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51.
The application of cyclopropenium ion as a phase transfer catalyst for benzylic fluorination in high yields is reported. Integral to the mechanisms of these fluorination reactions was the role of in situ derived cyclopropenium fluoride complexes, the existence of which was supported by 1H, 19F NMR and UV–Vis spectroscopy. Density functional theory calculations were applied to gain insight into the mechanism of these reactions. 相似文献
52.
53.
Darryl N. Williams Katie A. Gold Tracey R. Pulliam Holoman Sheryl H. Ehrman Otto C. Wilson Jr. 《Journal of nanoparticle research》2006,8(5):749-753
Magnetite nanoparticles were synthesized and functionalized by coating the particle surfaces with gum arabic (GA) to improve particle stability in aqueous suspensions (i.e. biological media). Particle characterization was performed using transmission electron microscopy (TEM) and dynamic light scattering (DLS) to analyze the morphology and quantify the size distribution of the nanoparticles, respectively. The results from DLS indicated that the GA-treated nanoparticles formed smaller agglomerates as compared to the untreated samples over a 30-h time frame. Thermogravimetric analyses indicated an average weight loss of 23%, showing that GA has a strong affinity toward the iron oxide surface. GA most likely contributes to␣colloid stability via steric stabilization. It was determined that the adsorption of GA onto magnetite exhibits Langmuir behavior. 相似文献
54.
A star k-edge-coloring is a proper k-edge-coloring such that every connected bicolored subgraph is a path of length at most 3.The star chromatic indexχ'st(G)of a graph G is the smallest integer k such that G has a star k-edge-coloring.The list star chromatic index ch'st(G)is defined analogously.The star edge coloring problem is known to be NP-complete,and it is even hard to obtain tight upper bound as it is unknown whether the star chromatic index for complete graph is linear or super linear.In this paper,we study,in contrast,the best linear upper bound for sparse graph classes.We show that for everyε>0 there exists a constant c(ε)such that if mad(G)<8/3-ε,then■and the coefficient 3/2 ofΔis the best possible.The proof applies a newly developed coloring extension method by assigning color sets with different sizes. 相似文献
55.
56.
Z. Vivian Feng Ian L. Gunsolus Tian A. Qiu Katie R. Hurley Lyle H. Nyberg Hilena Frew Kyle P. Johnson Ariane M. Vartanian Lisa M. Jacob Samuel E. Lohse Marco D. Torelli Robert J. Hamers Catherine J. Murphy Christy L. Haynes 《Chemical science》2015,6(9):5186-5196
Although nanomaterials facilitate significant technological advancement in our society, their potential impacts on the environment are yet to be fully understood. In this study, two environmentally relevant bacteria, Shewanella oneidensis and Bacillus subtilis, have been used as model organisms to elucidate the molecular interactions between these bacterial classes and Au nanoparticles (AuNPs) with well-controlled and well-characterized surface chemistries: anionic 3-mercaptopropionic acid (MPA), cationic 3-mercaptopropylamine (MPNH2), and the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH). The data demonstrate that cationic, especially polyelectrolyte-wrapped AuNPs, were more toxic to both the Gram-negative and Gram-positive bacteria. The levels of toxicity observed were closely related to the percentage of cells with AuNPs associated with the cell surface as measured in situ using flow cytometry. The NP concentration-dependent binding profiles were drastically different for the two bacteria strains, suggesting the critical role of bacterial cell surface chemistry in determining nanoparticle association, and thereby, biological impact. 相似文献
57.
Katie M. Lewis Jennifer Kelley LeRoy PetersonJr. Mark D. Smith Rachel C. Severance Shae A. Vaughn Hans-Conrad zur Loye 《Journal of chemical crystallography》2010,40(10):867-871
Abstract
A new iodobismuthate of formula [BiI2(terpy)2][BiI4(terpy)] (terpy = 2,2′:6′,2′′-terpyridine), was prepared solvothermally in an ethanolic mixture composed of bismuth (III) iodide, terpy, and ruthenium (III) iodide. The compound crystallizes in the space group P [`1] \bar{1} , with Z = 2, a = 9.8491(4) ?, b = 15.4181(7) ?, c = 17.5323(8) ?, α = 89.8140(10)°, β = 80.4160(10)°, γ = 77.9020(10)°. Single-crystal X-ray analysis reveals that the compound is composed of a [BiI2(terpy)2]+ cation and a [BiI4(terpy)]− anion. It is an uncommon example where an iodobismuthate cation and anion are simultaneously incorporated into the same crystal structure. 相似文献58.
Harry J. Sterling Michael P. Daly Geoffrey K. Feld Katie L. Thoren Alexander F. Kintzer Bryan A. Krantz Evan R. Williams 《Journal of the American Society for Mass Spectrometry》2010,21(10):1762-1774
The effects of two supercharging reagents, m-nitrobenzyl alcohol (m-NBA) and sulfolane, on the charge-state distributions and conformations of myoglobin ions formed by electrospray ionization
were investigated. Addition of 0.4% m-NBA to aqueous ammonium acetate solutions of myoglobin results in an increase in the maximum charge state from 9+ to 19+,
and an increase in the average charge state from 7.9+ to 11.7+, compared with solutions without m-NBA. The extent of supercharging with sulfolane on a per mole basis is lower than that with m-NBA, but comparable charging was obtained at higher concentration. Arrival time distributions obtained from traveling wave
ion mobility spectrometry show that the higher charge state ions that are formed with these supercharging reagents are significantly
more unfolded than lower charge state ions. Results from circular dichroism spectroscopy show that sulfolane can act as chemical
denaturant, destabilizing myoglobin by ∼1.5 kcal/mol/M at 25 °C. Because these supercharging reagents have low vapor pressures,
aqueous droplets are preferentially enriched in these reagents as evaporation occurs. Less evaporative cooling will occur
after the droplets are substantially enriched in the low volatility supercharging reagent, and the droplet temperature should
be higher compared with when these reagents are not present. Protein unfolding induced by chemical and/or thermal denaturation
in the electrospray droplet appears to be the primary origin of the enhanced charging observed for noncovalent protein complexes
formed from aqueous solutions that contain these supercharging reagents, although other factors almost certainly influence
the extent of charging as well. 相似文献
59.
Bunyakul N Edwards KA Promptmas C Baeumner AJ 《Analytical and bioanalytical chemistry》2009,393(1):177-186
Fluorescence and electrochemical microfluidic biosensors were developed for the detection of cholera toxin subunit B (CTB)
as a model analyte. The microfluidic devices were made from polydimethylsiloxane (PDMS) using soft lithography from silicon
templates. The polymer channels were sealed with a glass plate and packaged in a polymethylmethacrylate housing that provided
leakproof sealing and a connection to a syringe pump. In the electrochemical format, an interdigitated ultramicroelectrode
array (IDUA) was patterned onto the glass slide using photolithography, gold evaporation and lift-off processes. For CTB recognition,
CTB-specific antibodies were immobilized onto superparamagnetic beads and ganglioside GM1 was incorporated into liposomes. The fluorescence dye sulforhodamine B (SRB) and the electroactive compounds potassium hexacyanoferrate
(II)/hexacyanoferrate (III) were used as detection markers that were encapsulated inside the liposomes for the fluorescence
and electrochemical detection formats, respectively. Initial optimization experiments were carried out by applying the superparamagnetic
beads in microtiter plate assays and SRB liposomes before they were transferred to the microfluidic systems. The limits of
detection (LoD) of both assay formats for CTB were found to be 6.6 and 1.0 ng mL−1 for the fluorescence and electrochemical formats, respectively. Changing the detection system was very easy, requiring only
the synthesis of different marker-encapsulating liposomes, as well as the exchange of the detection unit. It was found that,
in addition to a lower LoD, the electrochemical format assay showed advantages over the fluorescence format in terms of flexibility
and reliability of signal recording. 相似文献