Interfacial properties of arabinofuranosylcytosine diphosphate diacylglycerol, a synthetic liponucleotide

Abstract

The interfacial properties of a synthetic liponucleotide [1-β- d-arabinofuranosylcytosine 5′-diphosphate 1,2- l-diacylglycerol (ara-CDPdiacylglycerol)] were investigated at 23°C. Surface properties studied included the quasi-equilibrium surface pressure-area (π- A) behavior of solvent-spread monolayers on a Wilhelmy balance, dynamic surface tension lowering at high cycling rate with an oscillating bubble, and the adsorption kinetics of aqueous dispersions. The π- A isotherm of ara-CDPdiacylglycerol was greatly expanded compared with that of egg phosphatidylcholine (egg PC), which had identical fatty acyl chain composition, and this feature was most pronounced at low surface pressures. Molecular areas of the liponucleotide and egg PC were more similar at higher surface pressures with film collapse areas of 60 and 53 Å 2/molecule, respectively. Collapse pressures were 40 dynes/cm for ara-CDPdiacylglycerol and 46 dynes/cm for egg PC at a low cycling rate of 4 Å 2/molecule/min, and these increased only slightly to 44 and 48 dynes/cm, respectively, for a 15-fold increase in cycling rate on the Wilhelmy balance. Maximum surface pressures for these surfactants also did not change significantly in complementary oscillating bubble studies, even at rates as high as 20 cycles/min. Additivity analyses of Wilhelmy balance (π- A) data for mixed monolayers of ara-CDPdiacylglycerol and egg PC suggested that these compounds form ideally miscible films at the air-water interface. Finally, in terms of the additional surface property of adsorption, aqueous dispersions of ara-CDPdiacylglycerol displayed a markedly greater adsorption rate and magnitude than egg PC, correlating with its larger critical micelle concentration. The rapid adsorption found for the synthetic liponucleotide, coupled with its ability to expand phosphatidylcholine monolayers, may give such molecules the potential for biomembrane toxicity.