Anomalous Ultrasonic Absorption of Liposome Suspensions in the Liquid Crystal Phase

概要

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Ultrasonic velocity and absorption of liposome suspensions of dimyristoyl phosphatidylcholine in the liquid crystal phase were measured in the megahertz region, varying the temperature and the size of liposomes. Temperature dependence of ultrasonic properties indicated a critical phenomenon due to the get-liquid crystal transition at about 24℃, which is characterized by a dip in ultrasonic velocity and an anomalous increase in absorption. However, the anomalous frequency dependence of ultrasonic absorption remained significant even at 35℃ where the critical phenomenon almost disappeared. This additional absorption anomaly strongly depended on the size of liposomes. The value of viscosity of multilamellar liposome suspensions estimated from the ultrasonic absorption was inversely proportional to the frequency of the ultrasound and diverged to infinity in the low-frequency limit, while this kind of anomaly was not observed for small unilamellar lipid vesicles. This liposome size dependence indicated clearly that the additional absorption anomaly in multilamellar liposomes was due to the fluctuation of their lamellar structure, The possibility of estimating the content of stacked membrane layers in biological tissue by ultrasonic absorption is discussed based on the ultrasonic measurements of liposomes.
社団法人応用物理学会の論文
1997-05-15