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101.
Reiss TO Khaneja N Glaser SJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,154(2):192-195
Based on principles of geometric optimal control theory, coherence transfer building blocks can be derived which achieve optimal sensitivity. Here, experimental pulse sequences are presented that achieve the best possible coherence-order-selective in-phase transfer (S(-)-->I(-)) for a heteronuclear 2-spin system for any given mixing time in the absence of relaxation. For short mixing times, the optimal experiment improves the sensitivity of isotropic mixing by up to 12.5%. 相似文献
102.
Double stranded DNA chain is known to have non-trivial elasticity. We study the effect of this elasticity on the denaturation
profile of DNA oligomer by constraining one base pair at one end of the oligomer to remain in unstretched (or intact) state.
The effect of this constraint on the denaturation profile of the oligomer has been calculated using the Peyrard-Bishop Hamiltonian.
The denaturation profile is found to be very different from the free (i.e. without the constraint) oligomer. We have also
examined how this constraint affects the denaturation profile of the oligomer having a segment of defect sites located at
different parts of the chain. 相似文献
103.
The modification of mitochondrial proteins enriched from rat forebrain by the major lipid peroxidation product 4-hydroxy-2-nonenal (HNE) was investigated using high performance liquid chromatography (HPLC) and tandem mass spectrometry. Subcellular fractionation in conjunction with a 'shotgun-based' approach that involved both conventional data-dependent and neutral loss (NL)-driven MS(3) data acquisition on a hybrid linear ion trap-Fourier transform ion cyclotron resonance mass spectrometer (LTQ-FT) was utilized. Using a relatively rapid linear HPLC gradient (1 h) for complex mixture analysis, 24 sites of HNE modification on 15 unique proteins were identified which corresponded exclusively to Michael adduct formation on histidine residues. Since a number of HNE-modified peptides produced a predominant HNE NL fragment-ion signal upon collision-induced dissociation (CID), NL-driven MS(3) data-dependent acquisition was a valuable method to enhance fragmentation information for these particular modified peptides. Of the 24 HNE modification sites identified, approximately 25% were determined from the MS(3) spectra alone. We envision the reported methodology as an efficient screening approach for HNE modification site selectivity that could ultimately provide a foundation for the development of targeted schemes for the characterization of in vivo HNE-protein adducts. 相似文献
104.
Covalent adduction of the model protein apomyoglobin by 4-hydroxy-2-nonenal, a reactive end-product of lipid peroxidation,
was characterized by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR). The
high mass resolving power and mass measurement accuracy of the instrument facilitated a detailed compositional analysis of
the complex reaction product without the need for deconvolution and transformation to clearly show the pattern of adduction
and component molecular weights. Our study has also demonstrated the value of electron capture dissociation over collision-induced
dissociation for the tandem mass spectrometric determination of site modification for the 4-hydroxy-2-nonenal adduct of oxidized
insulin B chain as an example.
Figure FTICR allowed characterization of 4-hydroxy-2-nonenal (HNE)-modified apomyoglobin (an expanded spectrum of the +15 charge
state is shown) 相似文献
105.
Optimal control based NCO and NCA experiments for spectral assignment in biological solid-state NMR spectroscopy 总被引:1,自引:1,他引:0
Kehlet C Bjerring M Sivertsen AC Kristensen T Enghild JJ Glaser SJ Khaneja N Nielsen NC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,188(2):216-230
We present novel pulse sequences for magic-angle-spinning solid-state NMR structural studies of (13)C,(15)N-isotope labeled proteins. The pulse sequences have been designed numerically using optimal control procedures and demonstrate superior performance relative to previous methods with respect to sensitivity, robustness to instrumental errors, and band-selective excitation profiles for typical biological solid-state NMR applications. Our study addresses specifically (15)N to (13)C coherence transfers being important elements in spectral assignment protocols for solid-state NMR structural characterization of uniformly (13)C,(15)N-labeled proteins. The pulse sequences are analyzed in detail and their robustness towards spin system and external experimental parameters are illustrated numerically for typical (15)N-(13)C spin systems under high-field solid-state NMR conditions. Experimentally the methods are demonstrated by 1D (15)N-->(13)C coherence transfer experiments, as well as 2D and 3D (15)N,(13)C and (15)N,(13)C,(13)C chemical shift correlation experiments on uniformly (13)C,(15)N-labeled ubiquitin. 相似文献
106.
107.
In this paper, we introduce algorithms based on Fourier synthesis for designing phase compensating rf pulse sequences for high-resolution nuclear magnetic resonance (NMR) spectroscopy in an inhomogeneous B0 field. We show that using radio frequency pulses and time varying linear gradients in three dimensions, it is possible to impart the transverse magnetization of spins phase, which is a desired function of the spatial (x,y,z) location. Such a sequence can be used to precompensate the phase that will be acquired by spins at different spatial locations due to inhomogeneous magnetic fields. With this precompensation, the chemical shift information of the spins can be reliably extracted and high resolution NMR spectrum can be obtained. 相似文献
108.
Cross-sections for production of evaporation residues from the compound nucleus96Ru* formed by fusion reactions28Si+68Zn,32S+64Ni,37Cl+59Co and45Sc+51V have been obtained from the yields of their characteristicγ-rays. The measurements span an excitation energy range of 55 MeV to 70 MeV of the compound nucleus. The evaporation residue
(ER) cross-sections have been analysed in terms of statistical model for the decay of the compound nucleus. A good agreement
is found between statistical model calculation and the experimental evaporation residue cross-sections in all the four cases.
It is shown that the average angular momentum
of the compound nucleus can be deduced from a comparison of the experimentally measured and the statistical model predictions
for the ER cross-sections. The validity of this method of deriving
has been discussed for the case of16O+154Sm system. 相似文献
109.
S Nagaraj H C Jain P K Joshi S D Paul R Palit H V Panchal B S Naidu A Chatterjee A Navin 《Pramana》2001,57(1):219-222
A recoil mass spectrometer (RMS) has been designed, fabricated and installed at the 15° S beam-line of the Pelletron at TIFR.
The RMS consists of a quadrupole doublet just after the target chamber followed by an ‘electrostatic deflector’, a magnetic
dipole and a second electrostatic deflector. The recoils produced in the 12C + 58Ni reaction using 60 MeV 12C beam were focussed with the help of electric and magnetic fields and detected in a strip detector placed at the focal plane
of the RMS. Further testing of the spectrometer to obtain mass resolution and efficiency are in progress. 相似文献
110.
We investigate the locally rotationally symmetric (LRS) Bianchi type-Ⅰ cosmological model for stiff matter and a vacuum solution with a cosmological term proportional to R^-m (R is the scale factor and m is a positive constant). The cosmological term decreases with time. We obtain that for both the cases the present universe is accelerating with a large fraction of cosmological density in the form of a cosmological term. 相似文献