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Phase behavior of DOPE/TritonX100 (reduced) in dilute aqueous solution: aggregate structure and pH-dependence

Johnsson, Markus LU and Bergstrand, Nill (2004) In Colloids and Surfaces B: Biointerfaces 34(2). p.69-76
Abstract
The phase behavior of dilute mixtures of dioleoylphosphatidylethanolamine (DOPE) and reduced TritonX100 (TX100(r)) has been investigated at pH 7.4 and 10. Using simple turbidity measurements and optical observations, together with cryo-transmission electron microscopy (cryo-TEM), we estimate the phase boundaries. We show that at both pH 7.4 and 10, a very large amount of surfactant is needed for the onset of micelle formation (X-TX100(r) similar to 0.60-0.70) as well as for a complete solubilization of DOPE into mixed micelles (X-TX100(r) > 0.94). We find that the micelles that are formed at high TX100(r) concentrations are of spherical shape. Increasing the pH from 7.4 to 10 has a comparably small effect on the transition from a... (More)
The phase behavior of dilute mixtures of dioleoylphosphatidylethanolamine (DOPE) and reduced TritonX100 (TX100(r)) has been investigated at pH 7.4 and 10. Using simple turbidity measurements and optical observations, together with cryo-transmission electron microscopy (cryo-TEM), we estimate the phase boundaries. We show that at both pH 7.4 and 10, a very large amount of surfactant is needed for the onset of micelle formation (X-TX100(r) similar to 0.60-0.70) as well as for a complete solubilization of DOPE into mixed micelles (X-TX100(r) > 0.94). We find that the micelles that are formed at high TX100(r) concentrations are of spherical shape. Increasing the pH from 7.4 to 10 has a comparably small effect on the transition from a lamellar (L-alpha) to a micellar (L-1) phase. However, the reversed hexagonal phase (H-II) that is present at low surfactant content at pH 7.4 is absent at pH 10. This is due to the partial negative charge of DOPE at pH 10. We determine the fraction of charged DOPE (alpha = 0.34) at pH 10 in a 150 mM NaCl buffer using zeta-potential (zeta-potential) measurements in combination with a Poisson-Boltzmann (PB) model. The intrinsic pK(a) of the primary amino group of DOPE, in a pure DOPE membrane, is estimated to 9.15 +/- 0.2. (C) 2003 Elsevier B.V. All rights reserved. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Liposome zeta-potential, Solubilization, Lipid, Surfactant, Intrinsic liposomal pKa
in
Colloids and Surfaces B: Biointerfaces
volume
34
issue
2
pages
69 - 76
publisher
Elsevier
external identifiers
  • pmid:15261076
  • wos:000220271800001
  • scopus:1442350555
ISSN
1873-4367
DOI
10.1016/j.colsurfb.2003.11.006
language
English
LU publication?
yes
id
fa5606e3-4384-41fe-8222-319e041bff09 (old id 154094)
date added to LUP
2007-07-11 13:20:36
date last changed
2017-01-01 06:52:30
@article{fa5606e3-4384-41fe-8222-319e041bff09,
  abstract     = {The phase behavior of dilute mixtures of dioleoylphosphatidylethanolamine (DOPE) and reduced TritonX100 (TX100(r)) has been investigated at pH 7.4 and 10. Using simple turbidity measurements and optical observations, together with cryo-transmission electron microscopy (cryo-TEM), we estimate the phase boundaries. We show that at both pH 7.4 and 10, a very large amount of surfactant is needed for the onset of micelle formation (X-TX100(r) similar to 0.60-0.70) as well as for a complete solubilization of DOPE into mixed micelles (X-TX100(r) > 0.94). We find that the micelles that are formed at high TX100(r) concentrations are of spherical shape. Increasing the pH from 7.4 to 10 has a comparably small effect on the transition from a lamellar (L-alpha) to a micellar (L-1) phase. However, the reversed hexagonal phase (H-II) that is present at low surfactant content at pH 7.4 is absent at pH 10. This is due to the partial negative charge of DOPE at pH 10. We determine the fraction of charged DOPE (alpha = 0.34) at pH 10 in a 150 mM NaCl buffer using zeta-potential (zeta-potential) measurements in combination with a Poisson-Boltzmann (PB) model. The intrinsic pK(a) of the primary amino group of DOPE, in a pure DOPE membrane, is estimated to 9.15 +/- 0.2. (C) 2003 Elsevier B.V. All rights reserved.},
  author       = {Johnsson, Markus and Bergstrand, Nill},
  issn         = {1873-4367},
  keyword      = {Liposome zeta-potential,Solubilization,Lipid,Surfactant,Intrinsic liposomal pKa},
  language     = {eng},
  number       = {2},
  pages        = {69--76},
  publisher    = {Elsevier},
  series       = {Colloids and Surfaces B: Biointerfaces},
  title        = {Phase behavior of DOPE/TritonX100 (reduced) in dilute aqueous solution: aggregate structure and pH-dependence},
  url          = {http://dx.doi.org/10.1016/j.colsurfb.2003.11.006},
  volume       = {34},
  year         = {2004},
}