ID: 2213

• Title:
  Quantum chemical simulations of the interaction of Fe2+ with glycerophospholipids
  
  Authors:
  

  Kondrotaite, Terese - Vytautas Magnus University, Kaunas, Lithuania
  Gruodis, Alytis - Institute of Chemical Physics, Vilnius University, Vilnius, Lithuania
  Saulis, Gintautas - Vytautas Magnus University, Kaunas, Lithuania

  
  
  Abstract:
  Glycerophospholipids are the main component of any cell plasma membrane. Under normal physiological conditions, most molecules cannot directly permeate through the membrane without physical or chemical perturbation of the bilayer. Pulses of electric field, acidic and/or alkaline media, and localization of aggressive metal ions cause cell membrane damage through lipid conformational and destructive processes. Since the membrane structure is a layered lipid, it is necessary to evaluate not only the physical but also the chemical aspects: the redox reactions taking place at the membrane create many ionized components that essentially catalyze the above-mentioned factors. Metal ions belong to these factors.
  
  To understand the dynamics of the formation of the pore in the lipid bilaer and its subsequent closure at the molecular level, modeling of the structure of phospholipids and iron ion complexes by quantum molecular theory methods was performed. Quantum chemical simulations were run using Gaussian16 [1] package.
  
  Optimization of associate geometry was performed by Gaussian16 [1] program, using the semi-empirical density function method B3LYP by means of Gaussian basis set 6-31G. Influence of the solvent media (water) was evaluated by Polarized Continuum Model (PCM).
  
  It has been found that metal ion fixation to the lipid chain is insignificant to cause lipid conformational movement. Similarly, metal ion fixation in the case of the –N–3(CH3)3 head in the lipid head group was not observed. The iron ion binds two lipid molecules in the orthophosphoric region, forming an energetically stable bridge between orthophosphoric fragments. Both saturated and unsaturated phosphatidylserine (PS) have been reported to be similarly resistant to iron-dependent lipid peroxidation. It is believed that the PS head group is responsible for this effect, as it binds the iron ion, reducing the concentration of free iron ions [2]. As a result of this process, the lipid aliphatic chains change their conformation - a curved chain around the metal ion centre is formed from a straight structure.
  
  A typical molecular charge redistribution during excitation was determined and described. It is stated that due to the energetically favorable Fe2+ ion position, one lipid becomes a charge donor and the other – a charge acceptor. A typical associate contains two phospholipids bridged by Fe2+ ion in the orthophosphoric region. Molecular orbitals correspond to a forbidden electronic transition of 0.50 eV from the ground state (MO 210,211) to the first excited state (MO 226). The iron ion binds two lipid molecules in the orthophosphoric region, forming an energetically stable bridge between the orthophosphoric fragments. As a result, the lipid aliphatic chains change the conformation - a curved chain about the centre of the metal is formed from the straight structure.
  
  
  
  Keywords:
  Fe2+ ion, phospholipids, lipid-Fe-lipid complex, complex stability,
  
  Refs:
  [1] M. J. Frisch, G. W. Trucks, H. B. Schlegel et al., Gaussian 16, Revision B.01, Gaussian, Inc., Wallingford CT, 2016. [2] K. Yoshida, J. Terao, T. Suzuki, K. Takama, Biochem. Biophys. Res. Commun., 179, 1077-1081 (1991).
  
  Topic 1:
  2. Biophysics and biochemistry of interaction mechanisms
  
  Topic 2:
  3. Modelling and simulation of exposures and effects