SOLUTE EFFECTS ON THE THERMAL-STABILITY OF GLYCEROL MONOSTEARATE AMYLOSE COMPLEX SUPERSTRUCTURES

Thermally induced order-disorder transitions of two distinct structural forms of the glycerol monostearate-amylose complex (form I, Tm 99° and form II, Tm 117°) have been investigated by differential scanning calorimetry in various solvent environments. For neutral salts, the effectiveness of anions and cations in stabilizing or destabilizing the ordered chain domains of the complex followed, in general, the classical Hofmeister series. Thus, with Na+ as the sole counterion, the Tm of the transition (at <1.0m) increased in the order of SCN- < I- < NO3- < F- < Cl- < CH3COO- < SO42-. With Cl- as the common anion, the ranking of the cations was NH4+ < K+ < Na+ < Li+ </ Ca2+ </ Mg2+. Interestingly, ranking of certain ions (e.g., CH3COO-) differed between the two forms of the complex, particularly at high electrolyte concentrations. This implies that some solutes can act differently at various levels of supermolecular structure. Glucose and malto-oligosaccharides were effective stabilizers and resulted in non-equilibrium phase transition behaviour for the metastable superstructures of the complex (melting with reorganization during heating). These effects were proportional to the molecular weight and concentration of the small carbohydrate solute. © 1990.