SOLVENT MAGNETIZATION ARTIFACTS IN HIGH-FIELD NMR-STUDIES OF MACROMOLECULAR HYDRATION

With the use of high magnetic fields and improved quality factor ratin gs of the probeheads in modern NMR spectrometers, radiation damping be comes more and more important. In addition, the demagnetizing field ef fect from protonated solvents gains significance with the increase of the magnetic field strength. During a typical NMR pulse sequence the m agnetic fields caused by these effects become time-dependent, which ma kes the system nonlinear and may, for example, measurably influence th e precession frequencies of all nuclei in the sample. Since radiation damping can affect signals that are several kilohertz away from the so lvent resonance, the amplitude, phase, and frequency of the desired si gnals can be disturbed so as to give rise to spectral artifacts. In pa rticular when difference methods are used to obtain the final spectrum , the data sets may be severely deteriorated by such artifacts. This p aper investigates effects from the demagnetizing field and from radiat ion damping with a selection of pulse sequences in use for studies of macromolecular hydration, and strategies are described for the detecti on and elimination of the ensuing artifacts. (C) 1998 Academic Press.