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131.
General,Highly Selective Synthesis of 1,3‐ and 1,4‐Difunctionalized Building Blocks by Regiodivergent Epoxide Opening 下载免费PDF全文
Nico Funken Felix Mühlhaus Prof. Dr. Andreas Gansäuer 《Angewandte Chemie (International ed. in English)》2016,55(39):12030-12034
We describe a regiodivergent epoxide opening (REO) featuring a catalyst‐controlled synthesis of enantiomerically and diastereomerically highly enriched or pure syn‐ and anti‐ 1,3‐ and 1,4‐difunctionalized building blocks from a common epoxide precursor. The REO is attractive for natural product synthesis and as a branching reaction for diversity‐oriented synthesis with epoxides. 相似文献
132.
Increasing the Chemical‐Shift Dispersion of Unstructured Proteins with a Covalent Lanthanide Shift Reagent 下载免费PDF全文
Dr. Christoph Göbl Moritz Resch Dr. Madeleine Strickland Christoph Hartlmüller Martin Viertler Dr. Nico Tjandra Prof. Dr. Tobias Madl 《Angewandte Chemie (International ed. in English)》2016,55(47):14847-14851
The study of intrinsically disordered proteins (IDPs) by NMR often suffers from highly overlapped resonances that prevent unambiguous chemical‐shift assignments, and data analysis that relies on well‐separated resonances. We present a covalent paramagnetic lanthanide‐binding tag (LBT) for increasing the chemical‐shift dispersion and facilitating the chemical‐shift assignment of challenging, repeat‐containing IDPs. Linkage of the DOTA‐based LBT to a cysteine residue induces pseudo‐contact shifts (PCS) for resonances more than 20 residues from the spin‐labeling site. This leads to increased chemical‐shift dispersion and decreased signal overlap, thereby greatly facilitating chemical‐shift assignment. This approach is applicable to IDPs of varying sizes and complexity, and is particularly helpful for repeat‐containing IDPs and low‐complexity regions. This results in improved efficiency for IDP analysis and binding studies. 相似文献
133.
134.
Chin PT Donega Cde M van Bavel SS Meskers SC Sommerdijk NA Janssen RA 《Journal of the American Chemical Society》2007,129(48):14880-14886
In this work we present the preparation of highly luminescent anisotropic CdTe/CdSe colloidal heteronanocrystals. The reaction conditions used (low temperature, slow precursor addition, and surfactant composition) resulted in a tunable shape from prolate to branched CdTe/CdSe nanocrystals. Upon CdSe shell growth the heteronanocrystals show a gradual evolution from type-I to type-II optical behavior. These heteronanocrystals show a remarkably high photoluminescence quantum yield (up to 82%) and negligible thermally induced quenching up to temperatures as high as 373 K. 相似文献
135.
Katrina A. Jolliffe Mercedes Crego Calama Roel Fokkens Nico M. M. Nibbering Peter Timmerman David N. Reinhoudt 《Angewandte Chemie (International ed. in English)》1998,37(9):1247-1251
The high affinity of Ag + ions for aromatic π donors and cyano groups is exploited in a novel MALDI-TOF mass spectrometric method for the identification of hydrogen-bonded assemblies. The interaction with the Ag+ ions—which, for example, can be complexed by two phenyl groups in a sandwich-type manner (see drawing on the right)—provides positively charged assemblies in a nondestructive way. 相似文献
136.
Osamu Sekiguchi Takuya Masuda Susumu Tajima Nico M. M. Nibbering 《Journal of the American Society for Mass Spectrometry》1998,9(10):1029-1034
The metastable decompositions of trimethylsilylmethanol, (CH3)3SiCH2OH (MW: 104, 1) and methoxytrimethylsilane, (CH3)3SiOCH3 (MW: 104, 2) upon electron ionization have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectroscopy and D labeling. The metastable ions of 1 ·+ decompose to give the fragment ions m/z 89 (CH 3 · loss) and 73 (·CH2OH loss), whereas those of 2 ·+ only yield the fragment ion m/z 89 (CH 3 · loss). The latter fragment ion is generated by loss of a methyl radical from the trimethylsilyl group via a simple cleavage reaction as shown by D labeling. However, the fragment ions m/z 89 and 73 from 1 ·+ are generated following an almost statistical exchange of the original methyl and methylene hydrogen atoms in the molecular ion as shown also by D labeling. This exchange indicates a complex rearrangement of the molecular ion of 1 ·+ prior to metastable decomposition for which as key step a 1,2-trimethylsilyl group migration from carbon to oxygen is suggested. A different behavior is also found between the source-generated m/z 89 ions from 1 ·+ which decompose in the metastable time region to give ions m/z 61 by loss of ethylene and those from 2 ·+ which decompose in the metastable region to yield ions m/z 59 by elimination of formaldehyde. 相似文献
137.
Bogdan Bogdanov Henri E. K. Matimba Steen Ingemann Nico M. M. Nibbering 《Journal of the American Society for Mass Spectrometry》1996,7(7):639-652
The mechanism of propene loss from protonated phenyl n-propyl ether and a series of mono-, di-, and trimethylphenyl n-propyl ethers has been examined by chemical ionization (CI) mass spectrometry in combination with tandem mass spectrometry experiments. The role of initial proton transfer to the oxygen atom and the aromatic ring, respectively, has been probed with the use of deuterated CI reagents, D2O, CD3OD, and CD3CN (given in order of increasing proton affinity), in combination with deuterium labeling of the β position of the n-propyl group or the phenyl ring. The metastable [M + D]+ ions of phenyl n-propyl ether—formed with D2O as the CI reagent—eliminate C3H5D and C3H6 in a ratio of 10:90, which indicates that the added deuteron is incorporated to a minor extent in the expelled neutral species. In the experiments with CD3OD as the CI reagent, the ratio between the losses of C3H5D and C3H6 from the metastable [M + D]+ ions of phenyl n-propyl ether is 18:82, whereas the ratio becomes 27:73 with CD3CN as the reagent. A similar trend in the tendency to expel a propene molecule that contains the added deuteron is observed for the metastable [M + D]+ ions of phenyl n-propyl ether labeled at the β position of the alkyl group. Incorporation of a hydrogen atom that originates from the aromatic ring in the expelled propene molecule is of negligible importance as revealed by the minor loss of C3H5D from the metastable [M + H]+ ions of C6D5OCH2CH2CH3 irrespective of whether H2O, CH3OH, or CH3CN is the CI reagent. The combined results for the [M + D]+ ions of phenyl n-propyl ether and deuterium-labeled analogs are suggested to be in line with a model that assumes that propene loss occurs not only from species formed by deuteron transfer to the oxygen atom, but also from ions generated by deuteron transfer to the ring. This is substantiated by the results for the methyl-substituted ethers, which reveal that the position as well as the number of methyl groups bonded to the ring exert a marked effect on the relative importances of the losses of C3H5D and C3H6 from the metastable [M + D]+ ions of the unlabeled methyl-substituted species. 相似文献
138.
Hana Robson Marsden Nina A. Elbers Paul H. H. Bomans Dr. Nico A. J. M. Sommerdijk Dr. Alexander Kros Dr. 《Angewandte Chemie (International ed. in English)》2009,48(13):2330-2333
Let's get together : A minimal model system was developed to mimic the SNARE‐protein‐mediated fusion of biological membranes (see picture). Fusion between two populations of liposomes is controlled by a pair of complementary lipidated oligopeptides that form noncovalent coiled‐coil complexes and thereby force the membranes into close proximity to promote fusion. The model system displays the key characteristics of in vivo fusion events.
139.
Solvated ions are becoming increasingly important for (bio)molecular simulations. But there are not much suitable data to validate the intermediate-range solution structure that ion-water force fields produce. We compare six selected combinations of four biomolecular Na-Cl force fields and four popular water models by means of effective ion-ion potentials. First we derive an effective potential at high dilution from simulations of two ions in explicit water. At higher ionic concentration multibody effects will become important. We propose to capture those by employing a concentration dependent dielectric permittivity. With the so obtained effective potentials we then perform implicit solvent simulations. We demonstrate that our effective potentials accurately reproduce ion-ion coordination numbers and the local structure. They allow us furthermore to calculate osmotic coefficients that can be directly compared with experimental data. We show that the osmotic coefficient is a sensitive and accurate measure for the effective ion-ion interactions and the intermediate-range structure of the solution. It is therefore a suitable and useful quantity for validating and parametrizing atomistic ion-water force fields. 相似文献
140.
On the one hand, it is well known that Gaussian beams possess the ability to stimulate Rayleigh waves, resulting in the Schoch effect, a lateral beam displacement. This effect, often characterized by a reflected sound pattern consisting of two anti-phase beams, is due to the re-radiation of sound because of the stimulation of leaky Rayleigh waves. On the other hand, fringed sound beams are characterized by the fact that they consist of a number of neighboring anti-phase narrow beams. They are a first approximation of a sound field originating from a phased array of harmonic vibrating crystals in which each crystal vibrates in anti-phase compared to its neighbor. The individual lobes within the fringed sound pattern diverge much less than standard Gaussian beams of the same size. The current study investigates the interaction of fringed beams with a liquid-solid interface. It is found that under certain conditions, a fringed beam, incident at the Rayleigh angle, produces a reflected sound pattern that contains a wide lobe that is not fringed. It is also shown that under other conditions, contrary to the famous forward displacement of the reflected sound for incident Gaussian beams, a strong backward displacement occurs for fringed beams. 相似文献