Patil G S, Dorman N J, Cornwell D G
J Lipid Res. 1979 Jul;20(5):663-8.
At 24-26 degrees C, force-area isotherms show that unionized dipalmitoyl phosphatidic acid forms a solid-condensed film while unionized egg and dioleoyl phosphatidic acids form liquid-expanded films. Surface area is a characteristic feature of a specific phosphatidic acid and the purity of a phosphatidic acid preparation can be established by the surface area of the unionized phosphatidic acid (acid subphase) at 17 dynes/cm (castor oil piston). Ionized dipalmitoyl phosphatidic acid desorbs from a monolayer at a measurable rate while ionized egg and dioleoyl phosphatidic acids desorb too slowly for rate studies. The apparent surface pK(2) for dipalmitoyl phosphatidic acid, calculated from desorption rates, is 9.4. Surface areas of the phosphatidic acids expand with ionization. Solid dipalmitoyl phosphatidic acid films expand only in the pK(2) region, showing one inflection point which indicates that the K(1)/K(2) ratio is less than 100 and that, as a consequence of this ratio, the apparent surface pK(1) is greater than 7.4. Liquid egg and dioleoyl phosphatidic acid films have two inflection points, expanding in both the pK(1) and pK(2) regions. The apparent surface pK(1) and pK(2) values, calculated from inflection points in surface area data, are 3.5 and 8.0, respectively. Film expansion with phosphatidate anions is less than anticipated, showing the presence of weak transient hydrogen bonds. Expanded phosphatidate anion films are condensed by alkaline earth cations. The Ca(2+) and Ba(2+) salts of completely ionized phosphatidic acids collapse from monolayers, showing that the phosphatidate anion may function as an ionophore for the transport of alkaline earth ions.-Patil, G. S., N. J. Dorman, and D. G. Cornwell. Effects of ionization and counterion binding on the surface areas of phosphatidic acids in monolayers.
在24 - 26摄氏度下，力-面积等温线表明，未电离的二棕榈酰磷脂酸形成固态凝聚膜，而未电离的鸡蛋磷脂酸和二油酰磷脂酸形成液态扩张膜。表面积是特定磷脂酸的一个特征，磷脂酸制剂的纯度可以通过未电离的磷脂酸（酸性亚相）在17达因/厘米（蓖麻油活塞）时的表面积来确定。电离的二棕榈酰磷脂酸以可测量的速率从单分子层解吸，而电离的鸡蛋磷脂酸和二油酰磷脂酸解吸太慢，无法进行速率研究。根据解吸速率计算，二棕榈酰磷脂酸的表观表面pK(2)为9.4。磷脂酸的表面积随电离而扩大。固态二棕榈酰磷脂酸膜仅在pK(2)区域扩大，显示一个拐点，这表明K(1)/K(2)比值小于100，因此，表观表面pK(1)大于7.4。液态鸡蛋磷脂酸和二油酰磷脂酸膜有两个拐点，在pK(1)和pK(2)区域均扩大。根据表面积数据中的拐点计算，表观表面pK(1)和pK(2)值分别为3.5和8.0。磷脂酸阴离子引起的膜扩张小于预期，表明存在弱的瞬时氢键。扩张的磷脂酸阴离子膜被碱土金属阳离子凝聚。完全电离的磷脂酸的Ca(2+)和Ba(2+)盐从单分子层塌陷，表明磷脂酸阴离子可能作为碱土金属离子运输的离子载体。-帕蒂尔，G. S.，N. J. 多尔曼，和D. G. 康韦尔。电离和抗衡离子结合对单分子层中磷脂酸表面积的影响。
