Triple resonance probes

All NMR experiments were performed on a Bruker DRX700 spectrometer operating at 700 MHz H frequency and equipped with a triple resonance probe and a triple axis gradient coil. DHPR concentration was 75 pM (300 mM monomer) in 25 pM d1rTris buffer, pH = 7.8 and 7=303 K. (Taken from Ref. [4]). 

Almost all spectra were acquired on a AMX-600 Bruker NMR spectrometer equipped with a 5 mm inverse broad-band probe. The only exception were the gradient-enhanced spectra acquired on an INOVA-600 Varian NMR spectrometer using a 5 mm triple-resonance probe with z gradients. The experimental details are given for each spectrum in the figure captions. 

FIGURE 40. 29Si detected 29Si— 13C correlated 2D spectrum enhanced by 1H—- Si INEPT (50% solution of polymer silicon oil in CD3COCD3 triple resonance probe with 1H inner coil double tuned to 13C frequency, 64 increments with 128 scans each, 1024 data points in F2 relaxation delay 3 s, d = 7 111s and A = 30 ms). Reproduced by permission of Academic Press from Reference 297... 

Fig. 15. Comparison of HMBC spectra for a 20 gg sample of retrorsine (3) dissolved in 150 pL rf4-metlianol in a sealed 3 mm NMR tube. The data shown in both panels are 8 Hz optimized non-gHMBC spectra. The spectrum shown in Panel A was acquired in 15 h using a 5 mm 500 MHz cryogenic gradient inverse triple resonance. Almost all of the expected resonances are observed when these data are compared to those for a 700 pg sample of 3 shown in Fig. 2. In contrast, the spectrum shown in Panel B, which was acquired with identical conditions using a 3 mm gradient inverse triple resonance probe, shows the most prominent responses in the spectrum and only a relatively small number of the other responses expected. For a sample of this size to yield a useful HMBC spectrum, it would be necessary to acquire data for a weekend when using a conventional 3 mm NMR gradient inverse-detection NMR probe.

If / is not H, then a three-channel machine, and triple resonance probe are required. 

For HMQC spectroscopy in which both the detector I and indirect S nuclei are heteronuclei , a third spectrometer channel is required. An inverse broadband, triple resonance probe head in which the inner coil is tuned to H, I and lock, and the outer coil is broadbanded is then the best option, particularly where a single / nuclide or H will be used for detection. Such probe heads are stock items for some manufacturers (Bruker). Although it may be possible to build probe heads in which two channels are broadbanded, the lead time on such a probe head is likely to be long, and the performance markedly inferior due to the technical difficulties involved. 

In this section, aspects of Hartmann-Hahn experiments are discussed that are important for practical applications. There are obvious instrumental differences between heteronuclear and homonuclear Hartmann-Hahn experiments, such as the necessity for one or several heteronuclear rf channels and double- or triple-resonance probes. In addition, the rf amplitude of the channels must be matched, that is, the duration of the respective 90° pulses must be carefully adjusted such that the difference is not larger than a few percent. A detailed discussion of setup experiments for the calibration of hetero pulses has been given, for example, by Griesinger et al. (1994). 

For non-deuterated complexes, NMR experiments were performed on either Vaiian Unity600 or Varian Unity+500 spectrometers. The 600 MHz instrument was equipped with a triple resonance probe and a PTS synthesizer as a pseudo fourth channel. The 500 MHz spectrometer was a four channel instrument with a triple resonance probe with an actively shielded pulsed field gradient coil. All experiments were performed at 37 C. The heteronuclear experiments shown in Figure 1 were performed as described in Zhang et al (11) and Revington et al (24). For all 3D ex riments 32 transients were required for sufficient signal to noise. This necessitated the use of fewer increments and the use of linear prediction (25)... 

Fig. 5. Comparison of conventional 3 and 5 mm cryogenic gradient inverse triple resonance probe performance for long-range data aequisition using a 2 mg sample of the oxazoli-...

Tlie most simple design for a triple-resonance probe head contains two doubly tuned coils adjusted to the frequencies of H, D and two different heteronuclei (popular combinations include C/ N, or which are... 

It should be mentioned that in cases where one of the heteronuclei is F, D or Li. the use of designated triple-resonance probe heads for "X, Y correlations can be avoided, and standard equipment may be used. The resonance frequency of F is far outside the range of other heteronuclei, but close to the H frequency, so that F, "X correlations can frequently be performed by detuning the proton coil of a standard multinuclear probe head. Even if this procedure may result in longer pulses and some loss of sensitivity for experiments with F detection, many experiments are still practicable due to the high receptivity of fluorine. Of course, experiments with this set-up... 

D correlation spectra, for which dual H and receivers and a triple-resonance probe were employed [133]. A yet more sophisticated approach employing dual receivers provides both one-bond and long-range correlation spectra, a... 

Fig. 3. Sensitivity obtainable in high-pressure borosilicate glass cells and sapphire eells. The sample contained 0.5 mM uniformly N-enriched Csp from Thermotoga maritima (TwCsp) in 50mM phosphate buffer (pH 6.5), 20mM NaCl, 0.2mM Na-EDTA, 0.1 pM NaNj, 10% D2O and 90% H20. Gradient selected sensitivity enhanced H- N-HSQC spectra were recorded under identical experimental conditions either in a sapphire cell (left) with an outer diameter of 3.18 mm, inner diameter of 1.72 mm or a borosilicate glass capillary (right) with an outer diameter of 5.0 mm and an inner diameter of 1.2 mm. Data were recorded with a 8 mm inverse triple-resonance probe at 600 MHz proton frequency. Total acquisition time, approximately 2.5 h resolution, 2048 points in the direct dimension and 256 points in the indirect dimension. The temperature was adjusted to 303 K. (Top) Only a small part of the spectra are shown and plotted at the same contour levels for the two experiments. (Bottom) 1-D trace through the maximum of the H -signal of K19. (After ref. 35.)...

About 150 mg of each sample (1 , 2" and 3 generation wedges(41 was dissolved in 0.7mL deuterated acetone in a 5 mm NMR tube for NMR studies. NMR spectra were obtained on a Varian Vnityplus 750 MHz NMR spectrometer equipped with four RF chatmels, a Performa II z axis pulse field gradient (PPG) accessory, and a Varian H/ C/ P/ H foin chapel triple resonance probe with a PFG coil. Acetone-de was also used as internal references for both H (2.05 ppm) and C (29.92 ppm) chemical shifts. All experiments were performed at 25.0 0.1 °C. All data were processed with Varian s VNMR software on a SUN Ultra-10 workstation. 

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