Synthesis Of Supercritical Carbon Dioxide-philic Phospholipids And Determination Their Solubility

In recent decades,supercritical carbon dioxide(ScCO₂)has been widely used in the fields of food and medicine because of its green,environmental protection,and pollution-free characteristics.Natural phospholipids are inexpensive,rich in resources.They act as excellent surfactants due to their molecular structure possess both hydrophilic and hydrophobic groups.However,they have some disadvantages,such as easy oxidation and poor hydrophilicity.The solubility of natural phospholipids in ScCO₂ is also poor.It limits the application of phospholipids in supercritical fluid technology.To this end,this thesis designed and synthesized a modified phospholipid with ScCO₂-philic properties,explored the phase behavior of the prepared phospholipids in ScCO₂,discussed the influences of various operating conditions on the solubility of modified phospholipids in detail.It has been reported that polyvinyl acetate is a ScCO₂-friendly material with excellent biocompatibility and biodegradability.Therefore,in this study,the RAFT reagents with carboxyl-terminated structures(i.e.,narrow molecular weight distributions of polyvinyl acetates with carboxyl-terminated groups)are prepared via reversible addition-fragmentation chain transfer polymerization(RAFT)method.The molecular weight and molecular distribution of the prepared RAFT reagents are confirmed by gel chromatography.Then,polyvinyl acetate and glycerophosphorylcholine with different molecular weights are used as raw materials to prepare polyvinyl acetate phosphatidylcholines via a condensation reaction in the presence of a base and a condensing agent.The structure of the product is confirmed by infrared spectrum and nuclear magnetic resonance hydrogen spectrum.Next,the experimental conditions for the process are optimized by orthogonal experiments with three factors and three levels.The effects of reaction time,temperature,and feed ratio on the experimental yield are determined.Under the optimal conditions,the yield of modified phospholipids is as high as61.2%.In this study,the static cloud point method is used to determine the solubility of modified phospholipids with s weights of 779 g/mol,1098 g/mol,and 1366 g/mol in ScCO₂ with the co-solvent(i.e.,ethanol)concentrations of 0.5 mol%,1 mol%,and 2 mol%at temperatures of313.15 K,318.15 K,323.15 K,328.15 K,and pressures of 9 to 15 MPa.The experimental results show that the modified phospholipids synthesized in this article are indeed more soluble in ScCO₂ than natural phospholipids.The solubility increases with the enhancing pressure and the co-solvents concentration as well as the decreasing temperature and molecular weight of modified phospholipids are decreased.In addition,four modified semi-empirical equations,named Chrastil,Mendez-Santiago-Teja(MST),Reddy,and Pérez models,are used to correlate the solubility data.The AARD values are 7.92%,6.13%,6.40%,and 3.01%,respectively,indicating that they can well predict the solubility data.