نتایج جستجو برای: nmr shielding tensor

تعداد نتایج: 110240  

Journal: :journal of physical & theoretical chemistry 2005
m. monajemi m.a seyed sajjadi r. sayyadi g. ghassemi

structural and magnetic properties of purine and pyrimidine nucleotides (cmp, ump, dtmp, amp, gmp, imp) were studied at different levels of ab initio molecular orbital theory. these calculations were performed at the hartree-fock level and density functional b3lyp methods. geometries were fully optimized by following cs symmetry restrictions. the standard 6-31g** basis set which includes polari...

Journal: :Journal of the American Chemical Society 2006
E Janette Ruiz Devin N Sears Alexander Pines Cynthia J Jameson

Cryptophane cages serve as host molecules to a Xe atom. Functionalization of cryptophane-A has permitted the development of Xe as a biosensor. Synthetic routes used to prepare cryptophanes result in racemic mixtures of the chiral cages. In the preparation of a tethered cryptophane-A cage for biosensor applications, some achiral and chiral substituents such as left-handed amino acids have been u...

Journal: :journal of physical & theoretical chemistry 2008
s. irani m. monajjemi s.m atyabi m. sadegizadeh m. heshmat

p53 is one of the gene that has important role in human cell cycle and in the human cancers too.models of codon substitution make it possible to separate mutational biases in the dna fromselective constraints on the protein, and offer a great advantage over amino acid models forunderstanding the evolutionary process of proteins and protein-coding dna sequences. in thiswork, we investigated abou...

Abstractl Density functional theory (DFT) was used to investigate the effects of intra-moecular interactions and implicit water molecules on the relative stability and the NMR shielding tensors of hallucinogenic harmine in the monomeric and dimeric states. Results represented that the relative stability and the NMR shielding tensors are dependent on the resonance interactions and chemical envir...

Journal: :Journal of the American Chemical Society 2005
David L Bryce Alexander Grishaev Ad Bax

Incomplete motional averaging of chemical shift anisotropy upon weak alignment of nucleic acids and proteins in a magnetic field results in small changes in chemical shift. Knowledge of nucleus-specific chemical shift (CS) tensor magnitudes and orientations is necessary to take full advantage of these measurements in biomolecular structure determination. We report the determination by liquid cr...

2001
Lucio Frydman

This work investigates the nature of second order effects resulting in solid state nuclear magnetic resonance ~NMR!, from cross-correlations between the quadrupolar and shielding couplings. Using an average Hamiltonian theory, it is shown that these effects can bring the nonsecular terms of the shielding interaction into the realm of conventional detection. Such terms include the antisymmetric ...

2015
Desmond MacLeod Carey Tatiana Gomez Cesar Morales-Verdejo Alvaro Muñoz-Castro

The complexation of metal cations into a host-guest situation is particularly well exemplified by [2.2.2]paracyclophane and Ag(I), which leads to a strong cation-π interaction with a specific face of the host molecule. Through this study we sought a deeper understanding of the effects the metal center has on the NMR spectroscopic properties of the prototypical organic host, generating theoretic...

Journal: :iranian journal of chemistry and chemical engineering (ijcce) 2015
jamshid najafpour ali akbar salari forouzan zonouzi mohammad porghamdaryasari

hartree-fock (hf) and density functional theory (dft) methods employed to study the effect of conformational change on the 13c chemical shifts of 6-mono axial and equatorial substituted and 6,7-di axial-axial, equatorial-equatorial and axial-equatorial substitutedderivatives of 5,6,7,8-tetrahydrodibenzo[a,c]cyclo-octene. the geometry of the conformers have been optimized in the gas phase employ...

Journal: :The journal of physical chemistry. A 2008
Gang Wu Victor Terskikh

We report a multinuclear solid-state ( (23)Na, (39)K, (87)Rb, (133)Cs) NMR study of tetraphenylborate salts, M[BPh 4] (M = Na, K, Rb, Cs). These compounds are isostructural in the solid state with the alkali metal ion surrounded by four phenyl groups resulting in strong cation-pi interactions. From analyses of solid-state NMR spectra obtained under stationary and magic-angle spinning (MAS) cond...

Journal: :Physical review letters 2001
S Latil L Henrard C Goze Bac P Bernier A Rubio

We compute the magnetic shielding tensor within the London approximation and estimate the Knight shift of single-wall carbon nanotubes. Our results indicate that high resolution 13C NMR should be able to separate the metallic and insulator character of the nanotubes since a 11 ppm splitting is predicted from the respective resonances. As a model for disorder, bending, and defects in these struc...

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