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41.
Yoon MS Ahn KH Cheung RW Sohn H Link JR Cunin F Sailor MJ 《Chemical communications (Cambridge, England)》2003,(6):680-681
Free-standing porous Si multilayer dielectric mirrors, prepared by electrochemical etching of crystalline Si, are treated with a ruthenium ring-opening metathesis polymerization (ROMP) catalyst followed by norbornene to produce flexible, stable composite materials in which poly(norbornene) is covalently attached to the porous Si matrix. 相似文献
42.
David N. -S. Hon 《Journal of polymer science. Part A, Polymer chemistry》1980,18(6):1857-1869
The formation and behavior of photo-and mechanoinduced free radicals in cellulose were studied by ESR spectroscopy and the capability of these free radicals to initiate graft copolymerization reactions was demonstrated. Although an 11-line ESR signal was detected from cellulose irradiated with ultraviolet (UV) light, a higher-intensity ESR signal with a five-line pattern was detected from a sample mechanically milled at 77 K. The decay of photoinduced free radicals when heated took place monotonously, whereas mechanoradicals exhibited an anomalous behavior with an increased signal intensity at 150 K before decaying at a higher temperature. Mechanoradicals have been found to react more efficiently and rapidly with oxygen and methyl methacrylate (MMA) than photoinduced free radicals. The peroxy mechanoradicals, however, were mobile and decayed more rapidly than the peroxy photoinduced radicals. Simultaneous graft copolymerizations of MMA to cellulose demonstrated that mechano-and photoinduced free radicals are capable of initiating grafting reactions, but a higher degree of grafting efficiency was obtained from cellulose treated mechanically. 相似文献
43.
Nyok-Sai Hon 《Journal of polymer science. Part A, Polymer chemistry》1976,14(10):2513-2525
Free-radical formation in various modifications of celluloses, namely, wood cellulose I, II, III, and IV, rayon cellulose, amorphous cellulose, cotton linters, and absorbent cotton, irradiated with ultraviolet light, has been studied by means of ESR spectroscopy at 77°K. Various types of free radicals were generated from these samples. The line shapes and the signal intensities of the ESR spectra depended greatly upon the degree of crystallinity, the lattice type, and the arrangement of molecules in cellulose. The effect of degree of crystallinity and the amount of sensitizer (Fe3+) absorbed revealed that photochemical reactions in cellulose occurred exclusively in the amorphous regions of the polymer. Free radicals formed in these samples behaved distinctively upon a warm-up process. Phenomena of radical migration and formation of new radicals were observed from the sensitized samples of rayon cellulose and amorphous cellulose. 相似文献
44.
LEE H. PrattYukio SMMAZAKIT†Yasunori Inoue†Masaki Furuya† 《Photochemistry and photobiology》1982,36(4):471-477
Phototransformation of the red-absorbing form of phytochrome (Pr) to the far-red-absorbing form (Pfr) was followed with a custom-built transient spectrum analyzer. Large phytochrome, which consisted of approximately 120000-dalton monomers, was immunopurified or conventionally purified from etiolated oat (Avena sativa L., cv. Garry) shoots. Phototransformation was initiated by exciting Pr with a 115-mJ, 600-ns half-width, 655-nm laser pulse. Absorption spectra were recorded on a microsecond time scale at predetermined times after the flash. It has been reported earlier that flash excitation of large oat Pr produces a transformation intermediate with maximum absorbance near 700 nm in a difference spectrum and that this intermediate decays by two kinetically distinct reactions. Difference spectra for these two reactions are indistinguishable. Both show bleaching centered at 690 nm with no detectable associated absorbance increase between 570 and 830 nm. Subsequent appearance of absorbance at 724 nm, which presumably but not necessarily represents the appearance of Pfr, had earlier been shown to occur by two kinetically distinct reactions for large oat phytochrome. Data presented here indicate in addition the occurrence of a third, slower reaction. Difference spectra for the two faster reactions are indistinguishable, both with maxima near 728 nm and minima near 650 nm. The difference spectrum for the slowest component, however, was qualitatively different exhibiting a maximum near 722 nm with no corresponding minimum. About 15-20% of the absorbance increase at 724 nm occurred by this slowest reaction, which exhibited a half-life of 3 s at 25°C and a Q10 of 1.2 for immunopurified and 1.5 for conventionally purified phytochrome. The percentage occurring by this reaction was independent of temperature over the range studied (1-25dEC). For immunopurified phytochrome the enthalpy of activation, Gibbs free energy of activation, and entropy of activation of this slowest reaction were found to be about lOkJ-mol-1, 75kJ.mol-1, and -220 J.mol-1 K-1, respectively, and for conventionally purified phytochrome 25kJ.mol-1, 75kJ.mol-1and —170 J.mol-1 K-1, respectively. The thermodynamic characteristics of this reaction indicate that it may involve a significant ordering of the protein moiety as it transforms to Pfr. 相似文献
45.
Functionalized o-carboranes are interesting ligands for transition metals. Reaction of LiC2B10H11 with Me2NCH2CH2Cl in toluene afforded 1-Me2NCH2CH2-1,2-C2B10H11 (1). Treatment of 1 with 1 equiv. of n-BuLi gave [(Me2NCH2CH2)C2B10H10]Li ([1]Li), which was a very useful synthon for the production of bisfunctional o-carboranes. Reaction of [1]Li with RCH2CH2Cl afforded 1-Me2NCH2CH2-2-RCH2CH2-1,2-C2B10H10 (R = Me2N (2), MeO (3)). 1 and 2 were also prepared from the reaction of Li2C2B10H10 with excess Me2NCH2CH2Cl. Treatment of [1]Li with excess MeI or allyl bromide gave the ionic salts, [1-Me3NCH2CH2-2-Me-1,2-C2B10H10][I] (4) and [1-Me2N(CH2=CHCH2)CH2CH2-2-(CH2=CHCH2)-1,2-C2B10H10][Br] (6), respectively. Interaction of [1]Li with 1 equiv. of allyl bromide afforded 1-Me2NCH2CH2-2-(CH2=CHCH2)-1,2-C2B10H10 (5). Treatment of [1]Li with excess dimethylfulvene afforded 1-Me2NCH2CH2-2-C5H5CMe2-1,2-C2B10H10 (7). Interaction of [1]Li with excess ethylene oxide afforded an unexpected product 1-HOCH2CH2-2-(CH2=CH)-1,2-C2B10H10 (8). 1 and 3 were conveniently converted into the corresponding deborated compounds, 7-Me2NHCH2CH2-7,8-C2B9H11 (9) and 7-Me2NHCH2CH2-8-MeOCH2CH2-7,8-C2B9H10 (10), respectively, in MeOH-MeOK solution. All of these compounds were characterized by various spectroscopic techniques and elemental analyses. The solid-state structures of 4 and 6-10 were confirmed by single-crystal X-ray analyses. 相似文献
46.
An efficient and regioselective synthesis of 2-methyl-2H-indazoles and 2-ethyl-2H-indazoles using trimethyloxonium tetrafluoroborate or triethyloxonium hexafluorophosphate is reported. 相似文献
47.
Ka-Man Cheung 《Journal of organometallic chemistry》2005,690(2):253-260
Treatment of Ni(HP1) (H3P1 = meso-5-[4′-(2″-pyridyl)phenyl]-10,15,20-triphenyporphyrin) with K2[PdCl4] in EtOH afforded [Pd{Ni(P1)}]2(μ-Cl)2 that reacted with NaS2CNEt2 to give Pd(S2CNEt2)[Ni(P1)]. Reaction of Ni(HP1) with [Ir(H)2(PPh3)2(Me2CO)2][BF4] afforded Ir(H)Cl(PPh3)2[Ni(P1)]. The crystal structures of Pd(S2CNEt2)[Ni(P1)] and Ir(H)(Cl)(PPh3)2[Ni(P1)] have been determined. 相似文献
48.
Carina Hey Pui Cheung Jianchao Xu Chi Lung Lee Yanfeng Zhang Ruohan Wei Donald Bierer Xuhui Huang Xuechen Li 《Chemical science》2021,12(20):7091
Herein, we report the development of a facile synthetic strategy for constructing diverse peptide structural architectures via chemoselective peptide ligation. The key advancement involved is to utilize the benzofuran moiety as the peptide salicylaldehyde ester surrogate, and Dap–Ser/Lys–Ser dipeptide as the hydroxyl amino functionality, which could be successfully introduced at the side chain of peptides enabling peptide ligation. With this method, the side chain-to-side chain cyclic peptide, branched/bridged peptides, tailed cyclic peptides and multi-cyclic peptides have been designed and successfully synthesized with native peptidic linkages at the ligation sites. This strategy has provided an alternative strategic opportunity for synthetic peptide development. It also serves as an inspiration for the structural design of PPI inhibitors with new modalities.Methods of introducing peptide salicylaldehyde esters and hydroxyl amine functionality into the peptide side chain have been developed. Diverse peptide structural motifs were constructed via ligation with native amide linkages at the ligation sites. 相似文献
49.
Ka-Man Cheung Ka-Wang Chan Ian D. Williams 《Journal of organometallic chemistry》2005,690(12):2913-2921
Treatment of [Ir(ppy)2(μ-Cl)]2 and [Ir(ppy)2(dtbpy)][OTf] (ppy = 2-(2′-pyridyl)phenyl; dtbpy = 4,4′-di-tert-butyl-2,2′-bipyridine; OTf = triflate) with pyridinium tribromide in the presence of Fe powder led to isolation of [Ir(4-Br-ppy)(μ-Br)]2 (1) and [Ir(4-Br-ppy)2(dtbpy)][OTf] (2), respectively. Pd-catalyzed cross-coupling of 2 with RB(OH)2 afforded [Ir(4-R-ppy)2(dtbpy)][OTf] (R = 4′-FC6H4 (3)), 4′-PhC6H4 (4), 2′-thienyl (5), 4′-C6H4CH2OH (6). Treatment of 4 with B2(pin)2 (pin = pinacolate) afforded [Ir{4-(pin)B-ppy}2(dtbpy)][OTf] (7). The alkynyl complexes [Ir(4-PhCC-ppy)2(dtbpy)][OTf] (8) and [Ir{4-Me2(OH)CC-ppy}(4-Br-ppy)(dtbpy)][OTf] (9) were prepared by cross-coupling of 2 with PhCCSnMe3 and Me2C(OH)CCH, respectively. Ethynylation of [Ir(fppy)2(dtbpy)][OTf] (fppy = 5-formyl-2-(2′-pyridyl)phenyl) with Ohira’s reagent MeCOC(N2)P(O)(OEt)2 afforded [Ir{5-HCC-ppy}2(dtbpy)][OTf] (10). The solid-state structures of 2, 5, 7, and 10 have been determined. 相似文献
50.