Low‐power composite CPMG HSQMBC experiment for accurate measurement of long‐range heteronuclear coupling constants

Abstract

A modified version of CPMG-HSQMBC pulse scheme is presented for the measurement of long-range heteronuclear coupling constants. The method implements adiabatic inversion and refocusing pulses on the heteronucleus. Low-power composite 180° XY-16 CPMG pulse train is applied on both proton and X nuclei during the evolution of long-range couplings to eliminate phase distortions due to co-evolution of homonuclear proton-proton couplings. The pulse sequence yields pure absorption antiphase multiplets allowing precise and direct measurement of the (n)J(XH) coupling constants regardless from the size of the proton-proton couplings. The applicability of the method is demonstrated using strychnine as a model compound. The selective 1D version of the method is also presented.

P.E.HSQMBC: Simultaneous measurement of proton–proton and proton–carbon coupling constants

“…The proper combination of multiple proton excitation and nonuniform sampling can allow a faster measurement of all these couplings in small and medium size molecules. Alternatively, the experiment could be also implemented in a broadband mode, using for instance a CPMG-BIRD element instead of the selective INEPT block [26][27][28]. However, complete suppression of protonproton coupling evolution and undesired sample heating remains to be solved.…”

Probing pattern and dynamics of disulfide bridges using synthesis and NMR of an ion channel blocker peptide toxin with multiple diselenide bonds

“…To improve the sensitivity of 1 H- 77 Se multiple bond correlation measurements, a modified, 77 Se-decoupled variant of the CPMG-HSQMBC experiment30–32 has been developed in our group. This experiment considerably reduces the adverse line broadening effect of conformational exchange and also efficiently suppresses the undesired co-evolution of proton–proton couplings (such as the large geminal coupling between the H β protons of Sec) during the long scalar coupling evolution period matched to the intra- and interresidue multiple bond 1 H- 77 Se couplings.…”

Measurement and Applications of Long‐Range Heteronuclear Scalar Couplings: Recent Experimental and Theoretical Developments

“…Ad: Rapid acquisition of the coupling data; superior resolution for unfolded protein Lim: Not a robust sequence for medium-sized or large folded proteins [40] CPMG HSQMBC Method implements adiabatic inversion and refocusing pulses on the heteronucleus; allows determination of long-range heteronuclear couplings of very small magnitudes Ad: Provides couplings for both quaternary and protonated carbon atoms Lim: The narrow bandwidth of the low-power pulses in the CPMG cycle can give non-uniform excitation [39] Selective 1D CPMG HSQMBC Same as for CPMG HSQMBC except the G-BIRD module Ad: Shorter experimental time Lim: Same as for CPMG HSQMBC but more experiments have to be carried out to derive all the coupling parameters. Necessity of well-resolved multiplet for the selective pulse to be applied [39] The F 1 /F 2 plane pertains to the INADEQUATE spectrum with all the expected 13 C- 13 C correlations.…”

“…Necessity of well-resolved multiplet for the selective pulse to be applied [39] The F 1 /F 2 plane pertains to the INADEQUATE spectrum with all the expected 13 C- 13 C correlations. The subsequent stage acquires information about direct and long-range 13 C-1 H correlations.…”