DOTP versus DOTA as Ligands for Lanthanide Cations: Novel Structurally Characterized Ce and Ce Cyclen-Based Complexes and Clusters in Aqueous Solutions.

The coordination and redox chemistry of aqueous Ce macrocyclic compounds were studied by using the ligands DOTA and DOTP (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid), respectively). The hydrolysis tendency of the tetravalent cation in the presence of DOTA is shown to result in the formation of a highly ordered, fluorite-like [Ce (O) (OH) (H O) (DOTAH) ] oxo-hydroxo structure both in solution and in the solid state. The lifetime of the analogous species formed in the presence of DOTP was found to be much shorter.

Oligomers Intermediates in Between Two New Distinct Homonuclear Uranium(IV) DOTP Complexes*.

Two new aqueous U complexes were synthesized by the interaction between the tetravalent uranium cation and the (1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid) (DOTP) macrocyclic ligand. Two distinct homonuclear complexes were identified; the first was characterized by X-ray crystallography as a unique "out-of-cage", [U(DOTPH ) ] complex, in which the U cation is octa-coordinated to 4 phosphonic arms from each ligand in a square anti-prism geometry, with a C symmetry. The second is the "in-cage" [U(DOTPH )] complex, in which the tetravalent cation is located between the macrocycle O and N planes.

On the Aqueous Chemistry of the U -DOTA Complex.

The 1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) aqueous complex of U with H O, OH , and F as axial ligands was studied by using UV/Vis spectrophotometry, ESI-MS, NMR spectroscopy, X-ray crystallography, and electrochemistry. The U -DOTA complex with either water or fluoride as axial ligands was found to be inert to oxidation by molecular oxygen, whereas the complex with hydroxide as an axial ligand slowly hydrolyzed and was oxidized by dioxygen to a diuranate precipitate. The combined data set acquired shows that, although axial substitution of fluoride and hydroxide ligands instead of water does not seem to significantly change the aqueous DOTA complex structure, it has an important effect on the electronic configuration of the complex.

Crystal structure determination of -11'-(1-acetyl-1-indazol-3-yl)-11',11'-di-hydro-10',17'-spiro-[indene-2,18'-[5a,16]methano-tri-indeno[1,2-:1',2'-:2'',1''-]oxocine]-1,3,10',12',17'(10')-penta-one aceto-nitrile 1.5-solvate.

The title compound, CHNO·1.5CHCN, is the aldol condensation product of bindone with indazole-3-carbaldehyde followed by double inter-molecular cyclization. The asymmetric unit, which has monoclinic 2/ symmetry, contains two independent mol-ecules of the title compound and three aceto-nitrile mol-ecules.

Structural Basis for p53 Lys120-Acetylation-Dependent DNA-Binding Mode.

Normal cellular homeostasis depends on tight regulation of gene expression, which requires the modulation of transcription factors' DNA-binding specificity. That said, the mechanisms that allow transcription factors to distinguish between closely related response elements following different cellular signals are not fully understood. In the tumor suppressor protein p53, acetylation of loop L1 residue Lys120 within the DNA-binding domain has been shown to promote the transcription of proapoptotic genes such as bax.

Acridine 0.75-hydrate.

The title compound, C(13)H(9)N·0.75H(2)O was obtained during a study of the polymorphic system of acridine, by slow evaporation from an ethanol-water solution. There are two acridine mol-ecules (indicated by I and II, respectively) and one and a half water mol-ecules in the asymmetric unit.

Crystal structures of Escherichia coli KDO8P synthase complexes reveal the source of catalytic irreversibility.

The enzyme 3-deoxy-D-manno-2-octulosonate-8-phosphate synthase (KDO8PS) catalyses the condensation of arabinose 5-phosphate (A5P) and phosphoenol pyruvate (PEP) to obtain 3-deoxy-D-manno-2-octulosonate-8-phosphate (KDO8P). We have elucidated initial modes of ligand binding in KDO8PS binary complexes by X-ray crystallography. Structures of the apo-enzyme and of binary complexes with the substrate PEP, the product KDO8P and the catalytically inactive 1-deoxy analog of arabinose 5-phosphate (1dA5P) were obtained.

Refined structure of c-phycocyanin from the cyanobacterium Synechococcus vulcanus at 1.6 A: insights into the role of solvent molecules in thermal stability and co-factor structure.

The crystal structure of the light-harvesting phycobiliprotein, c-phycocyanin from the thermophilic cyanobacterium Synechococcus vulcanus has been refined to 1.6 A resolution based on the previously determined lower resolution structure (PDB entry 1I7Y). The improved data was collected using synchrotron radiation at 100 K.