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971.
Wang J Kubicki J Hilinski EF Mecklenburg SL Gustafson TL Platz MS 《Journal of the American Chemical Society》2007,129(44):13683-13690
Ultrafast photolysis of 9-diazofluorene (DAF) produces a broadly absorbing transient within the instrument time resolution (300 fs), which is assigned to an excited state of the diazo compound. The diazo excited state fragments to form fluorenylidene (Fl) in both its lowest energy singlet state (1Fl, 405-430 nm, depending on the solvent) and a higher energy singlet state (370 nm, 1Fl*). The excited singlet carbene has a lifetime of 20.9 ps in acetonitrile and decays to the lower energy singlet state (1Fl), which relaxes to the triplet ground state (3Fl) in acetonitrile, cyclohexane, benzene, and hexafluorobenzene. The equilibrium mixture of singlet and triplet fluorenylidene reacts with these solvents. Singlet fluorenylidene reacts with methanol and cyclohexene in competition with relaxation to 3Fl. One of the reaction products in methanol is the 9-fluorenyl cation. The rate of intersystem crossing (ISC) in hexafluorobenzene and other halogenated solvents is remarkably slow given that carbene ISC rates are generally fastest in nonpolar solvents. An explanation of this effect is advanced. 相似文献
972.
973.
Clifford JN Bell TD Tinnefeld P Heilemann M Melnikov SM Hotta J Sliwa M Dedecker P Sauer M Hofkens J Yeow EK 《The journal of physical chemistry. B》2007,111(25):6987-6991
The single-molecule fluorescence blinking behavior of the organic dye Atto647N in various polymer matrixes such as Zeonex, PVK, and PVA as well as aqueous media was investigated. Fluorescence blinking with off-times in the millisecond to second time range is assigned to dye radical ions formed by photoinduced electron transfer reactions from or to the environment. In Zeonex and PVK, the measured off-time distributions show power law dependence, whereas, in PVA, no such dependence is observed. Rather, in this polymer, off-time distributions can be best fitted to monoexponential or stretched exponential functions. Furthermore, treatment of PVA samples to mild heating and low pressure greatly reduces the frequency of blinking events. We tentatively ascribe this to the removal of water pockets within the polymer film itself. Measurements of the dye immobilized in water in the presence of methylviologen, a strongly oxidizing agent, reveal simple exponential on- and off-time distributions. Thus, our data suggest that the blinking behavior of single organic molecules is sensitive to their immediate environment and, moreover, that fluorescence blinking on- and off-time distributions do not inherently and uniquely obey a power law. 相似文献
974.
Moya SE Azzaroni O Kelby T Donath E Huck WT 《The journal of physical chemistry. B》2007,111(25):7034-7040
The conformational behavior of poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) brushes with different chain density in the presence of large benzyltributylammonium chloride (BTBAC) ions has been studied by a Quartz Crystal Microbalance with Dissipation (QCM-D) and Scanning Force Microscopy. Dense brushes do not collapse in the presence of BTBAC solutions of increasing ionic strength, contrary to what is observed in the presence of NaCl. Brush collapse can be observed for low-ionic-strength solutions of BTBAC when the brush density has been reduced. These phenomena can be explained by considering the Hofmeister series as well as ion size and free space in the brush. 相似文献
975.
Constable EC 《Chemical Society reviews》2007,36(2):246-253
This tutorial review describes the use of 2,2':6',2'-terpyridine (tpy) metal-binding domains in supramolecular chemistry. The origins of tpy chemistry are described and the reasons for its current importance in supramolecular chemistry are explained. Examples of tpy compounds in a wide variety of supramolecular chemistry are presented. The content will be of interest to organic, inorganic, supramolecular and nanoscale chemists. 相似文献
976.
Synthesis and Structures of the Dinuclear Nitrido Complexes [(Me2PhP)3(MeCN)ClRe≡N–MCl5] with M = Sn and Zr The water sensitive complexes [(Me2PhP)3(MeCN)ClRe≡N–MCl5] (M = Sn ( 1 ) und Zr ( 2 )) are obtained in dichloromethane from [ReNCl2(PMe2Ph)3] and the acetonitrile adducts of SnCl4 or ZrCl4. The compounds crystallize as dichloromethane solvate isotypically with [(Me2PhP)3(MeCN)ClRe≡N–TiCl5] · CH2Cl2 in the space group P21/n. From toluene crystallize monoclinic crystals of 1 · MeCN · C7H8. In the diamagnetic complexes 1 and 2 an anion [MCl5]– coordinates to the nitrido ligand of the cationic complex [ReNCl(MeCN)(PMe2Ph)3]+. The resulting nitrido bridges Re≡N–M are almost linear and asymmetric with Re–N = 169.5 pm, Sn–N = 230.1 pm and Re–N–Sn = 164.5° for 1 and Re–N = 168.4 pm, Zr–N = 237.2 pm and Re–N–Zr = 165.6° for 2 . The phosphine ligands at the Re atom are in a meridional arrangement. 相似文献
977.
978.
Rob G. H. Lammertink Mark A. Hempenius Edwin L. Thomas G. Julius Vancso 《Journal of Polymer Science.Polymer Physics》1999,37(10):1009-1021
A series of poly(styrene‐block‐ferrocenyldimethylsilane) copolymers (SF) with different relative molar masses of the blocks were prepared by sequential anionic polymerization. The bulk morphology of these polymers, studied by TEM and SAXS, showed well‐ordered lamellar and cylindrical domains as well as disordered micellar structures. Temperature‐dependent rheological measurements exhibited an order–disorder transition for SF 17/8 (the numbers refer to the relative molar masses in 103 g/mol) between 170 and 180°C, and an order–order transition for SF 9/19 between 190 and 200°C. The morphologies of binary blends of the diblocks with homopolymer were also investigated. In the blends the molar mass of the homopolymer was always less than the molar mass of the matching block. Ordered spheres on a bcc lattice and double‐gyroid morphology were observed for the blends. The double‐gyroid morphology was found only in F‐rich diblock/homopolymer systems. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1009–1021, 1999 相似文献
979.
Edwin R. Sukandar Sutin Kaennakam Pia Raab Xuehong Nst Kitiya Rassamee Rudolf Bauer Pongpun Siripong Taslim Ersam Santi Tip-pyang Warinthorn Chavasiri 《Molecules (Basel, Switzerland)》2021,26(21)
Garcinia picrorhiza, a woody plant native to Sulawesi and Maluku Islands, Indonesia, has been traditionally used as a wound healing ointment. In our continuous search for bioactive compounds from this plant, 15 phenolic compounds were isolated from its stem bark, including a previously undescribed dihydroisocoumarin, 2′-hydroxyannulatomarin, and two undescribed furanoxanthones, gerontoxanthone C hydrate and 3′-hydroxycalothorexanthone. The structures of the new metabolites were elucidated on the basis of spectroscopic analysis, including 1D and 2D NMR and HRESIMS. Gerontoxanthone C hydrate possessed cytotoxicity against four cancer cells (KB, HeLa S3, MCF-7, and Hep G2) with IC50 values ranging from 5.6 to 7.5 µM. Investigation on the anti-inflammatory activities showed that 3′-hydroxycalothorexanthone inhibited NO production in RAW 264.7 and BV-2 cell lines with IC50 values of 16.4 and 13.8 µM, respectively, whereas only (−)-annulatomarin possessed inhibition activity on COX-2 enzyme over 10% at 20 µM. This work describes the presence of 3,4-dihydroisocoumarin structures with a phenyl ring substituent at C-3, which are reported the first time in genus Garcinia. These findings also suggest the potential of furanxanthone derivatives as cytotoxic and anti-inflammatory agents for further pharmacological studies. 相似文献
980.