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71.
Peter Kozma Andras Hamori Kaspar Cottier Sandor Kurunczi Robert Horvath 《Applied physics. B, Lasers and optics》2009,97(1):5-8
An interferometric sensor based on gratings on a planar waveguide is introduced. The device combines the advantages of known
interference-based waveguide sensors with the simplicity of grating couplers. In the presented configuration, two parallel
and coherent light beams, laterally separated in the direction of mode propagation, are coupled into a planar waveguide through
a grating. One of the coupled beams is phase modulated using a periodically relaxing liquid crystal modulator, resulting in
a time varying intensity signal at the end face of the waveguide. Refractive index changes within the waveguide section between
the two coupling regions are monitored by observing characteristic changes in the intensity signal. 相似文献
72.
Michele Ghisletta Kaspar Hegetschweiler Hans-Peter Jalett Tobias Gerfin Volker Gramlich 《Helvetica chimica acta》1992,75(7):2233-2242
A new, convenient, and safe route to 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) was investigated by hydrogenation of azo-coupled derivatives of phloroglucinol. In the presence of acetic anhydride, the reduction of trisphenylazophloroglucinol (H2/Pd(5%) on C) resulted in the formation of tri-, hexa-, and nona-acetylated derivatives of triaminophloroglucinol. All three compounds are air-stable, colorless solids. However, the succeeding hydrogenation to the cyclohexane derivative failed. Trisodiumtris(p-sulfonatophenylazo)phloroglucinol could be hydrogenated in a one-pot reaction to the desired taci· 1.5H2SO4 using a Pt/Rh oxide as catalyst. taci provides two distinct chair conformations with either three amino or three hydroxy groups for metal binding. The unique metal-binding properties are discussed in terms of minimal conformational changes required for coordination. Conformational analysis, based on X-ray structural data of [BiCl6][H3(taci)] ·2 H2O (Pnma, a = 24.314 (5) Å, b = 10.215 (2) Å, c = 7.422 (8) Å, R = 5.8%) and [Co(taci)2(NO3)3]·2H2O (C2/c, a = 22.912 (8) Å, b = 8.942 (2) Å, c = 14.731 (3) Å, β = 128.66 (2)°, R = 4.9%) and the previously investigated [Cr(taci)2]3+ revealed an almost ideal chair conformation in all three molecules. 相似文献
73.
Y. Du D.J. Kim T.C. Kaspar S.E. Chamberlin I. Lyubinetsky S.A. Chambers 《Surface science》2012,606(17-18):1443-1449
The growth of TiO2 anatase films on Nb‐doped SrTiO3(001) molecular beam epitaxy has been studied in-situ by scanning tunneling microscopy. We show that the initial growth follows the Stranski–Krastanov mode, where islands form on top of a wetting layer consisting of two monolayers (ML) of TiO2. The epitaxial islands subsequently nucleate and coalesce into large commonly oriented crystallites. The reconstruction observed by reflection high-energy electron diffraction (RHEED) is shown to result from the coexistence of individual (4 × 1) and (1 × 4) reconstructions present on different crystallite surfaces. The anatase grows in units of bilayers, resulting in a step height of 2 ML (~ 0.5 nm). This result explains the fact that the measured period of the RHEED specular-beam intensity oscillations corresponds to the time required for deposition of 2 ML. Ar ion sputtering and UHV annealing results in a transformation to coexisting (4 × 1) and (1 × 4) reconstructed terraces on individual crystallites, as commonly observed by ex-situ STM studies. 相似文献
74.
75.
Mateusz Piontek Bernd Morgenstern Nils Steinbrück Bastian Oberhausen Guido Kickelbick Kaspar Hegetschweiler 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(6):678-685
Liu et al. [Chin. J. Struct. Chem. (1996). 15 , 371–373] reported the structure of 6‐hydroxy‐1,4‐diazepane di(hydrogen bromide), C5H12N2O·2HBr, which was interpreted in terms of neutral diazepane and HBr molecules. We found, however, ample evidence that the formation of an organic salt, consisting of a diammonium cation and two bromide anions, is more plausible. This interpretation is also in agreement with thermogravimetric analysis and with the observed solution behaviour. The crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide, C5H14N2O2+·2Br?, measured at 142 K, crystallized in the orthorhombic space group P212121. The structure displays O—H…Br and N—H…Br hydrogen bonding. Contact distances are given. A search in the Cambridge Structural Database for the singly‐bonded H—Br moiety revealed a total of 69 structures. The question, whether these structures really include HBr as neutral molecules or rather Br? anions and a protonated substrate such as an amine, is addressed. 相似文献
76.
Kaspar F. Burri 《Helvetica chimica acta》1989,72(6):1416-1427
Derivatives of isothiazol-3(2H)-one 1,1-dioxide react regiospecifically with 1,3-dipolar agents. The main regiocontrolling factor is ascertained to be the C?O group of the dipolarophile. The topology of the adducts is also in general agreement with predictions based on perturbation theory. Several adducts can be aromatized to heterocyclic equivalents of saccharin, and may then be elaborated into structural analogs of tenoxicam (Tilcotil® and piroxicam (Feldene®)). 相似文献
77.
Kaspar Bott 《Angewandte Chemie (International ed. in English)》1979,18(4):259-265
Whereas the protonation of α-diazo-β-diketones and α-diazo-β-oxo esters with hydrogen chloride and antimony pentachloride yields the corresponding hydroxyalkenediazonium hexachloroantimonates, the “acid-sensitive” α-diazomonocarbonyl compounds can be transformed into resonance-stabilized alkenediazonium salts by an analogous O-alkylation with triethyloxonium hexachloroantimonate. A general route for synthesizing these compounds consists in the transformation of the p-toluenesulfonylhydrazones of α-halogenated aldehydes and ketones with Lewis acids. Alkenediazonium ions which are not resonance stabilized can be isolated at room temperature only if their decomposition at higher temperatures leads, via evolution of nitrogen, to vinyl cations in particularly high energy levels. Facile substitution reactions at the CC double bond with anisole and methanol demonstrate the strongly electrophilic nature of alkenediazonium salts. When electron-donating substituments are attached to C2 of an ethylenediazonium ion, the bond order of the NN triple bond can be reduced to a level comparable with that in diazoacetic ester. 相似文献
78.
A generalized E ? ? Jahn-Teller hamiltonian with a parameter δ (δ = ?1/4 in the JT case) is studied. As in the Jahn-Teller case, the angular momentum is a constant of the motion with the eigenvaluesj + 1/2 where j is a non-negative integer. For j fixed, consider two values δ1 = ?j/2 ?1/2 and δ2 = ?gd1 ?1/2. The spectrum and the eigenfunctions for δ2 are completely determined by the spectrum and the eigenfunctions for δ1. 相似文献
79.
Salignac B Grundler PV Cayemittes S Frey U Scopelliti R Merbach AE Hedinger R Hegetschweiler K Alberto R Prinz U Raabe G Kölle U Hall S 《Inorganic chemistry》2003,42(11):3516-3526
The water exchange process on [(CO)(3)Re(H(2)O)(3)](+) (1) was kinetically investigated by (17)O NMR. The acidity dependence of the observed rate constant k(obs) was analyzed with a two pathways model in which k(ex) (k(ex)(298) = (6.3 +/- 0.1) x 10(-3) s(-1)) and k(OH) (k(OH)(298)= 27 +/- 1 s(-1)) denote the water exchange rate constants on 1 and on the monohydroxo species [(CO)(3)Re(I)(H(2)O)(2)(OH)], respectively. The kinetic contribution of the basic form was proved to be significant only at [H(+)] < 3 x 10(-3) M. Above this limiting [H(+)] concentration, kinetic investigations can be unambiguously conducted on the triaqua cation (1). The variable temperature study has led to the determination of the activation parameters Delta H(++)(ex) = 90 +/- 3 kJ mol(-1), Delta S(++)(ex) = +14 +/- 10 J K(-1) mol(-1), the latter being indicative of a dissociative activation mode for the water exchange process. To support this assumption, water substitution reaction on 1 has been followed by (17)O/(1)H/(13)C/(19)F NMR with ligands of various nucleophilicities (TFA, Br(-), CH(3)CN, Hbipy(+), Hphen(+), DMS, TU). With unidentate ligands, except Br(-), the mono-, bi-, and tricomplexes were formed by water substitution. With bidentate ligands, bipy and phen, the chelate complexes [(CO)(3)Re(H(2)O)(bipy)]CF(3)SO(3) (2) and [(CO)(3)Re(H(2)O)(phen)](NO(3))(0.5)(CF(3)SO(3))(0.5).H(2)O (3) were isolated and X-ray characterized. For each ligand, the calculated interchange rate constants k'(i) (2.9 x 10(-3) (TFA) < k'(I) < 41.5 x 10(-3) (TU) s(-1)) were found in the same order as the water exchange rate constant k(ex), the S-donor ligands being slightly more reactive. This result is indicative of I(d) mechanism for water exchange and complex formation, since larger variations of k'(i) are expected for an associatively activated mechanism. 相似文献
80.
Protection (O5') of 2',3'-anhydroadenosine with tert-butyldiphenylsilyl chloride and epoxide opening with dimethylboron bromide gave the 3'-bromo-3'-deoxy xylo isomer which was treated with benzylisocyanate to give the 2'-O-(N-benzylcarbamoyl) derivative. Ring closure gave the oxazolidinone, and successive deprotection concluded an efficient route to 3'-amino-3'-deoxyadenosine. Analogous treatment of the antibiotic tubercidin [7-deazaadenosine; 4-amino-7-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine] gave 3'-amino-3'-deoxytubercidin. Trifluoroacetylation of the 3'-amino function, elaboration of the heterocyclic amino group into a (1,2,4-triazol-4-yl) ring with N,N'-bis[(dimethylamino)methylene]hydrazine, and nucleophilic aromatic substitution with dimethylamine gave puromycin aminonucleoside [9-(3-amino-3-deoxy-beta-D-ribofuranosyl)-6-(dimethylamino)purine] and its 7-deaza analogue. Aminoacylation [BOC-(4-methoxy-L-phenylalanine)] and deprotection gave puromycin and 7-deazapuromycin. Most reactions gave high yields at or below ambient temperature. Equivalent inhibition of protein biosynthesis in a rabbit reticulocyte system and parallel growth inhibition of several bacteria were observed with the 7-aza/deaza pair. Replacement of N7 in the purine ring of puromycin by "CH" has no apparent effect on biological activity. 相似文献