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Tetrakis(4-nitrophenyl)methane is a new host material with considerable structural adaptability over a range of solvents. The crystal structures of 14 of these solvates have been determined and classified into three groups. The diamondoid group, wherein the host molecules form a 2-fold interpenetrated diamondoid network structure, is unprecedented in that network connections are made exclusively with weak C-H...O and pi...pi interactions. This group consists of the solvates of THF, dioxane, nitrobenzene, 4-bromoanisole, anisole, phenetole, p-xylene, and chlorobenzene. The rhombohedral group, which is characterized by specific host.guest interactions of the C-H...O and halogen...O2N type, consists of the solvates of CHCl3 and CHBr3 and somewhat surprisingly DMF, which shows an unusual 3-fold disorder mimicking in part the shape and size of the haloform molecules though not their orientation. The third group comprises solvent-rich solvates of the host with mesitylene, collidine, and o-xylene with quite different crystal structures. The THF solvate was found to lose solvent over limited temperature ranges transforming reversibly from the diamondoid structure to the rhombohedral structure. A mechanism for this process is outlined. Material from which solvent has been removed by heating was also found to resolvate upon soaking in appropriate solvents. In summary, the title compound forms a host network that is partially robust and in part flexible. It is possible that this fluxional nature of the host network derives from the weakness of the connecting interactions.

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In principle, an organic diamondoid structure could follow from any of four possibilities: a single molecule of the type AX 4 assembles via X‚‚‚X interactions; two molecules, e.g. AX 4 and BY 4 , assemble via X‚‚‚Y interactions; either of the first two possibilities is modified with appropriate linear spacer molecules; a single molecule AX 2 Y 2 assembles via X‚‚‚Y interactions. This communication deals with the last possibility, wherein the X‚‚‚Y link is based on the polarizationassisted I‚‚‚O 2 N synthon. A notable feature of the crystal structure of 4,4′-diiodo-4′′,4′′′-dinitrotetraphenylmethane (1) is the existence of a divergent mode of iodo-nitro association. The T d nodes of 1 are interconnected with the I atom bifurcated by O atoms from two NO 2 groups such that each molecule of 1 is connected to eight others through I‚‚‚O contacts. The result is a combination of 5-fold diamondoid and 3-fold square grid networks. All I‚‚‚O interactions observed are short and strong, and there is a pronounced tendency to achieve close packing with the two coexisting networks.

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Protein kinases are involved in many diseases like cancer, inflammation, cardiovascular disease, and diabetes. They have become attractive target classes for drug development, making kinase inhibitors as important class of therapeutics. The success of small-molecule ATP-competitive kinase inhibitors such as Gleevec, Iressa, and Tarceva has attracted much attention in the recent past. Kinases make use of ATP for phosphorylation of a specific residue(s) on their protein substrates. More than 400 X-ray structures of about 70 different kinases are publicly available. These structures provide insights into selectivity and mechanisms of inhibition. However, prediction of binding specificity of kinase inhibitors based on structural information alone appears to be insufficient. Here, we will review these observations to gain insights into the rules that govern protein kinase inhibitor selectivity.

The crystal chemistry and engineering of a new family of host-guest complexes is described. 4,4Ј-Dicyanobiphenyl (DCBP) forms a 1:1 complex, 1 with urea wherein the DCBP host forms large hexagonal channels via C᎐Hؒ ؒ ؒN hydrogen bonds and the urea guest molecules are arranged in N᎐Hؒ ؒ ؒO ribbons which fit completely within the host channels. By analogy, 4,4Ј-bipyridine N,NЈ-dioxide (BPNO) was selected as a molecule that can form a corresponding C-Hؒ ؒ ؒO based channel. BPNO forms complexes with urea (2), thiourea (3) and water (4). Structures 2 and 3 provide some points of comparison with the structure of 1 but are not fully equivalent to it. In structure 4, the smaller guest water is able to fit neatly within the smaller hexagonal channel of BPNO and in this sense, the degree of structural predictability is satisfactory. To obtain another structure similar to that of 1, 4,4Ј-dinitrobiphenyl (DNBP) was identified as an alternative host compound. This choice was justified by the structure of its 1:1 complex, 5 with urea. In all cases, the guest molecules interact with each other via strong hydrogen bonds and form an essential template for the weak hydrogen bonded assembly of the host network structure but the latter is still of some significance. One finds consequently, in complexes 1-5, a constructive interplay of strong and weak hydrogen bonds.