Development of a 13C-optimized 1.5-mm high temperature superconducting NMR probe

Abstract

We report a 1.5-mm NMR probe based on high temperature superconductors operating at 14.1 T optimized for 13C detection. The probe has a total sample volume of about 35 microliters (μL) with an active volume of 20 μL and provides exceptional mass sensitivity for 13C detection. The probe also has excellent 1H sensitivity and employs a 2H channel lock; 15N irradiation capability can be added in the future. The coils are cooled to about 20 K using a standard Agilent cryogenic refrigeration system, and the sample temperature is regulated near room temperature. The coil design considerations are discussed in detail. This probe is ideal for directly detected 13C NMR experiments for natural products chemistry and metabolomics applications, for which 35 μL is an optimal sample volume. The outstanding 13C sensitivity of this probe allowed us to directly determine the 13C connectivity on 1.1 mg of natural abundance histidine using an INADEQUATE experiment. We demonstrated the utility of this probe for 13C-based metabolomics using a synthetic mixture of common natural abundance metabolites whose concentrations ranged from 1 to 5 mM (40 to 200 nmol).

13C NMR Metabolomics: INADEQUATE Network Analysis

“…In Figure 1A we show our previously published results of an INADEQUATE spectrum recorded using 200 mM (1.1 mg) of histidine at natural abundance 13 C using our specialized HTS 13 C optimized NMR probe. 15 This spectrum required about 48 hours and has relatively low signal-to-noise (S/N). Figure 1B shows an INADEQUATE spectrum collected with the same probe and spectrometer with 2 mM (100×lower concentration) uniformly 13 C histidine (Cambridge Isotope Labs) in just 4 hours with much greater S/N.…”

“…15 The total time for each INADEQUATE experiment was ~14 hours. A spectral width of 202 ppm (30487.8 Hz) along F2 and a 404 ppm (60975.6 Hz) along F1 was used.…”

“…We utilized a custom 1.5-mm 13 C-optimized high temperature superconducting (HTS) probe, 15 which allowed us to efficiently analyze sample volumes of just 40 µL. To demonstrate the approach, we compared unfractionated INADEQUATE spectra from both the endometabolome (i.e.…”

Applications of NMR spectroscopy to systems biochemistry

“…Thus to reach a signal-to-noise ratio (SNR) of 10:1 in 10 min acquisition, about 0.6 nmol of material are needed under ideal conditions. Significantly lower quantities are needed in smaller diameter coils such as 1.7 mm or even 1 mm diameter (<10 μL sample needed) where a performance boost of up to 2–3-fold for the same amount of material can be expected, despite the considerably poorer filling factor of a very small diameter tube [76,77]. These probes are best suited for analyzing mass limited samples.…”

A directed-overflow and damage-control N-glycosidase in riboflavin biosynthesis

“…Spectra were obtained using volumes of just 50 μl by incubating labeled GTP with COG3236 in the 1.5-mm NMR tubes. An exceptionally sensitive custom 13 C-optimized NMR probe made from high temperature superconducting material [56] was utilized. The red overlay in the ribose region of ‘Intermediate 1 + COG3236’ is the ribose-5-phosphate spike of the same spectrum in black.…”