Pulse Programming

Fig. 2.9.12 Phase shift maps measured as the difference in the signal phases with and without current pulses. The rf, field gradient and current pulse program are shown in Figure 2.9.2. The phase shift maps must be unwrapped as the original evaluation yields phase angles only in the principal range between —7t/2 and +7r/2 as a consequence of the 7r periodicity of the tangent function formed as the quotient of the imaginary and real signal...

Fig. 8.4 Schematic representation of the pulse program IPAP-[ l-l-15N]-HSQC. Narrow and wide bars represent 90° and 180° pulses, with phase x unless indicated. The white bars represent pulses that are applied only when the anti-phase spectrum is acquired. The anti-phase and in-phase...

Additional files, FORMAT.TEMP, PULSEPROGRAM, VDLIST, TITLE, OUTD, PARAM.TXT, META and others may also be present if you have imported your NMR data directly from a Bruker spectrometer. These files contain additional information and settings initialized by the spectrometer operator and relate to the acquisition pulse program, lists of variable delays, spectrum title, the spectral layout and others and are non-essential for off-line data processing. 

The PCs of the system administrator and a few special users have direct access to the DRX-spectrometer.s via the central Server using the FTP protocol. This special group have direct access to any files in the spectrometer s data system, i.e. data files, variou.s lists, pulse programs,... and may transfer files to and from the spectrometers. In addition, they also have the option to create or delete directories, to modify pulse programs and to do other jobs on the spectrometer s data system. As is usual in security sensitive situations, this special group require a password to acces.s the spectrometer. 

Load the "C DEPT spectrum D NMRDATA GLUCOSE 1D C GCDP 001999.R and try out the Pulse Program... button, available in the Output pull-down menu, to inspect the DEPT pulse program. 

Compared to ID WIN-NMR the scope of the output options available with 2D WIN-NMR is less comprehensive. The inclusion of graphics elements (e.g. structural formulae), additional text files (e.g. pulse programs) and the interactive drawing of lines and rectangles is limited or not possible with 2D WIN-NMR. However the more powerful layout capabilities of ID WIN-NMR may also be exploited by 2D data sets (section 4.10.5). 

The repetition time tr of the pulse sequence is independent of 7j, which may be different for nonequivalent nuclei. The optimum repetition time has been found to be t, = 4 r [22]. DEFT NMR requires careful adjustment of pulse widths for 90° and 180° pulses and (computer-controlled) pulse programming for accurate timing between pulses and pulse sequences. Other methods for improving signal noise using other pulse sequences and spin echo trains have been described [22, 25]. DEFT NMR, however, appears to be the most efficient method so far, as long as Tj and T2 are of the same order of magnitude. 

Various parameters must be taken into account when an NMR experiment is performed. Different manufacturers (e.g., Bruker, Varian, Jeol) label some of these parameters differently however, the user manuals usually contain enough details about basic acquisition and processing. For the NMR experiments included in this protocol, the authors recommend referring to Braun et al. (1998) for descriptions of the pulse programs and important acquisition and processing parameters. The nomenclature used in this protocol... 

The standardized pulse program for a proton decoupled 13C spectrum is shown in Figure 4.2a. The sequence is relaxation delay (Rd) (see Section 4.2.3), rf pulse (6), and signal acquisition (t2). The proton channel has the decoupler on to remove the H—13C coupling, while a short, powerful rf pulse (of the order of a few microseconds) excites all the 13C nuclei simultaneously. Since the carrier frequency is slightly off resonance FID (free induction decay), for all the 13C frequencies, each 13C nucleus shows a FID, which is an exponentially decaying sine wave. 

We notice that the S/N grows proportionately to Vns, where ns is the number of scans or repetitions of the pulse program. This relationship is not typically a problem with H experiments where only a few pg to a mg of material is enough to get good S/N in a few scans. As mention previously, l3C is 6000 times less sensitive than H, and therefore requires either more sample (N), higher field strengths B0 (or better probe technology, i.e., a cryo-probe), or an increase in the number of scans (ns). 

Bruker has no corresponding parameter for dm and homo because these options are written into each pulse program. 

Now that we have the basic concept of the pulse program written down, we can start to customize and enhance it, and to consider details of making it work correctly. First of... 

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