Band selective shaped pulse

Frequency-selective REDOR (fsREDOR) is a very powerful technique developed for the study of 13C and 15N uniformly labeled peptides or proteins [92]. The basic idea of this technique is to combine REDOR and soft n pulses to recouple a selected 13C-15N dipole-dipole interaction in a multiple-spin system. Usually one could use Gaussian shaped pulses to achieve the required selective n inversions. Other band selective shaped pulses have been developed for a more uniform excitation profile [93]. In its original implementation, fsREDOR was used to extract the intemuclear distances of several model crystalline compounds [92], In the past few years, this technique has proven to be very useful for the study of amyloid fibrils as well. For the Ure2p10 39 fibril samples containing 13C and 15N uniformly... 

Figure 3 Pulse schemes to obtain pure shift HSQC spectra. (A) HSQC-RESET experiment which uses a pseudo-3D BIRD-based ZS acquisition scheme (B) PS-HSQC experiment using real-time homodecoupling by the combination of a hard 180°( H)-BIRD element during data acquisition (C) sensitivity-improved PS-HSQC (D) HOBS-HSQC experiment using real-time homodecoupling during detection achieved by applying a pair of hard/band-selective 180° pulses (represented as solid and shaded shapes). In (B-D), the homodecoupling element is applied at the middle of 2t=AQ//i periods, where AQ is the acquisition time and n is the number of concatenated loops. See original publications for a more detailed description.

Shaped pulses are created from text files that have a line-by-line description of the amplitude and phase of each of the component rectangular pulses. These files are created by software that calculates from a mathematical shape and a frequency shift (to create the phase ramp). There are hundreds of shapes available, with names like Wurst , Sneeze , Iburp , and so on, specialized for all sorts of applications (inversion, excitation, broadband, selective, decoupling, peak suppression, band selective, etc.). The software sets the maximum RF power level of the shape at the top of the curve, so that the area under the curve will correspond to the approximately correct pulse rotation desired (90°, 180°, etc.). When an experiment is started, this list is loaded into the memory of the waveform generator (Varian) or amplitude setting unit (Bruker), and when a shaped pulse is called for in the pulse sequence, the amplitudes and phases are set in real time as the individual rectangular pulses are executed. 

Such excitations have been called shaped pulses, and a considerable effort has been expended in an attempt to optimize their shapes. A simple Gaussian shape is a considerable improvement over a rectangular pulse, but is not entirely effective in achieving an optimal peak shape. The use of more elaborate mathematical functions improves the shape of the signal, although with increasing loss of intensity. The BURP Band selective. Uniform Response, Pure phase) family utilizes an exponentially dependent sinusoidal series of Gaussians with considerable success in a variety of situations (EBURP for REBURP for 180 ). 

The excitation sculpting method was expended to the selective inversion of z-magnetisation. The method utilises DANTE train of hard pulses combined with gradient suppression of transverse magnetisation. Application of the selective inversion to z-magnetisation reduces relaxation loses and extends selective methods to larger molecule. Use of shaped pulses in DANTE train produces band-selective inversion. The proposed inversion method can be... 

Inversion of water-flanking signals during shaped pulse presaturation Multiplet-selective excitation, band-selective excitation, water suppression Separation of resonances on the basis of electrophoretic migration rates. 

Table 5.17 Pulse shapes of frequency selective, band selective and adiabatic pulses.

Julian, Jr, R.K. Cooks, R.G. Broad-band excitation in the quadmpole ion trap mass spectrometer using shaped pulses created with the inverse Fourier transform. Anal. Chem. 1993, 58, 1827-1833 Soni, M.H. Cooks, R.G. Selective injection and isolation of ions in quadmpole ion trap mass spectrometry using notehed waveforms created using the inverse Fourier transform. Anal. Chem. 1994,66, 2488-2496. 

Microwave fields are used in many different schemes in order to modify laser light in one or the other way, like side band production, laser pulse shaping, etc. Only a limited selection of the overwhelming number of papers... 

The experimental techniques of fluorescence line narrowing and hole burning were invented, in part, to access this dynamic information. They each involve selective excitation by a narrow-band laser of a nearly resonant subset of chromophores. The resulting fluorescence line shape or hole shape reflects the spectral dynamics of the members of this subset, unobscured by the other chromophores. In a similar vein, in the time-domain photon echo experiment, after the application of a short pulse the inhomogeneous dephasing of all of the chromophores is then rephased by a second pulse, and so the echo decay again reflects only transition frequency fluctuations. 

RF Pulse Pulse of radio-frequency (RF) energy transmitted by an RF coil in nuclear magnetic resonance computerized tomography. Its frequency coq is represented as 0)0 = y Ho, where y is the gyromagnetic ratio and Ho is the main magnetic field strength. Its shape and amplitude determine the selectivity in the frequency band and the amount of spin rotation. 

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