Microscopic molecular mobility of amorphous AG-041R measured by solid-state 13C NMR.
OBJECTIVE
AG-041R is characterized to be stable in amorphous state and difficult to crystallize at normal period of time. In order to investigate the molecular mobility in microscopically, the spin-lattice relaxation time (T1) of AG-041R was investigated by solid-state CP/MAS 13C NMR at temperature below and above glass transition temperature (Tg).


METHODS
CP/MAS measurement and T1 measurement were performed by means of 13C NMR, where the measurement temperatures were 60, 70, 80, 100, and 110 degrees C. The spin-lattice relaxation time (T1) of AG-041R was calculated from the relaxation curves.


RESULTS
From the analysis of T1 of amorphous AG-041R, it was clarified that all of the carbons did not start moving drastically at Tg and there were some groups of carbon in terms of temperature dependency of T1. One is a type, such as the carbons in benzene ring: their T1 was drastically changed at Tg. On the other hand, T1 of carbonyl carbons gradually decreased, and above Tg their T1 was still higher than that of the other carbons. There was no significant change of T1 in the methyl carbons around Tg. From the study of IR and 1H NMR in solution, the inter- and intramolecular hydrogen bondings between NH and C=O were found in AG-041R. Due to hydrogen bonding, the inter- and/or intramolecular interaction is considered to retain even at supercooled liquid state.


CONCLUSIONS
The structure that contributes glass transition is the main skeleton structure, such as benzene ring, while small group, like methyl, start to move at lower temperature than Tg. On the other hand, for the carbons, such as carbonyl, their structure was restricted by inter- and/or intramolecular interaction, therefore, their molecular mobility was significantly low above Tg.
Koga
Akiko
A
Department of Pharmaceutics, School of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan.
Yonemochi
Etsuo
E
Machida
Minoru
M
Aso
Yoshinori
Y
Ushio
Hidetoshi
H
Terada
Katsuhide
K
D002250:Carbon Radioisotopes; D003460:Crystallization; D006860:Hydrogen Bonding; D007211:Indoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D044367:Phase Transition; D013997:Time Factors; D044366:Transition Temperature
C109755:AG-041R; D002250:Carbon Radioisotopes; D007211:Indoles