Band-selective

As explained before, the scores of the spectra can be plotted in the space defined by the two principal components of the data matrix. The appearance of the scores plot depends on the way the rows (spectra) and the columns have been normalized. If the spectra are not normalized, all spectra are situated in a plane (see Fig. 34.5). From the origin two straight lines depart, which are connected by a curved line. We have already explained that the straight line segments correspond with the pure spectra which are located in the wings of the elution bands (selective retention time... 

Figure 28 Excerpts of an HMBC (top), BS-HMBC (middle) and CT-BS-HMBC (bottom) spectra showing the carbonyl part of cyclosporine using the standard HMBC pulse sequence and the CT-BS-HMBC of Claridge.73 The conventional non-selective HMBC was acquired with a 200-ppm, 3C window. The band-selective (middle) and the constanttime band-selective (bottom) HMBC were acquired with a 6-ppm window cantered at 172 ppm. Selective excitation was achieved with a 13C 1 ms 180° seduce-1 pulse.

The band-selective constant-time HMBC, or the ultra resolved 10-ppm HMBC, aiming at providing a better resolution in the 13C dimension,... 

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... 

Another useful technique which is closely related to fsREDOR is the band-selective transferred echo double resonance (BASE TEDOR) [102]. As shown in Fig. 6, the... 

Fig. 6.4 Pulse schemes for MQ [37] (a) and TROSY [45] (b) HCN experiments. The thin and thick bars represent nonselective 90° and 180° pulses, respectively. <5=1.60 ms forJci hv or 1.25 ms for Jc6/8H6/sl zl = 15 ms. The band-selective pulses are set as follows (500 MHz) proton 4 ms band-selective 180° REBURP pulses centered at 5.7 ppm and 7.8 ppm for HI and H6/8 correlations, respectively 3.0 ms REBURP centered at 90 ppm for HsCNb (a) or 2.5 ms REBURP centered at 140 ppm for HbCNb correlations in b ...

This contribution will describe the manipulation of spin multiplets as a whole, and the word selective - or soft - will be used for multiplet-selective pulses, in contrast to band-selective, which refers to a broader bandwidth which may affect several spins, and to transition selective when only one line is affected. The discussion will be based on proton spectra, but all aspects are similar for other nuclei. Soft pulses use lower amplitudes and much longer irradiation times than non-selective hard pulses. Typical durations for soft pulses are of the order of 1 to 500 ms with a peak amplitude... 

Better profiles may sometimes be needed, in which case an E-BURP-1 is recommended, particularly for band-selective experiments. The calibration is relatively easy and very narrow transition regions are very useful (fig. 1). If a universal pulse is needed, the E-BURP-1 may either be replaced by a pulse, or if only a conversion of or ly into Iz is required, by a time-reversed E-BURP-1. 

Another way of avoiding overlaps seen in two-dimensional spectra is to introduce the third dimension. This has been illustrated with the 3D NOESY-HOHAHA [21-25], 3D HOHAHA-NOESY [25-27], NOESY-COSY [28, 29], COSY-NOESY [28] and ROESY-TOCSY [23] experiments. A principal drawback, associated with homonuclear 3D techniques, is the low digital resolution achievable along the first and second spectral axes. This limitation can to certain extent be removed by implementing band selective pulses into the 3D homonuclear experiments [21, 26, 28-31]. 

The DANTE-Z sequence has been employed successfully as a ID substitute in pseudo 3D experiments [7] and also as a band-selective technique in multidimensional experiments [8] in order to improve the spectral resolution. The efficiency of the DANTE-Z procedure over the simple DANTE sequence is illustrated by the spectra shown in fig. 2. 

One of the most interesting applications of Femtochemistry is the stroboscopic measuring of observables related to molecular motion, for instance the vibrational periods or the breaking of a bond [1], Because femtosecond laser fields are broadband, a wave packet is created by the coherent excitation of many vibrational states, which subsequently evolves in the electronic potential following mostly a classical trajectory. This behavior is to be contrasted to narrow band selective excitation, where perhaps only two (the initial and the final) states participate in the superposition, following typically a very non-classical evolution. In this case one usually is not interested in the evolution of other observables than the populations. 

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. 

The unique feature of ultra-fast MAS NMR spectroscopy is the possibility of using the band-selective CP experiment. This approach was recently reported by... 

Band-selective SPECIFIC-CP experiment can be also carried out for phosphorus samples with distinct 31P chemical shifts. To the applicability of this approach, we present a model compound 1 (Scheme 1) with P = S and P = 0 residues separated by 60 ppm. 

Band-selective 1H—31P CP transfer can be achieved using either ZQ or DQ matching conditions if careful attention is paid to the choice of the RF field amplitudes and 31P carrier. SPECIFIC transfer is possible whenever one of the following conditions is fulfilled ... 

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