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991.
Elisabeth T. Oakley Donald F. Magin Gordon H. Bokelman William S. Ryan Jr. 《Journal of carbohydrate chemistry》2013,32(1):53-65
A procedure is described for a simple preparation that produces mixtures of a majority of the possible O-methylated alditol acetate derivatives of neutral monosaccharides. The derivatives can be used as standards to determine both the linkage positions and the precise identities of sugar constituents in cell wall poly-saccharides. 相似文献
992.
Dr. Shenglai Yao Dr. Peter Hrobárik Dipl.‐Chem. Florian Meier Dipl.‐Chem. Robert Rudolph Dr. Eckhard Bill Dr. Elisabeth Irran Prof. Dr. Martin Kaupp Prof. Dr. Matthias Driess 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1246-1253
A unique heterobimetallic disulfur monoradical, complex 2 , with a diamond‐shaped {NiS2Pt} core has been synthesized by two‐electron reduction of a supersulfido‐(nacnac)nickel(II) complex (nacnac=β‐diketiminato) with [Pt(Ph3P)2(η2‐C2H4)] as a platinum(0) source and isolated in 82 % yield. Strikingly, the results of DFT calculations in accordance with spectroscopic (EPR, paramagnetic NMR) and structural features of the complex revealed that the bonding situation of the S2 ligand is between the elusive “half‐bonded” S2 radical trianion (${{\rm S}{{{{\bullet}}3- \hfill \atop 2\hfill}}}$ ) and two separated S2? ligands. Accordingly, the NiII center is partially oxidized, whereas the PtII site is redox innocent. The complex can be reversibly oxidized to the corresponding Ni,Pt‐disulfido monocation, compound 3 , with a S? S single bond, and reacts readily with O2 to form the corresponding superoxonickel(II) and disulfidoplatinum(II) ( 4 ) complexes. These compounds have been isolated in crystalline form and fully characterized, including IR and multi‐nuclear NMR spectroscopy as well as ESI mass spectrometry. The molecular structures of compounds 2 – 4 have been confirmed by single‐crystal X‐ray crystallography. 相似文献
993.
Arne Wagner Dr. Elisabeth Kaifer Prof. Dr. Hans‐Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7395-7409
The coordination chemistry of the doubly base‐stabilised diborane(4), [HB(hpp)]2 (hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido‐[1,2‐a]pyrimidinate), was extended by the synthesis of new late transition‐metal complexes containing CuI and RhI fragments. A detailed experimental study was conducted and quantum‐chemical calculations on the metal–ligand bonding interactions for [HB(hpp)]2 complexes of Group 6, 9, 11 and 12 metals revealed the dominant B? H? M interactions in the case of early transition‐metal fragments, whereas the B? B? M bonding prevails in the case of the late d‐block compounds. These findings support the experimental results as reflected by the IR and NMR spectroscopic parameters of the investigated compounds. DFT calculations on [MeB(hpp)]2 and model reactions between [B2H4 ? 2NMe3] and [Rh(μ‐Cl)(C2H4)2] showed that the bicyclic guanidinate allows in principle for an oxidative addition of the B? B bond. However, the formation of σ‐complexes is thermodynamically favoured. The results point to the selective B? H or B? B bond‐activation of diborane compounds by complexation, depending on the chosen transition‐metal fragment. 相似文献
994.
Helge Lange Henning Schröder Elisabeth Oberem Dr. Alexander Villinger Dr. Jabor Rabeah Prof. Dr. Ralf Ludwig Prof. Dr. Klaus Neymeyr Prof. Dr. Wolfram W. Seidel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11492-11502
Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side-on λ5-phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD-DFT. Low-temperature 31P NMR and EPR spectroscopic measurements combined with time-dependent IR-spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard-modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations. 相似文献
995.
Ute Wild Petra Walter Dr. Olaf Hübner Dr. Elisabeth Kaifer Prof. Hans-Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16504-16513
Proton-coupled electron transfer (PCET) is currently intensively studied because of its importance in synthetic chemistry and biology. In recent years it was shown that redox-active guanidines are capable PCET reagents for the selective oxidation of organic molecules. In this work, the scope of their PCET reactivity regarding reactions that involve C−H activation is explored and kinetic studies carried out to disclose the reaction mechanisms. Organic molecules with potential up to 1.2 V vs. ferrocenium/ferrocene are efficiently oxidized. Reactions are initiated by electron transfer, followed by slow proton transfer from an electron-transfer equilibrium. 相似文献
996.
Shi Guo Yuta Nishina Alberto Bianco Ccilia Mnard‐Moyon 《Angewandte Chemie (International ed. in English)》2020,59(4):1542-1547
A method for the double functionalization of graphene oxide (GO) under mild alkaline conditions has been developed. Two functional groups were covalently linked to GO in two steps: the first group was attached by an epoxide ring‐opening reaction and the second, bearing an amine function, was covalently conjugated to benzoquinone attached to the GO. The doubly functionalized GO was characterized by several techniques, confirming the sequential covalent modification of the GO surface with two different functional groups. This method is straightforward and the reaction conditions are mild, allowing preservation of the structure and properties of GO. This strategy could be exploited to prepare multifunctional GO conjugates with potential applications in many fields ranging from materials science to biomedicine. 相似文献
997.
Clment Chauvier Lucie Finck Elisabeth Irran Martin Oestreich 《Angewandte Chemie (International ed. in English)》2020,59(30):12337-12341
A method for the catalytic generation of functionalized aryl alkali metals is reported. These highly reactive intermediates are liberated from silyl‐protected aryl‐substituted diazenes by the action of Lewis basic alkali metal silanolates, resulting in desilylation and loss of N2. Catalytic quantities of these Lewis bases initiate the transfer of the aryl nucleophile from the diazene to carbonyl and carboxyl compounds with superb functional‐group tolerance. The aryl alkali metal can be decorated with electrophilic substituents such as methoxycarbonyl or cyano as well as halogen groups. The synthesis of a previously unknown cyclophane‐like [4]arene macrocycle from a 1,3‐bisdiazene combined with a 1,4‐dialdehyde underlines the potential of the approach. 相似文献
998.
Matteo Andrea Lucherelli Yue Yu Giacomo Reina Gonzalo Abelln Eijiro Miyako Alberto Bianco 《Angewandte Chemie (International ed. in English)》2020,59(33):14034-14039
The synthesis of a drug delivery platform based on graphene was achieved through a step‐by‐step strategy of selective amine deprotection and functionalization. The multifunctional graphene platform, functionalized with indocyanine green, folic acid, and doxorubicin showed an enhanced anticancer activity. The remarkable targeting capacity for cancer cells in combination with the synergistic effect of drug release and photothermal properties prove the great advantage of a combined chemo‐ and phototherapy based on graphene against cancer, opening the doors to future therapeutic applications of this type of material. 相似文献
999.
We present a computational study on the folding and aggregation of proteins in an aqueous environment, as a function of its concentration. We show how the increase of the concentration of individual protein species can induce a partial unfolding of the native conformation without the occurrence of aggregates. A further increment of the protein concentration results in the complete loss of the folded structures and induces the formation of protein aggregates. We discuss the effect of the protein interface on the water fluctuations in the protein hydration shell and their relevance in the protein-protein interaction. 相似文献
1000.
Lars Erik Eng Eibak Knut Einar Rasmussen Elisabeth Leere Øiestad Stig Pedersen-Bjergaard Astrid Gjelstad 《Analytica chimica acta》2014
The repeatability and extraction recoveries of parallel electromembrane extraction (Pa-EME) was thoroughly investigated in the present project. Amitriptyline, fluoxetine, and haloperidol were isolated from eight samples of pure water, undiluted human plasma, and undiluted human urine, respectively; in total 24 samples were processed in parallel. The repeatability was found to be independent of the different sample matrices (pure water samples, human plasma, and water) processed in parallel, although the respective samples contained different matrix components. In another experiment seven of the 24 wells were perforated. Even though the perforation caused the total current level in the Pa-EME setup to increase, the intact circuits were unaffected by the collapse in seven of the circuits. In another approach, exhaustive extraction of amitriptyline, fluoxetine, and haloperidol was demonstrated from pure water samples. Amitriptyline and haloperidol were also isolated exhaustively from undiluted human plasma samples; the extraction recovery of fluoxetine from undiluted human plasma was 81%. Finally, the sample throughput was increased with the Pa-EME configuration. The extraction recoveries were investigated by processing 1, 8, 68, or 96 samples in parallel in 10 min; neither the extraction recoveries nor the repeatability was affected by the total numbers of samples. Eventually, the Pa-EME was combined with ultra performance liquid chromatography (UPLC) to combine high-throughput sample preparation with high-throughput analytical instrumentation. The aim of the present investigation was to demonstrate the potential of electromembrane extraction as a high throughput sample preparation platform; and hopefully to increase the interest for EME in the bioanalytical field to solve exisiting and novel analytical challenges. 相似文献