SYSTEMATIC AB-INITIO SCF CONFORMATIONAL-ANALYSIS OF INDOL-3-YLACETIC ACID PHYTOHORMONE (AUXIN) - COMPARISON WITH EXPERIMENT AND MOLECULAR MECHANICS CALCULATIONS

Indol-3-ylacetic acid (IAA) is a plant growth hormone (auxin) which co ntrols a number of physiological functions in higher plants. Molecular recognition approaches based on structure/activity correlations inclu de the conformational properties of the substrate. Thus a detailed ab initio SCF (RHF) conformational analysis of IAA has been performed wit h the basis sets STO-3G, 3-21G, 4-31G, 6-31G and 6-311G**. A signific ant basis set dependence occurs for the two smallest basis sets; the r esults obtained with the largest basis sets agree well with experiment al gas phase and solid state data. Comparison of the ab initio results with those obtained from MM calculations with MM2(87), MM3, CVFF, and cff91 shows considerable differences: MM calculations are unable to l ocate two of the four different ab initio conformers. (C) 1995 John Wi ley & Sons, Inc.