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991.
PHOTOCHEMICAL COUPLING OF 5-BROMOURACIL TO TRYPTOPHAN, TYROSINE AND HISTIDINE, PEPTIDE-LIKE DERIVATIVES IN AQUEOUS FLUID SOLUTION 总被引:4,自引:0,他引:4
Direct irradiation of 5-bromouracil (BU) in aqueous fluid solution in the presence of tryptophan (trp), tyrosine (tyr) or histidine (his) derivatives using a XeCl excimer laser at 308 nm yielded photocoupling of BU to the aromatic ring of each amino acid. Irradiation of BU at 308 nm most likely results in excitation of the n-φ* transition, intersystem crossing to the triplet manifold, and coupling via electron transfer from the aromatic amino acid. The coupling observed was regiospecific between the 5-position of uracil (U) and the 2-position of the indole and phenol rings and the 5-position of the imidazole ring of the respective amino acids. Quantum yields of photocoupling to BU ranged from 1 × 10-3 to 7 × 10-3 and paralleled known rates of electron transfer and ionization potentials of the aromatic rings. The photocoupling between BU and some of the aromatic amino acid peptide-like derivatives possibly mimics photocrosslinking of BU-DNA to associated proteins, a potentially useful photoreaction for studying nucleic acid-protein interactions. Formation of crosslinks of the type proposed here might be detected by the characteristic fluorescence emission of the uracil amino acid adducts. 相似文献
992.
Summary The complexing of Fe(II) with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine in the presence of Fe(III) represents a rapid alternative to the usual methods and provides good sensitivity. The results show that this method can also be used with very different Fe(II) or Fe(III) contents. The application described for the automatic determination of Fe(II) in ores and sinter with the continuous flow technique shows that this method can also be used in connection with automated systems. However, particular attention must be paid here to the fact that the working conditions have to be optimised for each matrix.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
993.
A. Wrońska V. Hejny C. Wilkin S. Dymov C. Hanhart V. Komarov H. R. Koch A. Kulikov A. Magiera T. Mersmann S. Mikirtytchiants H. Ohm D. Prasuhn R. Schleichert H. J. Stein H. Ströher 《The European Physical Journal A - Hadrons and Nuclei》2005,26(3):421-428
The dd↦4Heη reaction has been investigated near threshold using the ANKE facility at COSY-Jülich. Both total and differential cross-sections
have been measured at two excess energies, Q = 2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q = - 2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution
reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition
into partial amplitudes and their consequences for the determination of the s-wave ηα scattering length are discussed. 相似文献
994.
995.
Peter Beckmann Werner Koch Gernot Schreider 《Zeitschrift für Physik B Condensed Matter》1990,79(2):317-323
The driven varactor oscillator is investigated by numerical integration of its ODEs using the standard model of circuit theory. Attention is given to some properties of the basic relaxation mechanism. For time dependent amplitudes of the sinusoidal driving voltage the post-ponement of the bifurcations is characterized by transient Lyapunov numbers. The postponement of the first bifurcation shows the same dependence on the sweep velocity as in the case of the nonautonomous quadratic map. The shapes of the attractors are displayed in extended phase space. Generalized Renyi-dimensionsD
0 andD
1 have been determined in the chaotic region. A corresponding twodimensional Pioncaré map indicates selfsimilarity. 相似文献
996.
Helmut Spreitzer Ingrid Rößlhuber Harald Kienzl Elke Dörrer Gerhard Buchbauer 《Monatshefte für Chemie / Chemical Monthly》1990,121(2-3):195-201
Summary To study the structure/odour relationships of -santalol analogues two homologous -santalol derivatives5 and6 were synthesized. The key steps thereby were the -alkylation of the bicyclic starting ketones8 and14 accomplished by using more drastic conditions as usual. The odours of5 and6 are described in detail.
Auszugsweise vorgetragen am 19th International Symposium on Essential Oils and Other Substrates, 9. September 1988, Greifensee/Dübendorf, Schweiz 相似文献
997.
An energy-independent partial-wave analysis has been performed on pion-nucleon elastic and charge-exchange differential cross sections and elastic polarizations, for lab. momenta below 500 MeV/c. The amplitudes were constrained by a simultaneous fixed momentum transfer analysis, which leads to a unique and smooth solution. The masses and widths of Δ++ and Δ0 have been redetermined from total cross sections as mΔ++ = 1230.9 ± 0.3 MeV, mΔ0 = 1233.6 ± 0.5 MeV, ΓΔ++ = 111 ± 1 MeV and ΓΔ0 = 113 ± 1.5 MeV. For the pion-nucleon coupling constant the value |2 = 0.079 ± 0.001 was obtained. 相似文献
998.
999.
H.-G. Hundeck A. Sauerbrei U. Hübner T. Scheper K. Schügerl R. Koch G. Antranikian 《Analytica chimica acta》1990
A newly developed four-channel enzyme thermistor system is presented and its application to biotechnological process monitoring is discussed. Different sugars were detected on-line during the cultivation of Cephalosporium acremonium and Bacillus licheniformis on technical media and during a starch hydrolysis process with immobilized thermostable enzymes. Immobilized enzymes and entrapped microorganisms were used as biological compounds in this biosensor. 相似文献
1000.