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The automated identification of chiral centres in molecular residues is a non-trivial task. Current tools that allow the user to analyze crystallographic data entries do not identify chiral centres in some of the more complex ring structures, or lack the possibility to determine and compare the chirality of multiple structures. This article presents an approach to identify asymmetric C atoms, which is based on the atomic walk count algorithm presented by Rücker & Rücker [(1993), J. Chem. Inf. Comput. Sci. 33, 683-695]. The algorithm, which we implemented in a computer program named ChiChi, is able to compare isomeric residues based on the chiral centres that were identified. This allows for discrimination between enantiomers, diastereomers and constitutional isomers that are present in crystallographic databases. ChiChi was used to process 254 354 organic entries from the Cambridge Structural Database (CSD). A thorough analysis of stereoisomerism in the CSD is presented accompanied by a collection of chiral curiosities that illustrate the strength and versatility of this approach. [ABSTRACT FROM AUTHOR]

A coupled batch grinding method is used to obtain resolution of a scalemic mixture of asparagine monohydrate conglomerate crystals, which are not racemizable in solution. For this method in two separate vessels a scalemic mixture of crystals is vigorously ground, while the two saturated solutions in contact with the crystals are continuously exchanged. Application of the method yields a 100% resolution with a yield of 50% (S) and 50% (R) crystals in the two vessels. To obtain a successful outcome, the grinding rates, temperatures and the amount of solids must be similar in both vessels. The experimental results are supported by a simple analytical model. It confirms that the process parameters are quite critical and that the incorporation of small clusters formed by grinding into the larger crystals of the same chirality is a prerequisite to obtain complete resolution. [ABSTRACT FROM AUTHOR]

The design of pharmaceutical cocrystals has initiated widespread debate on the classification of cocrystals. Current attempts to classify multicomponent crystals suffer from ambiguity, which has led to inconsistent definitions for cocrystals and for multicomponent crystals in general. Inspired by the work of Aitipamula et al. (Cryst. Growth Des. 2012, 12, 2147-2152), we present a feasible classification system for all multicomponent crystals. The present classification enables us to analyze and classify multicomponent crystal structures present in the Cambridge Structural Database (CSD). This reveals that all seven classes proposed are relevant in terms of frequency of occurrence. Lists of CSD refcodes for all classes are provided. We identified over 5000 cocrystals in the CSD, as well as over 12 000 crystals with more than two components. This illustrates that the possibilities for alternative drug formulations can be increased significantly by considering more than two components in drug design. [ABSTRACT FROM AUTHOR]

Most organic and protein crystals have more than one growth unit in the unit cell. For these structures different growth mechanisms apply as compared to the simple cubic Kossel crystal, since growth becomes a multiple step process. New model systems need to be developed to describe such processes. We present the results of a Monte Carlo simulation study of the kink incorporation and step propagation of several growth steps on a non-Kossel crystal structure. We will compare these results with several theoretical models. Our results show that the growth of the A–B crystal cannot be described by one universal expression, but that the local structure of the step is of great importance and influences the shape of the step velocity versus supersaturation curve. [Copyright &y& Elsevier]

In this paper, the equilibrium and growth behaviour of faces (hkl) with more than one connected net is studied. It is shown that for these types of orientation different surface phases exist under equilibrium conditions as a function of temperature. Depending on the exact bonding topology at the surface, flat, rough or disordered flat phases are found. Moreover, the growth rate R[sub hkl], of such faces can differ significantly from the usually calculated relative growth rates based on the attachment energy. Monte Carlo simulations confirm the results from the Hartman-Perdok analyses and offer a tool for the prediction of the crystal habit as a function of supersaturation. [ABSTRACT FROM AUTHOR]

Part II. Discusses the role of connected nets in predicting crystal morphology. Symmetry roughening of nets; Framework of the periodic bond chain analysis; Crystal graph model.

Part I. Explores the use of Hartman-Perdok theory for predicting crystal morphology. Crystal growth; Statistical thermodynamical models of simple crystal surfaces; Role of the step free energy in crystal morphology.