DNA based gold nanoparticles colorimetric sensors for sensitive and selective detection of Ag(I) ions

In this work, we reported both unlabeled and labeled sensing strategies for Ag(I) ions detection by using the DNA based gold nanoparticles (AuNPs) colorimetric method. In the unlabeled strategy, C-base riched single strand DNA (C-ssDNA) enwinded onto AuNPs to form AuNPs/C-ssDNA complex. In the labeled method, sulfhydryl group modified C-ssDNA (HS-C-ssDNA) was covalently labeled on AuNPs to produce AuNPs-S-C-ssDNA complex. In both strategies, C-ss DNA or HS-C-ssDNA could enhance the AuNPs stability against the salt-induced aggregation. However, the presence of Ag(I) ions in the obtained AuNPs/C-ssDNA or AuNPs-S-C-ssDNA complex would decrease such stability to display purple even blue colors due to the formation of Ag(I) ions mediated C-Ag(I)-C base pairs. Through this phenomenon, Ag(I) ions could be detected qualitatively and quantitatively using both unlabeled and labeled sensing strategies.

Magnetic Coupling between Copper(II) Ions Mediated by Hydrogen-Bonded (Neutral) Water Molecules

A new hydrogen-bonded dinuclear copper(II) coordination compound has been synthesized from the Schiff-base ligand 6-(pyridine-2-ylhydrazonomethyl)phenol (Hphp). The molecular structure of [Cu-2(php)(2)(H2O2)(2)(ClO4)](ClO4)- (H2O) (1), determined by single-crystal X-ray diffraction, reveals the presence of two copper(II) centers held together by means of two strong hydrogen bonds, with O center dot O contacts of only 2.60-2.68 angstrom. Temperature-dependent magnetic susceptibility measurements down to 3 K show that the two metal ions are antiferromagnetically coupled (J = -19.8(2) cm(-1)). This exchange is most likely through two hydrogen-bonding pathways, where a coordinated water on the first Cu, donates a H bond to the O atoms of the coordinated php at the other Cu. This strong O center dot H (water) bonding interaction has been clearly evidenced by theoretical calculations. In the relatively few related cases from the literature, this exchange path, mediated by a (neutral) coordinated water molecule, was not recognized.

Surface plasmon resonance and electrochemistry for detection of small molecules using catalyzed deposition of metal ions on gold substrate

Small molecules are difficult to detect by conventional surface plasmon resonance (SPR) spectroscopy due to the fact that the changes in the refractive index resulted from the binding process of small biomolecules are quite small. Here, we report a simple and effective method to detect small biomolecule using SPR spectroscopy and electrochemistry by catalyzed deposition of metal ions on SPR gold film. As an example, the ascorbic acid-mediated deposition of Ag on gold film was monitored by in situ SPR spectrum. The deposition of Ag atom on gold film resulted in an obvious decrease of depth in SPR angular scan curves of reflectance intensity and minimum reflectivity angle. The depth change of the SPR reflectance intensity and minimum reflectivity angle curves mainly relied on the amount of Ag atom deposited on gold film that can be controlled by the concentration of ascorbic acid. By monitoring the deposition of Ag atom on gold film, ascorbic acid was detected in the concentration range of 2 x 10(-5) M to 1 x 10(-3) M. After each of detections, the SPR sensor surface was completely regenerated by a potential step that stripped off the Ag atom. Furthermore, the regeneration process of the sensor surface provides the feasibility for detecting the concentration of ascorbic acid by electrochemical method.

Assembly of 12-tungstosilicic acid and 4-aminobenzo-15-crown-5 ether based on the electrostatic attraction through bridging of oxonium ions on different substrates

Based on the electrostatic attraction Keggin-type polyoxometalate H4SiW12O40 (SiW12) and small molecule 4-aminobenzo-15-crown-5 ether (4-AB15C5) were alternately deposited on poly (allylamine hydrochloride) (PAH)-derived indium tin oxide (ITO) substrate through a layer-by-layer (LBL) self-assembly, forming a supramolecular multilayer film (film-A). SiW12 was also deposited on a glassy carbon electrode (GCE) derived by 4-AB15C5 via covalent bonding in 0.1 M NaCl aqueous solution and formed a composite monolayer film (film-B). UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy measurements demonstrated that the interactions between SiW12 and 4-AB15C5 in both two film electrodes were the same and caused by the bridging action of oxonium ions. But, the nanostructure in the two film electrodes was different. 4-AB15C5 in film-A was oriented horizontally to ITO substrate, however, that in film-B was oriented vertically to GCE. Namely film-A corresponded to a layer structure, and film-B corresponded to an intercalation structure.

Effects of bridge ions, DNA species, and developing temperature on flat-lying DNA monolayers

Recently, we have successfully constructed flat-lying DNA monolayers on a mica surface (J. Phys. Chem. B 2006, 110, 10792-10798). In this work, the effects of various factors including bridge ions, DNA species, and developing temperature on the configuration of DNA monolayers have been investigated by atomic force microscopy (AFM) in detail. AFM results show that the species of bridge ions and developing temperature play a crucial role during the formation process. For example, the divalent cation Zn2+ resulted in many DNA chains stuck side by side in the monolayers due to the strong interactions between it and DNA's bases or the mica surface. Most DNA chain's conglutinations disappeared when the developing temperature was higher than 40 degrees C. Cd2+ and Ca2+ produced more compact DNA monolayers with some obvious aggregations, especially for the DNA monolayers constructed by using Ca2+ as the bridge ion. Co2+ produced well-ordered, flat-lying DNA monolayers similar to that of Mg2+. Furthermore, it was found that the flat-lying DNA monolayers could still form on a mica surface when plasmid DNA pBR 322 and linear DNA pBR 322/Pst I were used as the DNA source. Whereas, it was hard to form DNA monolayers on a (3-aminopropyl)triethoxysilane-mica surface because the strong interactions between DNA and substrate prevented the lateral movement of DNA molecules.

Synthesis, crystal structure, and thermal property of a novel supramolecular assembly: (NH42810424)(CHNO) O-[H(V)O(]2H)4(10)28(2), constructed from decavanadate and caffeine

A novel 3D supramolecular assembly constructed from decavanadate and caffeine building blocks, (NH4)(2)(C8H10N4O2)(4)[H4V10O28].2H(2)O (1), has been synthesized in aqueous solution and characterized by elemental analysis, IR, H-1 NMR, V-51 NMR, TG-DTA, and single crystal X-Ray diffraction. The compound 1 crystallizes in monoclinic system, space group P2(1)/n, a = 15.801(1) Angstrom, b = 12.914(1) Angstrom, c = 15.913(2) Angstrom, beta = 113.55degrees, V = 2976.4 (5) Angstrom(3), Z = 2, R = 0.0498 with 6818 reflections. Water molecules, ammonium ions, and caffeine act as "cement" linking the polyanions into 1D chain along the c-axis by hydrogen bonding. In compound 1, extensive hydrogen-bond contacts and strong pi-pi interactions lead to an ordered 3D supramolecular framework. TG-DTA curves indicate that the weight loss of the complex can be divided into three stages.

Effects R3+ on the photoluminescent properties of Ca2R8(SiO4)(6)O-2 : A (R = Y, La, Gd; A= Eu3+, Tb3+) phosphor films prepared by the sol-gel process

Using CaCO3, metal oxides (all dissolved by nitric acid) and tetraethoxysilane Si(OC2H5)(4) (TEOS) as the main starting materials, Ca2R8(SiO4)(6)O-2:A (R = Y, La, Gd; A = EU3+, Tb3+) phosphor films have been dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the 1000 degreesC annealed films are isomorphous and crystallize with the silicate oxyapatite structure. AFM and SEM studies revealed that the phosphor films consisted of homogeneous particles ranging from 30 to 90 nm, with an average thickness of 1.30 mum. The Eu3+ and Tb3+ show similar spectral properties independent of R 3, in the films due to their isomorphous crystal structures. However, both the emission intensity and lifetimes of Eu3+ and Tb3+ in Ca2R8(SiO4)(6)O-2 (R = Y, La, Gd) films decrease in the sequence of R = Gd > R = Y > R = La, which have been explained in accordance with the crystal structures.

Fabrication and luminescent properties of rare earths-doped Gd-2(WO4)(3) thin film phosphors by Pechini sol-gel process

Rare earth ions (Eu3+ and Dy3+)-doped Gd-2(WO4)(3) phosphor films were prepared by a Pechini sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting powders and films. The results of XRD indicate that the films begin to crystallize at 600degreesC and the crystallinity increases with the elevation of annealing temperatures. The film is uniform and crack-free, WO(4)(2-)mainly consists of closely packed fine particles with an average grain size of 80 nm. Owing to an energy transfer from 4 groups, the rare earth ions show their characteristic emissions in crystalline Gd-2(WO4)(3) phosphor films, i.e., D-5(J) -F-7(J), (J = 0, 1, 2, 3; J' = 0 1, 2, 3, 4, not in all cases) transitions for Eu3+ and F-4(9/2)-H-6(J) (J = 13/2, 15/2) transitions for D Y3+, with the hypersensitive transitions D-5(0)-F-7(2) (Eu3+) and F-4(9/2) - H-6(13/2) (Dy3+) being the most prominent groups, respectively.

Fabrication, patterning and luminescence properties of X-2-Y2SiO5 : A (A = Eu3+, Tb3+, Ce3+) phosphor films via sol-gel soft lithography

X-2-y(2)SiO(5):A (A = Eu3+, Tb3+, Ce3+) phosphor films and their patterning were fabricated by a sol-gel process combined with a soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy (SEM) optical microscopy and photoluminescence (PL) were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 900 degreesC with X-1-Y2SiO5, which transformed completely to X-2-Y2SiO5 at 1250 degreesC. Patterned thin films with different band widths (5 pin spaced by 5 pm and 16 pm spaced by 24 pm) were obtained by a soft lithography technique (micromoulding in capillaries, MIMIC). The SEM and AFM study revealed that the nonpattemed phosphor films were uniform and crack free, and the films mainly consisted of closely packed grains with an average size of 350 run. The doped rare earth ions (A) showed their characteristic emissions in X-2-Y2SiO5 phosphor films, i.e., D-5(0)-F-7(J) (J = 0, 1, 2,3,4) for Eu3+, D-5(3), (4)-F-7(J) (J = 6, 5, 4, 3) for Tb3+ and 5d (D-2)-4f (F-2(2/5),(2/7)) for Ce3+, respectively. The optimum doping concentrations for EU3+, Tb3+ were determined to be 13 and 8 mol% of Y3+ in X-2-Y2SiO5 films, respectively.

Liquid-liquid extraction of cerium(IV) from nitric acid media by di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP)

In this paper, the extraction of Ce(IV) from nitric acid solutions is investigated using di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP, B) in heptane as extractant. Ce(IV) can be extracted effectively from nitric acid solution, whereas it is poorly extracted from sulfuric acid solution. Compared with some other organophosphorus esters, DEHEHP has moderate extractablity for Ce(IV). The extraction efficiency varies with diluent in the order: aliphatic hydrocarbons > nitrobenzene > aromatic hydrocarbons > carbon tetrachloride > chloroform. Regeneration and loading capacities of DEHEHP have also been examined. Ce(IV) extraction in HNO3 solutions as well as extraction of HNO3 and H2O have been systematically studied. The Ce(IV) extraction increases with an increasing of HNO3 concentration and exhibits the maximum distribution ratio at 1-1.5 mol/L HNO3. Nitric acid, as a source of nitrate ion, enhances the extraction of metal ion. But it also competes with metal ions for extractant molecules by its own extraction under high acidities. The proposed extraction process is described by the following equilibrium equations

Heptaaquatetra-mu(3)-hydroxy-hexa-mu(2)-L-leucine-(L-leucine)tetraytterbium(III) tetrachlorozinc(II) trichlorohydroxyzinc(II) tetrachloride octahydrate

The title bimetallic compound, [Yb-4(mu(3)-OH)(4)(C6H13NO2)(7)-(H2O)(7)][ZnCl4][ZnCl3(OH)]Cl-4.8H(2)O, was synthesized at near physiological pH (6.0). The compound exhibits some novel structural features, including an asymmetric [Yb-4(mu(3)-OH)(4)(L-leucine)(7)(H2O)(7)](8+) complex cation in which four OH groups act as bridging ligands, linking four Yb3+ cations into a Yb4O4 structural unit. Each pair of adjacent Yb3+ ions is further bridged by one carboxy group from a leucine ligand. Water molecules and a monodentate leucine ligand also coordinate to Yb3+ ions, completing their eight-coordinate square-antiprismatic coordination. The Yb-4(mu(3)-OH)(4)(L-leucine)(7)(H2O)(7)](8+) cation, the [ZnCl4](2-), [ZnCl3OH](2-) and Cl- anions, and the lattice water molecules are linked via hydrogen bonds.

Syntheses, structures and near-IR luminescent studies on ternary lanthanide (Er-III, Ho-III, Yb-III, Nd-III) complexes containing 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dionate

The ligand Hhfth [4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dione], which contains a heptafluoropropyl group, has been used to synthesize several new ternary lanthanide complexes (Ln = Er, Ho, Yb, Nd) in which the synergistic ligand is 1,10-phenanthroline (phen) or 2,2'-bipyridine (bipy). The two series of complexes are [Ln(hfth)(3)phen] [abbreviated as (Ln)1, where Ln = Er, Ho, Yb] and [Ln(hfth)(3)bipy] [abbreviated as (Ln)2, where Ln = Er, Ho, Yb, Nd]. Members of the two series have been structurally characterized. The growth morphology, diffuse reflectance (DR) spectra, thermogravimetric analyses, and photophysical studies of these complexes are described in detail. After ligand-mediated excitation of the complexes, they all show the characteristic near-infrared (NIR) luminescence of the corresponding Ln(3+) ions (Ln = Er, Ho, Yb, Nd). This is attributed to efficient energy transfer from the ligands to the central Ln(3+) ions, i.e. an antenna effect. The heptafluorinated substituent in the main hfth sensitizer serves to reduce the degree of vibrational quenching. With these NIR-luminescent lanthanide complexes, the luminescent spectral region from 1300 to 1600 nm, which is of particular interest for telecommunication applications, can be covered completely.

Room-temperature strategy for networked nonspherical gold nanostructures from Au(III)-[G-2]-CO2H dendrimer complex

The present work describes a convenient approach to fabricate networked nonspherical gold nanostructures by using [G-2]-CO2H dendrimer and toluene as capping and bridging agents in a CH2Cl2 and H2O biphasic system. A controlled linear assembly is achieved without the use of any catalyst at room temperature. UV-vis spectrum, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) analysis show that the product is well networked nanostructures with diameter of 4-10 nm and consists of coalesced face-centered cubic gold nanocrystals. Extended experiments reveal that both benzene and dimethylbenzene can also inhabit the gold ions to make them crosslinked, prolong the nucleation points and eventually facilitate the formation of the networks.

Synthesis, crystal structure, and photoluminescent property of a novel heterobimetallic Zn(II)-Ag(I) cyano-bridged coordination polymer incorporating,a pentameric unit [Ag(CN)(2-)](5) assembled by argentophilic interaction

A new photoluminescent heterobimetallic Zn(II)-Ag(I) cyano-bridged coordination polymer, [Ag5Zn2(tren)(2)(CN)(9)] (tren = tris(2-aminoethyl)amine) (1), has been synthesized and structurally characterized. It features rare linear pentameric unit of dicyanoargentate(I) ions assembled by d(10)-d(10) interaction as building blocks. Solid state emission spectrum of I shows strong ultraviolet luminescence with emission peak in the range of 376 nm.