I. Najfeld et al., A ROBUST METHOD FOR ESTIMATING CROSS-RELAXATION RATES FROM SIMULTANEOUS FITS TO BUILDUP AND DECAY CURVES, Journal of magnetic resonance [1997], 124(2), 1997, pp. 372-382
Citations number
21
Categorie Soggetti
Physics, Atomic, Molecular & Chemical","Biochemical Research Methods
This paper introduces a novel computational method for estimating rela
xation rates among pairs of spin orders. This method simultaneously es
timates all the auto- and cross-relaxation rates from the same measure
ments, and avoids the ill-conditioning problems associated with multie
xponential fits, The method models the relaxation dynamics by a system
of linear differential equations, and assumes that measurements of th
e spin orders have been made at an equally spaced sequence of time poi
nts. It computes a nonlinear least-squares fit of the exponential of t
he rate matrix at the shortest time point to these measurements. Preli
minary estimates of the exponential matrix and initial spin orders fro
m which to start the computations are obtained by solving simpler line
ar-least-squares problems. The performance of the method on simulated
2 x 2 test problems indicates that when measurements at eight or more
equally spaced times spanning the maximum and inflection points of the
build-up curves are available, the relative errors in the rates are u
sually less than the relative errors in the measurements. The method i
s further demonstrated by applying it to the problem of determining th
e cross correlation-induced cross-relaxation rates between the in-phas
e and antiphase coherence of the amide groups in the N-15-labeled prot
ein oxidized flavodoxin. Finally, the possibility of extending the met
hod to other kinds of relaxation measurements and larger spin systems
is discussed. (C) 1997 Academic Press.