Mixing Phase Behavior of 1,3‐Dipalmitoyl‐2‐Oleoyl‐sn‐Glycerol (POP) and 1,2‐Dipalmitoyl‐3‐Oleoyl‐rac‐Glycerol (PPO) in n‐Dodecane Solution

Abstract

AbstractWe examined the mixing phase behavior of 1,3‐dipalmitoyl‐2‐oleoyl‐sn‐glycerol (POP) and 1,2‐dipalmitoyl‐3‐oleoyl‐rac‐glycerol (PPO) in organic solutions containing n‐dodecane (C12) as a solvent to confirm whether the molecular compound (MC) crystals of POP/PPO are formed as metastable and most stable forms in the dilute solution by using DSC and synchrotron radiation X‐ray diffraction. The POP/PPO mixtures were prepared at different concentration ratios of POP and PPO with a 10 % increment in two solutions having weight concentration ratios of (POP+PPO):C12 of 50:50 (50 % solution) and 20:80 (20 % solution). We found that MC crystals formed at a ratio of POP/PPO = 50/50 having the melting point of 23.1 and 20.6 °C in 50 and 20 % solution systems in stable states of incubated samples, respectively. The metastable (β′) and stable (β) forms of MC of POP/PPO = 50/50 having a double‐chain‐length structure were confirmed in kinetic behavior and thermodynamically stable states attained after long time incubation, in contrast to the triple‐chain‐length structure of stable forms of POP (β) and PPO (β′). In addition, we observed the formation of MC crystals of POP/PPO in diluted solutions having n‐dodecane concentrations up to 98 % and conclude that molecular interactions between POP and PPO molecules to form MC crystals are not altered by solvent molecules in diluted solutions.