INTRODUCTION Three species of all kinds of membrane proteins have been demonstrated to possess water channels properties; the aquaporins, the cotransporters, and the uniports. Water traverses ORIENTAL JOURNAL OF CHEMISTRY www.orientjchem.org An International Open Free Access, Peer Reviewed Research Journal ISSN: 0970-020 X CODEN: OJCHEG 2014, Vol. 30, No. (3): Pg. 1303-1310 Theoretical Studies of AQP4 in Water & Gas Phases, Nano Simulation of the Monte Carlo Method by Molecular Mechanics Force Fields EBRAHIM SHAHMANSOORIAN 1 , MARYAM HASHEMY 1 , SAHARNAZ AHMADI 1 , ZOHREH JAMALI 2 , NASTARAN ASGHARI MOGHADDAM 1 and REZA RASOOLZADEH 1,3 * 1 Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran. 2 Department of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, Iran. 3 Young Researchers and Elites Club, Science and Research Branch, Islamic Azad University, Tehran, Iran. *Corresponding author E-mail: Reza.Rasoolzadeh@yahoo.com http://dx.doi.org/10.13005/ojc/300347 (Received: June 06, 2014; Accepted: July 23, 2014) ABSTRACT Aquaporins are membrane water channels that play critical roles in controlling the water contents of cells. These channels are widely distributed in all kingdoms of life, including bacteria, plants, and mammals. More than ten different aquaporins have been found in human body, and several diseases, such as congenital cataracts and nephrogenic diabetes insipidus, are connected to the impaired function of these channels. They form tetramers in the cell membrane, and facilitate the transport of water and, in some cases, other small solutes across the membrane. However, the water pores are completely impermeable to charged species, such as protons, a remarkable property that is critical for the conservation of membrane’s electrochemical potential, but paradoxical at the same time, since protons can usually be transferred readily through water molecules. The present investigation is profound manifesting of thermodynamics characteristics of the impressive AQP4 role in biology. To clarify the majestic AQP4 role in biology, it was modeled. So we use pc-based modeling and simulation software package called HyperChem by applying four different force fields. The results of our simulations have now provided new insight into the optimal stability of AQP4. Key words: AQP4, Aquaporins, Monte Carlo, Water & Gas Phases, Molecular Mechanics. from cell membrane lipid bilayer by two passage ways: One is diffusion across lipid bilayer and another is water channel reputed as aquaporin (1 and 2 3). Aquaporins are an ilk of small transmembrane proteins that predominantly facilitate water transportation across plasma