Viscoelasticity Measurements at the Air/Water Interface on Monolayers of Dimyristoylphosphatidylserine (DMPS) and of Bovine Brain Phosphatidylserine (BBPS)

B. M. Abraham*, John B Ketterson

*Corresponding author for this work

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

Monolayers of dimyristoylphosphatidylserine (DMPS) and purified bovine brain phosphatidylserine (BBPS) were spread on aqueous substrates buffered to pH 4 and 7 with McIlvaine's buffer. Monolayers were compressed slowly in discrete steps. After each compression (area change), the surface tension was determined from the change in the wavelength of driven capillary waves propagated on the surface. At a number of stages of compression, the response of the film to a shearing stress was determined as a function of time. From the data collected, both the elasticity and the viscosity were calculated by using a Maxwell liquid (spring and dash pot in series) for the viscoelastic model. The π-A diagram for DMPS shows a slight pH dependence; the diagram at pH 4 is slightly more expanded than that at pH 7. The diagram for BBPS, on the other hand, is essentially pH independent. The molecular areas of both DMPS and BBPS are consistent with the serine phosphate moiety lying parallel to the water surface. Monolayers of DMPS at pH 4 and 7 have the same viscosity at π = 10 dyn/cm, but the viscosities diverge as the surface pressure increases. At 10 dyn/cm the value is 10 (dyn s)/cm and at 35 dyn/cm the values are 2.2 (dyn s)/cm for pH 7 and 46.4 (dyn s)/cm for pH 4. By contrast, the viscosity of BBPS is surface density independent, remaining essentially constant at 1 (mdyn s)/cm. The viscosity displayed by DMPS is attributed to weak networks which result from hydrogen bonding between the water and the serine moiety of the phospholipid. The large number of double bonds in BBPS expand the monolayer, which reduces both head and tail group interactions and lowers the viscosity.

Original languageEnglish (US)
Pages (from-to)801-805
Number of pages5
JournalLangmuir
Volume2
Issue number6
DOIs
StatePublished - Jan 1 1986

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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