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81.
Michael T. Huggins Chris Musto Lyndsay Munro Vincent J. Catalano 《Tetrahedron》2007,63(52):12994-12999
We present our investigations of 2-ethyl-3-methyl-(10H)-dipyrrin-1-one, its self-association, and anion binding properties. This receptor is easily accessible in a facile single step synthesis with a straightforward workup. An examination of the concentration dependence of the dipyrrinone NH chemical shifts in CDCl3 and (CDCl2)2 over the temperature range from −20 °C to 100 °C determined the self-association constant to be 3850 M−1. Molecular recognition studies have shown that it has a preference for guests with an OH moiety, such as hydrogen sulfate (HSO4−) and carboxylic acids (RCO2H). 相似文献
82.
H. Schettler J. Liu W. Weppner R. A. Huggins 《Applied Physics A: Materials Science & Processing》1993,57(1):31-35
Several types of solid reference electrodes for potentiometric gas sensors based on solid sodium ion conductors (e.g., Na+-/-Alumina or NASICON) are described and the observed experimental results are discussed in view of theoretical predictions. Defined sodium activities are established by appropriate equilibria of binary and ternary phases. The binary systems Na-Sb and Na-Bi, and the ternary systems Na-M-O (M is a transition-metal, Co or Ni) were found to show excellent kinetic performance and are capable to fix the chemical potential of sodium well defined over extended periods of time. Some of the sodium reference electrodes are even stable in air. The results are compared with the application of elemental sodium as reference electrode. 相似文献
83.
Eric B. Monroe Beth Anne Koszczuk Jenna L. Losh John C. Jurchen Jonathan V. Sweedler 《International journal of mass spectrometry》2007,260(2-3):237
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) has been used for the discovery of hundreds of novel cell to cell signaling peptides. Beyond its advantages of sensitivity and minimal sample preparation requirements, MALDI MS is attractive for biological analyses as high quality mass spectra may be obtained directly from specific locations within prepared tissue sections. However, due to the large quantity of salts present in physiological tissues, these mass spectra often contain many adducts of cationic salts such as sodium and potassium, in addition to the molecular ion [M + H]+. To reduce the presence of cation adducts in MALDI mass spectra obtained directly from tissues, we present a methodology that uses a slow condensation procedure to enable the formation of distinct regions of matrix/analyte crystals and cation (salt) crystals. Secondary ion mass spectrometric imaging suggests that the salts and MALDI matrix undergo a mutually exclusive crystallization process that results in the separation of the salts and matrix in the sample. 相似文献
84.
The galvanostatic intermittent titration technique (GITT) has been used to electrochemically determine the chemical and component diffusion coefficients, the electrical and general lithium mobilities, the partial lithium ionic conductivity, the parabolic tarnishing rate constant, and the thermodynamic enhancement factor in “Li3Sb” and “Li3Bi” as a function of stoichiometry in the temperature range from 360 to 600°C. LiCl, KCl eutectic mixtures were used as molten salt electrolytes and Al, “LiAl” two-phase mixtures as solid reference and counterelectrodes. The stoichiometric range of the antimony compound is rather small, 7 × 10?3 at 360°C, whereas the bismuth compound has a range of 0.22 (380°C), mostly on the lithium deficit side of the ideal composition. The thermodynamic enhancement factor in “Li3Sb” depends strongly on the stoichiometry, and has a peak value of nearly 70 000; for “Li3Bi” it rises more smoothly to a maximum of 360. The chemical diffusion coefficient for “Li3Sb” is 2 × 10?5 cm2 sec?1 at negative deviations from the ideal stoichiometry and increases by about an order of magnitude in the presence of excess lithium at 360°C. The corresponding value for “Li3Bi” is 10?4 cm2 sec?1 with high lithium deficit, and increases markedly when approaching ideal stoichiometry. The activation energies are small, 0.1–0.3 eV, depending on the stoichiometry, in both phases. The mobility of lithium in “Li3Bi” is about 500 times greater than in “Li3Sb” with a lithium deficit. The ionic conductivity in “Li3Sb” increases from about 10?4 Ω?1 cm?1 in the vacancy transport region to about 2 × 10?3 where transport is probably by interstial motion at 360°C. For “Li3Bi” a practically constant value of nearly 10?1 Ω?1 cm?1 is found at 380°C. The parabolic tarnishing rate constant shows a sharp increase at higher lithium activities in “Li3Sb” whereas in “Li3Bi” it has a roughly linear dependence upon the logarithm of the lithium activity. The tarnishing process is about 2 orders of magnitude slower for “Li3Sb” than for “Li3Bi.” Because of the fast ionic transport in these mixed conducting materials, “Li3Sb” and “Li3Bi” may be called “fast electrodes.” 相似文献
85.
Delanson R. Crist Arnold P. Borsetti Mary Beth Kass 《Journal of heterocyclic chemistry》1981,18(5):991-995
The polarographic behavior of a series of N,N-dimethyl-2-arylaziridinium fluorosulfonates was investigated as another example of ring-opening reactions of this important class of compounds. Half-wave potentials showed that in water reduction was facilitated by electron-donating groups. This unusual result was explained in terms of electron transfer to an aminocarbonium ion-like species. In methylene chloride, however, two one-electron waves were observed, with the first showing a normal substituent effect (? = 0.17 ± 0.03 V). This result indicated direct electron transfer to the aziridinium ion itself to form a radical species which was detected by cyclic voltammetry. Reasons for the change in mechanism are presented, and E1/2 values for selected aziridinium salts illustrate the importance of steric effects on the reduction process. 相似文献
86.
Cameron BR Darkes MC Baird IR Skerlj RT Santucci ZL Fricker SP 《Inorganic chemistry》2003,42(13):4102-4108
The preparation of a series of [Ru(III)(tacn)(eta(2)-dtc)(eta(1)-dtc)][PF(6)] (tacn = 1,4,7-triazacyclononane; dtc = dimethyldithiocarbamate, diethyldithiocarbamate, pyrrolidinedithiocarbamate, l-prolinedithiocarbamate, l-prolinemethyl ester dithiocarbamate, l-N-methylisoleucinedithiocarbamate) complexes, 5-11, is described. Complex 5 reacts with NO to form the ruthenium nitrosyl complex 12. A series of [Ru(III)(tacn)(pyc)Cl][PF(6)] (pyc = 2-pyridinecarboxylic acid, 2,4- and 2,6-pyridinecarboxylic acid) complexes, 14-16, were prepared along with [Ru(III)(tacn)(mida)][PF(6)] (mida = N-methyliminodiacetic acid), 13, and [Ru(III)(Hnota)Cl], 17, (Hnota = 1-acetic acid-4,7-bismethylcarboxylate-1,4,7-triazacyclononane). Complexes 5-17 were evaluated for use as NO scavengers in an in vitro assay using RAW264 murine macrophage cells. [Ru(III)(tacn)(eta(2)-dtc)(eta(1)-dtc)][PF(6)] complexes 5-11 are very efficient NO scavengers in this assay. 相似文献
87.
Zhan CG Deng SX Skiba JG Hayes BA Tschampel SM Shields GC Landry DW 《Journal of computational chemistry》2005,26(10):980-986
We have performed a series of first-principles electronic structure calculations to examine the reaction pathways and the corresponding free energy barriers for the ester hydrolysis of protonated cocaine in its chair and boat conformations. The calculated free energy barriers for the benzoyl ester hydrolysis of protonated chair cocaine are close to the corresponding barriers calculated for the benzoyl ester hydrolysis of neutral cocaine. However, the free energy barrier calculated for the methyl ester hydrolysis of protonated cocaine in its chair conformation is significantly lower than for the methyl ester hydrolysis of neutral cocaine and for the dominant pathway of the benzoyl ester hydrolysis of protonated cocaine. The significant decrease of the free energy barrier, approximately 4 kcal/mol, is attributed to the intramolecular acid catalysis of the methyl ester hydrolysis of protonated cocaine, because the transition state structure is stabilized by the strong hydrogen bond between the carbonyl oxygen of the methyl ester moiety and the protonated tropane N. The relative magnitudes of the free energy barriers calculated for different pathways of the ester hydrolysis of protonated chair cocaine are consistent with the experimental kinetic data for cocaine hydrolysis under physiologic conditions. Similar intramolecular acid catalysis also occurs for the benzoyl ester hydrolysis of (protonated) boat cocaine in the physiologic condition, although the contribution of the intramolecular hydrogen bonding to transition state stabilization is negligible. Nonetheless, the predictability of the intramolecular hydrogen bonding could be useful in generating antibody-based catalysts that recruit cocaine to the boat conformation and an analog that elicited antibodies to approximate the protonated tropane N and the benzoyl O more closely than the natural boat conformer might increase the contribution from hydrogen bonding. Such a stable analog of the transition state for intramolecular catalysis of cocaine benzoyl-ester hydrolysis was synthesized and used to successfully elicit a number of anticocaine catalytic antibodies. 相似文献
88.
Parsons JG Stachurska-Buczek D Choi N Griffiths PG Huggins DA Krywult BM Marino ST Nguyen T Sheehan CS James IW Bray AM White JM Boyce RS 《Molecules (Basel, Switzerland)》2004,9(6):449-458
The synthesis of (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methoxyphenyl)- propionic acid, (2S)-2-benzyloxymethyl-3-(2-fluoro-4-methylphenyl)propionic acid and (2S)-2-benzyl-oxymethyl-3-(2,4-dimethylphenyl)propionic acid has been achieved by TiCl4 mediated alkylation of the corresponding (4R)-4-benzyl-3-[3-(2-fluoro-4-methoxyphenyl-, 2-fluoro-4-methylphenyl-, 2,4- dimethylphenyl-)propionyl]-2-oxazolidinones, followed by hydrolysis of the chiral auxiliary. The stereochemistry of the alkylation reaction was confirmed by an X-ray crystal structure of (4R)-4-benzyl-3-[(2S)-2-benzyloxymethyl-3-(2- fluoro-4-methylphenyl)propionyl]-2-oxazolidinone. 相似文献
89.
Kerry Wilkinson Renata Ristic Imogen McNamara Beth Loveys WenWen Jiang Mark Krstic 《Molecules (Basel, Switzerland)》2021,26(24)
It has been well established that bushfire/wildfire smoke can taint grapes (and therefore wine), depending on the timing and duration of exposure, but the risk of smoke contamination from stubble burning (a practice employed by some grain growers to prepare farmland for sowing) has not yet been established. This study exposed excised bunches of grapes to smoke from combustion of barley straw and pea stubble windrows to investigate the potential for stubble burning to elicit smoke taint. Increased levels of volatile phenols (i.e., chemical markers of smoke taint) were detected in grapes exposed to barley straw smoke (relative to control grapes), with smoke density and the duration of smoke exposure influencing grape volatile phenols. However, the sensory panel did not perceive wine made from grapes exposed to low-density smoke to be tainted, despite the presence of low levels of syringol providing compositional evidence of smoke exposure. During the pea stubble burn, grapes positioned amongst the burning windrows or on the edge of the pea paddock were exposed to smoke for ~15–20 and 30–45 min, respectively, but this only resulted in 1 µg/kg differences in the cresol and/or syringol concentrations of smoke-affected grapes (and 1 µg/L differences for wine), relative to controls. A small, but significant increase in the intensity of smoke aroma and burnt rubber flavor of wine made from the grapes positioned amongst the burning pea stubble windrows provided the only sensory evidence of any smoke taint. As such, had vineyards been located immediately downwind from the pea stubble burn, it is unlikely that there would have been any smoke contamination of unharvested grapes. 相似文献
90.
Nickel hydroxide is widely used as an active material in Ni-Cd and Ni-MeH batteries. The electrochemical properties such as
charge acceptance, electronic conductivity etc. can be dramatically influenced by doping β-Ni(OH)2 with small amounts of Co, Cd or Zn. Stabilizing of α-Ni(OH)2 offers the possibility to obtain nickel electrodes with enhanced capacity. The stabilizing of α-Ni(OH)2 is achieved by replacing at least 20% of the nickel by a trivalent metal ion.
The structural features of the undoped and doped nickel hydroxides and the resulting electrochemical properties are discussd
and reviewed.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献