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. 2004 Jun;86(6):3783-93.
doi: 10.1529/biophysj.103.036681.

Investigation of temperature-induced phase transitions in DOPC and DPPC phospholipid bilayers using temperature-controlled scanning force microscopy

Z V Leonenko  1 , E Finot, H Ma, T E S Dahms, D T Cramb
Affiliations

Investigation of temperature-induced phase transitions in DOPC and DPPC phospholipid bilayers using temperature-controlled scanning force microscopy

Z V Leonenko et al. Biophys J. 2004 Jun.

Abstract

Under physiological conditions, multicomponent biological membranes undergo structural changes which help define how the membrane functions. An understanding of biomembrane structure-function relations can be based on knowledge of the physical and chemical properties of pure phospholipid bilayers. Here, we have investigated phase transitions in dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) bilayers. We demonstrated the existence of several phase transitions in DPPC and DOPC mica-supported bilayers by both atomic force microscopy imaging and force measurements. Supported DPPC bilayers show a broad L(beta)-L(alpha) transition. In addition to the main transition we observed structural changes both above and below main transition temperature, which include increase in bilayer coverage and changes in bilayer height. Force measurements provide valuable information on bilayer thickness and phase transitions and are in good agreement with atomic force microscopy imaging data. A De Gennes model was used to characterize the repulsive steric forces as the origin of supported bilayer elastic properties. Both electrostatic and steric forces contribute to the repulsive part of the force plot.

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Figures

FIGURE 1
FIGURE 1
AFM topography images showing the phase transition in DPPC bilayer in liquid cell upon heating and cooling back to room temperature. (a) Heating DPPC bilayer to room temperature, 22°C; (b) heating to 50°C; (c) heating to 52°C; (d) heating to 54°C; (e) heating to 60°C; (f) cooling back to 54°C; (g) cooling back to 51°C; (h) cooling back to 49°C; and (i) cooling back to room temperature, 22°C.
FIGURE 2
FIGURE 2
AFM topography images showing the phase transition in fully hydrated DPPC bilayer during cooling back from 60°C to room temperature. Bilayer was formed from water solution by applying 30 μL of 0.5 mg/mL onto freshly cleaved pure mica for 5 min, then the cell was rinsed and covered with nanopure water. (a) Cooling back to 50°C; (b) to 36°C; (c) to 30°C; and (d) to 22°C.
FIGURE 3
FIGURE 3
AFM topography images showing the expansion of DOPC fluid-phase bilayer during heating. DOPC bilayer was formed from buffer solution by applying 70 μL of 0.5 mg/mL onto freshly cleaved pure mica for 30 min, then the cell was rinsed and covered with nanopure water. The images shown are after: (a) heating to 50°C; (b) 1 h scanning at 50°C; and (c) cooling to 45°C.
FIGURE 4
FIGURE 4
Cantilever deflection Zc as a function of the piezo translation Zp during the retraction of the tip from the DPPC layer for four temperatures. The curve monitored on mica is independent of temperature, and is shown for comparison.
FIGURE 5
FIGURE 5
Cantilever deflection Zc as a function of the piezo translation Zp during the retraction of the tip from DPPC layer for three scan rates v at a temperature T = 60°C.
FIGURE 6
FIGURE 6
(A) Evolution of the repulsive force F acting on the tip as a function of the distance D between the AFM tip and the DPPC bilayer deposited on mica. Forces were monitored during the approach of the tip onto the sample for three temperatures (▵, T = 22°C; □, T = 36°C; and ○, T = 65°C). (B) Experimental data represented by asterisks were fitted using Eq. 1. The theoretical fits are shown in solid line for the electrostatic force (Eq. 1) and dashed line for the steric force (Eq. 2). The logarithmic representation helps in determination of the range of reliability of the equation and therefore the evaluation of the thickness of the bilayer.
FIGURE 7
FIGURE 7
(A) Evolution of the force acting on the tip as a function of the distance between the tip and mica covered by a DOPC bilayer. Force curves were monitored during the approach of the tip onto the sample for three temperatures (▵, T = 60°C; □, T = 50°C; and ○, T = 22°C). (B) Experimental data represented by symbols were fitted using Eq. 1. The theoretical fit is shown in solid line. The logarithmic representation helps in determination of the range of reliability of the equation and therefore the evaluation of the thickness of the bilayer.
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