各種リポソーム試料の表面荷電量の測定

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書誌事項

タイトル別名
  • Measurement of surface charge on the various liposome.
  • カクシュ リポソーム シリョウ ノ ヒョウメン カデンリョウ ノ ソクテイ

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Surface charge on the liposome formed from purified phospholipids was determined by colloidal microtitration with potassium polyvinylsulfate (PVSK) and polydiallydimethylammonium chloride (Cat-Floc). The end point was detected by the color change of 0.1% TB from blue to red-violet. A micro colloidal titration apparatus (Gilmont ultra-precision micrometer syringe, No. S3200) was used for titration. Phospholipids used in this experiment were as folows: phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and phosphatidylserine (PS). The chloroform solution of the phospholipid was transferred into a 25-ml stoppered teat tube and evaporated to dryness in vacuo at 3536°C. The thin film of the phospholipid in the vessel was suspended in distilled water (20 mg of lipid/2 ml) by sonicating for 30 min at room temperature. Stability of the liposome, whcih is a closed system composed of the lipid bilayer, was checked by using liposome entrapping glucose. From the results of colloidal titration, the surface of PC liposome was found not to be charged over the pH range from 2 to 11. This is considered due to formation of the intramolecular salt linkage between the phosphate group (pKa_??_2) and quarternary ammonium group of choline (pKa_??_13). PG liposome was negatively charged at above pH 3 with a constant value, (0.633±0.020) × 10-6 eq/10-6 eq of phosphorus. The plots of the equivalent of negative charge against the amount of phospholipid gave a straight line. The results of three separate determinations indicated good reproducibility. PE liposome showed a constant value, 0.646×10-6 eq/10-6 eq of phosphorus, at above pH 10.5. In the case of PS liposome, the constituent ratio of the functional groups was well corelated to the results of colloidal titration. From the constant values in the pH range of 6 to 7 and 10 to 11, the amounts of negative charge of the carboxyl and phosphate groups were determined as 0.541 and 0.546 ×10-6 eq/1 0-6 eq of phosphorus, respectively. This negative charge of the liposome was considered to reflect the surface charge of the closed vesicle of the bilayer of the phospholipids. Colloidal micro-titration is useful not only for detecting the state of the functional groups over a wide pH range, but also for quantitative determination of the negative charge on the surface of a small amount (0.5 to 1.0 mg of lipid/sample) of the phospholipid liposome.

収録刊行物

  • 分析化学

    分析化学 36 (7), 403-406, 1987

    公益社団法人 日本分析化学会

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