Crystals grown from precipitant-free ultralow concentrate ATP (adenosine triphosphate) solutions with extremely low DC potential

Abstract

ATP crystals are grown under bare conditions of DC potential, ionic strength, and solute concentration without a precipitant. A 1.6 V cm⁻¹ DC field supplied internally to aqueous solutions containing as low as 0.003 mg mL⁻¹ ATP in 1 mM phosphate buffer appears sufficient for the growth of orthorhombic crystals. The effect of the electric field (EF) on molecular ionization and monomer → aggregate transition are analyzed by UV–visible and fluorescence spectroscopy. The aggregation process starts in less than an hour after turning the DC field on, and the aggregates appear to nucleate and enter the crystal phase in hours or days. Processes innate to electrochemistry are minimized or do not interfere with the interaction of the EF with the molecular dipole, forcing predominant aggregation in the solution itself. The crystals are imaged and indexed using electron microscopy and powder X-ray diffractogram. A series of experiments in which the amount crystallized as a function of initial concentration of ATP in the 0.003–13 mg mL⁻¹ range was determined yields an indicator isotherm of crystallization at 298 K that shows that the amount of ATP used up to produce the crystalline phase decreases rapidly with the initial concentration used.