Reaction field calculation combined with the AM1 molecular orbital method is applied in order to understand why intermolecular hydrogen bonding is stabilized at the lipid−water interface. Here, we focus on the interaction between a guanidinium-functionalized lipid (1) and phosphate and between a diaminotriazine-functionalized lipid (2) and thymine. The interface is approximated by a double layer composed of two dielectrics. The lower dielectric medium with a dielectric constant of 2 corresponds to the lipid layer, and the higher dielectric medium with dielectric constant of 80 to the aqueous subphase. A pair of interacting molecules is placed on/near the interface, and the binding energy profile is obtained. For comparison, the calculation of binding energy is also performed for a homogeneous system defined as a single dielectric constant, corresponding to a normal solution system. It is shown that the calculation reproduces well the observed binding constants, when the position of the interface is appropriately displaced relative to the interacting molecules. One of the most important findings is that hydrogen bonding is remarkably strengthened even if the binding site is exposed to the aqueous subphase. The results for the binding profiles are interpreted from those for Mulliken population analysis.

The interaction between a lipid monolayer with positive surface charges and anionic species dissolved in the aqueous phase is investigated using the Poisson-Boltzmann equation. The monolayer and the aqueous phase are approximated by dielectric continuums whose dielectric constants are 2 and 80, respectively. It is assumed that positive charges are periodically distributed on the interface formed by the two dielectrics. For such a system, the Poisson-Boltzmann equation is analytically solved with the Debye-Hückel approximation. It is indicated that the potential on the water side is significantly modulated by the presence of the lipid phase. This effectively contributes to a strengthening of intermolecular interaction near or on the interface. In addition, the interaction depends on the surface charge density on the monolayer. Combining these findings and the results of a previous quantum chemical study (Part 1 in a series of our studies), we discuss the reason why intermolecular binding is enhanced at the air-water interface.

Starting from basic molecular structure and redox properties of its components, we build a macroscopic cellular electrophysiological model. We first present a murburn purview that could explain ion-distribution in bulk-milieu/membrane-interface and support the origin of transmembrane potential (TMP) in cells. In particular, the discussion focuses on how cells achieve disparity in the distribution of monovalent and divalent cations within (K + > Na + > Mg 2+ > Ca 2+ ) and outside (Na + > K + > Ca 2+ > Mg 2+ ). We explore how TMP could vary for resting/graded/action potentials generation and project a model for impulse conduction in neurons. Outcomes based in murburn bioenergetic equilibriums leading to solubilization of ionpairs, membrane's permittivity, protein channels' fluxes, and proteins' innate ability to bind/adsorb ions selectively are projected as the integral rationale. We also provide experimental modalities to ratify the projections.

No abstract

According to standard membrane theory, the generation of membrane potential is attributed to transmembrane ion transport. However, there have been a number of reports of membrane behavior in conflict with the membrane theory of cellular potential. Putting aside the membrane theory, we scrutinized the generation mechanism of membrane potential from the view of the long-dismissed adsorption theory of Ling. Ling's adsorption theory attributes the membrane potential generation to mobile ion adsorption. Although Ling's adsorption theory conflicts with the broadly accepted membrane theory, we found that it well reproduces experimentally observed membrane potential behavior. Our theoretical analysis finds that the potential formula based on the GHK eq., which is a fundamental concept of membrane theory, coincides with the potential formula based on Ling's adsorption theory. Reinterpreting the permeability coefficient in the GHK eq. as the association constant between the mobile ion and adsorption site, the GHK eq. turns into the potential formula from Ling's adsorption theory. We conclude that the membrane potential is generated by ion adsorption as Ling's adsorption theory states and that the membrane theory of cellular potential should be amended even if not discarded.