Molecular orbital study of the structure and interactions of ylidene rhodanines |
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Authors: | Richard J Loncharich Jeffrey S Nissen Donald B Boyd |
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Institution: | (1) Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana;(2) Department of Chemistry, Indiana University-Purdue University at Indianapolis, 46202-3274 Indianapolis, Indiana |
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Abstract: | Semiempirical (with the AM1 Hamiltonian) and ab initio (mainly with the 6-31G* and LANL2DZ+ +(d,p) basis sets) molecular oribital calculations show the predominant tautomer of gas phase methylidene rhodanine is 2-thioxo-4-thiazolidinone in agreement with earlier work on other types of rhodanines. Inclusion of solvation effects in the AM1 calculations corroborates with this tautomer is also preferred in aqueous solution. Energy-optimized bond lengths and angles show good agreement with those for a crystalline benzylidene rhodanine. The geometry of a hydrogen bonded dimer matches closely the crystalline state arrangement. The two N-H O hydrogen bonds that form in the dimer. provide a stabilization energy of about - 10 kcal/mol. The interactions of methylidene rhodanine with a calcium ion are modeled with basis sets as large as LANL2DZ+ +(d,p). The preferred binding site is near the carbonyl oxygen for the neutral rhodanine and near the nitrogen and thione sulfur in a bidentate arrangement for the rhodanine anion. Implications for the interaction of benzylidene rhodanines with various possible protein and metalloprotein receptors are discussed. |
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Keywords: | Rhodanines 4-thiazolidinone-2-thiones molecular orbital calculations hydrogen bonding calcium complexes |
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