Ma Gang, Allen Heather C
Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, USA.
Langmuir. 2007 Jan 16;23(2):589-97. doi: 10.1021/la061870i.
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.
利用振动和频产生(VSFG)光谱研究了混合朗缪尔单分子层中氘代二棕榈酰磷脂酰胆碱(DPPC-d62)与棕榈酸(PA)之间的相互作用。棕榈酸是外源性肺表面活性剂制剂(如固尔苏和珂立苏)中的一种添加剂。研究了PA对DPPC在液-扩张相和凝聚相中的链构象和取向的影响。通过VSFG观察到PA对DPPC有凝聚作用。在12 mN/m时,单独的DPPC-d62处于液-扩张相。添加PA会增加DPPC链的构象有序性,并使DPPC从扩张相转变为凝聚相。在42 mN/m时,DPPC-d62和PA在凝聚相中形成混合结构。PA的存在降低了DPPC的链倾斜角,增加了DPPC链的取向有序性。在42 mN/m时,PO2-对称伸缩振动的频率红移也表明,在凝聚相中PA的羧基与DPPC的磷酸基团形成了氢键。从这项工作可知,PA对DPPC的影响有两方面:(1)PA增加了DPPC的链有序性,促进了液-扩张相和液-凝聚相的相分离;(2)由于在凝聚相中DPPC与PA的混溶性,PA降低了塌陷压力。