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141.
Kristiansen UR Mattei PO Pinhede C Amielh M 《The Journal of the Acoustical Society of America》2011,130(4):1851-1855
It is well known that airflow in a corrugated pipe can excite whistling at the frequencies of the pipe's longitudinal acoustic modes. This short contribution reports on the results of experiments where a low frequency, oscillating flow with velocity magnitudes of the same order as the airflow has been added. Depending on the oscillation strength, it has been found that this flow may silence the pipe or move the whistling to higher harmonics. It is also shown that the low frequency oscillation itself may excite higher frequency whistling sounds in the pipe. 相似文献
142.
Germain AR Bruggemeyer DM Zhu J Genet C O'Brien P Porco JA 《The Journal of organic chemistry》2011,76(8):2577-2584
Enantioselective syntheses of the azaphilone natural products (+)-sclerotiorin and (+)-8-O-methylsclerotiorinamine that possess the natural R-configuration at the quaternary center are reported. The syntheses were accomplished using copper-mediated asymmetric dearomatization employing bis-μ-oxo copper complexes prepared from readily available (+)-sparteine surrogates. Of note, site-selective O-methylation of a vinylogous pyridone was used to access the isoquinolin-6(7H)-one core of (+)-8-O-methylsclerotiorinamine. 相似文献
143.
Donohoe TJ Callens CK Flores A Lacy AR Rathi AH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(1):58-76
1,2-Amino alcohols are high-value, versatile functional groups that are found in scores of biologically active molecules and other interesting synthetic targets such as ligands and auxiliaries. Given their prominent position within organic compounds of import, it is no surprise to note that many routes have been developed to access this motif and there are many different starting points from which a synthetic chemist might embark on a synthesis. However, one particular approach stands out from the others, and this is the direct conversion of an alkene to a vicinal amino alcohol derivative (oxyamination). Research in this field has been particularly active in recent years and many interesting new methodologies have been reported. The purpose of this review is to give the reader a tour of the methods that have emerged in the last few years so one can appreciate the myriad of different metals and reagents that can accomplish the oxyamination of alkenes. There are still many challenges to be overcome and, herein, we also outline the areas that are ripe for further development and which bode well for the future. 相似文献
144.
Cedric Maton Dr. Neil R. Brooks Prof. Dr. Luc Van Meervelt Prof. Dr. Koen Binnemans Dr. Stijn Schaltin Prof. Dr. Jan Fransaer Prof. Dr. Christian V. Stevens 《Chemphyschem》2013,14(15):3503-3516
Novel peralkylated imidazolium ionic liquids bearing alkoxy and/or alkenyl side chains have been synthesized and studied. Different synthetic routes towards the imidazoles and the ionic liquids comprising bromide, iodide, methanesulfonate, bis(trifluoromethylsulfonyl)imide ([NTf2]?), and dicyanamide {[N(CN)2]?} as the anion were evaluated, and this led to a library of analogues, for which the melting points, viscosities, and electrochemical windows were determined. Incorporation of alkenyl moieties hindered solidification, except for cations with high symmetry. The alkoxy‐derivatized ionic liquids are often crystalline; however, room‐temperature ionic liquids (RTILs) were obtained with the weakly coordinating anions [NTf2]? and [N(CN)2]?. For the viscosities of the peralkylated RTILs, an opposite trend was found, that is, the alkoxy derivatives are less viscous than their alkenyl‐substituted analogues. Of the crystalline compounds, X‐ray diffraction data were recorded and related to their molecular properties. Upon alkoxy substitution, the electrochemical cathodic limit potential was found to be more positive, whereas the complete electrochemical window of the alkenyl‐substituted imidazolium salts was shifted to somewhat more positive potentials. 相似文献
145.
Valérie Marvaud Juan M. Herrera Thomas Barilero Fabien Tuyeras Raquel Garde Ariane Scuiller Caroline Decroix Martine Cantuel Cédric Desplanches 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):149-163
This paper points out some recent achievements in the chemistry and physics of high spin and anisotropic molecules based
on polycyanometalate complexes. Following a step by step synthetic strategy and using a localized electron orbital model,
isotropic high spin molecules were obtained with ground spin states ranging from S = 9/2 to 27/2. In the same way, anisotropic molecules with various nuclearities (bi, tri, tetra, hexa, and hepta-nuclear
complexes) have been synthesized. Mixing these two approaches, it has been possible to obtained anisotropic high spin molecules
that behave as single molecule magnets. The paper reviews some of the steps that lead to these findings and some of the prospects
opened in the field of single molecule magnets.
Corresponding author. E-mail: marvaud@ccr.jussieu.fr
Received July 19, 2002; accepted July 23, 2002 相似文献
146.
Cedric Poulain Nicolas Mazellier Philippe Gervais Yves Gagne Christophe Baudet 《Flow, Turbulence and Combustion》2004,72(2-4):245-271
In this paper we report an experimental investigation of various statistical properties of the spatial Fourier modes of the vorticity field in turbulent jets for a large range of Reynolds numbers (530 ≤R λ≤ 6100). The continuous time evolution of a spatial Fourier mode of the vorticity distribution, characterized by a well-defined wavevector, is obtained from acoustic scattering measurements. The spatial enstrophy spectrum, as a function of the spatial wave-vector, is determined by scanning the incoming sound frequencies. Time-frequency analysis of the turbulent vorticity fluctuations is also performed for different length scales of the flows. Vorticity time-correlations show that the characteristic time of a Fourier mode behaves as the sweeping time. Finally, we report preliminary Lagrangian velocity measurements obtained using acoustic scattering by soap bubbles inflated with helium. Gathering a large number of passages of isolated bubbles in the scattering volume, one is able to compute the Lagrangian velocity PDF and velocity spectrum. Despite the spatial filtering due to the finite size of the bubble, the latter exhibits a power law, with the -2 exponent predicted by the Kolmogorov theory, over one decade of frequencies. 相似文献
147.
Cedric L. Hugelshofer Thomas Magauer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(42):11533-11537
The first asymmetric total synthesis of the antifeedant terpenoids (+)‐norleucosceptroid A, (−)‐norleucosceptroid B, and (−)‐leucosceptroid K has been accomplished. This highly concise synthetic route was guided by our efforts to develop a platform for the collective synthesis of a whole family of antifeedant natural products. The synthesis features a Hauser–Kraus‐type annulation followed by an unprecedented, highly efficient intramolecular dilactol aldol‐type condensation reaction to produce the 5,6,5 skeleton. The developed synthetic route proceeds for norleucosceptroid A and B in 16 steps (longest linear sequence) from known compounds. 相似文献
148.
An efficient modified Hantzsch reaction is described for the synthesis of optically pure thiazole amino acid derivatives from the corresponding amino acids. The method is exemplified by the synthesis of a derivative of L-(Gln)Thz, the novel chiral thiazole amino acid moiety of dolastatin 3. The Cotton effects of thiazole amino acids correlate well with the absolute stereochemistry of these compounds. 相似文献
149.
Visinescu D Desplanches C Imaz I Bahers V Pradhan R Villamena FA Guionneau P Sutter JP 《Journal of the American Chemical Society》2006,128(31):10202-10212
Two main questions are addressed in this study: (i) What increase of exchange interaction can be expected when replacing a paramagnetic metal ion with a heavier congener located farther down the periodic table (i.e., 3d-4d-5d), and (ii) for a molecular unit with higher coordination numbers, eight in the present case, how is the magnetic information transferred from the metal ion to its ligand set? Qualitative and quantitative investigations on a series of trimetallic cyano-bridged {MoV(CN)8-NiII} and {WV(CN)8-NiII} compounds revealed ferromagnetic interactions but with a strength modulated by the spin organization and their nature. DFT calculations have been used to examine the mechanism and strengths of the exchange coupling, as well as the influence of the local symmetry of the cyanometalate unit on the spin density distribution. Both the experimental and the calculated behaviors underline a noticeable difference between the Mo and the W derivatives (JMoNi = 26.9 cm(-1) and JWNi = 37.3 cm(-1)) that is correlated to the spin density transferred from the metal center to its ligand set. It is also shown that the shape of the {M(CN)8} polyhedron may lead to nonequivalent CN sites and, consequently, to different strengths of the exchange interaction as a result of the position of the bridging ligands. 相似文献
150.
Nazeeruddin MK Wang Q Cevey L Aranyos V Liska P Figgemeier E Klein C Hirata N Koops S Haque SA Durrant JR Hagfeldt A Lever AB Grätzel M 《Inorganic chemistry》2006,45(2):787-797
A new ruthenium(II) complex, tetrabutylammonium [ruthenium (4-carboxylic acid-4'-carboxylate-2,2'-bipyridine)(4,4'-di(2-(3,6-dimethoxyphenyl)ethenyl)-2,2'-bipyridine)(NCS)(2)] (N945H), was synthesized and characterized by analytical, spectroscopic, and electrochemical techniques. The absorption spectrum of the N945H sensitizer is dominated by metal-to-ligand charge-transfer (MLCT) transitions in the visible region, with the lowest allowed MLCT bands appearing at 25 380 and 18 180 cm(-1). The molar extinction coefficients of these bands are 34 500 and 18 900 M(-1) cm(-1), respectively, and are significantly higher when compared to than those of the standard sensitizer cis-dithiocyanatobis(4,4'-dicarboxylic acid-2,2'-bipyridine)ruthenium(II). An INDO/S and density functional theory study of the electronic and optical properties of N945H and of N945 adsorbed on TiO(2) was performed. The calculations point out that the top three frontier-filled orbitals have essentially ruthenium 4d (t(2g) in the octahedral group) character with sizable contribution coming from the NCS ligand orbitals. Most critically the calculations reveal that, in the TiO(2)-bound N945 sensitizer, excitation directs charge into the carboxylbipyridine ligand bound to the TiO(2) surface. The photovoltaic data of the N945 sensitizer using an electrolyte containing 0.60 M butylmethylimidazolium iodide, 0.03 M I(2), 0.10 M guanidinium thiocyanate, and 0.50 M tert-butylpyridine in a mixture of acetonitrile and valeronitrile (volume ratio = 85:15) exhibited a short-circuit photocurrent density of 16.50 +/- 0.2 mA cm(-2), an open-circuit voltage of 790 +/- 30 mV, and a fill factor of 0.72 +/- 0.03, corresponding to an overall conversion efficiency of 9.6% under standard AM (air mass) 1.5 sunlight, and demonstrated a stable performance under light and heat soaking at 80 degrees C. 相似文献