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Crystal polymorphs of barbital: news about a classic polymorphic system.

Zencirci N, Griesser UJ, Gelbrich T, Apperley DC, Harris RK - Mol. Pharm. (2013)

Bottom Line: The metastable modification III is present in commercial samples and has a high kinetic stability.The solid-state NMR spectra provide information on aspects of crystallography (viz., the asymmetric units and the nature of hydrogen bonding).The known correlation between specific N-H···O═C hydrogen bonding motifs of barbiturates and certain IR characteristics was used to predict the H-bonded pattern of polymorph IV.

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Affiliation: Institute of Pharmacy, University of Innsbruck , Innrain 52, 6020 Innsbruck, Austria.

ABSTRACT
Barbital is a hypnotic agent that has been intensely studied for many decades. The aim of this work was to establish a clear and comprehensible picture of its polymorphic system. Four of the six known solid forms of barbital (denoted I(0), III, IV, and V) were characterized by various analytical techniques, and the thermodynamic relationships between the polymorph phases were established. The obtained data permitted the construction of the first semischematic energy/temperature diagram for the barbital system. The modifications I(0), III, and V are enantiotropically related to one another. Polymorph IV is enantiotropically related to V and monotropically related to the other two forms. The transition points for the pairs I(0)/III, I(0)/V, and III/IV lie below 20 °C, and the transition point for IV/V is above 20 °C. At room temperature, the order of thermodynamic stability is I(0) > III > V > IV. The metastable modification III is present in commercial samples and has a high kinetic stability. The solid-state NMR spectra provide information on aspects of crystallography (viz., the asymmetric units and the nature of hydrogen bonding). The known correlation between specific N-H···O═C hydrogen bonding motifs of barbiturates and certain IR characteristics was used to predict the H-bonded pattern of polymorph IV.

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FT-IR spectra of the Btl forms I0, III, IV, and V.
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fig8: FT-IR spectra of the Btl forms I0, III, IV, and V.

Mentions: The distinct characteristicsof the FT-IR spectra of forms I0, III, IV, and V (Figure 8) make it easy to identify the Btl polymorph in hand. Spectroscopicdifferences, especially in the N–H stretching vibrations regionat around 3200 cm–1 and in the carbonyl bands ataround 1700 cm–1 (Table 2) arise from different N–H...O=C interactions.We have recently investigated the general correlation between theIR characteristics of barbiturates and their N–H...O=C bond topologies.35 Our experimentson Btl forms confirmed these earlier assertions about specific IRcharacteristics associated with the types C-4, C-2, and L-1.


Crystal polymorphs of barbital: news about a classic polymorphic system.

Zencirci N, Griesser UJ, Gelbrich T, Apperley DC, Harris RK - Mol. Pharm. (2013)

FT-IR spectra of the Btl forms I0, III, IV, and V.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4066893&req=5

fig8: FT-IR spectra of the Btl forms I0, III, IV, and V.
Mentions: The distinct characteristicsof the FT-IR spectra of forms I0, III, IV, and V (Figure 8) make it easy to identify the Btl polymorph in hand. Spectroscopicdifferences, especially in the N–H stretching vibrations regionat around 3200 cm–1 and in the carbonyl bands ataround 1700 cm–1 (Table 2) arise from different N–H...O=C interactions.We have recently investigated the general correlation between theIR characteristics of barbiturates and their N–H...O=C bond topologies.35 Our experimentson Btl forms confirmed these earlier assertions about specific IRcharacteristics associated with the types C-4, C-2, and L-1.

Bottom Line: The metastable modification III is present in commercial samples and has a high kinetic stability.The solid-state NMR spectra provide information on aspects of crystallography (viz., the asymmetric units and the nature of hydrogen bonding).The known correlation between specific N-H···O═C hydrogen bonding motifs of barbiturates and certain IR characteristics was used to predict the H-bonded pattern of polymorph IV.

View Article: PubMed Central - PubMed

Affiliation: Institute of Pharmacy, University of Innsbruck , Innrain 52, 6020 Innsbruck, Austria.

ABSTRACT
Barbital is a hypnotic agent that has been intensely studied for many decades. The aim of this work was to establish a clear and comprehensible picture of its polymorphic system. Four of the six known solid forms of barbital (denoted I(0), III, IV, and V) were characterized by various analytical techniques, and the thermodynamic relationships between the polymorph phases were established. The obtained data permitted the construction of the first semischematic energy/temperature diagram for the barbital system. The modifications I(0), III, and V are enantiotropically related to one another. Polymorph IV is enantiotropically related to V and monotropically related to the other two forms. The transition points for the pairs I(0)/III, I(0)/V, and III/IV lie below 20 °C, and the transition point for IV/V is above 20 °C. At room temperature, the order of thermodynamic stability is I(0) > III > V > IV. The metastable modification III is present in commercial samples and has a high kinetic stability. The solid-state NMR spectra provide information on aspects of crystallography (viz., the asymmetric units and the nature of hydrogen bonding). The known correlation between specific N-H···O═C hydrogen bonding motifs of barbiturates and certain IR characteristics was used to predict the H-bonded pattern of polymorph IV.

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