Accordion-optimized long-range heteronuclear

Accordion-optimized Long-range Heteronuclear Shift... 

The available accordion-optimized long-range heteronuclear shift correlation experiments were surveyed in a recent chapter. No novel accordion-optimized methods have been reported, but following the author s initial report on the advantages of using the IMPEACH-MBC sequence for long-range studies, Kline and Cheatham have... 

Accordion-optimized long-range heteronuclear shift correlation experiments... 

Fig. 8.28 The (/, -HMBC experiment is the most sophisticated accordion-optimized long-range heteronuclear shift correlation experiment reported to date [148]. The experiment uses a pulse sequence operator known as a STAR (selectively tailored F, accordion refocusing) to selectively manipulate two-bond and three-bond long-range correlations to protonated carbon or nitrogen resonances. A. STAR operator used in the (/, J-HMBC experiment. The experiment takes advantage of the ability of a BIRD(x,x,x) pulse to refocus the one-bond heteronuclear coupling of a protonated carbon. By doing this, the coupling to this proton...

To provide the means of sampling a wider range of potential long-range heteronuclear coupling constants, an alternative version of this heteronuclear shift correlation experiment is called the accordion-optimized HMBC, or ACCORD-HMBC [50]. Additional modifications of this experiment are also available [51]. 

Nearly simultaneously with the report of the BIRD-HMBC experiment, Meissner and Sprensen described another modification of the basic long-range hetero-nuclear shift correlation experiment that they refer to as broadband HMBC. The authors employ the gradient dual-stage low-pass J-filter used in the accordion-optimized experiments described above (Section 3.3.5) followed by a delay. A, which replaces the accordion-optimized delay or a normal fixed delay for the evolution of long-range heteronuclear components of magnetization. Instead, Meissner and Sprensen acquire a series of several experiments with different... 

In 2001, Meissner and Sprensen described methods for the measurement of Jhh anO "Jch couplings employing the broadband excitation approach (see Section 3.3.7) with the report of the broadband XLOC and broadband J-HMBC experiments, respectively. In a further extension of the idea of accordion optimization, Williamson ef reported the development of the J-IMPEACH-MBC pulse sequence. This approach is similar to the EXSIDE experiment previously described by Krishnamurthy and the J-resolved HMBC experiments of Furihata and Seto"- in its use of J-scaling to render small, long-range heteronuclear couplings conveniently measurable. Finally, Williamson e/ also described a new method, G-BIRDr-HSQMBC, that was reported in their survey of the available methods. 

Fig. 19. Pulse sequence for the J, J-HMBC experiment described by Krishnamurthy ei This experiment represents the most refined version of the accordion-optimized experiments to be developed thus far and allows the differentiation of Jxh from Jxh long-range correlations to protonated heteroatoms ( - C and N). The experiment further modifies the concept of the constant time variable delay used in the IMPEACH-MBC and CIGAR-HMBC experiments to even more selectively manipulate various components of magnetization. This is done using the pulse sequence operator given the acronym STAR (Selectively Tailored Accordion F Refocusing) (.see also Fig. 20). Differentiation of various components of heteronuclear long-range magnetization is accomplished within the STAR operator, with the balance of the pulse sequence similar to that of the IMPEACH-MBC and CIGAR-HMBC experiments.

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