Farnesol and geranylgeraniol modulate the structural properties of phosphatidylethanolamine model membranes

Figures & data

Figure 1. Structure of the isoprenoids farnesol (FN) and geranylgeraniol (GG).

Figure 2. DSC heating (a, c) and cooling (b, d) thermograms of aqueous dispersions of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) in absence and in presence of farnesol (FN) and geranygeraniol (GG) at the molar ratio indicated. The arrows (panel c) indicate the endothermic peak of the L_α-to-H_II phase transition. The scan rate was 2°C/min. (e) Deconvolution of the calorimetric peak of DEPE:FN (20:1, mol:mol) corresponding to the L_β-to-L_α transition (heating scan): experimental data (solid line), fitted overall (broken line) and individual components (dotted lines).

Table I.  Calorimetric data of the effect of FN and GN in DEPE mixtures.

Samples	Molar ratio	Tm(1) (°C)	Tm(2) (°C)	Hm(1 + 2) (kcal/mol)	Hm(1) (%)	Hm(2) (%)	Th (°C)	Hh (kcal/mol)
DEPE	1:0	–	37.1	7.2	–	100.0	65.2	0.6
DEPE:FN	40:1	33.7	36.0	7.0	19.0	73.6	57.2	0.6
DEPE:FN	20:1	34.1	35.7	7.2	15.0	77.9	56.4	0.6
DEPE:FN	10:1	34.2	35.1	7.2	16.0	78.5	51.9	0.6
DEPE:GG	40:1	34.3	36.2	7.3	11.2	84.6	58.0	0.6
DEPE:GG	20:1	34.6	35.8	7.2	7.8	87.4	54.4	0.6

The enthalpy value of the L_β-to-L_α and L_α-to-H_II transitions correspond to the whole area of the curve. The transition temperature represent the maximum of the excess heat flow vs. temperature curves. T_m1 and T_m2 are the transition temperature of the two peaks obtained in the deconvolution of the L_β-to-L_α transition curve. H_m1 and H_m2 are the relative area of each peak. The scan rate was 2°C/min.

Figure 3. Sequence of SAXS (left) and WAXS (right) scattering patterns of (a, b) DEPE, (c, d) DEPE:FN (20:1, mol:mol) and (e, f) DEPE:GG (20:1, mol:mol). The scan rate was 1°C/min. Successive diffraction patterns were collected for 15 s every minute. The thermal sequence of the transition from (Lc + H_II) to L_α and L_α-to-H_II phases was clearly observed in the heating scan. A L_β phase occur at the end of the cooling scan. The Lc and L_β phases were identified by the reflections in the WAXS region. The L_α phase was identified by a single peak of reflection in the SAXS region with a very good signal-to-noise ratio. The H_II phase was characterised by the appearance of three diffraction orders in the SAXS region with a d-spacing ratio of 1:1/√3:1/√4.

Figure 4. Sequence of scattering patterns from DEPE:FN (20:1, mol:mol). (a) In the heating scan, the transition from Lc to L_α is seen on the WAXS part of the scattering. Also the transition from Lc into H_II (associated peaks marked by arrows) and L_α (sharp peaks) is evidenced. (b) In the cooling sequence, the transition from H_II+Lc to L_α and the re-entrant H_II co-existing with L_β is shown.

Figure 5. Dependence of the interplanar repeat distance (d) on temperature for (a) DEPE heating run, (b) DEPE:FN (40:1, mol:mol) heating run, (c) DEPE:FN (20:1, mol:mol) heating and (d) cooling run, (e) DEPE:GG (40:1, mol:mol) heating run and (f) DEPE:GG (20:1, mol:mol) heating run. The different phases represented are: Lc, L_β, L_α and H_II. The co-existence of the Lc + H_II and L_α+H_II phases is indicated by the interval temperature range covered by the vertical lines. The spacing corresponding to the first order of the re-entrant H_II phase is not plotted for simplicity of the figure.

Table II.  Summary of the structural properties.

Mixture		DEPE:FN	DEPE:FN	DEPE:FN	DEPE:GG	DEPE:GG	DEPE:GG
Molar ratio	DEPE	20:1^a	40:1	60:1	20:1^b	40:1	60:1
dLc (28°C)	–	5.39	5.40	5.39	5.34	5.38	5.40
ΔTLc–HII	–	34–38	35–40	37–38	36–42	37–42	36–42
δd/δT (HII)	–	0.22	0.22	0.22	0.27	0.28	0.27
dLα (45°C)	5.52	5.50	5.49	5.49	5.50	5.51	5.57
ΔTLα–HII	66–69	39–59	60–66	60–65	51–62	56–64	67–69
δd/δT (HII)^c	−0.021	−0.025	−0.022	−0.022	−0.022	−0.025	−0.023
dHII (72°C)	6.59	6.46	6.43	6.48	6.31	6.39	6.44
dLβ (28°C)	6.63	6.54	6.57	6.53	6.55	6.52	6.66

^aThis sample was kept at low temperature for several days prior to the X-ray measurements, while the others were pre-heated.

^bThe co-existence of Lc and H_II phases has been ignored due to the extremely low contribution of the H_II phase to the scattering patterns (signals above background level). d_Lc (28°C): interbilayer distance for the lamellar crystalline Lc phase in the heating scan. ΔT_Lc–HII: temperature range of Lc and H_II phase co-existence. δd/δT (H_II): thermal expansion co-efficient of the H_II phase upon initial heating.

^cThermal expansion coefficient of the second H_II phase upon heating. d_Lα (45°C): interbilayer distance of the L_α phase. ΔT_Lα–HII: temperature range of the L_α and H_II phase co-existence. d_HII (72°C): interplanar distance of the H_II phase. d_Lβ (28°C): interbilayer distance for the L_β phase in the cooling scan.