IMPEACH-MBC　～Improvement of wide ⁿJ_CH range ¹H-detected long-range shift correlation measurements～

In HMBC measurements, signal intensities of long-range correlation peaks depend on magnetization transfer time 1/2 ⁿJ_CH. A basic HMBC pulse sequence, assuming a fixed value of ⁿJ_CH, cannot give correlation peaks derived from various ⁿJ_CH values at once (Fig.3 top). ACCORD-HMBC, incorporating variable delays, acquires a wider range of ⁿJ_CH orrelations, but its spectrum may distort along the indirect axis (Fig.3 middle). IMPEACH-MBC (IMproved PErformance ACcordion HMBC) solves this problem, by adding cancelling inverse variable delays to ACCORD-HMBC to generate a constant-time sequence. IMPEACH-MBC measurements give spectra where long-range shift correlations can easily be analysed (Fig.3 bottom).

Fig.1　Pulse diagram of IMPEACH-MBC measurements.

τ₁ = 1/2{¹J_CH^max + 0.146(¹J_CH^max – ¹J_CH^min)}^–1, τ₂ = 1/2{¹J_CH^max – 0.146(¹J_CH^max – ¹J_CH^min)}^–1
vd = 1/2(ⁿJ_CH^min)^–1 – y_point[{1/2(ⁿJ_CH^min)^–1 – 1/2(ⁿJ_CH^max)^–1}/(y_points – 1)]
D = initial_delay^* + y_point[{1/2(ⁿJ_CH^min)^–1 – 1/2(ⁿJ_CH^max)^–1}/(y_points – 1)]
^*initial_delay = 2(PFG + recovery time)

Fig.2　IMPEACH-MBC spectrum of 4-methyl umbelliferone.
ⁿJ_CH^max = 10 Hz, ⁿJ_CH^min = 2 Hz, ¹J_CH^max = 170 Hz, ¹J_CH^min = 120 Hz, y_points = 512

Spectrometer：JNM-ECX400

HMBC

hmbc_pfg.ex2
long_range_j = 8 Hz
j_constant = 140 Hz

↓ cover a wide range of ⁿJ_CH

ACCORD-HMBC

hmbc_accord_dec_pfg.ex2
y_points = 256
lr_j_min = 1 Hz
lr_j_max = 16 Hz
j_ch_min = 120 Hz
j_ch_max = 160 Hz

↓ remove J_HH-modulation

IMPEACH-MBC

impeach_mbc_dec_pfg.ex2
y_points = 512
lr_j_min = 2 Hz
lr_j_max = 10 Hz
j_ch_min = 120 Hz
j_ch_max = 170 Hz

Spectrometer：JNM-ECX400

Reference

C.E. Hadden, G.E. Martin and V.V. Krishnamurthy, J. Magn. Reson., 140, 274 (1999)