PNNL

Abstract

Although several mechanisms concerning the biological function of lithium salt, a drug having tranquilizing abilities, have been proposed so far, the key mechanism for its selectivity and subsequent interaction with neurotransmitters has not been established yet. We report ultraviolet (UV) and infrared (IR) spectra under ultra-cold conditions of Li+ and Na+ complexes of noradrenaline (NAd, norepinephrine), a neurotransmitter responsible for the body’s response to stress or danger. A detailed analysis of the IR spectra, aided by quantum chemical calculations, reveals that the Li+-noradrenaline (NAd-Li+) complex forms only the extended structure, while the NAd-Na+ and protonated (NAd-H+) complexes form both the folded and extended structures. This conformational preference of the NAd-Li+ complex is further explained from considering specific conformational distributions in solution. Our results clearly discern the unique structural motifs that Li+ adopt when interacting with NAd when compared with other abundant cations in the human body (Na+) and can form the basis towards a molecular level understanding of the selectivity of Li+ in biological systems.