Study of the molecular conformation of α- and keto-mycolic acid monolayers by the Langmuir-Blodgett technique and fourier transform infrared reflection-absorption spectroscopy
Study of the molecular conformation of α- and keto-mycolic acid monolayers by the Langmuir-Blodgett technique and fourier transform infrared reflection-absorption spectroscopy
复制标题
通过 Langmuir-Blodgett 技术和傅里叶变换红外反射吸收光谱研究 α- 和酮-霉菌酸单层的分子构象
作者：
T. Hasegawa;Sanae Amino;S. Kitamura;Lisa Matsumoto;Shin;J. Nishijo
利用LB技术和红外反射吸收光谱比较了α-和酮-分枝菌酸单分子膜对单分子膜压缩的构象变化。分枝杆菌酸（MA）是分枝杆菌细胞被膜中特有的主要化学成分，它们被认为在很大程度上影响细胞的性质，如药物渗透性。在我们以前的研究中，发现α-MA中的长烃链在单层压缩过程中至少有两种不同的分子构象：完全伸展和折叠形式。在本研究中，酮-MA的表面压力-面积等温线表明，酮-MA分子的构象变化的响应与α-MA的不同的单层压缩。单层LB膜的红外RA光谱很容易收集到监测构象的变化。RA光谱的二阶导数分析清楚地表明，即使在高表面压力下，酮-MA分子中的长烃链仍保持折叠状态，而α-MA中的长链则未折叠。这些结果表明，小的取代酮基对分子构象的变化有很大的影响。
Conformational changes of α- and keto-mycolic acid monolayers, which respond to monolayer compression, have been compared by use of the Langmuir-Blodgett (LB) technique and infrared reflection-absorption (RA) spectroscopy. Mycolic acids (MA) are major chemical components specifically found in cell envelopes of mycobacteria, and they are considered to largely influence the cell properties such as drug permeability. In our previous study, the long hydrocarbon chain in α-MA was found to have at least two distinct molecular conformations during the monolayer compression: fully extended and folded forms. In the present study, a surface pressure-area isotherm of keto-MA has suggested that keto-MA molecules have a different response of conformational changes to the monolayer compression from that of α-MA. The infrared RA spectra of the monolayer LB films were readily collected to monitor the conformational changes. The second-derivative analysis of the RA spectra clearly suggested that the long hydrocarbon chain in the keto-MA molecule remains folded even when a high surface pressure is applied to the monolayer, while the long chain in α-MA is unfolded. These results suggest that the small substituted keto group greatly influences the change of molecular conformation against the external pressure.