Crystal Structure and Growth Behavior of Aspartame Form I-A

Abstract

The structure, morphology, and growth behavior of aspartame form I-A are presented. This form can be obtained from a purely aqueous solution and is the form with the highest industrial importance. The aspartame molecules are arranged around large hydrophilic channels filled with water molecules. The crystal morphology of this compound is needlelike with polar growth behavior in the needle direction. The side faces show a large nucleation barrier for growth, whereas the top faces possess a much smaller barrier. Monte Carlo simulations are performed for this crystal structure, and the resulting growth rate, morphology, and polarity are all in agreement with the experimental observations.

Carbon–Deuterium Rotational-Echo Double-Resonance NMR Spectroscopy of Lyophilized Aspartame Formulations

“…Crystal structures for various forms of aspartame indicate that the C-C distance between the labeled carbon and the methyl carbon is around 7 Å; thus, the average distance to the rotating 2 H nuclei would be slightly longer than 7 Å. [37][38][39][40] Carbon-deuterium distances up to 4.4 Å have been reported, though to the best of our knowledge, nothing longer than this has been precisely measured. The distance of 4.36 Å reported by Gullion et al 33 was derived from a measured 13 C-2 H dipolar coupling of 55 Hz and required accurate measurement of the REDOR difference signal at dephasing times up to 30 ms.…”

Polar Vector Property of the Stationary State of Condensed Molecular Matter

“…• orientational disorder of dipolar entities and the forms of twinning related to the spatial distribution of the polarization, we can, however, answer the aforementioned key question: for crystals expressing a polar morphology by their (hkl) faces, a mono-domain, i.e., a homogeneous polarization distribution, may be observed experimentally [5][6][7][8][9][10][11][12]. This is a kinetic effect due to the critical slowing down occurring in real growth that hinders the reversal transition into a bi-polar state, as predicted by statistical mechanics calculations [2,3] (Figure 1a).…”

“…If we exclude ionic systems (salts) to only consider neutral small molecules, there remain about 9% of the polar structures. Although twinning and disorder are currently addressed, we notice that only a small number of structural investigations have provided some knowledge on: (i) the absolute orientation of the polar axis in relation to the morphology [5][6][7][8][9][10][11][12]; and (ii) just in a few cases, the spatial distribution of the electrical polarization P el has been analyzed [13][14][15]. As a matter of fact, we do not know much about the polar domain states of (non-ferroelectric) molecular crystals.…”

Towards an atomic-scale understanding of crystal growth in solution

“…17 The same is true for needle-shaped morphologies, where the step energy in the needle direction is found to be close to zero. 25 For all these cases, the step energy method predicts a vastly improved morphology.…”