GHz Class NMR

The strength of the magnetic field is one of the most important properties of an NMR spectrometer. The dispersion (i.e. the “distance” of two peaks in an NMR spectrum) is enhanced at higher magnetic fields. For the investigation of substances with a large number of peaks, higher magnetic fields render it possible to separate different peaks from one another, making GHz-class NMR an invaluable tool for structure determination. An example is shown in Figure 1.  

Another great advantage of higher magnetic fields is the improved sensitivity that can be achieved in an NMR experiment. Higher magnetic fields lead to a larger number of nuclear spins of the sample residing in the lower energy quantum state, which results in a stronger NMR signal. This is particularly beneficial for multi-dimensional NMR experiments, where the sensitivity increases additionally with the power of the number of dimensions.

For many years, high-resolution NMR was limited to a magnetic field of 23.5 Tesla, equivalent to a proton resonance frequency of 1.0 GHz. This limit was set by the physical properties of metallic, low-temperature superconductors (LTS), and it was first reached in 2009 with an Avance 1000 spectrometer at the Ultra-High Field NMR Center in Lyon, France.

High-temperature superconductors (HTS), first discovered in the 1980s, opened the door towards even higher magnetic fields at low temperatures, but considerable challenges in YBCO HTS tape manufacturing and in superconducting magnet technology made further UHF progress daunting until the early 2020ies.

Bruker's 1.0 GHz Ascend Evo, and 1.1 and 1.2 GHz Ascend magnets utilize a sophisticated hybrid design with high-temperature superconductor (HTS) in the inner sections and low-temperature superconductors (LTS) in the outer sections of the magnet, as illustrated in Figure 2. Bruker’s GHz-class NMR magnets feature a 54 mm room-temperature bore (“standard bore”) and have exquisite homogeneity and field stability compatible with the demanding requirements of high-resolution NMR.

The enhanced resolution and sensitivity make GHz-class NMR the ideal tool for many areas of research, in particular for material science and structural biology. The most important benefits are the following:

• Reduced sample quantity needed: Due to the enhanced sensitivity, UHF NMR typically requires only small amounts of sample, which is particularly advantageous for rare and limited samples.
• Atomic-level resolution: GHz-class NMR provides atomic-level resolution on an unprecedented level. For biological samples, this is particularly pronounced for small and medium-sized proteins.
• Solution-state information: GHz-class NMR can work in solution, offering insights into the behavior of biomolecules in conditions closer to their native environment, which is essential for understanding their biological functions.
• Analysis of dynamic structures: GHz-class NMR spectroscopy is excellent for studying the dynamics and motions of biomolecules in solution, providing insights into conformational changes, flexibility, and interactions. This capability to study dynamics is particularly beneficial in understanding protein folding, function, and interactions.
• Ability to study ligand interactions: UHF NMR is well-suited for studying interactions between proteins and small molecules, enabling detailed analysis of binding sites and dynamics, crucial for drug discovery and design.

Bruker’s GHz-class spectrometers are available with a large selection of NMR probes, including CryoProbes for solution-state NMR and fast-spinning MAS solid-state NMR probes. The most popular probes for Bruker’s GHz-class NMR spectrometers are the following:

• TCI (“inverse”) triple-resonance CryoProbes with dedicated channels and cold preamplifiers for H, C and N. These TCI solution-state probes are optimized for proton detection. They are equipped with a deuterium lock channel and a gradient coil.
• TXO (“observe”) triple-resonance CryoProbes with dedicated channels and cold preamplifiers for H, C and N. The TXO probes are optimized for X-detection (i.e. N and C). They are equipped with a deuterium lock channel and a gradient coil.
• TXI triple-resonance room-temperature probes feature dedicated channels for H, C and N, as well as a deuterium lock channel and a gradient coil.
• BBI dual-resonance room-temperature probes have a proton channel, a broadband channel, a deuterium lock channel, and a gradient coil. They make solution-state GHz-class spectrometers particularly versatile, as the broadband channel expands the range of accessible nuclei considerably.
• The advantages of GHz-class spectrometers are particularly pronounced in solid-state NMR. Bruker offers an extensive range of CPMAS probes. For GHz-class spectrometers, probes with the fastest spinning speeds (i.e. probes for 0.4 mm, 0.7 mm, 1.3 mm and 1.9 mm rotors) are typically employed. The most common probes are triple-resonance probes (HCN), as well as probes primarily dedicated to material science (HX).
• Bruker's well-known magnetic resonance (MR) microscopy probes are also available for GHz-class spectrometers. MR microscopy is used to image small samples. With GHz-class spectrometers, highest spatial resolutions or spatially localized chemical information can be achieved.

NMR research has entered a new era with the introduction of GHz-class spectrometers, which enable unprecedented resolution and sensitivity for studying complex biological systems and materials. Europe has been at the forefront of this innovation, with several 1.2 GHz NMRs already in operation across the continent. The US and Asia-Pacific are also embracing this technology, with the first 1.2 GHz NMR in the US and the first 4.2 K single-story 1.0 GHz NMR in Japan. More GHz-class NMRs are being installed or planned in these regions, reflecting the growing demand and recognition for this powerful and versatile tool for scientific discovery.
Below, you can find more information about some of the leading research institutions that have chosen GHz-class NMR for their projects.