3-Substituted and 3,4-disubstituted pyrroline nitroxides containing an ethynyl group or two ethynyl groups were achieved by the reaction of a paramagnetic aldehydes with dimethyl (1-diazo-2-oxopropyl)phosphonate (Bestmann–Ohira reagent). The new compounds containing an ethynyl group were found to be useful building blocks in Sonogashira coupling, cyclization, and cycloaddition reactions producing potentially “azido-specific” cross-linking spin labels, paramagnetic ligands, and polyradical scaffolds. 相似文献
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.
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.
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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. 相似文献
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. 相似文献
The discharge flow method with laser induced fluorescence detection of CH3O was applied to determine the rate constant, k1, for the reaction CH3O + HBr → products (1) k1 (298 K) = (8.41 ± 0.80(1σ)) 1011 cm3 mol-1 s-1. The unusually large k1 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. 相似文献
Variational calculation of the two-electron reduced-density matrix (2-RDM), using a new first-order algorithm [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)], is applied to medium-sized organic molecules. The calculations reveal systematic trends in the accuracy of the energy with well-known chemical concepts such as hybridization, electronegativity, and atomic size. Furthermore, correlation energies from hydrocarbon chains indicate that the calculation of the 2-RDM subject to two-positivity conditions is size extensive, that is, the energy grows linearly with the number of electrons. Because organic molecules have a well-defined set of functional groups, we employ the trends in energy accuracy of the functional groups to design a correction to the 2-RDM energy for an arbitrary organic molecule. We apply the 2-RDM calculations with the functional-group correction to a large set of organic molecules with different functional groups. Energies with millihartree accuracy are obtained both at equilibrium and nonequilibrium geometries. 相似文献
We solve a problem of W. Kuperberg, who designed an intricate arrangement of eight cylinders and asked if among them there are two which do not have a common point. 相似文献