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991.
Andreas Mauracher Matthias Daxner Stefan E. Huber Johannes Postler Michael Renzler Stephan Denifl Paul Scheier Andrew M. Ellis 《Angewandte Chemie (International ed. in English)》2014,53(50):13794-13797
The formation of dianions in helium nanodroplets is reported for the first time. The fullerene cluster dianions (C60)n2? and (C70)n2? were observed by mass spectrometry for n≥5 when helium droplets containing the appropriate fullerene were subjected to electron impact at approximately 22 eV. A new mechanism for dianion formation is described, which involves a two‐electron transfer from the metastable He? ion. As well as the prospect of studying other dianions at low temperature using helium nanodroplets, this work opens up the possibility of a wider investigation of the chemistry of He?, a new electron‐donating reagent. 相似文献
992.
Martin Fischnaller Rania Bakry Rainer M. Vallant Lukas A. Huber Günther K. Bonn 《Analytica chimica acta》2013
Phosphorylation of proteins is an important cellular regulatory process. The analysis of protein phosphorylation is challenging due to the high dynamic range and low abundance natures of phosphorylated species. Mass spectrometry (MS) of phosphopeptides obtained from tryptic protein digests is the method-of-choice for characterization of phosphorylated proteins. However, determination of phosphopeptides by MS represents a major challenge, especially in the presence of unmodified peptides. Due to lower ionization efficiency of phosphopeptides, as well as the fact that the stoichiometry of phosphorylation is often present at low relative abundance, efficient enrichment of the phosphorylated peptides prior to MS analysis is therefore of high demand. In addition, successful identification of peptides with different phosphorylation grades still remains challenging. 相似文献
993.
Revannath L. Sutar Elric Engelage Raphael Stoll Stefan M. Huber 《Angewandte Chemie (International ed. in English)》2020,59(17):6806-6810
Even though halogen bonding—the noncovalent interaction between electrophilic halogen substituents and Lewis bases—has now been established in molecular recognition and catalysis, its use in enantioselective processes is still very rarely explored. Herein, we present the synthesis of chiral bidentate halogen‐bond donors based on two iodoimidazolium units with rigidly attached chiral sidearms. With these Lewis acids, chiral recognition of a racemic diamine is achieved in NMR studies. DFT calculations support a 1:1 interaction of the halogen‐bond donor with both enantiomers and indicate that the chiral recognition is based on a different spatial orientation of the Lewis bases in the halogen‐bonded complexes. In addition, moderate enantioselectivity is achieved in a Mukaiyama aldol reaction with a preorganized variant of the chiral halogen‐bond donor. This represents the first case in which asymmetric induction was realized with a pure halogen‐bond donor lacking any additional active functional groups. 相似文献
994.
Noël Pairault Hui Zhu Dennis Jansen Alexander Huber Constantin G. Daniliuc Stefan Grimme Jochen Niemeyer 《Angewandte Chemie (International ed. in English)》2020,59(13):5102-5107
Heterobifunctional rotaxanes serve as efficient catalysts for the addition of malonates to Michael acceptors. We report a series of four different heterobifunctional rotaxanes, featuring an amine‐based thread and a chiral 1,1′‐binaphthyl‐phosphoric‐acid‐based macrocycle. High‐level DFT calculations provided mechanistic insights and enabled rational catalyst improvements, leading to interlocked catalysts that surpass their non‐interlocked counterparts in terms of reaction rates and stereoselectivities. 相似文献
995.
Elric Engelage Dominik Reinhard Prof. Stefan M. Huber 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3843-3861
Halogen-bond donors (halogen-based Lewis acids) have now found various applications in diverse fields of chemistry. The goal of this study was to identify a parameter obtainable from a single DFT calculation that reliably describes halogen-bonding strength (Lewis acidity). First, several DFT methods were benchmarked against the CCSD(T) CBS binding data of complexes of 17 carbon-based halogen-bond donors with chloride and ammonia as representative Lewis bases, which revealed M05-2X with a partially augmented def2-TZVP(D) basis set as the best model chemistry. The best single parameter to predict halogen-bonding strengths was the static σ-hole depth, but it still provided inaccurate predictions for a series of compounds. Thus, a more reliable parameter, Ωσ*, has been developed through the linear combination of the σ-hole depth and the σ*(C−I) energy, which was further validated against neutral, cationic, halogen- and nitrogen-based halogen-bond donors with very good performance. 相似文献
996.
997.
J.J. Romero J. Johannsen M. Mond K. Petermann G. Huber E. Heumann 《Applied physics. B, Lasers and optics》2005,80(2):159-163
Lanthanum scandium borate (LSB) has been proved to be an interesting laser matrix when doped with Nd3+ and Er3+ ions. In this paper, we demonstrate that it is also a very efficient laser material when doped with Yb3+ ions. The main spectroscopic characteristics of the system are presented, showing very broad absorption and emission bands, comparable to those found in Yb-doped GdCOB and YCOB crystals. From spectroscopic measurements the relevant laser parameters have been obtained, and a tunability of about 50 nm could be deduced. Room-temperature, continuous-wave laser action of Yb-doped LSB is demonstrated at a wavelength of 1045 nm with a slope efficiency as high as 64%. PACS 42.55.Rz; 42.70.Hj; 78.55.-m 相似文献
998.
Scanning force microscopy (SFM) was used to measure the adhesion forces between BSA, a saliva protein, and two dental surfaces, natural enamel and a filling material (Dyract AP™). Measurements were taken in phosphate buffered aqueous solutions (PBS). Forces were resolved down to the piconewton regime. The dependency of the adhesion force on the interaction time, pH-value and substrate surface was monitored. In a further step, surface samples were fixed on an enamel brace and carried for a defined time in the oral cavity. The formed biofilm, called pellicle, shows a different morphology on the different substrates. This can be explained by the above-mentioned substrate dependence of the adhesion force. 相似文献
999.
The detection of long-lived plutonium isotopes in ultra-trace amounts by resonance ionization mass spectrometry (RIMS) is
a well-established routine method. Detection limits of 106 to 107 atoms and precise measurements of the isotopic composition have been achieved. In this work multi-step resonance ionization
of plutonium atoms has been performed with tunable lasers having very different output intensities and spectral properties.
In order to compare different ways for the resonance ionization of plutonium broadband pulsed dye and titanium:sapphire lasers
as well as narrow-band cw-diode and titanium:sapphire lasers have been applied for a number of efficient excitation schemes.
It has been shown, that for identical excitation schemes the optical isotope selectivity can be improved by using cw-lasers
(bandwidths < 10 MHz) instead of pulsed lasers (bandwidths > 2 GHz). Pulsed and cw-laser systems have been used simultaneously
for resonance ionization enabling direct comparisons of pulsed and continuous ionization processes. So far, a three-step,
three-color laser excitation scheme has been proven to be most practical in terms of efficiency, selectivity and laser wavelengths.
Alternatively a newly discovered three-step, two-color excitation scheme which includes a strong two-photon transition from
an excited state into a high-lying autoionizing state yields similar ionization efficiencies. This two-photon transition was
characterized with respect to saturation behavior and line width. 相似文献