JP2009092424A - Magic angle adjustment mechanism - Google Patents

Abstract

A magic angle adjusting mechanism in an NMR apparatus capable of correcting a deviation of a magic angle during an experiment in a short time.
A magic angle adjustment mechanism in a MAS method in an NMR apparatus, wherein an angle adjustment unit that changes and adjusts a gradient angle of a static magnetic field with respect to a set sample in a stepwise manner, and for each step change in the tilt angle. A pulse applying means for applying an NMR pulse to the sample, a detecting means for detecting a signal derived from the sample after the application of the NMR pulse, and a signal derived from the sample by applying the NMR pulse together with the tilt angle at that time And a static magnetic field angle setting means for extracting a tilt angle at which the signal is maximum from the data stored in the storage means and irradiating a static magnetic field with the tilt angle.
[Selection] Figure 2

Description

  The present invention relates to a solid-state NMR probe, and more particularly to a technique for controlling the rotation axis of a high-speed spinner for solid-state NMR measurement.

  In the NMR spectrum of a solid-state sample, interactions that are eliminated by rotational Brownian motion appear in the solution, such as dipole interactions, so the spectral line width becomes extremely wide, and the chemical shift term is It will be obscured. For this reason, in the NMR spectrum, the signal peak of each part of the measurement molecule could not be separated, and as a result, the solid NMR method was considered unsuitable for molecular structure analysis.

A method for overcoming this phenomenon and obtaining a sharp solid state NMR spectrum was described in 1958 by E.I. R. Discovered by Andrew. The principle is that the sample tube is tilted by 54.7 ° from the direction of the static magnetic field B ₀ and rotated at a high speed to remove the anisotropic interaction and extract the chemical shift term. MAS (Magic This is called the “Angle Sample Spinning” method.

  FIG. 1 shows a block diagram of a mechanism for adjusting the angle of the rotation axis of the sample tube in the solid-state NMR apparatus. In the figure, 1 indicates the entire probe. Reference numeral 2 denotes a sample tube into which a sample is put. The sample tube is put into a spinner rotor of 3, and a sample tube 2 is rotated at high speed by using a medium such as compressed air or nitrogen gas.

  4 is a movable mechanism such as a gear for changing the angle of the spinner rotor 3. Reference numeral 5 denotes, for example, a shaft that is connected to the movable mechanism 4 and operates the movable mechanism 4 from the outside. A knob 6 is connected to the shaft 5 and is accessed by a human when the magic angle is actually adjusted.

By rotating the sample tube around the magic angle (54.7 °) with respect to the static magnetic field B ₀ , the chemical shift anisotropy can be eliminated and the line width of the NMR spectrum can be narrowed. Adjust the magic angle.

  If the rotation axis deviates from the magic angle, the influence of chemical shift anisotropy appears, and as a result, the line width of the NMR spectrum becomes wider and the resolution of the spectrum becomes worse.

  Therefore, when adjusting the magic angle, in addition to the initial adjustment, the rotation axis may deviate from the magic angle due to thermal expansion or contraction of the probe material when a large impact is applied to the probe or after temperature variable measurement is performed. May need readjustment. In addition, when used for a long period of time, there may be a slight shift due to mechanical error of the adjusting mechanism, vibration during magic angle spinning, and the like. In such a case, readjustment is performed.

In general, the magic angle is adjusted by putting the reference material KBr into the sample tube and turning the knob 6 at the bottom of the probe while actually observing the spectrum of the ⁷⁹ Br nucleus so that the spinning sideband of KBr is maximized. Make adjustments.

JP 2003-177172 A JP 2006-90767 A

  However, in the method of FIG. 1 described above, the magic angle is adjusted immediately before the experiment, and the magic angle shift during the experiment cannot be corrected. Therefore, there is a problem that the accuracy of the spectrum cannot be obtained. Further, since the magic angle is adjusted while viewing the spectrum, there is a problem that it takes time.

  An object of the present invention is to provide a magic angle adjustment mechanism capable of correcting a deviation of a magic angle during an experiment in a short time in view of the above points.

In order to achieve this object, the magic angle adjustment mechanism according to the present invention is:
A magic angle adjustment mechanism in the MAS method in the NMR apparatus,
An angle adjusting means for changing and adjusting the inclination angle of the static magnetic field with respect to the set sample in stages;
Pulse applying means for applying an NMR pulse to the sample for each step change of the tilt angle;
Detection means for detecting a signal derived from a sample after application of the NMR pulse;
Storage means for storing a signal derived from the sample by application of the NMR pulse together with the tilt angle at that time;
It is characterized by comprising a static magnetic field angle setting means for extracting a tilt angle at which the signal is maximum from data stored in the storage means and irradiating a static magnetic field with the tilt angle.

According to the magic angle adjustment mechanism of the present invention,
A magic angle adjustment mechanism in the MAS method in the NMR apparatus,
An angle adjusting means for changing and adjusting the inclination angle of the static magnetic field with respect to the set sample in stages;
Pulse applying means for applying an NMR pulse to the sample for each step change of the tilt angle;
Detection means for detecting a signal derived from a sample after application of the NMR pulse;
Storage means for storing a signal derived from the sample by application of the NMR pulse together with the tilt angle at that time;
From the data stored in the storage means, it is composed of a static magnetic field angle setting means for extracting a tilt angle at which the signal is maximum and irradiating a static magnetic field with the tilt angle.
It has become possible to provide a magic angle adjustment mechanism that can correct the deviation of the magic angle during the experiment in a short time.

  Hereinafter, embodiments of the invention will be described with reference to the drawings.

  FIG. 2 shows an embodiment of a new magic angle adjustment mechanism of the NMR apparatus according to the present invention. The embodiment of the present invention will be described below with reference to FIG.

  FIG. 2 shows an NMR apparatus having a mechanism capable of remotely adjusting the magic angle. In the figure, reference numeral 2 denotes a sample tube into which a sample is put. This sample tube is put into a spinner rotor 3 and a sample tube 2 is rotated at high speed using a medium such as compressed air or nitrogen gas.

  Reference numeral 4 denotes a movable mechanism such as a gear for changing the angle of the spinner rotor. Reference numeral 5 denotes, for example, a shaft that is connected to the movable mechanism 4 and operates the movable mechanism 4 from the outside. A magic angle adjustment controller 7 drives an internal motor to move the shaft 5 via the flexible wire 8.

  A coupling 9 is prepared between the flexible wire 8 and the shaft 5 and connects the two. The coupling 9 may have a simple joining function, but it is possible to improve the rotation accuracy by providing a speed reduction mechanism constituted by a worm gear or the like.

  Of course, the shaft 5 may be directly driven by the magic angle adjustment controller without using the flexible wire 8. Conversely, the flexible wire 8 may be directly connected to the movable mechanism 4 without using the shaft 5 and driven by the magic angle adjustment controller 7.

  Furthermore, if the motor used in the magic angle adjustment controller 7 is not affected by a strong magnetic field (for example, an ultrasonic motor), the motor may be directly connected to the shaft 5.

In the figure, reference numeral 10 denotes command means for sending a command to the magic angle adjustment controller 7. Considering a switch box, for example, the operator puts the reference material KBr for magic angle adjustment into the sample tube, and while actually observing the spectrum of the ⁷⁹ Br nucleus, adjusts the magic angle of the probe remotely from the switch box. And adjust so that the KBr spinning sideband is maximized.

Further, when 10 in the figure is not a switch box but a control unit connected to a host computer for processing NMR spectra or the host computer itself, the operator puts a reference material KBr for magic angle adjustment into the sample tube, and the host computer Sends a signal to the magic angle adjustment controller so that the spinning sideband of the spectrum of the ⁷⁹ Br nucleus is maximized, and controls the probe to have the best magic angle.

  The magic angle control method will be described. As shown in FIG. 3, first, the high frequency oscillated from the oscillator 11 is pulsed in the gate circuit 12 and amplified by the power amplifier 13, and then the directional coupler 14. To the NMR probe 15.

  The high-frequency pulse supplied to the NMR probe 15 is applied to a sample tube (not shown) that rotates at a high speed about an axis inclined approximately 57.4 ° from a sample coil (not shown). After applying the high frequency pulse, a weak FID (free induction decay) is emitted from the sample, and this FID is sent to the detector 16 via the directional coupler 14, and after detection, after being digitized by the AD converter 17. Then, it is taken into the host computer 18 and Fourier-transformed into an NMR signal.

  In such a configuration, while the sample tube is rotated at a high speed, the tilt angle of the sample tube is changed stepwise around 54.7 °, and a high frequency pulse is applied to the sample each time the tilt angle is changed. A signal derived from the sample obtained after application of the high frequency pulse is stored in the storage device of the host computer 18 in correspondence with the value of the tilt angle.

  After a series of variable measurements, determine the tilt angle that maximizes the height of the NMR signal, and fine-tune the magic angle of the sample tube so that the angle is the tilt angle of the sample tube with respect to the static magnetic field. To do.

  That is, the host computer 18 controls the pulse generator 19 so that the height of the NMR signal emitted from the sample is maximized, and the motor driver uses the pulse signal generated from the pulse generator 19. 20 is operated and the pulse motor 21 is driven to finely adjust the rotation axis of the sample tube.

In Example 1 described above, magic angle adjustment is automatically performed using the spinning sideband derived from the ⁷⁹ Br nucleus of the reference material KBr, but during the NMR measurement waiting time using the NMR signal derived from the sample. You may adjust the magic angle.

  FIG. 4 schematically shows the timing for adjusting the magic angle during NMR measurement. First, a normal NMR pulse is irradiated on the sample, and the signal is captured. Usually, there is a waiting time of several seconds to several hundred seconds until the next NMR pulse irradiation. During this time, a pulse for measuring the magic angle is irradiated and the NMR spectrum is repeatedly observed A times. Correct the angle. The method for selecting the optimum angle is the same as in the first embodiment.

  It can be widely used for solid-state NMR apparatus.

It is a figure which shows an example of the conventional magic angle adjustment mechanism. It is a figure which shows one Example of the magic angle adjustment mechanism concerning this invention. It is a figure which shows one Example of the magic angle adjustment mechanism concerning this invention. It is a figure which shows one Example of the solid-state NMR measuring method concerning this invention.

Explanation of symbols

1: whole probe, 2: sample tube, 3: spinner rotor, 4: moving mechanism, 5: shaft, 6: knob, 7: magic angle adjustment controller, 8: flexible wire, 9: coupling, 10: command means, 11 : Oscillator, 12: gate circuit, 13: power amplifier, 14: directional coupler, 15: NMR probe, 16: detector, 17: AD converter, 18: host computer, 19: pulse generator, 20: motor Driver, 21: Pulse motor

Claims (1)

A magic angle adjustment mechanism in the MAS method in the NMR apparatus,
An angle adjusting means for changing and adjusting the inclination angle of the static magnetic field with respect to the set sample in stages;
Pulse applying means for applying an NMR pulse to the sample for each step change of the tilt angle;
Detection means for detecting a signal derived from a sample after application of the NMR pulse;
Storage means for storing a signal derived from the sample by application of the NMR pulse together with the tilt angle at that time;
A magic angle comprising: a static magnetic field angle setting means for extracting a tilt angle at which the signal is maximum from data stored in the storage means and irradiating a static magnetic field with the tilt angle. Adjustment mechanism.

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