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141.
A series of new fluorescent Zinpyr (ZP) chemosensors based on the fluorescein platform have been prepared and evaluated for imaging neuronal Zn(2+). A systematic synthetic survey of electronegative substitution patterns on a homologous ZP scaffold provides a basis for tuning the fluorescence responses of "off-on" photoinduced electron transfer (PET) probes by controlling fluorophore pK(a) values and attendant proton-induced interfering fluorescence of the metal-free (apo) probes at physiological pH. We further establish the value of these improved optical tools for interrogating the metalloneurochemistry of Zn(2+); the novel ZP3 fluorophore images endogenous stores of Zn(2+) in live hippocampal neurons and slices, including the first fluorescence detection of Zn(2+) in isolated dentate gyrus cultures. Our findings reveal that careful control of fluorophore pK(a) can minimize proton-induced fluorescence of the apo probes and that electronegative substitution offers a general strategy for tuning PET chemosensors for cellular studies. In addition to providing improved optical tools for Zn(2+) in the neurosciences, these results afford a rational starting point for creating superior fluorescent probes for biological applications. 相似文献
142.
Using high-performance liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry (ESI-MS) the sequences of the microheterogeneous peptide mixture of the 18-residue "peptaibol" antibiotics trichotoxins A-40, isolated from the mold Trichoderma viride strain NRRL 5242, were reinvestigated. The structures of two major and one minor component [J. Chromatogr., 296 (1984) 236] could be confirmed and hitherto not known sequences of a further major and two minor peptides could be determined. It is demonstrated that ESI-MS in the positive ionization mode is advantageously completed by applying negative ionization. The methods used make possible the sequence determination of components of peptaibols without previous isolation and allow, in certain cases, sequencing of peptides which are incompletely or not resolved by HPLC. 相似文献
143.
J. Bogaczek und M. Jaworski 《Fresenius' Journal of Analytical Chemistry》1970,251(3):174-176
Zusammenfassung Die Anwendbarkeit der Polarographie für die kontinuierliche Messung des Acrylnitrils in wäßrigen Absorptionslösungen wurde untersucht. Eine Anordnung wird beschrieben, welche eine kontinuierliche Zirkulation des Quecksilbers der Meßelektrode im geschlossenen Kreislauf ermöglicht. Die angewandte Gegenelektrode (Ag/AgCl) von großer Oberfläche zeigt eine große Potentialbeständigkeit, trotz wechselnder Grenzstromstärke. Durch die Verwendung einer Quecksilberelektrode mit hoher Tropffrequenz ist die Messung in strömenden Lösungen im Bereich von 5–30 ml/min möglich. Der Fehler der Bestimmungen beträgt ± 8,5%.
Continuous polarographic determination of acrylonitrile
The applicability of polarography to a continuous determination of acrylonitrile in aqueous absorption solutions was investigated. A device is described providing a continuous circulation of the electrode mercury in a closed system. The large surface electrode (Ag/AgCl) used displayed a considerable potential stability in spite of the fact that the limiting current was fluctuating. Using a mercury electrode with a high drop frequency, determinations in flowing industrial streams are readily possible in the range of 5 to 30 ml/min with an error of ± 8.5%.相似文献
144.
Wojciech Jaworski 《Israel Journal of Mathematics》1996,94(1):201-219
Let μ be a probability measure on a locally compact second countable groupG defining a recurrent (but not necessarily Harris) random walk. Denote byG
∞ the space of paths and byB
(a)the asymptotic σ-algebra. Let the starting measure be equivalent to the Haar measure and writeQ for the corresponding Markov measure onG
∞. We prove thatL
∞(G∞, B(a), Q) is in a canonical way isomorphic toL
∞(G/N) whereN is the smallest closed normal subgroup ofG such that μ(zN)=1 for somez∈G. The groupG/N is either a finite cyclic group with generatorzN or a compact abelian group having the cyclic group
as a dense subgroup. As a corollary we obtain that the set of all φ∈L
1(G) such that
coincides with the kernel of the canonical mapping ofL
1(G)ontoL
1(G/N). In particular, when μ is aperiodic, i.e.,G=N, then the random walk is mixing:
for every φ∈L
1(G) with ∝ φ=0. 相似文献
145.
146.
Jan S. Jaworski Ewa Leniewska Marek K. Kalinowski 《Journal of Electroanalytical Chemistry》1979,105(2):329-334
Polarographic reduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone and 9,10-anthraquinone was studied in pyridine, acetone, hexamethylphosphoramide, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide and propylene carbonate. The variation of the E1/2-values proper for the first electron transfer step (measured against oxidation potential of ferrocene) with the properties of solvent is analyzed in terms of the donor-acceptor concept. Linear correlations of E1/2 vs. acceptor number are observed; the slopes of corresponding lines correlate with the spin densities at oxygen atoms of semiquinones. 相似文献
147.
148.
149.
Babson J Barish B Becker-Szendy R Bradner H Cady R Clem J Dye ST Gaidos J Gorham P Grieder PK Jaworski M Kitamura T Kropp W Learned JG Matsuno S March R Mitsui K O'Connor D Ohashi Y Okada A Peterson V Price L Reines F Roberts A Roos C Sobel H Stenger VJ Webster M Wilson C 《Physical review D: Particles and fields》1990,42(11):3613-3620
150.
Oscillating flow near the end of a stack of parallel plates placed in a standing wave resonator is investigated using particle
image velocimetry (PIV). The Reynolds number, Re
d
, based on the plate thickness and the velocity amplitude at the entrance to the stack, is controlled by varying the acoustic
excitation (so-called drive ratio) and by using two configurations of the stacks. As the Reynolds number changes, a range
of distinct flow patterns is reported for the fluid being ejected from the stack. Symmetrical and asymmetrical vortex shedding
phenomena are shown and two distinct modes of generating “vortex streets” are identified. 相似文献