216 Journal of Applied Solution Chemistry and Modeling, 2013, 2, 216-224 E-ISSN: 1929-5030/13 © 2013 Lifescience Global Ab Initio and Density Functional Predictions of Solvation Free Energies of Cyclic Polyethers (CH 2 CH 2 O) n (n=2,6) in Aqueous and Tetrachloromethane Solutions B. Ariche 1,2,* , A. Rahmouni 1 , H. Brahim 1 , A. Guendouzi 1 and K. Alali 1 1 Modeling and Calculation Methods Laboratory, Taher Moulay University, B.P. 138, En-Nasr Avenue, Mascara Road, 20002 Saida, Algeria 2 Department of Chemistry, University of Oran 1, PO Box 1524 Elmnaouer, Oran 31000, Algeria Abstract: Solvation free energies G sol tot of cyclic polyethers (CH2CH2O)n (n=2,6) in aqueous and tetrachloromethane solutions have been calculated at HF, MP2 and B3LYP/6-311G (d,p) levels of theory using CPCM, IEFPCM and SMD implicit solvation models. It has been found that G sol tot are negative for both solvents, they increase linearly with system sizes and they are more important in water solution. The electrostatic contributions to the solvation free energies G sol ele are also more important in water because of their polar nature. In water, CPCM and IEFPCM models give a close values, which are slightly different from SMD values. In tetrachloromethane solvent CPCM model seems overestimate G sol ele. For both solvents the non-electrostatic contributions to the solvation free energies G sol n-ele provided by SMD are remarkably different to those given by CPCM and IEFPCM models. Keywords: Continuum model, Solvation free energy, Cyclic polyether, Water, Tetrachloromethane. 1. INTRODUCTION Many theoretical studies have been performed to understand the solvation of crown ethers in liquid phases [1-5]. Continuum solvation model is one of the powerful tools to provide accurate estimates of solvation free energies at a reasonable computational cost [6-22]. Compared to the explicit solvation model arranging a few solvent molecules around the solute, the continuum model places a solute molecule in a solvent cavity surrounded by a polarizable continuum, whose reaction field modifies the energy and properties of the solute. Hence, the calculations using the continuum solvation model are cheaper, simpler, and more convenient than those using the explicit solvation model [23]. Conductor-like polarizable continuum model (CPCM) [13,16] and integral equation formalism polarizable continuum model (IEFPCM) [7-12] are two of many successful solvation models. In their approaches, the solute interacts with the solvent represented by a dielectric continuum model. The solute molecule is embedded into a cavity surrounded by a dielectric continuum of a given permittivity. CPCM and IEFPCM define the cavities as envelopes of spheres centered on atoms or atomic groups. Inside the cavity the dielectric constant is the same as in vacuo, outside it takes the value of the desired solvent. *Address correspondence to this author at the Modeling and Calculation Methods Laboratory, Taher Moulay University, B.P. 138, En-nasr Avenue, Mascara Road, 20002 Saida, Algeria; Tel/Fax: +21348471508; E-mail: berkane.ariche@univ-saida.dz Once the cavity has been defined, the surface is smoothly mapped by small regions, called tesserae. Each tessera is characterized by the position of its centre, its area, and the electrostatic vector normal to the surface passing through its centre. Unlike the previous models, universal solvation model based on solute electron density (SMD) [20,21] is based on the quantum mechanical charge density of a solute molecule interacting with continuum description of the solvent. The SMD bulk electrostatic contribution to the free energy of solvation arises from a self-consistent reaction field treatment that involves solution of the nonhomogeneous Poisson equation by the Integral- Equation-Formalism Polarizable Continuum Model [20]. Cyclic polyethers (CH 2 CH 2 O) n , commonly known as crown ethers [24], are synthesized originally by Pederson in 1967 [25]. They exhibit conformational mobility and have the structure of a cavity that is lined inside with the electron pairs of the donor atoms and surrounded from the outside by the hydrocarbon framework [26]. The principal interest of crown ethers arises from their potential to form stable complexes with a wide variety of ionic and neutral species [27-36]. This property is the basis of their broad practical applications in various areas of inorganic and organic chemistry, chemical fertilizers and pesticides, metallurgy, nuclear energy, biology, pharmacology and medicine [37,38]. Several thermodynamic studies of crown ethers solvation and complexation have recently appeared [3,26,39-44], investigation of solvation and association states of such important macrocycle ligands can help to