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11.
Dr. Sebastian Lars Müller Xinglong Zhou Dr. Peter Leonard Oxana Korzhenko Dr. Constantin Daniliuc Prof. Dr. Frank Seela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):3077-3090
Silver-mediated α-dC–Ag+–β-dC hybrid base pairs decorated with 5-iodo- or 5-octadiynyl residues are well accommodated in duplex DNA. A strong Tm increase and favorable thermodynamic data for duplex DNA were observed after addition of silver ions. The phenomenon is particularly obvious when both nucleobases of the base pairs are functionalized. Neither the position of the base pair, nor the type of 5-substituent had a negative influence. On the contrary, functionalization of conventional silver-mediated β-dC–Ag+–β-dC homo base pairs showed a negative impact induced by the bulky substituents. To this end, cytosine modified 12-mer oligodeoxynucleotides were prepared by solid-phase synthesis employing new α-anomeric 2′-deoxycytidine phosphoramidites. A multigram scale synthesis was developed for 5-iodo-α-d -2′-deoxycytidine ( 1 ) employing the direct glycosylation of cytosine with Hoffer's α-d -halogenose followed by separation of anomeric DMT nucleosides. Regarding base-pair stability and functionalization silver-mediated α/β-dC hybrid base pairs were found to be superior to β/β-dC homo pairs. According to their extraordinary properties, they might find applications in DNA diagnostics, material science, or nanotechnology. 相似文献
12.
13.
Immobilized Catalysts for Iridium‐Catalyzed Allylic Amination: Rate Enhancement by Immobilization
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Dr. Chandi C. Malakar Prof. Dr. Günter Helmchen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7127-7134
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments. 相似文献
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15.
Thomas Wittmann Dr. Renée Siegel Nele Reimer Dr. Wolfgang Milius Prof. Dr. Norbert Stock Prof. Dr. Jürgen Senker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):314-323
The resistance of metal–organic frameworks towards water is a very critical issue concerning their practical use. Recently, it was shown for microporous MOFs that the water stability could be increased by introducing hydrophobic pendant groups. Here, we demonstrate a remarkable stabilisation of the mesoporous MOF Al‐MIL‐101‐NH2 by postsynthetic modification with phenyl isocyanate. In this process 86 % of the amino groups were converted into phenylurea units. As a consequence, the long‐term stability of Al‐MIL‐101‐URPh in liquid water could be extended beyond a week. In water saturated atmospheres Al‐MIL‐101‐URPh decomposed at least 12‐times slower than the unfunctionalised analogue. To study the underlying processes both materials were characterised by Ar, N2 and H2O sorption measurements, powder X‐ray diffraction, thermogravimetric and chemical analysis as well as solid‐state NMR and IR spectroscopy. Postsynthetic modification decreased the BET equivalent surface area from 3363 to 1555 m2 g?1 for Al‐MIL‐101‐URPh and reduced the mean diameters of the mesopores by 0.6 nm without degrading the structure significantly and reducing thermal stability. In spite of similar water uptake capacities, the relative humidity‐dependent uptake of Al‐MIL‐101‐URPh is slowed and occurs at higher relative humidity values. In combination with 1H‐27Al D ‐HMQC NMR spectroscopy experiments this favours a shielding mechanism of the Al clusters by the pendant phenyl groups and rules out pore blocking. 相似文献
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Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
18.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
19.
P. Seelig A. Dax S. Faber M. Gerlach G. Huber T. Kühl D. Marx P. Merz W. Quint F. Schmitt H. Winter M. Würtz 《Hyperfine Interactions》1998,114(1-4):135-139
The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric
and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique
using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics
from an ion beam at relativistic velocities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point. 相似文献