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111.
Clapham KM Batsanov AS Greenwood RD Bryce MR Smith AE Tarbit B 《The Journal of organic chemistry》2008,73(6):2176-2181
A general method for the synthesis of functionalized pyridazinylboronic acids/esters is described involving a directed ortho metalation (DoM)--boronation protocol (Schemes 1 and 2). A comprehensive study of the reactivity of the C-B bond in palladium-catalyzed cross-couplings with aryl/heteroaryl halides is presented. Aryl-/heteroarylpyridazines are thereby obtained in synthetically viable yields (typically 40-75%) although in some cases competing protodeboronation has been observed. A series of pyridazin-3(2H)-one derivatives, including 4,6-diaryl/heteroaryl derivatives, have been obtained from the corresponding 3-methoxypyridazines in straightforward procedures (Schemes 3 and 4). Several X-ray crystal structures of aryl-/heteroarylpyridazines and derived pyridazin-3(2H)-one derivatives are reported. These multi-ring systems are of considerable interest in contemporary N-heterocyclic chemistry. 相似文献
112.
J. Hiles R. A. Mott H. D. Greenwood J. W. Cobb W. C. Anderson A. P. Schachno M. D. Shukowskaja Y. Kosaka H. Toda M. I. Posin J. A. van Dijk J. C. Jacobs W. P. Zybassow S. A. Dymschitz K. M. Dworkina G. Lambris H. Boll L. Donn A. R. Rescorla F. L. Carnahan M. R. Fenske S. S. Kurtz Jr. C. E. Headington O. Diéls K. Alder G. Pastonesi W. I. Karshew 《Analytical and bioanalytical chemistry》1939,116(11-12):456-461
113.
In this paper we obtain the equivalence of the large deviation principle for Gibbs measures with and without an external field. For the Ising model, the equivalence allows us to study the result of competing influences of a positive external fieldh and a negative boundary condition in the cube ((B/h) ash0 for variousB. We find a critical balance at a valueB
0 ofB. 相似文献
114.
Paul F. Greenwood Gary D. Willett Michael A. Wilson 《Journal of mass spectrometry : JMS》1993,28(8):831-840
Ions produced by the 1064 nm Nd:YAG laser ablation of various Si–C samples include mixed silicon carbon (SixCy) cluster ions of low molecular mass. Unique SixCy cluster ion distributions are observed. A charge state effect for SixCy clusters is evident from differences between the respectively charged distributions. This may be accounted for by either differing energetics and/or differing formation mechanisms for positive and negative SixCy cluster ions. Several specific SixCy clusters of probable high stability consistently dominate the mass spectra. The chemistry of the more abundant SixCy ions was probed by collision-induced dissociation and ion–molecule reactivity experiments. Similar SixCy+˙ dissociation results in the common loss of an Si ion. Parent SixCy ion and small neutral reagent reactants give rise to oxidation, addition and exchange reactions. 相似文献
115.
116.
C. von der Heide J. Brand W. Kerp A. Gautier P. Clausmann H. D. Gibbs C. C. James A. Hubert F. Alba K. Heumann J. Wiernik L. Medicus Chr. Mebold A. C. Langmuir E. W. T. Jones J. Ryder A. Greenwood W. Thomson J. P. Shenton und C. Strzyzowski 《Fresenius' Journal of Analytical Chemistry》1909,48(7-8):497-502
Ohne Zusammenfassung 相似文献
117.
Effects of charge location on the absorptions and lifetimes of protonated tyrosine peptides in vacuo
Kelly O Calvert CR Greenwood JB Zettergren H Nielsen SB Wyer JA 《The journal of physical chemistry. A》2012,116(7):1701-1709
Nearby charges affect the electronic energy levels of chromophores, with the extent of the effect being determined by the magnitude of the charge and degree of charge-chromophore separation. The molecular configuration dictates the charge-chromophore distance. Hence, in this study, we aim to assess how the location of the charge influences the absorption of a set of model protonated and diprotonated peptide ions, and whether spectral differences are large enough to be identified. The studied ions were the dipeptide YK, the tripeptide KYK (Y = tyrosine; K = lysine) and their complexes with 18-crown-6-ether (CE). The CE targets the ammonium group by forming internal ionic hydrogen bonds and limits the folding of the peptide. In the tripeptide, the distance between the chromophore and the backbone ammonium is enlarged relative to that in the dipeptide. Experiments were performed in an electrostatic ion storage ring using a tunable laser system, and action spectra based on lifetime measurements were obtained in the range from 210 to 310 nm. The spectra are all quite similar though there seems to be some changes in the absorption band between 210 and 250 nm, while in the lower energy band all ions had a maximum absorption at ~275 nm. Lifetimes after photoexcitation were found to shorten upon protonation and lengthen upon CE complexation, in accordance with the increased number of degrees of freedom and an increase in activation energies for dissociation as the mobile proton model is no longer operative. 相似文献
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120.
We study the evolution of time-dependent fluctuations and particle production in an expanding dS and contracting AdS universe. Using the functional Schrödinger formalism we are able to probe the time-dependent regime which is out of the reach of the standard approximations like the Bogolyubov method. In both cases, the evolution of fluctuations is governed by the harmonic oscillator equation with time-dependent frequency. In the case of an expanding dS universe we explicitly show that the frequency of fluctuations produced at a certain moment diminish in time, while the distribution of the created particles quickly approaches the thermal radiation of the dS space. In the case of a contracting AdS universe we show that the frequency of fluctuations produced at a certain moment grow in time. Nominally, the temperature of radiation diverges as the Big Crunch is approaching, however, increasing oscillations of the spectrum make the temperature poorly defined, which is in agreement with the fact that AdS space does not have an event horizon which would cause thermal radiation. Unlimited growth of fluctuations indicates that an eventual tunneling into AdS vacuum would have catastrophic consequences for our universe. 相似文献