Radiation damping on cryoprobes

Radiation damping on 600 and 800 MHz cryoprobes was investigated. The phase angle beta between a vector 90 degrees phase shifted to the precessing magnetization and the rf field induced in the coil was found to depend markedly on whether an FID was being acquired or not. The magnitude of the radiation damping field was sufficiently strong to restore 95% of the equilibrium water magnetization of a 90% H(2)O sample in a 5 mm sample tube within about 5 ms following a 165 degrees pulse. This can be exploited in water flip-back versions of NOESY and TOCSY experiments of proteins, but care must be taken to limit the effect of the radiation damping field from the water on the H(a) protons. Long water-selective pulses can be applied only following corrections. We developed a program for correcting pulse shapes if beta is non-zero. The WATERGATE scheme is shown to be insensitive to imperfections introduced by radiation damping. (C) 2011 Elsevier Inc. All rights reserved.