Dynamic NMR: combined use of 1D selective EXSY and complete lineshape analysis of spectra subjected to reference deconvolution and linear prediction or the maximum entropy method

Abstract

In dynamic NMR lineshape analysis and in handling other curve-fitting problems, the quality of the adjusted parameters improves if the iterative procedure is constrained by introducing additional conditions. It is demonstrated on a simple model of a two-site exchange system that in the complete lineshape analysis of spectra subjected to reference deconvolution and linear prediction or the maximum entropy method in combination with 1D EXSY experiments, the unknown parameters can be reduced to only one, the rate constant. This approach ensures excellent results for the activation parameters. It is also shown that 1D selective EXSY (1D SEXSY) experiments using E-BURP pulses could successfully be used as a substitute to the more (experimentally) demanding 2D EXSY measurements.

Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen

“… 46 – 50 The slow dynamic processes exhibited by the complexes studied here were monitored by EXSY methods. 51 …”

Creatinine and creatininium cation in DMSO‐d6 solution. Structure and restricted internal rotation of NH2 group

“…The lineshape imperfections and the influence of the magnetic field inhomogeneity were shown to be removable from the experimental spectra by application of the reference deconvolution and linear prediction or the maximum entropy method. 29 The problems due to magnetic field inhomogeneity can also be avoided when recording spectra with the use of the spin-echo pulse sequence and interpreting effective transverse relaxation rates rather than total lineshapes. 30 On the other hand, in the situation when the slow exchange temperature range is inaccessible for measurements and there are sound reasons to expect that all the shape parameters are temperature dependent, as was the case with our samples, the situation is much worse.…”

“…The chemical shift difference, υ, derived from the analyses of the spectra measured at temperatures below the coalescence point can be extrapolated to higher temperatures. According to Vassilev and Dimitrov,29 in a particularly convenient situation only the rate parameter has to be fitted during the analysis of a dynamic spectrum. It seems, however, that the adjustment of the mean chemical shift υ av , intensity factor, baseline level and zero-order phase parameter for each spectrum during the least-squares analysis simultaneously with the rate parameter is safer than finding their values independently and keeping them constant during the iterative procedure.…”

SABRE hyperpolarisation of vitamin B3 as a function of pH

“…NMR characterization data was collected using a range of 1-D and 2-D methods that included nOe, COSY and HMQC procedures. 28 – 32 …”