Detection of freely propagating terahertz radiation by use of optical second-harmonic generation

We report the application of electric-field-induced optical second-harmonic generation as a new technique for measuring the field of freely propagating terahertz radiation. Using silicon as the nonlinear medium, we demonstrate subpicosecond time resolution and a sampling signal that varies linearly with the terahertz electric field. This approach, which is attractive for centrosymmetric media, permits a significantly broadened class of materials to be exploited for free-space sampling measurements.     

Isolated singularities of Monge-Ampère equations

Letz=z(x, y) be a real-valued twice continuously differentiable solution of the elliptic Monge-Ampère equationAr+2Bs+Ct+rt – s ²=E in the punctured disk 0<(x–x ₀)²+(y–y ₀)²<². Assume thatq is continuous at (x₀, y₀). Our aim is to give sufficient conditions on the coefficientsA,..., E which ensure that the singularity (x ₀,y ₀) is removable. This generalizes an earlier result of Jörgens (Math. Ann. 129 (1955), 330–344).     

Ordered Mesostructured Silica Films: Effect of Pore Surface on its Sensing Properties

An electrochemical resistive-type sensor device, with a mesoporous silica thin film as sensitive membrane, has been developed and characterised. The silica film has been obtained via evaporation-induced self-assembly (EISA) using a tri-block copolymer (Pluronic F-127) as templating agent. It has been deposited by dip-coating on a silicon substrate with metallic interdigitated electrodes. Fast, reversible and reproducible electrical responses to relative humidity changes have been observed for the sensor device. The conduction mechanism has been related to chemical properties, structural order and surface morphology of the porosity in the silica film, confirming the dependence on the film preparation method and overall the importance of calcination temperature.     

An Efficient Synthesis of O-Methyl Protected Emodin Aldehyde and Emodin Nitrile

An efficient synthesis of tri-O-methylemodin aldehyde was achieved via bromination of tri-O-methylemodin utilizing N-bromosuccinimide yielding the monobromo and dibromo derivatives. Sommelet reaction of the monobromomethyl derivative as well as hydrolysis of the dibromomethyl analog with aqueous silver nitrate afforded the protected aldehyde in good yield. Accordingly, both bromo derivatives can be used even when they are obtained as a mixture of the bromination reaction, which could not be controlled easily to yield the bromo products selectively. From the aldehyde the tri-O-methylemodin nitrile was prepared in a one-pot reaction using hydroxylamine-O-sulfonic acid.     

Qualitative Kationenanalyse unter Verwendung von Metallindicatoren

Zusammenfassung 1-(2-Pyridyl-azo)-2-naphthol gibt mit einer Reihe von Metallkationen gefärbte Chelatkomplexe, die sich zum Teil mit organischen Lösungsmitteln extrahieren lassen. Durch systematische Prüfung wurden die für die Chelatbildung günstigsten p_H-Bereiche ermittelt. Durch Maskierung und/oder durch Zerlegung der gebildeten Chelate mit spezifischen Reagentien lassen sich selektive Nachweise im Mikrogrammbereich durchführen. Es werden spezifische Bestimmungen für Zink, Cadmium, Mangan, Indium, Gallium, Uranyl und Kobalt mitgeteilt. Auch Kupfer, Palladium und Nickel lassen sich gut nachweisen.I. Mitteilung: diese Z. 154, 114 (1957).     

Optisch aktive 3-Amino-2H-azirine als Bausteine für enantiomerenreine α,α-disubstituierte α-Aminosäuren: Synthese des α-Methylphenylalanin-Synthons and Einbau in Modell-Peptide

Optically Active 3-Amino-2H-azirines as Synthons for Enantiomerically Pure αα-Disubstituted α-Amino Acids: Synthesis of the α-Methylphenylalanine Synthons and Some Model Peptides The synthesis of a novel 2-benzyl-2-methyl-3-amino-2H-azirine derivative with a chiral amino group is described. Chromatographic separation of the diastereoisomer mixture yielded the pure diastereoisomers 9a and 9b (Scheme 4) which are the D - and L -2-methylphenylalanine ((α-Me)Phe) synthons, respectively. The reaction of 9a and 9b with thiobenzoic acid and with Z-leucine yielded the monothiodiamides 10a and 10b (Scheme 5) and the dipeptide derivatives 11a and 11b (Scheme 6), respectively. Methanolysis of 11b yielded 12b . The absolute configuration of 10a was established by X-ray crystallography. The absolute configuration of (α-Me)Phe in 12b has been deduced from the known configuration of L -leucine.     

119Sn- and 31P-NMR. Spectroscopy of the 5-coordinate complexes [Rh (SnClnBr(3−n)) (norbornadiene) (tertiary phosphine)2]

The products of the reaction of [RhCl (NBD)]₂ (NBD = norbornadiene), with four equivalents tertiary phosphine and two equivalents of tin (II) bromide have been studied by ¹¹⁹Sn- and ³¹P-NMR. spectroscopy. The solution data suggest that halogen scrambling occurs during the preparation and results in a mixture of complexes containing SnBr₃, SnClBr₂, and SnCl₂Br and SnCl₃ ligands, and this is confirmed by independent synthesis of the SnCl₃ and SnBr₃ complexes. The metalmetal coupling constants, ¹J (¹¹⁹Sn, ¹⁰³Rh), vary from 452 to 580 Hz and are linearly related to: (a) δ(¹¹⁹Sn) in the complexes [Rh (SnCl_nBr_(3-n))NBD (PEtPh₂)₂] and (b) the sum of the Pauling electronegativities for the halogens on tin.     

An Efficient Route to Emodic Amine and Analogous <Emphasis Type="Italic">O</Emphasis>-Methyl Protected Derivatives Starting from Emodin

Summary. Emodic amine could be synthesized in a five-step approach in excellent overall yield by following a modified Curtius rearrangement strategy, starting from the naturally occurring emodin. This unique emodin derived 6-amino substituted polyhydroxylated anthraquinone may serve as a promising synthon for a new class of amino functionalized photodynamically active hypericin derivatives. In addition, the partially O-methyl protected 6-amino- and 6-carboxy-anthraquinones could be synthesized in high yields via selective O-methyl ether cleavage from the corresponding tri-O-methyl derivatives.     

Mass spectrometric studies of dithiophosphinato metal complexes

Electron impact induced fragmentation reactions of planar, tetrahedral, octahedral and oligomeric metal dithiophosphinates Me(II)L₂ (L=Et₂PS₂^?; Me(II)=Zn, Cd, Hg, Pb, Co, Mn, Ni, Pd, Pt), Me(III)L₃ (Me(III) = Sb, Bi, In, Rh, Ir) and (Me(I)I)_n (Me(I)/n=Tl/1, Au/2, Cu/4) have been studied. Fragmentation patterns, which are in accordance with metastable peak determinations by linked scans, are reported. In the case of the transition metals the spectra of the complexes show abundant [M]^+· predominantly metal containing ions and, the former being weak and the intensities of the latter being considerably reduced in the case of metal complexes with filled d shells. With planar or tetrahedral transition metal complexes no dependence of fragmentation on the coordination geometry can be observed. The dependence of fragmentation on d configuration, ionization energy of the metal and metal ligand π bonding is discussed. In the case of the oligomeric complexes strong metal-metal interaction is observed even under electron impact.