Sensitivity boost for solid-state NMR

As the market leader, Bruker introduces the world’s first commercially available solid-state dynamic nuclear polarization-enhanced NMR system (DNP-NMR)

Bruker’s 263, 395, 527 and 593 GHz DNP-NMR Spectrometers are the world’s first commercially available solid-state dynamic nuclear polarization (DNP-NMR) systems . All DNP-NMR spectrometers enable extended solid-state NMR experiments with unsurpassed sensitivity for exciting new applications in biomolecular research, material science, and pharmaceuticals. The Bruker DNP spectrometers have a proven record of performance over 35 systems installed worldwide. 

DNP samples are prepared by adding a polarizing agent or exploiting a native radical on the sample of interest. Experiments are performed at a low temperature of ~100 K with continuous microwave irradiations and benefit from the innovative low-temperature MAS probe that enables sample polarization in-situ, directly at the NMR field.

Signal enhancements range from 20 to a factor of 400, driven by microwave irradiation to transfer polarization from unpaired electron spins to nuclear spins. The unique high power gyrotron systems, delivering microwaves at 263 GHz, 395 GHz, 527 GHz and 593 GHz are robust, safe and easy-to-use, enabling long term DNP experiments without time limitations. A 263 GHz klystron is also available for DNP experiments at 400 MHz, delivering top-notch signal enhancements at a lower cost and with reduced infrastructure requirements.

DNP Boltzmann Polarization
  • Turn-key solution for DNP-enhanced solids NMR experiments at high field
  • Polarization enhancement yields factor up to 200 gain in sensitivity for solid-state NMR
  • Unsurpassed sensitivity for new applications in biomolecular research, material science and pharmaceuticals
  • Unique high power microwave sources with easy-to-use software
  • Optimum beam propagation to the sample ensured by microwave transmission lines
  • Low-temperature MAS probe technology with built-in waveguide and cold spinning gas supply
  • AVANCE™ NEO 400, 600 and 800 wide bore NMR system with sweep coils

Gyrotron Microwave Source

The gyrotron includes a sealed custom-designed gyrotron tube, superconducting magnet, and control system, all designed to provide high stability, reliability, and ease of operation. Beam propagation to the sample is ensured by high microwave beam quality and corrugated waveguide. The sample is polarized in-situ in a low-temperature NMR MAS probe.

1H NMR FrequencyWB NMR MagnetGyrotron FrequencyGyrotron Magnet
400 MHz400/89 Ascend DNP 263 GHz 4.8 T cryogen-free
600 MHz 600/89 Ascend DNP 395 GHz7.2 T cryogen-free
800 MHz 800/89 USP RS 527 GHz 9.7 T cryogen-free

263 GHz Klystron Microwave Source

The 263 GHz klystron is a continuous-wave microwave source designed and manufactured for extended DNP NMR at 400 MHz 1H frequency and 100 K sample temperature. The klystron provides a DNP option with lower purchase price, operating costs, footprint, and facility requirements compared to the gyrotron product line while retaining high DNP sensitivity and stability. At 5 W output power, it reaches 90-100% DNP efficiency on biological samples and small molecules in frozen solution while dense material samples perform at > 80% compared to the 263 GHz gyrotron.

The system assembly consists of: (1) extended interaction klystron oscillator (EIK), (2) a control system with graphical user interface, safety interlocks, power supply and cooling network, and (3) a low-loss microwave transmission line. It is compatible with a 400 WB Ascend DNP solid-state NMR spectrometer and Bruker low-temperature MAS (LTMAS) probes.

LT MAS Probe

  • Low sample temperature (~ 100 K)
  • Cold sample coil and RF circuit
  • 3.2 mm MAS rotor (15 kHz max at 100 K)
  • WB triple or double resonance probe (HCN, HXY, or HX NMR circuits))
  • Insert/eject of cold samples
  • Dry low-temperature nitrogen gas supply
  • 3 cold gas lines: bearing, drive and VT
  • Automatic refill of liquid nitrogen supply
  • Waveguide for microwave irradiation
  • Long term operation (days, weeks)
Image technical dnp enc2016
263 GHz Klystron

1.3 and 1.9 mm DNP MAS Probe

DNP experiments are performed at low temperature (100 K) for efficient transfer of polarization from electron spins to nuclear spins. Until recently, the spinning frequency at 100 K was limited to 15 kHz with a 3.2 mm rotor. With the introduction of the Bruker 1.3 and 1.9 mm low-temperature MAS (LTMAS) probe, DNP experiments can now be performed at up to 40 kHz (1.3) and 24 kHz (1.9) MAS MAS frequency for enhanced spectral resolution. The fast MAS probes include pneumatic insert/eject capability at ambient and cold temperature. The ability to change samples while the probe remains cold is critical for optimal use of experiment time. The probe is available with HCN, HXY, or HX NMR circuits.

Control Systems

  • User interface
  • Controls and regulation
  • Temperatures, voltages, water cooling, gyrotron magnet

Sample Preparation and DNP-Enhanced CPMAS of 13C-Proline

The DNP samples are prepared by adding a polarizing agent (such as e.g. TOTAPOL biradical) to a shared solvent or alternatively by utilizing a native radical on the sample of interest. The samples are measured under MAS while at low temperatures, typically 100–120 K. Unmodified NMR experiments are performed while benefitting from continuously DNP-enhanced signal intensity through CW microwave irradiation.

DNP-Enhanced CPMAS of 13C-Proline
DNP-Enhanced CPMAS of 13C-Proline in Glycerol/Water with 10 mM AMUPOL at 395 GHz/600 MHz: 25 µl sample, 1.5 mg U-13C-15N Proline, 8 kHz MAS, CPMAS with Spinal 64 decoupling, 100 k sample temperature, 8 scans and 10 s recycle delay for both microwaves on and off spectra.

Improved sensitivity from DNP allows the characterization of expansin protein binding to plant cell walls

DNP experiments allow rapid detection of ~1% U-13C,15N expansin mixed with plant cell walls. A REDOR filter selects only signals from the expansin 13C signals and spin diffusion mixing following the REDOR filter reveals correlations between expansin and the cell-wall polysaccharides. Comparison of the wild-type protein with two mutants indicate that site-specific cellulose binding is correlated with strong wall-loosening activity.

DNP fig3 improved
Fig. 3. (A) Graphic depicting expansin binding to plant cell walls. WT (B) and RKK mutant (C) spin diffusion spectra showing the buildup of signals from the protein to the cell-wall polysaccharides. (D) Comparison of signals transferred from the WT and two mutants to the plant cell walls. (E) 2D 13C-13C spectrum showing direct evidence of protein-polysaccharide correlations through spin diffusion.
T. Wang et al. PNAS 2013, 110, 16444-16449

DNP-enhanced NMR in biological solids

A wide range of biological samples have been successfully enhanced on the Bruker DNP-NMR spectrometer including small peptides, soluble proteins, membrane proteins, and large biological complexes.

DNP-enhanced NMR in biological solids
z-filtered (ZF) TEDOR experiment comparing sensitivity and spectral content at 300 K, 700 MHz without DNP and 100 K, 400 MHz with DNP.
M. J. Bayro, et al. J. Am. Chem. Soc., 2011, 133, 13967

Material Science

DNP NMR allows the characterization, at the molecular level, of hybrid organic silica material. These materials are key compounds for applications in catalysis, drug delivery, separation and purification devices.

DNP in material science
DNP experiments on natural abundance Mat-PrIm: (a) Structure of bCTbK polarizing agent; DNP-enhanced 13C, (b) and 15N (c) 1D spectra and 1H- 13C (d), 1H- 15N (e), 1H-29Si, (f) heteronuclear correlation spectra. 1H DNP signal enhancement = 78 at 100.
K. A. Zagdoun et al. J. Am. Chem. Soc., 2012, 134, 2284

DNP with Fast MAS: Rapid Structural Characterization

25 kHz MAS improves the resolution of DNP spectra, enables long-range inter-residue polarization transfers, and is helpful for extending assignments. DNP experiments were performed on Pf1 bacteriophage with non-uniform sampling (NUS) for rapid acquisition of multidimensional experiments.

DNP with Fast MAS
Fast spinning leads to longer relaxation times and assignments are simplified by use of long-range transfer sequences (e.g. CANCOCA, sequential sidechain correlation). Full assignment of intact virus particle was possible in under 1 week of experiment time
Reference: Sergeyev I. et al. (2017) Proc Natl Acad Sci USA, 114: 5171

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