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排序方式: 共有120条查询结果,搜索用时 15 毫秒
101.
102.
Riedel K Herbst C Leppert J Ohlenschläger O Görlach M Ramachandran R 《Journal of biomolecular NMR》2007,37(4):277-286
At high magic angle spinning (MAS) frequencies the potential of tanh/tan adiabatic RF pulse schemes for 13C chemical shift correlation without 1H decoupling during mixing has been evaluated. It is shown via numerical simulations that a continuous train of adiabatic
13C inversion pulses applied at high RF field strengths leads to efficient broadband heteronuclear decoupling. It is demonstrated
that this can be exploited effectively for generating through-bond and through-space, including double-quantum, correlation
spectra of biological systems at high magnetic fields and spinning speeds with no 1H decoupling applied during the mixing period. Experiments carried out on a polycrystalline sample of histidine clearly suggest
that an improved signal to noise ratio can be realised by eliminating 1H decoupling during mixing. 相似文献
103.
104.
Michela Carella Oliver Ohlenschläger Ramadurai Ramachandran Matthias Görlach 《Biomolecular NMR assignments》2010,4(1):93-95
The 1H, 13C and 15N resonance assignment of a type-B zinc-binding methionine sulfoxide reductase lacking a ‘recycling’ cysteine from the thermophilic archeabacterium Methanothermobacter thermoautotrophicus is reported. 相似文献
105.
106.
The F-spondin genes are a family of extracellular matrix molecules united
by two conserved domains, FS1 and FS2, at the amino terminus plus a
variable number of thrombospondin repeats at the carboxy terminus.
Currently, characterized members include a single gene in Drosophila and
multiple genes in vertebrates. The vertebrate genes are expressed in the
midline of the developing embryo, primarily in the floor plate of the
neural tube. To investigate the evolution of chordate F-spondin genes, I
have used the basal position in chordate phylogeny of the acraniate
amphioxus. A single F-spondin-related gene, named AmphiF-spondin, was
isolated from amphioxus. Based on molecular phylogenetics, AmphiF-spondin
is closely related to a particular subgroup of vertebrate F-spondin genes
that encode six thrombospondin repeats. However, unlike these genes,
expression of AmphiF-spondin is not confined to the midline but is found
through most of the central nervous system. Additionally, AmphiF-spondin
has lost three thrombospondin repeats and gained two fibronectin type III
repeats, one of which has strong identity to a fibronectin type III repeat
from Deleted in Colorectal Cancer (DCC). Taken together, these results
suggest a complex evolutionary history for chordate F-spondin genes that
includes (1) domain loss, (2) domain gain by tandem duplication and
divergence of existing domains, and (3) gain of heterologous domains by
exon shuffling.
相似文献
107.
Riedel K Herbst C Leppert J Ohlenschläger O Görlach M Ramachandran R 《Journal of biomolecular NMR》2006,35(4):275-283
A simple approach is demonstrated for designing optimised broadband inversion pulses for MAS solid state NMR studies of biological systems. The method involves a two step numerical optimisation procedure and takes into account experimental requirements such as the pulse length, resonance offset range and extent of H1 inhomogeneity compensation needed. A simulated annealing protocol is used initially to find appropriate values for the parameters that define the well known tanh/tan adiabatic pulse such that a satisfactory spin inversion is achieved with minimum RF field strength. This information is then used in the subsequent stage of refinement where the RF pulse characteristics are further tailored via a local optimisation procedure without imposing any restrictions on the amplitude and frequency modulation profiles. We demonstrate that this approach constitutes a generally applicable tool for obtaining pulses with good inversion characteristics. At moderate MAS frequencies the efficacy of the method is experimentally demonstrated for generating double-quantum NMR spectra via the zero-quantum dipolar recoupling scheme RFDR. 相似文献
108.
Kirschstein A Herbst C Riedel K Carella M Leppert J Ohlenschläger O Görlach M Ramachandran R 《Journal of biomolecular NMR》2008,40(4):227-237
We have explored the design of broadband scalar coupling mediated 13C–13C and cross-relaxation suppressed 1H–1H TOCSY sequences employing phase/amplitude modulated inversion pulses. Considering a variety of supercycles, pulsewidths
and a RF field strength of 10 kHz, the Fourier coefficients defining the amplitude and phase modulation profiles of the 180°
pulses were optimised numerically so as to obtain efficient magnetisation transfer within the desired range of resonance offsets.
The coherence transfer characteristics of the mixing schemes were assessed via numerical simulations and experimental measurements
and were compared with commonly used sequences based on rectangular RF pulses. The efficacies of the clean 1H–1H TOCSY sequences were also examined via numerical simulations for application to weakly oriented systems and sequences with
efficient, broadband and clean dipolar transfer characteristics were identified. In general, the amplitude and phase modulated
TOCSY sequences presented here have moderately better performance characteristics than the sequences currently employed in
biomolecular NMR spectroscopy. 相似文献
109.
Kirschstein A Herbst C Riedel K Carella M Leppert J Ohlenschläger O Görlach M Ramachandran R 《Journal of biomolecular NMR》2008,40(4):277-283
The design of mixing sequences for heteronuclear J cross-polarisation in the liquid state has been examined employing supercycles of amplitude/phase modulated RF pulses. The
Fourier coefficients defining the modulation profiles of the pulses were optimised numerically so as to achieve efficient
magnetisation transfer within the desired range of resonance offsets. A variety of supercycles, pulsewidths and RF field strengths
were considered in implementing heteronuclear anisotropic and isotropic mixing sequences. The coherence transfer characteristics
of the sequences obtained were evaluated by numerical simulations. The experimental performances of the sequences were tested
by measurements carried out on a moderate sized protein at 750 MHz. The results presented demonstrate that the approach adopted
in this study can be employed effectively to tailor, as per the experimental requirements and constraints, the RF-field modulation
profiles of the pulses constituting the mixing scheme for generating heteronuclear J cross-polarisation sequences. 相似文献