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21.
Ralph de Laubenfels 《Semigroup Forum》1986,33(1):257-263
We show that a linear operator (possibly unbounded), A, on a reflexive Banach space, X, is a scalar-type spectral operator, with non-negative spectrum, if and only if the following conditions hold.
- A generates a uniformly bounded holomorphic semigroup {e?zA}Re(z)≥0.
- If \(F_N (s) \equiv \int_{ - N}^N {\tfrac{{\sin (sr)}}{r}} e^{irA} dr\) , then {‖FN‖} N=1 ∞ is uniformly bounded on [0,∞) and, for all x in X, the sequence {FN(s)x} N=1 ∞ converges pointwise on [0, ∞) to a vector-valued function of bounded variation.
22.
J. D. Petke Gerald M. Maggiora‡ Lester Shipman‡ Ralph E. CHRISTOFFERSEN‡ 《Photochemistry and photobiology》1979,30(2):203-223
Abstract— Ab initio configuration interaction wavefunctions and energies are reported for the ground state and many low-lying excited singlet and triplet states of ethyl pheophorbide a (Et-Pheo a) and ethyl chlorophyllide a (Et-Chl a), and are employed in an analysis of the electronic absorption spectra of these systems. In both molecules the visible spectrum is found to consist of transitions to the two lowest-lying 1(π, π*) states, S1 and S2. The configurational compositions of S1 and S2 in both molecules are similar, and are described qualitatively in terms of a four-orbital model. The S1← S0 transition in each case is predicted to be intense, and is largely in-plane y-polarized, while the S2← S0 transition is predicted to be extremely weak and in-plane polarized. The orientation of the S2← S0 transition dipole is not conclusively established in the present calculations. The Soret band in both molecules is composed of transitions to no less than ten states (S3-S12 in Et-Chl a and S3-S7S9-S12. and S14 in Et-Pheo a), which exhibit primarily (π, π*) character. The configurational compositions of these states are generally a complex mixture of excitations from both occupied macrocyclic π molecular orbitals and occupied orbitals with electron density in the cyclopen-tanone ring and the carbomethoxy chain. No clear correspondences are evident between respective Soret states of the two systems. Transitions to these states are generally intense and display a variety of in-plane polarizations. Two additional Soret states of Et-Pheo a, S8 and S13, exhibit primarily (n. π*) character. S8 is characterized by excitations from u and non-bonding regions of the carbomethoxy chain, while S13 is described by n →π* excitations involving the nitrogen atom of ring II. No corresponding (n, π*) states were found for Et-Chl a. In both molecules the lowest two triplet states, T1 and T2, are found to lie lower in energy than S1. while T, and S1 are approximately degenerate. The configurational compositions of T1-T4 of both molecules are nearly identical, and may be described by a four-orbital model. However, the compositions of T1-T4 differ sharply from those of S1 and S2. A number of higher-lying 3(π, π*) states of both molecules (T5-T13 in Et-Chi a and T8-T9, T11-T13 in Et-Pheo a) are found to have energies similar to the singlet Soret states, relative to S0. They are characterized by a complex mixture of configurations which do not include significant contributions involving the four-orbital model. In addition, two 3(n, π*) states of Et-Pheo a, T10 and T14, are found, which are somewhat analogous to S8 and S13. Additional data presented include the charge distributions and molecular dipole moments of the S0. S1, and T1 states of both molecules, as well as energies and oscillator strengths of computed Sn←S1 and Tn←1 transitions. 相似文献
23.
Puzenko A Hayashi Y Ryabov YE Balin I Feldman Y Kaatze U Behrends R 《The journal of physical chemistry. B》2005,109(12):6031-6035
We discuss the relaxation dynamics of glycerol-water mixtures, as studied by dielectric spectroscopy in the frequency range from 1 Hz to 250 MHz and at temperatures between 173 and 323 K. The experimental results obtained for the glycerol-rich mixtures suggest that the main dielectric relaxation process, as well as the so-called high-frequency "excess wing" (EW) and dc conductivity, follow the same temperature dependence. This result indicates that all of these processes are induced by the same molecular origin. A new phenomenological function is proposed to describe the whole dielectric spectrum in the covered frequency range, and some possible mechanisms of dielectric behaviors through the dc conductivity, the main relaxation process, and the EW are discussed. 相似文献
24.
A. v. Richthofen Rainer Cremer Ralph Domnick Dieter Neuschütz 《Analytical and bioanalytical chemistry》1997,358(1-2):308-311
Ti-Al-O layers were deposited on Si-<100> wafers at 500 °C by means of reactive magnetron sputtering ion plating (R-MSIP).
An Al-target was sputtered in rf-mode and a Ti-target in dc-mode simultaneously by an oxygen/argon plasma. The influence of
the Al- and Ti-sputter powers on composition, structure, and morphology of the Ti-Al-O layers and the binding states of the
components were investigated. The analysis with EPMA, XPS, AES and TEM yielded the following results: Ti-Al-O coatings with
different Ti, Al, and O contents in the range of TiO2 to Al2O3 were grown. TEM structure analysis revealed: the pure TiO2 film consisted of the tetragonal phases rutile and anatase; the two structures were found in the titanium-rich Ti-Al-O film,
too, but with significant smaller lattice constants. The aluminium-rich Ti-Al-O film displayed the same cubic structure of
γ-Al2O3 as determined for the pure Al2O3 film, but the lattice constant is significant lower. Evaluation of the TEM pattern of the film with a Ti/Al ratio of 0.8
indicates a hexagonal structure with lattice constants similar to those of κ′-Al2O3. All films are nanocrystalline and not textured.
Received: 24 June 1996 / Revised: 27 December 1996 / Accepted: 4 January 1997 相似文献
25.
Samuel K Yin W Stearns RA Tang YS Chaudhary AG Jewell JP Lanza T Lin LS Hagmann WK Evans DC Kumar S 《Journal of mass spectrometry : JMS》2003,38(2):211-221
Metabolic activation of drug candidates to electrophilic reactive metabolites that can covalently modify cellular macromolecules may result in acute and/or idiosyncratic immune system-mediated toxicities in humans. This presents a significant potential liability for the future development of these compounds as safe therapeutic agents. We present here an example of an approach where sites of metabolic activation within a new drug candidate series were rapidly identified using online liquid chromatography/multi-stage mass spectrometry on an ion trap mass spectrometer. This was accomplished by trapping the reactive intermediates formed upon incubation of compounds with rat and human liver microsomes as their corresponding glutathione conjugates and mass spectral characterization of these thiol adducts. Based on the structures of the GSH adducts identified, potential sites and mechanisms of bioactivation within the chemical structure were proposed. These metabolism studies were interfaced with iterative structural modifications of the chemical series in order to block these bioactivation sites within the molecule. This strategy led to a significant reduction in the propensity of the compounds to undergo metabolic activation as evidenced by reductions in the irreversible binding of radioactivity to liver microsomal material upon incubation of tritium-labeled compounds with this in vitro system. With the efficiency and throughput achievable with such an approach, it appears feasible to identify and address the metabolic activation potential of new drug leads during routine metabolite identification studies in an early drug discovery setting. 相似文献
26.
Huwe A Mazitschek R Giannis A 《Angewandte Chemie (International ed. in English)》2003,42(19):2122-2138
Cell division (mitosis) is one of the basic requirements for multicellular oranisms. The capability of a cell to replicate enables a complex assembly to be created. Faulty regulation of the control mechanism in the cell cycle leads to an excessive cell proliferation and is the cause of cancer. The key position of the cyclin-dependent kinases (CDKs) and their direct partners, as well as the fact that the majority of malign illnesses show defects in at least one of these key players of the cell cycle, is of great interest for the development of low-molecular-weight CDK inhibitors. In this Review an overview of the different structural classes of ATP-competitive inhibitors of CDKs are given, whose devlopment was aimed at battling cancer. The Review shows how far the development of selective CDK inhibitors has progressed and to what extent the expectations for such drugs have so far been fulfilled. 相似文献
27.
Julliane Diniz Yoneda Magaly Giro Albuquerque Ktia Zaccur Leal Peter R. Seidl Ralph A. Wheeler Scott E. Boesch Ricardo Bicca de Alencastro Maria Cecília B.V. de Souza Vitor F. Ferreira 《Journal of Molecular Structure》2006,778(1-3):97-103
Conformational analysis of nucleosides may have direct applications to the structure–activity relationship (SAR) studies and in the design of new drug candidates. Although conformational analysis may be accessed in many different ways, in this work it was performed using molecular dynamics (MD) simulation in order to study the dynamic behavior of a nucleoside derivative of 1,4-dihydro-4-oxoquinoline-3-carboxylic acid, synthesized by our group as a potential antiviral agent. The MD simulation was carried out during 10 ns in vacuum and in a box of water at two different temperatures (i.e., 300 and 600 K) using the AMBER force field. The in vacuum MD simulation results are in agreement with the crystallographic structure and with the DFT calculations of the nucleoside, revealing the anti conformer as the more stable one. The simulation in water, however, shows that both conformers may exist at 300 K, the temperature of the in vivo and in vitro assays, revealing that both the syn and anti conformers should be considered in a MD simulation study of the inhibitor–enzyme complex. Simulations are also in agreement with the NOE experiment, which shows that the anti conformer is the preferential one in DMSO-d6 solution at 298 K. 相似文献
28.
M. J. Musmar M. Robert Willcott Gary E. Martin Robert T. Gampe Masatomo Iwao Milton L. Lee Ralph E. Hurd Leroy F. Johnson Raymond N. Castle 《Journal of heterocyclic chemistry》1983,20(6):1661-1669
Development of successively higher field nmr spectrometers has facilitated the study of increasingly more complex molecules, although smaller molecules such as phenanthro[3,4-b]thiophene still offer very substantial assignment problems because of the highly congested nature of their 1H- and 13C-nmr spectra. Assignments of such spectra, if they are to be unequivocal, frequently require the utilization of two-dimensional nmr spectroscopic techniques. Total assignments of the 1H- and 13C-nmr spectra of phenanthro[3,4-b]thiophene are reported. Assignments were based on a conventional high resolution 500 MHz 1H-nmr spectrum, autocorrelated two-dimensional 1H-nmr spectra (COSY), two-dimensional 1H-13C chemical shift correlation spectra and a modified version of autocorrelated 13C-13C double quantum coherence two-dimensional nmr spectroscopy. From NOE measurements, a separation of 1.99 Å between H1 and H11 was computed, suggesting that phenanthro[3,4-b]thiophene has a pronounced helical conformation in solution. 相似文献
29.
The products of the reaction of butadiene with diethyl malonate catalysed by a palladium complex and of butadiene with acetaldehyde catalysed by a nickel(0) complex have been used in two syntheses of 3,7-dimethylpentadecan-2-ol. 相似文献
30.
The alkylhalide-halide association ions, [RX2]? that are observed in the negative chemical ionization mass spectra of alkyl halides appear to be directly related to the corresponding SN2 transition states in solution. ‘Frontside’ association of halide ions with bridgehead alkyl halides does not occur in our system. The Change in heats and entropies of association for the chloromethane series is consistent with delocalization in the [RX]2? ions. 相似文献