Ab initio calculations on indole–water, 1-methylindole–water and indole–(water)2

The structures of indole–water are optimized with second-order Møller–Plesset (MP2) perturbation theory and augmented correlation consistent basis sets. The binding energies and hydrogen bond distances are corrected for BSSE. By extrapolating the correlation interaction energy to estimate the complete basis-set limit, the equilibrium binding energies De of the two indole–water minima are 24.27±0.5 and 21.23±0.5 kJ/mol. We calculated binding energies D0 of 18.13 and 17.9 kJ/mol for the global minimum of indole–water and methylindole–water, which are, unlike previous theoretical estimates, in quite good agreement with experiment (19.52–20.25 and 17.15 kJ/mol, respectively).