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991.
Susumu K Frail PR Angiolillo PJ Therien MJ 《Journal of the American Chemical Society》2006,128(26):8380-8381
We report variable temperature X-band EPR spectroscopic data for the cation radical states of meso-to-meso ethyne-bridged (porphinato)zinc(II) (PZnn) oligomers. These [PZn2-PZn7]+ species span an average 18-75 A length scale and display peak-to-peak EPR line widths (DeltaBp-p) that diminish with conjugation length. Analysis of these EPR data show that PZnn+ structures possess the largest hole polaron delocalization lengths yet measured; experiments carried out over a 4-298 K temperature domain demonstrate remarkably that the charge delocalization length remains invariant with temperature. These cation radical EPR data are well described by a stochastic, near barrierless, one-dimensional charge hopping model developed by Norris for N equivalent sites on a polymer chain, where the theoretical EPR line width is given by DeltaBp-p(N-mer) = (1/N1/2)DeltaBp-p(monomer); PZnn+ oligomers are the first such systems to verify a Norris-type hole delocalization mechanism over a substantial ( approximately 75 A) length scale. Given the time scale of the EPR measurement, these data show that either (i) Franck-Condon effects are incapable of driving charge localization in [PZn2-PZn7]+, resulting in cation radical wave functions which are globally delocalized over a spatial domain that is large with respect to established benchmarks for hole-doped conjugated materials, or (ii) polaron hopping rates in these oligomers exceed 107 s-1, even at 4 K. Finally, this study demonstrates that polymeric building blocks having low magnitude inner sphere reorganization energies enable the development of electronic materials having long polaron delocalization lengths. 相似文献
992.
Patil NT Lutete LM Wu H Pahadi NK Gridnev ID Yamamoto Y 《The Journal of organic chemistry》2006,71(11):4270-4279
A conceptually novel approach for asymmetric intramolecular hydroamination, hydroalkoxylation and hydrocarbonation of alkynes using chiral palladium catalysts are described. The reactions of the aminoalkynes 5, alkynols 7, and alkynylmethines 9 in the presence of Pd2(dba)3 x CHCl3/PhCOOH/renorphos 4 in benzene (or benzene-hexane) at 100 degrees C gave the corresponding cyclization products (nitrogen heterocycles 6, oxygen heterocycles 8, and carbocycles 10) in good yields with good enantioselectivities. The origins of enantioselectivities in the hydroamination reaction are discussed based on DFT computations. 相似文献
993.
Suri JT Mitsumori S Albertshofer K Tanaka F Barbas CF 《The Journal of organic chemistry》2006,71(10):3822-3828
Dihydroxyacetone variants have been explored as donors in organocatalytic aldol reactions with various aldehyde and ketone acceptors. The protected form of dihydroxyacetone that was chosen for in-depth study was 2,2-dimethyl-1,3-dioxan-5-one, 1. Among the catalysts surveyed here, proline proved to be superior in terms of yield and stereoselectivities in the construction of various carbohydrate scaffolds. In a fashion analogous to aldolase enzymes, the de novo preparation of L-ribulose, L-lyxose, D-ribose, D-tagatose, 1-amino-1-deoxy-D-lyxitol, and other carbohydrates was accomplished via the use of 1 and proline. In reactions using 2,2-dimethyl-1,3-dioxan-5-one 1 as a donor, (S)-proline can be used as a functional mimic of tagatose aldolase, whereas (R)-proline can be regarded as an organocatalytic mimic of fuculose aldolase. 相似文献
994.
Borate complexes formed in the ternary system at pH 9.2 containing borate, (S)-3-amino-1,2-propanediol (SAP), and DL-pantothenic acid (DL-PTA) were identified by 13C and 11B NMR, and it is confirmed that the binary complexes, [B(OH)2(SAP)], [B(SAP)2]+ [B(OH)2(D- or L-PTA)]2-, and [B(D- or L-PTA)2]3- (including [B(D-PTA)(L-PTA)]3-), and the ternary complexes, [B(SAP)(D- or L-PTA)]-, coexist at equilibrium in the ternary system. Thermodynamic experiments by variable-temperature 11B NMR revealed that the ternary complex, [B(SAP)(D-PTA)]-, is entropically more stable than [B(SAP)(L-PTA)]-. Because two geometrical isomers are possible for the respective ternary complexes, semi-empirical molecular orbital calculations were performed by PM5, PM3, and AM1 methods in order to obtain the optimized structures. It is indicated from the calculated heats of formation and experimentally obtained thermodynamic parameters that the (S)-isomer is more probable for the respective ternary complexes with D- and L-PTA. In the optimized structure of (S)-[B(SAP)(D-PTA)]- in water, the SAP and D-PTA ligands were oppositely oriented to form a rather linear structure, while the diastereomer, (S)-[B(SAP)(L-PTA)]-, had a folded structure. Because such a difference in the solvated structure of the ternary complexes can give a different electrophoretic velocity in CE, the enantioseparation of DL-PTA in CE is reasonably attributed to a difference in the observed electrophoretic mobility for the equilibrated ternary systems containing the respective ternary complexes. 相似文献
995.
Six reducing monosaccharides (mannose, galactose, fucose, glucose, xylose, and arabinose) were derivatized with 1-phenyl-3-methyl-5-pyrazolone (PMP) and chiral resolution of these racemic PMP-monosaccharides was studied by ligand-exchange CE using borate anion as a central ion of the chiral selector and (S)-3-amino-1,2-propanediol (SAP) as a chiral selector ligand. PMP-mannose, PMP-galactose and PMP-fucose were successfully enantioseparated. Lowering the capillary temperature increased the resolution of PMP-mannose system, but decreased that of PMP-galactose and PMP-fucose systems. Whereas the maximum resolution was obtained at pH 8.9 in the PMP-mannose system, resolution increased gradually with pH in the PMP-galactose and PMP-fucose systems. Expecting the formation of the ternary borate complexes with SAP and PMP-monosaccharide in the CE experiments, the optimized structures of the borate diastereomers were obtained by semiempirical molecular orbital calculations to discuss the structural difference of the diastereomers in connection with the enantioseparation behaviors. 相似文献
996.
Yuko S. Yamamoto Mitsuru Ishikawa Yukihiro Ozaki Tamitake Itoh 《Frontiers of Physics》2014,9(1):31-46
We review recent our results in the fundamental study of surface-enhanced Raman scattering (SERS) with emphasis on experiments that attempted to identify the enhancement and blinking mechanism using single Ag nanoparticle dimers attached to dye molecules. These results are quantitatively discussed in the framework of electromagnetic mechanism. We also review recent our results in basic SERS applications for biological sensing regarding detections of cell surface molecules and distinction of disease marker molecules under single cell and single molecule level. 相似文献
997.
Takahiro Tsukahara Yusuke Sakamoto Daisuke Aoshima Makoto Yamamoto Yasuo Kawaguchi 《Experiments in fluids》2012,52(4):877-890
The installation of windbreak sand fences around sand dunes is one of the most promising methods to suppress windblown sand
movement. In the study reported in this paper, we investigated the influence and validity of a small fence mounted on a model
sand dune, in order to understand the fence’s suppression mechanism on the sand movement. The flow field around the dune and
the process of sand-dune erosion were measured using LDV, PIV, and laser-sheet visualization techniques. A non-porous fence
was found to suppress sand movements in its upstream area, but to enhance erosion downstream of the fence. This intensive
erosion was caused by separated shear flow from the leading edge of the fence. In this study, four levels of porosity rate
of the fence were tested. The fence-porosity dependences of the turbulent flow field and the erosion were discussed. The shapes
of eroded sand dunes were found to depend on the porosity rate. The relationship between the sand-dune erosion and the flow
field around the dune was illustrated with schematic diagrams. We concluded that the most desirable fence porosity should
be 30% in order to avoid dune erosion if installed at a middle height on the stoss surface of a dune. This porosity provides
a mean velocity reduction with avoiding a separated flow, although the flow bleeding through the porous fence is accompanied
by grid turbulence and induces serious erosion in a narrow space behind the fence. Furthermore, we confirmed that the empirical
correlation of the critical friction velocity can be applied to sand movements influenced by a fence. 相似文献
998.
Stereoselective Synthesis of cis,cis‐Configured Perhydroquinoxaline‐5‐Carbonitrile from Cyclohex‐2‐en‐1‐ol 下载免费PDF全文
cis,cis‐Configured perhydroquinoxaline‐5‐carbonitrile 10 was synthesized stereoselectively by ditosylation of trans,cis‐2,3‐dihydroxycyclohexane‐1‐carbonitrile 4 and subsequent reaction with ethylenediamine. The diol precursor 4 was stereoselectively obtained by regioselective opening of the epoxide 3 with KCN in water avoiding hazardous Et2AlCN. 相似文献
999.
Akihiko Okumura Yasuaki Takada Susumu Watanabe Hiroaki Hashimoto Naoya Ezawa Yasuo Seto Yasuo Takayama Ryoji Sekioka Shintaro Yamaguchi Shintaro Kishi Takafumi Satoh Tomohide Kondo Hisayuki Nagashima Tomoki Nagoya 《Journal of the American Society for Mass Spectrometry》2016,27(7):1219-1226
We propose detecting a fragment ion (Ph2As+) using counter-flow introduction atmospheric pressure chemical ionization ion trap mass spectrometry for sensitive air monitoring of chemical warfare vomiting agents diphenylchloroarsine (DA) and diphenylcyanoarsine (DC). The liquid sample containing of DA, DC, and bis(diphenylarsine)oxide (BDPAO) was heated in a dry air line, and the generated vapor was mixed into the humidified air flowing through the sampling line of a mass spectrometer. Humidity effect on the air monitoring was investigated by varying the humidity of the analyzed air sample. Evidence of the in-line conversion of DA and DC to diphenylarsine hydroxide (DPAH) and then BDPAO was obtained by comparing the chronograms of various ions from the beginning of heating. Multiple-stage mass spectrometry revealed that the protonated molecule (MH+) of DA, DC, DPAH, and BDPAO could produce Ph2As+ through their in-source fragmentation. Among the signals of the ions that were investigated, the Ph2As+ signal was the most intense and increased to reach a plateau with the increased air humidity, whereas the MH+ signal of DA decreased. It was suggested that DA and DC were converted in-line into BDPAO, which was a major source of Ph2As+. 相似文献
1000.
Junichiro Kugai Satoshi Seino Takashi Nakagawa Takao A. Yamamoto 《Journal of nanoparticle research》2014,16(3):1-9
A facile chemical process has been developed for the preparation of magnetic FeCo nanoparticles. The FeCo nanoparticles were mono-dispersed, obtained by the safe and ecofriendly method, possessed saturation magnetization up to 187 emu/g, and demonstrated excellent chemical stability. In this work, we have studied how to control Fe/Co ratio by variation of precursor ratio, and how to vary particle size from 9.3 to 12.3 nm by surfactant amount used. The cytotoxicity of as-synthesized nanoparticles was investigated after coating with the poly(methyl methacrylate-co-butyl acrylate) by the emulsion process and the results demonstrated high biocompatibility. Similarly, the same synthesis method was used with the single precursor FeO(OH) or Co3O4. The results showed that this method can also fabricate 10 nm mono-dispersed spherical Fe3O4 particles and self-assembly Co nanoneedles. 相似文献