title: Chain interdigitation in DPPC bilayers induced by HgCl2: evidences from continuous wave and pulsed EPR.
abstract: Continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy and electron spin echo methods of pulsed EPR of phosphatidylcholine spin-labeled at different positions, n, in the sn-2 chain (n-PCSL, n=5, 7, 10, 12, 14, and 16) are used to study the interaction of inorganic mercury chloride HgCl2 with multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC). For temperatures through the gel phase of DPPC multilayers, the CW-EPR spectra show that an increase of HgCl2 content in the dispersion medium slightly increases the rotational mobility of 5-PCSL and markedly restricts the motion of 16-PCSL. Mercury chloride at 100mM (HgCl2/lipid molar ratio=2:1) removes the gradient of increasing mobility along the chain found in DPPC bilayers in the gel phase. In contrast, HgCl2 does not influence the DPPC chain flexibility profile in the fluid phase. It also suppresses the pre-transition and moderately downshifts the main transition temperature of DPPC membranes. These findings indicate that HgCl2 affects the lipid chain packing of DPPC bilayers and are consistent with the induction of an interdigitated gel phase. Further, D2O-electron spin echo envelope modulation spectroscopy indicates that in the interdigitated phase a higher water permeation is favored at any chain position and the sigmoidal transmembrane water accessibility profile of DPPC bilayers is abolished. Accordingly, the positional dependence of (14)N-hyperfine splitting, 2Azz, shows that the typical hydrophobic barrier of DPPC is significantly altered in the interdigitated phase and all the segments of the lipid chains result to be in a more polar environment.
authors.affiliation: Department of Physics, Molecular Biophysics Laboratory, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Stirpe
authors.affiliation: Department of Physics, Molecular Biophysics Laboratory, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy.
authors.forename: Manuela
authors.initials: M
authors.lastname: Pantusa
authors.affiliation: CNISM Unit, University of Calabria, Italy; Department of Physics, Molecular Biophysics Laboratory, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy.
authors.forename: Rita
authors.initials: R
authors.lastname: Guzzi
authors.affiliation: CNISM Unit, University of Calabria, Italy; Department of Physics, Molecular Biophysics Laboratory, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy. Electronic address: rosa.bartucci@fis.unical.it.
authors.forename: Rosa
authors.initials: R
authors.lastname: Bartucci
authors.affiliation: CNISM Unit, University of Calabria, Italy; Department of Physics, Molecular Biophysics Laboratory, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Sportelli
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008627:Mercuric Chloride / Q000737:chemistry*; D008968:Molecular Conformation; D044367:Phase Transition; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D015060:1,2-Dipalmitoylphosphatidylcholine; D008627:Mercuric Chloride