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81.
82.
Gunter Radig 《Ultrasonics》1967,5(4):235-238
This article describes in detail the elucidation of an equivalent RF-circuit diagram for an electronic ultrasonic image converter tube, and discusses practical aspects of the construction of the tube itself. 相似文献
83.
84.
Gero P. Hooff Nina Patel W. Gibson Wood Walter E. Müller Gunter P. Eckert Dietrich A. Volmer 《Analytical and bioanalytical chemistry》2010,398(4):1801-1808
The isoprenoids farnesyl-(FPP) and geranylgeranylpyrophosphate (FPP and GGPP) are two major lipid intermediates in the mevalonate
pathway. They participate in post-translational modification of members of the superfamily of small guanosine triphosphatases
(GTPases; Ras, Rab, Rac, etc.) via prenylation reactions. Due to the important role of these proteins in a number of cell
processes, in particular cell growth, division, and differentiation, investigation of the involvement of isoprenoids in these
processes is of great interest. In a previously published report, we described a fully validated assay for the quantitation
of the two isoprenoids using a high-performance liquid chromatography (HPLC)–fluorescence detection (FLD) method. The current
work expands on the previous method and enhances it greatly by using a much faster state-of-the-art ultrahigh-performance
liquid chromatography (UHPLC) technique coupled to tandem mass spectrometry (MS/MS). The method exhibited a linear concentration
range of 5–250 ng/mL for FPP and GGPP in human brain tissue; it was shown to be unaffected by ion suppression and provided
results almost six times faster than the HPLC–FLD assay. Comparison of UHPLC–MS/MS and HPLC–FLD yielded excellent comparability
of the two assays for both isoprenoids. Based on the UHPLC–MS/MS assay, a novel in vitro test system was implemented to study
enzyme specificity for distinct amino acid CAAX motifs, which is potentially useful for investigating target interactions
of new therapeutics for diseases involving pathological regulation of isoprenoids and/or small GTPases. 相似文献
85.
Bounds on the exponential decay of generalized eigenfunctionsof bounded and unbounded selfadjoint Jacobi matrices in are established. Two cases are considered separatelyand lead to different results: (i) the case in which the spectralparameter lies in a general gap of the spectrum of the Jacobimatrix and (ii) the case of a lower semibounded Jacobi matrixwith values of the spectral parameter below the spectrum. Itis demonstrated by examples that both results are sharp. Weapply these results to obtain a "many barriers-type" criterionfor the existence of square-summable generalized eigenfunctionsof an unbounded Jacobi matrix at almost every value of the spectralparameter in suitable open sets. In particular, this leads toexamples of unbounded Jacobi matrices with a spectral mobilityedge, i.e., a transition from purely absolutely continuous spectrumto dense pure point spectrum. 相似文献
86.
87.
88.
Jeongbin Yim Sujeong Kim Gunter Walcher Wolfgang Pfleiderer 《Helvetica chimica acta》1993,76(5):1970-1979
The nonenzymatic synthesis of aurodrosopterin ( 5 ) from 6-acetyl-2-amino-3, 7, 8, 9-tetrahydro-4H-pyrimido-[4,5-b][1,4]diazepin-4-one ( 3 ) and 7,8-dihydrolumazine ( 4 ) at pH 3 (HCl) was performed. The identity of the synthesized compound with the natural eye pigment isolated from drosophila heads was confirmed by thin-layer chromatography on cellulose and by comparisons of the 1H-NMR and UV/VIS spectra. The nonenzymatic synthesis of a neodrosopterin-like red pigment from 3 and 2,4-diamino-7,8-dihydropteridine was also carried out, but its identity could not be established. This pigment, called aminodrosopterin, has an absorption peak at 489 nm, which is very close to that of neodrosopterin. 相似文献
89.
Mara E. F. Braibante Gunter Clar Marcos A. P. Martins 《Journal of heterocyclic chemistry》1993,30(4):1159-1160
1-Methyl-5-(trifluoromethyl)-1H-pyrazoles 2, 3 and 4,5-dihydro-1-phenyl-5-(trifluoromethyl)-1H-pyrazol-5-ol 4 were prepared by reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones 1 and hydrazine, methylhydrazine, and phenylhydrazine, respectively, in good yields. Compound 1 proved to be a versatile building block for the regiospecific construction of pyrazole rings having an 5-trifluoromethyl substituent. 相似文献
90.
Flamigni L Talarico AM Serroni S Puntoriero F Gunter MJ Johnston MR Jeynes TP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(11):2649-2659
[2]Catenanes made up of several polyether-strapped porphyrin macrocycles interlinked with the cyclic electron acceptor cyclobis(paraquat-p-phenylene) were spectroscopically, photophysically, and electrochemically characterized. The catenanes exhibit very rich redox behavior due to the presence of several different and interacting electro-active subunits. The redox patterns represent useful "fingerprints" that provide detailed information on the electronic interactions and the chemical environments that the electroactive subunits experience in the supramolecular arrays. A photoinduced electron transfer from the porphyrin excited state (charge separation CS) occurs with tau=20 ps in the catenanes with a larger strap and faster than 20 ps (instrumental resolution) in the catenanes with a shorter strap. The resulting charge-separated state recombines to the ground state (charge recombination CR) with lifetimes similar in all cases, 41+/-4 ps. Comparison of the electron transfer rates CS and CR in the host-guest complexes of the same porphyrins with the noncyclic electron acceptor paraquat, indicate slower reactions in the [2]catenanes. This behavior is assigned to the different separation between reacting partners determined by the type of bond (weak interaction or mechanical) and to a two-step consecutive electron transfer to different sites of the macrocyclic electron acceptor in the catenanes which retards charge recombination. 相似文献