Structural characteristics of monopalmitin monolayers spread on aqueous sugar solutions

Monopalmitin films spread on aqueous solutions of sugars were studied as a function of temperature and subphase composition (sugar type and its concen tration in the aqueous bulk phase). The addition of sugars expanded the str ucture of monopalmitin monolayers, especially if they had previously adopte d a liquid-condensed structure. The extension of this expansion depends on the type of sugar added (glucose, fructose, and sucrose at 0.1 and 0.5 M), Thermodynamic parameters associated with transition from liquid-condensed t o liquid-expanded structures are in concordance with the structural changes observed from rr-A isotherms, The experimental data taken from the isother ms were fitted to some representative state equations. For solid and liquid -condensed structures, a lineal regression was used, with higher slope for the more condensed monolayer structure. For liquid-expanded monolayers, mod els derived from the kinetic theory of two-dimensional gases fit the pi-A e xperimental data better. (C) 1999 Academic Press.