The solution structure of bis(acetylacetonato)oxovanadium(IV)

The behaviour of the bis-chelated oxovanadium(IV) complexes formed by acetylacetone (acac) and five of its derivatives was re-examined through a combination of spectroscopic methods in different solvents. It has been found that the complexes are penta-coordinated with a geometry close to the square pyramid and maintain in solution the same structure as in the solid state. The results rule out a cis-trans isomerism of the species VOL₂S (L = acac or derivative, S = solvent) in solution. Depending on the coordinating ability of the solvent a sixth molecule can be bound, more or less strongly, to the free axial position of the complexes. The combined application of the electronic absorption and IR spectroscopies allows to establish if the complexes in solution are penta- or hexa-coordinated.     

Re(CO)(3)(H(2)O)(3)(+) binding to lysozyme: structure and reactivity

The reaction of Re(CO)(3)(H(2)O)(3)(+) with hen egg white lysozyme in aqueous solution results in a single covalent adduct. Both NMR spectroscopy and single crystal X-ray diffraction show that the rhenium tricarbonyl cation binds to His15 via replacement of one of the coordinated water molecules. The formation of this adduct does not greatly affect the structure of the protein.     

Molecular and crystal structure of (1----3)-alpha-D-glucan triacetate.

A crystal and molecular structure for GTA I, the low temperature polymorph of (1----3)-alpha-D-glucan triacetate, is proposed on the basis of X-ray diffraction analysis of well-oriented films, combined with stereochemical model refinement. The unit cell is monoclinic with parameters a = 30.17 A, b = 17.42 A, c (fibre axis) = 12.11 A, and beta = 90 degrees C. The probable space group is P2(1) with b axis unique. Six molecular chains pass through the unit cell with alternating polarity and with three independent chains comprising the asymmetric unit. The chain axes are located in a hexagonal packing arrangement. The chain backbone conformation is a left-handed, three-fold helix, but all nine O(6) acetyl groups of the asymmetric unit are in non-equivalent rotational positions. The most probable structure is indicated by X-ray residuals R = 0.261 and R" = 0.283, based on 62 reflection intensities (41 observed and 21 unobserved).     

Isomer abundance of bis(beta-diketonato) complexes of titanium(IV). Crystal structures of the antitumor compound budotitane [Ti(IV)(bzac)(2)(OEt)(2)] and of its dichloro-derivative [Ti(IV)(bzac)(2)Cl(2)] (bzac=1-phenylbutane-1,3-dionate)

The molecular tumor inhibiting titanium compound budotitane [Ti(IV)(bzac)(2)(OEt)(2)] (1) and its dichloro-derivative [Ti(IV)(bzac)(2)Cl(2)] (2) (bzac=1-phenylbutane-1,3-dionate) have been crystallized and characterized by X-ray crystallography and further physical methods. Budotitane (1) crystallizes in the tetragonal, non-centrosymmetric space group P4(1) with two molecules in the asymmetric unit. Both molecules adopt the cis-cis-trans configuration with the acetyl ends of the benzoylacetonate ligands in the trans position. The dichloro-derivative of budotitane, [Ti(IV)(bzac)(2)Cl(2)] (2) crystallizes in the monoclinic, centrosymmetric space group P2(1)/n with one molecule only in the asymmetric unit. In contrast to budotitane (1), (2) shows a cis-trans-cis arrangement with the benzoyl groups in the trans position. In both complexes there are equal numbers of Delta and Lambda enantiomers within the unit cell. The phenyl groups in (1) as well as in (2) are in approximately coplanar conjugation to the metal enolate rings. The thermal degradation of budotitane (1) was investigated in the temperature range from 25 degrees C up to 800 degrees C and reveals the formation of Ti(IV)O(bzac(2-)) as an intermediate and of the rutile phase of TiO(2) as a final product. It may be worthwhile to introduce budotitane in the form of isomerically pure crystals in the preparation of the drug used for future tests.     

The preparation and crystal structure analysis of bis(L-Arginine)Cu(II)(acetate)2trihydrate

The crystal structure of bis(L-arginine)Cu(II)(acetate)₂trihydrate has been determined by X-ray analysis. The complex crystallizes in the monoclinic space group P2₁, with cell dimensions a = 15.948(2), b = 16.878(2), c = 10.378(2) Å, β = 108.47(1)°, Z = 4. There are two independent formula units in the asymmetric unit. The Cu atoms were located from a Patterson synthesis and the remaining atoms from difference Fourier syntheses. The structure was refined by least-squares to R = 0.079 and R = 0.11. Each copper atom has an essentially square planar coordination with the two arginine molecules chelated via the carboxy oxygens and the α-amino nitrogens, but with distorted six-fold coordinations completed by weak Cu…O (acetate) interactions. Electrostatic interactions between the acetates and the protonated ends of the amino acid residues link the two independent [Cu(L-arginine)₂(acetate)₂] units into dimers, which are then connected via hydrogen bonds, also involving the water molecules, into an infinite network.     

Nuclease activity of [Cu(sulfathiazolato)(2)(benzimidazole)(2)]2MeOH. Synthesis, properties and crystal structure

The [Cu(sulfathiazolato)(2)(benzimidazole)(2)]2MeOH complex has been synthesised and characterised. It crystallises in the monoclinic system, space group C1c1, with unit cell dimensions a=18.829(7) A, b=12.206(3) A, c=17.233(5) A, alpha=90.06(2) degrees, beta=97.28(3) degrees, gamma=90.21(3) degrees and Z=4. The geometry around the copper(II) ion is intermediate between tetrahedral and square planar. The complex produces cleavage of plasmid pUC18 in presence of reducing agents. The efficiency of cleavage reaction of the title compound with pUC18 and with different reducing agents follows the order ascorbate-H(2)O(2)>ascorbate>MPA>dithiothreitol>H(2)O(2).     

Molecular structure, bioavailability and bioactivity of [Cu(o-phen)2(cnge)](NO3)2.2H2O and [Cu(o-phen)(cnge)(H2O)(NO3)2] complexes

Two Cu(II) complexes with cyanoguanidine (cnge) and o-phenanthroline, [Cu(o-phen)(2)(cnge)](NO(3))(2).2H(2)O (1) and [Cu(o-phen)(cnge)(H(2)O)(NO(3))(2)] (2), have been synthesized using different experimental techniques and characterized by elemental analyses, FTIR, diffuse and UV-vis spectra and EPR and magnetic moment measurements techniques. The crystal structures of both complexes were solved by X-ray diffraction methods. Complex (1) crystallizes in the monoclinic space group C2/c with a=12.621(5), b=31.968(3), c=15.39(1)A, beta=111.68(4) degrees, and Z=8 and complex (2) in the monoclinic space group P2(1)/n with a=10.245(1), b=13.923(2), c=12.391(2)A, beta=98.07(1) degrees, and Z=4. The environments of the copper(II) center are trigonal bipyramidal (TBP) for [Cu(o-phen)(2)(cnge)](2+) and an elongated octahedron for [Cu(o-phen)(cnge)(H(2)O)(NO(3))(2)]. Solution studies have been performed to determine the species distribution. The superoxide dismutase (SOD) activities of both complexes have also been tested in order to determine if these compounds mimic the enzymatic action of the enzyme SOD that protects cells against peroxide radicals.     

The crystal structure of delta(3)-delta(2)-enoyl-CoA isomerase

The active-site geometry of the first crystal structure of a Delta(3)-Delta(2)-enoyl-coenzyme A (CoA) isomerase (the peroxisomal enzyme from the yeast Saccharomyces cerevisiae) shows that only one catalytic base, Glu158, is involved in shuttling the proton from the C2 carbon atom of the substrate, Delta(3)-enoyl-CoA, to the C4 atom of the product, Delta(2)-enoyl-CoA. Site-directed mutagenesis has been performed to confirm that this glutamate residue is essential for catalysis. This Delta(3)-Delta(2)-enoyl-CoA isomerase is a hexameric enzyme, consisting of six identical subunits. It belongs to the hydratase/isomerase superfamily of enzymes which catalyze a wide range of CoA-dependent reactions. The members of the hydratase/ isomerase superfamily have only a low level of sequence identity. Comparison of the crystal structure of the Delta(3)-Delta(2)-enoyl-CoA isomerase with the other structures of this superfamily shows only one region of large structural variability, which is in the second turn of the spiral fold and which is involved in defining the shape of the binding pocket.     

Molecular and crystal structure of the regenerated form of (1----3)-alpha-D-mannan.

The crystal structure of the hydrated form of (1----3)-alpha-D-mannan, obtained by solid-state deacetylation of the partially O-acetylated mannan, was analyzed by combined X-ray diffraction and stereochemical-model refinement techniques. The structure crystallizes in a four-chain, monoclinic unit cell with parameters a = 11.33 A, b = 18.36 A, c (fiber repeat) = 8.25 A, and gamma = 101.75 degrees, and the most probable space group is P2(1). In the most probable structure the chain-backbone conformation is a two-fold helix, but with all four O-6 rotational positions nonequivalent. The chains pack with antiparallel polarity and are connected by pairs of intermolecular hydrogen bonds that form an infinite, zig-zag sheet. There are 16 water molecules in the unit cell, generally embedded between the sheets in crystallographic positions, providing additional hydrogen bonding and establishing a three-dimensional hydrogen-bond network in the crystal structure. The reliability of the structure analysis is indicated by the X-ray residual R" = 0.281, based on 98 hkl reflection intensities.     

The structure and antiviral activity of ribavirin analogs. III. Molecular and crystal structure of 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-carboxamide

The crystal and molecular structure of a ribavirin acyclic analogue, 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-3-carboxamide, has been determined by X-ray diffraction method. The space group is P1, unit cell parameters: a = 5,237, b = 6,960, c = 11,483 A, alpha = 93,89, beta = 97,43, gamma = 94,26 degrees; Z = 2. The structure was solved by the direct method and refined by least-squares procedure to R = 3.7%. Two molecular conformers statistically coexist in the unit cell, differing in the hydroxyethoxymethyl group conformation. Trans-conformation about O4'-C4' bond and gauche about C4'-C5' bond are observed in both molecules. C1'-O4' bond is approximately perpendicular to the aglicon.     

The crystal and molecular structure of tri-o-ethylamylose (tea 3)

The crystal and molecular structure of a tri-O-ethylamylose polymorph, TEA 3, has been solved by stereochemical conformation and packing analysis, combined with X-ray fibre diffraction analysis. The unit cell is orthorhombic, space group P2₁2₁2₁, with a  15.36 (±0.03) Å, b  12.18 (±0.05) Å, and c (fibre repeat)  15.48 (±0.01) Å. The actual chain conformation is a 4₃ helix with the EtO-6 group in the tg position, as was found in the polymorph TEA 1.     

Synthesis and spectroscopic studies of mono(cyclopentadienyl)titanium(IV) derivatives with heterocyclic thioketones

The reactions of mono(cyclopentadienyl)titanium(IV) trichloride with two different classes of heterocyclic thioketones viz. 1-substituted-2-thiohydantoins and 1-substituted tetrazoline-5-thione were studied in anhydrous dichloromethane. The reaction products were characterized on the basis of elemental analyses electrical conductance, magnetic susceptibility and spectral (electronic, infrared and ¹H NMR) data.     

Triboluminescence and crystal structure of the centrosymmetric complex [Tb(NO3)2(Acac)(Phen)2]·H2O

The atomic structure of crystals of the complex [Tb(NO₃)₂(Acac)(Phen)₂]·H₂O, (AA – acetylacetonate anion, Phen – 1,10‐phenanthroline) characterized by an intensive luminescence and triboluminescence has been determined by means of an X‐ray structural analysis method. Centrosymmetric crystals have a monoclinic syngony: a = 11.2298(1), b = 9.6492(1), c = 13.2745(1) Å, β = 101.290(1), space group P2/n, Z = 2, ρ_calc = 1.790 g/cm³. The crystal structure is represented by individual С₂₉Н₂₅N₆O₉Tb complexes linked through van der Waals interactions with clearly expressed cleavage planes. The Tb(III) atom coordination polyhedron reflects the state of a distorted square antiprism. The structural aspects of the suggested model of formation of the triboluminescent properties were considered and the role of the cleavage planes discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Speciation study of the anti-inflammatory drug tenoxicam (Htenox) with Cu(II): X-ray crystal structure of [Cu(tenox)(2)(py)(2)].EtOH

A speciation study was carried out in aqueous solution of the anti-inflammatory drug tenoxicam (Htenox), under quasi-physiological conditions (temperature of 37 degrees C and ionic strength 0.15 M NaCl) in order to determine the acidity constants from spectrophotometric studies, the pK(a) values found being pK(1)=1.143+/-0.008 and pK(2)=4.970+/-0.004. Subsequently, the spectrophotometrical speciation of the different complexes of Cu(II) with the drug was performed under the same conditions of temperature and ionic strength, observing the formation of Cu(Htenox)(2)(2+) with log beta(212)=20.05+/-0.01, Cu(tenox)(2) with log beta(012)=13.6+/-0.1, Cu(Htenox)(2+) with log beta(111)=10.52+/-0.08, as well as Cu(tenox)(+) with log beta(011)=7.0+/-0.2, all of them in solution, and solid species Cu(tenox)(2)(s) with an estimated value of log beta(012)(s) approximately 18.7. The crystalline structure of the complex [Cu(tenox)(2)(py)(2)]. EtOH, was also determined, and it was observed that tenoxicam employs the oxygen of the amide group and the pyridyl nitrogen to bond to the cation.     

The structure and antiviral activity of ribavirin analogs. II. Molecular and crystal structure of 1-(1,5-dihydroxy-3-oxapent-2-yl)-1,2,4-triazole-5-carboxamide

X-ray structure of the title compound, an antiviral agent moderately active towards Herpes simplex virus type 1, has been determined. The space group is P2i/n, unit cell parameters: a = 10,119, b = 7,529, c = 13,585 A, beta = 107,82 degrees, Z = 4. The structure was solved by the direct method and refined by least-squares procedure to R = 2.9%. The gauche-conformation about C4'-C5' bond and trans-conformation about O4'-C4' bond are realized in the molecule. The carboxyamide group at the C5 atom of triazol cycle provides a steric opportunity for the intramolecular hydrogen bond C1'-H1'...O6 formation.     

Synthesis, characterization and crystal structure of novel mononuclear peroxotungsten(VI) complexes. Insulinomimetic activity of W(VI) and Nb(V) peroxo complexes

Two new mononuclear peroxo complexes of tungsten of the formula (gu)₂[WO₂(O₂)₂] (1) and (gu)[WO(O₂)₂(quin-2-c)] (2a) (where gu⁺ = guanidinium ion, and quin-2-c = quinoline-2-carboxylate ion) have been synthesized and characterized by elemental analysis, infrared, Raman, UV-visible and ¹H NMR spectroscopies. The crystal structure of (gu)[WO(O₂)₂(quin-2-c)] · H₂O (2b) determined by X-ray diffraction indicates that the side-on peroxo groups and the bidentate quinaldate ligand bind the W(VI) centre leading to an hepta coordination mode. The guanidinium ion occurring as a counterion and the hydrogen-bound interactions stabilize the complexes. The in vitro insulin-mimetic effect of the complexes has been evaluated by the inhibitory effect on free fatty acid release in isolated fat adipocytes treated with epinephrine. Moreover the niobate analogues, synthesized and characterized previously, (gu)₃[Nb(O₂)₄] and (gu)₂[Nb(O₂)₃(quin-2-c)] · H₂O have been tested for the insulin-like activity.     

Syntheses and crystal structures of dimethyltin (IV) derivatives with 2,6-pyridinedicarboxylic acid

A novel cyclic dimethyltin complex [Me₂Sn(2,6-pdc)]₃ (1) (2,6-pdc = 2,6-pyridinedicarboxylate) was synthesized by the reaction of dimethyltin (IV) dichloride and 2,6-pyridinedicarboxylate acid in methanol under solvothermal conditions (150 °C). However, under room temperature (25 °C), we obtained a ladder complex [Me₂Sn(2,6-pdc)]₂(MeOH)₂ (2). Characterization of complexes 1 and 2 was achieved using elemental analysis, IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectra and X-ray diffraction. X-ray data of 1 revealed that it was an unusual cyclic complex with a discrete cyclotrinuclear unit, in which the 12-membered cyclic cavity is almost completely planar. X-ray data of 2 showed that it was a ladder complex, in which a crystallizing methanol molecule is found in each formula unit.     

The structure and antiviral activity of ribavirin analogs. I. Molecular and crystal structure of 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-5-carboxamide

The crystal and molecular structures of the antiviral compound 1-(2-hydroxyethoxymethyl)-1,2,4-triazole-5-carboxamide has been determined by the X-ray diffraction method. The space group is P2i/c, unit cell parameters a = 4,381, b = 18,679, c = 10,776 A, beta = 107,40 degrees, Z = 4. The structure was solved by the direct method and refined by a full-matrix least-squares procedure to R = 4.9%. Two planar groups of atoms can be distinguished in the molecule. The first group involves the atoms of triazole ring, C6, and C1', the second one contains C5, C6, O6 and N6 atoms. The angle between these planes is 5.6 degrees. The carboxyamide group is rotated by 180 degrees in comparison with this group in ribavirin. That is why the intramolecular hydrogen bond C1'-H1'. 1...O6 can form. Torsion angle O5'-C5'-C4'-O4' is 73.9 degrees and it corresponds to gauche-rotamer. The conformation about O4'-C4' bond is trans. The C1'-C4' bond is approximately perpendicular to the aglycone.