C. Guguta

The hydration/dehydration behavior of aspartame revisited.

Aspartame, l-aspartyl-l-phenylalanine methyl ester, has two hydrates (IA and IB), a hemi-hydrate (IIA) and an anhydrate (IIB). The hydration/dehydration behavior of aspartame was investigated using hot-humidity stage X-ray powder diffraction (XRPD) and molecular mechanics modeling in combination with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of this study are compared to earlier studies on aspartame as described in literature. It is shown that earlier transition studies were hampered by incomplete conversions and wrong assignment of the forms. The combination of the techniques applied in this study now shows consistent results for aspartame and yields a clear conversion scheme for the hydration/dehydration behavior of the four forms.

FIDDLE: a method for simultaneous indexing and structure solution from powder diffraction data

from X-ray, synchrotron and neutron diffraction can be combined regardless of the powder or single crystal nature of samples and refined jointly in order to get a structure model profiting from unique features of various experimental techniques. The most obvious and widely used case is combination of neutron powder data yielding good resolution for light atoms with carefully measured X-ray single crystal data in order to improve the overall quality of the structure model. The joint refinement is also very useful for magnetic structure determination which is often done from limited neutron powder data set at very low temperature. Joint refinement with complete low temperature X-ray data opens possibility to investigate relationship between magnetic and conventional structure. As a special case refinement of multiphase single crystal data should be mentioned. In this contribution we shall summarize our experience with joint refinement gathered during the last two years. Several practical examples will be presented as well as technical aspects of the joint refinement.

Structural diversity of synthetic estrogen solvates.

Abstracts of the 24th European Crystallographic Meeting Marrakech, Morocco, 22-27 August 2007

The crystal structure of Aspartame Anhydrate from powder diffraction data.

Aspartame (L-aspartyl-L-phenylalanine methyl ester) is adipeptidesweetener,∼200timessweeterthansucrose.Becauseof its dietary and pharmaceutical usefulness, various charac-teristics of aspartame, including the model of its receptor siteand its conformation in aqueous solution, have been studiedextensively [1, 2]. Aspartame is known to grow in differentpseudo-polymorphicforms,IA,IB,IIAandIIB,eachcontaininga different amount of water and all having a needle-likemorphology. Although a lot of information on aspartame canbe found in literature, no clear and complete picture can beobtainedofthedehydrationprocessatthemolecularlevel.Oneobjectofourworkwastoobtainthe″missing″crystalstructureoftheanhydrateformandthestudyofitsrelationtotheotherforms.TheemployedtechniquewasX-rayPowderDiffraction(XRPD), using a Bruker AXS D8 ADVANCE X-ray PowderDiffractometerintransmissioncapillarygeometry.ThecrystalstructureoftheaspartameanhydratewassolvedusingtheDASHsoftware[3].ThefinalRietveldrefinementwasperformedwiththe Topas software [4]. The anhydrate crystallizes in themonoclinic system with space group