Table 1 Measured and calculated values for the lipids used in the study.

From: Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

 

Gel transition temp (°C)

Surface area (Å2)

pKa

σ (mC m−2)*

σeff (mC m−2)†

σPNP (mC m−2)‡

DPPE

63 (ref. 53)

39.9 (ref. 54)

11.1 (Nh3+) (ref. 55) ≤1 (P04−) (ref. 55)§

0

0

5.3±5.6

DPPG

41 (ref. 53)

46.7 (ref. 56)

2.9–3.1 (P04−) (ref. 55)

−188

−42.8

−44±9

DPTAP

45 (ref. 57)

46.0 (ref. 58)

—‖

348

11.5

15.1±12.8

Mica

     

−36.3±4.2

  1. The lipids were all expected to be in gel phase at room temperature, and literature values for surface area and dissociation constants are, as far as possible, matching the experimentally used conditions.
  2. *Surface charge density calculated from the Gouy–Chapman–Helmholtz–Stern model.
  3. †Effective surface charge density calculated from the EPB approximation.
  4. ‡Surface charge of lipid bilayers measured by QSCM.
  5. §values for (12:0)2 PE.
  6. ‖The trimethylammonium group in DPTAP is a quaternary ammonium and is expected to be charged at all pH values.
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