Descripción: Two copper complex solvatomorphs, namely (3,10-C-meso-3,5,7,7,10,12,14,14- octamethyl-1,4,8,11-tetraazacyclotetradecane)bis(perchlorato-κO)copper(II) 1.2-hydrate, [Cu(ClO4)2(C18H 40N4)]·1.2H2O, (I), and (3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane) bis(perchlorato-κO)copper(II), [Cu(ClO4)2(C 18H40N4)], (II), are described and compared with each other and with a third, already reported, anhydrous diastereomer, denoted (III). Both compounds present very similar centrosymmetic coordination environments, with the CuII cation lying on an inversion centre in a distorted 4+2 octahedral environment, defined by the macrocyclic N4 group in the equatorial sites and two perchlorate groups in trans-axial positions [one of the perchlorate ligands in (I) is partially disordered]. The most significant difference in molecular shape is seen in the orientation of the perchlorate anions, and the influence of this on the intramolecular hydrogen bonding is discussed. The (partially) hydrated state of (I) favours the formation of chains along [011], while the anhydrous character of (II) and (III) promotes loosely bound structures with low packing indices. © 2013 International Union of Crystallography.

Descripción: The three transition-metal complexes, (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (perchlorato-κO)copper(II), [Cu(ClO4)2(C18H40N4)], (I), (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (nitrato-κO)zinc(II), [Zn(NO3)2(C18H40N4)], (II), and aqua chlorido (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetraazacyclo tetra decane-κ4 N)copper(II) chloride, [CuCl(C18H40N4)(H2O)]Cl, (III), are described. The mol ecules display a very similarly distorted 4+2 octa hedral environment for the cation [located at an inversion centre in (I) and (II)], defined by the macrocycle N4 group in the equatorial sites and two further ligands in trans-axial positions [two O-ClO3 ligands in (I), two O-NO2 ligands in (II) and one chloride and one aqua ligand in (III)]. The most significant difference in mol ecular shape resides in these axial ligands, the effect of which on the intra- and inter molecular hydrogen bonding is discussed. In the case of (I), all strong hydrogen-bond donors are saturated in intra molecular inter actions, while weak inter molecular C - H⋯O contacts result in a three-dimensional network. In (II) and (III), instead, there are N - H and O - H donors left over for inter molecular inter actions, giving rise to the formation of strongly linked but weakly inter acting chains. © 2013 International Union of Crystallography.

Descripción: The crystal structure of the title complex, [Ni(C3H4N2)6](C4H 4O5)·C2H5OH, is a tightly woven three-dimensional network composed of [Ni(Him)6]2+ cations (Him is imidazole) interlinked by the oxydiacetate anion through six different N-H⋯O bonds, in which all the N-H imidazole groups, as well as all the carboxylate O atoms, take part. This structure is the first to show an [Ni(Him)6]2+ group which does not display any crystallographic symmetry. © 1999 International Union of Crystallography.

Descripción: The title complex, aqua(2,2′-bipyridy-N,N′(3-thiapentanedioate-O,S,O′)zinc(II) tetrahydrate, [Zn(C4H4-O4S)(C10H8N 2)(H2O)].4H2O, is mononuclear with a coordination sphere consisting of one S, two N and three O atoms. The Zn atom is linked to a tridentate thiodiacetate ligand, a bidentate 2,2′-bipyridine ligand and an aqua ligand resulting in a slightly distorted octahedral coordination geometry. The molecular units are linked together in the crystal by an extensive hydrogen-bonding network and by intermolecular S⋯S interactions.

Descripción: The title compound, C 9H 14N +· CHB 11Cl 11 -, was obtained in the course of our continuing studies of the low-melting salts of closo- and nido-carborane cage anions with alkyl-pyridinium and dialkyl-imidazolium cations. The title compound is the first example of a pyridinium salt of a perchlorinated carborane anion. The structure consists of one N-butyl-pyridinium cation counterbalanced by one perchlorinated carborane cage anion per asymmetric unit. By changing the counter-ion, different packings are observed, and to try to understand this the new structure is compared with five similar compounds. © 2011 International Union of Crystallography.

Descripción: A new polymeric phase of zinc(II) oxydiacetate, catena-poly[[[diaquazinc(II)]-μ-oxydiacetato] hydrate], {[Zn(C4H4-O5)(H2O)2] ·H2O}n, isomorphous with the Co homologue [Hatfield, Helms, Rohrs, Singh, Wasson & Weller (1987). Proc. Indian Acad. Sci. Chem. Sci. 98, 23-31], is reported. It presents a chain-like structure, generated by ZnO6 cores which are bridged by carboxylate groups in an anti-anti conformation along the unique crystallographic b axis. The chains are held together through hydrogen-bonding interactions with the three water molecules.

Descripción: The crystal structure of the dimeric title compound, C19H 22O5H, is dominated by a head-to-head hydrogen-bonding inter-action between centrosymmetrically related carboxyl groups in each monomer. The result is a dimeric axis of unusual length (ca 34 Å), but still shorter than what could be expected for a fully extended chain, owing to two turning points in the oligo-eth-oxy ends. This allows for an explanation of the structure of the smectic mesophase exhibited by this compound and at the same time fully validates former geometric estimations based on PM3 calculations. © 2009 International Union of Crystallography.

Descripción: The crystal structure of the title compound, C12H8-N2O6S, has been determined by single-crystal X-ray diffraction. The compound crystallizes in the noncentrosymmetric P21 space group. The substituted aromatic ring has a slightly deformed boat conformation. The ο-NO2 and p-NO2 groups are twisted out of the plane of the phenyl ring. The unsubstituted aromatic ring is planar and the dihedral angle between the mean plane of the rings is 71.1 (2)○. Short C - H⋯O intermolecular contacts stabilize the three-dimensional structure.

Descripción: An interesting case of 'halogen-bonding-promoted' crystal structure architecture is presented. The two title compounds, C8H8Br2O2 and C8H8I2O2, have almost indistinguishable mol-ecular structures but very different spatial organization, and this is mainly due to differences in the halogen-bonding inter-actions in which the different species present, i.e. Br and I, take part. The dibromo structure exhibits a π-bonded columnar array involving all four independent mol-ecules in the asymmetric unit, with inter-columnar inter-actions governed by C - Br⋯Br - C links and with no C - Br⋯O/N inter-actions present. In the diiodo structure, instead, the C - I⋯O synthon prevails, defining linear chains, in turn inter-linked by C - I⋯I - C inter-actions. © 2008 International Union of Crystallography.

Descripción: The major cAMP receptors in eukaryotes are the regulatory (R) subunits of PKA, an allosteric enzyme conserved in fungi through mammals. While mammals have four R-subunit genes, Saccharomyces cerevisiae has only one, Bcy1. To achieve a molecular understanding of PKA activation in yeast and to explore the evolution of cyclic-nucleotide binding (CNB) domains, we solved the structure of cAMP-bound Bcy1(168-416). Surprisingly, the relative orientation of the two CNB domains in Bcy1 is very different from mammalian R-subunits. This quaternary structure is defined primarily by a fungi-specific sequence in the hinge between the αB/αC helices of the CNB-A domain. The unique interface between the two CNB domains in Bcy1 defines the allosteric mechanism for cooperative activation of PKA by cAMP. Some interface motifs are isoform-specific while others, although conserved, play surprisingly different roles in each R-subunit. Phylogenetic analysis shows that structural differences in Bcy1 are shared by fungi of the subphylum Saccharomycotina. © 2010 Elsevier Ltd.

Descripción: In contrast to the wide spectrum of cytochrome P450 monooxygenases, there are only 2 heme-based dioxygenases in humans: tryptophan dioxygenase (hTDO) and indoleamine 2,3-dioxygenase (hIDO). hTDO and hIDO catalyze the same oxidative ring cleavage reaction of L-tryptophan to N-formyl kynurenine, the initial and rate-limiting step of the kynurenine pathway. Despite immense interest, the mechanism by which the 2 enzymes execute the dioxygenase reaction remains elusive. Here, we report experimental evidence for a key ferryl intermediate of hIDO that supports a mechanism in which the 2 atoms of dioxygen are inserted into the substrate via a consecutive 2-step reaction. This finding introduces a paradigm shift in our understanding of the heme-based dioxygenase chemistry, which was previously believed to proceed via simultaneous incorporation of both atoms of dioxygen into the substrate. The ferryl intermediate is not observable during the hTDO reaction, highlighting the structural differences between the 2 dioxygenases, as well as the importance of stereoelectronic factors in modulating the reactions.

Descripción: The isomorphous title compounds, [Tr(S4O6)(C 12H12N2)2]·2C 3H7NO (Tr = CdII and ZnII), consist of metal centres to which one tetrathionate and two 4,4′-dimethyl-2, 2′-bipyridine chelating ligands bind. The structures are completed by two symmetry-related dimethylformamide solvent molecules. Each metal-centred complex is bisected by a twofold axis running through the metal centre and halving the chelating tetrathionate dianion through the central S - S bond. The ancillary symmetry-related 4,4′-dimethyl-2,2′-bipyridine ligands act as chelates. This results in a distorted six-coordinate geometry, with similar Tr - O/N distances but central angles differing substantially from 90 and 180°. Both ligands are basically featureless from a geometric point of view, with torsion angles in both coordinated tetrathionate groups suggesting a trend linking metal size (covalent radius) and ligand 'openness'. Packing is directed by (C - H)aromatic⋯O bridges and π-π offset stacked interactions defining chains along [001], further linked by weaker (C - H)methyl⋯O bridges, some of them mediated by the dimethylformamide solvent molecules. © 2013 International Union of Crystallography.

Descripción: The energetic contributions of individual DNA-contacting side chains to specific DNA recognition in the human papillomavirus 16 E2C-DNA complex is small (less than 1.0 kcal mol-1), independent of the physical and chemical nature of the interaction, and is strictly additive. The sum of the individual contributions differs 1.0 kcal mol-1 from the binding energy of the wild-type protein. This difference corresponds to the contribution from the deformability of the DNA, known as "indirect readout." Thus, we can dissect the energetic contribution to DNA binding into 90% direct and 10% indirect readout components. The lack of high energy interactions indicates the absence of "hot spots," such as those found in protein-protein interfaces. These results are compatible with a highly dynamic and "wet" protein-DNA interface, yet highly specific and tight, where individual interactions are constantly being formed and broken. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: The truncated hemoglobin N, HbN, of Mycobacterium tuberculosis is endowed with a potent nitric oxide dioxygenase (NOD) activity that allows it to relieve nitrosative stress and enhance in vivo survival of its host. Despite its small size, the protein matrix of HbN hosts a two-branched tunnel, consisting of orthogonal short and long channels, that connects the heme active site to the protein surface. A novel dual-path mechanism has been suggested to drive migration of O 2 and NO to the distal heme cavity. While oxygen migrates mainly by the short path, a ligand-induced conformational change regulates opening of the long tunnel branch for NO, via a phenylalanine (PheE15) residue that acts as a gate. Site-directed mutagenesis and molecular simulations have been used to examine the gating role played by PheE15 in modulating the NOD function of HbN. Mutants carrying replacement of PheE15 with alanine, isoleucine, tyrosine and tryptophan have similar O 2 /CO association kinetics, but display significant reduction in their NOD function. Molecular simulations substantiated that mutation at the PheE15 gate confers significant changes in the long tunnel, and therefore may affect the migration of ligands. These results support the pivotal role of PheE15 gate in modulating the diffusion of NO via the long tunnel branch in the oxygenated protein, and hence the NOD function of HbN. © 2012 Oliveira et al.

Descripción: The structures of three new polymeric lanthanide complexes, poly[[bis-(2,2′-bipyridine)-μ4-itaconato-di-μ3-itaconato- digadolinium(III)] tetra-hydrate], {[Gd 2(C 5H 4O 4) 3(C 10H 8N 2) 2]̇4H 2O} n , (I),poly[diaqua-(2,2′- bipyridine)di-μ3-itaconato-μ2-ita-conato-digadolinium(III)], [Gd 2(C 5H 404) 3(C 10H 8N 2)(H 2O) 2] n , (II), and poly-[[bis-(2,2′-bipyridine)-μ4-itaconato-di-μ3-itaconato-di- holmium(III)] dihydrate], {[Ho 2(C 5H 4O 4) 3(C 10H 8N 2) 2]̇2H2O} n , (III), have been solved from twinned specimens. Compound (I) presents a two-dimensional polymeric structure parallel to (011) built up around two independent nine-coordinated Gd centres displaying similar GdO 7N 2 environments, with both N-donor atoms in each provided by a chelating 2,2′-bipyridine (bpy) unit. The coord-inating O atoms are from three different itaconate (ita) anions (itaconic acid is 2-methyl-idene-butane-dioic acid). Compound (II) also presents two independent Gd centres (one ten- and the other ight-coordinated), but the overall formula and individual coordinations are different from those of (I). The chemical unit is in this case completed by one bpy ligand, three ita anions (one of them displaying a new, hitherto unreported, mu;3-O,O′:O′,O′′: O′′′ binding mode) and two aqua ligands. The whole structure is built up around a twofold rotation axis passing through both cations, as well as through the centre of the bpy ligand and one of the ita anions, thus making only half of the chemical unit independent. Finally, compound (III) presents a single independent Ho centre, a bpy unit and one and a half ita anions (one of them bisected by a twofold rotation axis) in the asymmetric unit, plus two (disordered) nonbonded solvent water mol-ecules. In compounds (II) and (III), those ita anions bisected by a symmetry element incompatible with the inter-nal symmetry of the ligand exhibit disorder in the C=CH 2 group. © 2009 International Union of Crystallography.