T. Carlomagno et C. Griesinger, Errors in the measurement of cross-correlated relaxation rates and how to avoid them, J MAGN RES, 144(2), 2000, pp. 280-287
Cross-correlated relaxation rates Gamma are commonly obtained from constant
time experiments by measuring the effect of the desired cross-correlated r
elaxation on an appropriate coherence during the constant time T. These mea
surements are affected by systematic errors, which derive from undesired cr
oss-correlated relaxation effects taking place before and after the constan
t time period T. In this paper we discuss the sources and the size of these
errors in an example of two pulse sequences. Higher accuracy of the measur
ed data can be obtained by recording a set of experiments with different T
values. Cross-correlated relaxation rates me measured in constant time expe
riments either from the differential relaxation of multiplet components (J-
resolved Gamma experiments) or from the efficiency of magnetization transfe
r between two coherences (quantitative Gamma experiments). In this paper we
calculate analytically the statistical errors in both J-resolved and quant
itative Gamma experiments. These formulae provide the basis for the choice
of the most efficient experimental approach and parameters for a given meas
urement time and size of the rate. The optimal constant time T for each met
hod can be calculated and depends on the relaxation properties of the molec
ule under investigation. Moreover, we will show how to optimize the relativ
e duration of cross and reference experiments in a quantitative Gamma appro
ach. (C) 2000 Academic Press.