نتایج جستجو برای: asymmetric 13 dipolar

تعداد نتایج: 403606  

Journal: :Journal of biomolecular NMR 2012
K Schmidt-Rohr K J Fritzsching S Y Liao Mei Hong

Several techniques for spectral editing of 2D (13)C-(13)C correlation NMR of proteins are introduced. They greatly reduce the spectral overlap for five common amino acid types, thus simplifying spectral assignment and conformational analysis. The carboxyl (COO) signals of glutamate and aspartate are selected by suppressing the overlapping amide N-CO peaks through (13)C-(15)N dipolar dephasing. ...

Mohammad Javad Taghizadeh

Synthesis of enantiomerically pure isoxazolidine via an asymmetric 1,3- dipolar cycloaddition reaction of nitrone with electron-deficient dipolarophile was described. The process occurs at room temperature in aqueous ethanol as a green solvent and in the presence of a bidendate bis(imine)–Cu(II)triflate complex as catalyst. The reaction mechanism is discussed on the basis of the assignment of t...

Dipolar-dephasing method provides some information about the strength of dipolar coupling in solids. Dipolar dephasing technique measures the time for a polarized carbon nucleus to lose its magnetization once the proton locking field is terminated. The dynamics of guest molecules adsorbed within the cavities and channels of nonporouszeolite strongly depend on the structure and chemical composit...

2013
K. Ajay Kumar

The 1,3-Dipolar cycloaddition reactions are the classic reaction in modern synthetic organic chemistry. The concept of these reactions was introduced by Huisgen and his co-workers in the early 1960’s. 1,3-Dipolar cycloaddition reactions are simple but powerful tool for the construction of five membered heterocycles such as isoxazoles, isoxazolines, pyrazoles, pyrazolones, 1,2,4-oxadiazolines et...

2009
B. Thimme Gowda Miroslav Tokarčík Jozef Kožíšek K. Shakuntala Hartmut Fuess

The asymmetric unit of the title compound, C(12)H(13)NO(3), contains two independent mol-ecules. The conformation of the N-H bond and the C=O bond in the amide segment are anti to each other. The mol-ecular conformation of each mol-ecule is stabilized by an intra-molecular O-H⋯O hydrogen bond. In the crystal, mol-ecules are connected through intermolecular N-H⋯O hydrogen bonds. In addition, the...

Journal: :The Journal of chemical physics 2008
Lasse Arnt Straasø Morten Bjerring Navin Khaneja Niels Chr Nielsen

Dipolar truncation prevents accurate measurement of long-range internuclear distances between nuclei of the same spin species, e.g., within (13)C-(13)C spin pairs in uniformly (13)C-isotope-labeled proteins, using magic-angle spinning solid-state NMR spectroscopy. Accordingly, one of the richest sources of accurate structure information is at present not exploited fully, leaving the bulk part o...

Journal: :Journal of physics. Condensed matter : an Institute of Physics journal 2012
Frank Smallenburg Hanumantha Rao Vutukuri Arnout Imhof Alfons van Blaaderen Marjolein Dijkstra

Colloidal particles with a dielectric constant (magnetic susceptibility) mismatch with the surrounding solvent acquire a dipole moment in a homogeneous external electric (magnetic) field. The resulting dipolar interactions can lead to aggregation of the particles into string-like clusters. Recently, several methods have been developed to make these structures permanent. However, especially when...

Journal: :Chemical communications 2011
Qing-Hua Li Min-Chao Tong Jun Li Hai-Yan Tao Chun-Jiang Wang

Trifluoromethylated pyrrolidines have been synthesized via catalytic asymmetric 1,3-dipolar cycloaddition with excellent stereoselectivity for the first time. Epimerization of the endo-pyrrolidines obtained from cis-4,4,4-trifluorocrotonate into the exo-pyrrolidines was also revealed.

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