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991.
992.
Dr. Felix Armbruster Dipl.‐Chem. Timo Augenstein Dr. Pascual Oña‐Burgos Prof. Dr. Frank Breher 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17899-17906
We report on the first homoleptic tetrakis(silyl) complexes of zerovalent Group 10 metals. The compounds [MLi4{Si(3,5‐Me2pz)3}4] (M=Pd and Pt; 3,5‐Me2pz=3,5‐dimethylpyrazolyl) exhibit very appealing metal‐centred heterocubane structures with the central d10 metal atoms surrounded by four silicon and four lithium atoms. Both compounds were characterised in detail, including X‐ray crystal‐structure analysis and 2D NMR spectroscopic methods such as 7Li,29Si and 7Li,195Pt HMQC. Cyclic voltammetry studies, in combination with density functional theory (DFT) calculations, revealed that the corresponding mononuclear cationic d9‐MI and dicationic d8‐MII complexes are accessible by stepwise one‐electron oxidation of the title compounds. Electron paramagnetic resonance (EPR) investigations provided evidence for the existence of the corresponding paramagnetic palladium(I) and platinum(I) complexes. 相似文献
993.
María Casimiro Dr. Pascual Oña‐Burgos Dr. Jens Meyer Steffen Styra Dr. Istemi Kuzu Prof. Dr. Frank Breher Prof. Dr. Ignacio Fernández 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(2):691-701
2D 7Li,15N heteronuclear shift correlation through scalar coupling has successfully been applied to several lithium organyls consisting of polydentate N ligands such as N,N,N′,N′‐tetramethylethylenediamine (tmeda), N,N,N′,N′,N′′‐pentamethyldiethylentriamine (pmdta) and (?)‐sparteine. Structural insights on the conformation of benzyllithium ? pmdta ( 5 ) in a toluene solution and the strength of ion pairing in combination with PGSE NMR measurements, 1H,1H‐NOESY and 1H,7Li‐HOESY experiments are presented. By studying in detail the formation of 5 in solution, a transient species has been observed for the first time and assigned to a pre‐complex of nBuLi and pmdta. In addition, the solution behaviour of the complex formed between benzyllithium and (?)‐sparteine ( 8 ) has been studied by PGSE and multinuclear NMR spectroscopy. The straightforward synthesis and first applications in asymmetric lithiations are also reported, which show that the new system benzyllithium ? (?)‐sparteine ( 8 ) provide poorer enantioselective induction than the classical nBuLi ? (?)‐sparteine ( 6 ). The results were supported by deprotonation experiments confirming that the formation of 8 relies on two relevant factors, namely temperature and lithiating reagent. The existence of 8 may thus interfere with the asymmetric induction when the system nBuLi ? (?)‐sparteine is used in the enantioselective deprotonations of N‐Boc‐N‐(p‐methoxyphenyl)‐benzylamine conducted in toluene. 相似文献
994.
Javier Alarcón Ricardo Aucejo M. Teresa Albelda Sérgio Alves M. Paz Clares Enrique García-España 《Supramolecular chemistry》2013,25(8):573-580
Speciation studies in aqueous solution on the interaction of Cu2+ and Zn2+ with a series of polyaminic ligands N-naphthalen-1-ylmethyl-N′-{2-[(naphthalen-1-ylmethyl)-amino]-ethyl}-ethane-1,2-diamine (Ll), N-naphthalen-1-ylmethyl-N′-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethylamino}-ethyl)-ethane-1,2-diamine (L2) and N-naphthalen-1-ylmethyl-N′-[2-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethylamino}-ethylamino)-ethyl]-ethane-1,2-diamine (L3) containing two naphthylmethyl groups at their termini and N 1-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethylamino}-ethyl)-ethane-1,2-diamine (L4) containing just one naphthylmethyl group have been carried out at 298.1 K in 0.15 mol dm?3 NaCl. In the case of the tetraamines L2 and L4, their coordination capabilities towards Cd2+, Ni2+, Co2+ and Pb2+ have also been considered. The stability constants follow the general Irving-Williams sequence. The steady-state fluorescence emission studies on the interaction with metal ions show that while Cu2+ produces a chelation enhancement of the quenching (CHEQ), the interaction with Zn2+ leads to a chelation enhancement of the fluorescence (CHEF). Finally, ligands L1, L2 and L3 have been successfully covalently attached to silica surfaces and some preliminary results of their emissive properties are given. 相似文献
995.
Ignacio Garcia Natalia M. Vior Javier González-Sabín Alfredo F. Braña Jürgen Rohr Francisco Moris Carmen Méndez José A. Salas 《Chemistry & biology》2013,20(8):1022-1032
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996.
Qingyun Qian Dr. Javier Ruiz‐Martínez Prof. Dr. Mohamed Mokhtar Prof. Dr. Abdullah M. Asiri Prof. Dr. Shaeel A. Al‐Thabaiti Prof. Dr. Suliman N. Basahel Hendrik E. van der Bij Dr. Jan Kornatowski Prof. Dr. Bert M. Weckhuysen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11204-11215
The formation of hydrocarbon pool (HCP) species during methanol‐to‐olefin (MTO) and ethanol‐to‐olefin (ETO) processes have been studied on individual micron‐sized SAPO‐34 crystals with a combination of in situ UV/Vis, confocal fluorescence, and synchrotron‐based IR microspectroscopic techniques. With in situ UV/Vis microspectroscopy, the intensity changes of the λ=400 nm absorption band, ascribed to polyalkylated benzene (PAB) carbocations, have been monitored and fitted with a first‐order kinetics at low reaction temperatures. The calculated activation energy (Ea) for MTO, approximately 98 kJ mol?1, shows a strong correlation with the theoretical values for the methylation of aromatics. This provides evidence that methylation reactions are the rate‐determining steps for the formation of PAB. In contrast for ETO, the Ea value is approximately 60 kJ mol?1, which is comparable to the Ea values for the condensation of light olefins into aromatics. Confocal fluorescence microscopy demonstrates that during MTO the formation of the initial HCP species are concentrated in the outer rim of the SAPO‐34 crystal when the reaction temperature is at 600 K or lower, whereas larger HCP species are gradually formed inwards the crystal at higher temperatures. In the case of ETO, the observed egg‐white distribution of HCP at 509 K suggests that the ETO process is kinetically controlled, whereas the square‐shaped HCP distribution at 650 K is indicative of a diffusion‐controlled process. Finally, synchrotron‐based IR microspectroscopy revealed a higher degree of alkylation for aromatics for MTO as compared to ETO, whereas high reaction temperatures favor dealkylation processes for both the MTO and ETO processes. 相似文献
997.
Javier Ramos‐Soriano Ulf Niss Dr. Jesús Angulo Dr. Manuel Angulo Dr. Antonio J. Moreno‐Vargas Dr. Ana T. Carmona Prof. Dr. Sten Ohlson Prof. Dr. Inmaculada Robina 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17989-18003
The synthesis of several non‐carbohydrate ligands of cholera toxin based on polyhydroxyalkylfuroate moieties is reported. Some of them have been linked to D ‐galactose through a stable and well‐tolerated S‐glycosidic bond. They represent a novel type of non‐hydrolyzable bidentate ligand featuring galactose and polyhydroxyalkylfuroic esters as pharmacophoric residues, thus mimicking the GM1 ganglioside. The affinity of the new compounds towards cholera toxin was measured by weak affinity chromatography (WAC). The interaction of the best candidates with this toxin was also studied by saturation transfer difference NMR experiments, which allowed identification of the binding epitopes of the ligands interacting with the protein. Interestingly, the highest affinity was shown by non‐carbohydrate mimics based on a polyhydroxyalkylfuroic ester structure. 相似文献
998.
Trypsin digestion is a major component of preparing proteins for peptide based identification and quantification by mass spectral (MS) analysis. Surprisingly proteolysis is the slowest part of the proteomics process by an order of magnitude. Numerous recent efforts to reduce protein digestion to a few minutes have centered on the use of an immobilized enzyme reactor (IMER) to minimize both trypsin autolysis and vastly increase the trypsin to protein ratio. A central question in this approach is whether proteolysis with an IMER produces the same peptide cleavage products as derived from solution based digestion. The studies reported here examined this question with transferrin; a model protein of known resistance to trypsin digestion. Results from these studies confirmed that a trypsin‐IMER can in fact digest transferrin in a few minutes; providing tryptic peptides that subsequent to MS analysis allow sequence identification equivalent to solution digestion. Although many of the peptides obtained from these two trypsin digestion systems were identical, many were not. The greatest difference was that the trypsin‐ IMER produces (i) numerous peptides bearing multiple lysine and/or arginine residues and (ii) identical portions of the protein sequence were found in multiple peptides. Most of these peptides were derived from five regions in transferrin. These results were interpreted to mean that proteolysis in the case of transferrin occurred faster than the rate at which buried lysine and arginine residues were unmasked in the five regions providing peptides that were only partially digested. 相似文献
999.
Eva Tudela Jairo Gonzlez Rubn Vicente Javier Santamaría Miguel A. Rodríguez Alfredo Ballesteros 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(45):12293-12296
An allylic gold(I) cation, proposed as key intermediate in the gold‐promoted rearrangement of 1,5‐enynes bearing a fixed conformation, has been detected and characterized by NMR spectroscopy. Moreover, its participation in the overall transformation was confirmed. Computational studies indicate that the gold‐catalyzed transformation occurs through an uncommon rearrangement. Additionally, this study led us to isolate and characterize a stable homoantiaromatic carbocation. 相似文献
1000.
Mario Pacheco Alicia Cuevas Javier González-Platas Jorge S. Gancheff 《Journal of Coordination Chemistry》2014,67(23-24):4028-4038
Two nitrosyl Re(II) complexes formulated as [Ni(bipy)3][Re(NO)Br4(pyz)]2 and [Cu(bipy)2Br][ReNOBr4(pyz)] (pyz = pyrazine, bipy = 2,2′-bipyridine) were synthesized and characterized by single-crystal X-ray diffraction. The pyrazine in [Re(NO)Br4(pyz)]? was not able to act as bridge toward a second metal ion, and the two salts were obtained. Computational studies at the density functional level of theory show that the charge on the nitrogen, which could be available for bridging, is dramatically reduced to less than half, decreasing its capability to bind a second metal ion. 相似文献