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951.
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
952.
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
953.
The present work investigates the structure of large polystyrene (PS) chains in solutions of small poly(ethyl methacrylate) (PEMA) microgel particles in toluene. Toluene is a good solvent for the PS chains. The PEMA colloids have an outer radius of R=11 nm which is much smaller in size than the radius of gyration Rg=58 nm of the PS chains. The system is considered to represent the protein limit of polymer-colloid mixtures. Structural investigation is performed by small-angle neutron scattering (SANS) using an appropriate contrast matching. This could be achieved by dissolving fully deuterated PS chains (D8-PS) in solutions of hydrogenated PEMA colloids in hydrogenated toluene (H-toluene). It is first demonstrated that PEMA colloids are satisfactorily contrast matched for SANS in H-toluene if the PEMA concentration does not exceed 200 g/l. Based on these findings, D8-PS is investigated by SANS in pure H-toluene and three different PEMA concentrations in H-toluene. The results indicate a drastic shrinking of D8-PS chain dimensions with increasing PEMA content. Comparison with model curves of star-branched Gaussian chains and Gaussian rings suggest a striking similarity of the respective density-density correlation of those models with the shrunken D8-PS chains. Along with this, a shrinking as large as 0.5 was estimated when the PEMA content reached 200 g/l. 相似文献
954.
Katja Melchior Andreas Tholey Sabrina Heisel Andreas Keller Hans-Peter Lenhof Eckart Meese Christian G. Huber 《Journal of chromatography. A》2010,1217(40):6159-6168
The availability of robust and highly efficient separation methods represents a major requirement for proteome analysis. This study investigated the characteristics of two different gel-free proteomic approaches to the fractionation of proteolytic peptides and intact proteins, respectively, in a first separation dimension. Separation and mass spectrometric detection by matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) were performed at the peptide level in both methods. Bottom-up analysis (BU) was carried out employing well established peptide fractionation in the first separation dimension by strong cation-exchange chromatography (SCX), followed by ion-pair reversed-phase chromatography (IP-RPC) in the second dimension. In the semi-top-down approach (STD), which involved intact protein fractionation in the first dimension, the separation mode in both dimensions was IP-RPC utilizing monolithic columns. Application of the two approaches to the proteome analysis of proteins extracted from a tumor tissue revealed that the BU method identified more proteins (1245 in BU versus 920 in STD) while STD analysis offered higher sequence coverage (14.8% in BU versus 17.5% in STD on average). The identification of more basic and larger proteins was slightly favored in the BU approach, most probably due to higher losses of these proteins during intact protein handling and separation in the STD method. A significant degree of complementarity was revealed by an approximately 33% overlap between one BU and STD replicate, while 33% each of the protein identifications were unique to both methods. In the STD method, peptides obtained upon digestion of the proteins contained in fractions of the first separation dimension covered a broad elution window in the second-dimension separation, which demonstrates a high degree of “pseudo-orthogonality” of protein and peptide separation by IP-RPC in both separation dimensions. 相似文献
955.
C. Brandt S. T. Fredrich-Thornton K. Petermann G. Huber 《Applied physics. B, Lasers and optics》2011,102(4):765-768
Photoconductivity has been found in the dielectric laser materials Yb3+:YAG and Yb3+:Lu2O3 under 940?nm irradiation with an unexpected high photocurrent up to several 100 nanoampères. The nonlinear intensity dependence points to the occurrence of a cooperative upconversion mechanism with 2?C3 excited Yb3+-ions in YAG and 2 excited Yb3+-ions in Lu2O3 being involved. According to the results two tentative models of this upconversion process are discussed. 相似文献
956.
Excited state absorption and stimulated emission of Nd3+ in crystals. Part 2: YVO4, GdVO4, and Sr5(PO4)3F 总被引:1,自引:0,他引:1
L. Fornasiero S. Kück T. Jensen G. Huber B.H.T. Chai 《Applied physics. B, Lasers and optics》1998,67(5):549-553
3+ ion in the crystals YVO4, GdVO4, and Sr5(PO4)3F. The measurements were performed in the spectral region of the main laser transitions 4F3/2→4I9/2, 4F3/2→4I11/2, and 4F3/2→4I13/2by a continuous wave pump and probe technique. The calibrated gain and ESA spectra are presented and possible implications
of ESA on the laser performance are estimated. It is shown that ESA can be a small loss factor to the laser emission near
1060 nm but does considerably diminish the effective emission cross sections near 1340 nm especially in Nd:YVO4 and Nd:GdVO4.
Received: 29 January 1998/Revised version: 8 May 1998 相似文献
957.
L. Huber 《Accreditation and quality assurance》1996,1(1):24-34
The quality process for commercial analytical equipment starts with the selection of the vendor. It is recommended that vendors
be selected who are recognized as having quality processes in place for instrument design, development, manufacturing, testing,
service, and support, for example, ISO 9001 registration. When the instrument arrives in the laboratory, the installation
process should follow well-documented procedures. This includes a visual inspection that the instrument is not damaged and
checking that the instrument, documentation and accessories such as cables and tubings are complete. Before the instrument
is used it should be verified that it meets functional and performance specification. During operation the instruments should
be periodically inspected and tested, verified to meet performance, and calibrated. The instrument should be labeled with
the calibration status, indicating the dates of the last successful and the next performance verification and calibration.
Defective instruments should be removed from the testing area or should at least be labeled as being "out of order."
Received 23 August 1995 Accepted 6 September 1995 相似文献
958.
Mark Huber 《Random Structures and Algorithms》2019,55(2):356-370
Randomized approximation algorithms for many #P‐complete problems (such as the partition function of a Gibbs distribution, the volume of a convex body, the permanent of a {0,1}‐matrix, and many others) reduce to creating random variables X1,X2,… with finite mean μ and standard deviation σ such that μ is the solution for the problem input, and the relative standard deviation |σ/μ| ≤ c for known c. Under these circumstances, it is known that the number of samples from the {Xi} needed to form an (?,δ)‐approximation that satisfies is at least . We present here an easy to implement (?,δ)‐approximation that uses samples. This achieves the same optimal running time as other estimators, but without the need for extra conditions such as bounds on third or fourth moments. 相似文献
959.
Jones GB Wright JM Hynd G Wyatt JK Warner PM Huber RS Li A Kilgore MW Sticca RP Pollenz RS 《The Journal of organic chemistry》2002,67(16):5727-5732
Efficient routes to three classes of 10-membered oxa-enediynes are presented. The electronic and stereoelectronic contributions to half-lives are supported by density functional theory calculations. One member of this class cyclizes to give an isochroman which binds to and degrades the aryl hydrocarbon receptor (AhR). 相似文献
960.
Bohris C Schreiber WG Jenne J Simiantonakis I Rastert R Zabel HJ Huber P Bader R Brix G 《Magnetic resonance imaging》1999,17(4):603-610
A new quantitative method has been developed for real-time mapping of temperature changes induced by high intensity focused ultrasound (HIFU). It is based on the temperature dependence of the T1 relaxation time and the equilibrium magnetization. To calibrate the temperature measurement, the functional relationship between T1 and temperature was examined in different samples of porcine muscle and fatty tissue. The method was validated by a comparison of calculated temperature maps with fiber-optic measurements in heated muscle tissue. The experiment showed that the accuracy of the MR method for temperature measurements is better than 1 degree C. Since the acquisition time of the employed MR sequence takes only 3 s per slice and the calculation of the temperature map can be performed within seconds, the imaging technique works nearly in real-time. The temperature measurement could be realized during HIFU showing no disturbances by ultrasound sonication. In comparison to other MR approaches, the advantages of the introduced method lie in a sufficient accuracy and time resolution combined with a reasonable robustness against motion as well as the feasibility for temperature monitoring in fatty tissues. 相似文献