Key Differences of the Hydrate Shell Structures of ATP and Mg.ATP Revealed by Terahertz Time-Domain Spectroscopy and Dynamic Light Scattering

ATP is one of the main biological molecules. Many of its biological and physicochemical properties, such as energy capacity of the phosphate bonds, significantly depend on hydration. However, the structure of the hydration shell of the ATP molecule is still a matter of discussion. In this work, the hydration shells of ATP in water and MgCl2 solutions were examined by terahertz time-domain spectroscopy and dynamic light scattering. Terahertz spectroscopy reveals the distorted water structure in the ATP water solution displaying tightly bound water molecules, which could be explained by the hydration of phosphate groups. Upon ATP binding to a Mg2+ ion, the situation is principally different: Instead of the distorted water structure, its arranged structure with increased hydrogen bond number is observed. Dynamic light scattering showed that the hydrodynamic diameter of ATP increases by 0.5 nm after Mg2+ binding. Meanwhile, according the characteristics of scattering, the increase of the shell size occurs via formation of a layer with a refraction coefficient similar to water. This layer can be interpreted as hydration shell differing from unaltered water by increased number of hydrogen bonds.

Automated summary

The study investigates the hydration shells of ATP in water and MgCl2 solutions using terahertz time-domain spectroscopy and dynamic light scattering. It was found that the water structure in the ATP water solution is distorted, indicating tightly bound water molecules due to the hydration of phosphate groups. On the other hand, when ATP binds to Mg2+ ions, an arranged structure with increased hydrogen bond number is observed, leading to a different hydration shell compared to unaltered water. Additionally, the hydrodynamic diameter of ATP increases by 0.5 nm after Mg2+ binding, and there is evidence of the formation of a layer with a refraction coefficient similar to water, suggesting an increased number of hydrogen bonds in the hydration shell.