Quantum chemistry computations of properties of acrylamide dimers
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Quantum chemistry computations of properties of acrylamide dimers Yi-Siang Wang, Yi-De Lin, Sheng D. Chao Institute of Applied Mechanics, National Taiwan University, Taipei 10617, Taiwan ABSTRACT Intermolecular interaction potentials of the acrylamide dimer in 12 equilibrium configurations have been calculated using the second-order Møller-Plesset (MP2) perturbation theory. We have employed Pople’s medium size basis sets [up to 6-311++G(3df,2p)] and Dunning’s correlation consistent basis sets (up to aug-cc-pVTZ). We have also carried out density functional theory (DFT) type calculations and compared the results with those calculated with the MP2 theory. INTRODUCTION Acrylamide (2-propenamide , C3H5NO) has been used in industries for the production of polymerized acrylamide such as paper, textile and construction[1]. Recently, relatively high levels of acrylamide have been measured in different food and food products[2][3][4]. Although polymerized acrylamide is known to be non-toxic, the acrylamide monomer was reported as a human neurotoxin, a rodent carcinogen and is classified as “probable carcinogen to humans”[5]. Acrylamide appeared to be formed during high temperature processes such as frying, baking, and roasting of foods, especially of carbohydrate-rich foods. The neurotoxicity of acrylamide in humans is well-known from occupational and accidental exposures[1]. In this paper we carried out the MP2 and DFT calculations with the basis sets up to aug-ccpVTZ for 12 stable configurations of the C3H5NO dimer. The infrared spectra were also analyzed. THEORY All the quantum chemistry calculations were performed at the MP2[6] level of theory under the Gaussian 09 program package[7]. The isolated C3H5NO molecule was first optimized at the MP2/aug-cc-pVTZ level and was found to have two stable configurations. The 12 conformers of dimer chosen to sample the orientational dependence are depicted in Figure 3.The first to the fourth configurations are composed of the syn-syn [8] monomers, the fifth to the seventh configurations are composed of the skew-skew monomers and the eighth to the twelfth configurations are composed of the syn-skew monomers. Pople’s medium size basis sets [up to 6-311++G(3df, 2p)] [9] and Dunning’s correlation consistent basis sets (cc-pVXZ and aug-ccpVXZ, X=D, T) [10] were employed in the calculations. The basis set superposition errors (BSSEs) were corrected by the counterpoise method of Boys and Bernardi [11]. Subsequently the carbon-carbon (C-C) distance, denoted as R, was sampled for a large range with 19 potential points for each conformer. A total of 228 configuration points were actually sampled and the energies calculated. During the scan we fixed the monomer geometry (rigid monomer assumption) and the conformer symmetry. We have checked this rigid monomer assumption to be valid by comparing the potential curves for selective conformers. For example, the relaxation of the rigid monomer assumption only increases the binding energies by about 1%.
DISCUSSION Geometries of monomer The optimized
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