Old Drugs, New Tricks: The Effect of Molecule−Ion Interactions on the Precipitation−Dissolution Equilibrium of Lithium Carbonate in Aqueous Solution and on the Chiral Recognition of Cyclodextrins to d-,l-Tryptophan

Abstract

In the present work, the influence of molecule-ion interactions on the precipitation-dissolution equilibrium of a typical inorganic drug, lithium carbonate (Li2CO3), in water and on the chiral recognition behaviors and binding abilities of alpha-, beta-, gamma-, and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (CD) to D- and L-tryptophan (Trp) was investigated. Our results revealed that the solubility of Li2CO3 was increased to a large extent and the phase solubility diagram of Li2CO3 belonged to the AN type. This finding provided a new insight into the link between molecule-ion interactions and precipitation-dissolution equilibriums of poorly dissolving inorganic salts. Furthermore, despite having a negative effect on the isomer recognition behaviors, the molecule-ion interaction between CDs and Li2CO3 effectively increased the binding abilities of these CDs to both D- and L-Trp synchronously. The observation gave an important implication that buffer solutions consisting of inorganic salts are used with caution in molecular recognition fields between host and guest or between acceptor and donor. Further analyses confirmed the interaction among Li2CO3, beta-CD, and L-Trp using an electrospray ionization mass spectrum.