Surface Pressure Isotherms, Dilatational Rheology, and Brewster Angle Microscopy of Insoluble Monolayers of Sugar Monoesters

Abstract

Surface pressure isotherms of insoluble monolayers of high purity, enzymatically synthesized sucrose, lactose, glucose, and galactose stearate at the air-water and n-tetradecane-water interfaces were obtained. The dilatational moduli of these surfactant monolayers were also determined by oscillations of the interface at 0.1 Hz. Results have indicated similarities in the properties of sucrose and lactose stearate. Brewster angle microscopy has shown the transitions from gaseous to liquid expanded to liquid condensed phases upon compression of these monolayers at the air-water (A-W) interface. It was also shown that the interfacial phase separation is strongly dependent on the rate of deformation of the interface. Glucose and galactose stearate formed more aggregated monolayers at the A-W interface and (particularly galactose stearate) had higher dilatational moduli, compared to sucrose and lactose stearate. Brewster angle microscopy confirmed the extensive aggregation and the formation of a solid phase in the case of galactose stearate. The isotherms of glucose and galactose stearate at the oil-water (O-W) interface exhibited a first-order phase transition, suggesting a different aggregation pattern, in comparison to the aggregation at the A-W interface, where, possibly, no solid phase was formed. This suggested that more extended aggregation was taking place, where the interactions between the monosaccharide headgroups was the major attractive force.

Viscoelastic properties of insoluble amphiphiles at the air/water interface

“…A number of techniques using step or oscillatory movement of the barriers of the Langmuir trough [9,10] and other forms of surface rheometer or capillary waves have been developed to determine these moduli [11,12]. Techniques based on analysis of the shape of an oscillating drop offer some advantages, particularly in the study of biological substances, since they are not invasive and require only small quantities of these, frequently scarce, materials.…”

PFGSE–NMR study of the self-diffusion of sucrose fatty acid monoesters in water

“…Critical micellar concentrations (CMCs) have been determined in the literature, either on mixtures or on pure sucrose esters obtained by enzymatic or by chemical synthesis (Table 1), and the data related to surface tension measurement, notably area per molecule, have been worked out. The behavior of monolayers of sucrose monostearate obtained by enzymatic synthesis have also been studied, giving the surface area per molecule for these water-insoluble sucrose esters [14]. A detailed study of the micelle structure of a homologous series of mixtures of sucrose monoesters by X-ray diffraction have also been described, in micellar solutions of Mixture Transesterification/base 0.00513 [19] a All the samples described in these studies have been purified to be devoid of sucrose esters of higher substitution degrees.…”

“…Monosubstituted sucrose esters have been prepared, namely octanoates (C8), decanoates (C10), laurates (C12), myristates (C14), and palmitates (C16), and ester with an unsaturated chain, dodec-5-cis-enoate (C12:1). Stearates have not been investigated, since they are not soluble in water at 25 • C, as has previously been reported in the literature [14,15,22]. They have been synthesized by selective chemical synthesis, using the Mitsunobu reaction, leading to the isomers in position 6 as the main product, by enzymatic synthesis mainly giving the 1 isomer by the usual transesterification reaction, leading to mixtures containing mainly the isomers on the three primary positions (Fig.…”

Shape Dependence in the Formation of Condensed Phases Exhibited by Disubstituted Sucrose Esters

“…Keywords: fatty acids · glycolipids · liquid crystals · phase transitions · sucrose esters ied less extensively than other kinds of nonionic surfactants, such as polyoxyethylenic surfactants or alkylpolyglucosides. Although the surface activities and other properties for monosubstituted sucrose esters in solution are well documented, [17][18][19][20][21][22][23][24] the thermotropic liquid-crystal properties for such materials have only recently been investigated in detail. One commercial mixture of sucrose oleate has been studied, [25] along with the shear-induced phase transitions of sucrose stearate blends.…”