Natural Submicron Heterogeneities in Aqueous Solutions of ATP

Submicron heterogeneities (SMHs) spontaneously arising in aqueous solutions of adenosine triphosphate (ATP) are studied. Their size of about 100 nm is close to the size of SMHs earlier detected in other solutions. The SMHs have a ζ-potential of about –10 mV. It is one of their stability factors. It is shown that the tendency for ATP to form SMHs depends on the ionic composition. After removal of SMHs from the ATP solution by filtering they do not form for more than two hours in the presence of Ca²⁺, while when Ca²⁺ is absent or replaced with Mg²⁺, the SMHs form in less than 30 min. In some cases, fast formation of SMHs hampers their adequate investigation. Analysis of dielectric spectra of ATP solutions in the presence of Ca²⁺ before and after filering has shown that hydration of Ca·ATP complexes inside SMHs is manifested by lower binding of water molecules and smaller number of free water molecules as compared to hydration of Ca·ATP complexes not included in SMHs.