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961.
Ernesto Mesto Fernando Scordari Maria Lacalamita Luisa De Cola Roberta Ragni Gianluca Maria Farinola 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(5):480-482
The title complex, [Ir2(C18H13FNO2S)4Cl2]·C7H8, was crystallized from dichloromethane solution under a toluene atmosphere. It is a dimeric complex in which each of the two IrIII centres is octahedrally coordinated by two bridging chloride ligands and by two chelating cyclometalated 2‐(4‐benzylsulfonyl‐2‐fluorophenyl)pyridine ligands. The crystal structure analysis unequivocally establishes the trans disposition of the two cyclometalated ligands bound to each IrIII centre, contrary to our previous hypothesis of a cis disposition. The latter was based on the 1H NMR spectra of a series of dimeric benzylsulfonyl‐functionalized dichloride‐bridged iridium complexes, including the compound described in the present work [Ragni et al. (2009). Chem. Eur. J. 15 , 136–148]. The toluene solvent molecules, embedded in cavities in the crystal structure, are highly disordered and could not be modelled successfully; their contribution was removed from the refinement using the SQUEEZE routine in the program PLATON [Spek (2009). Acta Cryst. D 65 , 148–155]. 相似文献
962.
Surya K. De 《合成通讯》2013,43(16):2768-2774
Paal–Knorr condensation of 2,5-hexadione with primary amines in the presence of a catalytic amount of praseodymium(III) trifluoromethanesulfonate under solvent-free conditions has been accomplished with an excellent yield. This method is a very easy, rapid, and high-yielding reaction for the synthesis of N-substituted pyrrole derivatives. 相似文献
963.
Murat Güney Selçuk Eşsiz Arif Daştan Metin Balci Ottorino De Lucchi Ertan Şahin Fabrizio Fabris 《Helvetica chimica acta》2013,96(5):941-950
Stereoisomerically pure endo‐ and exo‐7‐halo‐7‐(trimethylstannyl)benzonorcar‐3‐enes (=endo‐ and exo‐(1‐halo‐1a,2,7,7a‐tetrahydro‐1H‐cyclopropa[b]naphthalen‐1‐yl)trimethylstannane) 4 and 6 were selectively obtained by lithium? tin or magnesium? tin transmetalation in good yields (Scheme 2 and 3). The reaction of these compounds with copper(I) thiophene‐2‐carboxylate (CuTC) produced in both cases the corresponding CS‐symmetric bicyclopropylidene (=cyclopropylidenecyclopropane) syn‐ 1 , a single diastereoisomer (Schemes 5 and 6). The structure of syn‐ 1 was undoubtedly elucidated by X‐ray single crystal diffraction. The coupling mechanism of the carbenoid cyclopropane is discussed (Scheme 7). 相似文献
964.
A. D. Milov Y. D. Tsvetkov M. De Zotti C. Prinzivalli B. Biondi F. Formaggio C. Toniolo M. Gobbo 《Journal of Structural Chemistry》2013,54(1):73-85
The X band PELDOR spectroscopy was used to investigate the magnetic dipole-dipole interactions in glassy solutions of nitroxide mono-labeled tylopeptin B and heptaibin peptaibiotics at 77 K. Specifically, a study was performed of the tylopeptin B peptides labeled at either position 3, 8, or 13, denoted as T3, T8, and T13, respectively. The heptaibin analogs labeled at either position 2 or 14, denoted as H2 and H14, respectively, were also investigated. It was shown that in frozen glassy peptide solutions in methanol, the spin labels are randomly distributed over the solvent volume. This result points to the absence of specific dipolar interactions between the peptides under these conditions. However, peptide aggregation was detected in weakly polar methanol/toluene environments. To study the properties of the resulting aggregates, we examined the depth of modulation for the PELDOR traces as a function of the concentration of the peptides in solution and the distances between the spin labels in the aggregates. Based on the concentration dependencies, the number of peptide molecules in the aggregates was estimated. We find that this value ranges from 2 to 3, depending on the position of the spin label in the peptide sequence. The combined analysis of the distance spectra and the number of peptide molecules in the aggregates allows us to suggest that dimer formation is the prevailing mode of self-association. In the case of spin-labeled tylopeptin B, the molecules in the dimer are head-to-head oriented. In addition, the distance spectra of the aggregates show that the C-termini of the molecules in the tylopeptin B dimer are more mobile than the Ntermini. This phenomenon leads to an increase in the spread of the distances between the nitroxides as the label position is approaching the peptide C-terminus. For heptaibin, we show that two forms of dimerization (head-to-head and head-to-tail) occur. Finally, in addition to dimers, aggregates containing 3 or 4 peptide molecules, which give broad lines in the distance spectra, are seen in solution. 相似文献
965.
A series of novel 5‐aryl‐1‐(aryloxyacetyl)‐3‐(tert‐butyl or phenyl)‐4‐(1H‐1,2,4‐triazol‐1‐yl)‐4,5‐dihydropyrazole 3a – 3n were synthesized by the annulation of 2‐aryloxyacetohydrazides with 3‐aryl‐1‐t‐butyl (or phenyl)‐2‐(1H‐1,2,4‐triazol‐1‐yl)prop‐2‐en‐1‐ones ( 2 ) in the presence of a catalytic amount of acetic acid. Compounds 2 were obtained by the Knoevenagel reactions of 1‐t‐butyl (or phenyl)‐2‐(1H‐1,2,4‐triazol‐1‐yl)ethanone ( 1 ) with aromatic aldehydes in the presence of piperidine. Their structures were confirmed by IR, 1H‐NMR, ESI‐MS, and elemental analyses. The preliminary bioassay indicated that some compounds displayed moderate to excellent fungicidal activity. For example, compounds 3l , 3m , and 3n possessed 100% inhibition against Cercospora arachidicola Hori at the concentration of 50 mg/L. 相似文献
966.
The synthesis of the title compound is described. The key-step is the photochemical coupling between 5-iodo-2-thienylcarbaldehyde and 2-bromothio-phene to give 5-bromo-2,2′-bithienyl-5′-carbaldehyde. 相似文献
967.
4-Methyl-4-(4-methoxyphenyl)-benzo[h]-4H-chromene is synthesised by condensation of 4-methoxyacetophenone and ethyl acetate in strong base, followed by coupling with 1-naphthol, reduction to the epimeric lactols and elimination of water. 相似文献
968.
Giovanni Di Fabio Valeria RomanucciMauro De Nisco Silvana PedatellaCinzia Di Marino Armando Zarrelli 《Tetrahedron letters》2013
A new and preparative oxidation of silibinin has been developed to give access to two different silibinin derivatives known for their enhanced antioxidant properties. Conventional heating methods were compared with results obtained from microwave (MW) heating. The base-catalysed oxidation of silibinin under MW heating is a very efficient method for the preparation of 2,3-dehydrosilybin and a related silybin rearrangement product. This latter compound shows enhanced radical scavenging properties. Optimised conditions were used to prepare 2,3-dehydrosilybins A and B from optically pure silybins A and B. An efficient, preparative purification method was also developed to enable isolation of different products in high purity. 相似文献
969.
Clemente Bretti Concetta De Stefano Claudia Foti Silvio Sammartano 《Journal of solution chemistry》2013,42(7):1452-1471
The protonation constants and solubilities of three complexons [ethylenediamine-N,N′-disuccinic acid (EDDS), ethylene glycol bis(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) and 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CDTA)] are reported in aqueous solutions of NaCl with different ionic strength values (0 ≤ I ≤ 4.8 mol·L?1) and, in the case of CDTA, in (CH3)4NCl (0.1 ≤ I ≤ 2.7 mol·L?1). The dependence on ionic strength of the protonation constants of these three complexons and four other complexons that were previously reported (NTA, EDTA, DTPA and TTHA), is analyzed in NaCl solution; the ionic strength influences quite strongly the protonation constants (as an example for CDTA, log10 K 1 = 10.54 and 9.25 at I = 0.1 and 1 mol·L?1, respectively), while the effect of (CH3)4NCl concentration is lower. Based on the total solubility S T and the protonation constant data at different salt concentrations, the solubility of the neutral species S 0 and the solubility products K S0 are obtained. The Setschenow coefficients k m and the solubility values S 0 0 in pure water are also reported (S 0 0 = 0.55, 0.21 and 0.75 mmol·kg?1 for EDDS, EGTA and CDTA, respectively). The dependence of the protonation constants on ionic strength is also interpreted in terms of ion pair formation, and the formation constants of Na+ species are reported. 相似文献
970.
Kalipada Adhikari Sudip Chattopadhyay Barin Kumar De Amitava Sharma Ranendu Kumar Nath Dhiman Sinha 《Journal of computational chemistry》2013,34(15):1291-1310
A valence‐universal multireference coupled cluster (VUMRCC) theory, realized via the eigenvalue independent partitioning (EIP) route, has been implemented with full inclusion of triples excitations for computing and analyzing the entire main and several satellite peaks in the ionization potential spectra of several molecules. The EIP‐VUMRCC method, unlike the traditional VUMRCC theory, allows divergence‐free homing‐in to satellite roots which would otherwise have been plagued by intruders, and is thus numerically more robust to obtain more efficient and dependable computational schemes allowing more extensive use of the approach. The computed ionization potentials (IPs) as a result of truncation of the (N−1) electron basis manifold involving virtual functions such as 2h‐p and 3h‐2p by different energy thresholds varying from 5 to 15 a.u. with 1 a.u. intervals as well as thresholds such as 20, 25, and 30 a.u. have been carefully looked into. Cutoff at around 25 a.u. turns out to be an optimal threshold. Molecules such as C2H4 and C2H2 (X = D,T), and N2 and CO (X = D,T,Q) with Dunning's cc‐pVXZ bases have been investigated to determine all main and 2h‐p shake‐up and 3h‐2p double shake‐up satellite IPs. We believe that the present work will pave the way to a wider application of the method by providing main and satellite IPs for some problematic N‐electron closed shell systems. © 2013 Wiley Periodicals, Inc. 相似文献