Electric Field-Induced Changes in Lipids Investigated by Modulated Excitation FTIR Spectroscopy

Abstract

The effect of electric fields on dry oriented multibilayers of dimyristoylphosphatidylcholine (DMPC) was investigated by transmission Fourier transform infrared electric field modulated excitation (E-ME) spectroscopy. A periodic rectangular electric potential (0-150 V, 1.25 Hz, 28.4 degrees C +/- 0.2 degrees C) was applied across the sample. To discriminate electric field-induced effects from possible temperature-induced effects resulting from a current flow (<1 pA) across the sample, corresponding temperature-modulated excitation (T-ME) measurements within the temperature uncertainty limits of +/-0.2 degrees C at 28.4 degrees C were performed. T-ME induced reversible gauche defects in the hydrocarbon chains, whereas E-ME resulted in reversible compression of dry DMPC bilayers. Periodic variation of the tilt angle of the hydrocarbon chains is suggested. The degree of absorbance modulation in the CH-stretching region was found to be in the order of 1:700, corresponding to a variation of the bilayer thickness of Deltaz = 0.0054 nm. Using a series connection of capacitors as equivalent circuit of the cell resulted in E = (1.2 +/- 0.7) x 10(7) V/m for the electric field in DMPC. Young's elasticity modulus of DMPC could be calculated to be E( perpendicular ) = 2.2 x 10(6) Pa +/- 1.8 x 10(6) Pa, which is in good agreement with published data obtained by electric field-dependent capacitance measurements.

Biophysics of α-synuclein induced membrane remodelling

“…On the other hand, the transverse elastic modulus of membrane bilayers E zz , which describes the change in membrane thickness upon applying a force vertical to the membrane surface, is typically between 0.4~4 MPa 41 . The membrane binding energy of one α-synuclein molecule can lead to a squeezing of a piece of membrane originally with thickness d and area a by $$\mathrm{normal\Delta }d=-\mathrm{normal\Delta }G/false(a{E}_{zz}false)$$ Assuming conservation of lipid volume, the reduction in membrane thickness should be directly correlated with an expansion of the membrane area Δ a $$\mathrm{normal\Delta }a=\frac{ad}{true[d-\frac{\mathrm{normal\Delta }G}{a{E}_{zz}}true]}-a$$ Typical bilayers are about 4nm thick and molecular dynamic simulations indicate that individual α-synuclein molecules usually act upon a membrane area of about 50nm 2 11 .…”

Mechanical Properties of Bilayer Lipid Membranes and Protein–Lipid Interactions

“…Recently, the excitation FTIR spectroscopy has been applied to study electrostriction of supported lipid multilayers composed of dimyristoylphosphatidylcholine (DMPC) [35]. A periodic rectangular electric potential induced periodic variation of the tilt angle of the hydrocarbon chains by 0.09 AE 0.015 .…”

ATR-FTIR Spectroscopy of Membrane Bound Ras Protein

“…Such a modulated response was not observed during the GDP nucleotide circulation (Figure 40), but was observed after the NO-mediated GTP exchange of the Ras protein ( Figure 45a). Lipid methylene stretching vibrations were not shifting ( Figure 37a and 50); so, the observation (Figure 45a) was not due to the effect of temperature [242,243].…”

“…Modulated excitation (ME) is applicable to the ATR-FTIR, provided that the sample of interest admits (periodic) excitation by the modulation of an external parameter and the weak absorption changes which are hindered due to a huge background noise are revealed by this means [242,243]. Such a modulated response was not observed during the GDP nucleotide circulation (Figure 40), but was observed after the NO-mediated GTP exchange of the Ras protein ( Figure 45a).…”