ON THE STRUCTURE OF AGGREGATED KAPPA-CARRAGEENAN HELICES - A STUDY BYCRYO-TEM, OPTICAL-ROTATION AND VISCOMETRY

Cryo-transmission electron microscopy (cryo-TEM), viscometry and optic al rotation have been used to study the microstructure of dilute solut ions of helical K-carrageenan under varied electrolyte composition (0. 1 M of NaI, CsI and mixtures of the two salts). Microfibers (300-400 n m in length) were observed above a critical cesium content, while belo w that no microstructure was seen in the micrographs. A drastic increa se in the specific viscosity and an onset of thermal hysteresis in the optical rotation above the same critical cesium content provide clear evidence of aggregate formation. This leads to the conclusion that th e observed microfibers are aggregates consisting of several helices. A t high proportions of cesium, further aggregation of the microfibers w as observed by cryo-TEM.