Crystallization force--a density functional theory concept for revealing intermolecular interactions and molecular packing in organic crystals.

Organic molecules are prone to polymorphic formation in the solid state due to the rich diversity of functional groups that results in comparable intermolecular interactions, which can be greatly affected by the selection of solvent and other crystallization conditions. Intermolecular interactions are typically weak forces, such as van der Waals and stronger short-range ones including hydrogen bonding, that are believed to determine the packing of organic molecules during the crystal-growth process. A different packing of the same molecules leads to the formation of a new crystal structure. To disclose the underlying causes that drive the molecule to have various packing motifs in the solid state, an electronic concept or function within the framework of conceptual density functional theory has been developed, namely, crystallization force. The concept aims to describe the local change in electronic structure as a result of the self-assembly process of crystallization and may likely quantify the locality of intermolecular interactions that directs the molecular packing in a crystal. To assess the applicability of the concept, 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, so-called ROY, which is known to have the largest number of solved polymorphs, has been examined. Electronic calculations were conducted on the seven available crystal structures as well as on the single molecule. The electronic structures were analyzed and crystallization force values were obtained. The results indicate that the crystallization forces are able to reveal intermolecular interactions in the crystals, in particular, the close contacts that are formed between molecules. Strong correlations exist between the total crystallization force and lattice energy of a crystal structure, further suggesting the underlying connection between the crystallization force and molecular packing.

Catastrophic systemic embolization from a left atrial myxoma.

We report the fatal course of a left atrial myxoma: its systemic embolization to the coronary, cerebral, renal, and peripheral vascular beds in a 39-year-old woman resulted in rapid clinical deterioration, multiorgan failure, and death. Among reported cases of left atrial myxoma, this degree of embolic burden is exceedingly rare. In addition to reporting the patient's case, we discuss the presentation and diagnosis of possible intracardiac sources of systemic emboli.

Primary and secondary hepatic lymphomas diagnosed by image-guided fine-needle aspiration: a retrospective study of clinical and cytomorphologic findings.

OBJECTIVES: To explore the diagnosis of hematolymphoid malignancies of the liver (hepatic lymphoma [HeL]) by image-guided fine-needle aspiration (FNA), which can often be difficult due to a low index of suspicion and nonspecific patient presentations, especially in the rare cases where the liver is the only site of disease (primary HeL [PHeL]). Understanding the clinical setting in which such lesions arise, as well as the cytomorphologic findings, may assist cytopathologists in making an accurate diagnosis and triaging samples for ancillary studies. METHODS: In this retrospective study of 32 patients with HeL, the largest such study to our knowledge, we review the clinical and diagnostic features of HeL. RESULTS: HeL and especially PHeL most commonly show a diffuse large B-cell lymphoma phenotype and have a poor prognosis (median survival of seven months). PHeL is strongly associated with human immunodeficiency virus infection (12/16 patients). CONCLUSIONS: Image-guided FNA with immediate evaluation is a reliable means to obtain diagnostic material and triage for ancillary tests.

The polymorphism of indomethacin: an analysis by density functional theory calculations.

PURPOSE: Indomethacin exhibits conformational polymorphism. Crystal structures of two polymorphs have been solved bearing different molecular conformations. Herein, the conformational variance in the crystals was examined by density functional theory (DFT) calculations in order to understand the mutual influence between electronic structures and crystal packing. METHODS: Electronic structures of the two polymorphs and the single molecule of indomethacin were calculated with quantum mechanical methods. Electronic properties based upon conceptual density functional theory were thereby analyzed. A potential energy surface was generated with regard to the conformational flexibility, which was identified by the electronic analysis. Lattice energies of the two polymorphs were further calculated with an empirically augmented DFT method. RESULTS: Electronic properties, including electronic and nuclear Fukui functions, provided a fundamental understanding of the energetic competition in the indomethacin molecule between delocalization of p-orbitals of two aromatic rings and steric repulsions. Two dihedral angles (the tau1 and tau2 in Fig. 1) were found playing a crucial role in affecting such competition and determining the variation of molecular conformations. The existing polymorphs, alpha- and gamma-forms, were located in local minima on the energy surface based on the two dihedral angles of their molecular conformations. Calculated lattice energies suggest the alpha-form is more stable than the gamma-form at the zero K. CONCLUSIONS: The polymorphism of indomethacin lies in various meta-stable conformations of the molecule that are results of different orientations between the two aromatic indole and phenyl rings. The analysis of electronic and nuclear Fukui functions permits the revelation of local energy barriers that determine the conformational diversity and, for the case of indomethacin, the conformational polymorphism.

Reaction Mechanism of 1,3,5-Trinitro-s-triazine (RDX) Deciphered by Density Functional Theory.

1,3,5-Trinitro-s-triazine, or cyclotrimethylene trinitramine, or RDX, is a sensitive, secondary explosive, which has been the subject of a number of studies regarding the sensitivity and mechanism of decomposition in energetic materials. Several initial mechanistic steps have been proposed for RDX decomposition, with no conclusive agreement upon any one as the definitive pathway. Our research utilizes density functional theory (DFT)-based calculations and concepts, particularly the nuclear Fukui function, to analyze the effects of additive/depletive electronic perturbation upon vapor conformers and crystal RDX structures. Since the nuclear Fukui function is a measure of the physical stress that a nucleus encounters upon a change in the electron population, it may provide useful information regarding the role of each atom in unimolecular decomposition. The results illustrate that both homolytic cleavage of N-N bonds and elimination of HONO from RDX exhibit favorability as initial steps in the decomposition of RDX in either phase. The nuclear Fukui function proved a valuable tool for gaining insight into the initial steps of unimolecular reactions.