Owusu-Ware, S., Leharne, S., Chowdhry, B. and Antonijevic, M. ORCID: 0000-0002-5847-7886 (2011) Studies of the relationship between molecular mobility and the thermal stability of the isomers of aminobutyric acid. AAPS Journal, 13 (S2). ISSN 1550-7416

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Abstract

Purpose: Within the last decade a number of studies have demonstrated that solid-state molecular mobility is one of the most important factors determining physical and chemical stability. However, the majority of these studies focused on large molecular amorphous materials. Little is known about the relationship between molecular mobility and thermal stability of non-amorphous small molecule materials. The foregoing study aims to probe the relationship (if any) between the slid-state molecular mobility (as measured by thermally stimulated current (TSC) spectroscopy) and the thermal stability of structural isomers of aminobutyric acid.

Methods: Thermal gravimetric analysis (TGA 2950, TA instrument) studies were performed using 2-3 mg sample of DL-α-aminobutyric acid (DL-AABA), DL-β-aminobutyric acid (DL-BABA) and γ-aminobutyric acid (GABA). TSDC studies were undertaken using SETARAM TSC II with Norhof LN2 system. Each sample was heated to the temperature of polarisation (Tp) and held isothermal for 2 min, during which 100 V/mm of static filed is applied. The sample was then rapidly cooled to -100˚C. This was followed by linear heating at 10˚C/min to 120˚C.

Results: Based on the extrapolated onset of weight change, TGA results (Figure 1(a)) show that DL-AABA is the most thermally stable of the three structural isomers of aminobutyric acid (234 ± 1˚C). This is followed by GABA (216 ± 1˚C), then DL-BABA (210 ± 2˚C) TSC results (Figure 1(b)) show that GABA exhibits greater solid-state molecular mobility at a lower temperature in comparison to DL-BABA and DL-AABA. No significant difference in molecular mobility is observed for DL-BABA and DL-AABA.

Figure 1. Overlays of the outputs obtained for AABA, BABA and GABA by TGA (a) and TSC (b) experiments at 10˚C/min.

Conclusion: Preliminary results suggest that when considering the onsets of weight change, there exist no relationship between molecular mobility and thermal stability of the aminobutyric acids studied. Further work is underway to enable comparison of the thermodynamic and kinetic parameters associated with molecular mobility and the thermal events observed at higher temperatures. We believe this will provide greater insight into the relationship between molecular mobility and thermal stability of these molecules.

Item Type:	Article
Additional Information:	[1] Published in AAPS Journal (2011), Volume 13, S2 - AAPS Pharmaceutical Sciences World Congress Abstracts. [2] Online-only journal.
Uncontrolled Keywords:	thermal analysis, aminobutyric acid, structural isomers
Subjects:	Q Science > QD Chemistry
Faculty / School / Research Centre / Research Group:	Faculty of Engineering & Science > School of Science (SCI)
Related URLs:	Publisher
Last Modified:	07 Dec 2016 14:16
URI:	http://gala.gre.ac.uk/id/eprint/7193

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