Study of Biological Ion Channels by Using PNP/ECP Model
Yang, Zhicheng
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https://hdl.handle.net/2142/81021
Description
Title
Study of Biological Ion Channels by Using PNP/ECP Model
Author(s)
Yang, Zhicheng
Issue Date
2007
Doctoral Committee Chair(s)
Ravaioli, Umberto
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
Ion channels are proteins embedded in the membrane of all biological cells, folded in a manner that creates nanoscopic pores that control the flow of ions in and out of the cell. All ion channels carry a highly localized distribution of permanent charge and possess specific properties (e.g., selectivity and switching) that are interesting to the device engineering community. The Poisson-Nernst-Planck (PNP) theory, also known as drift-diffusion theory, can be used to compute macroscopic current in ion channels reasonably quickly. However, PNP theory can be problematic when applied to regions of constricted volume, such as the interior of ion channels. Additionally, traditional PNP theory ignores the finite volume occupied by the ions and water molecules, as well as the non-singular distribution of charge on the ion. As a result, Coulombic screening can be overestimated, particularly in highly charged regions. The entropic effects of finite-sized ions and water molecules, and the non-singular charge distribution on the ion can be introduced into the PNP formalism by including an additional component to the electrochemical potential. The so-called excess chemical potential (ECP) represents the difference between the electrochemical potential of a real ionic solution and that of an idealized solution. The ECP terms are added to the electrostatic potential in the flux equations, yielding a modified set of PNP equations.
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