In situ recognition of molecular chirality by mass spectrometry: Hydration effects on differential stability of homo- and heterochiral dimethyltartrate clusters

Abstract: We explored a possibility of using atmospheric pressure ionization techniques like corona discharge chemical ionization and surface thermoionization for distinguishing the chiral chemical compounds in situ. In both cases of ionization techniques we used home built ion sources coupled with non-modified ThermoFinnigan interfaces. For the proof-of-principle demonstration of recognition of molecule chirality in situ we used dimethyltartrate as a model chiral substance. We demonstrated that both ionization methods produce dimers and trimers of the dimethyltartrate molecules with pronounced chiral discrimination effects. In the case of corona discharge ionization we detected H3O+ and H2O+ based dimers and trimers. K+ based dimers and trimers dominated the mass spectra in the case of thermoionization. Homochiral domination in the potassiumated dimers and H2O+ based dimers can be attributed to inherited chirality effect from the trimers. We showed that addition of the water molecules to dimers strongly influenced the effect of chirality on dimer stability by making heterochiral dimer more stable than homochiral in case of addition of one water molecule and removing the influence of chirality on dimers stability by addition of two or more water molecules. The experimental observations agree well with the results of the quantum chemical calculation obtained for dimers containing different number of water molecules. [Copyright &y& Elsevier]