A NONLINEAR-REGRESSION METHOD FOR THE ANALYSIS OF H-1 T-2 DISPERSION-CURVES INCLUDING COMMENTS ON THE ROLE OF POLYDISPERSITY

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.