UV/Vis Spectroscopic Properties of N -(2′-Hydroxy-4′- N , N -dimethyl-aminobenzylidene)-4-nitroaniline in Various Solvents and Solid Environments

 N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of ν_max is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil^? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing an unprecedented bathochromic shift.     

Chemotaxonomic features associated with flavonoids of cannabinoid-free cannabis (Cannabis sativa subsp. sativa L.) in relation to hops (Humulus lupulus L.)

The major flavonoids present in the leaves and flowers of the cannabinoid-free cannabis (Cannabis sativa subsp. sativa L.) cultivars Felina and Futura are orientin (1), vitexin (2), luteolin-7-O-beta-D-glucuronide (3), and apigenin-7-O-beta-D-glucuronide (4), while prenylated flavonoids, to which the potent estrogenicity of hops (Humilus lupulus L.) is associated, are absent. The different composition of flavonoids has chemotaxonomic value.     

Aufbau und Abbau von (NH4)[BF4] und H3N‐BF3

Production and Decomposition of (NH₄)[BF₄] and H₃N‐BF₃ (NH₄)[BF₄] is produced as single crystals during the reaction of elemental boron and NH₄HF₂ (B : NH₄HF₂ = 1 : 2) and NH₄F (B : NH₄F = 1 : 4), respectively, in sealed copper ampoules at 300 °C. The crystal structure (baryte type, orthorhombic, Pnma, Z = 4) was redetermined at ambient temperature (a = 909.73(18), b = 569.77(10), c = 729.47(11) pm, R_all = 0.0361) and at 140 K (a = 887.3(2), b = 574.59(12), c = 717.10(12) pm, R_all = 0.0321). Isolated (NH₄)⁺ and [BF₄]^— tetrahedra are the important building units. The thermal behaviour of (NH₄)[BF₄] was investigated under inert (Ar, N₂) and reactive conditions (NH₃) with the aid of DTA/TG and DSC measurements and with in‐situ X‐ray powder diffraction as well. Finally, (NH₄)[BF₄] is decomposed yielding NH₃ and BF₃, BN is not produced under the current conditions. Colourless single crystals of H₃N‐BF₃ were prepared directly from the components NH₃ and BF₃. The crystal structure was determined anew at 293 and 170 K (orthorhombic, Pbca, Z = 8, a = 815.12(10), b = 805.91(14), c = 929.03(12) pm, R_all = 0.0367; a = 807.26(13), b = 800.48(10), c = 924.31(11) pm, R_all = 0.0292, T = 170 K). The crystal structure contains isolated molecules H₃N‐BF₃ in staggered conformation with a B‐N distance of 158 pm. The thermal behaviour of H₃N‐BF₃ was studied likewise.     

Reaction of 2‐(Polyfluoroacyl)cycloalkanones with Hydroxylamine

The 2‐acylcycloalkanones 1a – g and 3a – c , possessing a polyfluoroalkyl group, react with hydroxylamine regio‐ and stereoselectively to yield 4,5‐dihydroisoxazol‐5‐ols 2a – g and 4a – c , respectively, i.e., products of N‐addition to the oxo group at the cycloalkane ring (Schemes 1 and 2). The products 2 and 4 can be dehydrated under drastic conditions only (Schemes 3 and 4). The structure of one of the 4,5‐dihydroisoxazol‐5‐ols was confirmed by X‐ray crystal‐structure analysis.     

Direct observation of key reaction intermediates on gold clusters

Using ultraviolet photoelectron spectroscopy, we provide direct experimental evidence that di-oxygen species are stable on anionic gold dimer and tetramer clusters at room temperature. The stabilization of molecular oxygen is crucial for the high activities of the low-temperature reactions on gold catalysts.     

Ultrafast Single-Scan 2D NMR Spectroscopic Detection of a PHIP-Hyperpolarized Protease Inhibitor

Two-dimensional NMR spectroscopy is one of the most important spectroscopic tools for the investigation of biological macromolecules. However, due to the low sensitivity of NMR spectroscopy, it takes usually from several minutes to many hours to record such spectra. Here, the possibility of detecting a bioactive derivative of the sunflower trypsin inhibitor-1 (SFTI-1), a tetradecapeptide, by combining parahydrogen-induced polarization (PHIP) and ultrafast 2D NMR spectroscopy is shown. The PHIP activity of the inhibitor was achieved by labeling with O-propargyl-l -tyrosine. In 1D PHIP experiments a signal enhancement of a factor of approximately 1200 compared to standard NMR was found. This enhancement permits measurement of 2D NMR correlation spectra of low-concentrated SFTI-1 in less than 10 seconds, employing ultrafast single-scan 2D NMR detection. As experimental examples PHIP-assisted ultrafast single-scan TOCSY spectra of SFTI-1 are shown.     

Effect of heterogeneity on the quantitative determination of trace elements in concrete

Laser-induced breakdown spectroscopy has been used for quantitative measurement of trace elements, e.g. sulfur and chlorine, in concrete. Chloride and sulfate ions have a large effect on the durability of concrete structures, and quantitative measurement is important for condition assessment and quality assurance. Concrete is a highly heterogeneous material in composition and grain-size distribution, i.e. the spatial distribution of elements. Calibration plots were determined by use of laboratory-made reference samples consisting of pressings of cement powder, hydrated cement, cement mortar, and concrete, in which the heterogeneity of the material is increasing because of the aggregates. Coarse aggregate and cement paste are distinguishable by the intensity of the Ca spectral lines. More advanced evaluation is necessary to account for the effect of the fine aggregate. The three series of reference samples enable systematic study of the effects of heterogeneity on spectral intensity, signal fluctuation, uncertainty, and limits of detection. Spatially resolved measurements and many spectra enable statistical evaluation of the data. The heterogeneity has an effect on measurement of the sulfur and chlorine content, because both occur mainly in the cement matrix. Critical chloride concentrations are approximately 0.04% (m/m). The chlorine spectral line at 837.6 nm is evaluated. The natural sulfur content of concrete is approximately 0.1% (m/m). The spectral line at 921.3 nm is evaluated. One future application may be simultaneous determination of the amount of damaging trace elements and the cement content of the concrete.     

Synthesis and Crystal Structure of Rubidium Lanthanum Tetraacetate,RbLa(CH3COO)4

The anhydrous rubidium tetraacetato lanthanate, RbLa(CH₃COO)₄, is obtained together with Rb₂La(CH₃COO)₅(H₂O) as colourless single crystals from a 1 : 2 mixture of Rb₂CO₃ and La(CH₃COO) · 1.5 H₂O in acetic acid by slow evaporation. The crystal structure [orthorhombic, Pnnm, Z = 2, a = 1242.0(3), b = 1650.1(4), c = 698.0(4) pm, R = 0.028, R_w = 0.071] contains La³⁺ nine coordinate by oxygen atoms of six acetate ligands. The polyhedra are connected to dimers and further to double chains running parallel to [001]. These [La(CH₃COO)₄]^– double chains are surrounded by four like double chains and connected by Rb⁺ ions that are seven coordinate by oxygen atoms.