The oligonucleotide d(TX)9 , which consists of an octadecamer sequence with alternating non-canonical 7-deazaadenine (X) and canonical thymine (T) as the nucleobases, was synthesized and shown to hybridize into double-stranded DNA through the formation of hydrogen-bonded Watson-Crick base pairs. dsDNA with metal-mediated base pairs was then obtained by selectively replacing W-C hydrogen bonds by coordination bonds to central silver(I) ions. The oligonucleotide I adopts a duplex structure in the absence of Ag(+) ions, and its stability is significantly enhanced in the presence of Ag(+) ions while its double-helix structure is retained. Temperature-dependent UV spectroscopy, circular dichroism spectroscopy, and ESI mass spectrometry were used to confirm the selective formation of the silver(I)-mediated base pairs. This strategy could become useful for preparing stable metallo-DNA-based nanostructures.

DNA sequences comprising noncanonical 7-deazaguanine ( G) and canonical cytosine (C) are capable of forming Watson-Crick base pairs via hydrogen bonds as well as silver(I)-mediated base pairs by coordination to central silver(I) ions. Duplexes I and II containing G and C have been synthesized and characterized. The incorporation of silver(I) ions into these duplexes has been studied by means of temperature-dependent UV spectroscopy, circular dichroism, and DFT calculations. The results suggest the formation of DNA molecules comprising contiguous metallated G-Ag -C Watson-Crick base pairs that preserve the original B-type conformation. Furthermore, additional studies performed on duplex III indicated that, in the presence of Ag ions, G-C and A-T Watson-Crick base pairs ( A, 7-deazadenine; T, thymine) can be converted to metallated G-Ag -C and A-Ag -T base pairs inside the same DNA molecule whilst maintaining its initial double helix conformation. These findings are very important for the development of customized silver-DNA nanostructures based on a Watson-Crick complementarity pattern.

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This material has been used as a photo catalyst for water splitting since 1972 when Fujishima and Honda reported its ability to generate hydrogen and oxygen from water molecules. [1] Titanium dioxide is normally used in advanced oxidation processes, [2] in systems capable of elimi nating a wide variety of chemicals in air and water, as well as solar fuel production (such as H 2 ). [3,4] The photoactivated pro cesses of titanium dioxidebased photo catalysts are achieved when the irradiation energy is higher than its band gap. This generates electrons in the conduction band and holes in valence band, which rapidly migrate to the TiO 2 surface and provoke the generation of extremely reactive spe cies. For example, H 2 O 2 and the radicals OH • , O 2-• formed after the electron and the holes reach the external surface of titanium dioxide, are very important for the photodecomposition of organic pol lutants to CO 2 and H 2 O, which is true for the most active titanium dioxidebased materials. [5,6] The band gap value has a direct impact on the rate of electronhole (e --h +) recombination during the photocatalytic processes. In the case of titanium dioxide, the relatively large band gap, means there is a slow recombination rate compared to most of the other photocatalysts. [7] Three main phases are present in TiO 2 : 1) Anatase (tetrag onal, a = b = 3.785 Å, c = 9.54 Å), 2) brookite (orthorhombic, a = 5.143 Å, b = 5.456 Å, c = 9.182 Å), and 3) rutile (tetragonal a = b = 4.593 Å, c = 2.959 Å). [8,9] The thermodynamically meta stable phases, anatase, and brookite, irrevocably pass into the stable phase of rutile at high temperatures. [7] Each of these phases show its own morphological characteristics and band gap value: In the case of anatase the band gap is of 3.2 eV, while rutile and brookite have band gaps of 3.0 and 3.3 eV, respec tively. In general, anatase shows the most attractive photocata lytic behavior due to its versatility and textural properties. [10][11][12] However, the anatase phase, due to its band gap, can only be activated by UV light, which accounts for approximately only 4% of the solar spectrum. Thus, in order to stabilize the anatase phase at elevated temperatures, and to utilize UV and visible light for photocatalysis, chemical modifiers and dopants are generally employed for the modification of the photocatalytic Titanium dioxide nanomaterials with improved catalytic and photo catalytic properties through codoping with copper and fluorine are synthesized and contain optimal textural and compositional properties, which are not possible without doping or with a single doping of Cu or F separately. The codoped systems promote the generation of a synergistic effect increasing activity of the systems in photocatalytic processes of both potential environmental or energy interest. The photocatalysts show very effective degradations of industrial and emerging contaminants such as ciprofloxacin (80% degradation) and naproxen (72% degradation) using UV light (300 W) in short periods of up to 15 min. An ad...