A quantitative basis for a scale of Na+ affinities of organic and small biological molecules in the gas phase

High-pressure mass spectrometric experiments and ab initio calculations hav e been carried out in order to establish a series of accurate gas-phase sod ium ion affinities of organic molecules with a wide variety of functional g roups. Ab initio calculations have also been performed on the sodium comple xes of three amino acids: serine, cysteine, and proline. A systematic criti cal evaluation of experimental and computational literature results shows t hat a significant number require revision. Based on comparisons with accura te experimental measurements, the ab initio procedure used is shown to yiel d sodium ion affinities with an accuracy of ca. kcal.mol(-1). This enables the construction of the first reliable table of gas-phase Na+ affinities fo r organic and small biological molecules.