Conformational Analysis of Single Perfluoroalkyl Chains by Single-Molecule Real-Time Transmission Electron Microscopic Imaging

详细信息    查看全文

• 作者：Koji Harano ; Shinya Takenaga ; Satoshi Okada ; Yoshiko Niimi ; Naohiko Yoshikai ; Hiroyuki Isobe ; Kazu Suenaga ; Hiromichi Kataura ; Masanori Koshino ; Eiichi Nakamura
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：January 8, 2014
• 年：2014
• 卷：136
• 期：1
• 页码：466-473
• 全文大小：609K
• ISSN：1520-5126

文摘

Whereas a statistical average of molecular ensembles has been the conventional source of information on molecular structures, atomic resolution movies of single organic molecules obtained by single-molecule real-time transmission electron microscopy have recently emerged as a new tool to study the time evolution of the structures of individual molecules. The present work describes a proof-of-principle study of the determination of the conformation of each C鈥揅 bond in single perfluoroalkyl fullerene molecules encapsulated in a single-walled carbon nanotube (CNT) as well as those attached to the outer surface of a carbon nanohorn (CNH). Analysis of 82 individual molecules in CNTs under a 120 kV electron beam indicated that 6% of the CF₂鈥揅F₂ bonds and about 20% of the CH₂鈥揅H₂ bonds in the corresponding hydrocarbon analogue are in the gauche conformation. This comparison qualitatively matches the known conformational data based on time- and molecular-average as determined for ensembles. The transmission electron microscopy images also showed that the molecules entered the CNTs predominantly in one orientation. The molecules attached on a CNH surface moved more freely and exhibited more diverse conformation than those in a CNT, suggesting the potential applicability of this method for the determination of the dynamic shape of flexible molecules and of detailed conformations. We observed little sign of any decomposition of the specimen molecules, at least up to 10⁷ e路nm^鈥? (electrons/nm²) at 120 kV acceleration voltage. Decomposition of CNHs under irradiation with a 300 kV electron beam was suppressed by cooling to 77 K, suggesting that the decomposition is a chemical process. Several lines of evidence suggest that the graphitic substrate and the attached molecules are very cold.