Abstract
Abstract The electron density distribution (EDD) of a tetrasaccharide composed of four benzoylated fructopyranosyl units was obtained by refinement with scattering factors from the invariom library. X-ray diffraction data was downloaded from the Cambridge Structural Database (CSD). Bond topological and atomic properties were obtained by application of Bader’s QTAIM formalism. From a large number of 105 C–C bonds in the molecule average bond orders for 33 single and 72 aromatic bonds were calculated yielding values of 1.33 and 1.61. Molecular Hirshfeld and electrostatic potential (ESP) surfaces show that only weak non-covalent interactions exist. The phenyl rings of the benzoyl fragments in the outer regions of the molecule generate a positive ESP shell with repulsive properties between adjacent molecules. Weak surface interactions result in a rather unusual low density around 1.3 g cm−3, which is understandable when compared to other carbohydrates where strong O–H⋯O hydrogen bonds allow a 20% more dense packing with densities >1.5 g cm−3 as determined by single crystal X-ray diffraction.
Highlights
Carbohydrates played an interesting role in the history of crystal structure analysis
Weak surface interactions result in a rather unusual low density around 1.3 g cm−3, which is understandable when compared to other carbohydrates where strong O–H⋯O hydrogen bonds allow a 20% more dense packing with densities >1.5 g cm−3 as determined by single crystal X-ray diffraction
In 2007 we reported an electron density (ED) analysis of sucrose based on a full aspherical multipole refinement of a high-resolution data set of ca. 86,000 reflections measured at 20 K [10]
Summary
Carbohydrates played an interesting role in the history of crystal structure analysis. It turned out that the invariom based topological descriptors, and bond topological and atomic properties, were comparable to the results of the multipole refinement using high-order data, and within the limits of transferability indices introduced by Grabowsky et al [14] These findings encouraged us to carry out an invariom based ED study of a larger carbohydrate, the title tetrasaccharide, consisting of 236 atoms. Dittrich: Benzoylated tetrafructopyranose structure determination was recently published by these authors [15] They measured an exceptionally high quality X-ray diffraction data set at a temperature of 173 K up to a resolution of (sinθ/λ)max = 0.60 Å−1. The invariom formalism [12, 13] allowed reconstructing the ED of the molecule, which was further analyzed This approach permits a more accurate refinement, followed by further analysis of the ED to be performed, for conventional low-resolution X-ray data sets. The potential presence of weak non-covalent interactions in the crystal structure is an interesting aspect of this work
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