900 MHz Static Low-E Probe for Biological Solids

Purpose

The protein samples studied by solid state biological NMR are often damaged by the energy that they tend to absorb from the electric field E of the RF coil at ¹H frequency. Solid state probes suppressing the ¹H electric fields have a great advantage for biological samples. Ability to study large sample volumes is another important advantage for inherently dilute protein preparations.

In our low-E design [1], the observe coil is placed within an orthogonal loop gap resonator which produces the ¹H decoupling field with minimal E field component, reducing heating of protein samples by an order of magnitude if compared to a conventional solid-state probe with solenoid of similar dimension. Physical separation of high and low frequency coils allows one to increase the size of sample (or the number of turns in observe coil) while at the same time achieving very high RF field homogeneity in the ¹H channel. One of the standard PISEMA arrangements for this probe uses the rectangular observe coil with a sample clearance as large as 470 uL.

This 900 MHz low-E probe is routinely used by our users and internal scientists for SS NMR studies of oriented membrane proteins (e.g. ¹⁵N PISEMA [2], ¹⁷O studies [3]). Low-E resonators allowed us to conduct experiments with lesser risk of dehydration or other damage to the sample, which is especially valuable at 900 MHz. Versatile design allows swapping RF sample coils to suit different sample shape geometries. A 7.5x5.5x11 mm flat coil is available for mechanically oriented proteins with RF fields of up to 100 kHz at ¹H and up to 70 kHz at ¹⁵N frequencies. A sample coil with circular cross-section (5 mm ID) is also available for bicelle preparations.

Sample supplies for flat and bicelle coils

Sample Coils and Observe Nuclei

Procedure for switching coils and observe nuclei in static low-E probes, as well as physical location of chip capacitors mentioned below, is given on a separate page here. For flat coil there is an additional chip capacitor (C3A) which is added across ¹H variable trimmer. In tuning table below, symbol "||" stands for parallel connection and "—" for capacitors in series.

Flat coil, 7.5x5.5x11 mm 896.5

Isotope C8A C8B C7A C5A C3A 35Cl 18 || 2.7 pF n/a 3.9 pF 8.2—8.2 pF 5.6—5.6 pF 15N 18 || 1.5 pF n/a 3.9 pF none 5.6—5.6 pF 17O 8.2 pF n/a none n/a 5.6—5.6 pF

Bicelle coil, ID = 5 mm

Isotope C8A C8B C7A C5A C3A 15N 15 pF n/a 3.9 pF n/a none

If your isotope is not in the above table, contact Peter Gor'kov to see if it can be arranged.

Publications
    using this intrument

1.  P.L Gor'kov et al., J. Magn. Reson. 185 77-93 (2007), PDF
2.  C. Li et al., J. Am. Chem. Soc. 129 (17) 5304 (2007), PDF
3.  E.Y. Chekmenev et al., J. Am. Chem. Soc. 128 (16) 5308 (2006), PDF
4.  J. Hu et al., J. Am. Chem. Soc. 127 (34) 11922 (2005), PDF

900 MHz PISEMA spectra of uniformly 15N-labeled KdpF protein expressed in E. coli (33 residues) and reconstituted into a mixture of lipids, DMPC and DMPG in a 4:1 molar ratio, as reported in [2].