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71.
S Y Chang T A Moore L L Devaud L C Taylor E B Hollingsworth 《Journal of chromatography. A》1991,562(1-2):111-118
Gas chromatography-high-resolution selected-ion monitoring mass spectrometry was used to analyze catecholamine metabolites in rat brain microdialysate. Dialysate samples were collected in vials containing stable isotope analogues of homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 5-hydroxyindoleacetic acid (5HIAA) and analyzed as their trimethylsilyl derivatives. The metabolite levels were monitored at 20-min intervals throughout the time course of the experiment, beginning immediately after surgery and implantation of the dialysis probe and ending 4 h after amphetamine treatment. The levels of HVA were observed to decrease after amphetamine treatment, while those of MHPG and 5HIAA did not change significantly. 相似文献
72.
J. Billiter K. Bennewitz N. Bjerrum N. E. Loomis S. F. Acree C. N. Murray G. M. Kline M. R. Meacham Florence Fenwick Fr. L. Hahn M. Frommer I. Lifschitz M. Reggiani D. A. Mc Innes M. Dole C. W. Foulk M. Hollingsworth L. R. Parks H. C. Beard K. W. Franke J. J. Willaman Lava Hemedes H. T. S. Britton R. A. Robinson W. H. Harrison P. N. Vridhachalam J. J. Shukoff G. P. Awsejewitsch L. W. Elder Jr. P. Jolibois G. Fouretier P. Dubois H. A. Bromley L. W. Causer A. de Waele T. Callan S. Horrobin R. J. Fosbinder E. H. Ducloux 《Analytical and bioanalytical chemistry》1932,90(11-12):432-443
73.
Furis M Hollingsworth JA Klimov VI Crooker SA 《The journal of physical chemistry. B》2005,109(32):15332-15338
In an effort to elucidate the spin (rather than charge) degrees of freedom in colloidal semiconductor nanocrystal quantum dots, we report on a series of static and time-resolved photoluminescence measurements of colloidal CdSe quantum dots in ultrahigh magnetic fields up to 45 T. At low temperatures (1.5-40 K), the steady-state photoluminescence (PL) develops a high degree of circular polarization with applied magnetic field, indicating the presence of spin-polarized excitons. Time-resolved PL studies reveal a marked decrease in radiative exciton lifetime with increasing magnetic field and temperature. Except for an initial burst of unpolarized PL immediately following photoexcitation, high-field time-resolved PL measurements reveal a constant degree of circular polarization throughout the entire exciton lifetime, even in the presence of pronounced exciton transfer via F?rster energy transfer processes. 相似文献
74.
Jeong S Achermann M Nanda J Ivanov S Klimov VI Hollingsworth JA 《Journal of the American Chemical Society》2005,127(29):10126-10127
We study the effect of thiols on the emission efficiency of aqueous CdSe/ZnS core/shell nanocrystal quantum dots (NQDs). We observe that the impact of thiol addition on emission quantum yields (QYs) is time-, concentration-, and pH-dependent. Further, we use a combination of time-resolved spectroscopic methods to determine the mechanism by which thiol addition can cause either increases or decreases in QYs. Specifically, through transient absorption measurements, we show that thiol addition can improve passivation of electron traps, increasing QYs at low thiol concentrations. Further, using nanosecond photoluminescence (PL), we observe that at higher thiol concentrations, hole traps are introduced that reduce PL QYs. Last, through a combination of pH-dependence and control studies (e.g., addition of 2-methyl thioethanol to an aqueous NQD solution and addition of dodecanethiol to a hexane NQD solution), we demonstrate that it is the ability of thiols in aqueous solution to generate thiolate that is the source of both favorable and adverse QY changes. Our results contribute to the understanding of the role of surface ligands, which is critical to the design of stable, high-quantum-yield, nonblinking NQDs. 相似文献
75.
Dussault PH Lee IQ Lee HJ Lee RJ Niu QJ Schultz JA Zope UR 《The Journal of organic chemistry》2000,65(25):8407-8414
The Lewis acid-mediated reaction of alkene nucleophiles with peroxyacetals provides an effective route for the synthesis of homologated peroxides and hydroperoxides. In the presence of Lewis acids such as TiCl(4), SnCl(4), and trimethylsilyl triflate, peroxyacetals and peroxyketals undergo reaction with allyltrimethylsilane, silyl enol ethers, and silyl ketene acetals to afford homoallyl peroxides, 3-peroxyketones, and 3-peroxyalkanoates, respectively. Reactions of peroxyacetals are Lewis acid dependent; TiCl(4) promotes formation of ethers while SnCl(4) and trimethylsilyl triflate promote formation of peroxides. Lewis acid-promoted reactions of silylated hydroperoxyacetals furnish silylated hydroperoxides, which can be deprotected to homologated hydroperoxides. Hydroperoxyketals undergo Lewis acid-mediated allylation to furnish 1,2-dioxolanes via attack of hydroperoxide on the intermediate carbocation. Lewis acid-mediated cyclization of unsaturated peroxyacetals furnishes 1,2-dioxanes, 1,2-dioxepanes, and 1,2-dioxacanes through 6-endo/exo, 7-endo/endo, and 8-endo/endo pathways. The corresponding reactions involving 6-endo/endo and 5-endo/exo pathways were unsuccessful. 相似文献
76.
The stereoselective synthesis of N-acyl--4,5-dialkyloxazolidines (precursors to -β-amino alcohols) through a procedure involving amidomethylation of a 2° allylic alcohol followed by mercuric-ion inititated cyclofunctionalization is reported. 相似文献
77.
Hollingsworth N Kanna M Kociok-Köhn G Molloy KC Wongnawa S 《Dalton transactions (Cambridge, England : 2003)》2008,(5):631-641
Reaction of the amino-alkoxides HOCH(CH(2)NMe(2))(2) (Hbdmap) and HOC(CH(2)NMe(2))(3) (Htdmap) with [Ti(OR)(4)] yields a series of heteroleptic titanium alkoxides [Ti(OR)(4-n)(L)(n)] (L = bdmap, tdmap). Substitution of the monodentate alkoxide with the chelating alkoxides becomes progressively more difficult, with homogeneous products being obtained only for n = 1, 2. The structure of [Ti(OEt)(3)(bdmap)](2), a mu-OEt bridged dimer, has been determined. Hydrolysis of [Ti(OR)(2)(L)(2)], by adventitious moisture affords the dimeric oxo-alkoxides [Ti(O)(L)(2)](2), both of which have been characterised crystallographically. These two compounds have also been prepared by reaction of [Ti(NMe(2))(2)(L)(2)] with the hydrated metal salts [Zn(acac)(2).2H(2)O] and [Zn(OAc)(2).2H(2)O] using the intrinsic water molecules in these salts to react with the labile amido groups, though the former also produces Me(Me(2)N)C=C(H)C(O)Me from reaction of liberated HNMe(2) with the coordinated acac ligand, while the latter also affords the ligand exchange product [Zn(OAc)(bdmap)]. In neither case does the free dimethylamino group of [Ti(O)(L)(2)](2) coordinate a second metal. The dimeric structure of [Zn(OAc)(bdmap)](2) has been established, and the structure of the tetrameric oxo-alkoxide [Ti(O)(OPr(i))(OCH(2)CH(2)NMe(2))](4) is reported for comparison with others in this study. [Ti(OEt)(3)(bdmap)](2) has been used as a precursor in AACVD (Aerosol-Assisted Chemical Vapour Deposition) to generate amorphous TiO(2) films on glass at 440 degrees C, and TiO(2)@C nanoparticles of approximate diameter 350 nm with a carbon coating of width ca. 75 nm on heating in a sealed container at 700 degrees C. 相似文献
78.
79.
Hailiang Dong Tullis C. Onstott Chun-Han Ko Andrew D. Hollingsworth Derick G. Brown Brian J. Mailloux 《Colloids and surfaces. B, Biointerfaces》2002,24(3-4):229-245
Our earlier results concerning bacterial transport of an adhesion-deficient strain Comamonas sp. (DA001) in intact sediment cores from near South Oyster, VA demonstrated that grain size is the principle factor controlling bacterial retention, and that Fe and Al hydroxide mineral coatings are of secondary importance. The experimentally determined collision efficiency (α) was in the range of 0.003–0.026 and did not correlate with the Fe and Al concentration. This study attempts to theoretically predict α, and identifies factors responsible for the observed low α. The modified Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to calculate the total intersurface potential energy as a function of separation distance between bacterial and sediment surfaces and to provide insights into the relative importance of bacterial and sediment grain surface properties in controlling magnitude of α. Different models for calculating theoretical α were developed and compared. By comparing theoretical α values from different models with previously published experimental α values, it is possible to identify a suitable model for predicting α. When DA001 bacteria interact with quartz surfaces, the theoretical α best predicts experimental α when DA001 cells are reversibly attached to the secondary minimum of the energy interaction curve and α depends on the probability of escape from that energy well. No energy barrier opposes bacterial attachment to clean iron oxide surface of positive charge at sub-neutral pH, thus the model predicts α of unity. When the iron oxide is equilibrated with natural groundwater containing 5–10 ppm of dissolved organic carbon (DOC), its surface charge reverses, and the model predicts α to be on the order of 0.2. The theoretical
for DA001 in the natural sediments from South Oyster, VA was estimated by representing the surface potential of the sediment as a patch-wise binary mixture of negatively charged quartz (ζ=−60 mV) and organic carbon coated Fe–Al hydroxides (ζ=−2 mV). Such a binary mixing approach generates α that closely matches the experimental α. This study demonstrates that it is possible to predict α from known bacterial and grain surface properties. 相似文献
80.