DANTE method

In some spectrometers it is not feasible to generate BURP or related tailored soft pulses. A useful alternative is the DANTE pulse sequence (delays alternating with nutation for tailored excitation). Normal high excitation power is used, but rather than apply a single 90° pulse, the DANTE method uses a sequence of small angle pulses that sum to 90° but with a short time between pulses during which nuclei... 

In the early days of selective excitation, spectrometers were not equipped to generate amplitude modulated rf pulses and the DANTE method (Delays Alternating with Nutation for Tailored Excitation) was devised, [49] requiring only short, hard pulses. Although largely superseded by the amplitude modulated soft pulses, DANTE may still be the method of choice on older instramentation or on those newer instmments which lack waveform generators. 

The major difference between soft shaped pulses and DANTE methods is the occurrence of strong sideband excitation windows either side of the principal window with DANTE. These occur at offsets from the transmitter at multiples of the hard-pulse frequency, 1/x. They arise from magnetisation vectors that are far from resonance and which process full circle during the x period. Since this behaviour is precisely equivalent to no precession, they are excited as if on-resonance. Further sidebands at 2/x, 3/x and so on also occur by virtue of trajectories completing multiple full circles during x. Such multisite excitation can at times be desirable [50,51] but if only a single excitation window is required, the hard pulse repetition frequency must be adjusted by varying x to ensure the sideband excitations do not coincide with other resonances. 

California Department of Health. Air and Industrial Hygiene Laboratory. Calibration and Standardization of Continuous Photometric Analyzers of Atmospheric On-dants. Recommended Method No. 5-B. Berkel California State Department of Health 1970. 18 pp. 

Mohebbi and Shaka (1991b) also developed selective homonuclear Hartmann-Hahn experiments based on zero-quantum analogs of DANTE sequences (Bodenhausen et al., 1976 Morris and Freeman, 1978) and binomial solvent suppression methods (Plateau and Gueron, 1982 Sklenaf and Starcuk, 1982 Hore, 1983) (see Section X.C). 

In the homonuclear case, the synchronous and matched irradiation at two frequencies and Vj can be implemented by placing the transmitter midway between the selected frequency ranges Rj and Rj and by modulating a band-selective multiple-pulse sequence with cos r(i, — Vj)/2]. This method can be regarded as an extension of the doubly selective HOHAHA experiment (Konrat et al., 1991), where a weak square pulse, rather than a multiple-pulse sequence, is amplitude-modulated. Implementations based on the principle of interleaved DANTE sequences (Morris and Freeman, 1978 Patt, 1992 Kupce and Freeman, 1992c) are also feasible. 

From our experience the largest difficulty (or activation barrier) that homogeneous chemists encounter in trying to deal with the electrochemical literature is directly related to electrochemical jargon rather than to fundamental concepts. Although electrochemistry was born as a synthetic method (by Kolbe, Haber, and Fichter, among others), most electrochemical textbooks use an analytic approach to these fundamental concepts. As a result, mathematical formulations and jargon invade most of the presentations, which often results in an effect similar to the caveat at the entrance of Dante s Inferno ... 

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... 

Shaped and composite pulses are devoid of free precession periods between periods of rf excitation. Pulse sequences combine both free precession and rf pulses. Clearly, given the manifold of shaped and composite pulses, there is an infinite number of pulse sequences which can be constructed from them. A variety of such sequences is used for volume localization. This topic is discussed in Section 10.2. Here two methods relevant to the acquisition of NMR images are reviewed. These are the DANTE technique for single-shot localization, and the Hadamard technique as an example of multi-shot localization. 

When implementing this sequence it may be necessary to add attenuation to the transmitter to increase the duration of each pulse so that the shorter elements do not demand very short (< 1 xs) pulses (note the similarity with the requirements for the DANTE hard-pulse selective excitation described above). The binomial sequences can be adjusted to provide an arbitrary overall tip angle by suitable adjustment of the tip angles for each element. For example, inversion of all off-resonance signals can be achieved by doubling all elements relative to the net 90 condition. Exactly this approach has been exploited in the gradient-echo methods described below. 

The demise of BioCAD spawned two new approaches to pharmacophore discovery My former colleagues at BioCAD, joined by Barnum, introduced Hiphop [22], a variant of the MNMM approach with a statistical metric added, to alleviate some of the known problems with HypoGen. This author joined Upjohn (now Pharmacia, Kalamazoo, MI), which provided him the opportunity to develop and publish his novel pharmacophore discovery method, DANTE. The two key innovations in DANTE were its use of the principle of selectivity [23,24] to rank possible pharmacophore solutions arising from the MNMM method, and the automatic inference of sterically forbidden regions (another concept that originates from... 

All of these methods can easily be coupled to a 3D database search. In particular, the Hiphop and HypoGen pharmacophores can directly be used as input to the Catalyst 3D database search engine. DANTE pharmacophores can be converted into Catalyst 3D search queries, via scripts that convert DANTE output into the Catalyst.chm format. Both DISCO and HypoGen pharmacophores have been used to perform the alignment prior to a CoMFA study. 

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