JP2895611B2 - Semi-selective decoupling method by jump return pulse - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semi-selective decoupling method using a jump return pulse used in nuclear magnetic resonance (NMR) measurement.

[Conventional technology]

In general, when the peak of an NMR spectrum obtained from a nucleus is split into a plurality of peaks, decoupling is performed in order to cut off the bond with an unobserved nucleus and reduce the number of peaks to one.

For example, when the carbon nucleus at the α-position and the carbon nucleus at the β-position are bonded as shown in FIG. 12, if the bonding with other nuclei is not considered, as shown in FIG. NMR
The spectrum is split into two parts under the influence of each other and observed.

Conventionally, in order to reduce the number of split NMR spectra to one, a non-observed nucleus coupled to the observed nucleus is irradiated with a decoupling pulse, and the phase of the spin is randomized to eliminate the effect on the observed nucleus. That is being done.

In addition, a 180 ° pulse is applied to the non-observed nucleus, the spin is reversed, and observation is performed after a predetermined time, so that the phase of the spin of the unobserved nucleus is randomized to eliminate the influence on the observed nucleus. Laws are also in place.

[Problems to be solved by the invention]

As described above, the conventional decoupling method can perform decoupling, but when a large number of unobserved nuclei are irradiated with the decoupling pulse, the decoupling pulse also excites the observed nucleus, and as a result, NM
There is a problem that the peak of the R spectrum cannot be observed.

Therefore, since the decoupling pulse is applied only to the non-observed nucleus without affecting the observed nucleus, a pulse with a wide time width and a narrow band pulse is irradiated, and it tunes only to the non-observed nucleus. Although decoupling has been performed using an active pulse, good results have not always been obtained.

The present invention has been made to solve the above-mentioned problem, and even when a peak frequency of an NMR spectrum such as a homonuclear nucleus is extremely close, a half return by a jump return pulse that can be semi-selectively decoupled. It is an object to provide a selective decoupling method.

[Means for solving the problem]

The present invention relates to an NMR measurement method for irradiating pulsed radio waves to excite nuclear spins and performing decoupling to obtain a multidimensional NMR spectrum, wherein N rotations of nuclear spins (N = 0, 1, 2,...) And a semi-selective decoupling by irradiating a 90 ° pulse consisting of at least one pair of pulsed radio waves having an adjustable pulse interval corresponding to the development time of Features.

[Action]

The present invention irradiates at least one set of pulses (jump return pulses) having a phase difference of 90 ° from each other at a time δ. Spins that do not evolve within δ time or spins that return more than one rotation (360 °) during δ time return to the original direction by jump return pulse irradiation do not have any effect because they return to the original direction by the irradiation of the jump return pulse. Spins that perform a predetermined development in time are affected because they are directed in a direction different from the original direction by the irradiation of the jump return pulse. Therefore, by adjusting the time of δ, the affected spins and the unaffected spins can be selected, and
Even homonuclear nuclei close to the NMR peak can be semi-selectively excited and decoupled by the jump return pulse.

〔Example〕

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

1 to 3 are views for explaining a decoupling method of the present invention.

FIG. 1 is a schematic diagram of a pulse train for obtaining a two-dimensional NMR spectrum.

For example, excited by 90 degrees pulses including a pulse-like radio wave, to detect the free damped oscillation after t ₁ a (F1D) sampling pulse having a predetermined period (t ₂ domains) with different t ₁ little by little to the data acquisition with ( A two-dimensional NMR spectrum is obtained by performing Fourier transform on t ₁ domain), t ₁ , and t ₂ .

In such a two-dimensional NMR, a time interval of δ and a time interval of t _{1/2 of} the excitation pulse,
° x and 90 ° -x pulse, i.e. irradiating the jump return pulse, detecting the FID after t _2/2. For example, the second
As shown in the figure, nuclear spins oriented in the z-direction by irradiation at 90 ° x rotate as shown by the arrow A and fall in the y-direction. Then, after δ hours, the nuclear spin tilted in the y direction does not expand, or when a 90 ° -x pulse is irradiated when returning to the original position after one or more rotations in the x, y plane, This nuclear spin is oriented in the original z direction as shown by arrow B. Therefore, the jump return pulse has no effect on such nuclear spins.

On the other hand, the nuclear spins tilted in the y direction at 90 ° x and expanded at a predetermined angle in δ time are tilted as shown by the arrow C by the pulse of 90 ° -x, and the original direction is not turned, and the jump return It is excited by the pulse. Therefore, if there is a set of nuclear spins with similar chemical shifts, by adjusting the δ time, it is possible to excite only one nucleus without affecting one nucleus,
Decoupling can be semi-selectively performed by the jump return pulse.

As described above, the nuclear spin rotating N times in the δ time is not affected by the jump return pulse, so that the δ time which does not affect a specific nuclear spin has periodicity. That is, as shown in FIG. 3, a region ND that is not affected by the jump return pulse, that is, a region ND that is not decoupled, and a region D that is decoupled appear periodically.

Therefore, if the δ time is adjusted so that one corresponds to the region D and the other corresponds to the region ND, the peaks of the spectrum between homonuclei such as ( ¹ H, ¹ H) and ( ¹³ C, ¹³ C) are obtained. Decoupling can be performed semi-selectively even in the case of extremely close proximity.

When the frequency of the decoupling region is away from the observation region by Δν, there is a relation of δ = 1 / 2Δν between δ and Δν. What is necessary is just to set to the center of the ND area of FIG.

Then, in the two-dimensional NMR spectrum diagram of FIG.
The conventional decoupling method is used for the ¹ H axis where the spectrum peaks are far apart, and the jump return pulse is used for the ¹³ C side of the homogeneous nucleus, so that a high accuracy can be achieved.
One-dimensional NMR spectra can be obtained.

In the above description, 1 is used as the jump return pulse.
Although a set of pulses was used, the present invention is not limited to this. As shown in FIG. 5, a pair of pulses having a phase difference of 90 degrees, such as (90 ° x, 90 ° y, 90 ° -y, 90 ° -x), is used. May be excited by combining two sets of pulses composed of a set of pulses, or n sets of pulses composed of a pair of pulses having a phase difference of 90 degrees from each other. It is also possible to use a pulse having an arbitrary pulse width θ.

FIG. 6 is an explanatory diagram when the decoupling method of the present invention is applied to HMQC.

In the case of HMQC, protons and carbon are not originally coupled, so after irradiating a 90 ° pulse, refocusing is performed by 180 pulses, and conventional decoupling is performed to detect the FID. On the other hand, carbon nuclei are coupled with other carbon nuclei, and a 90 ° pulse is applied to unobserved nuclei.
Jump return pulse θφ ₁ , θφ ₂ during 90 ° pulse
Is irradiated for a predetermined time δ to perform decoupling and observation.

FIG. 7 is an explanatory view in the case where the decoupling method of the present invention is applied to SQC. After irradiating a 90 ° pulse to a proton, the proton is refocused by a 180 ° pulse, and further a 90 ° pulse is applied.
A 180 ° pulse is irradiated during the 0 ° pulse to perform decoupling with carbon nuclei by the spin inversion pulse method.
After refocusing the 0 ° pulse, FID is detected by performing decoupling by a conventional method. On the other hand, the carbon nucleus is similarly refocused with a 180 ° pulse, decoupled by irradiating a jump return pulse between the 90 ° pulses, and refocusing with a 180 ° pulse to obtain the observed nucleus. Will be observed.

FIGS. 8 and 9 show two-dimensional NMR spectra of HMQC. FIG. 8 shows a two-dimensional NMR spectrum observed by the conventional method. FIG. 9 shows a two-dimensional NMR spectrum obtained by applying the decoupling method of the present invention.
It is an R spectrum.

As can be seen from FIGS. 8 and 9, it can be seen that the present invention is effectively decoupled.

FIG. 10 and FIG. 11 show two-dimensional NMR spectra of SQC,
FIG. 10 shows a two-dimensional image obtained by decoupling by the conventional method, and FIG. 11 shows a two-dimensional image obtained by decoupling by the method of the present invention.
It is an NMR spectrum.

As can be seen from the figure, it can be seen that decoupling is effectively performed in the case of SQC as well as in the case of HMQC.

In the above description, two-dimensional NMR is taken as an example, but the present invention can be similarly applied to three-dimensional or higher-dimensional NMR.

〔The invention's effect〕

As described above, according to the present invention, a jump return pulse is used for semi-selective decoupling over a wide range, and it is possible to semi-selectively and effectively decouple even a homogeneous nucleus.

[Brief description of the drawings]

FIGS. 1, 2, and 3 are diagrams for explaining the decoupling method of the present invention, FIG. 4 is a diagram showing a two-dimensional NMR spectrum, and FIG. 5 is a diagram for explaining another jump return pulse. , FIG. 6 is a diagram showing a pulse train when applied to HMQC, FIG. 7 is a diagram showing a pulse train when applied to SQC, FIG. 8 and FIG. 9 are two-dimensional NMR spectra of HMQC. FIG. 10, FIG. 10 and FIG. 11 show two-dimensional NMR spectra of SQC, and FIG. 12 and FIG. 13 are diagrams for explaining the splitting of the NMR spectrum peak.

Claims (1)

(57) [Claims] The present invention relates to an NMR measurement method for irradiating a pulsed radio wave to excite nuclear spins and performing decoupling to obtain a multidimensional NMR spectrum.
Irradiating a 90 ° pulse consisting of at least one set of pulsed radio waves having an adjustable pulse interval corresponding to the development time of the rotation (N = 0, 1, 2,. A semi-selective decoupling method using a jump return pulse, wherein decoupling is selectively performed.