Halogen Bonding in Supramolecular Chemistry

2,3,6,7-Tetra-kis(bromo-meth-yl)naphthalene

The title compound, C₁₄H₁₂Br₄, crystallizes with imposed inversion symmetry. In the crystal, the mol­ecules pack in layers parallel to (10). The layers involve two Br⋯Br and one H⋯Br contact. Between the layers, one contact each of types Br⋯Br, H⋯Br and Br⋯π is observed.

Synthesis, structural analysis, and chiral investigations of some atropisomers with EE-tetrahalogeno-1,3-butadiene core

The atropenantiomers of stable 1,2,3,4-tetrahalo-1,3-butadiene derivatives (where halogeno stands for bromine or iodine) were separated with use of chiral HPLC. The barriers for the enantiomerization process were determined on-line by dynamic HPLC (DHPLC) or off-line by classical kinetic measurements. In the case of the tetrachloro compound, the barrier was too low for DHPLC and its value was obtained by dynamic NMR experiments. The obtained barriers for chloro, bromo, and iodo derivatives correlate with the van der Waals radii of the halogens. The absolute configuration of the isolated enantiomers of the tetraiodo and tetrabromo compounds was assigned by comparison of the experimental and conformations averaged calculated VCD spectra. The identification of a signature band of the absolute configuration of the butadiene core, the sign and location of which are independent from the different conformations and substituents, allowing the safe assignment of the absolute configuration of the enantiomers of chiral 1,3-butadienes, is also reported.

Structure and structural transition of chiral domains in oligo(p-phenylenevinylene) assembly investigated by scanning tunneling microscopy

OPV3-CHO molecules are employed to prepare assembly on highly oriented pyrolytic graphite, and the so-prepared assembly is investigated by scanning tunneling microscopy. In the assembly chiral domains are observed with various structures such as linear and windmill. The chiral structural formation, stability, transition, and possible unification are intensively studied. After thermal annealing, linear structure was the only structure. To achieve a unified assembly with a single structure, an efficient method is proposed by coadsorption of OPV3-CHO with selected molecules. For example, an assembly with side-by-side helix structure is formed by a simple coadsorption of OPV3-CHO with alkyl bromide (C(n)H(2n+1)Br, n = 15-18). The experiments by cocrystallization of OPV3-CHO/C(n)H(2n+1)X (X = Cl, Br, and I) show the important role of halogen bonding in formation of the uniform structure. The results are significant in understanding the intermolecular noncovalent interactions that dominate the surface structure and chirality.

Complementary halogen and hydrogen bonding: sulfur⋯iodine interactions and thioamide ribbons

Complementary halogen bonding and hydrogen bonding coexist in co-crystals of organoiodines with molecules containing the thioamide functionality. Thiourea·organoiodine co-crystals are shown to exhibit a remarkably reliable synthon with complementary N–H⋯S ribbons and S⋯I interactions.

Controlled room temperature ROP of L-lactide by ICl3: a simple halogen-bonding catalyst

The ability of ICl₃ to activate electrophilic substrates through halogen bonding and its catalytic activity towards the ring-opening polymerization of L-lactide is demonstrated in this communication. Association of techniques highlights the production of narrowly dispersed PLA of predictable molecular weights from this commercially available molecule.

7-Benzyl-oxymethyl-9-bromo-6-chloro-9-deaza-purine

The title compound, C(14)H(11)BrClN(3)O, crystallizes with two independent mol-ecules in the asymmetric unit. In the crystal, the molecules are linked by C-N⋯Br halogen bonds, as well as weak methyl-ene C-H⋯π, phenyl C-H⋯π, C-H⋯Br and phenyl C-H⋯O(ether) inter-actions.

A mammalian reductive deiodinase has broad power to dehalogenate chlorinated and brominated substrates

Iodotyrosine deiodinase is essential for iodide homeostasis and proper thyroid function in mammals. This enzyme promotes a net reductive deiodination of 3-iodotyrosine to form iodide and tyrosine. Such a reductive dehalogenation is uncommon in aerobic organisms, and its requirement for flavin mononucleotide is even more uncommon in catalysis. Reducing equivalents are now shown to transfer directly from the flavin to the halogenated substrate without involvement of other components typically included in the standard enzymatic assay. Additionally, the deiodinase has been discovered to act as a debrominase and a dechlorinase. These new activities expand the possible roles of flavin in biological catalysis and provide a foundation for determining the mechanism of this unusual process.

Recent advances on structure-informed drug discovery of cyclin-dependent kinase-2 inhibitors

Serine and threonine kinases play an important role in signal-transduction pathways. Within this kinase family, cyclin-dependent kinase (CDK)2 is an attractive target for oncology involved in cell cycle regulation. In recent years, kinase inhibition has become a major area for therapeutic involvement. As we discuss here, these efforts have resulted in a considerable increase in the number of available high-resolution structures of CDK2–inhibitor complexes. A large amount of structural-based and computational work has allowed the identification of novel chemical scaffolds and structural motifs to design potent CDK2 inhibitors. Of any kinase, CDK2 has the most structures available from the protein databank, averaging 22 new structures per year since 2002. A protein–ligand interaction fingerprint analysis of the available CDK2 protein–ligand complexes indicates that structural diversity is attainable from the structure-based design of CDK2 inhibitors. Since the first CDK2 structure was published in 1996, seven new chemical entities (NCEs) have been advanced to clinical stages. To date, only three of these NCEs have had their complexes published in the protein databank. This review summarizes the structurally informed efforts in the field of CDK2 inhibitor design.

Molecular symmetry and isostructural relations in crystal phases of trihalomethanes CHCl3, CHBrCl2, CHBr2Cl, and CHBr3

Bromodichloromethane (CHBrCl(2)), dibromochloromethane (CHBr(2)Cl), and their parent trihalomethanes, chloroform (CHCl(3)) and bromoform (CHBr(3)), form an intriguing series of isostructural crystal phases, the sequence of which depends on the Br/Cl substitution and thermodynamic conditions. The phase behavior of these compounds has been studied by isobaric calorimetry and isothermal compression, and the crystal structure of CHBrCl(2) has been determined at 0.10 MPa/200 K, 0.73, 1.26, 2.53 GPa (all at 295 K), and that of CHBr(2)Cl at 0.43, 1.24 GPa (all at 295 K). CHBrCl(2) frozen by isobaric cooling at 0.10 MPa crystallizes in space group P1 with Z = 2, while its high-pressure polymorph in space group Pnma (Z = 4) is stable at 295 K from its freezing pressure at 0.48 to at least 2.53 GPa. At the freezing pressure of 0.29 GPa, CHBr(2)Cl crystallizes in space group P6(3), with Z = 2, and at 1.27 GPa, it transforms to the orthorhombic structure, space group Pnma (Z = 4); CHCl(3) has the identical symmetries, but their reverse sequence was observed. A subtle isostructural phase transition has been observed at 0.10 MPa and 214.9 K in CHBr(2)Cl. The relations between isostructural phases, their symmetry, and site occupation factors of halogen atoms observed in the low-temperature and high-pressure phases of trihalomethanes (CHCl(3), CHBrCl(2), CHBr(2)Cl, and CHBr(3)) have been explained by the directional character of electrostatic interactions between the molecules. A gradual ordering of the disordered Br and Cl atoms has been achieved in the compressed crystals, where the narrower volume of the atomic sites correlates with the increased occupancy of the smaller atom (chlorine). The molecular symmetry has been shown to control the molecular aggregation in the crystalline state, consistent with the crystal site-symmetry and the balance of electrostatic matching and dispersion forces between molecules.