The widely used antitumor drug cis-diamminedichloroplatinum(II) (cisplatin or cis-DDP) reacts with DNA, cross-linking two purine residues through the N7 atoms, which reside in the major groove in B-form DNA. The solution structure of the short duplex [d(CAT-AGCTATG)]2 cross-linked at the GC:GC site was determined by nuclear magnetic resonance (NMR). The deoxyguanosine-bridging cis-diammineplatinum(II) lies in the minor groove, and the complementary deoxycytidines are extrahelical. The double helix is locally reversed to a left-handed form, and the helix is unwound and bent toward the minor groove. These findings were independently confirmed by results from a phase-sensitive gel electrophoresis bending assay. The NMR structure differs markedly from previously proposed models but accounts for the chemical reactivity, the unwinding, and the bending of cis-DDP interstrand cross-linked DNA and may be important in the formation and repair of these cross-links in chromatin.

Pure rutile and rutile-anatase composite TiO(2) nanoparticles have been successfully synthesized via an ionic liquid-assisted method by hydrolysis of titanium tetrachloride in hydrochloric acid. It is found that the phase composition (ratio of rutile to anatase) of the products increases with increasing the content of ionic liquid [Emim]Br (1-ethyl-3-methyl-imidazolium bromide), therefore, TiO(2) nanoparticles with controlled phase compositions can be obtained in high yields. The structural and morphological characterizations of the resulting samples are investigated by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Brunauer-Emmett-Teller (BET) analysis, and the results indicate that the diameters of the anatase nanoparticles are in the range of 4-6 nm and the well-defined rutile nanorods are about 3-6 nm in diameter and 20-60 nm in length. More importantly, we find that the [Emim](+) ions can serve as capping agents based on their strong interactions with the (110) facets of rutile, and the [Emim]Br favors the formation of the rutile structure with a rod-like shape due to the mutual pi-stacking interactions of imidazole rings. We believe that this method can be developed into a general way to synthesize other metal oxide nanoparticles on a large scale.

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In certain contexts the DNA triplet GGA, when juxtaposed on opposite strands of a DNA duplex, shows the unusual property of pairing with itself in an antiparallel orientation to form the (GGA)2 motif. In this motif the central guanines do not pair but intercalate and stack between sheared G.A pairs. Similar studies with GCA triplets reveal that they do not form analogous paired (GCA)2 motifs but instead strongly promote formation of a hairpin, the structure of which is now reported here. The GCA hairpin loop consists of a single cytidine residue closed by a sheared G.A pair and this structure is discussed in the context of triplet expansions in triplet-repeat diseases.

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