Detection of adsorption of Ru(II) and Os(II) polypyridyl complexes on gold and silver nanoparticles by single-photon counting emission measurements

The present study describes a new application of ruthenium(II) tris(bipyridine) (Ru(bpy)3(2+)) and osmium(II) tris(bipyridine) (Os(bpy)3(2+)) as phosphorescent labels for the quantification of surface binding of molecules to gold and silver nanoparticles. The fraction of Ru(bpy)3(2+) and Os(bpy)3(2+) that is in solution can be distinguished from the surface-bound fraction by the relative lifetimes and integrated emission yields as determined by time-correlated single-photon counting (TCSPC) spectroscopy. Complementary steady-state measurements were carried out to confirm surface attachment of the phosphorescent label molecules. Although the emission of solutions of Ru(bpy)3(2+) and Os(bpy)3(2+) is quenched proportional to the concentration of 10 nm Au or 20 nm Ag nanoparticles, the quenching is static and not diffusional quenching observed in Stern-Volmer plots. The results demonstrate that time-resolved spectroscopy provides a rapid method for the measurement of surface binding of labeled molecules on metallic nanoparticles. While steady-state measurements require the preparation of a series of samples with varying quencher concentrations and a reference, the method described herein requires a single sample plus reference. The mechanism for phosphorescence quenching on Au and Ag nanoparticles is discussed in terms of energy and electron transfer theories.     

Preparation and crystal structure of Nb6.74 Ta5.26S4 – a new compound in the ternary system Ta?Nb?S

Nb_6.74Ta_5.26S₄ has been prepared by high temperature techniques. The crystal structure has been determined from single crystal X-ray diffraction data (R/R_w = 0.0588/0.0655). The compound crystallizes in the orthorhombic space group Pnma with unit cell dimensions a = 959.11 (26) pm, b = 336.37 (10) pm, and c = 3282.51 (74) pm. The orthorhombic cell contains four formula units. Its structure is similar to that of Nb-rich sulfides, rather than to that of Ta-rich sulfides. The metal coordinations are capped distorted cubic prisms and pentagonal prisms while the coordinations of sulfur are capped trigonal prisms.     

Covalent attachment of a nickel nitrilotriacetic acid group to a germanium attenuated total reflectance element

The surface of a germanium internal reflectance element (IRE) was modified to bind 6X-histidine (his)-tagged biomolecules. The step-by-step surface modification was monitored via single-pass attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR). Initially an adlayer of 7-octenyltrimethoxysilane (7-OTMS) was formed on the Ge crystal through the surface hydroxyl groups, which were produced via ozonolysis of the Ge surface. The vinyl moiety of 7-OTMS was oxidized to a carboxylic acid, which was activated by 1,1'-carbonydiimidazole (CDI) to produce a labile imidazole. The labile imidazole that resulted from the CDI coupling was then displaced by the primary amine of nitrilotriacetic acid (NTA). Nickel sulfate was added to the system, and it coordinated with the three carbonyl groups and the nitrogen on NTA, thus leaving the ability of Ni to coordinate with two adjacent histidine residues. Binding of his-tagged biotin to nickel nitrilotriacetic acid (Ni-NTA) was observed by ATR-FT-IR spectroscopy. The surface modification method presented in this paper had minimal nonspecific binding, the Ni-NTA surface was reusable if stored properly, and complete removal of the organic surface was achievable.     

Defect ordering in early transition-metal sulfides with the NaCl-type structure

The defect rock-salt type materials Zr_1?xS, Sc_1?xS, and Lu_1?xS have been shown to exhibit a complex variety of ordered superstructures. These superstructures are reviewed within the context of Landau's theory of symmetry and phase transitions, and it is concluded that there is a significant similarity in the transitions when they are considered from the point of view of reciprocal space.     

XPS spectra of some transition metal and alkaline earth monochalcogenides

The first-row transition-metal monosulfides and alkaline-earth chalcogenides were studied by means of X-ray photoelectron spectroscopy. It is shown that the bonding in the alkaline earth compounds is relatively ionic with XPS evidence for significant charge separation. On the other hand, transition metal sulfides, with the exception of MnS, appear to be principally metallic with little or no charge separation. Values for the inner orbital binding energy shifts are reported for a large number of monochalcogenides.     

Characterization of single- and double-stranded DNA on gold surfaces

Single- and double-stranded deoxy ribonucleic acid (DNA) molecules attached to self-assembled monolayers (SAMs) on gold surfaces were characterized by a number of optical and electronic spectroscopic techniques. The DNA-modified gold surfaces were prepared through the self-assembly of 6-mercapto-1-hexanol and 5'-C(6)H(12)SH -modified single-stranded DNA (ssDNA). Upon hybridization of the surface-bound probe ssDNA with its complimentary target, formation of double-stranded DNA (dsDNA) on the gold surface is observed and in a competing process, probe ssDNA is desorbed from the gold surface. The competition between hybridization of ssDNA with its complimentary target and ssDNA probe desorption from the gold surface has been investigated in this paper using X-ray photoelectron spectroscopy, chronocoulometry, fluorescence, and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS). The formation of dsDNA on the surface was identified by PM-IRRAS by a dsDNA IR signature at approximately 1678 cm(-)(1) that was confirmed by density functional theory calculations of the nucleotides and the nucleotides' base pairs. The presence of dsDNA through the specific DNA hybridization was additionally confirmed by atomic force microscopy through colloidal gold nanoparticle labeling of the target ssDNA. Using these methods, strand loss was observed even for DNA hybridization performed at 25 degrees C for the DNA monolayers studied here consisting of attachment to the gold surfaces by single Au-S bonds. This finding has significant consequence for the application of SAM technology in the detection of oligonucleotide hybridization on gold surfaces.     

Thermodynamic properties of two metal-rich tantalum sulfides: Ta2S and Ta6S

The incongruent vaporization reactions of Ta₂S and Ta₆S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of P_S(obs) to equilibrium the enthalpies of the reactions $\text{3}\text{2}\text{Ta}{}_2\text{S(s)}\text{=}\text{1}\text{2}\text{Ta}{}_6\text{S(s) + S(g)}$ and Ta₆S = 6 Ta(s) + S(g) were found to be $\text{ΔH}{}^0{}_{298}\text{R}\text{= 53.0(0.3) · 10}{}^3\text{K}$ and $\text{ΔH}{}^0{}_{298}\text{R}\text{= 58.1(0.4) · 10}{}^3\text{K}$, respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation.     

Spectral and scattering theory for a Schrödinger operator with a class of momentum-dependent long-range potentials

Let be the selfadjoint operator for the static electromagnetic field where W _j for 0, 1, 2, ..., n is a sum of (i) a short-range potential and (ii) a smooth long-range potential decreasing at as |x|^- with in (0, 1]. Then for >1/2, asymptotic completeness holds for the scattering system (H, H ₀).