engleski

Critical evaluation of empirical force-field models for simulation of plasticity of copper(II) coordination

The plasticity of the copper(I1) coordination sphere was simulated with the empirical force-field (molecular mechanics) method. Altogether five models for copper coordination were checked on the trans-CuN202 “complex” : (1) a simple model with an angle bending-potential for only cis (N-Cu-O) angles, (2) a “dummy” atom model with two apically placed “dummy” atoms, (3) a model with a distortion potential (defined as quadratic function of the angle between bisectors of two opposite valence angles) and a quadratic function for bending of cis angles, (4) a model with a distortion potential and an angle-bending potential with two minima (at 90 and 109.47o) for O-Cu-N angles and (5) a newly proposed model with a distortion angle and an angle-bending potential with two minima for all valence angles around copper. The simplest model (1) did not give geometrically defined minima, and model (2) yielded besides the trans configuration three minima with superimposed atoms. Models with a distortion potential yielded better results: with model (3) only the trans configuration was obtained upon minimization, and model (4) yielded trans and tetrahedral configurations besides three “false” configurations of the same (zero) energy. Improving model (4), by proposing model (5), only two configurations (trans and tetrahedral) with zero energy were obtained. Model (5) was also proved best in reproducing the crystal geometry and diastereoselectivity of copper(I1) bis-aminoacidates.

copper(II) ; amino acids ; molecular mechanics ; force field ; distortion potential

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