Inverse detection probe

The size of sample required has been reduced by a number of technical developments including micro inverse probes and micro cells (references in Martin et al. 1998), and has been reduced even further using a newly developed 1.7-mm submicro inverse-detection gradient probe (Martin et al. 1998). The combined use of inverse detection probes with solenoid microcoils has also been developed to reduce sample volumes for NMR (Subramanian and Webb 1998). 

Figure 7.3.1.6 Representative circuit diagram for inverse detection probes showing the requisite RF coils and capacitor layout...

Fig. 18. Comparison spectra for a sealed 3 mm NMR sample tube containing 40 pg (120 nmol) of strychnine (5) dissolved in 165 pL CDC13.234 All of the spectra were acquired and processed identically. The non-gHSQC spectrum shown in Panel A was acquired in 90 m using a 3 mm inverse-detection cryogenic NMR probe operating with an rf coil temperature of 12 K. The sealed 3 mm sample was used to acquire the 90 m spectrum shown in Panel B in a conventional 3 mm gradient inverse-detection probe. All parameters were identical. Panel C shows the results obtained for the sealed 3 mm sample in a conventional 3 mm NMR probe with an overnight (17.5 h) acquisition. (Reprinted with permission from J. Nat. Prod., 63, 1049 (2000). Copyright 2000, American Chemical Society and American Society of Pharmacognosy.)...

All NMR spectra were collected on a Varian Unity 500 MHz spectrometer ( H frequency 499.8 MHz) equipped with a 5 mm inverse detection probe. Sample concentrations were typically 1 -2 mM and sample temperatures maintained at 25 C (unless otherwise noted). Sample pH was typically 3.5 - 4.0. Onedimensional H data were acquired with a H sweepwidth of 6000 Hz and an acquisition time of 2.3 seconds. The residual water signal was suppressed by presaturation. H DQF-COSY, NOESY and TOCSY (15) spectra were collected and processed using standard methods. All chemical shifts were referenced relative to internal DSS. 

Crouch RC, Martin GE (1992a) Micro inverse-detection a powerful technique for natural product structure elucidation. J Nat Prod 55 1343-1347 Crouch RC, Martin GE (1992b) Comparative evaluation of conventional 5 mm inverse and micro inverse-detection probes at 500 MHz. Magn Reson Chem 30 S66-S70 Crouch RC, Andrews CW, Martin GE, Luo J-K, Castle RN (1990a) HMQC-NOESY application to a polynuclear aromatic at natural abundance. Magn Reson Chem 28 774-778. ... 

NMR experiments were carried out at 15 C on a Bruker AMX-500 spectrometer equipped with a 5 mm inverse detection probe and an X-32 computer. All ID spectra were recorded with a 5500 Hz spectral width and 8k data points. The water resonance was suppressed either by a pre-saturation irradiation or by using a tailored jump-return excitation pulse l. Phase-sensitive detection in the tl dimension of 2D experiments was achieved using the time-proportional phase incremental scheme. ... 

All H NMR spectra were obtained with three signals suppression, i. e., water, methyl and methylene of ethanol signals in a 5 mm inverse-detection probe head. Eight FIDs were collected as 65536 data points using a 8.5 ps pulse (90°) spectral width, 8013 Hz acquisition time, 4.1 s and relaxation delay, 6.4 s. Spectra were processed using 32768 data points by applying an exponential line broadening of 0.3 Hz for sensitivity enhancement before Fourio transformation and were accurately phased, baseline adjusted and converted into JCAMP format to build the data matrix. 

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