DANTE spectra

Mass Spectrometry Ethers like alcohols lose an alkyl radical from their molecular ion to give an oxygen stabilized cation Thus m/z 73 and m/z 87 are both more abun dant than the molecular ion m the mass spectrum of sec butyl ethyl ether... 

Fig. 2. Left Experimental profiles of the conventional DANTE sequence (top) and of the DANTE-Z sequence (bottom). The sample used was 5% H2O in D2O with a tiny amount of copper sulfate added (leading to a T of approximately 3 s). The different traces were obtained by shifting the carrier frequency in 50 Hz steps without readjustment of the spectrometer phase. For each experiment, four scans were acquired in order to perform the complete phase cycling of DANTE-Z. Right (a) The conventional H spectrum of a small protein (toxin 7 60 residues) in D2O at 318 K (b) selection of the aromatic region by the conventional DANTE sequence (c) same as (b) using the DANTE-Z procedure. Experiments were performed at 200 MHz using a routine AC200 Bruker spectrometer.

Fig. 4. Bottom the Double-Band-Filtered COSY spectrum obtained by selection through DANTE-Z of the H region (prior to the evolution interval) and by the selection through SPlN-PlNGING [11] of the amide region (before the acquisition interval) of toxin 7. Top the corresponding region of a standard COSY spectrum. Note, in the bottom diagram, the considerable increase in spectral resolution as well as the occurrence of additional crosspeaks (indicated with asterisks). Experiments were performed at 360 MHz (Bruker AMX360) in H2O at 318 K. The 50 W class C amplifier of the proton channel was used as transmitter.

Fig. 2. (a) 400 MHz partial H spectrum of a trisaccharide in CDClj. (b)-(e) ID TOCSY difference spectra with selective inversion of Hj// by a DANTE pulse train, and mixing times of 30, 60, 120 and 180 ms, respectively. IOtz values (of 16 scans each) were used for the 2-filter. (Reproduced with permission from Wessel et al. [26a]. Copyright 1991 Verlag... 

An alternative solution to the problem of selectively observing, for example, the H NMR spectrum of a metal-hydride in protio-, rather than deutero-solvent is to excite just that region of the NMR spectrum that contains signals of interest. This can be done using a shaped soft pulse, using a DANTE (delays alternating with nutation for tailored excitation) type sequence or, on a modem... 

Figure 10 H NMR spectrum of WiUdnson s hydride, [Rh(H)2 (PPh3)3Cl], recorded in C7H8 CD2Cl2 (1 1) with (bottom) no filtering, (middle) digital filtering, and (top) using a DANTE-Z pulse. Note the suppression of the solvent resonances. The distortions at the edges of the bottom spectrum are artefacts from digital filtration...

DANTE is highly selective it can be used in crowded regions of the spectrum. 

Fig. 5.3.12 Selective excitation by the DANTE sequence, (a) The DANTE sequence and the excitation spectrum. Adapted from [Cal2] with permission from Oxford University Press.

DANTE-type frequency-selective pulses have also been used to selectively excite specific nuclei in the spin system and this has been employed to simplify MQ spectra. This approach is limited to relatively simple spin systems where the resonances of some nuclei are well separated from the normally overlapped signals in the spectrum.28,29... 

Simulate the 1D selective COSY spectrum of glucose using the configuration file ch5333.cfg. The experiment uses a DANTE-Z element for the selective excitation of the proton at 3.9 ppm. Note depending upon the computer speed this simulation may take several minutes. 

Selective excitation was accomplished by using a delays alternating with nutations for tailored excitation (DANTE) sequence of 20 short rf pulses of x =0.6 is duration [4]. The pulse separation used was 20 ps resulting in the total duration of the DANTE sequence of x,=400 [iS and the corresponding spectral excitation width A of the center band of 2.5 kHz. The excitation sidebands were separated from the centerband by (Xp) = 50 kHz and did not affect the NMR spectrum. After a recovery period,x of at least 35 ps a final 90° pulse was applied followed by the detection of the free induction decay. 

Figure 11 illustrates the application of this technique to a sample of Rhlzoclonlum cellulose. Spectrum llA and IIB are different only in that the low-level comb of c Dante pulses is absent (llA) or present (IIB). Proton decoupling was applied for 20ms during the Dante sequence this decoupling was also present in the experiment without the Dante pulses in order to make comparison between these two experiments most meaningful. 

In order to demonstrate crystalline polymorphy more fully. Figure 12 shows the results of three Rhizoclonium cellulose experiments, like those of Figure 11, in which three different lines were initially perturbed. Spectrum 12A is the parent spectrum (like spectrum HA). The remaining six spectra, in pairs, consist of profiles of an original population perturbation (like spectrum HE) caused by the Dante inversion followed by the... 

A data base containing C-n.m.r. parameters of monosaccharides and their glycosides, which allows computerized structure analysis of an unknown compound from its C-n.m.r. spectrum has been established, and a library of optimized geometries and conformations based on molecular mechanics calculations (MM2 CARS) has been compiled for a number of common monosaccharides. Use of the double-DANTE sequence in ID Hartmann-Hahn- and n.O.e.-spectroscopy has been recommended for overcoming some typical problems encountered in the n.m.r. analysis of carbohydrates. ... 

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