A new tool for NMR analysis of complex systems: selective pure shift TOCSY

Abstract

A new NMR experiment aids the identification of components in complex systems, including mixtures.

Combining pure shift and J‐edited spectroscopies: A strategy for extracting chemical shifts and scalar couplings from highly crowded proton spectra of oligomeric saccharides

“…It should also be stressed that the presence of a J ‐resolved dimension in this correlation spectrum avoids signal overlaps because every proton that is not coupled to the probed coupling network only yields a singlet, which is not the case for a COSY spectrum where the separation of correlations is only based on the dispersion of chemical shifts along both spectral dimensions. We also remark that 1D TOCSY experiments that are often used to extract coupling networks from crowded spectra cannot provide such resolved scalar coupling measurements, although being useful for identifying coupled proton sites …”

Multiplicity‐edited 1H‐1H TOCSY experiment

“…The resulting spectra allow a simple analysis and obvious interpretation, in the same way as other ME experiments. The typical strategy based on column analysis affords 1D traces equivalent to selective 1D pure‐shift TOCSY spectra but with added ME information that helps to identify the number and nature of each cross‐peak. Whereas ME‐TOCSY should be recommended for small molecules with no overlap of 2D cross‐peaks, MEHD‐TOCSY is strongly recommended for more challenging molecules having complex regions, as reported for progesterone.…”

Homonuclear decoupling in the 13C indirect dimension of HSQC experiments for 13C‐enriched compounds

“…Still, notable artifacts were observed about the C(25) signal, related to the second-order effects caused by the very similar chemical shifts of the 1 H and 13 C of the directly bound methyls, 26 and 27. The C(7) and C(8) resonances also have quite similar chemical shifts, and one of the H (7) protons is almost isochronous to the H(8), but in that case, little artifacts were observed probably because the coupling pattern due to the 1 J CH separates the relevant transitions of the multiplets of C(7) and C(8) during the t 1 evolution.…”

“…For the chirps decoupling experiments, the two 60 kHz saltire chirps [3] had (each) a duration of 7, 15, 30, and 50 ms with a maximal radio frequency amplitudes of 322.03, 219.99, 155.55, and 120.49 Hz, respectively, with 20% smoothing. The power of each double saltire chirp is set automatically by the pulse program but was verified using the following calculations [5] : (a) A single adiabatic phase modulated chirp (sweeping from low to high frequency) was generated according to the desired durations (7,15,30, and 50 ms, respectively), bandwidth (60 kHz), and number of points (14,000) and saved; the same was repeated for a chirp sweeping from high to low frequency. The two phase modulated chirps sweeping in opposite directions were added by using the Manipulate/Add Shapes option in the Shape Tool by aligning to the center of the shape and scaling to 100%.…”