Application of Accordion excitation in ~1H-~(15)N long-range heteronuclear shift correlation experiments at natural abundance

摘要

Accordion excitation provides the means of sampling a broadd rnage of potential long-range heteronuclear couplings in a single experiment. Two long-range heteronuclear experiments, ACCORD-HMBC and IMPEACH-MBC, have been developed thus far that offer accordion excitation. The results obtained with these experiments for ~1H-~(15)N heteronuclear shift correlation at snatural abundance are compared. Low digitization in the second(F_1) frequency domain of ~2H-~(15)N ACCORD-HMBC potentially hampers this use of the experiment since it is prone to coupling modulation in the second frequency domain as a function of the accordion excitation delay. The constant time variable delay used in lieu of a simple accordion delay in the IMPEACH-MBC ecperiment circumvents homonuclear coupling modulation in F_1, thereby improving resolution relative to the ACCORD-HMBC experiment for the same number of increments of the evolution period. Results obtained using accordion-optimized experiments are contrasted with conventional gradient HMBC(GHMBC). Accordion-optimized experiments offer a potential advantage for ~H-~(15)N long-range heteronuclear shift correlation experiments due to the wide variability of long-range ~1H-~(15)N couplings. Copyright