Physical properties of arabinofuranosylcytosine diphosphate diacylglycerol, an antitumor liponucleotide.

Dispersed from a dry film into buffer (5 mM phosphate, 0.15 M NaCl, pH 7.4), the liponucleotide 1-beta-D-arabinofuranosylcytosine 5'-diphosphate L-1,2-diacylglycerol (ara-CDPdiacylglycerol) spontaneously forms vesicles which are several microns in diameter and probably unilamellar. Their average size immediately begins to decrease, and after 2 h none can be seen in the light microscope. During 1-2 days in unstirred solutions at 25 degrees C, the vesicles are transformed to spherical or nearly spherical micelles having an apparent partial specific volume of 0.835 ml . g-1, a maximum possible aggregation number of about 150, and an anhydrous radius of about 37 A. The critical micelle concentration (CMC) is about 10 microM in buffer and 20 microM in distilled water, but micelle-monomer equilibration requires at least 1 week at a total concentration of 66 microM. This exceedingly slow equilibration is unique among reported detergents. The standard enthalpy and entropy of micellization are - 13 kJ . mol-1 and 87 J . mol-1 . K-1, respectively. These values are within the range reported for other detergents. Sonication accelerates the vesicle-micelle transformation to 30 min.