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991.
992.
993.
A mild and efficient methodology for the rearrangement of protected asparagine and protected glutamine is reported; good results are obtained with a wide selection of protecting groups. 相似文献
994.
Mastropietro TF Armentano D Grisolia E Zanchini C Lloret F Julve M De Munno G 《Dalton transactions (Cambridge, England : 2003)》2008,(4):514-520
Three new compounds of formula {[Cu(gua)(H(2)O)(3)](BF(4))(SiF(6))(1/2)}(n) (1), {[Cu(gua)(H(2)O)(3)](CF(3)SO(3))(2).H(2)O}(n) (2) and [Cu(gua)(2)(H(2)O)(HCOO)]ClO(4).H(2)O.1/2HCOOH] (3) [gua = 2-amino-1H-purin-6(9H)-one] showing the unprecedented coordination of neutral guanine, have been synthesised and structurally characterized. The structures of the compounds 1 and 2 contain uniform copper(II) chains of formula [Cu(gua)(H(2)O)(3)](n)(2n+), where the copper atoms are bridged by guanine ligands coordinated via N(3) and N(7). The electroneutrality is achieved by uncoordinated tetrafluoroborate and hexafluorosilicate (1) and triflate (2). Each copper atom in 1 and 2 is five-coordinated in a distorted square pyramidal environment: two water molecules in trans positions and the N(3) and N(7a) nitrogen atoms of two guanine ligands build the basal plane whereas a water molecule fills the axial position. The values of the copper-copper separation across the bridging guanine ligand are 7.183(1) (1) and 7.123(1) A (2). is an ionic salt whose structure is made up of mononuclear [Cu(gua)(2)(H(2)O)(HCOO)](+) cations and perchlorate anions plus water and formic acid as crystallization molecules. The two guanine ligands in the cation are coordinated to the copper centre through the N(9) atom. The copper atom in 3 is four-coordinated with two monodentate guanine molecules in the trans position, a water molecule and a monodenate formate ligand building a quasi square planar surrounding. Magnetic susceptibility measurements for 1 and 2 in the temperature range 1.9-300 K show the occurrence of significant intrachain antiferromagnetic interactions between the copper(ii) ions across the guanine bridge [J = -9.6(1) (1) and -10.3(1) cm(-1) (2) with H = -J summation operator(i)S(i).S(i+1)]. 相似文献
995.
Mardones C von Baer D Hidalgo A Contreras A Sepúlveda C 《Journal of separation science》2008,31(6-7):1124-1129
An ultrasonic bar-assisted extraction and CE separation procedure for the determination of pentachlorophenol (PCP) and 2,4,6-tribromophenol (TBP) residues in sawdust was developed and applied. For this purpose, micellar electrokinetic capillary chromatography (MEKC) was used and compared with a GC/MS methodology. This methodology allowed the quantification of PCP and TBP in a concentration range of 2.5-12.0 mg/kg for TBP and 2.8-12.0 mg/kg for PCP. Different sample treatment processes were evaluated in order to extract these compounds from sawdust. Better results were obtained when the residues were extracted with ultrasound-assisted hexane, filtered, evaporated, dissolved in Na(2)CO(3), and injected into the CE equipment. The optimal option for GC/MS was extraction with Na(2)CO(3 )followed by a derivation using acetic anhydride and liquid-liquid extraction with hexane. This method allowed the quantification of TBP and PCP in sawdust in a concentration range of 0.19-12.00 mg/kg and 0.14-12.00 mg/kg, respectively. The CE method was compared with the GC/MS as reference method. The results were shown to be statistically similar by both methods for PCP as well as for TBP. 相似文献
996.
Prof. Guowei Li Dr. Qun Yang Prof. Kaustuv Manna Dr. Yudi Zhang Dr. Patrick Merz Chandra Shekhar Yang Zhang Dr. Hua Lv Dr. Anastasios Markou Dr. Yan Sun Prof. Claudia Felser 《Angewandte Chemie (International ed. in English)》2023,62(27):e202303296
The study of heterogeneous reactions for enantiomeric processes based on inorganic crystals has been resurgent in recent years. However, the question remains how homochirality develops in nature and chemical reactions. Here, the successful growth of B20 group PdGa single crystals with different chiral lattices enabled us to achieve enantioselective recognition of 3,4-dihydroxyphenylalanine (DOPA) based on a new mechanism, namely orbital angular momentum (OAM) polarization. The orbital textures of PdGa crystals indicate large OAM polarization near the Fermi level and carrying opposite signs. A positive or negative magnetization in the [111] direction is expected depending on the chiral lattice of PdGa crystals. Due to this, the adsorption energies of PdGa crystals and DOPA molecules differ depending on how well the O-2p orbital of DOPA pairs with the Pd-4d orbital of PdGa. The results provide one possible explanation for how chirality arises in nature by providing an enantioselective route with pure inorganic crystals. 相似文献
997.
Dr. Claudia Herrera León Noel Angelo Kalacas Dr. Alejandra Mier Dr. Peyman Sakhaii Dr. Franck Merlier Elise Prost Dr. Irene Maffucci Dr. Valentina Montagna Dr. Helena Mora-Radó Dr. Pradeep K. Dhal Dr. Bernadette Tse Sum Bui Prof. Dr. Karsten Haupt 《Angewandte Chemie (International ed. in English)》2023,62(34):e202306274
Tumor Necrosis Factor-α (TNF-α) is a cytokine that is normally produced by immune cells when fighting an infection. But, when too much TNF-α is produced as in autoimmune diseases, this leads to unwanted and persistent inflammation. Anti-TNF-α monoclonal antibodies have revolutionized the therapy of these disorders by blocking TNF-α and preventing its binding to TNF-α receptors, thus suppressing the inflammation. Herein, we propose an alternative in the form of molecularly imprinted polymer nanogels (MIP-NGs). MIP-NGs are synthetic antibodies obtained by nanomoulding the 3-dimensional shape and chemical functionalities of a desired target in a synthetic polymer. Using an in-house developed in silico rational approach, epitope peptides of TNF-α were generated and ‘synthetic peptide antibodies’ were prepared. The resultant MIP-NGs bind the template peptide and recombinant TNF-α with high affinity and selectivity, and can block the binding of TNF-α to its receptor. Consequently they were applied to neutralize pro-inflammatory TNF-α in the supernatant of human THP-1 macrophages, leading to a downregulation of the secretion of pro-inflammatory cytokines. Our results suggest that MIP-NGs, which are thermally and biochemically more stable and easier to manufacture than antibodies, and cost-effective, are very promising as next generation TNF-α inhibitors for the treatment of inflammatory diseases. 相似文献
998.
Cybele Lotti Claudia S. Isaac Marcia C. Branciforti Rosa M.V. Alves Susana Liberman Rosario E.S. Bretas 《European Polymer Journal》2008,44(5):1346-1357
In this work, high density polyethylene (HDPE) was mixed in a twin screw extruder with organophilic treated clay, Cloisite 20A, and a compatibility agent, a HDPE grafted with maleic anhydride (PEMA). The screw profile was changed from a less dispersive (Profile 1) to a high dispersive configuration (Profile 2). A masterbatch procedure was used to obtain a final organoclay concentration of 5 wt.%. Both profiles allowed the intercalation of the HDPE into the clay, increasing the clay’s gallery distance to 3.7 nm. However, the samples produced with Profile 2 (Nano 2 samples) were more elastic and had a more stable structure than the samples produced with Profile 1. Therefore, two kind of blown films of Nano 2 samples were made: FN1 and FN2. The last one was blown at a higher screw velocity than the FN1. Both films had an increase of 95% in the elastic modulus and a reduction of 60% and 45% in O2 and water vapor permeability rates, respectively, compared to the film of pure HDPE. However, the FN2 structure was more unstable than the FN1 structure. It was concluded that both screw profiles gave the same level of HDPE intercalation in the clay; however, the more dispersive profile produced more time-stable and elastic structures. The increase in the elongation rate during the film blowing process produced also more time-stable morphologies; however, this higher orientation created matrix/filler interfacial defects. 相似文献
999.
Bazzicalupi C Bencini A Bonaccini C Giorgi C Gratteri P Moro S Palumbo M Simionato A Sgrignani J Sissi C Valtancoli B 《Inorganic chemistry》2008,47(12):5473-5484
The hydrolytic ability toward plasmid DNA of a mononuclear and a binuclear Zn(II) complex with two macrocyclic ligands, containing respectively a phenanthroline (L1) and a dipyridine moiety (L2), was analyzed at different pH values and compared with their activity in bis( p-nitrophenyl)phosphate (BNPP) cleavage. Only the most nucleophilic species [ZnL1(OH)]+ and [Zn2L2(OH)2]2+, present in solution at alkaline pH values, are active in BNPP cleavage, and the dinuclear L2 complex is remarkably more active than the mononuclear L1 one. Circular dichroism and unwinding experiments show that both complexes interact with DNA in a nonintercalative mode. Experiments with supercoiled plasmid DNA show that both complexes can cleave DNA at neutral pH, where the L1 and L2 complexes display a similar reactivity. Conversely, the pH-dependence of their cleavage ability is remarkably different. The reactivity of the mononuclear complex, in fact, decreases with pH while that of the dinuclear one is enhanced at alkaline pH values. The efficiency of the two complexes in DNA cleavage at different pH values was elucidated by means of a quantum mechanics/molecular mechanics (QM/MM) study on the adducts between DNA and the different complexed species present in solution. 相似文献
1000.
Schollenberger M Müller HM Rüfle M Suchy S Dejanovic C Frauz B Oechsner H Drochner W 《Journal of chromatography. A》2008,1193(1-2):92-96
A sensitive and selective method for the simultaneous determination of a spectrum of trichothecenes in residuals of biogas production has been developed. It comprises sample clean-up by liquid/liquid partition for digested manure and solid phase extraction for digested solid phase. Quantification of A- and B-type trichothecenes as their trifluoroacetyl derivatives is performed by gas chromatography mass spectrometry (GC/MS), that of B-type trichothecenes alternatively by high-performance liquid chromatography (HPLC). Fluorescence detection (FLD) after post-column derivatisation using methylacetoacetate and ammonium acetate after alkaline decomposition of toxins was applied. Detection limits in digestates were between 1 and 30 microg/l and 20 and 50 microg/l for GC/MS and HPLC/FLD, respectively. Recovery rates were between 52 and 129% for GC/MS detection with the exception of T-2 tetraol with 22%, and between 56 and 123% for HPLC/FLD. 相似文献