The first time I implemented Indirect Covariance NMR in MestReC, I found that the computational effort required was quite high. Of course, in indirect covariance NMR spectroscopy, the spectral resolution along both frequency axes is determined by the sampling along the evolution t1 time. In other words, it brings in a sensitivity increase of 8 over a 13C detected experiment. The advantage is obvious: Indirect Covariance NMR yields a 13C-13C TOCSY correlation without having to detect the 13C nucleus. It is important to mention that both experiments must be acquired and processed under identical conditions, temperature, number of scans etc. In the other EXSY experiment, the EXSY reference experiment, no cross peaks due to magnetization exchange should be observed (thermal equilibrium) and the amplitudes of just the diagonal peaks of those signals in exchange, A(0), have to be measured. In this experiment the amplitudes (intensities) of those signals in exchange, A(tm), have to be quantified for both diagonal and cross peaks. In the former experiment the mixing time (tm) need to be large enough for the magnetization exchange process to take place.

For the calculation of rate constants, the program requires that the user supplies the experimental amplitudes of certain NMR peaks obtained in two different EXSY experiments, one is an EXSY experiment acquired at a certain mixing time (tm), and the other is an EXSY experiment acquired at 0 or very short mixing time (reference experiment).

Mestrenova diffusion units