Understanding DNA–ligand binding interactions requires ligand screening, crystallization, and structure determination. In order to obtain insights into the amyloid peptide precursor (APP) gene–Thioflavin T (ThT) interaction, single crystals of two DNA sequences 5′-GCCCACCACGGC-3′ (PDB 8ASK) and d(CCGGGGTACCCCGG)2 (PDB 8ASH) were grown in the presence of ThT or its analogue 2-((4-(dimethylamino)benzylidene)amino)-3,6-dimethylbenzo[d]thiazol-3-ium iodide (XRB). Both structures were solved by molecular replacement. In the case of 8ASK, the space group was H3 with unit cell dimensions of a = b = 64.49 Å, c = 46.19 Å. Phases were obtained using a model generated by X3DNA. The novel 12-base-pair B-DNA structure did not have extra density for the ThT ligand. The 14-base-pair A-DNA structure with bound ThT analog XRB was isomorphous with previously the obtained apo-DNA structure 5WV7 (space group was P41212 with unit cell dimensions a = b = 41.76 Å, c = 88.96 Å). Binding of XRB to DNA slightly changes the DNA’s buckle parameters at the CpG regions. Comparison of the two conformations of the XRB molecule: alone and bound to DNA indicates that the binding results from the freedom of rotation of the two aromatic rings.
Powder samples of Li 2 CaGeO 4 , Ca 2 GeO 4 , and Ca 5 Ge 3 O 11 doped by 0.5, 1, 2, 3, 4 and 5 at% Eu 3+ relative to the Ca 2+ , were prepared using a conventional solid-state synthesis technique. X-ray diffraction (XRD) analyses confirmed obtaining the pure phases at all dopant concentrations. In parallel, single crystals of the three compounds with the experimentally found optimal Eu 3+ concentration were grown using a flux method. Structural investigation on the single crystals were done with a special attention to the form of the Ca-O polyhedron, the mean Ca-O distance, the Ca-Ca distance in the structure, the distortion degree of the polyhedron, as well as the Eu-Ca substitution site. The main spectral characteristics were analyzed and several relationships between the structural and spectra features were found. The optimal dopant concentration was 3 at% for Ca 2 GeO 4 and 4at% for Ca 5 Ge 3 O 11 and Li 2 Ca-GeO 4 . Commission Internationale de l'éclairage coordinates of the samples showed emission colours in the red region close to the standard red coordinates and slightly influenced by the active ion concentration. The obtained results showed that europium-doped Li 2 CaGeO 4 , Ca 2 GeO 4 , and Ca 5 Ge 3 O 11 could be used as red phosphors.
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