Three metal(II) complexes constructed using the 2-(1H-benzo[d]imidazol-2-yl)quinoline ligand

2-(1H-benzo[d]imidazol-2-yl)quinoline (BQ) as ligand and three coordination compounds of formula {Zn(BQ)Cl2} (1), {Pb(BQ)Cl2} n (2) and {[Cu(BQ)2(OC(O)CH3)]OC(O)CH3 · CH3COOH} (3) have been synthesized and fully characterized. The complexes crystallize in triclinic space group P 1 ‾ $P‾{1}$ . In complexes 1 and 2, the coordination geometry is a distorted tetrahedral environment around the zinc center and a distorted sixfold coordination geometry around the lead center, respectively. In complex 3 the central Cu(II) center is in a trigonal bipyramidal coordination geometry. The Cu(II) ion is surrounded by two bidentate 2-(2′-quinolyl)benzimidazole (BQ) ligands and one coordinated acetate molecule. One further acetate anion associated by a strong hydrogen bond with a molecule of acetic acid balances the charge of the compound.

Palladium-catalyzed microwave-assisted Hirao reaction utilizing the excess of the diarylphosphine oxide reagent as the P-ligand; a study on the activity and formation of the “PdP2” catalyst

The microwave-assisted Hirao reaction of bromobenzene and diarylphosphine oxides was performed at 120 °C using triethylamine as the base, and 5% of palladium acetate as the catalyst in ethanol. 5% Excess of the >P(O)H reagent served as the reducing agent, while another 10% as the preligand (in the >POH tautomeric form). It was found that the P–C coupling reaction was significantly faster with (2-MeC6H4)2P(O)H (A) and (3,5-diMeC6H3)2P(O)H (B), than with Ph2P(O)H (C) and (4-MeC6H4)2P(O)H (D). Moreover, species A and B could be applied as selective P-ligands in the reaction of bromobenzene with C or D. Dependence of the effectiveness of “PdP2” catalysts with diarylphosphine oxide preligands on the methyl substituents followed a reversed order as the reactivity of the diarylphosphine oxide species in the P–C coupling itself. Formation of the “PdP2” catalyst from palladium acetate and diarylphosphine oxide has never been studied, but now it was evaluated by us at the B3LYP level of theory applying 6-31G(d,p) for C,H,P,O and SDD/MW28 for Pd including the explicit-implicit solvent model. The novel mechanism requiring three equivalents of the >P(O)H species for each of the palladium acetate molecule was in agreement with the preparative experiments. The ligation of palladium(0) with different P(III) species comprising the >POH form of the >P(O)H reagent was also studied, and the critical role of the steric hindrance on the ligation, and hence on the activity of the “PdP2” catalyst was substantiated. Last but not least, the influence of the Me substituents in the aromatic ring of the P-reagents on the energetics of the elemental steps of the Hirao reaction itself was also evaluated.

Crystal structure of 4-{(E)-[2-(pyridin-4-ylcarbonyl)hydrazin-1-ylidene]methyl}phenyl acetate monohydrate

The asymmetric unit of the title compound, C15H13N3O3·H2O, comprises a 4-{(E)-[2-(pyridin-4-ylcarbonyl)hydrazinylidene]methyl}phenyl acetate molecule and a solvent water molecule linked by O—H...O and O—H...N hydrogen bonds from the water molecule and a C—H...O contact from the organic molecule. The compound adopts anEconformation with respect to the azomethine bond and the dihedral angle between the pyridine and benzene rings is 21.90 (7)°. The azomethine bond [1.275 (2) Å] distance is very close to the formal C=N bond length, which confirms the azomethine bond formation. An extensive set of O—H...O, O—H...N, N—H...O and C—H...O hydrogen bonds builds a two-dimensional network progressing along thecaxis.

{5′-O-[Bis(4-methoxyphenyl)(phenyl)methyl]-2′-deoxy-β-D-threopentofuranosyl}thymine ethyl acetate 0.25-solvate

The title compound, C31H32N2O7·0.25C4H8O2, is a key intermediate in the synthesis of [18F]fluorine-labelled thymidine (18F-FLT), which is the most widely used molecular imaging probe for positron emission tomography (PET). The crystallographic asymmetric unit contains two independent thymine molecules plus one partially occupied site for an ethyl acetate molecule. The two independent thymine molecules show similar geometrical features, except that the dimethoxytrityl groups adopt different orientations with respect to the remainder of the molecule. Each thymine base adopts ananticonformation with respect to the attached deoxyribose ring, and the deoxyribose rings show C3-endopuckering. The conformation of the side chain at the C1 position of the deoxyribose ring isgauche+. Intermolecular N—H...O and O—H...O hydrogen bonds link the molecules into one-dimensional chains.

Analysis of the Loading and Hydroxylation Steps in Lankamycin Biosynthesis in Streptomyces rochei

ABSTRACT The biosynthetic gene cluster of lankamycin (LM), a 14-member macrolide antibiotic, is encoded on the 210-kb linear plasmid pSLA2-L in Streptomyces rochei 7434AN4. LM contains a 3-hydroxy-2-butyl group at the C-13 position, which is different from an ethyl group in erythromycin. The following two possibilities could be considered for the origin of this starter moiety of LM biosynthesis: (i) an extra module exists in the biosynthetic gene cluster and loads an additional acetate molecule, or (ii) 3-hydroxy-2-butyrate or its equivalent is loaded and incorporated as a starter. The former possibility was eliminated by the complete sequencing of pSLA2-L, which showed no extra module. On the other hand, the latter was confirmed by incorporation of deuterium in [3-2H]dl-isoleucine into the C-14 position of LM. The timing of hydroxylation reactions at the C-15 and C-8 positions of LM was studied by constructing disruptants of two P450 hydroxylase genes, lkmF (orf26) and lkmK (orf37). The lkmF disruptant produced 8-deoxylankamycin, while the lkmK disruptant produced both 15-deoxylankamycin and 8,15-dideoxylankamycin. These results clearly showed that LkmF is a C-8 hydroxylase and LkmK is a C-15 hydroxylase in LM biosynthesis and in addition suggested the order of hydroxylation steps; namely, hydroxylation may occur at first at C-15 by LkmK and then at C-8 by LkmF.

4-Oxo-2,3,5,6-tetraphenylpiperidine-1-carbonitrile ethyl acetate hemisolvate

In the title compound, C30H24N2O·0.5C4H8O2, the piperidone ring adopts the chair conformation and all the phenyl rings are equatorially oriented. The ethyl acetate molecule is present as a space filler and does not participate in the hydrogen-bonding network. The crystal structure is stabilized through C—H...N and C—H...O hydrogen bonds. No significant C—H...π and π–π interactions are observed.

Superexchange in copper acetates

It was demonstrated in the preceding papers that the antiferromagnetic exchange coupling in a binuclear cobalt carboxylate is dominated by a superexchange mechanism via the carboxylate n bonds. In the present paper it is argued th at a similar process can account for all ground state properties of the structurally analogous, copper acetate molecule. The magnitudes, temperature-dependences and orientations of the principal magnetic susceptibilities can all be reproduced within this superexchange model. The g-values and zero-field splitting, previously considered to demonstrate the presence of a weak 8 bond between the copper atoms, have been shown to furnish no proof whatever of any particular coupling mechanism, provided there is an(x 2 - y 2 ground state for the copper atoms. The superexchange mechanism proposed is made possible essentially not via spin-orbit mixing of {xy) and (x 2 y 2) — states but via configurational mixing of such functions caused by the close proximity of the second metal atom.

Interferometric studies in diffusion. II. Influence of concentration and orientation on diffusion in cellulose acetate

The techniques developed in part I are used to study the diffusion of the five penetrants, chloroform, acetone, methylene chloride, water and methyl alcohol into stretched cellulose acetate sheet. The diffusion coefficient—concentration relationship for diffusion at right angles to the direction of stretch is obtained at 25° C for the first three penetrants and also at 40° C for chloroform. In each case a marked increase in diffusion coefficient occurs at a volume concentration of penetrant of about 60 to 70 %. The results for chloroform indicate a mean activation energy of about 6 kcal. Photographs of interferometer fringe systems in the neighbourhood of a corner of the cellulose acetate sheet are shown for each penetrant. Each photograph reveals anisotropic behaviour. This behaviour is due partly to the diffusion coefficient being less in the direction of stretch, than perpendicular to it, and partly to the overall range of concentration being less as a result of the restricted swelling of the polymer in the former direction. The degree of anisotropy is studied quantitatively for chloroform and acetone. New evidence is provided on the nature of the sharp boundaries seen under the microscope when a penetrant enters a polymer. In particular the middle boundary, which approximately indicates the concentration at which the polymer relaxes and becomes isotropic, is found to occur at a volume concentration of 60 to 70 % for each penetrant examined quantitatively. On inspecting a model of a cellulose acetate molecule it seems likely that at this volume concentration the polymer chains are sufficiently well separated to allow one repeating unit of the polymer chain to rotate about the axis of the chain without hindrance from neighbouring chains. An analogy with second-order transition phenomena is drawn.