A novel approach for simultaneous determination of polycyclic aromatic hydrocarbons by Shpol'skii non-linear variable-angle synchronous fluorescence spectrometry

A new method of combining low-temperature Shpol'skii effect with non-linear variable-angle synchronous fluorescence spectrometry (L-NLVASFS) has been proposed to increase spectral resolution. This coupled method was applied successfully to the simultaneous identification and quantification of some polycyclic aromatic hydrocarbons (PAHs) in mixtures, which cannot be determined by non-linear variable-angle synchronous fluorescence spectrometry at room-temperature (R-NLVASFS). The usefulness of this method is demonstrated by the analyses of synthetic mixtures and several real samples of airborne particulates.     

Coherent anti-Stokes Raman Scattering Microscopy.

Coherent anti-Stokes Raman scattering (CARS) microscopy is presented as a new nonlinear optical technique. The combination of vibrational spectroscopy and microscopy allows highly sensitive investigations of unlabelled samples. CARS is an ideal tool for studying a broad variety of samples. The main drawback of the technique is its non-zero-background nature, which implies that the signal has to be detected against a nonresonant background. The need to solve this problem is reflected in the rapid technological developments that have been observed during the last decade. Recent results show that CARS microscopy has the potential to become an important complementary technique that can be used with other well-established microscopic methods. Although it has some limitations, it offers unique access to many problems that cannot be tackled with conventional techniques. For this reason, it can be expected that the impressive growth of the field will continue.     

Orthogonal PbS nanowire arrays and networks and their Raman scattering behavior

Three-dimensional, orthogonal lead sulfide (PbS) nanowire arrays and networks have been prepared by using a simple, atmospheric pressure chemical vapor deposition (APCVD) method. These uniform nanowires (average diameter 30 nm) grow epitaxially from the surface of the initial PbS crystal seeds and form orthogonal arrays and networks in space. The growth mechanism has been explored, and the process was classified as homogeneous, epitaxial growth in the 200 directions. Furthermore, Raman spectra of PbS nanowires are reported here, and their characteristic Raman peak (190 cm(-1), no shoulder) could be used as a unique probe for the study of PbS nanomaterials.     

Neurosteroid analogues: synthesis of 6-aza-allopregnanolone

An efficient synthesis of 6-azapregnane derivatives and their biological activity is described. The nitrogen was introduced into the B ring using Beckmann rearrangement of the (E)-oxime of 6-oxo-B-nor-5α-pregnane derivatives. The required 3α-hydroxyl was produced either by solvolysis of the corresponding 3β-mesyloxy group or by the Meerwein-Ponndorf-Verley reduction of the 3-oxo group; this reduction could be carried out selectively with an unprotected 3,20-dioxo derivative. The binding of the 6-aza-steroids to the γ-aminobutyric acid receptor (GABA_A) was measured using [³⁵S]-tert-butyl-bicyclo[2.2.2]phosphorothionate (TBPS) and [³H]flunitrazepam. The only analogue to be slightly active was that lacking any oxygen function in position 3.     

Optical emission spectroscopy as a real time diagnostic tool for plasma-assisted deposition of TiN

Real-time optical emission spectroscopy (OES) was used to monitor the deposition of TiN both from mixtures of tetrakis(dimethylamino)titanium (TDMATi)-N₂ and TiCl₄-H₂-N₂ in an electron cyclotron resonance chemical vapor deposition system. The accurate control of the ratio of the emission intensities of ionized nitrogen at 391.4 nm and molecular nitrogen at 357.7 nm (N ₂ ⁺ /N₂) led to low temperature deposition of stoichiometric TiN (Ti/N ≈ 1) and very low resistivity in both cases. It was found that high ion density plasmas are crucial for a considerable reduction of the deposition temperature while maintaining good film quality. OES shows that the abundance of certain excited plasma species is not only dependent on the gas mixture and the deposition parameters, such as total pressure and microwave power, but also is strongly affected by the magnetic field configuration. The deposition rate and the film resistivity can be related to the emission intensity ratio, I(N ₂ ⁺ )/I(N₂). Finally, the two processes are compared in terms of the quality of as-deposited and heat-treated films. The comparison shows that the films obtained with TDMATi exhibit lower resistivity and are thermally more stable than with TiCl₄.     

Thiol- and disulfide-modified oligonucleotide monolayer structures on polycrystalline and single-crystal Au(111) surfaces

We provide a comprehensive study of single- (ss) and double-strand (ds) oligonucleotides with either 25 or 10 bases or base pairs (bp) immobilized on polycrystalline and single-crystal Au(111) surfaces. The study is based on X-ray photoelectron spectroscopy, cyclic and differential pulse voltammetry, interfacial capacitance data, and electrochemical scanning tunnelling microscopy (in situ STM). The sequences used were the 25-bp sequence from the BRCA1 gene (25-mer), while the 10-bp oligonucleotides contained solely linear adenine and thymine sequences. The oligonucleotides were modified by the dimethoxytrityl group (DMT) via a disulfide group [DMT-S-S-ss25-mer and DMT-S-S-ds(AT)₁₀], a pure disulfide group (A₁₀-S-S-T₁₀), or a thiol group [HS-ss25-mer and HS-ds-(AT)₁₀], all via a hexamethylene linker. The overall pattern suggests strategies for controlled adsorption of DNA-based molecules and recognition of complementary strands or other molecules.     

Electron microscopic phase analysis of BN-thin films

A series of BN films was deposited by means of r.f. magnetron sputtering of a h-BN target onto Si(1OO) surfaces. Hereby, the substrate bias voltage was varied. Special interest is focussed to the influence of the deposition parameters on the orientation of the growing hexagonal BN film with respect to the substrate. For structural investigation, cross section samples were prepared. In addition to HRTEM and diffraction investigations, especially electron energy loss spectroscopy (EELS) was applied successfully for phase identification. For negative bias voltages of U _B =–300 V and U _B =–350V, we found a phase system consisting of a first-grown 25 nm thick layer of hexagonal structure with the c axis parallel to the substrate surface followed by the cubic phase.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Synthesis and Spectroscopic Study of Some New Phosphoramidates,Crystal Structures of N‐Benzoyl‐N′,N″‐bis(azetidinyl)phosphoric Triamide and N‐Benzoyl‐N′,N″‐bis(hexamethylenyl)phosphoric Triamide

Some new N‐carbonyl, phosphoramidates with formula C₆H₅C(O)N(H)P(O)R₂ (R = NC₃H₆ ( 1 ), NC₆H₁₂ ( 2 ), NHCH₂CH=CH₂ ( 3 ), N(C₃H₇)₂ ( 4 )) and CCl₃C(O)N(H)P(O)R′₂ (R′ = NC₃H₆ ( 5 ), NHCH₂CH=CH₂ ( 6 )) were synthesized and characterized by ¹H, ¹³C, ³¹P NMR and IR spectroscopy and elemental analysis. The structures were determined for compounds 1 and 2 . Compound 1 exists as two crystallographically independent molecules in crystal lattice. Both compounds 1 and 2 produced dimeric aggregates via intermolecular ‐P=O…H‐N‐ hydrogen bonds, which in compound 2 is a centrosymmetric dimer. In compounds with four‐membered ring amine groups, ³J(P,C)>²J(P,C), in agreement with our previous studies about five‐membered ring amine groups. Also, ³J(P,C) values in compounds 1 and 5 are greater than in compounds with five‐, six‐ and seven‐membered ring amine groups.     

Synthesis and Structure of Mixed Ba12F19ClδBr5–δ Crystals

In the structure Ba₁₂F₁₉Cl₅ [hexagonal space group P6 2m] the two chlorides on the sites Cl(1) and Cl(2) can partially be replaced by bromide ions. Single crystals of the type Ba₁₂F₁₉Cl_δBr_5–δ with a chloride to bromide ratio up to 2 : 3 could be obtained by cooling a flux of 75 mol% BaF₂ and 25 mol% BaX₂ with X = Cl, Br. The crystal quality decreases with increasing bromide concentration. Structural parameters of five selected single crystals with different chloride/bromide ratio were studied by single crystal X-ray diffraction methods. The refined total Cl^?/Br^? population ratio in the crystals is close to the one of the flux. The lattice parameters and interatomic distances change in various ways, when the smaller chloride ion is replaced by the bigger bromide ion. The refinements show a statistical disorder on the halide sites with preferential bromide substitution on site Cl(1).     

Photoelectron Spectra of Nonmetal Compounds and Their Interpretation by MO Models

The results of (low energy) photoelectron spectroscopy render possible a better appreciation of the “Nature of the Chemical Bond”. The application of this new experimental method is demonstrated utilizing representative compounds of the nonmetal elements, and a close symbiosis delineated with molecular orbital models. In particular, general consequences are discussed concerning electron deficiency, σ- and π-interactions, electron pair delocalization, and substituent effects or geometric perturbations. Photoelectron spectroscopic ionization energies permit evaluation of parameters for specified molecular groups, allow correlation with numerous other experimental data, and are didactically valuable in the teaching of general chemistry.