Mak. Williams et al., A NONLINEAR-REGRESSION METHOD FOR THE ANALYSIS OF H-1 T-2 DISPERSION-CURVES INCLUDING COMMENTS ON THE ROLE OF POLYDISPERSITY, Magnetic resonance in chemistry, 36(3), 1998, pp. 163-173
A nonlinear regression method is described in detail for analysing H-1
T-2 (Carr-Purcell-Meiboom-Gill) dispersion curve measurements obtaine
d from water-rich systems containing molecules possessing labile proto
ns. The method is routine, provides well specified error statistics an
d does not make assumptions about the accessibility or mobility of the
guest molecule site. The approach is validated using data simulated w
ith the Carver-Richards two-site exchange model and experimental measu
rements carried out on a series of methanol-d(4)-water mixtures of var
ying pH. Further simulations are described which investigate the role
of polydispersity in determining the form of the dispersion curve and
the relevance of the parameters extracted by fitting a composite curve
to a single Carver-Richards function. The procedure is subsequently u
sed to fit experimental dispersion curves originating from maltodextri
n-water systems and the interpretation of the results is shown to be c
onsistent with previously suggested ideas for molecular interactions i
n polysaccharide systems, involving discrete units of double helical n
ature, which can further aggregate to develop structure at a supramole
cular level.