Beiträge zur Chemie der Pyrrolpigmente, 3. Mitt.1: Die NH-Tautomerie von substituierten Pyrromethenen: Protonenresonanzspektrometrische Untersuchungen

NMR-spectra of several pyrromethenes were measured at different temperatures, concentrations and in different solvents. The chemical shifts of all protons were assigned and long range coupling constants determined. This variation of temperature, concentration and solvent provided evidence forintra- andinter-molecular proton transfer. In all pyrromethenes investigated the tautomeric NH exchanges are too fast—even at –100°C—to be measured by NMR.

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CD spectrometric methods for the simultaneous determination of ethisterone and its delta5-isomer

Quick and accurate direct and indirect circular dichroism (CD) spectrometric methods were developed for the simultaneous determination of ethisterone (17alpha-ethinyl-17-hydroxy-4-androstene-3-one) and its delta(5)-isomer (delta(5)-ethisterone). The direct method is based on the selective negative Cotton effect of the delta(4)-3-oxo group in ethisterone (negative maximum at 348 nm in dioxan) and measurement of the ellipticity at 296 nm (positive maximum of delta(5)-ethisterone), where the measured ellipticity is the sum of those of the two isomers. In the indirect procedure delta(5)-ethisterone is transformed to ethisterone by base-catalysed isomerization and the ellipticities are measured at 339 nm in ethanol before and after isomerization. Preliminary experiments show the usefulness of CD detector in the HPLC determination of the mixture of the isomers. A major advantage of the direct CD spectrometric and the HPLC/CD methods is that the delta(5)-isomer with extremely low UV activity can also be directly measured with high sensitivity.     

Zur Kenntnis sterischer Einflüsse auf Ringschlußreaktionen

Ohne Zusammenfassung     

trans-Resveratrol and trans-Piceid Content of Hungarian Wines

Plant polyphenols are naturally occurring secondary plant metabolites, synthesized in response to environmental stress factors. As anti-oxidants and free-radical scavengers they serve as essential components of the human diet. Among polyphenols well studied representatives are the trans-resveratrol and trans-piceid molecules, the latter being the glycoside of trans-resveratrol. trans-Resveratrol is known to have anti-inflammatory, anti-tumor, cardio- and vasoprotective effects which help in the prevention of chronic cardiovascular and tumorous diseases.

In the present study, 42 Hungarian wines were analyzed using LC-DAD detection. The wines were from Villány and Eger wine regions representing three wineries from 2003 to 2007 vintage years. The trans-resveratrol amount in the processed wines ranged from 0.75 to 10.4 mg mL⁻¹ and for trans-piceid from 0.1 to 3.7 mg mL⁻¹.

     

Nano-hydroxyapatite preparation from biogenic raw materials

Hydroxyapatite (HAp) was successfully produced from recycled eggshell, seashell and phosphoric acid. The phases obtained depended on the ratio of calcined eggshell/ seashell to phosphoric acid, the calcination temperature and the mechanochemical activation method (ball milling or attrition milling). The HAp structures were characterized by X-ray diffraction, scanning electron microsopy and infrared spectroscopy. Attrition milling was more effective than ball milling, yielding nanosize, homogenous and pure Hap.      

Polar effect in the reaction of CH3O with HBr

The discharge flow method with laser induced fluorescence detection of CH₃O was applied to determine the rate constant, k ₁, for the reaction CH₃O + HBr → products (1) k ₁ (298 K) = (8.41 ± 0.80(1σ)) 10¹¹ cm³ mol^-1 s^-1. The unusually large k ₁ value was explained by the polar nature of the transition state of the reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Coordination of methanol clusters to benzene: a computational study

Benzene-methanol cluster structures were investigated with theoretical chemistry methods to describe the microsolvation of benzene and the benzene-methanol azeotrope. Benzene-methanol (MeOH) clusters containing up to six methanol molecules have been calculated by ab initio [MP2/6-311++G(d,p)//MP2/6-31+G(d,p) + BSSE correction] method. The BSSE was found quite large with this basis set, hence, different extrapolation schemes in combination with the aug-cc-pVxZ basis sets have been used to estimate the complete basis set limit of the MP2 interaction energy [ΔE(MP2/CBS)]. For smaller clusters, n ≤ 3, DFT procedures (DFTB+, MPWB1K, M06-2X) have also been applied. Geometries obtained for these clusters by M06-2X and MP2 calculations are quite similar. Based on the MP2/CBS results, the most stable C(6)H(6)(MeOH)(3) cluster is characterized by a hydrogen bonded MeOH trimer chain interacting with benzene via π···H-O and O···H-C(benzene) hydrogen bonds. Larger benzene-MeOH clusters with n ≥ 4 consist of cyclic (MeOH)(n) subclusters interacting with benzene by dispersive forces, to be denoted by C(6)H(6) + (MeOH)(n). Interaction energies and cooperativity effects are discussed in comparison with methanol clusters. Besides MP2/CBS calculations, for selected larger clusters the M06-2X/6-311++G(d,p)//M06-2X/6-31+G(d,p) procedure including the BSSE correction was also used. Interaction energies obtained thereby are usually close to the MP2/CBS limit. To model the benzene-MeOH azeotrope, several structures for (C(6)H(6))(2)(MeOH)(3) clusters have been calculated. The most stable structures contain a tilted T-shaped benzene dimer interacting by π···H-O and O···H-C (benzene) hydrogen bonds with a (MeOH)(3) chain. A slightly less negative interaction energy results for a parallel displaced benzene sandwich dimer with a (MeOH)(3) chain atop of one of the benzene molecules.     

Tailoring GaN semiconductor surfaces with biomolecules

Functionalization of semiconductors constitutes a crucial step in using these materials for various electronic, photonic, biomedical, and sensing applications. Within the various possible approaches, selection of material-binding biomolecules from a random biological library, based on the natural recognition of proteins or peptides toward specific material, offers many advantages, most notably biocompatibility. Here we report on the selective functionalization of GaN, an important semiconductor that has found broad uses in the past decade due to its efficient electroluminescence and pronounced chemical stability. A 12-mer peptide ("GaN_probe") with specific recognition for GaN has evolved. The subtle interplay of mostly nonpolar hydrophobic and some polar amino acidic residues defines the high affinity adhesion properties of the peptide. The interaction forces between the peptide and GaN are quantified, and the hydrophobic domain of the GaN_probe is identified as primordial for the binding specificity. These nanosized binding blocks are further used for controlled placement of biotin-streptavidin complexes on the GaN surface. Thus, the controlled grow of a new, patterned inorganic-organic hybrid material is achieved. Tailoring of GaN by biological molecules can lead to a new class of nanostructured semiconductor-based devices.     

Representations of Shavitt Graphs Within the Graphical Unitary Group Approach

The Shavitt graph is a visual representation of a distinct row table (DRT) within the graphical unitary group approach. The DRT is a compact representation of the entire configuration state function expansion space within a molecular electronic structure calculation. Each node of the graph is associated with an integer triple (a _k,b _k,c _k). These integers may be mapped to other quantum numbers, including the number of orbitals, number of electrons, and spin quantum number, and used to display Shavitt graphs in various ways that emphasize different aspects of the expansion space or that reveal different aspects of computed wave functions. The features of several graph density plots are discussed, including electron–hole symmetries and the bonding–antibonding wave function character. © 2019 Wiley Periodicals, Inc.