International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.7, pp. 311-312

Section 3.7.2.4.5. Amoxicillin

J. A. Kaduka,b,c*

aDepartment of Chemistry, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL 60616, USA,bDepartment of Physics, North Central College, 131 South Loomis Street, Naperville, IL 60540, USA, and cPoly Crystallography Inc., 423 East Chicago Avenue, Naperville, IL 60540, USA
Correspondence e-mail: kaduk@polycrystallography.com

3.7.2.4.5. Amoxicillin

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The amoxicillin powder from a commercial antibiotic capsule was highly crystalline. Its powder pattern (files kadu918.gsas, KADU918.raw, d8v3.prm and KADU921.rd) was matched well by the PDF entries 00-039-1832 and 00-033-1528 for amoxicillin trihydrate, but there was an additional peak at a d-spacing of 16.47 Å (5.37° 2θ). With such a low-angle peak, it seemed prudent to measure the pattern again starting at 3°, and another peak was observed at d = 24.80 Å (3.56° 2θ).

A search of the PDF-4/Organics 2013 for phases having two such peaks among their longest (lowest-angle) peaks yielded entry 00-005-0010 for calcium stearate at the top of the hit list, as well as two lead stearates. We can safely assume that lead stearate is not present in a pharmaceutical. Calcium stearate, however, has its strongest peak at 1.76°, so another pattern was measured starting at 1.5° 2θ. This peak is indeed present (Fig. 3.7.11[link]).

[Figure 3.7.11]

Figure 3.7.11 | top | pdf |

Phases identified in amoxicillin powder from a commercial capsule.

The primary literature suggests that the compound in PDF entry 00-005-0010 is really calcium stearate monohydrate, and that its structure (like those of many other stearate salts) has not yet been determined. The CSD entry for amoxicillin trihydrate (AMOXCT10; Boles et al., 1978[link]) contained some incorrect H-atom positions and was missing an H atom, so these were corrected before a Rietveld refinement was carried out.

References

Boles, M. O., Girven, R. J. & Gane, P. A. C. (1978). The structure of amoxycillin trihydrate and a comparison with the structures of ampicillin. Acta Cryst. B34, 461–466.Google Scholar








































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