An X-Ray Study of the Stepwise Melting of Anhydrous Sodium Palmitate

Abstract

X-ray powder patterns on anhydrous sodium palmitate show that the five phases already known to occur between crystal and isotropic melt can be grouped into two basic structures. Both structures are liquid crystalline, i.e., crystalline in the direction of the long spacing and liquid-like laterally. Between the lower temperature "waxy" structure, which includes the previously known subwaxy, waxy, and superwaxy phases, and the higher temperature "neat" structure, which includes subneat and neat, there is a pronounced break in the curve of long spacing vs. temperature; in addition, the three waxy phases exhibit two diffuse short spacing rings, whereas the neat phases exhibit only one. These pattern differences lead to the interpretation that the waxy phases contain structural restraints on molecular position and motion not present in the neat phases.

X‐Ray diffraction study of sodium soaps of monounsaturated and polyunsaturated fatty acids

“…The less ordered phases of the sodium soaps include phases described as waxy polymorphs. The waxy phases of sodium palmitate found between 117 and 208~ yielded short spacings similar to those observed for the polyunsaturated waxy phases with broad lines in the 4.6-4.8 A and 2.8-2.9 A regions (7). The pattern of the long spacings of the waxy phases of the polyunsaturated soaps that we studied at room temperature is similar to that found for sodium oleate at temperatures of 55-119~ (phases II and II) (1).…”

“…The relationship of the diffraction patterns to the array and conformation of molecules in the less ordered soap phases is not well understood. We can, however, interpret the data in light of the studies of the polymorphism of sodium oleate and sodium palmitare as a function of temperature (1,7), the relationship of long spacing to the number of double bonds in a fatty acid, and predictions of the expected dimensions of the hydrocarbon chains.…”

Phase transitions and fluidity characteristics of lipids and cell membranes

“…The various regions were referred to as curd to waxy, waxy to subneat, subneat to neat, and neat to isotropic. Nordsieck, Rosevear & Ferguson (1948) examined these systems using X-ray methods and showed that sharp, short spacings occur up to n o °C and above this temperature that the short spacings were diffuse. They considered that their data showed that there was order in the long spacing direction and liquid or amorphous order laterally.…”

The use of synthetic membranes in biophysical research

“…Early work on phase transitions of lipid like molecules was carried out on dry materials [24][25][26][27]. In 1941 Bear et al [28,29] studied nerve lipids in a hydrated condition but it was not until 1967 that these studies were taken up again [17,30,31].…”