INTERACTION OF PHOSPHOTUNGSTATE IONS WITH PHOSPHOLIPID MONOLAYERS - ASYNCHROTRON X-RAY STUDY

The surface pressure-area isotherms of monolayers of several phospholi pids are markedly altered by the presence of phosphotungstate ions in the aqueous subphase at low values of pH (Gorwyn, D.; Barnes, G. T. La ngmuir 1990, 6, 222). These changes have now been studied by grazing i ncidence synchrotron X-ray diffraction. Where the monolayer was in a c ondensed monolayer state the 2 theta scans revealed a single peak cons istent with hexagonal packing of the acyl chains despite the diacyl st ructure of the phospholipids. Addition of phosphotungstate to the subp hase at pH 2 caused this peak to disappear, suggesting a disruption of the regular chain packing, and examination of the concomitant surface pressure-area isotherms showed that there had been a transition from a condensed to an expanded phase.