Structural aspects of dehydration and rehydration in the adenosine 5′-diphosphate (ADP)–potassium–water system

Abstract

This work presents the solution crystallization, post-crystallization dehydration and structural studies of hydrated and anhydrous potassium salts of adenosine 5′-diphosphate obtained in this way. ADP is crucial for cellular energy processes. K⁺ is the most abundant metal cation in cells. However, both ADP and nucleotide–K systems are poorly understood in terms of crystal structure. We report three hydrated salts: K(ADP)·4H₂O, K(ADP)·2H₂O, and (H₅O₂)K(ADP)₂·4.25H₂O and one anhydrous salt, K(ADP), formed by dehydration of K(ADP)·2H₂O, proceeding as a single crystal to single crystal (SC-to-SC) process, which were tested by single crystal XRD, variable temperature micro-PXRD and TGA/DTA methods. The phase transition in (H₅O₂)K(ADP)₂·4.25H₂O was observed. The structural description of the dehydration–rehydration process in the ADP–potassium–water system was presented. The most important interaction types and structural motifs as well as the function of water molecules in the studied ADP crystals were identified.