Condensing effect of palmitic acid on DPPC in mixed Langmuir monolayers.
Condensing effect of palmitic acid on DPPC in mixed Langmuir monolayers.
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DOI：
10.1021/la061870i
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发表时间：
2007-01
期刊：
影响因子：
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通讯作者：
Gang Ma;H. Allen
中科院分区：
文献类型：
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作者：
Gang Ma;H. Allen
用振动和频产生（VSFG）光谱研究了氘代二棕榈酰磷脂酰胆碱（DPPC-d 62）与棕榈酸（PA）在混合单分子膜中的相互作用。棕榈酸是外源性肺表面活性物质制剂（如Survanta和Surfaxin）的添加剂。考察了PA对DPPC在液相膨胀相和凝聚相中链构象和取向的影响。用VSFG观察到PA对DPPC的凝聚效应。在12 mN/m下，单独的DPPC-d 62处于液体膨胀相。PA的加入增加了DPPC链的构象有序性，并导致DPPC从膨胀相转变为凝聚相。在42 mN/m下，DPPC-d 62和PA在凝聚相中形成混合结构。PA的存在减小了DPPC的链倾角，增加了DPPC链的取向有序性。在42 mN/m，也有证据表明，从频率红移的PO 2对称的拉伸，PA的羧基形成氢键与磷酸基团的DPPC在凝聚相。PA对DPPC的影响是双重的：（1）PA增加了DPPC的链序，促进了LE和TC的相分离;（2）由于DPPC和PA在凝聚相中的相容性，PA降低了崩溃压力。
The interaction between deuterated dipalmitoylphosphatidylcholine (DPPC-d62) and palmitic acid (PA) in mixed Langmuir monolayers is studied using vibrational sum frequency generation (VSFG) spectroscopy. Palmitic acid is an additive in exogenous lung surfactant preparations such as Survanta and Surfaxin. The effect of PA on the chain conformation and orientation of DPPC in the liquid-expanded and condensed phases is explored. A condensing effect of PA on DPPC is observed with VSFG. At 12 mN/m, DPPC-d62 alone is in the liquid-expanded phase. Adding PA increases the conformational ordering of DPPC chains and causes DPPC to transition from the expanded phase into the condensed phase. At 42 mN/m, DPPC-d62 and PA form a mixed structure in the condensed phase. The presence of PA decreases the chain tilt angle of DPPC, increasing the orientational ordering of DPPC chains. At 42 mN/m, there is also evidence from the frequency red shift of the PO2- symmetric stretch that the carboxyl group of PA forms a hydrogen bond with the phosphate group of DPPC in the condensed phase. From this work the effect of PA on DPPC is 2-fold: (1) PA increases the chain ordering of DPPC and promotes the LE and TC phase separation and (2) due to the miscibility between DPPC and PA in the condensed phase, PA decreases the collapse pressure.