The DEPTQ+ Experiment: Leveling the DEPT Signal Intensities and Clean Spectral Editing for Determining CHn Multiplicities

Abstract

We propose a new 13C DEPTQ+ NMR experiment, based on the improved DEPTQ experiment, which is designed to unequivocally identify all carbon multiplicities (Cq, CH, CH2, and CH3) in two experiments. Compared to this improved DEPTQ experiment, the DEPTQ+ is shorter and the different evolution delays are designed as spin echoes, which can be tuned to different 1JCH values; this is especially valuable when a large range of 1JCH coupling constants is to be expected. These modifications allow (i) a mutual leveling of the DEPT signal intensities, (ii) a reduction in J cross-talk in the Cq/CH spectrum, and (iii) more consistent and cleaner CH2/CH3 edited spectra. The new DEPTQ+ is expected to be attractive for fast 13C analysis of small-to medium sized molecules, especially in high-throughput laboratories. With concentrated samples and/or by exploiting the high sensitivity of cryogenically cooled 13C NMR probeheads, the efficacy of such investigations may be improved, as it is possible to unequivocally identify all carbon multiplicities, with only one scan, for each of the two independent DEPTQ+ experiments and without loss of quality.

A Versatile Broadband Attached Proton Test Experiment for Routine 13C Nuclear Magnetic Resonance Spectroscopy

“…The broadband APT (BAPT) pulse sequence differs from the recommended CAPT3 pulse sequence [ 24 ] as follows ( Figure 1 ): (i) Instead of a delay, Δ 1 , set to one single 1 J CH value, three delays, Δ 1 , Δ 2 , and Δ 3 , are used and set for three estimated one-bond coupling constants, 1 J 1 CH , 1 J 2 CH , and 1 J 3 CH , a long-known strategy that has been implemented in low-pass J filters [ 32 ], in SEMUT-GL [ 27 ], in HMBC experiments [ 33 ], and, recently, in DEPTQ+ experiments [ 16 ]. (ii) Like the basic APT experiment, the BAPT experiment can be used to provide either an APT spectrum or a Cq-only spectrum.…”

“…The added sensitivity gain achieved with polarization transfer experiments such as DEPT or INEPT has almost stopped the further development of APT-related experiments. However, the simplicity of the APT sequences, and in particular the ability to obtain all the carbon multiplicities, including Cq, is an important advantage that is otherwise only achieved with the polarization enhancement nurtured during attached nucleus testing (PENDANT) [ 12 , 13 ] and the DEPTQ sequences [ 14 , 15 , 16 ]. Furthermore, and with respect to other applications such as the study of perfluorinated compounds CF n , the APT experiment is easier to use than DEPT.…”