CONFORMATIONAL CHANGE AND AGGREGATION OF KAPPA-CARRAGEENAN STUDIED BYFLOW FIELD-FLOW FRACTIONATION AND MULTIANGLE LIGHT-SCATTERING

The relatively novel combination of flow field-flow fractionation (FFF ) and multiangle light scattering (MALS) was employed to study a nonde graded kappa-carrageenan in different 0.1M salt solutions. The applica bility of the technique was tested, and the effects of salt type and s alt composition on the molar mass and radius of gyration were studied. A conformational ordering was induced at room temperature by switchin g the solvent from 0.1M NaCl (coil form) to 0.1M NaI (helix form). An approximate doubling of the average molar mass and an increase in radi us of gyration was then observed, in agreement with results obtained p reviously using size exclusion chromatography-MALS. This increase in s ize was attributed to conformational ordering and to the formation of double helices. Severe aggregation was observed above 40% CsI in the 0 .1M mixed salt solution of CsI and NaI. This was ascribed to the assoc iation of helices into large aggregates. For these large associates, h aving molar masses of several millions, a reversal of the elution orde r in flow FFF was detected. (C) 1998 John Wiley & Sons, Inc.