temporin-LK1 (1) with D-alanine, L-phenylglycine, and L-naphthylalanine, respectively. Peptides 1–4 were evaluated against multidrug-resistant (MDR) strains of Staphylococcus aureus and Pseudomonas aeruginosa. Analog 2 was found active against all MDR strains of S. aureus and P. aeruginosa at a much lower dose than the clinically used antibiotics.     

Nitromethane pyrolysis in shock tubes and a micro flow reactor with a controlled temperature profile

Nitromethane has many applications, such as in racing, as a gasoline fuel additive, and as a monopropellant. Despite a large number of studies and the small size of the molecule, the combustion chemistry of nitromethane is still not well understood. To improve models, the pyrolysis of nitromethane (CH₃NO₂) was investigated experimentally in shock tubes and in a micro flow reactor with a controlled temperature profile (MFR), under dilute conditions. Several spectroscopic diagnostics were used in the shock tubes to follow the concentration time histories of CO, H₂O (both using IR laser absorption), and CH₃NO₂ (UV light absorption). A quadrupole mass spectrometer was used to measure CH₃NO₂, NO₂, CH₄, C₂H₄, and C₂H₂ at various temperatures with the MFR. These unique experimental results were compared to modern, detailed kinetics models from the literature, and no mechanism was able to reproduce these data over the wide range of conditions investigated. Predictions for the CO and H₂O levels were generally inaccurate, and the CH₄, C₂H₄, and C₂H₂ predictions were poor in most cases for the MFR data. Importantly, all models largely differ in their predictions. A numerical analysis was performed to identify ways to improve the next generation of nitromethane models. Results indicate that nitromethane decomposition needs to be improved below 1050 K, and that hydrocarbon-NOx interactions still need to be further investigated.     

Ultrasound-Assisted Extraction of Carotenoids from Carrot Pomace and Their Optimization through Response Surface Methodology

Ultrasound-assisted extraction (UAE) was used to extract carotenoids from the carrot pomace. To investigate the effect of independent variables on the UAE, the response surface methodology (RSM) with central-composite design (CCD) was employed. The study was conducted with three independent variables including extraction time (min), temperature (°C), and ethanol concentration (%). The results showed that the optimal conditions for UAE were achieved with an extraction time of 17 min, temperature of 32 °C, and ethanol concentration of 51% of total carotenoids (31.82 ± 0.55); extraction time of 16 min, temperature of 29 °C, and ethanol concentration of 59% for a combination of β-carotene (14.89 ± 0.40), lutein (5.77 ± 0.19), and lycopene (2.65 ± 0.12). The non-significant (p > 0.05) correlation under optimal extraction conditions between predicted and experimental values suggested that UAE is the more productive process than conventional techniques for the extraction of carotenoids from the carrot pomace.     

Key factor affecting the basicity of mesoporous silicas MCM-41: effect of surfactant extraction time and Si/Al ratio

Mesoporous silica Si-MCM-41 was prepared by hydrothermal method using TEOS and CTAB as the source of silica and structuring agent, respectively. The surface of the as-synthesized material was treated using HCl/ETOH solvent to remove the CTA surfactant instead of using the calcination. Characterization of the catalysts was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen sorption at 77 K, scanning and transmission electronic microscopy (SEM, TEM), and thermogravimetric analysis TGA. The catalytic properties of the prepared materials in the condensation of acetophenone with ethyl cyanoacetate were studied. The effects of the catalyst type, Si/Al ratio, reaction kinetics, and reaction temperature were also investigated to find an optimal parameter. The results show that an interesting yield was obtained (about 96%) in a short reaction time; it is found that the yields of products depend not only on the amount of surfactant inside the mesopores but also on the Si/Al ratio. The catalyst reuse shows that this catalyst can be used up to five cycles, and at temperatures higher than 50 °C, the yield of products decreases due to the slight destruction of the catalyst as confirmed by the XRD analysis. Based on the results obtained, a possible mechanism of the condensation reaction of acetophenone was proposed.