Enhanced resolution of Mentha piperita volatile fraction using a novel medium‐polarity ionic liquid gas chromatography stationary phase

The evaluation of a novel medium‐polarity ionic‐liquid‐based gas chromatography column, SLB‐IL60, towards the analysis of a complex essential oil, namely, a peppermint essential oil sample, is reported. The SLB‐IL60 30 m column was subjected to bleeding measurements, by means of conventional gas chromatography with mass spectrometry. The SLB‐IL60 column was then evaluated in the analysis of pure standard compounds, chosen as typical constituents of peppermint essential oil. Resolution and peak symmetry (expressed as tailing factors at 10% of peak height) were measured and the results were compared to those obtained on the most widely used columns in such an application, namely a medium‐polarity [100% poly(ethyleneglycol)] stationary phase, and an apolar 5% diphenyl/95% dimethyl siloxane. The final part of the evaluation was dedicated to the gas chromatography with mass spectrometry analysis of a peppermint essential oil sample and again the data were compared to those obtained on the 100% poly(ethyleneglycol) and the 5% diphenyl/95% dimethyl siloxane phase. Linear retention indices were determined for all the identified components on the ionic liquid capillary.     

Faithful tropicalisation and torus actions

For any affine variety equipped with coordinates, there is a surjective, continuous map from its Berkovich space to its tropicalisation. Exploiting torus actions, we develop techniques for finding an explicit, continuous section of this map. In particular, we prove that such a section exists for linear spaces, Grassmannians of planes (reproving a result due to Cueto, Häbich, and Werner), matrix varieties defined by the vanishing of 3 × 3-minors, and for the hypersurface defined by Cayley’s hyperdeterminant.     

Highly symmetric hypertopes

We study incidence geometries that are thin and residually connected. These geometries generalise abstract polytopes. In this generalised setting, guided by the ideas from the polytope theory, we introduce the concept of chirality, a property of orderly asymmetry occurring frequently in nature as a natural phenomenon. The main result in this paper is that automorphism groups of regular and chiral thin residually connected geometries need to be C-groups in the regular case and \({C^+}\)-groups in the chiral case.     

A multifunctional nanoassembly of mesogen-bearing amphiphiles and porphyrins for the simultaneous photodelivery of nitric oxide and singlet oxygen

We report a molecular nanoassembly able to supply simultaneously, in the same region of space and under the exclusive control of visible light, nitric oxide and singlet oxygen, two species playing a key role in the therapy of cancer; the considerable fluorescence of this nanoaggregate and its reduced size (ca. 40 nm) represent additional advantages that make this photoactive vehicle an appealing candidate to be tested in biological systems.     

The catalytic reduction of nitrobenzene at the [MoVIO2(O2CC(S)(C6H5)2)2]2− complex intercalated in a Zn(II)–Al(III) layered double hydroxide host: A kinetic model for the molybdenum–pterin binding site in nitrate reductase

The heterogeneous reduction of nitrobenzene by thiophenol catalyzed by the dianionic bis(2‐sulfanyl‐2,2‐diphenylethanoxycarbonyl) dioxomolybdate(VI) complex, [Mo^VIO₂(O₂CC(S)(C₆H₅)₂)₂]²⁻, intercalated into a Zn(II)–Al(III) layered double hydroxide host [Zn_3−xAl_x(OH)₆]^x+, has been investigated under anaerobic conditions. Aniline was found to be the only product formed through a reaction consuming six moles of thiophenol for each mol of aniline produced. The kinetics of the system have been analyzed in detail. In excess of thiophenol, all reactions follow first‐order kinetics (ln([PhNO₂]/[PhNO₂]₀) = −k_appt) with the apparent rate constant k_app being a complex function of both initial nitrobenzene and thiophenol concentrations, as well as linearly dependent on the amount of solid catalyst used. A mechanism for this catalytic reaction consistent with the kinetic experiments as well as the observed properties of the intercalated molybdenum complex has thiophenol inducing the initial coupled proton–electron transfer steps to form an intercalated Mo^IV species, which is oxidized back to the parent Mo^VI complex by nitrobenzene via a two‐electron oxygen atom transfer reaction that yields nitrosobenzene. This mechanism is widespread in enzymatic catalysis and in model chemical reactions. The intermediate nitrosobenzene thus formed is reduced directly by excess thiophenol to aniline. The values of rate coefficients indicate that reduction of nitrobenzene proceeds much faster than proton‐assisted oxidation of thiophenol. This may account for the observation that the presence of protonic amberlite IR‐120(H) increases considerably the rate of the overall reaction catalyzed. Activation parameters in excess of the protonic resin and PhSH were ΔH^≠ = 80 kJ mol⁻¹ and ΔS^≠ = −70 J mol⁻¹ K⁻¹. The large negative activation entropy is consistent with an associative transition state. The present system is characterized by a well‐defined catalytic cycle with multiple‐turnovers reductions of nitrobenzene to aniline without appreciable deactivation. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 212–224, 2001     

Formation and compatibilizing effect of the grafted copolymer in the reactive blending of 2-diethylsuccinate containing polyolefins with poly-ϵ-caprolactam (nylon-6)

The intermolecular reaction and its role in determining the partial compatibility between diethylsuccinate containing linear low-density polyethylene or ethylene propylene copolymer and poly-ϵ-caprolactam (PA6) has been investigated in the melt using a Brabender mixer. The reaction product has been submitted to selective solvent extraction with formic acid and n-heptane; the characterization of the two extracted fractions and the insoluble residue has demonstrated the formation of a polyolefin–nylon (PO–PA6) grafted copolymer. The formation of grafted copolymer has an evident effect on the compatibilization of the two original polymers, indeed the differential scanning calorimetry analysis shows a remarkable decrease of temperature and enthalpy of PA6 crystallization. Moreover scanning electron microscopy micrographs show clear evidence of size reduction of PA6 domains associated with improved interface interactions. © 1998 John Wiley & Sons, Ltd.     

The Hyperfine Transition for the Definition of the Second

The unit of time of the International System of Units (SI), the “atomic second” was defined through a constant of physics in 1967. It is derived from the frequency of the hyperfine transition of the atom of cesium 133. From the astronomical definition of the second until today, the accuracy of the realization of the second has improved by eight orders of magnitude, with a rate that has increased since the development of the cesium frequency standards, to reach parts in 10¹⁶ for the best clocks today. In 2018, when the new SI was adopted, the time metrology community proved that a new generation of frequency standards operating in optical wavelengths has uncertainties at the level of 10^–18, and challenge the implementation of high accurate frequency and time comparison techniques to decide on a revision of the definition of the second. Herein, the progress in the definition and realization of the second from astronomy until today is reviewed, an inventory of the present resources is assembled and a brief view for the future given.     

NMR analysis of a series of substituted pyrazolo[3,4-d] pyrimidines-4-amines

A series of 21 substituted pyrazolo[3,4-d]pyrimidines-4-amines were studied by (1)H and (13)C NMR. The application of two-dimensional techniques, HMQC and HMBC, allowed the complete assignment of the spectra for all the compounds.     

Molecular Complexes of Simple Anions with Electron‐Deficient Arenes: Spectroscopic Evidence for Two Types of Structural Motifs for Anion–Arene Interactions

Anion–π interactions between a π‐acidic aromatic system and an anion are gaining increasing recognition in chemistry and biology. Herein, the binding features of an electron‐deficient aromatic system (1,3,5‐trinitrobenzene (TNB)) and selected anions (OH^?, Br^?, and I^?) are examined in the gas phase by using the combined information derived from collision‐induced dissociation experiments at variable energy, infrared multiple‐photon dissociation spectroscopy, and quantum chemical calculations. We provide spectroscopic evidence for two different structural motifs of anion–arene complexes depending on the nature of the anion. The TNB–OR^? complexes (R=H, or alkyl groups which were studied earlier) adopt an anionic σ‐complex structure whereby RO^? attacks the aromatic ring with covalent bond formation, and develops a tetrahedral ring carbon bound to H and OR. The halide complexes rather conform to a structure in which the TNB moiety is hardly altered, and the halogen is placed on an unsubstituted carbon atom over the periphery of the ring at a C–X distance that is appreciably longer than a typical covalent bond length. The ensuing structural motif, previously characterized in the solid state and named weak σ interaction, is now confirmed by an IR spectroscopic assay in the gas phase, in which the sampled species are unperturbed by crystal packing or solvation effects.