JP3103443B2 - Isotropic shift cross-correlation multidimensional solid state nuclear magnetic resonance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an isotropic shift cross-correlation multidimensional solid-state nuclear magnetic resonance (NMR) method using J interaction and dipole interaction.

[0002]

2. Description of the Related Art Dipole interaction and J interaction are known as methods for causing magnetization transfer between nuclear spins. The former is a magnetization transfer due to the interaction between spatially adjacent dipoles, and can be used to elucidate the geometric structure of matter.The latter is a magnetization transfer through covalent electrons, and is used to elucidate the chemical structure of matter. Available. 2. Description of the Related Art Conventionally, in solid-state NMR, for example, as a method of causing magnetization transfer between nuclear spins in a ¹³ C nucleus, a ¹ H- ¹³ C dipole interaction is used. That is, ¹ placing the H state which is not decoupled, ¹ and a H each other strong bond rotates faster, due to its influence ¹³ C temporally varies, the magnetization moves thereby returned to the binding of ¹³ C between Is caused. The same applies to ¹⁵ N and the like in addition to the ¹³ C nucleus.

[0003]

However, solid-state NMR
In this case, since there is no molecular motion, a sharp signal is obtained by rotating the sample at a magic angle of about 5 KHz, for example. However, when the sample is rotated, the dipole interaction and the anisotropic chemical shift have a time dependency, and it is difficult to perform a quantitative theoretical analysis. The sample rotation was ¹ H- ¹ H, ¹³
Since it has the effect of weakening the interaction of C- ^{13C, the} magnetization transfer efficiency is reduced, and several seconds are required for the magnetization transfer time. Further, since ¹ H is related to the magnetization transfer in addition to the ¹³ C nucleus, it is extremely difficult to estimate parameters related to the molecular structure such as the internuclear distance from the ¹³ C nucleus.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and is directed to an isotropic shift using a J interaction or a dipole interaction, which enables magnetization transfer to be performed in a short time even under a magic angle sample rotation. It is an object to provide a cross-correlation multidimensional solid-state NMR method.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a nuclear magnetic system in which a measurement sample is rotated at a high speed at a magic angle, and magnetization transfer between nuclear spins is performed while irradiating ¹ H with a decoupling high-frequency magnetic field. In the resonance method, a homogenous nuclear dipole interaction is eliminated, a step of irradiating a pulse train that reduces a chemical shift frequency to an isotropic shift value, and irradiating the pulse train to develop a homogenous nucleus after an expansion period t _1. Mixing by irradiating a spin echo pulse train using a composite pulse for performing magnetization transfer by J interaction or homogeneous nuclear dipole interaction, and after mixing, an observation period t ₂
And detecting a spin echo signal. Further, the present invention is characterized in that the chemical shift is developed using different chemical shift scale factors between the period t _{1 and the} period t ₂ .

[0006]

According to the present invention, while rotating the magic angle sample and decoupling ¹ H, the homonuclear dipole interaction is eliminated during the development period t _1, and the frequency of the chemical shift is reduced to obtain an isotropic shift value. A pulse sequence is irradiated, and a spin echo pulse train using a composite pulse for causing magnetization transfer by homonuclear J interaction or homonuclear dipole interaction during the mixing period is irradiated, and the observation period t ₂
In this case, a spin echo signal is detected, and magnetization transfer can be performed in a short time in solid-state NMR.

[0007]

Embodiments of the present invention will be described below. FIG. 1 is a diagram for explaining the concept of the NMR method of the present invention. Since the object of the present invention is solid-state NMR, in order to obtain a sharp signal as shown in FIG. 1 (a), the measurement was performed by rotating the sample at a high speed at a magic angle. as shown, ¹ to ¹ H does not come in relation to the magnetization transfer H
While decoupling the RF magnetic field. ^{When 1} H is decoupled, the isotropic chemical shift, an
The isotropic chemical shift, the J interaction, and the homonuclear dipole interaction remain, but the magic angle spinning annihilates the anisotropic chemical shift and, as described later, the dipole interaction.

[0008] ¹³ To describe the case of C measurement, the time series for ¹³ CRF channel by two-dimensional NMR method, as shown in FIG. 1 (c), [initial pulse train - evolution period t ₁ - combination period - observation period t
₂ ]. The periods t ₁ and t _{2 are} periods determined by the isotropic chemical shift interaction. For example, the period t ₁ is a pulse sequence for making an isotropic shift, and a W sequence for eliminating homonuclear dipole interactions and reducing the frequency of chemical shift.
AHUHA pulse sequence (M. Mehring 'Principles of Hig
h Resolution NMR in Solids'Splinger-Verlag, Berlin,
1983), t ₂ period not the RF pulse irradiation anything. As described above, by irradiating the pulse train in the period t ₁ and not irradiating the pulse in the period t ₂ , the scale ratio can be changed between the vertical axis and the horizontal axis when displaying two-dimensional NMR.

[0009] During the mixing period, magnetization transfer by homonuclear J interaction or dipole interaction is performed. [J Interaction] In the case of using the J interaction, an RF multiple pulse is applied so that only the J interaction remains except for the influence of the interaction between the chemical shift and the dipole. In other words, anisotropic chemical shifts and dipole interactions have disappeared due to magic penguin spinning, but isotropic
90 ° pulse, 270 ° as chemical shift remains
The spin is eliminated by combining the pulses and rotating and averaging the spin.

The timing of the pulse in each period is as follows. t ₁ : WAHUHA pulse sequence modified by Mehring t ₂ : The observed nucleus does not emit radio waves. Mixed period: The pulse sequence was designed mainly based on the mean Hamiltonian theory. In mixing by J-bonding, pulses of R ₆ and R ′ ₆ are irradiated. Here, R ₆ = [− τ _1- (90 °) ₀ ^. (270 °) ₉₀ ^. (90 °) ₀ ^. −2τ ₁ − (90 °) ₀ ^. (270 °) ₉₀ ^. (97.2) ₀ ^. −τ ₁ −] ₆ R ′ ₆ = [− τ ₂ − (90 °) ₁₈₀ ^. (270 °) ₂₇₀ ^. (90 °) ₁₈₀ ^. −2τ ₂ − (90 °) ₁₈₀ ^. (270 °) ₂₇₀ ^. (82.8) ₁₈₀ ^. −τ ₂ −] ₆ . Here,-[tau]-represents a period during which RF is not irradiated, ([theta]) _a is an RF phase a, and represents a radio pulse having a flip angle [theta]. The lengths of R ₆ and R ′ ₆ are each equal to the period of one rotation of the sample, and τ ₁ and τ ₂ and the radio wave intensity are adjusted so as to be equal. The magnetization transfer by the J interaction can be performed by the pulse train as described above.

[Dipole Interaction] When dipole interaction is used, multiple pulses are applied so that the dipole interaction does not disappear by rotation of the sample, except for chemical shift. Note that J
The interaction remains, but can be ignored compared to the dipole interaction. Assuming that the dipole interaction is Η, Η = G × S G... A part that changes the spin by physical rotation S... Here, G changes periodically at the magic angle spinning frequency as shown in FIG. Since S is constant irrespective of sample rotation, the sign of the dipole interaction Η periodically changes in the conventional magnetization transfer method, so that its integrated value becomes 0 and no magnetization transfer occurs. Therefore, in the present invention, as shown in FIG. 2B, the sign of the spin is changed in synchronization with the rotation of the sample. As a result, since G × S has a constant sign as shown in FIG. 2C, the integrated value does not become 0 and magnetization transfer can be caused. Assuming that ω _mas is the sample rotation angular velocity, Η = C ₁ cos ω _mas t + C ₂ cos ₂ ω _mas t + S ₁ sin ω _mas t + S ₂ sin ₂ ω _mas t, and Η has a time dependency, as shown in FIG. cos ω _mast , if we change it,
₂ , S ₁ and S ₂ components become 0 by averaging, and only C ₁ component can be extracted. In the following pulse sequence, thus the portion of C ₁ is prevented from being averaged. Here, ω _mas is the rotational angular velocity of the sample, and t is the origin at the beginning of the mixing period.

The pulse timing in each period is as follows. t ₁ : WAHUHA pulse sequence modified by Mehring t ₂ : The observed nucleus does not emit radio waves. Mixed period: The pulse sequence was designed mainly based on the mean Hamiltonian theory. AB (180 °) _{0 for} mixing by dipole coupling ^. AB '
(180 °) ₀ ^. Irradiate the pulse system. Here, A = [− τ ₃ − (180 °) ₀ ^. −2τ ₃ − (180 °) −2τ ₃ − (180 °) ₁₈₀ ^. −2τ ₃ − (180 °) ₁₈₀ ^. −τ ₃ −] ₂ B = (270 °) ₉₀ ^. [−τ ₄ − (90 °) ₀ ^. −2τ ₅ − (90 °) ₀ ^. −τ ₄ ] ₂ [−τ ₄ − (90 °) ₁₈₀ ^. −2τ ₅ − (90 °) ₁₈₀ ^. −τ ₄ −] ₂ [−τ ₄ − (90 °) ₀ ^. −2τ ₅ − (90 °) ₀ ^. −τ ₄ ] ₂ [−τ ₄ − (90 °) ₁₈₀ ^. −2τ ₅ − (90 °) ₁₈₀ ^. −2τ ₄ − (90 °) ₁₈₀ ^. −2τ ₅ − (90 ° −δ) ₁₈₀ ^. −τ ₄ −) (90 °) ₉₀ ^. Here, B ′ is obtained by replacing −δ in B with + δ (δ ≒ 30 °).

[0013] _{τ 3 = (τ mas -34τ 90} .) / 32 τ 4 = (τ mas -58τ 90.) / 64 τ 5 = τ 4 + τ 90. / 2 where τ _mas is the sample rotation period and τ ₉₀ ^. Is the 90 ° pulse width. An RF intensity of about 100 KHz and a sample rotation speed of about 5 KHz are used.

Next, a spectrum obtained by simulation for a solid powdered amino acid whose sample is 100% ¹³ C-labeled using the pulse sequence according to the above embodiment will be described with reference to FIGS. 3 and 4. FIG. FIG. 3 (a) is a spectrum obtained by first polarizing only carbonyl carbon and mixing after J mixing at 10.4 msec. FIG. 3B shows J for all Js.
= 0, the same measurement as in FIG. 3A was performed.
In FIG. 3B, the magnetization is transferred by dipole coupling.
In FIG. 3 (b) where magnetization transfer due to dipole coupling occurs, the α signal is 0, and in FIG. 3 (a) using the J mixed pulse, the α signal is detected. It can be seen that when used, magnetization transfer by the dipole hardly occurs. 3 (c) and 3 (d) are spectra measured after a 1.6 msec dipole mixing pulse. The amino acid conformation is different between FIG. 3 (c) and FIG. 3 (d). As can be seen from the difference in the signal intensity of the γ carbon between FIG. 3 (c) and FIG. 3 (d), information on the three-dimensional structure of the molecule can be obtained by this mixing method.

FIG. 4 is an isotropic shift correlation two-dimensional spectrum of solid powdered amino acid using mixing by J bond.
(B) is obtained by symmetrizing the two-dimensional spectrum shown in FIG. 4 (a). T ₁ period as described above, or performing RF pulse irradiation at t ₂ period, and changing the chemical shift scale by or not performed while the chemical shift scale by RF pulse irradiation spinning sidebands affected Absent. Therefore, the spinning side band does not exist symmetrically with respect to the diagonal line in FIG.
In the spectrum (b), it can be seen that the peak derived from the spinning side band has disappeared.

The present invention is not limited to the above description. For example, in the t ₁ period and the t ₂ period, another nuclear dipole decoupling pulse train or a chemical shift scaling pulse train of the same kind is applied. It is possible. Also, J
, The other composite pulse can be a component of the pulse sequence. As for the mixing stage by dipoles, C in addition to the coefficient C ₁ described above
It is also possible to create a pulse so that ₂ S ₁ and S ₂ do not disappear. Furthermore, for multi-dimensional NMR method of two or more dimensions,
These methods are applicable.

[0017]

As described above, according to the present invention, the solid NM
While magic angle sample spinning in R, ¹ H decoupling while J interactions, it is possible to perform in a short time the magnetization transfer by dipole interaction, the J mixing pulse sequence, the chemical shifts and dipole interactions Is used and J that does not depend on the dihedral angle is used, so that it is possible to identify the signal only from the chemical bond without depending on the three-dimensional structure. Further, in the dipole mixed pulse train, the pulse train is irradiated in synchronization with the rotation of the sample, so that the dipole interaction that disappears with the rotation of the sample can be recovered. In addition, since the pulse train is designed using the composite pulse, an effective pulse train can be created in a wide offset band. Also, t ₁
Period, because of the use of chemical shift scaling pulse train differ by t ₂ period, it is possible to erase the signals from spinning side bands by symmetrization process. Also, t ₁
Since the chemical shift and scaling are performed in the period, the side band intensity can be reduced. Further, since homonuclear decoupling is performed in the t ₁ phase, the signal intensity can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the concept of the NMR method of the present invention.

FIG. 2 is a diagram illustrating magnetization transfer due to dipole interaction.

FIG. 3 is a diagram showing a magnetization transfer due to a J interaction and a dipole interaction.

FIG. 4 is a diagram showing a two-dimensional display of magnetization transfer due to a J interaction.

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 24/00-24/14 G01R 33/20-33/64 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A high-speed rotation of a measurement sample at a magic angle,
^{This is} a nuclear magnetic resonance method in which the magnetization transfer between nuclear spins is performed while irradiating a decoupling high-frequency magnetic field to ¹ H. The homonuclear dipole interaction is eliminated, and the frequency of chemical shift is reduced. Irradiating a pulse train having an isotropic shift value; and spinning using a composite pulse for performing magnetization transfer by homonuclear J interaction or homonuclear dipole interaction after the development period t ₁ by irradiating the pulse train. Irradiating an echo pulse train for mixing; and, after mixing, detecting a spin echo signal in an observation period t ₂ , an isotropic shift cross-correlation multidimensional solid-state nuclear magnetic resonance method comprising: 2. The nuclear magnetic resonance method according to claim 1, wherein
An isotropic shift cross-correlation multidimensional solid-state nuclear magnetic resonance method characterized in that chemical shifts are developed with different chemical shift scale factors during a period t _{1 and a} period t ₂ .