Attempted prediction of the crystal structures of six monosaccharides

Abstract

A method is reported to generate possible crystal structures of the six hexopyranoses where comparison with an X-ray determination is possible. In these molecules, internal degrees of freedom are all-important. Using essentially only the information that the space group is P2~2~2~ with one molecule in the asymmetric unit, a systematic search was made for all low-energy crystal structures of these substances. The energies were minimized with respect to nine lattice and rigid-body parameters and six intramolecular dihedral angles. The number of possible structures within the range 10 kcal mo1-1 is of the order 1000. In all cases, the experimental structure was among them, and in four cases this was either the structure with the lowest energy or only a few tenths of a kcal mol -~ higher. However, in the two other cases the relative energy of the experimental structure was over 5 kcal mol -l. Such calculations can provide a sensitive test for force fields.

Conversion of cellulose Iα to Iβ via a high temperature intermediate (I-HT) and other cellulose phase transformations

“…Predicting the relative free energy of polymorphs with molecular simulation is challenging (Karamertzanis et al 2008;Price 2008). Using single structures to calculate the zero point energy of bulk unit cells at 0 K may not give the best estimate of the relative free energy ranking of finite sized crystals at higher temperatures (van Eijck and Mooij 1995;Verwer and Leusen 2007;van Eijck 2001;van Eijck et al 2001;Coombes et al 2002;Woodley and Catlow 2008;Li et al 2011). Entropic effects may play a role in the relative stability of polymorphs at a given temperature.…”

Introduction to the special issue on crystal structure prediction

“…The main approach to CSP has remained largely unchanged since the earliest published attempts at ab initio structure prediction (Dzyabchenko, 1984;Gavezzotti, 1991;Gdanitz, 1992;Holden, Du et al, 1993;van Eijck, Mooij et al, 1995;Williams, 1996): trial crystal structures are created and assessed based on their calculated energies. The perfect theoretical approach to lattice energy calculations still does not exist and we should not expect the field to converge to a single method; users of CSP methods benefit greatly from having a range of available, validated options for their calculations, to make choices depending on the type of molecule being studied and available computational resources.…”

Study of Polymorph Prediction For L-Ascorbic Acid

“…The program [11], which performs brute-force grid search for possible crystal structures, has been completely revised will be referred to a Crystal Packer [7][8][9]. The code has been altered to handle triclinic, monoclinic, and orthorhombic space groups to be able to search the most abundant space groups for organic molecules.…”

“…In the past several years there has been an increasing interest in the polymorph prediction of crystal structures on the basis of molecular information. Different methods have been developed to generate possible crystal structures [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. All researches agree that there will always be a large number of possible crystal structures, as judged from their lattice energy, and nearly all are successful in finding the experimental structure.…”