Comparison between Ab Initio and semiempirical net atomic charges of some nicotinic acetylcholine receptor agonists

We have calculated the net atomic charges and molecular electrostatic potentials of two potent nicotinic acetylcholine receptor agonists, isoarecolone and acetylpiperazine, by three different methods to see how well they correlate and if the simplest method gives the same predictive results. The calculational methods involved calculating net atomic charges by semiempirical (MNDO from MOPAC) and ab initio (Mulliken) and ab initio (potential derived) at STO‐3G basis set level. Some deviations were observed when comparisons were made atom by atom, but when group comparisons were made, good correlations were observed. When these partial charges were used to calculate the respective molecular electrostatic potentials on the van der Waals surface, very good correlations were obtained. This study shows that for routine electrostatic calculations, semiempirical MNDO calculations give similar results and thus lead to similar predictions.