Quantum chemical calculation of crystalline model of biomembrane

Abstract

AbstractA theoretical study on the possibility of protons transfer in biomembranes via continuous systems of hydrogen bonds was carried out on the basis of a simple crystalline model IPE–HCl (crystals of phosphatidylethanolamine titrated with HCl). A combined approach was used involving optimization of atomic structure by the method of molecular mechanics and subsequent nonempirical quantum chemistry calculation of the electronic structure of IPE–HCl. For hydrogen atoms, molecular mechanics yielded more precise positions compared to those found in the experimental X‐ray study (monoclinic space group C2/c, 240 atoms in primitive unit cell). Quantum chemistry calculation of the electronic structure of IPE–HCL crystal was performed on the basis of the optimized atomic positions. The nonempirical Hartree–Fock LCAO method is used as in computer code CRYSTAL. The calculated values of Mulliken charges on hydrogen atoms in P‐O‐H groups are essentially closer to those for protons than are the values of charge on other hydrogen atoms. This result supports the assumption about the importance of systems of hydrogen bonds in the membrane‐like structures. In agreement with the proton mechanism of energy transfer, presumed for biomembranes, total energy of the atomic configuration with transferred proton is close to that of undistorted structure. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004