A low-E magic angle spinning probe for biological solid state NMR at 750 MHz (original) (raw)
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Journal of Magnetic Resonance, 2007
RF heating of solid-state biological samples is known to be a destabilizing factor in high-field NMR experiments that shortens the sample lifetime by continuous dehydration during the high-power cross-polarization and decoupling pulses. In this work, we describe specially designed, large volume, low-E 15 N-1 H solid-state NMR probes developed for 600 and 900 MHz PISEMA studies of dilute membrane proteins oriented in hydrated and dielectrically lossy lipid bilayers. The probes use an orthogonal coil design in which separate resonators pursue their own aims at the respective frequencies, resulting in a simplified and more efficient matching network. Sample heating at the 1 H frequency is minimized by a loop-gap resonator which produces a homogeneous magnetic field B 1 with low electric field E. Within the loop-gap resonator, a multi-turn solenoid closely matching the shape of the sample serves as an efficient observe coil. We compare power dissipation in a typical lossy bilayer sample in the new low-E probe and in a previously reported 15 N-1 H probe which uses a double-tuned 4-turn solenoid. RF loss in the sample is measured in each probe by observing changes in the 1 H 360°pulse lengths. For the same values of 1 H B 1 field, sample heating in the new probe was found to be smaller by an order of magnitude. Applications of the low-E design to the PISEMA study of membrane proteins in their native hydrated bilayer environment are demonstrated at 600 and 900 MHz.
An efficient 1H/31P double-resonance solid-state NMR probe that utilizes a scroll coil
Journal of Magnetic Resonance, 2007
The construction and performance of a scroll coil double-resonance probe for solid-state NMR on stationary samples is described. The advantages of the scroll coil at the high resonance frequencies of 1 H and 31 P include: high efficiency, minimal perturbations of tuning by a wide range of samples, minimal RF sample heating of high dielectric samples of biopolymers in aqueous solution, and excellent RF homogeneity. The incorporation of a cable tie cinch for mechanical stability of the scroll coil is described. Experimental results obtained on a Hunter Killer Peptide 1 (HKP1) interacting with phospholipid bilayers of varying lipid composition demonstrate the capabilities of this probe on lossy aqueous samples.
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, 2010
High-resolution magic-angle spinning has become a valuable tool to study biologic samples; however, there are only a few high-resolution magic-angle spinning methodologies that have been explored specifically to deal with small semisolid biomaterials such as tissues. Here, we report a novel high-resolution (1)H NMR spectroscopic approach using magic-angle coil spinning. We demonstrate its potential for intact tissues by combining a resonant microcoil with a large-volume commercial magic-angle spinning rotor, where the microcoil offers incredible sensitivity and the large-volume magic-angle spinning rotor provides stable slow magic-angle spinning. This approach provides high-resolution spectra with high sensitivity and the preservation of living biologic specimens for an accurate chemical analysis.
SINGLE CHIP PROBE FOR HIGH RESOLUTION MAGIC ANGLE COIL SPINNING NMR OF BIOLOGICAL SAMPLES
ABSTRACT We report a single-chip probe for “magic angle coil spinning”-MACS nuclear magnetic resonance (NMR) spectroscopy. The probe consists in a wirebonded microcoil integrated with an on-chip interdigitated capacitor. This LC-circuit is resonant at 500 MHz (1H Larmor frequency at 11.7 T) enabling wireless inductive coupling of the NMR signal and spinning for high resolution NMR. We demonstrate stable spinning up to 110 Hz of the probe containing 330 nl water sample.
Journal of Magnetic …, 2007
A novel coil, called Z coil, is presented. Its function is to reduce the strong thermal effects produced by rf heating at high frequencies. The results obtained at 500 MHz in a 50 μl sample prove that the Z coil can cope with salt concentrations that are one order of magnitude higher than in traditional solenoidal coils. The evaluation of the rf field is performed by numerical analysis based on first principles and by carrying out rf field measurements. Reduction of rf heating is probed with a DMPC/DHPC membrane prepared in buffers of increasing salt concentrations. The intricate correlation that exists between the magnetic and electric field is presented. It is demonstrated that, in a multiply tuned traditional MAS coil, the rf electric field E1 cannot be reduced without altering the rf magnetic field. Since the detailed distribution differs when changing the coil geometry, a comparison involving the following three distinct designs is discussed: (1) a regular coil of 5.5 turns, (2) a variable pitch coil with the same number of turns, (3) the new Z coil structure. For each of these coils loaded with samples of different salt concentrations, the nutation fields obtained at a certain power level provide a basis to discuss the impact of the dielectric and conductive losses on the rf efficiency.
Biomolecules, 2021
The available magnetic field strength for high resolution NMR in persistent superconducting magnets has recently improved from 23.5 to 28 Tesla, increasing the proton resonance frequency from 1 to 1.2 GHz. For magic-angle spinning (MAS) NMR, this is expected to improve resolution, provided the sample preparation results in homogeneous broadening. We compare two-dimensional (2D) proton detected MAS NMR spectra of four membrane proteins at 950 and 1200 MHz. We find a consistent improvement in resolution that scales superlinearly with the increase in magnetic field for three of the four examples. In 3D and 4D spectra, which are now routinely acquired, this improvement indicates the ability to resolve at least 2 and 2.5 times as many signals, respectively.
Simple single-coil double resonance NMR probe for solid state studies
Review of Scientific Instruments, 1977
A single coil (solenoid), nuclear magnetic double resonance sample probe, suited for a wide variety of solid state studies , is described. It was designed to be used in double resonance experiments where it is necessary to generate intense rf magnetic fields (rotating components with amplitudes " .5O gauss) at two widel y spaced frequencies and to simultaneously detect microvolt-level signals. Designs for operation over the 12-270 MHz frequency range are discussed .
A large volume flat coil probe for oriented membrane proteins
Journal of Magnetic Resonance, 2006
15 N detection of mechanically aligned membrane proteins benefits from large sample volumes that compensate for the low sensitivity of the observe nuclei, dilute sample preparation, and for the poor filling factor arising from the presence of alignment plates. Use of larger multi-tuned solenoids, however, is limited by wavelength effects that lead to inhomogeneous RF fields across the sample, complicating cross-polarization experiments. We describe a 600 MHz 15 N-1 H solid-state NMR probe with large (580 mm 3 ) RF solenoid for high-power, multi-pulse sequence experiments, such as polarization inversion spin exchange at the magic angle (PISEMA). In order to provide efficient detection for 15 N, a 4-turn solenoidal sample coil is used that exceeds 0.27k at the 600 MHz 1 H resonance. A balanced tuning-matching circuit is employed to preserve RF homogeneity across the sample for adequate magnetization transfer from 1 H to 15 N. We describe a procedure for optimization of the shorted 1/4k coaxial trap that allows for the sufficiently strong RF fields in both 1 H and 15 N channels to be achieved within the power limits of 300 W 1 H and 1 kW 15 N amplifiers. The 8 · 6 · 12 mm solenoid sustains simultaneous B 1 irradiation of 100 kHz at 1 H frequency and 51 kHz at 15 N frequency for at least 5 ms with 265 and 700 W of input power in the respective channels. The probe functionality is demonstrated by 2D 15 N-1 H PISEMA spectroscopy for two applications at 600 MHz.
High-resolution 1H MAS RFDR NMR of biological membranes
Journal of Magnetic Resonance, 2009
The combination of magic angle spinning (MAS) with the high-resolution 1 H NOESY NMR experiment is an established method for measuring through-space 1 H… 1 H dipolar couplings in biological membranes. The segmental motion of the lipid acyl chains along with the overall rotational diffusion of the lipids provides sufficient motion to average the 1 H dipolar interaction to within the range where MAS can be effective. One drawback of the approach is the relatively long NOESY mixing times needed for relaxation processes to generate significant crosspeak intensity. In order to drive magnetization transfer more rapidly, we use solid-state radiofrequency driven dipolar recoupling (RFDR) pulses during the mixing time. We compare the 1 H MAS NOESY experiment with a 1 H MAS RFDR experiment on dimyristoylphosphocholine, a bilayer forming lipid, and show that the 1 H MAS RFDR experiment provides considerably faster magnetization exchange than the standard 1 H MAS NOESY experiment. We apply the method to model compounds containing basic and aromatic amino acids bound to membrane bilayers to illustrate the ability to locate the position of aromatic groups that have penetrated to below the level of the lipid headgroups.
Variable angle spinning (VAS) experiments can be used to measure long-range dipolar couplings and provide structural information about molecules in oriented media. We present a probe design for this type of experiment using a contactless resonator. In this circuit, RF power is transmitted wirelessly via coaxial capacitive coupling where the coupling efficiency is improved by replacing the ordinary sample coil with a double frequency resonator. Our probe constructed out of this design principle has shown favorable properties at variable angle conditions. Moreover, a switched angle spinning correlation experiment is performed to demonstrate the probe’s capability to resolve dipolar couplings in strongly aligned molecules.